Large Scale Central

Li-Ion Protection PCB question

Electronics Power and Sound
#1

Does anyone know the specification for State of Charge Mismatch on a Li-Ion protection PCB? I know the PCB will shut down a pack if it detects a SOC Mismatch, but I can’t find what the differential is anywhere.

I’m trying to revive a 4 cell pack that died prematurely after 3 or 4 cycles and probably 8 months of storage. When I opened the pack up I found a difference of .2V from the highest cell to the lowest.

My attempted fix was to use a single cell PCB to re-charge each cell individually since I do not own a balancing charger. When complete 3 of the 4 cells were at 4.17V but the one suspect cell is at 4.14V - a SOC mismatch of only .03V. I have seen higher SOC mismatches in a brand new pack that functions properly. This pack will not put out any voltage from the PCB outputs even after a “jump start” to reset the circuit.

Presently I am discharging that single cell under load and will re-charge it again for one more try. I’m beginning to suspect that the PCB is bad.

#2

Yes, I do. Give me a call on Monday.

Rick Isard

Cordless Renovations, LLC

RCS America

#3

Thanks Rick. I’ll call, but why is it a secret?

#4

I haven’t had a chance to call Rick, but I did manage to get the pack balanced to within .01V using my single cell charge method. I still cant get the pack to light up through the PCB. The B- / B+ pack voltage is a healthy 15.35, but no go. I’m almost certain the protection PCB is toast and the cells are fine.

#5

Jon,

I’m not being decreet, I can find out alot more about your situation by talking within you over the phone then from behind a keyboard!

That’s fine, call when you can. What do you mean by, “light up?” You only need to be within .03V of nominal voltage from cell to cell, you would need one of my analyzers to get it that exact.

Rick Isard

Cordless Renovations, LLC

RCS America

#6

Thanks Ric. Been crazy busy at work so I haven’t been free to call during office hours, but I will. By “light up” I mean give an output voltage at P+ and P-. I get 15.35 (on my older digital VOM) across B+ and B- and with the same meter I read within .01V from cell to cell. I suppose that meter could easily be off by .02V or more.

#7

For the record I did contact Rick and without physically inspecting the pack he couldn’t diagnose the exact problem - and I wouldn’t expect him to. He did offer a number of suggestions of things to try and someone to contact if they didn’t help resolve the problem.

Unfortunately I still haven’t figured it out. There is one more of Rick’s suggestions left to try, but I need to get the pack discharged enough to try them. Doing that safely without the PCB in-line has been a challenge.

To be fair to Rick, this is a low-cost Tenergy pack - not known for being the best - and I didn’t buy it from him. The PCB although similar to the ones he uses isn’t exactly the same.

One thing I have read on the spec pages for the controller chip is that there may be a fail-safe (in case of polyswitch failure) non-resettable fuse on the board. If there is that may be the issue.

#8

Jon,

How are you discharging the battery? A simple load can be used together with a volt meter and some patience (incandescent 12V light bulb(s) are typically used in lieu of an electronic load).

Discharging the pact verses single cells to a pre-determined voltage cut-off will reveal why “balance charge/discharge regimens” are desirable. You’ll realize that not all cells within a given pack have like IR (internal resistance) at the level these cells typically discharge and adsorb charge at this maybe a moot point but it’s there and easily documented.

Like replacement 4-cell PCM’s are readily available for $8.00 or so shipped.

PCM"s with balance technology built-in are also available, I am presently evaluating a couple of these for 4 and 5 cell use, specifically for Li-Poly, but it matters not as the requirements for Li-Ion and Li-Po are the same.

FWIW: I generally don’t use PCM’s in favor of balance chargers but that’s another topic.

Michael

#9

I give … What’s a PCM?

Edit: OK “Protection Circuit Module” … I guess.

#10

That PCM acronym threw me for a bit too.

I am discharging a couple of different ways. The last attempt was as a pack, but jumping around the PCB (B+ / B-) into a 12V auto tail light bulb monitored with my volt meter. Unfortunately, I got distracted just as the pack was falling under 12.5V and when I looked back the lamp was out, the volt meter was reading very low and the pack was quite warm. I disconnected it and let it sit for 24 hours. Testing each cell I did pull one under under 3V to about 2.5V.

I also tried discharging each cell individually though a single cell PCB. My load was a small motor and it took a long time to kill a cell.

Presently I am recharging each cell individually through the single cell PCB. Once that is done I’ll log each cell’s voltage again and see where we are at.

Where are you finding circuit boards fr $8 shipped? My source charges $7 flat rate shipping on small orders.

#11

Jon,

Try eBay and or run a search in Google for PCM or PCB 14.8V.

PCB = protection circuit board and is an acronym for Protection Circuit Module. Either is synonymous with a protection device in this application.

What do you mean by using a single cell PCM/PCB? Are your cells equipped with them integrally? Or do you have a loose single cell PCM in-play?

Michael

#12

Or, you can just purchase them from me!

Rick Isard

Cordless Renovations, LLC

RCS America

#13

@Michael - I have a loose single cell PCB purchased specifically for testing cells. I had two but a poorly placed meter probe let the magic smoke out of one :{

@Rick - I’ll give you a call before I order elsewhere.

#14

This project has been on the back burner for a while. Rick from Cordless Renovations brought some PCB’s to the ECLSTS and I picked up a few from him. I also scored a balancing charger from Bruce Chandler at the Drag-n-Brag for $20! It was missing the manual and balancing cables, but they weren’t too hard to come up with on my own from the net and electronic junk box.

First I used the Discharge function of the charger to discharge the pack independent of the PCB. Tonight I removed the old PCB and connected up the balancing leads. It’s on balance charge now and looks like it will come up fine.

I’ll replace the PCB tomorrow and see where we are at.

#15

Here’s the result of a single balance charge using my Drag-N-Brag find.

Frankenbattery

(http://lsc.cvsry.com/Post3/FrankenBattery.jpg)

One cell .01 V higher than the other 3. I think I’m declaring this pack good. Now to wire up the new PCB.