High current LiPo-like power supply - Page 1
Forum section: electronics / projects

author: gertorro
author_rank: Newbie
timestamp: July 08, 2012, 06:19:19 pm
content: Hi everybody in the forum.I'm an aeromodelist and i'd be interested in building a high current power supply to test my motors and stuff.I want the PS to be able to simulate several LiPo configuratios (1S,2S,3S,4S until 14S which is about 60V) and also to supply currents from 20 amps to 200 by means of modular construction. Also i want to have a current and drawn power measurement capability with a built in log, or computer interface to graph the output values.Any idea of which kind of strategy I should use to build my little monster?Thanks for your attention!

author: shebu18
author_rank: Frequent Contributor
timestamp: July 08, 2012, 06:27:47 pm
content: Hy, nice idea you have there.Start with finding a transformer to produce 60V and 200Amps, or you can use a switch mode PSU for this.

author: Simon
author_rank: Unknown
timestamp: July 08, 2012, 06:31:37 pm
content: Quote from: gertorro on July 08, 2012, 06:19:19 pm200 amps ? how big are these models ? I strongly suggest you look at getting a decent bench power supply probably of the sort used for CB radio. I bagged myself a 3-15V @25 amps power supply for £ 50. I really don't see what you need 200 amps for

author: gertorro
author_rank: Newbie
timestamp: July 08, 2012, 06:33:29 pm
content: Shure, I forgot to mention that point, trying to build a power supply of that power requieres a switched mode architecture. A linear one would beHUGEand impossible to build cheaply!And also replying to Simon, I need at least 100 amps for my EDF units, the smaller one is 75 amps at peak power!

author: T4P
author_rank: Super Contributor
timestamp: July 08, 2012, 06:38:02 pm
content: Quote from: Simon on July 08, 2012, 06:31:37 pmWell to accurately talk lipos ... they can source a mad amount of currentQuote from: gertorro on July 08, 2012, 06:33:29 pm60v ... 200amps ... 12000W ...Man you need a mini power station to do this, 5000W+ is where switched mode power supplies get expensive

author: gertorro
author_rank: Newbie
timestamp: July 08, 2012, 06:42:49 pm
content: I forgot to mention the peak power of the power supply would be about 4.8 kW. That's another important limit I hadn't made clear enough. Also it would be ideal a single phase mains input, but I know that power means a lot of current even here in Spain with 240/400V electrical network (with 120/230V it will need a wire thicker than my thumb!).

author: T4P
author_rank: Super Contributor
timestamp: July 08, 2012, 06:56:52 pm
content: Quote from: gertorro on July 08, 2012, 06:42:49 pmThat's why i basically mean you need a mini power station.

author: G7PSK
author_rank: Super Contributor
timestamp: July 08, 2012, 06:57:11 pm
content: Sounds like you should start with an inverter type welder and modify it.something like this might make the basis of what you want.http://www.ebay.co.uk/itm/200-AMP-INVERTER-ARC-WELDER-stick-rod-200amp-/390140865796?pt=LH_DefaultDomain_3&hash=item5ad6352d04

author: M. András
author_rank: Super Contributor
timestamp: July 08, 2012, 07:18:33 pm
content: hmm 12kw linear supply alone the transformer would be more than 50kg if not the double, multiple windings for each voltage level, you dont want to dissipate the power from full voltage to test a 7.4 setup at 120A, multiple paralelled switchmodes would be cheaper, but even the premade ones for RC world cant be wired sieries/paraller too easy without fry one i guessSimon as for the brushless motors. even the smallest one can go up to 50A larger ones beyond 200A easly, biggest i found cheaply is 8kw and not that large

author: Simon
author_rank: Unknown
timestamp: July 08, 2012, 07:19:22 pm
content: that could be a basis but it outputs 30ish volts if I'm right. Do you have 8KW available in spain ?

author: Simon
author_rank: Unknown
timestamp: July 08, 2012, 07:20:34 pm
content: Quote from: M. András on July 08, 2012, 07:18:33 pmI thought we were talking radio control planes ?

author: gertorro
author_rank: Newbie
timestamp: July 08, 2012, 07:27:47 pm
content: And we are, here you have and example of a high power motor:http://www.hobbyking.com/hobbyking/store/__19111__Turnigy_SK3_Fandrive_3994_850kv_120mm_EDF_.htmlThis one is rated at 4 kW aprox. peak power. And replying to you, yes here in Spain a household standard power delivery contract is able to supply a maximum of 11 kW in single phase installations and 33 kW in three phased schemes without any permissions.

author: Simon
author_rank: Unknown
timestamp: July 08, 2012, 07:34:39 pm
content: so 90A continuous through those "little" wires ? I think not. How about some very large output caps for peak demand ? I'm guessing the 90A is the stalling current and in that condition it's not much use to you.

author: gertorro
author_rank: Newbie
timestamp: July 08, 2012, 07:50:33 pm
content: We are talking of using the PS for extensive thrust testing, let's say 4.8 kW or 4.8 KJ per second, using a cell of supercaps rated at 100 kJ (more would be very expensive) that means less than a minute of testing in the best case scenario. The proposal of an arc welder inverter seems interesting, but the control of the voltage and current seems quite difficult. Also those welding units work on voltages lower than 32V, far from my requirements, but it will do as an initial aproach!

author: M. András
author_rank: Super Contributor
timestamp: July 08, 2012, 08:13:43 pm
content: yep those things runs warm and at very high rpm, however i sometimes wondering how the hell can those 4mm connectors even handle 100amps continous, most of the batteries can support this for 5-10mins the motors run barely warm if they have nice cooling holes and design, not designed for constant 24/7 running but it will run approx 1 hour fine if its get dcent cooling, the esc will fry first btw

author: Simon
author_rank: Unknown
timestamp: July 08, 2012, 08:16:10 pm
content: And I ask the same question, how big is the aeroplane ?

author: IanB
author_rank: Super Contributor
timestamp: July 08, 2012, 08:40:32 pm
content: Quote from: Simon on July 08, 2012, 07:34:39 pmSimon, I think you need to re-calibrate your expectations. Yes, those little brushless motors can produce tremendous power outputs and no that is not the stalling current it is the normal running current.You might remember another thread I made about London Underground trains where I calculated they draw about 3000 A from the rails. Those trains only have "little" motors attached to the wheels to handle all that power. (OK, not quite so small, but if you look under a train can you even see the motors?)Think about electric cars vs petrol engines, and think about how much power petrol engines produce compared to most wimpy electric vehicles. Then consider that radio controlled aircraft used to use little petrol engines before they went electric. The electric motors need to have tremendous performance to match what petrol engines could do.

author: IanB
author_rank: Super Contributor
timestamp: July 08, 2012, 08:45:47 pm
content: Quote from: gertorro on July 08, 2012, 06:19:19 pmI think building a complete power supply for this might be rather expensive and complicated.Have you considered setting up a bank of lead acid accumulators (car batteries) that you can switch into various configurations for your testing? They will handle the 200 A you need easily in short bursts. You can use inexpensive trickle chargers for them instead of big expensive power supply electronics. Use the batteries as a big energy bank.If you need to regulate power delivery during a test you could then construct a PWM output regulator which would be much simpler than the whole switched mode power supply thing.

author: gertorro
author_rank: Newbie
timestamp: July 08, 2012, 08:48:17 pm
content: That would be like using the LiPos, which is what I want to avoid!

author: IanB
author_rank: Super Contributor
timestamp: July 08, 2012, 08:55:51 pm
content: Quote from: gertorro on July 08, 2012, 08:48:17 pmHave you considered whether something like one or more of these would meet your needs?http://distributor.meanwellusa.com/webnet_usa/search/seriessearch.htmlLike, for instance:http://www.meanwell.com/search/rsp-2000/default.htmHowever, don't expect them to be cheap at the kind of power levels you are looking for!

author: M. András
author_rank: Super Contributor
timestamp: July 08, 2012, 09:11:13 pm
content: is the small capacitiy of the lipo cells are the drawback or you want to test the motors/modells to destruction?the small capacitiy is an issue build your own high cap packhttp://www.all-battery.com/37volt-10000mah10cli-polycell.aspxseries+paraller some of these with some protection circuits and you are good to even hours of testing with a single charge, wont cost thousands of dollars like a 5kw+ psuor to be absolute safe without blowing the lipoly use few of thesehttp://www.all-battery.com/LiFePo4_Lrg.aspxthese will handle 2-3C continous discharge, and that combined with a 100ah rating its hilarious amount of power

author: sorin
author_rank: Frequent Contributor
timestamp: July 08, 2012, 09:24:39 pm
content: Quote from: gertorro on July 08, 2012, 06:19:19 pmso 60*200=12000w 12KWthe electrical system in your house is limited to 25A so 25*220=5.5KWyou need a 3 phase connection

author: gertorro
author_rank: Newbie
timestamp: July 08, 2012, 09:38:50 pm
content: In reply to M András, the main drawback is the charging perior, for every 10 minute test, I would need at least a 3 h charge. And as all the LiPos, the more cycles you use them, the worse they perform.Answering sorin, I always read the whole thread before posting, also for the plug I would use a 32 amp blue single phase CETAC like this one:http://ferreteriagranvia.com/603-175125-large/clavija-cetac-3pt-32a-380v-13302-ip44.jpg

author: M. András
author_rank: Super Contributor
timestamp: July 09, 2012, 06:46:00 am
content: you cant just use a bigger connector if the fuses etc placed by the utility company wont support anything higher than 25 amps or so/phase.then my second suggestion could work those 100amp prismatics would be the best choice few hours of charging to full and you can test several cycles, and the capacity drop is specified for lipos 500-1000 cycles before it goes down the 80% of the original capacity with those li-fe prismatics its 2k cycles

author: amyk
author_rank: Super Contributor
timestamp: July 09, 2012, 07:39:06 am
content: How about something like a Xantrex XDC60-200. Perfectly matches your specifications.It's been discontinued so you should be able to find one used for (relatively) cheap.Two of them, not working, got sold very recently:http://www.ebay.com/itm/ws/eBayISAPI.dll?ViewItem&_trksid=p4340.l2557&item=160807949280&nma=true&rt=nc&si=u%252FkBoB3uvXrJ9w65XCXizv53LxE%253D&orig_cvip=true&rt=ncOr how about something with a little more power:http://www.ebay.com/itm/SORENSEN-SFA60-100-POWER-SUPPLY-0-60V-0-250A-15kW-1-/110895951639?pt=LH_DefaultDomain_0&hash=item19d1e9ef17

author: G7PSK
author_rank: Super Contributor
timestamp: July 10, 2012, 03:06:30 pm
content: Quote from: Simon on July 08, 2012, 08:16:10 pmCould it be like this one.

author: Simon
author_rank: Unknown
timestamp: July 10, 2012, 06:47:45 pm
content: Ah but then we are not talking about models anymore. Great achievement. So we should have electric planes soon

author: Simon
author_rank: Unknown
timestamp: July 10, 2012, 06:52:43 pm
content: The website is a bit crap, just loads of flashy rubbish, not actual information

author: M. András
author_rank: Super Contributor
timestamp: July 10, 2012, 08:12:20 pm
content: i guess the kind of testing he wants to do with a powersupply fed rc model. is durability of the motor/rotors etc. it doesnt mean it must be a big one, even a small 1:8 scale rc car can draw 150 amps around 7-15 volts, its not common for cars to go higher, for planes way to 10-12 cells which is lots of power at those 100amps+ systems, imagine that a small 4cmx8cm motor can lift up even 5-8kg from the ground if we talking about airplanes with front props or edf style-aka jets, for choppers dunno i never looked into them closely