Stuck building 48v battery

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mcristiani
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Re: Stuck building 48v battery

Post by mcristiani » Aug 16, 2017 7:44 pm

Thanks Fetcher. Settling back down to 4.23 after charger has been off for 5mins.

Am I crazy though. If I put my little 5v charger on the single cell using the two sense wires on either side of it, doesn't that only charge that one group/series?

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Re: Stuck building 48v battery

Post by mcristiani » Aug 16, 2017 8:12 pm

Separate battery from LunaCycle is sitting on my bench for awhile. Volt meter says 59.5v for a 14S.

That seems like they are sitting at 4.23 or 4.25v. I did replace a single group in this battery as well now that I think about it.

I have 48v and 54.4v chargers separated by using opposites of xt60 connector as distinguisher.

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Re: Stuck building 48v battery

Post by fechter » Aug 16, 2017 9:00 pm

mcristiani wrote:Thanks Fetcher. Settling back down to 4.23 after charger has been off for 5mins.

Am I crazy though. If I put my little 5v charger on the single cell using the two sense wires on either side of it, doesn't that only charge that one group/series?
Yes, it only charges that group. Because the sense wires are small, there will be a voltage drop in the wire as the charger is running. This voltage drop will add to your observed reading, depending on how the wires run.

Ideally you want to measure voltage directly on the cell can without going through any wires, but this is not practical in many cases. As long as there is no charge or discharge current, the voltage drop in the sense wires will be zero and the reading will be accurate.

4.23v is a little hot. Don't go over 4.2v. Most people don't even go that high for routine charging. To balance the pack, taking it to 4.2v is good since that's where the BMS starts to kick in.
"One test is worth a thousand opinions"

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Re: Stuck building 48v battery

Post by mcristiani » Aug 16, 2017 9:07 pm

Thanks again for the help.

How can this LunaCycle battery be at 59.9 for a 14S.

I am using a standard charger. Luna Charger says 58.6 on the sticker, but my volt meter is reading 60.6v out of the charging port. Other chargers say 54.6v but are reading 56.4v.

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Re: Stuck building 48v battery

Post by mcristiani » Aug 16, 2017 9:43 pm

With a generic charger, how do I charge less than the full amount? Monitor myself and unplug?

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Re: Stuck building 48v battery

Post by amberwolf » Aug 17, 2017 1:01 am

mcristiani wrote:Am I crazy in thinking that that pair did not get charged by the charger?
The charger charges all cell groups at the same time the same way and the same amount.

Any cells taht aren't charged to the same voltage are because of individual differences in the cells themselves (age, defects, different batches, etc).

(or defective BMS draining the cells that are low).


Regarding the voltage higher than normal on various things, you should check (or just change) the battery in the multimeter; whey the get low the meter can read higher than it should.

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Re: Stuck building 48v battery

Post by amberwolf » Aug 17, 2017 1:04 am

mcristiani wrote:With a generic charger, how do I charge less than the full amount? Monitor myself and unplug?
How did you do it before? Like here:
https://endless-sphere.com/forums/viewt ... 9#p1307359 ?
and here:
https://endless-sphere.com/forums/viewt ... 9#p1308914 ?

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Re: Stuck building 48v battery

Post by d8veh » Aug 17, 2017 3:25 am

The first thing to check is that your voltmeter is reading correctly. They go high when their battery goes flat, so check again with a different volteter. If your charger really is that high, it's for LiFePO4 batteries, not Li-ion. If it's an aluminium cased one, they normally have an adjuster screw in a blue block near the corner on the ouput side.

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Re: Stuck building 48v battery

Post by mcristiani » Aug 17, 2017 1:50 pm

Dude! I can't believe my volt meter was totally out of whack. You were right.

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Re: Stuck building 48v battery

Post by mcristiani » Aug 18, 2017 9:48 am

Morning.

Another battery with what looks like parasite drain. Not sure if it is relevant, but it is what I labeled as series 1.

I charged up to 4.14 and it is down to 4.04 now.

Just confirming this means I need to replace the bms? I really don't want to hear a 'yes' answer. Could this behavior also be because of individual cell defect/damage within a series?

It seems like all batteries I am touching are developing this problem. I guess I am not appreciating the sensitivity of the bms...

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Re: Stuck building 48v battery

Post by mcristiani » Aug 18, 2017 12:03 pm

What could be the diagnosis for a battery that reads 58.1v from negative to series 13. But at the charge and discharge connector, I only get 49.7.

I tried to reset it with load from bike controller/motor but will not turn on.

I don't really want to unseat and reseat the balancing harness since things seem to continually be breaking.

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Re: Stuck building 48v battery

Post by fechter » Aug 18, 2017 2:20 pm

Boy, you're just not having good luck at all.

On the parasitic drain, it could be either the BMS or something internal to one of the cells. Test by disconnecting the BMS and see if the voltage still drops. You could also see if the balancing resistor is getting warm when it's connected.

If your voltage is truly 58.1v on a 13 series pack, you should expect the pack to burst into flames any time now. I hope you have this thing in a safe place where a big fire won't cause massive property damage or loss of life.
58.1 / 13 = 4.47v. This is way above the safe maximum limit. This could happen if you used a charger made for 14s on a 13s pack and the BMS failed to cut off charge. You may still have issues with your voltmeter.

Assuming the pack is fully charged (and then some), but the voltage on both the charge and discharge ports is much lower, I would suspect a bad wire connection or miswire. Even if the BMS is tripped, the body diodes in the FET would pass voltage in one direction. You should be able to discharge through the charge connector (at reduced current) even if the BMS is tripped. I suppose it's possible for the FETs to go bad, but they almost always short when they fail, which would give you output.

Can you post a picture of your BMS? There are a lot of variations on these and it might help to know the general configuration.
"One test is worth a thousand opinions"

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Re: Stuck building 48v battery

Post by mcristiani » Aug 19, 2017 11:00 am

I really appreciate the empathy! I have been going nuts.

I believe that the combination of a low battery in the volt meter itself may have caused me confusion and/or, I may have misstated the 13S.

The battery is a 14S and currently reading 58.1 at board and at load connection. I am going to package back up and through a cycleanalyst on it to see how many amp hrs it runs for. Question: Can I get those

Attached is the BMS that I keep getting parasitic drain on. It comes from batteryspace.com - it is expensive at $64. Please see something wrong:)

I have resigned myself to the fact that I have to remove the BMS and reattach a new generic one I purchased. I am going to follow the steps fetcher said earlier in this thread.
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fechter
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Re: Stuck building 48v battery

Post by fechter » Aug 19, 2017 7:30 pm

That looks like a pretty typical Chinese BMS. It looks Ok in the picture. You should be able to find a replacement if that one is bad. When shopping, try to find one that has the exact same balance plug connector so you don't have to rewire the whole thing.

One thing I noticed is the balance plug seems to only have 14 pins. For a 14s pack, you need 15 connections, so one must be through either the B- or B+ wire. If you measure the voltage from B- to the first pin of the balance plug, you can tell how it's wired. This is important to know if you try using a different board.
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Re: Stuck building 48v battery

Post by mcristiani » Aug 20, 2017 11:21 am

You are correct. This battery is a 13S.

I'm sorry, but I have been working with 2-4 different batteries during this period.

I can guarantee the exact board through batteryspace in hayward, but it is $64. Maybe I should give it one more try knowing to be much more careful when connecting. Like you said, I wouldn't need to rewire everything. I do have a bunch of these as they are what keeps frying. Maybe I can plug in a different board and see if it drains a cell while I wait for the new one.

The description touts equilibrium as a function the pcm offers. Does this mean anything to you?

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Re: Stuck building 48v battery

Post by fechter » Aug 20, 2017 1:29 pm

mcristiani wrote:
The description touts equilibrium as a function the pcm offers. Does this mean anything to you?
Translation: It has a cell balancing function.

It would be good to make sure the cells aren't draining by themselves with the BMS disconnected. Just measure voltage, wait a long time, measure again.
"One test is worth a thousand opinions"

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Re: Stuck building 48v battery

Post by mcristiani » Aug 20, 2017 6:34 pm

I have waited for over 24hrs and the cells have not dropped in voltage.

I want to rewire a different bms on there - one of the three I have sitting around - tomorrow or the next day. I am hoping to leave the current balancing wires soldered.

I took this from a comment Fetcher made earlier, and intend to follow it:
  • When connecting a BMS to a pack, I recommend first attaching the B- connection, then plug in the balance wires by slightly angling the plug so the lower (closer to B-) cells make contact first. Then make the B+ connection, which should be redundant with one of the balance wires.
I will then check to see which group(s), if any, is experiencing a drain.

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Re: Stuck building 48v battery

Post by fechter » Aug 20, 2017 8:45 pm

If you have a bad balancing shunt, it will start to get warm pretty fast. You can also measure voltage across the balance bleeder resistors to see if a particular channel is on.
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Re: Stuck building 48v battery

Post by mcristiani » Aug 21, 2017 3:55 pm

I mounted one of the old bms's and it was terrible. All kinds of cells drained...

I ordered a new one and will give it one final go.

For a moment, I was wondering if it was for a LiFePo cell type, but it is 48.1v (13s) so I think that part is correct.

I will let you know the outcome at the end of the week.

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Re: Stuck building 48v battery

Post by mcristiani » Aug 21, 2017 4:05 pm

One question in the meantime though:

The steps for connecting bms are attach B- | connect wiring harness | attach B+

Once this is all together and I sense a problem, is there a procedure for disconnecting the wiring harness? For example, B- and B+ are already connected...

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Re: Stuck building 48v battery

Post by d8veh » Aug 22, 2017 3:44 am

It doesn't matter how you connect or disconnect those BMSs as long as connections go to the right locations. You have to be a bit more careful with the ones that have a B+ connection and a cpu. For those, it's always best to connect or disconnect the B+ first.

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Re: Stuck building 48v battery

Post by fechter » Aug 22, 2017 1:27 pm

d8veh wrote:It doesn't matter how you connect or disconnect those BMSs as long as connections go to the right locations.
I disagree. I've blown up enough of them. If you make the B- and B+ connections before the balance plug is in, you have a condition where all the BMS cell circuits are in series, but powered only at the ends. In some cases, the shunts will trigger on, causing destructively high voltages to appear on remaining cell circuits. This doesn't happen every time, but if you repeated it enough times, the chances of blowing something increase. Some models are more resistant to this failure than others too, but almost all of the cheap ones typical to bike packs can fail this way.

On disconnecting, it is not as critical but I would disconnect B+, balance plug, B- in that order.
"One test is worth a thousand opinions"

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Re: Stuck building 48v battery

Post by mcristiani » Aug 22, 2017 3:57 pm

Great input all around.

I have a new - expensive - board from batteryspace. I only purchased it because I didn't want to resolder a different harness on.

I will give it a try once I have all cells trued up.

Thanks again.

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Re: Stuck building 48v battery

Post by 999zip999 » Aug 22, 2017 6:08 pm

Your are best to write the state of charge down on paper like this.
1. 3.99
2. 4.09
3. 3.18v


13 or 14. Xxx volt. Which 48v you have. ?
Voltage of charger and voltage of battery.
How many amps can your bms deliver ? What controller and motor setup it do you have ? Where you getvthe cells ? What cells are they ?

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Re: Stuck building 48v battery

Post by mcristiani » Aug 26, 2017 6:27 pm

Newly built pack with different ebay board is built and running. Thank god! Cruised about 3 amp hrs. CA read 47v when drawing 7amps.

Of course, there has to be some snag though... When connecting a charger, I can't get the charger to kick on and charge. Resting voltage at both plugs is about 49v right now and I just charged a different 48v battery with the charger I am using.

Any thoughts?

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