Is there anyway to limit current on the cheap?

Electronics
#1

I recently purchased this adjustable power supply off amazon to charge some 36v lifepo4 batteries I’ve got.
https://www.amazon.com/dp/B0716XVR7P?aaxitk=V-71tO6tLmTRE-sFbTGfQw&pd_rd_i=B0716XVR7P&pf_rd_m=ATVPDKIKX0DER&pf_rd_p=3534726502&pd_rd_wg=u0Gzr&pf_rd_r=XQC76X41P70R4TW3RQ6E&pf_rd_s=desktop-sx-top-slot&pf_rd_t=301&pd_rd_w=nUKAf&pf_rd_i=adjustable+power+supply+drok&pd_rd_r=fd84e1e7-4cdf-4a50-9313-9372d746d174&hsa_cr_id=3780303930701

I didn’t read the listing to well and didn’t realize that the it doesn’t limit itself to the rated 10a. Apparently if I try to charge my batteries with this, it will try to supply way more amps than its rated for and probably fry.

I’ve inquired about returning it, but it doesn’t look like it’s going to happen since the error was on my side.

So to make use of this thing, I need to figure out a way to limit the current to 10amps.

I’ve been googling all morning, but haven’t come up with any great ideas.

Any help or ideas would be greatly appreciated

#2

The “dumbest” way to limit current is to put a series resistor in with your pack. Get a big beefy power resistor, throw it inline.

#3

You’re in luck I think. That looks just like a 30A supply that I had an equivalent experience with. The current was limited to something like 140% of its max rating.

I opened it up and immediately saw the three wire links it uses as a current shunt. I removed one link and it’s been happily chugging along limiting at some 90% of its rated current ever since.

Here you can see the two remaining links near the center of the photo.

20170321_123317
20170321_123317.jpg3264×1836 743 KB

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#4

Most power supplies will NOT supply more than the rated current. In fact most have protection circuits that monitor the output current and reduce the output voltage if the current is too high. It’s commonly called “foldover protection”.

That said, most batteries need a charge controller of some kind. Much cheaper in the long run to get a proper charger for your batteries, instead of damaging them ( with possible “exciting” side effects ) and then having to replace them.

#5

That would be great if that is the case. I’ll open it up after work today and have a look

#6

Yes, and it is rather easy to boot

#7

If you are going to charge lifepo4 batteries, do it right and get a charge controller. 36v is on the high end though and you won’t find a cheap RC charger for those batteries.

If you leave a regular power supply on them too long just once, that could go very wrong.

Something like this should work:


This company has several sizes depending on how fast you want to charge and the capacity of the batteries.

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#8

I’ve got about 8kwh worth of modules. Eventually I would need something beefy like this to charge in a timely manner:
http://www.electriccarpartscompany.com/36V-30A-br-Lithium-Battery-Intelligent-Charger-br-LiFePO4-Intelligent-Charger-br-CE-Certified_p_211.html

That thing is $723 though and I need to test my cells first to see if they are any good. This “small” power supply I purchased for testing purposes to help me determine that

#9

If it helps, the elab did recently get a lab power supply that will do the voltage you need at 10A. It’s the high voltage one that normally lives on the shelf above the computer. I still wouldn’t charge unattended but it should have reliable current and voltage regulation.

#10

We did? That’s awesome. Any link or information handy? I’d like to read up on what we have.

#11

Keithley 2260B-250-9

250V 10A 720W

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#12

Pwr sply is listed in the tool wiki and has links to the manuals.
https://dallasmakerspace.org/wiki/Tools#Electronics

While the pwr sply can protect itself from most misuse/abuse, please read the manual(s)!!

Edit: App Notes from National Semi (now part of TI) and Linear Tech (Analog Devices)

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#13

Here $10 bucks
I just got two of these but mine only go up to 30v
I like the first one with the case $6.80

http://www.droking.com/DROK:-13KHZ-PWM-DC-Motor-Controller-DC-12V-40V-10A-Motors-Electric-Pump-Fan-Speed-Stepless-Control-Module-with-Reverse-Polarity-Protection-High-Current-Protection?search=dc%20motor%20speed%2010a&description=true

#14

Thanks benemorius, I only had 2 shunts in mine. I cut one and it puts out 6.3amp now while charging my big modules. This is the simple solution is was looking for. Thank you!

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