Modifying a knock-off battery charger to be safer

Since we have been discussing the failure of LiPo batteries during charging, I thought that it would be interesting to post this article on the shortcomings of a knockoff LiPo battery charger and how it could, in its unmodified form, cause damage to a LiPo battery.

By 

Sometimes buying a low-cost clone off of eBay is a great option, but [Martin] wisely decided to test his counterfeit IMAX B6AC, and found it grossly lacking. His detailed breakdown shows an alarming array of problems, including poor design and construction, and a lack of warning if the balance circuit fails. In addition, the charger wasn’t properly calibrated. By using a precision multimeter, Martin found that the charger actually brought cells above critical voltage. So really, using a charger like this out of the box can both destroy your battery pack and/or start a fire. One other interesting detail – this model can only be calibrated once. Sweet features.

[Martin] detailed his fixes in a well-illustrated blog post. He first had to re-enable the calibration menu using this method which requires bricking the device first! Once un-bricked, however, he could do the recalibration using a voltage divider and a reliable power source.

This project really underscores the need for a precisely calibrated multimeter. Not only would [Martin] not have been able to test his charger properly, but the re-calibration wouldn’t have been as accurate as needed. As hobbyists, this is a reminder that we can only trust our tools if they are accurate.

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Developer
Comment by Arthur Benemann on September 17, 2013 at 9:03am

Does anyone has given some thoughts about designing a open-hardware LiPo charger?

Anyone know of an existing charger that had it's firmware replaced by an open source one? Or one with a good data output (maybe a serial port with info about the charge)?

The data from the charger could be exploited on a Android app to build a  nice interface, with some great features.

Comment by Nick Arsov on September 17, 2013 at 9:12am

Hi guys,

If you have the above mentioned IMAX B6AC, do immediately kick away the power supply.

It is really awful...poor design and the poorest manufacture.

My iMAX fired a few months ago because of the AC-DC power supply. The charger itself is good, but not the power supply.

I think it's better to buy a DC-DC version ( iMAX B6 ) and a well manufactured AC-DC external power module.

Best regards

Nick

Comment by Rob_Lefebvre on September 17, 2013 at 9:12am

Yeah, it would be awesome to be able to serial number your batteries, and have automatic loading of settings, and tracking of data.


Moderator
Comment by Sgt Ric on September 17, 2013 at 9:16am

RCG has a good section on chargers and several threads involving replacing components for better accuracy.

I hadn't thought of open-source FW, so I don't remember see any posts, but check them out.

RCG B6 forum


Developer
Comment by Arthur Benemann on September 17, 2013 at 9:17am

If I'm going to build a charger this are the base specs that I would design over:

  • Just LiPo for the first firmware revision
  • 1S to 6S (up to 4S would be enough for me, but extending to 6S covers a lot more people)
  • Up to 5A charge (that is 120W)
  • External power supply, this would just complicate the design. And since It would probably be a third party module there is no why not externalize that completely.
  • Cell balancing it's a must
  • Android app interface for the charger, maybe via USB or Bluetooth
  • About the charger design it would probably be the standard 4 buttons and an LCD design, with advanced features made on the android app. I would like to drop the LCD, but then it would be hard to make it work stand-alone.
  • Discharge is a though point, I would like to be able to discharge my batteries at operation rate to measure their performance (I can see I doing it periodically to check battery heath,if it was easy enough). But dissipating 500W is thought. The way to do it could be to implement the logic and power electronics on board, but keeping the discharge element as an external connection made by the user. 

I'm loaded with projects right now, but that is something that I would like to work on the future.

@TJC III: I'm sorry for doing this partial hijacking of your post, if there is interest on the topic I'll move this to the forum.


Developer
Comment by Arthur Benemann on September 17, 2013 at 9:22am

@Robert:

Yes, that is totally possible if we use something like RFID. Take a look at this product, it's already out there. That way the charger could be really simple to use, requiring user programming just via the android app.

Sgt Ric:

Thanks for the link.


Admin
Comment by Thomas J Coyle III on September 17, 2013 at 9:45am

Hi All,

Looks like my blog post has got a very stimulating discussion going and I like to see that. An open-source charger design sounds very interesting! Keep the good ideas coming in and we might just have a new project here:-)

Regards,

TCIII ArduRover2 Developer

Comment by Rob_Lefebvre on September 17, 2013 at 9:59am

Arthur: I wasn't even thinking of RFID.  Just write a number on it with a Sharpie. ;)  But RFID would be even better and make it even more failure (human) proof.

Comment by Phil P on September 18, 2013 at 2:39am
I have one of these and I found that it heats up excessively on any more than a 3A charge for my 3S 10Ah lipos. I put a fan on the air intake. I never thought to confirm the cutoff voltage though. Good point. I won't trust it now till I have the time to measure with a good multimeter.

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