Ok, I bought a (slightly) used duct tape (Vpower) battery...

[sangesf]

It's 36v "20 ah" with the (rather) large (Two-tiered) BMS.
I've only been able to get 15ah out of it..
So here's what I've done so far...
Charged it up with my 36v(45v max) 5a charger till HVC kicked in...
Then ran it to LVC... (i.e. Both HVC and LVC "work").
Charged it back up and discharged to 50%.. Then did that 4 more times..
Then charged and discharged fully and still only getting 15ah..
And yes, the dimensions and weight ARE correct for the battery..
On the last full discharge (LVC kicked in), I tested (via the balance leads) each cell group..
A couple were at 2.7 and the rest were about 3.1 or so..
Once fully charged (HVC kicked in), I tested again and 2 (not the same two) were at 3.75 and the rest (the other 10) were at 3.35.. (total of ~41.x volts when the HVC on the BMS kicks in)
My guess is (obviously) the cells groups are waayy out of balance..
When the HVC on the BMS kicks in, I'm guessing it reads the two at 3.75 and stops the charging...
Is it safe to say, I should just leave the charger attached (the BMS is prolly only letting a few miliamps) for a few days to try to balance 'em out... Or should I just go ahead and charge through the "balance leads" at 3.75v 500ma each?

Or any other ideas??

 

[BLUESTREAK]

V-POWER BATTRIES ARE FAMOUS AT ADVERTIZING 20AH BATS. THAT ONLY PRODUCE ABOUT 15AH.

 

[sangesf]

V-POWER BATTRIES ARE FAMOUS AT ADVERTIZING 20AH BATS. THAT ONLY PRODUCE ABOUT 15AH.

Except, I didn't buy it from Vpower, and I asked the person who sold it to me to test it out first..
They told me they tested it with a 20a draw and got 20ah out of it.

(obviously bull!)
MAYBE I can re-balance em..
I'm gonna try tonight..
I have a 6v SLA battery charger (tops out at 7v) which I can hook up to two at a time (while watching with two volt meters hooked up to each of the cell groups).

 

[DAND214]

You can balance them on a gram scale, and you will still only get about 20 to 30% less of what they claim.

I have 3 48v packs one is a 20ah and it tests at 17Ah and the 2 15Ah packs are close to 11Ah.

If you count the cells in a string ther will be about 18 cells. top mah rated is 1100mah or 1000mah per cell. They don't match the cells like we did in the old days of R/C. There all the same color they must be all the same. Put them togeathr and get it out of here is all they do.

The only LiFePo packs I have that is close or better are the ones from Ping. I haave a 36v20Ah pack that is now two years old that still is close to rated.

As for test the 20Ah pack with a 20 amp draw and say it's 20Ah is just not gonna happen with those cells.

Be happen you get as much as you do, being it used.

Dan

 

[amberwolf]

Charging each group thru the balance wires is probably the fastest way to do it, and the most certain, but even then you are only charging each group to the same voltage, not the same capacity.

But I would not use the SLA charger to do it, myself. I'd use a 3.65V power supply, preferably current-limited, most preferably one of those lab power supplies you can adjust both current and voltage on. Failing that, you're going to have to sit there and watch the voltage on both meters constantly.

Based on my experience so far with two packs like this, and reading of others, it is likely the cells are not capacity matched to start with and after usage and time they will get further apart. At some point the only way to regain the lost capacity is to replace some of the cells.

It's also possible that there are "leaky" cells in there, so that they are actually draining charge from other cells in the group, all the time (and during charge those cells probably get warmer than the others, so with an IR imager you could probably *see* the bad cells). If you do have leaky cells, like the two packs I've worked on so far, capacity will be even less than expected because of it--plus, capacity will drop just sitting there, after charging to full, so the longer after charging you wait to test it, the less total charge there will be.

How leaky the cell is determines how fast it loses charge/capacity, after refilling it.

To test for capacity in cells or groups requires charging and discharging and seeing which cells/groups are at a higher voltage.

To test for leaky cells is easier--just charge the whole thing up, then let it sit, unconnected to either BMS or charger. Periodically, use a DMM to check each cell group's voltage, and note them down. The ones taht drop have leaky cells in them, the faster they drop the leakier the cells are *or* the more leaky cells there are in that group.

To determine which actual cells are causing the problem you'd have to start cutting cells out of the group, preferably in a binary search (see my two pack repair threads, one for Vpower and one for Volgood).

 

[mihai_atanasiu]

Like amberwolf said it is difficult to repair the Vpower batteries;

I also bought one last year in the summer; 36V 20AH (18P12S) with 212 $ without shipping on an auction; In the first charge/ discharge one cell group died; the supplier sent me a "new" one; I opened the pack, cut the bad group and replaced it with the new one; after several charge and discharge cycles another group died; I also bought an watt meter and an RC charger - Turnigy 8150;
I tried to charge each cell group; the maximum capacity drained from the pack was 12AH;

At that moment I decided to reconfigure the pack; I removed the bad cell group - the second one - and I made some calculations: I had eleven groups, each group with 18 cells; that means 198 cells; with these cells I can made an 16P12S pack; I cut two cells from each string and made a good one;

Also I removed the huge BMS and bought an Signal AB one from Ping;

After two months of testings (week end) I found that the maximum capacity drained was about 13.5 AH; still another cell group that have bad cells; I bought 16 cells from another supplier and replace that string;

In the springtime, after a lot of tests with watt meter and 12V bulbs the maximum capacity was 15Ah;

Since springtime I use the pack with 15AH ( theoretical 17.6 AH) and I am satisfied with it.

 

[The Mighty Volt]

@ OP

The battery will have a brace of balance taps.

Get two small pieces of wire that fit inside the individual slots of the balance taps.

Identify where the positive and negative wires will go inside the balance tap. You can use a voltmeter to do this. The problem with the Volgood/Cammy batteries is that they have colour neutral taps.

It would look something like this

Get a dedicated 3.6v to 3.65v power supply like a phone charger or a more expensive but still affordable PSU with a display and a Current-Limiting option. Meanwells are no use to you here unless you got a 5v meanwell and even at that I'm not sure you could tune it down to 3.5v.

Once you have identified your terminals, insert the wires into the first two ports of the balance tap. Ports 1 and 2 do the first string, ports 2 and 3 do the second string, ports 3 and 4 will do the third string, ports 4 and 5 will do the fourth string, and so on and so forth.

The positive wire will always go into the port which is NEAREST to the main positive terminal of the block/battery whose strings you are testing. As I say this is EASY with the colour-coded taps I have but might take some investigation and care with the neutrals.

Be careful not to push the wires in too far. Short lengths of stiff wire are best.

 

[amberwolf]

Actually on these Vpower / CammyCC / Volgood packs with the two-tier big BMS, the balance taps only include the positive end of the most negative cell, the negative end of the most positive cell, and positive and negative of all the cells in between.

The main output wires of the pack are actually the negative of the most negative cell and the positive of the most positive cell.

See the pics in my Volgood repair thread for example.

 

[sangesf]

Well on this particular set of balance wires, it's the positive of the first positive cell and positive of the last cell..
(Can test via balance leads from first to 11th cell group and then from last cell group pos balance to neg coming out of pack.)
Well, yesterday I ran it down to LVC again.. (after charging all cell groups to 3.7v until they all stayed at ~ 3.6x, the night before).
Cell voltages are as follows (At 15ah on the nose).
Cell grp. 1 ... 2.5xV (this is cell group that hit LVC)
Group 2 ....... 3.06V
Group 3 - 11.. 3.20V
Group 12 ...... 3.06V

So it looks like group 1 is 15ah
Groups 2 and 12 are about 16ah
And the rest are somewhere between 16ah and 20ah..

What do you think?

 

[theRealFury]

Yes i would agree... cell groups 3-11 should give 17-20ah. Looks like you have one really bad cell group - group 1 and groups 2 and 12 possibly have cells in them that are a little weak. probably best bet would be to replace cell group 1 which might get you to about 17AH before LVC... other than that you will need to replace cell groups 1, 2 and 12 to get anywhere near close to 20ah im afraid.

 

[sangesf]

The seller offered to give back $50, which would make the cost $200 for a 36v 15ah battery. Not bad...
I'll take that $50 and add it to whatever I need so I can prolly get 3 new cell groups from Vpower...

I also have an 11s pack that's 10ah and I see another 11s 10ah pack for $100 on eBay..
I have a "36v" charger that puts out 40.2v, so I'll connect them in parallel and have a "33v" 20ah pack which I'm going to put in series with my 12v 36ah SLA (re: my other thread) and have a "48v" pack for the front motor and a 36v 20ah (after I add the replacement cell groups) for my rear motor.

So for about $200 more, I'll have a 1.6kwh setup.
Should get me back to about 100 miles+ capable distance..

 

[jimw1960]

If it has a BMS, why are your cells so out of balance after charging? Do you not have the correct charger? Hve you let the charger go overnight to let the BMS do its thing?

 

[amberwolf]

PRobably they are out of balance because there are leaky cells in them, that are dragging down the voltage of the rest of the group. It's apparently common in these packs. Both of the ones I've repaired have this problem.


@Sangesf, what are you planning to do with the replaced groups of cells, once you get new groups for the pack?
If you are not going to use them, I would be interested in them if they're cheap enough, as cells to repair my pack
http://www.endless-sphere.com/forums/viewtopic.php?f=14&t=22750
with as it has further failures over time, and possibly RTLSHIP's pack
http://www.endless-sphere.com/forums/viewtopic.php?f=14&t=30864
if he's ok with used cells to replace the two failed ones so far.

 

[sangesf]

PRobably they are out of balance because there are leaky cells in them, that are dragging down the voltage of the rest of the group. It's apparently common in these packs. Both of the ones I've repaired have this problem.


@Sangesf, what are you planning to do with the replaced groups of cells, once you get new groups for the pack?
If you are not going to use them, I would be interested in them if they're cheap enough, as cells to repair my pack
http://www.endless-sphere.com/forums/viewtopic.php?f=14&t=22750
with as it has further failures over time, and possibly RTLSHIP's pack
http://www.endless-sphere.com/forums/viewtopic.php?f=14&t=30864
if he's ok with used cells to replace the two failed ones so far.

I'll tell ya what...
I have some (silver-grey) lone cells (about 20 in various conditions) and I'll have at least one "bad" cell group from that pack and a 36v 3a (Lifepo4) charger...
Do you have any sensorless controllers, electric brake handles, handlebar switches or any other e-bike components you would trade?

 

[amberwolf]

I have a few ebrake handles of a couple of types; I'll have to find them and get pics.

No sensorless controllers, though. (most of the controllers I do have are dead ones for parts, maybe repairable, some definitely not).

I have somewhere a set of switches/handlebar controls from an EVGlobal, I think it was, that should be working (though the casings are not perfect condition) but I've not used them to test yet. I've managed to crack or break casings on all the other HB switch units I have had so far, IIRC. Was planning to use these on the Nishiki upright "spare" bike, but have yet to get around to that project.

Just about all the other ebike stuff I have is either in-use on CB2 or DGA, or broken, or waiting to be installed on the new bike if I can ever finish it's frame. :lol: But I can look around if there's anything specific you're after.

 

[sangesf]

So, here's an (interesting) turn of events..
Yesterday, I got home at 4pm after recharging at work and read the cell voltages and found only cell group one a bit lower than the rest.. (3.18v, while the rest were at 3.21-3.25 -- 12AH)
So I plug in charger and forget about it.. I go to bed early and wake up a little while ago..
Charging finished, and I check the battery side (before BMS) and read 43.2v, which equates to about 3.6v each.. I check via the balance leads and yes, they are ALL at 3.60v exactly!

What's weird is that they are all at 3.60 where during other recharge/charge cycles, they're normally anywhere in the neighborhood of 3.7 or so..

Why are they a little bit lower (after leaving charger on for 12hrs. plus)?
P.S. This is not the first time I've charged for 12hrs.

P.P.S. I remove charger for about 15 min and reconnect and it goes through another charge cycle for about 10 minutes (charger light goes yellow and I see voltage rising until 45.0v) and then 30 min later I check voltage again and they are all at 3.60v exactly again..

Any guesses as to what's going on?

FYI... 3.60v is good, yes?

 

[Spacey]

Sounds like the bms has actually done its job and balanced the pack, if a few cells are low then the other higher cells take up the rest of the voltage to make up the pack total.

 

[sangesf]

The thing is, what's with the discrepancy with the voltage differences in the cell groups between before and now...
3.60 is not exactly fully charged (albeit it's super close <yeah, I know its a surface charge and all>), BUT they used to go to 3.75 and now they only going to 3.6.

Still not sure what's going on with this BMS...

 

[amberwolf]

My best guess is that your BMS is set to balance (discharge each cell) to 3.60V, so that's why they end up there.

At least on my pack, the charger will kick in repeatedly after pack voltage drops sufficiently (I don't know exactly where, as I never managed to catch it and haven't manually drained it to see), and kick the voltage up again on all the cells, to anything up to 3.8V/cell, then it drops out and balancing drains the cells down again (I forget the voltage they stop at).

If yours no longer ever goes as high as it used to, then that means your charger is no longer outputting as high a total voltage, or else one (or more) cell group has such a high resistance compared to the rest that it is taking up all that extra during the charge when current is passing thru it, so the charger does reach the same peak voltage and then cuts out, but none of the other groups gets as high as it did, and the high-resistance group(s) are over-voltage by the leftover amount.

If the latter, probably it dissipates quickly, as it's not really charged that high; it's just an artifact of the voltage drop across the higher resistance, so balancing will quickly take it down to the level of the rest of the cells, and then down to the balancing setpoint--just as quickly as the rest of them, probably.

 

[sangesf]

Well charged up last night and cell group 1 got to 3.75 and the rest stayed at 3.35v when BMS cut off the charging.
Tried waiting about 20 min to see if I could charge again (hoping 3.75 cell group would be drained back down to 3.60) but to no avail...
I'm out on a ride right now and will see after I've drained a bit from the pack, what the next recharge cycle will bring.

 

[Spacey]

What charger do you have as most of the so called Lifepo4 chargers just turn off when the pack voltage hits it's overall voltage. You need the charger to allow enough energy to feed the BMS so that it does its job.

Their is usually a 3 legged transistor that you need to take out as it shuts the charger off completely once it hits a threshold.

 

[sangesf]

What charger do you have as most of the so called Lifepo4 chargers just turn off when the pack voltage hits it's overall voltage. You need the charger to allow enough energy to feed the BMS so that it does its job.

Their is usually a 3 legged transistor that you need to take out as it shuts the charger off completely once it hits a threshold.

I use two different LFP chargers..
One is 5a 45.0v and the other is a 3a 45.9v one..
Both have been used for charging and both work fine..
I watch the voltage on the pack (charger/post BMS side)...
This is what I saw this morning...
40.6v. So I check and the above was what I noticed..
Plugged charger in and voltage went right to 45.0v immediately (meaning the BMS cut off the input path of the charger).. So it's not the charger... Something is "funky" with the BMS.. That's for sure...
The BMS is sort of doing it's job, but only partly.. It's cutting off the 3.75v group, but not just putting a "resistance load" on just that cell group, and continuing to let the rest of the cells charge higher.

 

[amberwolf]

Remember that the resistance it uses is a tiny little thing, so it can't drain much power from a group very quickly. If one group is really high in SOC compared to the others, it could take a long time (hours, maybe days) to drain that.

Assuming it's about 100mA balancing current (i'm not sure, but you could measure it by putting a current meter between the balance plug pin for that group, and the input pin on the BMS), then to drain off a 1Ah imbalance would take 10 hours. 2Ah would take 20 hours, and so on. I don't know how imbalanced that group is from the others.

If you verify that the BMS *is* actually drawing current thru the balance wire, but you just need it to go faster, then you could shorten the time necessary to continue charging by draining just that group with a load like a small 12V halogen light bulb, or a high-wattage low-ohms power resistor. Since you'd probably be doing teh draining thru the balance wire, don't go too high on the current or you might melt the wire's insulation.

 

[sangesf]

Question is how do I drain from just that one cell group which is 3.75..
Pulling 12v from a 3.75 cell group wouldn't be advisable, I would think.

 

[amberwolf]

You can't pull any more voltage than already exists. (well, not without a boost converter)

I use a 12V 50W halogen as a drain load on various cells, and it works fine. At about 3.6-4V, it draws about 2A or so.

You can even use a regular household 100W bulb, but it will be a much lower current drain (because it is higher resistance).