Stuck building 48v battery

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Re: Stuck building 48v battery

Post by 999zip999 » Aug 02, 2017 2:24 pm

Do not walk away. The little will charger hit 4.15v and race to 4.2v and above fast. So keep an eye on it. Never over charge.

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Re: Stuck building 48v battery

Post by 999zip999 » Aug 02, 2017 3:15 pm

A bms is for keeping a balance pack balance. So fully balance your pack before hooking up the bms..

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Re: Stuck building 48v battery

Post by mcristiani » Aug 02, 2017 5:01 pm

Okay. Got the suspect set of cells up to 4.12. Put everything on the normal charger and it kicked on.

All cells moved up to 4.19 - 4.2 except this one which stayed around 4.12.

I am manually charging again to catch up and then am going to take it on a ride.

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Re: Stuck building 48v battery

Post by mcristiani » Aug 03, 2017 9:48 am

Rode the battery for a short bit and charged it again using the normal 54.6v charger.

The single group - s10 - did not charge at all. Everything else got up to 4.18v. Why would the single group not charge? New board since the original problem.

I am going to watch it to see if it leaks down again.

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Re: Stuck building 48v battery

Post by amberwolf » Aug 03, 2017 1:46 pm

mcristiani wrote:
Why would the single group not charge? New board since the original problem.
possibly: https://endless-sphere.com/forums/viewt ... 9#p1306337

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Re: Stuck building 48v battery

Post by mcristiani » Aug 03, 2017 2:00 pm

I think the link you included just pushes me back up to a previous post in this thread - I am new to Endless Sphere.

That post is saying a bad BMS. But I already installed a new bms, so I just have a hard time believing this is also broken.

I asked earlier as well 'Am I somehow shorting it when checking the pins with a volt meter'.

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Re: Stuck building 48v battery

Post by amberwolf » Aug 03, 2017 2:10 pm

mcristiani wrote:That post is saying a bad BMS. But I already installed a new bms, so I just have a hard time believing this is also broken.
Since I'm not sure if you're reading the right post, or all of the post pointed to, I've quoted it below with the key word highlighted.

It might not be the problem, but you can test for it.
amberwolf wrote:could also be a bad batch of bmses, where that channel has a wrong part or problem with traces, or a part installed in a wrong position, etc.

That you may be able to visually check by comparing channels between the wroking ones and the problematic one. A multimeter can also be used if no visual differences exist.

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Re: Stuck building 48v battery

Post by fechter » Aug 03, 2017 2:16 pm

You should charge the suspect cell group for a while, then let it rest for about 15 minutes and make a voltage measurement. Without doing anything to the pack, let it sit for hours or overnight, then repeat the voltage measurement and see if it drops.

Two bad BMSs is not really uncommon. When cells are in series, the charging current is forced to be the same in all of them (unless diverted away by the BMS). Typical BMS failure is for the balancing shunt to get stuck on, continuously draining the cell slowly. It's also easy to blow up the BMS while attaching it to the pack. Some are much more prone to this than others.

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.
"One test is worth a thousand opinions"

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Re: Stuck building 48v battery

Post by mcristiani » Aug 03, 2017 3:17 pm

Okay. I will check on that and report back.

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Re: Stuck building 48v battery

Post by d8veh » Aug 04, 2017 8:41 am

The BMS doesn't interfere with any cell to prevent it from charging. All charging is done in bulk. Only balancing/bleeding is done on a cell-by-cell basis. Most likely, you have a measurement error. If that cell group is truly down, then one cell has an internal short, maybe from damage (crushed or dented), in which case the whole group will need replacing unless the voltage stayed above say 2.5v.

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Re: Stuck building 48v battery

Post by kneedeep » Aug 04, 2017 9:02 am

Can you post a picture of the wire diagram for the new BMS? Does your new BMS charge and discharge on the same positive port or separate?
I have had 3 BMS with 3 different wire schematics off by one pin. If you are reading low voltage out after BMS this could be the issue.
My one BMS charges through the last balance wire not the main lead.
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Re: Stuck building 48v battery

Post by 999zip999 » Aug 06, 2017 3:01 pm

Do not walk away and let any cell group go higher then 4.2v ever. So as soon as you go to the refrigerator for a beer or take a piss that things going to run past 4.2v. Best for all cells to be balanced before hooking up bms. You can just connect to pos and neg of a parallel group to charge without unplugging sense wires if pack is open as in picture.

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Re: Stuck building 48v battery

Post by mcristiani » Aug 15, 2017 12:55 pm

Thanks for inputs to thread. I took a trip to Whistler with the family to ride bikes.

I guess I didn't give due concern to how quickly the charger can go from 4.15 to 4.20 as it reaches top of curve. It just takes forever to go from 3.8 to 4.1. the homemade charger for a single cell is working though. Thanks.

Unfortunately, I have given up on the original 48v battery. I keep getting welds popping off and then batteries out of sync and then dead groups again. I just don't get it. Two BMS's. I will post a picture now as requested.

I am starting with a new 13S3P version. They base cells are still from the suspect group of 100. My plan is to:
  • Spot weld pack then wait a day to see that all voltages hold
    Connect BMS - I am going to follow directions earlier in this thread. One question though: Should connect sense wires before or after B- | balancing harness | B+

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Re: Stuck building 48v battery

Post by mcristiani » Aug 15, 2017 1:03 pm

BMS Screenshot
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BMS screenshot
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Re: Stuck building 48v battery

Post by mcristiani » Aug 15, 2017 1:09 pm

I figured I would post the schematic that I built to make sure the battery was correct.

It isn't engineering grade, but if you see anything that would be great to know.
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Re: Stuck building 48v battery

Post by mcristiani » Aug 15, 2017 1:38 pm

I guess I could ask if there is a better sequence than not when spot-welding battery.

Can I do one whole side and then flip it over and do the other side?

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Re: Stuck building 48v battery

Post by amberwolf » Aug 15, 2017 2:36 pm

mcristiani wrote:I keep getting welds popping off and then batteries out of sync and then dead groups again. I just don't get it.
If welds break, then there are twisting stresses on the pack itself that are moving cells around.

You'll want to secure the cells together so they cannot move, and then secure the pack so it cannot twist, and then the welds won't break.


BTW, with really good welds, when they break it's possible for them to rip chunks out of the cell cans, and cause the cells to either leak electrolyte or admit air and moisture into the cell--either one is fatal for the cell, so any cells damaged that way need to be removed even if they electrically appear to still be working at that time (because they *will* fail later).

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Re: Stuck building 48v battery

Post by mcristiani » Aug 15, 2017 2:45 pm

Okay. So I am not supporting the twisting stresses at all. I am going to put a fiberglass side wall on both sides of the pack this time.

I have welded all of the parallel tabs. 13 separate groups all at ~+/- 4.12v.

I will wait till later then spot-weld series tabs.

Question: If group1 is 4.11v and the group2 is 4.13v do I need to make exactly 4.13v connecting?

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Re: Stuck building 48v battery

Post by fechter » Aug 15, 2017 10:17 pm

mcristiani wrote:
Question: If group1 is 4.11v and the group2 is 4.13v do I need to make exactly 4.13v connecting?
That should be close enough. I wouldn't allow much more than that though.
"One test is worth a thousand opinions"

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Re: Stuck building 48v battery

Post by mcristiani » Aug 16, 2017 10:01 am

I am so struggling with these batteries.

I just got back a different battery I built a while back for an ebike I made.

I fixed a broken weld and rode it about 12miles yesterday. Then put it back on the charger.

Now again, it looks like one of the series groups is not getting charged by the BMS. It is sitting at 3.66 when the rest are at 4.05v.

Any ideas on what to do for this? I would really appreciate it.

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Re: Stuck building 48v battery

Post by amberwolf » Aug 16, 2017 1:20 pm

The BMS does not charge the groups.

The BMS only drains down the groups (if they go above the HVC point, or if the BMS is broken or not built right in the first place).


If a cell group is not at the same voltage as other groups, either the BMS is defective or not built right in the first place (bad batch, as previously noted), or cells in the group are defective, etc.


If it is the same cell group as other packs with the same BMS, then you almost certainly have a bad batch of BMSs, and need to do the examination and testing on all of the BMSs that was already recommended to you.

Or you need to remove all of the BMSs and replace them with completely new ones from a completely different batch, or completely different type, or completely different supplier, etc.

Otherwise you'll probably continue to have these same problems over and over and over and over again.

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Re: Stuck building 48v battery

Post by mcristiani » Aug 16, 2017 3:35 pm

Thanks again for info.

Talking about this new battery, it is the first time it behaved like this. If I use a hand made 5v charger to get this bank/series charged back up and I can get it to 4.12 like the rest of the groups should I just wait a day or two and monitor that one set of cells?

Am I crazy in thinking that that pair did not get charged by the charger?

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Re: Stuck building 48v battery

Post by mcristiani » Aug 16, 2017 6:51 pm

Also, I feel like voltage in increasing on all cells when I have the 5v connector attached to the sense wires on either side of the single series/group I am trying to charge.

I am only trying to get the one series/group charged back up.

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Re: Stuck building 48v battery

Post by mcristiani » Aug 16, 2017 7:07 pm

Endless Sphere... I feel like Endless Questions right now.

Does it make sense that I am seeing 4.31v on ncr ga cells? I have a standard charger plugged into the standard charging port at the moment. Board is connected.

Thanks.

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Re: Stuck building 48v battery

Post by fechter » Aug 16, 2017 7:12 pm

Depending on your wiring setup, the voltage will read higher than the actual cell voltage while you are charging. You need to disconnect the charger, wait a little, then measure the cell voltage to get an accurate reading. If it's really 4.3v, that's too high.
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