100watt- 400 watt transistor to drive dc motor - Page 1
Forum section: electronics / beginners

author: krayvonk
author_rank: Regular Contributor
timestamp: March 29, 2020, 04:19:48 pm
content: I cant seem to find one of these things.What do they look like and how big are they?

author: andy3055
author_rank: Super Contributor
timestamp: March 29, 2020, 04:28:05 pm
content: One would use thyristors at those high voltages to drive heavy current loads such as motors.Years back I worked at a plywood plant in Fiji and that is what was used. Manufacturers like ABB/Siemens specialize in those thyristor drives.

author: StillTrying
author_rank: Super Contributor
timestamp: March 29, 2020, 04:39:40 pm
content: If it's just for on and off switching of the motor the idea is to dissipate nearly all of the power in the motor and not the switch.The motor's start up current is probably the most important to know.

author: madires
author_rank: Super Contributor
timestamp: March 29, 2020, 04:59:45 pm
content: It would help if you tell us more about your project. What is voltage of the DC motor? How do you want to drive it? Simple on/off, H bridge, or whatever? What about the driving signal?

author: krayvonk
author_rank: Regular Contributor
timestamp: March 29, 2020, 05:12:24 pm
content: Thanks for the help.Its just all on all off Left Right control.I want to switch it with an ldr (cause im going to commune with it through the screen of a laptop) , and its only a pretty small motor, only 100 watts will ever get to the motor,but i need 4 times that much to go through the transistor, cause my circuit is a little unorthodox. (but its like a h-bridge, but it has a constant back return)So when the transistor is on, im going right through the motor, when its off ive got another connection to battery that auto-returns it left.Doing it this way is not as good, but I only need 1 transistor per dimension. (and its a robot so its got tonnes of these) And it might get expensive 4 trannies per hinge.I wish I could just use the ldrs as a variable resistor but id need about 20 per dimension because theyd get so hot and they are too resistive, and transistors im guessing would be alot cheaper.Unorthodox 1 switch h-bridge->Ive tested the circuit, (only with resistors, and just a wire for the transistor) and its working fine, it has to decellerate before it goes in the opposite direction, and it goes a little faster in one direction than the other - and I lose power down the ungated pathways, so i get about half strength, and because it working back against itself its a quarter - but I think this wont come out of the battery so I should be ok in that regard.The transistor would go where the "Left Right" switch is.

author: madires
author_rank: Super Contributor
timestamp: March 29, 2020, 05:52:11 pm
content: Battery voltage? Motor voltage?

author: james_s
author_rank: Super Contributor
timestamp: March 29, 2020, 05:59:53 pm
content: If you're dissipating 400W in the transistors to control a 100W motor then you're doing it wrong. Re-think the whole approach, motor control is a very mature field, your problem has been solved before by somebody.

author: schmitt trigger
author_rank: Super Contributor
timestamp: March 29, 2020, 06:05:55 pm
content: Un orthodox bridge, indeed!Have you taken into account all the wasted energy through the resistors?

author: krayvonk
author_rank: Regular Contributor
timestamp: March 29, 2020, 06:06:35 pm
content: So is the difference between 400 watts and 100 watts significant?I dont even know what the dimensions of a transistor I need for it.In this video - do you think its running the motor off the 9v battery? Cause its going faster than mine with the 90 watt power supply cranked full.If this is sounding illogical, I know what you mean, Im not sure whats going on myself...I might have some problems getting my bot off the floor...Yes theres wasted energy through those 2 junctions through the resistors to negative, I have them at 10 ohm, but maybe 3 ohm would work (less resistance = more power) because the motor would only be about 2-3 ohm - and i need to make the loss 50/50 to fit my idea.Ive got my power supply cranked full, and its a pretty small motor, im definitely overpowering it if it was getting full power (but it actually isnt getting that much across the bridge.), but im not really sure what its rating is. My resistors are getting really hot, and they are rated at 10watts. I can only have it on a little at a time, but I can get bigger resistors if I want any time.If my calculations are correct its about 25 watts going to the motor. but its going slowish - and is 25 watts too much for going slow? I could do a video of it, if it helps.

author: james_s
author_rank: Super Contributor
timestamp: March 29, 2020, 06:09:30 pm
content: Quote from: krayvonk on March 29, 2020, 06:06:35 pmThe actual numbers are irrelevant, the fact that you're wanting to burn up 4 times as much power in the transistors as gets to the motor is very significant. You should aim for something like 5% losses, not 400% losses.SCRs (thyristors) were used to control motors back in the 1970s and into the 80s but they have been obsolete for a long time, now MOSFETs are used almost exclusively.

author: krayvonk
author_rank: Regular Contributor
timestamp: March 29, 2020, 06:22:53 pm
content: Its actually only 50% wastage of the battery, But because its on a "spring" It divides the power to the motor by 2 again, because it needs a left direction and a right direction.

author: krayvonk
author_rank: Regular Contributor
timestamp: March 29, 2020, 06:45:39 pm
content: heres a vid of it going. (I kept my mouth shut.) its a 90watt power supply and it was on halfway exact. and I had to bodge resistors I had on, so they arent exact omages, but its actually biased in one way even if you get them right cause of load differences.

author: schmitt trigger
author_rank: Super Contributor
timestamp: March 29, 2020, 06:47:35 pm
content: Quote from: krayvonk on March 29, 2020, 06:06:35 pmThat is a direct consequence of a completely incorrect way of controlling a DC motor.James-s is a very knowledgeable and helpful member. Heed its advice: re-think your approach.

author: krayvonk
author_rank: Regular Contributor
timestamp: March 29, 2020, 06:53:20 pm
content: haha np.I do get to purchase 4 times less transistors for my 4 times less power tho!

author: james_s
author_rank: Super Contributor
timestamp: March 29, 2020, 08:59:57 pm
content: Wait, are we talking just a dinky little toy motor? 100W is quite a lot of power, at 9V that would be over 11 amps, obviously not doable with a little 9V battery, you might find a motor that powerful in something like a cordless drill. Those little permanent magnet motors used in a lot of toys are maybe 5W max, typically quite a lot less. You should be able to easily control one with an H-bridge made of something cheap and easily available like BD139/BD140 or some small power mosfets. There are also integrated H-bridge ICs specifically designed for controlling motors. I've used one made by TI, I don't recall offhand which specific part it was though.

author: krayvonk
author_rank: Regular Contributor
timestamp: March 29, 2020, 09:07:11 pm
content: Thanks for those component codes.Thats exactly what I want! -THANKS!!!How come my motors arent frying?? Ive had them on 100% power for ages and ive only ever cooked one of them, and it seemingly happened at random, the rest seem to take it fine.I know that the amps and volts get better efficiency at a certain setting due to the topology of the motor, but im not experienced and ive just been putting them on max power. (I plugged a drill into my PS once, and it acted funny and someone told me its because it was some limiter it had.)Maybe ive got some magic spell on my motors that dont let them blow up or something, but how the hell am I supposed to work things out with miracles every where...

author: james_s
author_rank: Super Contributor
timestamp: March 29, 2020, 09:15:18 pm
content: I have no idea since you have not told us what power supply you are using or what specific motors you are using. Permanent magnet DC motors can operate over a very wide voltage range, one rated for 12V for example will usually run on 3V or less and will typically tolerate at least 24V without burning up. The current depends greatly on the mechanical load, if you load down the motor and try to run it at higher than rated voltage it will deliver more than the rated torque while drawing more than the rated current and if you run it hard enough long enough it will burn up.There's no magic, it's just physics.

author: krayvonk
author_rank: Regular Contributor
timestamp: March 29, 2020, 09:26:04 pm
content: So im pretty much strangling the little motors, and I should upgrade to something like this right ->https://www.motiondynamics.com.au/united-my6812-12v-dc-100w-2750-rpm-electric-motor.htmlExcept, my power supply is 30v 3amp.... so I know what I have to do, I NEED AMPS NOT VOLTS!!! I have to change my powersupply, plus I need a different transistor...Maybe something like this for the power supply.https://www.jameco.com/z/MDR-100-12-MEAN-WELL-AC-to-DC-DIN-Rail-Power-Supply-12-Volt-7-5-Amp-90-Watt_1943481.htmlAnd this for the transistor.https://au.element14.com/on-semiconductor/rfp12n10l/transistor-mosfet-n-100v-12a-to/dp/1017795?gclid=Cj0KCQjwjoH0BRD6ARIsAEWO9DuvxDkf3X78H0n2Lr6eX4DAWgTFNokJOJ3l3c3XiFUC16fB-b9gKzAaApOlEALw_wcB&mckv=s_dc|pcrid|380892800521|pkw||pmt||slid||product|1017795|pgrid|76493923343|ptaid|aud-435654578090:pla-841876761010|&CMP=KNC-GAU-GEN-SHOPPING-TEST-NEWI cant believe transistors are so cheap, they are like chips.And now we are getting dangerous. So I better be careful.

author: james_s
author_rank: Super Contributor
timestamp: March 29, 2020, 09:37:19 pm
content: Is this even a serious thread or are you just trolling? What you're saying makes no sense at all, I'm out.

author: krayvonk
author_rank: Regular Contributor
timestamp: March 29, 2020, 10:24:09 pm
content: Im a total n00b mate. If this seems completely illogical, I am NOT doing it on purpose!!! just trust me, ill get to average eventually. i promise.I just plugged in a transistor for the first time Just then (I just added it to the circuit), I got it working, but it amplified *less than I thought* So i boosted up the base contrast a little more and it ran.THATS THE FIRST TIME IVE EVER USED ONE. Ive learnt everything backwards order, I never went to uni, and in electronics class I was only a teenager so I thought it was more cool to not listen to the teacher.Im amazed by simple crap that you would never even dream of being impressive at all. Im a literal joke in your eyes.But. my robot is soon on the way! And im planning on starting a CPU company would you believe.I know its all easy crap in the end as well, thats the one thing I know that isnt a joke. But... Im not there yet...FIX...Ok thats it for the thread. THANKS EVERYONE FOR THE HELP!!!

author: Mechatrommer
author_rank: Super Contributor
timestamp: March 29, 2020, 10:44:01 pm
content: the motor you showed in video is around 12-20W, 60W at best during stall. the diagram above is the worst way i've seen to drive a motor direction. what you are doing is shorting your psu with 3+6 = 9 ohm on the right, 12 ohm on the left, this result in tremendous wasted power. its a good coffee heater though in a cup. try google h-bridge motor control.

author: krayvonk
author_rank: Regular Contributor
timestamp: March 29, 2020, 10:48:42 pm
content: half goes in the motor, half is wasted. its only half. woops, its actually 2/3 if the resistance is 3 ohms matching the motor, but if its 10ohms its only a little more than half wasted If transistors were more expensive, it would be more worthwhile to use it, but since they cost very little, its probably not a good idea.

author: Mechatrommer
author_rank: Super Contributor
timestamp: March 29, 2020, 11:33:55 pm
content: dont just try to invent things. people have done > 80% efficiency (8/10 to the motor) many millenia ago, today people can do almost 100% efficiency. but if you insist on your way, who am i to object? so may i suggest this maybe a good option for you as a start... to power your 10W motor...https://www.alibaba.com/product-detail/10KW-10000W-dc-regulated-power-supply_2006541291.html?spm=a2700.7724857.normalList.50.5bfb1e79hZJF1ohttps://www.alibaba.com/product-detail/Fixed-Painted-Wave-wire-Wound-Power_60813487562.html?spm=a2700.7724857.normalList.12.706d6112H5MlHm&s=p

author: Mechatrommer
author_rank: Super Contributor
timestamp: March 29, 2020, 11:51:49 pm
content: Quote from: james_s on March 29, 2020, 09:37:19 pmwhat he's trying to build is a high powered wheatstone bridge. by adjusting resistance in one arm of the bridge, reverse polarity voltage is achieved, hence reversed motor direction. but instead of a voltmeter, he put a motor in the middle to change direction, now he's planning to put a bigger motor and his problem is, he'll need to reduce resistance in every wheatstone bridge's arm to get a usable power to the motor for rotation... he made perfectly sense, just not that practical... in todays term, we call that a joke, no offense

author: wizard69
author_rank: Super Contributor
timestamp: March 30, 2020, 12:57:20 am
content: As others have already said you need to rethink things here. There are dozens, probably several hundred, types of low voltage DC motor driver IC's out there. Some are for the automotive market and others more general, in one chip you get your entire motor control circuit.Less thn 10 seocnds on Google, searching for "DC Motor Control IC", turned up this:https://media.digikey.com/pdf/Data%20Sheets/Infineon%20PDFs/TLE84106EL.pdfwhich gives you 6 channels in one IC. By the way this isn't a recommendation at all because Infineon's data sheets leave a lot to be desired. Rather it it the very first chip that my search turned up.

author: Mechatrommer
author_rank: Super Contributor
timestamp: March 30, 2020, 01:10:56 am
content: assuming your current knowledge, i will do this (attached) when i was a kid, this is my "invention" called "dpdt bridge"no bodged power resistors mess, no transistor and math headache, and the cheapest and most efficient possible solution.

author: krayvonk
author_rank: Regular Contributor
timestamp: March 30, 2020, 01:23:51 am
content: Thats excellent thanks. I bet that operates at the full power of the battery!When does what we do get into the stage of "impressing others" instead of making you look like a lunatic on the internet?

author: ratatax
author_rank: Regular Contributor
timestamp: March 30, 2020, 01:30:07 am
content: i think what you are searching for is:

author: Mechatrommer
author_rank: Super Contributor
timestamp: March 30, 2020, 01:38:24 am
content: Quote from: krayvonk on March 30, 2020, 01:23:51 amyes thats the idea when driving a motor, power needed is what power given (to the motor, not to the power resistors). want slower motor? use smaller voltage battery like 1.5V AA. another solution is $1 buck converter from china. but if you insist well, i've given you the other solutions much earlier.

author: krayvonk
author_rank: Regular Contributor
timestamp: March 30, 2020, 01:40:04 am
content: NEEDZ MOR RESISTAHZ!

author: gcewing
author_rank: Regular Contributor
timestamp: March 30, 2020, 01:58:43 am
content: Quote from: krayvonk on March 29, 2020, 06:06:35 pmThe difference is 300 watts -- that's a serious amount of power!You don't seem to have much of a feel for what these numbers mean, so to put it in perspective, here's something that dissipates 500 watts:http://www.goldair.co.nz/product-catalogue/heating/panel-heaters/gph150-500w-mechanical-panel-heaterAnd you're thinking of wasting this kind of power foreach axisof your robot. If your robot has 3 axes, that's getting on for 1000W -- enough to heat your living room in winter!Do you see how impractical the idea is now?As you've found, transistors are cheap. 300W power resistors, by comparison, are not cheap -- Mouser is listing them for around $30 each, and that doesn't include all the heatsinks, fans etc. you would need to get rid of the waste heat.Just use a 4-transistor H-bridge, or a chip made for the purpose. It's the only sane thing to do.

author: HackedFridgeMagnet
author_rank: Super Contributor
timestamp: March 30, 2020, 02:17:34 am
content: Here I found a 400W transistor for you.Guys just answer his question, no need to overthink this.

author: krayvonk
author_rank: Regular Contributor
timestamp: March 30, 2020, 02:39:06 am
content: Thanks gcewing for the info. (Yes I am way out of whack still, I need to take in more information.)$30? Thats more like it, all the transistors I was looking at were cheaper than the photo resistors! It was a little illogical seeming.Base in the middle is the only way to do it.

author: Mechatrommer
author_rank: Super Contributor
timestamp: March 30, 2020, 03:11:28 am
content: haha thats a nice trick! TO-18 can for 400W, you'll need to buy 10 of them until you figure out the truth. but then (if it is), you are going to need 500W PSU, my earlier link will cost you $1000 china brand. here's better deal i just remember i built (invent?) a "h-bridge esc" a while a go for my rc project, made the pcb but have not assemble and program it since i put rc project on hold. its designed to accept PPM or PWM signal and also from potentiometer, to control both directions and speed. in the rc market this kind of board only can control bldc 3 wire motor, and only PPM signal from radio receiver, where my board can use normal 2 wired brushed motor controlled from either 3 types of signal. for your project i guess potentiometer will be a convenient one. if you want i can assemble, program and sell to you at $60, no need upgrade psu, no need to buy even 2pcs 2N2906 to find out that you will be left with nothing. your 30V 3A PSU can make your 100W motor jump across room if you want or if not careful, and can be as slow as snail controlled with potentiometer, 80% efficiency guaranteed. with 2 pairs of IRF3205 and IRF4905 combo in the bridge, it can drive up to 1000W motor theoritically. just upgrade to 1KW PSU and start killing living things if you want to, cheers

author: krayvonk
author_rank: Regular Contributor
timestamp: March 30, 2020, 07:39:50 am
content: I dont need a 500 watt psu if i can just put a couple of wires in the wall socket. (+ and -) and I dont even need to wire up an oscillator either!Wow man, you know alot. Did you draw that whole schemmy up for me? Very nice. (I actually like it alot, I wish ppl would show work here more often, is it uncool?)The $60 offer is nice, for my project ill at least be spending about $100 on my components, But it just doesnt seem honest if I dont do the hard work myself.And... Whats everyone got against potentiometres! arent they as good as a relay if u glue them to a dc motor?

author: TheHolyHorse
author_rank: Regular Contributor
timestamp: March 30, 2020, 02:46:46 pm
content: Quote from: krayvonk on March 30, 2020, 07:39:50 amIf you're actually considering putting some wires in the mains outlet, please don't for your own and everyone else's safety.I'd suggest you start over from the beginning, forget everything you know about electronics and get someone to teach you and actually listen.

author: atmfjstc
author_rank: Regular Contributor
timestamp: March 30, 2020, 03:24:53 pm
content: There is NO WAY this guy isn't trolling. The only other possible explanation for his style is if he were a 13 year old kid - but his Youtube channel disproves that.

author: TheHolyHorse
author_rank: Regular Contributor
timestamp: March 30, 2020, 04:17:04 pm
content: Quote from: atmfjstc on March 30, 2020, 03:24:53 pmI wouldn't be so sure, he seems dead serious. Not everyone is meant for electronics and some should outride stay away from it. That's just how it is.

author: krayvonk
author_rank: Regular Contributor
timestamp: March 30, 2020, 04:21:55 pm
content: I agree with you. Maybe I should just stick to raytracing, newton physics engines and artificial intelligence on the gpu... and never bother making a computer, cause its just too hard... assembler is just gobblegook better stick with high level its much easier, and get back into the kitchen where i belong.

author: Zero999
author_rank: Super Contributor
timestamp: March 30, 2020, 10:11:29 pm
content: Quote from: krayvonk on March 29, 2020, 10:48:42 pmA linear power supply controlling a load will dissipate half the power, but that's only when half the voltage is being dropped across the load.Consider a 1 Ohm resistor connected to a 10V power supply. The maximum power dissipation will be P = 102/R = 100/1 = 100W. If a resistor is connected in series with the load to control the power level. Say we select a resistor value to sweep the voltage across the load between near 0V and 10V. We can't go all the way to zero or 10V, because it would involve a resistor value with zero or infinite resistance, which is impossible and will give a division by zero error. The plot shows the maximum power dissipation in the series resistor is only 25W.Note how the power in the load shows a square relationship with the voltage. The maximum power dissipated in Rs is a quarter of the maximum power dissipated in the load.linear PSU power dissipation.asc(0.74 kB - downloaded 39 times.)

author: Mechatrommer
author_rank: Super Contributor
timestamp: March 30, 2020, 10:57:26 pm
content: Quote from: atmfjstc on March 30, 2020, 03:24:53 pmNO. this guy reminds me of my younger brother. this type of guys is for real... if you have family of this type, you'll understand when they stated...Quote from: krayvonk on March 29, 2020, 10:24:09 pmi guess they got sucked by a mentality/propaganda/idea that skills is more important than knowledge/academic. the good thing is he got some balls in trying electronics, better than be on the street.

author: Ice-Tea
author_rank: Super Contributor
timestamp: April 02, 2020, 08:12:05 pm
content: Quote from: krayvonk on March 30, 2020, 07:39:50 amFeel free to ignore everything everyone is saying *except* for this: don't jam wires into the wall socket. Just... don't.