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Whoops. Burned up my BMS while trying to charge!

Started by Grummanflyer, January 16, 2022, 07:37:37 AM

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Grummanflyer

 I got this 2019 Rad Rover with 1100 miles on it a few days ago and so far I put 60 or so miles on it.  Everything was working well but when it got to two bars left it died very quickly thereafter, totally shutting down so I thought something was up with the battery.

Charged it up fully for 12 hours to try to let it balance and after 23 mile ride, all cell groups were at 3.58 and this cell group was at 3.44

So I attached my alligator clips to the two cell group tabs to charge at 4.2v and somehow I must have touched them to the circuit board in the exact wrong spot and whooof a big spark and lots of smoke. I am left with a tab that has melted itself off the circuit board.  So yeah I totally screwed myself trying to "fix" something.  There's nothing left on that circuit board to resolder the tab back to..all the metal is gone.

So I did a search and found user dickb has created a very detailed and extremely helpful guide to replace the BMS with an aftermarket bms on this exact battery (rad 48v 14ah)

I've already ordered the same BMS he used from greenbikekit.com

Here is a link https://ibb.co/XyBhcnp  to the image of the damage and a link to user DickB's wonderful guide https://www.radowners.com/index.php?topic=1647.0

DickB

I don't think that a.14V difference after full discharge is an issue.  When you get the new BMS installed, charge for 12 or more hours to give the BMS opportunity to balance the cells, then (carefully!) measure cell voltage.

There are BMSs available with Bluetooth that give diagnostic info.  I may try one sometime.

2 bars could be as little as 13% capacity left. (I created this chart by attaching a variable power supply to my bike in place of the battery.)

Grummanflyer

#2
Quote from: DickB on January 16, 2022, 05:28:16 PM

2 bars could be as little as 13% capacity left. (I created this chart by attaching a variable power supply to my bike in place of the battery.)

That's a very helpful chart you created.  Thank you  for that.

I'm curious where you got your reference for what percentage a certain voltage is? Ive refered to other charts that show a little bit higher percentages than what you show. Almost 20% in some cases.  I guess it depends on what the rad battery BMS cuts off?  As in what voltage is a dead battery?   I believe it is generally recognized that the operating range of a Lion cell is 4.2v-3v.

For example 45.6v in your chart for 2 bars is 43% in the chart I attached and you show it as 24%

DickB

I ran a test on my Standard Rad battery, running the bike on level ground at full throttle, stopping every 2 miles to measure battery voltage. The test ran 20 miles before the battery was basically empty, so about 1 mile per 5% capacity. Results in the chart.

Capacity depends upon how much current is being drawn. My test was at the high limit of Rad current draw.

info@lygte-info.dk ran tests on single cells at 1A and 3A, and you can see the results in the table. The Panasonic cell at the right of the table is the same or similar to one that Rad uses (in addition to Samsung cells). You can see the higher the current draw, the less capacity.

The Rad controller begins limiting current to the motor before the BMS would cut off current completely, so the effective low voltage is about 40V or 3.1V per cell.

Veggyhed

Love the charts. Thank you

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