My constant current load - 90W , 3A 30V - Page 1
Forum section: electronics / projects

author: Spikee
author_rank: Frequent Contributor
timestamp: November 20, 2012, 04:27:35 pm
content: OLD first post in this topic:Code:Schematic:[url=https://dl.dropbox.com/u/100819959/Schematic%20Prints.pdf]https://dl.dropbox.com/u/100819959/Schematic%20Prints.pdfInfo:I use a Atmega328 running Arduino IDE to program the code.I have an external rotary encoder to set the voltage to the dac ( 0-2048) and i instruct it to do a gain of 2.So the 12bit dac MCP4728 outputs a set 0-4.096V .The 12bit dac output goes to the first opamp (U4A).The gain is set by a 15 turn 1k pot to achieve ~12V at 4.096V input.R5 and C9 act as a low pass filter. I use S2 to switch between linear mode and pwm mode.The second opamp U4B is an regular voltage follower. The output has an pulldown resistor R4 (10K) to keep the gate of the mosfet low when needed.J2 connects to the source of the mosfet for feedback. J1 connects to the gate.S3 selects if A0 of the atmega is connected to measure voltage or not.Because if if I > 5A than it wont like it. [text in schematic is wrong]The mosfet , 100W power resistor is mounted on a fan assisted heatsink.U7 measures the temperature of the heatsink.feedback is appreciated.SpikeeUpdates:Update 1 :breadboard -https://www.eevblog.com/forum/projects-designs-and-technical-stuff/did-i-forget-anything-constant-current-load/msg166741/#msg166741Update 2 :Measurements + photos -https://www.eevblog.com/forum/projects-designs-and-technical-stuff/did-i-forget-anything-constant-current-load/msg166933/#msg166933Update 3 :Mosfet matching -https://www.eevblog.com/forum/projects/did-i-forget-anything-constant-current-load/msg168787/#msg168787Update 4 :status + pics -https://www.eevblog.com/forum/projects/did-i-forget-anything-constant-current-load/msg168847/#msg168847Update 5:made a youtube video for you guys:Update 6:new youtube video , fixed opamp problem:Update 7:new youtube video , testing 1ohm vs 0.1 ohm load resistor + running the load at 5V 10A.Update 8:Big progress , 4 IRFP064N on a big CPU cooler running 63A peak + videohttps://www.eevblog.com/forum/projects/did-i-forget-anything-constant-current-load/msg195585/#msg195585Update 9:Schematic :https://dl.dropbox.com/u/100819959/constant%20current%20load/Constant%20current%20EEVblog_Spikee.pdf

author: Harvs
author_rank: Super Contributor
timestamp: November 21, 2012, 02:49:03 am
content: Some thoughts:- The voltage regulators have no bulk capacitance following them. I would probably put a 10uf tantalum or 100uF electro on their output as well.- I don’t see a connection between the 12V bar on the op-amps and the output of the 12V reg.- I don’t see any bypass capacitance on the uC. A 100nF ceramic cap close to the power pins will reduce noise.- You’ve connected both AVCC and VREF directly to the power pins. At the very least AVCC and VREF should be decouple from the main supply noise through an LC circuit as shown in the ATmega328 datasheet. You have a very hard time trying to keep digital noise out of the ADC as it is, so you need all the help you can get. Further, if you are using a filtered 5V rail for the ADC just be aware that your accuracy is only going to be as good as your regulator.- I would swap D1 out for the fast UF4007, 1n4007 is generally too slow for switching applications. Cost difference is negligible.- The LM35CZ power source is best being powered by the filtered analogue power (reduce noise).- Instead of switching the input voltage from the analog pin, why don’t you just put a voltage divider (two resistors) between the input voltage and uC input? A switch as a protection measure is almost certain to get you into trouble one day (e.g. a voltage spike.)- The gate driving op-amp needs some compensation to stop it becoming unstable. If you have a look at my design posted a couple of days ago on here, you can see a resistor isolating the op-amp from the high mosfet gate capacitance and adding a capacitance between the op-amp output and the feedback path creating a dominant roll off in the op-amp response.- Can you talk more about what overall specs you’re trying to achieve, and I might be able to provide more feedback on the over parts and voltages in the design. There’s a few areas that look like they might not do what you’re intending (but that depends on what your intentions are…)

author: blackdog
author_rank: Frequent Contributor
timestamp: November 21, 2012, 12:30:09 pm
content: Hi Spikee,I do not see were you sense your current...Use a 0.1 Ohm resistor 3 a 5 Watt resistor in your Source.I made al little schematic for you, its a part of my Electronic Load.I hope this wil help you :-)Kind regarts,Blackdog

author: Spikee
author_rank: Frequent Contributor
timestamp: November 21, 2012, 04:19:18 pm
content: I sense the current using connector j2 (who is connected like your schematic on a big heatsink off the pcb) .I use the NXP buk652R7-30c fet 30V max 200W @25 deg. Celsius.My Resistor is : Ohmite TEH100 W 1ohmit is mounted on a ELV LK-40 heatsink capable of 100W when assisted whit the normal fan. 0,73 K / W @ 6.5 CFMI bought a new fan that does 24 cfm at max speed (delta FFB0412SHN ) 6W 13000 rpm.My specs are just to try some supply's of mine. My main Agilent psu does 30V @ 3A and it would be nice to fully test it.My design got some inspiration from jjoster and dave.The test pcb is beeing manufactured as you speak [for free] i will find / fix the problems after it gets back (a week or so) .U7 is actually on the heatsink, not on the board.U1,2 are on a heatsink , i just didn't make it 3d.Reply's :I added the switch (S3) because i rarely would be going over 5 amps.And i will replace the output cap of the voltage regulator whit a bigger one.The LM36 just gives a ballpark figure of the temperature. I don't need it to be super exact.The opamp (one lm324N ) is connected to the top rail of 12V and bottom rail of GND.I will replace the 1n4007 whit a faster equivalent . I will test if the gate capacitance gives me a hard time. If so i will solve it accordingly (bodge it) . The ADC could give me a hard time because of noise but i will have to experience it first hand and solve my mistake than.

author: blackdog
author_rank: Frequent Contributor
timestamp: November 21, 2012, 04:48:28 pm
content: Hi Spikee,If you use a 1 Ohm resistor and the design is for 5A, you wil lose 25 Wats in this resistor!And, the minimum voltage you can use 5A wil be around 6V.Also wil the opamp U4B have not enough drive voor 5A and 1 Ohm resistor.The drivelevel wil be: Voltage drop Sensresistor, Wires, Gatedrive voltage.This wil be around 10V.The output commonmode voltage of the LM324 on the + site is around 3V.Kind regarts,Blackdog

author: Spikee
author_rank: Frequent Contributor
timestamp: November 21, 2012, 05:28:53 pm
content: i can replace the LM7812 whit its 15v equivalent if it makes it any better. The max voltage i can get out the transformer is 23V .the current won't exceed 3A 99% of the time. i just had the heatsink laying around.

author: Harvs
author_rank: Super Contributor
timestamp: November 22, 2012, 10:21:30 am
content: Quote from: Spikee on November 21, 2012, 04:19:18 pmSo you want to test a 30V power supply, yet the absolute max Vds of that MOSFET is 30V... bad idea. Find a MOSFET with a max Vds of >1.5x that.Quote from: Spikee on November 21, 2012, 04:19:18 pmSo the heatsink is "capable" of 100W. I can't find it on the web but I'm guessing by that they mean at an ambient temp of 25C, you're heatsink will be near on 100C (100*0.73+25), and if you go any hotter the paint will have problems. If you want to understand why this is a bad idea, do some reading on thermal resistance for devices (junction to case, case to heatsink etc.)Quote from: Spikee on November 21, 2012, 04:19:18 pmAs above, if that heatsink has a 0.73 degrees/W thermal resistance, you don't have enough dissipation for 90W. The idea that you plan on doing it with a single MOSFET is really pushing shit up hill.Quote from: Spikee on November 21, 2012, 04:19:18 pmTo be honest I don't understand the mentality of putting a PCB out for production with what I consider basic errors (decoupling capacitance and ADC noise reduction are poking you in face if you read the datasheet.) If you wanted to experience these errors for yourself then by all means do so, but why wouldn't you just do it on a breadboard before you had a PCB messed up? At a guess, I get the feeling you were under a time pressure to get the board out so you could add it on a panel going for production free of charge. But then if you didn’t have time to fix up errors instead of resorting to bodging it up, why bother asking us for input?Edit: Appologies for sounding negative...

author: Spikee
author_rank: Frequent Contributor
timestamp: November 22, 2012, 03:47:23 pm
content: The pcb is a sample of a new pcb manufacturer i'm trying. So i needed something out fast to test the service .I am using a fan who pushes around 4 times the air of the normal fan (100w rating of heatsink) .Because i don't have the exact numbers i will need to test it out myself.I know that the mosfet is rated for 30V max and that the heatsink might not provide enough cooling capacity for 90W continious.But peek value will suffice for pwm mode.I agree that i should have made the complete circuit on a breadboard before getting a pcb built. But i just needed to test the service , the final pcb will be for another day. And i ordered a few extra breadboards because i ran out of room.Some background info:I'm a Student in the first year of college. I have had no electronics classes or anything like that. This is just hobby.Thanks for the feedback , i will adjust my circuit and test it next week.gr. Spikee

author: Harvs
author_rank: Super Contributor
timestamp: November 22, 2012, 09:22:29 pm
content: Fair enough mate. Just keep a list somewhere of stuff you need to change. It's always difficult to remember when you come back to it.

author: kaindub
author_rank: Regular Contributor
timestamp: November 22, 2012, 10:52:31 pm
content: What is the point of the Atmel?Since there is no feedback to the uP, you are just using it to chnage from digital setpoint to anaolog.get rid of the uP and just use a potdirect to the opamps.

author: Spikee
author_rank: Frequent Contributor
timestamp: November 22, 2012, 11:00:15 pm
content: Quote from: kaindub on November 22, 2012, 10:52:31 pmThe micro measures the heatsink temperature (can be programmed to shut off the output at overload) .And adjust the pwm to the heatsink fan. Because 13000 rpm continuously will not be fun.It also has an lcd to display the set current , measures current , heatsink temperature , pwm value etc ...Also a 10 turn pot will be more expensive than a 2 euro micro .

author: Spikee
author_rank: Frequent Contributor
timestamp: November 23, 2012, 09:11:56 am
content: how much current does the adc use ? i looked at the Electrical characteristics but didn't find much.I was thinking of putting a low pass rc / lc filter after the LM7812 and putting a precision 5v reference to power the adc and use it as the analog reference. Like the LT1027 precision 5v reference . It can source about 15mA so it should be enough. I will need to add some filter caps but i have to look what value.Thanks,Spikee

author: T4P
author_rank: Super Contributor
timestamp: November 23, 2012, 12:08:05 pm
content: Scary ... a sunon high dB turbofan by any chance?

author: Spikee
author_rank: Frequent Contributor
timestamp: November 23, 2012, 03:11:38 pm
content: Quote from: T4P on November 23, 2012, 12:08:05 pmOld fan was a sunon slow speed . New one is delta FFB0412SHN around 55dB at 13000 rpm.

author: Spikee
author_rank: Frequent Contributor
timestamp: November 28, 2012, 12:45:57 am
content: i have now made my circuit on a breadboard.some test results:25V 1Afan at 5Vheatsink temp ~35-38 deg Croom temp 21-22 deg Cheatsink Rth (j-a) ~ 0.56 - 0.68 deg. C/WWithout fan ~53 deg. C25V 1A[short test cuz of noise]fan at 10Vheatsink temp ~30 deg Croom temp 21-22 deg Cheatsink Rth (j-a) ~ 0.36 deg. C/W25V 2A[short test cuz of noise]fan at 10Vheatsink temp ~40 deg Croom temp 21-22 deg Cheatsink Rth (j-a) ~ 0.36 deg. C/Wlittle heatsink can hadle alot .The mosfet is dead now . Probably because it could not transfer enough heat fast enough.I have two Buz 11 mosfets here (50V 33A 90W max @ 25 deg. C ) and i will give them both a opamp channel and parallel the outputs.I will post the result later. The pcb should arrive in a few days.gr. SpikeeProblems:1. Changing arduino pwm timers messes up the rest of the program . - have to do some extra research. (default you hear the harmonics)2. Fan gave noise to the temp sensor so i tried an rc circuit. It didn't solve it so i hardwired the fan to 5V rail and it was gone. I will have to find an better solution for the final pcb.3. Blew up mosfet because it could not transfer the power fast enough. I have two Buz 11 mosfets and i will parallel the output of them to share the power.4. The current reading was a bit fiddly. I will have to change a bit in my Arduino code.5. The current setting whit the rotary encoder would act weird after some time. I will change the 100nF caps whit 10nF tomorrow. Maybe it will fix it.Thats kinda it for today , i will try some new things tomorrow.gr. spikee

author: Spikee
author_rank: Frequent Contributor
timestamp: November 28, 2012, 10:10:00 pm
content: I made some upgrades , the one nxp fet has been replaced by two BUZ 11 whit gate , drain , source connected together.some pictures:setup:https://dl.dropbox.com/u/100819959/2012-11-28%2023.00.45.jpgDisplay:https://dl.dropbox.com/u/100819959/2012-11-28%2023.01.06.jpgHeatsink:https://dl.dropbox.com/u/100819959/2012-11-28%2023.01.17.jpgPower supply (Agilent U8001A) and mosfet temp. measurement (Rigol DM3058) :https://dl.dropbox.com/u/100819959/2012-11-28%2023.03.05.jpgSome more tests:15V 3A - 45W fan at 5V:duration: 10 minutesheatsink temp : 50 deg. Cmosfet (2) temp : 55 deg. Croom temp: 21 deg. Cheatsink Rth (j-a) ~ 0.73 C/W20V 3A - 60W fan at 5V:duration: 15 minutesheatsink temp : 59.5 deg. Cmosfet (2) temp : 65 deg. C (still self balancing)room temp: 21 deg. Cheatsink Rth (j-a) ~ 0.73 C/WMosfet (2) failed at 60W 70 deg c. on package 60 deg c. heatsink. Because the the second fet failed the first one also did.The balancing was not good , mosfet (2) was 70 deg. c while mosfet (1) was 60 deg. c .I could ad balance resistors but i deoubt that it will fix much.The best solution would be one big TO264 package or so.I will need some help to find the good one.gr.spikee

author: peter.mitchell
author_rank: Super Contributor
timestamp: November 29, 2012, 02:38:04 am
content: did you use some thermal paste/grease or thermal pad? that would really help/hinder, also, make sure you tighten them on sufficiently, bigger packages (to-247 and to-264) will help a bit, but 60W should be fine with a TO-220, provided the heatsink is cool enough and thermal conductivity is high enough.

author: mrflibble
author_rank: Super Contributor
timestamp: November 29, 2012, 04:58:11 am
content: Quote from: Spikee on November 28, 2012, 10:10:00 pmYou can parallel those mosfets, but connecting it all together like that is not the best plan. ;-)At the very least use seperate gate resistors. See for example:http://www.irf.com/technical-info/appnotes/an-941.pdfAnyways, maybe parallelling is more trouble than it's worth. If you have enough cooling + a decent thermal contact then 1 device should be able to survive that 60 W.

author: blackdog
author_rank: Frequent Contributor
timestamp: November 29, 2012, 08:05:50 am
content: Hi SpikeeYou are making mistake's...Place the 2 powerfets in the middle of your heatsink, thats the place were your vancontroler sensor is.Mount the powrfets on the other side of the heatsink, that is turn is 90C.NOT on the edge were you coupled the heatsinkparts togetter...One on each side.If you do it this way your heatsink wil be ~0.73c/WattBe shure the Fet is mounted flat en use a good compound!Use a small Source resistor say 0.1 Ohm, use a current of 1A en measurethe voltagedrop over these resistors.If the voltage is within 15% its OK, other pair some fets or use a little higher source resistor.Mount the gateresistor direct on the Fet.Keep those wires short!Kind regarts,BlackdogPS (Dutch Mode)Als je ook op het forum van "Circuits Online" zit kan ik je wat beter helpen.Engels is nog steeds knap lastig voor mij :-)

author: Spikee
author_rank: Frequent Contributor
timestamp: November 29, 2012, 09:46:21 am
content: The mosfets were mounted this way: bolt - plastic washer - mosfet - thermal grease - mica plate - thermal grease - heatsink .I read in some study that it was the best way. After a second look i saw that i could move mosfet (2) , thats probably the reason that one got so much hotter than the other one.The mosfets i have laying around:5x MTP3055 - 50V 12A ~48W7X IRF510 - 100V 5.6A ~43W30x IRLB8721 - 30V 44A ~ 65W @ 25 deg. C 33W @ 100 deg. C (logic level)@blackdog ,Ik zit ook op Circuits online ( Spikee ) maar heb daar momenteel geen topic lopen.I will try to match a pair of those MTP3055 . What amount of gate resistor should i be looking for ?And i will mount the mosfets according to your post.Thanks for all the info and feeback.Spikee

author: Harvs
author_rank: Super Contributor
timestamp: November 29, 2012, 10:20:26 am
content: Without an insulator and using Arctic Silver thermal paste, I had 60W per TO220 mosfet being transferred into a CPU cooler (120W total), not getting above about 60 degrees C. But that's with a heatpipe cooler, I couldn't get close to that result with a standard alu heatsink.When paralleling mosfets I used two control loops. Tied the drains together to the input, then had separate load sense resistors and op-amps. If you just hook them together like you have, then you're going to struggle to get equal current sharing. Sense resistors and op amps are cheap...

author: Spikee
author_rank: Frequent Contributor
timestamp: November 29, 2012, 10:35:00 am
content: I prefer one big TO-264 package n channel mosfet. I saw some high power ones from IXYS at farnell at a reasonable price.I do not mind paying around 5-9 euro for one of those mosfets. The bigger packaging also is nicer to solder to.Now i need to find one that is suited for my application.Gate drive voltage : 0 -> 12VVoltage rating: from 75V and upCurrent rating: 10A and upWatt rating: 100W and up

author: blackdog
author_rank: Frequent Contributor
timestamp: November 29, 2012, 11:21:14 am
content: Hi SpikeeBuy 5 a 10 of these Fets:http://www.dickbest.nl/index.php?_a=viewProd&productId=2164Select the fet's, see pictureKind regarts,Blackdog

author: Harvs
author_rank: Super Contributor
timestamp: November 29, 2012, 11:32:00 am
content: Quote from: Spikee on November 29, 2012, 10:35:00 amNone of that is particularly difficult. The cheapest TO-264 mosfet on digikey, IXFK230N20T, could easily do it.With the junction to case and typical case to heatsink figures you're only looking at a 24 degree difference at 100W from junction to heatsink with a 175 degree max temp. Your difficulty will just be to keep the localized heating in your heatsink under control. That's where heatpipes are king.

author: Spikee
author_rank: Frequent Contributor
timestamp: November 29, 2012, 12:51:36 pm
content: I can't get the IXFK230N20T at farnell so that would be a bit of a problem.To prevent localized heating multiple fets would be the best solution.I have ordered the fets blackdog suggested and i will use his method to match a pair of them.They will arrive tomorrow or saturday . I will test them on sunday / monday .

author: Harvs
author_rank: Super Contributor
timestamp: November 30, 2012, 10:57:39 am
content: But they don't meet your voltage requirementAnyway you've bought them now, so just make sure you don't exceed that 55Vds.I would still use separate control loops and forget about matching FETs. But that's you're choice, and I guess you've already got that board made and the single high powered resistor.BTW, I only talked about the IXFK230N20T because it was the cheapest FET that met your package requirements. By no means was that a one off case, it's just the cheapest I could find.

author: Spikee
author_rank: Frequent Contributor
timestamp: November 30, 2012, 11:28:15 pm
content: @ Harvs :Sorry for the confusionmy specs are very loose ... i just made up some specs .I was very buzy whit a college project all week but today i had time to lasercut the front panel @ the FabLab in my school.(still have to sand of the exessive black marker ink. I should have selected higher power to engrave the text so it would be black but ... beginner fault)Pic:I still need to laser out some holes and make some extra markings , but it is a start.I have learned that seperate control loops and seperate load resistors is the way to go but i now have this pcb and i would like to use it.

author: Spikee
author_rank: Frequent Contributor
timestamp: December 05, 2012, 04:43:25 pm
content: Quote from: blackdog on November 29, 2012, 11:21:14 amThe results: (had to put a few 1k pots in series to get 1A accuratly ...)https://dl.dropbox.com/u/100819959/mosfet%20scatter.pdfIt won't be super accurate because the current would shift about. But i measured as good as i could.Fet 2 and 4 would be the best match. I will test the rest of my circuit in a few hours.gr. spikee

author: blackdog
author_rank: Frequent Contributor
timestamp: December 05, 2012, 05:49:24 pm
content: Hi Spikee,Fets 2 and 4 looks good :-)I know its a little drifty, thats wy i told you to mount the Fet on a heatsink.If i told you use 30V and 1.5A... No way, drift all over the place.You dit a fine job.Please let me see your final schematic.Kind regarts,Blackdog

author: Spikee
author_rank: Frequent Contributor
timestamp: December 05, 2012, 06:43:39 pm
content: i mounted it on the heatsink but they were still a bit drifting . The fan wasn't hooked up so i did a second test whit short on time and let the heatsink cool to the same temp. I got the same results =) . I just mounted the two fets and need to find a good spot to mount the resistor.I'm drawing a simple schematic for you.Output schematic:the gate resistor is mounted directly on the gate pin of the mosfet.Thanks spikee

author: blackdog
author_rank: Frequent Contributor
timestamp: December 05, 2012, 07:19:02 pm
content: Hi Spikee,For the best sharing of the currents give eacht Fet a small Source resistor (0.1 Ohm)And, don't forget to place the Fets on the good site of the heatsink!This is the way to do it...Kind regarts,Blackdog

author: Spikee
author_rank: Frequent Contributor
timestamp: December 05, 2012, 08:08:03 pm
content: Can i use the wires as source resistor ?i can 4-wire measure it to be exact.

author: robrenz
author_rank: Super Contributor
timestamp: December 05, 2012, 08:15:03 pm
content: Copper has a large resistance variation with temperature change so it would not be as good as a low temperature coefficient resistor

author: Spikee
author_rank: Frequent Contributor
timestamp: December 05, 2012, 08:19:49 pm
content: i have one laying around but another ... guess i will have to order another one from farnell.

author: blackdog
author_rank: Frequent Contributor
timestamp: December 05, 2012, 08:30:04 pm
content: Hi Spikee,0.1 Ohm wire resistor... Mmmm~ 9cm, copper wire, 0.1mm diameter.Try it,Kind regartsBlackdog

author: Spikee
author_rank: Frequent Contributor
timestamp: December 05, 2012, 09:18:53 pm
content: Most of the code is uploaded now. I still have to connect the mosfets together and screw the resistor on the heatsinkPics:Hello world :https://www.dropbox.com/s/i4czyuqh3wfhxnm/2012-12-05%2022.08.35.jpgMosfets on heatsink:https://www.dropbox.com/s/xdn9em9bar9b0d5/2012-12-05%2022.09.21.jpgMounting of mosfet:heatsink -> thermal grease -> mica plate -> thermal grease -> mosfet

author: robrenz
author_rank: Super Contributor
timestamp: December 05, 2012, 09:35:25 pm
content: Quote from: blackdog on December 05, 2012, 08:30:04 pmThat's called a fuse

author: Spikee
author_rank: Frequent Contributor
timestamp: December 06, 2012, 02:01:58 am
content: It is all hooked up now =) .i made a small mistake at the dac (upside down) and after i put it correctly it shorted somehow after a while.Since it is verry late and i should go to bed i just put it in pwm mode and play whit it.I got it around 80-90W and you could feel the mosfets get hot after a few minutes (not to hot .. just hot)the heatsink temp was climbing resonably fast (fan still on 5v , other people are sleeping) but did not get over 40 deg.c for the time i tested it.I need to order a new dac and that will take a few days, until then i can just play in pwm mode.gr spikee

author: LEECH666
author_rank: Frequent Contributor
timestamp: December 06, 2012, 10:23:54 am
content: Quote from: blackdog on December 05, 2012, 07:19:02 pmHi blackdog,what's the purpose of C1 in this circuit?Sorry I don't want to high jack this thread, but I am working on my noob attempt of a higher powered dummy load inthis thread. Should I add this capacitor in my circuit?

author: blackdog
author_rank: Frequent Contributor
timestamp: December 06, 2012, 11:13:48 am
content: Hi Leech666It's for stability, its best mounted close to the Fet end the lower site of the 0.1 resistor.You can keep it as small as posible if you modulate the current source with relativ high frequenties and low current's.In every design you make you have to check the values, is my design stable?In almost every schematic on the Internet I see no or not enough decoupling.Decoupeling is very important!!!Some info over decoupling and whyTIwww.ti.com/lit/an/sloa069/sloa069.pdfAnalog Deviceswww.bramcam.nl/MT-101.pdfKind regarts,Blackdog

author: Spikee
author_rank: Frequent Contributor
timestamp: December 06, 2012, 04:23:55 pm
content: So i ordered a few parts:Artic cooling freezer 7 pro rev. 2 :Artic silver thermal adhesive :http://www.arcticsilver.com/arctic_silver_thermal_adhesive.htm50k 10 turn pot12bit dac MCP4728 (samples)2 new 100W resistor 1ohm10 0.1 ohm 3w resistorsim gonna test how much power i can get out of one IRFP064N using a computer heatsink which has heat pipes.I want to see how close i can get to the 200W (@25deg c. ) value using 2 normal speed fans on the heatsink.This will be an interesting experiment .gr. spikee

author: blackdog
author_rank: Frequent Contributor
timestamp: December 06, 2012, 06:21:35 pm
content: Hi Spikee,I have here almost the same material as on your picture for a testOne tip, do not use a mica washer, mount the 2 Fets direct on the bottum of the heatsink.Check the bottum of the heatsink if it's realy flat!!!Chack the specs of the IRFP064Junction to Case 0.75C/Watt, Case to Heatsink 0.24C/Watt, total 1C/WattLinear Derating factor, 1.3W/CRespect the datasheet/FetsCheckout EEVBLOG #105 so that you NOT blow up your fets...Kind regarts,Blackdog

author: LEECH666
author_rank: Frequent Contributor
timestamp: December 07, 2012, 02:14:49 am
content: Wouldn't that potentially short the drains of the two FETs? I reckon that's a bad thing. How do you ensure insulation if you mount your FETs like that. Thermal grease?Cheers,Florian//EDITHERP DERP, confused drain with source. The metal part of the TO-247AC is internally connected to the drain but those are connected together anyway. Pleaase forget that I asked this question.

author: Spikee
author_rank: Frequent Contributor
timestamp: December 07, 2012, 02:45:08 am
content: Quote from: LEECH666 on December 07, 2012, 02:14:49 amIf you dont want electrical connection you need to make sure that the past of fet #1 does not hit the metal or paste of fet #2 .This is discribed in the artic silver guide / manual for this product.I did some thermal calculations and you can put around 115W in the mosfet and get a junction temp of 170 deg c. (175 max) so one fet would be enough for one cpu cooler.example:90W from psu (30V , 3A )The 1 ohm resistor will drop 3V ( 1 ohm *3 A )So the mosfet gets 27V and 3A (81W)Rt j-c = 0.75 maxRt c-h = 0.24 minRt h-a = 0.3 typ. - fan on high Freezer 7 pro(calculated from some results on the internet , seems to give around the same number)so Rth (j-a) is ~1.3 deg. C / WTemp ambient = 21 deg. C/WThis all results in a junction temp of 126.3 deg. C. (175 max)It all depends on how fast the heat pipes can transfer the heat but i'm guessing its kinda instant.If my calculations are correct in real life you would only use one mosfet per cpu heatsink because it can utilize it fully.gr.spikee

author: T4P
author_rank: Super Contributor
timestamp: December 08, 2012, 03:31:46 pm
content: Careful about using it at 175C, 125 is so hot the mosfet can unsolder themselves and seriously running them at the edge is no good for reliability and i suspect even wire insulation melting/board lamination peeling off or a track peeling offand be careful of the heatsink itself, that heatsink is about 0.21 at OPTIMUM settings with the fan hard on

author: Spikee
author_rank: Frequent Contributor
timestamp: December 08, 2012, 04:43:59 pm
content: Thanks for the info ... it was kinda obvious that insulation would melt but i didn't look at it in that wayMonday i will test and aim for a 90W total load whit heatsink and present the result here.

author: LEECH666
author_rank: Frequent Contributor
timestamp: December 08, 2012, 05:56:32 pm
content: Ah yes T4P! Good call.A problemthis guyalso faced.Subtitle translation: ... and this is what you get when you let too much current flow. The MOSFET is getting so hot that even solder starts to get soft (again.)And you can clearly see that he switched to some sort of screw terminal connection in the next two pictures.Cheers Florian

author: blackdog
author_rank: Frequent Contributor
timestamp: December 08, 2012, 06:04:18 pm
content: Hi Spikee,Some pictures of my Active Load, i'am testing it at the moment, and adjusting it.Full Speed!!! ~280 WattsTop View, yes, when I'm done is the wiring decentSide view,The temperature is just below 85C @ one off the MJ15004 transistors @ 220Watts total dissipation.Heatsink + 4x MJ15004Regarts,Blackdog

author: LEECH666
author_rank: Frequent Contributor
timestamp: December 08, 2012, 06:33:03 pm
content: Hi blackdog,nice construction!Is there any benefit in using BJTs instead of FETs?Cheers,Florian

author: blackdog
author_rank: Frequent Contributor
timestamp: December 08, 2012, 08:14:57 pm
content: Hi Leech666I tried to build him with the parts I had, and I had 20 pieces MJ15004.I Like the TO3 form because you can get good thermal contact.But i also use Fets a lot in TO247 package.Regarts,Blackdog

author: Spikee
author_rank: Frequent Contributor
timestamp: December 09, 2012, 05:34:27 pm
content: Is there any advantage in using an one ohm 100W power resistor instead of an 0.1 ohm 10W resistor ?I did some research in some other designs and youtube video's but i am not sure yet.In the ohmic region of the mosfet the resistor will only dissipate 9W (30v 3A -> 3v drop * 3A = 9w in power resistor 1ohm ) but when the mosfet is in full saturation the 90w will need to be dissipated almost fully in the load resistor.I'm not sure if im thinking correctly but if i use a 0.1ohm load resistor it will take in ohms region 0.9W (30v 3A -> 0.3 v drop *3 A = 0.9W )but in full saturation it still needs to take almost the full load of 90 W ?thanksspikee

author: T4P
author_rank: Super Contributor
timestamp: December 09, 2012, 06:05:59 pm
content: Let's say you are measuring 1amp, 1amp = 1 volt so therefore you get more resolution and accuracy at lower voltages but the dropout voltage is higher though at higher currentsUnless you use a specific DMM chip you know will work for sure with milliohms then with lower currents just go with a 1ohm shunt resistor

author: LEECH666
author_rank: Frequent Contributor
timestamp: December 09, 2012, 06:07:56 pm
content: Not really, you will only be able to dissipate more power in that specific resistor. If you want to parallel A LOT of FETs and only use a single shunt resistor is the only application I can think of where this matters. For example in one my dummy load units I want to be able to draw 1.25A.Power dissipated in 0.1 Ohm shunt resistor is:P= I² * R = (1,25A)² * 0.1R = 0,15625WI'll be using a 3W resistor that I'm having around, so that should more than do for my application.The maximum current that 0.1 Ohm / 3W resistor should be able to handle is:I_max = sqrt(P/R) = sqrt(3W/0.1) = sqrt(30) = 5.477AA 0.1 Ohm / 10W resistor should be able to handle:I_max = sqrt(P/R) = sqrt(10W/0.1) = sqrt(100) = 10AFor a 0,1 Ohm / 100W resitor that would be:I_max = sqrt(P/R) = sqrt(100W/0.1) = sqrt(1000) = 31.622ASo unless you want to draw more than 30 Amps, no it probably won't make sense to use a 100W resistor.//EDIT: Sorry I misread again. I thought you where talking about 0.1 Ohm / 100W vs. 0.1 Ohm / 10W.Cheers,Florian

author: blackdog
author_rank: Frequent Contributor
timestamp: December 09, 2012, 07:13:01 pm
content: HiHere are some pictures off my Active Load.He is really finished :-)Inside pictureKicking Ash! YES almost 300Watt's for 5 minutes, temp heatsing 85C.Now I just have to find the screws to close the case...Kind regarts,Blackdog

author: SeanB
author_rank: Super Contributor
timestamp: December 09, 2012, 07:19:10 pm
content: I think using a 100A plus stud mount diode is a little overkill for 20A........, and the heatsink on it is a little small anyhow.

author: blackdog
author_rank: Frequent Contributor
timestamp: December 09, 2012, 07:25:43 pm
content: Hi SeanB,Uhm, the diode is only for reverse protection...It is Not Mounted on a heatsink, just my way to mount it.The diode has only to blow the fuse.Regarts,Blackdog

author: Spikee
author_rank: Frequent Contributor
timestamp: December 09, 2012, 08:19:31 pm
content: Leech , you were almost correct . Whit a 1 ohm resistor of 100w i will be able to pull 10A max.My mosfet and heatsink can only handle around 120W max. At 12 volt i can utilize the resistors rating fully at 10 A.In my application i dont need to test high currents at low voltage so the 1 ohm 100W resistor is perfect.Thanks for the info , tomorrow i will recieve my parts and i can start testing the pc heatsink.Gr. Spikee

author: Spikee
author_rank: Frequent Contributor
timestamp: December 09, 2012, 10:19:49 pm
content: So i just mounted the 100W resistor and the mosfet on the heatsink. I mixed the artic silver stuff , put the two TO247 package opposite side of each other (to utilize the heatpipes fully) . Then i clamped them on the heatsink and applied ~10W on the 1ohm resistor so the curing would go faster.it was ambient temperature of 18 deg C here and now the heatsink is stable at 39 deg. C (no fan , upside down ) .You immediately see the advantages of heatpipes. the whole heatsink is at the same temperature and the fins got hot before the mounting plate.After a few mins the mounting plate and the fins get around the same temperature.Pic:Whole assembly:https://www.dropbox.com/s/3dse7kpoq3tft5k/2012-12-09%2023.05.08.jpgMosfet and power resistor:https://www.dropbox.com/s/v9hmkshzxbjd6d1/2012-12-09%2023.06.18.jpg

author: Spikee
author_rank: Frequent Contributor
timestamp: December 11, 2012, 11:44:47 am
content: So i just picked up my components at college.The 1ohm 100w resistors are huge , do i need to put them on an external heatsink ? or can they handle the 100W just mounted on the metal case.Item number: WH100-1R0JI maybe i can fit them on the top of the processor side.pic:50K ohm 10 turn pot2x 1ohm 100W resistors10x 0.1 ohm resistor 3W

author: T4P
author_rank: Super Contributor
timestamp: December 11, 2012, 01:50:31 pm
content: Check the given thermal specs (Tj-a and Tj-c) of the resistors as well as calculate roughly how much temperature rise you can tolerate on a heatsink (I would recommend not going over 85C if possible so)Think of the voltage drop (1V in your case so if you're pulling a amp it's 1W but surely it can handle it right? Actually such a huge resistor is somewhat overkill)If you're just pulling 3A, seriously it's only 9WI recommend using a fan or a better fan because those heatsinks IMO optimum-ly can't do more than 115W at 80C (50C rise i think?) at least

author: Spikee
author_rank: Frequent Contributor
timestamp: December 11, 2012, 03:18:10 pm
content: The resistor wattage is calculated for a max current of 10A.P = i^2 * Rp = 10^2 * 1p= 100WI probably wont use it fully 90% of the time . But i would like to have the possibility to do it . In price it did not matter that much.gr. spikee

author: T4P
author_rank: Super Contributor
timestamp: December 11, 2012, 03:43:42 pm
content: I guess if you would dare to use a low-priced but totally awesome heatsink from china it's called the Deepcool ice blade GS (In china it's translated as frostsaber player edition) 1kg raw weight and lots of cooling powerSimply because the artic cooling HSF is far too small for beyond 115WAside from that,At 10A with the resistors dissipation i doubt you even need the mosfets anymore if you want about 100W maxIf you want to continue using the shunts at >5A i think you'll have to use 0.1ohm resistors or switch them in and out with a comparator and a SSR (Might swamp the resistance of the resistor)

author: Spikee
author_rank: Frequent Contributor
timestamp: December 11, 2012, 10:00:19 pm
content: I have it running at 30.92V and 3.02A stable.Mosfet case temp: 53 deg C.heatsink temp (processor bottom) : 28 deg C.resistor temp : ~ 28 deg C.Fan: 12V DCThese cpu fans are a giant improvement , i ran into the limit of my power supply else i would have pushed it to 110 / 120 W .The only thing that is acting up is the LM324N , it worked fine the first hour but it will only shoot up to the top rail now.Things i did:Replace the LM324N (several times)check all the wiring (several times)added pull down resistor at output of op ampmeasured the output of the pot meter (no problems there)Result: still a non working voltage follower opamp ...Is the mosfet capacitance or something like that to high for the low power mosfet ?? i really don't know whats wrong :S .I connected the opamp now in this weird way and it works. It only changes a a couple of 10 mA from 0-> 30V so it is still constant current.pic:Why is it working ?if i pull out the wire of the feedback , the regulation wont work anymore and the mosfet will jump into saturation.i also made a youtube video for you guys:after the video i disconnected the fan to see how much it affects the heatsink temperature.Within 2 mins the heatsink went to 40 deg. C. (almost the same as mosfet temp) and kept rising.So i connected tge fan again and in 2-3 mins the heatsink went back to 29 deg. C. and the mosfet still at 40 deg. C. (normal) .I did some calculations and the Artic freezer 7 pro rev 2 is : 0.21 deg C. / W (mosfet 0.75 + 0.25 deg c /w ) which makes it a total of :1.21 deg C. /WSo i just tested a lead acid battery. I put my mosfet into saturation and you could immediatly see the disadvantage of using a 1 Ohm resistor at low voltages (10V) . I was limited to 7A @10.4A so i used one of my 3W 0.1 Ohm resistors i had laying around and i could get 20A + until the 10A fuse gave in my Rigol DM3058 (max 10A ) . i used my current clamp to measure the 20A + currents. I may make a relay or ssr in the final build so you can change from 1 Ohm 100W load resistor to a 0.1 Ohm 100W one. @ 20A i also saw some smoke coming from some of my leads , they were a bit thin.yet another day has ended 52 minutes ago ... guess i'll get some sleep now.gr. spikee... still not asleep but i checked the fuse of my rigol dm3058 and it has blown indeed. Seems it will be my current clamp for now on.

author: LEECH666
author_rank: Frequent Contributor
timestamp: December 12, 2012, 12:30:08 am
content: Looks to me like you're directly driving the MOSFET from the Pot now. The OP is basically redundant now.But I am not expert. Struggeling with OPs too atm.Cheers and good night,Florian

author: Harvs
author_rank: Super Contributor
timestamp: December 12, 2012, 02:43:55 am
content: Quote from: Spikee on December 11, 2012, 10:00:19 pmWhat exactly are you trying to do by that? The MOSFET gate should be connected to the op-amp output like in every other circuit that's posted around here. In that circuit the op-amp output will go to the positive rail because your -input is less that you're +input voltage. Simple as that, the op-amp would normally control the FET gate so that it can increase the current level until the - and + inputs match.

author: Jay_Diddy_B
author_rank: Super Contributor
timestamp: December 12, 2012, 04:10:32 am
content: Hi,I have been following this thread for a while. It is time to jump in and offer some advice that will lead to successful loads.Here is a simple load:The circuit is based on the LT1635. This is a combination of a 200mV reference and an op-amp.The circuit use a 0.1 Ohm resistor in the source of the MOSFET to give a maximum current of 2A.The datasheet for the LT1635 can be found here:http://www.linear.com/product/LT1635MOSFET selectionSome MOSFETs that have been optimized for switch mode power supplies will not work well in the Linear Region. We can tell this by looking at the Safe Operating Area curve on the datasheet. Here is a Vishay IRF530:This curve shows where it is safe to operate the MOSFET. This MOSFET is only limited by power dissipation.The second SOA curve shows a Renesas 2SK3481Note:It sis not safe to operate this MOSFET at high voltages and low currents.MORE Power, More MOSFETsTo increase the power handling more MOSFETs are required. It is not a good idea to parallel MOSFETs.Why??The transfer graph:shows that at currents below 10A the drain current will increase with temperature for a given gate source voltage. The hot MOSFET will hog the current and get hotter. We now have the possibility for thermal run away.Matching the MOSFETs may help a little, but the better way is to use an op-amp per MOSFET. This removes need to match the MOSFETs.This technique is found in most commercial loads.JDB

author: Harvs
author_rank: Super Contributor
timestamp: December 12, 2012, 04:50:21 am
content: QuoteSorry I'm probably missing something here, but how did you come to that conclusion?For DC loads the mosfet naturally has a Vds limit (the right hand line), a power dissipation limit (as marked on the line sloping down to the right), and a limit of the Rds(on). Apart from these things, what's not safe about operating this mosfet at say 80V, 0.15A?Cheers

author: Spikee
author_rank: Frequent Contributor
timestamp: December 12, 2012, 09:32:27 am
content: As i stated in my previous post the lm 324n wont regulate at all and the output will jump to the top rail. It looks like the lm324 cant drive the mosfet any more. Ill have to look if i have a higher power mosfet to drive the fet.

author: LEECH666
author_rank: Frequent Contributor
timestamp: December 12, 2012, 09:34:47 am
content: Quote from: Jay_Diddy_B on December 12, 2012, 04:10:32 amHi JDB,The Master/Slave design is exactly what I am trying to build in my "own variant" of a dummy load.I've linked to my thread previously but anyway here is the link againhttps://www.eevblog.com/forum/beginners/derpy-load-is-this-dummy-load-design-any-good/Cheers,Florian//EDIT:Spikee, since the LM324 is a quad OP: Did you properly terminate the unused gates? I read that if you leave the unused gates at undefined levels that this might interfere with the used gates.For example here:http://www.electro-tech-online.com/general-electronics-chat/42965-beginner-unused-half-dual-opamp.html#post353639and herehttp://twilightrobotics.com/wiki/Properly_Terminating_Unused_Op-Amps

author: Spikee
author_rank: Frequent Contributor
timestamp: December 12, 2012, 09:59:41 am
content: I will try your suggestion leech. I had them floating all the time. I will try it now.

author: LEECH666
author_rank: Frequent Contributor
timestamp: December 12, 2012, 10:05:49 am
content: http://www.maximintegrated.com/app-notes/index.mvp/id/1957This article by maxim is a bit more detailed, but I am not sure how large the impact of an undefined unused gate really is. I guess it's worth a try.

author: LEECH666
author_rank: Frequent Contributor
timestamp: December 12, 2012, 10:14:26 am
content: This thread is also informative ...https://www.eevblog.com/forum/beginners/dave's-constant-current-load-traps-for-young-players/

author: Spikee
author_rank: Frequent Contributor
timestamp: December 12, 2012, 11:57:07 am
content: So i replaced the LM324N whit a L2722 1A opamp and i terminated the unused pins. Now it works perfectly.I will now continue testing whit a lead acid battery to achieve higher currents.

author: Jay_Diddy_B
author_rank: Super Contributor
timestamp: December 12, 2012, 12:18:18 pm
content: Hi Harvs and the group,Harvs asked:Quote from: Harvs on December 12, 2012, 04:50:21 amIt comes from looking at the SOA curve for the Renesas 2SK3481 MOSFETIf you study the DC line.At 5V Vds the maximum current is 11A a dissipation of 55WAt 9V Vds the maximum current is 6A a dissipation of 55WAt 20V Vds the maximum current is 1.8A a dissipation of 36WAt 40V Vds the maximum current is 0.65A a dissipation of 26WYou can see how the maximum Dissipation is reduced at higher voltages.Some MOSFETs do not like being operated in this part of the SOA graph at all.For further reading on this:http://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/20100014777_2010016074.pdforhttp://powerelectronics.com/power_semiconductors/power_mosfets/power_trench_fets_fragile/NoteBipolar transistor have similar de-ratings, but the reason for the failure is very different. Google 'Second Breakdown BJT'JDB

author: Harvs
author_rank: Super Contributor
timestamp: December 12, 2012, 01:18:09 pm
content: Thanks JDB, I understand what you're talking about now.Cheers

author: Spikee
author_rank: Frequent Contributor
timestamp: December 12, 2012, 02:27:52 pm
content: I just made another video , the opamp problem is fixed . In some weird way mu arduino mega is getting reasonably hot. I might have to investigate that.I just went around town to find a new lead acid or gel battery but i coulden't find one anywhere ... so i will have to wait until the weekend so i can take the one i have home to my dorms .I also ordered a 0.1 ohm 100w resistor for low voltage , high current testing.

author: Spikee
author_rank: Frequent Contributor
timestamp: December 22, 2012, 02:17:29 am
content: It has been a while but i'm still buzy testing the current load.All my gel / lead batteries are dead so i bought a second hand Delta Elektronika M5-10 (5V - 10A ) power supply.In my youtube video i demonstrate the impact of a higher load resistance vs a lower one.In particular i test 1 ohm versus 0.1 ohm 100W resistor. I test the load on 10A 5V and at the end you see a connector melting because of the current.Youtube link:If you like my videos just Comment , rate and subscribe .Also a thumbs up really helps!

author: mazurov
author_rank: Frequent Contributor
timestamp: December 29, 2012, 04:19:08 am
content: JDB: I made a circuit from your model and it works very well!

author: mazurov
author_rank: Frequent Contributor
timestamp: December 29, 2012, 07:34:14 am
content: Here's the circuit heating up old Pentium Pro heatsink. Holds 1.9A current within several milliamps from cold start at RT to ~60C.

author: Jay_Diddy_B
author_rank: Super Contributor
timestamp: December 29, 2012, 01:47:37 pm
content: Hi,Here are some pictures of the load that I made. As shown the load is good for about 10W. This can be increased to 30W with a bigger heatsink and a fan. For higher power I would suggest using the Master/Slave configuration.I found a small load like this to be useful when testing multiple output power supplies.Outside view:Inside view:Board top side:Board solder side:Board Design:RegardsJay_Diddy_B

author: Spikee
author_rank: Frequent Contributor
timestamp: February 25, 2013, 02:55:32 am
content: So i had some more time and i worked on the constant current load.I have fitted 4 IRFP064N on a Hyper z600 CPU cooler and used one opamp for each mosfet. As a load resistor i use 0.1 Ohm 3W now but i will be switching them for 8 W equivalents. I will be testing the supply whit a 200W load tomorrow. But i already peak tested it at 63A , 10V = +-630W but some wires , shunt wattage etc was to low to run it for longer than a 5-10 seconds. This setup should be capable of 200W whitout getting hotter than 50-60 deg C. using one 120mm fan which has an resonable CFM. I can fit another fan to improve it ... but i have to make the pcb first. I need to get some connectors so i can hook up my 750W coolermaster pc power supply and see what the max of this cooling setup is. I think it is about 300-400W and then it will probably be around 60-80 degrees C.Sorry for the bad photo's / video my phone was empty and it is really late now ... but i'm just soo exitedPic of setup:https://dl.dropbox.com/u/100819959/constant%20current%20load/20130225_032839.jpgBreadboard:https://dl.dropbox.com/u/100819959/constant%20current%20load/20130225_032825.jpgFeedback + gate wires:https://dl.dropbox.com/u/100819959/constant%20current%20load/20130225_032828.jpgClose-up of resistors , mosfet construction:https://dl.dropbox.com/u/100819959/constant%20current%20load/20130225_033010.jpgTodo:-Make pcb-Bigger wiring on some places-Add intelligence (STM32 + touch screen lcd)-total current measurement (LT6100 whit 2m ohm shunt)-Put in an enclosure- ...

author: blackdog
author_rank: Frequent Contributor
timestamp: February 25, 2013, 11:51:20 am
content: Hi Spikee, :-)How dit you connect the powerfets to the heatsink, glue?Kind regarts,Blackdog

author: LEECH666
author_rank: Frequent Contributor
timestamp: February 25, 2013, 03:42:31 pm
content: I've talked to Spikee on Skype some time ago. The FETs are indeed glued onto the heatsink with some thermal adhesive.

author: Spikee
author_rank: Frequent Contributor
timestamp: February 25, 2013, 05:59:44 pm
content: Quote from: blackdog on February 25, 2013, 11:51:20 amI used Arctic Silver thermal adhesive. That stuff is super strong , it's almost impossible to get it off without sanding the heatsink.It conducts but that does not matter because all the drains are already connected whit wires. I'm making my schematic now in Altium and i will post it here. The fan puts alot of noise in the supply so extra schottky diode etc is advised. Without the schottky diode the output noise is around 20mV PP.gr.spikee63A peak current test:A few moment before i had it at 50-60A for 20 seconds and the insulation of my wires was melting.Schematic :https://dl.dropbox.com/u/100819959/constant%20current%20load/Constant%20current%20EEVblog_Spikee.pdf

author: rbola35618
author_rank: Frequent Contributor
timestamp: February 26, 2013, 01:31:03 pm
content: Nice video and projects Spikee.

author: grenert
author_rank: Frequent Contributor
timestamp: February 26, 2013, 03:20:48 pm
content: Jay_Diddy_B,Did that case come with the heatsink? Where did you find it?Thanks!

author: Spikee
author_rank: Frequent Contributor
timestamp: February 26, 2013, 03:24:23 pm
content: Quote from: rbola35618 on February 26, 2013, 01:31:03 pmThanks!Quote from: grenert on February 26, 2013, 03:20:48 pmHe used an off the shelf case. Got a metal plate the same size as the normal end cap. Drilled some mounting holes in it and mounted the heatsink on the plate.

author: Jay_Diddy_B
author_rank: Super Contributor
timestamp: February 26, 2013, 04:21:53 pm
content: Hi Grenert,Spikee is correct. Here are the details:The case was manufactured by Hammond part number 1598A.The rear panel was cut from aluminum sheet 0.062, 1.5mm.The Heatsink was cut from a length of aluminum extrusion. It is about 1 inch (25mm high)I drilled and tapped the heatsink to attach it to the metal plate.This design is good for about 10W dissipation.Regards,Jay_Diddy_B

author: clcham
author_rank: Newbie
timestamp: December 07, 2013, 07:47:14 am
content: Quote from: Spikee on February 25, 2013, 02:55:32 amHi Spikee, I've seen your schematic, I have a few questions:1) why do you need a pull down resistor?2) there is a 2.7k resistor in the feedback path, what is it for?3) what is the maximum voltage capable of discharging with this design?thanks

author: Spikee
author_rank: Frequent Contributor
timestamp: December 07, 2013, 09:12:32 am
content: 1. So the mosfets turn off when you apply no current.2. Probably some kind of filter (haven't looked at schematic , there is probably also a cap somewhere)3. It is limited by the voltage of the mosfet. The IRFP064N has a VDSS = 55V . If you need more then you need to change the mosfet.

author: ghent360
author_rank: Contributor
timestamp: November 30, 2019, 01:58:20 am
content: Hi Spikee,None of the links are working. Schematics gives 404- not found. Video does not play anymore. Would you kindly re-upload.