Stuck building 48v battery

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mcristiani
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Stuck building 48v battery

Post by mcristiani » Jul 19, 2017 11:34 am

I am stuck trying to get these batteries I built to work. I have built two successful batteries before using a spot welder from ebay and boards from batteryspace, but the current two keep behaving weird and are unusable.

I bought 100 18650 ncrb batteries from r-lsales on ebay. After following my schematic, I keep getting the same two series failing which then is making the whole battery not accept a charge. I proceeded to remove those and add a fresh series. This then also died.

This is happening on two separate batteries with two separate boards. I then purchased a discharge tester https://www.amazon.com/gp/product/B01EV ... UTF8&psc=1 and charged and discharged a series before again inserting. Again, there seems to be a slow drain on the same exact series.

So... Maybe the schematic I am using is creating some sort of drain? It seems that my initial conclusion that some cells were dead on arrival isn't correct anymore. Any ideas would really be helpful as I am not an electrical engineer.

I am sure there may be some more info that is needed, so please ask away...

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Re: Stuck building 48v battery

Post by fechter » Jul 19, 2017 12:28 pm

Sounds like a bad BMS is draining the cells.
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Re: Stuck building 48v battery

Post by mcristiani » Jul 19, 2017 5:07 pm

But on two separate batteries? Two separate BMS's?

Maybe I ruined the BMS checking the voltage where the sense wires connect to the board?

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Re: Stuck building 48v battery

Post by fechter » Jul 19, 2017 6:50 pm

I've seen the blow when they get connected. If it's the BMS draining the cells, one of the little shunt resistors on the BMS will be heating up when it's connected.

Make sure you have the balancing wires attached in the right order. Measure voltage at the connector. If you put the meter negative probe to the main pack negative and measure each balance wire in sequence, you should see the voltage increase by one cell's worth each position.

Another test is to disconnect the BMS, manually balance charge the low cells, then let it sit for a day or two then measure the voltages again.
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Re: Stuck building 48v battery

Post by amberwolf » Jul 20, 2017 3:21 am

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 d8veh » Jul 20, 2017 4:31 am

Almost certainly the BMS. It's simple to test: just unplug the multi-pin connector and see what happens. I've repaired many batteries where one of the bleed resistors on the BMS got stuck open.

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Re: Stuck building 48v battery

Post by mcristiani » Jul 20, 2017 7:35 pm

Thanks to everyone who responded.

I feel like I have been living with a volt meter in my hand for these things. I have been using it to check voltage between pins on the BMS - B0 to B1 | B1 to B2 | etc...

I did not get a chance to take a look, but I will look tomorrow and post an update.

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Re: Stuck building 48v battery

Post by mcristiani » Jul 21, 2017 1:16 am

I was able to get to the battery tonight, so I am posting an update. One of the series (what I calling s12) was at 0.2 volts.

I checked the balancing wires to make sure they were all routed correctly. They look good.

I replaced a series (s12) successfully and have left the bms unconnected. When I check each series by simply putting a volt meter to the positive and negative end, one series at a time, they all show up as 4.11v except for one of the originally two dead series (what I am calling s1) which is sitting at 3.29. Just to reiterate, the new series I put in is sitting at 4.11v as of now.

I will leave the pack as is without connecting the BMS. I expect nothing will change, which would lead to confirmation that the BMS is bad. Make sense?

I did think I was buying better boards that have an equilibrium function from batteryspace.com. If I can get the charger to kick-on, I am hoping in can bring the other series back up from 3.29. Is that a reasonable assumption?

Separately, since I feel like this same issue is happening on both batteries, I am wondering if I somehow ruined each board during assembly. Any thoughts or ideas?

Thanks again.

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Re: Stuck building 48v battery

Post by mcristiani » Jul 21, 2017 1:30 pm

Update: No change overnight without BMS connected.

I replaced the board this morning and have since connected it.

As I mentioned before, one of the series is sitting at 3.32. I put the battery on the charger hoping but it behaved as before, turning green after 5 minutes - keep in mind this is with a brand new board.

Question: Will I be able to get the series that is at 3.32 matched up with everything else if I leave it plugged in even though the green light is on?

Here is a link to the board. Is it worth the extra money? > http://www.batteryspace.com/protection- ... limit.aspx

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Re: Stuck building 48v battery

Post by fechter » Jul 21, 2017 11:16 pm

Once the charger goes green, it stops charging. I think the amount of imbalance is too much for the BMS to correct in a reasonable amount of time. If you kept repeating the charge cycle enough times it should eventually balance but it might take hundreds of cycles. If you can manually balance with a single cell charger, the BMS should keep them balanced.
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Re: Stuck building 48v battery

Post by d8veh » Jul 22, 2017 7:38 am

You need to charge that low cell separately to bring it up to match the others. it'll take forever using the normal charger to balance. If you don't have a proper lithium battery charger for a single cell, then use an old phone or USB charger, which are normally 5v. Keep an eye on the cell's voltage because you need to switch off the charger when you get to the right voltage.

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Re: Stuck building 48v battery

Post by mcristiani » Jul 22, 2017 12:39 pm

Maybe a dumb question...

Do I need to remove that series (two individual 18650 cells in parallel) from the whole pack before doing that?

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Re: Stuck building 48v battery

Post by mcristiani » Jul 22, 2017 12:44 pm

Different question that is related:

I have replaced the BMS and cell voltages are holding.

When I check voltage on the bms balancing pins (keeping negative ob B- out of battery and positive on B13 on board) I get 52.8v.

When I check the voltage at the anderson connectors for power to the motor, I only get 45v.

What is the best way to get this to reset? At the moment, I have been unplugging/re-plugging the balance wires.

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Re: Stuck building 48v battery

Post by fechter » Jul 22, 2017 3:54 pm

45v is not good.
Most reset by disconnecting the load (controller). I would avoid disconnecting the balance wires if possible. Connecting them is when you have a chance of blowing the BMS.

If disconnecting the load fails to reset it, it might indicate some other problem.
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Re: Stuck building 48v battery

Post by mcristiani » Jul 24, 2017 4:19 pm

I removed the bad series and charged by itself then reinstalled with the new bms. Looks like things are holding - finally!

Thanks to everyone for the help.

I have two follow on questions:

In the future, do I need to remove a bad series (two individual 18650 cells in parallel) from the whole pack to charge in the future or is there a way to target just that series?

I am going to begin repairs on a 48v 10.4ah I built. Is there a recommendation for a 48v bms that is a bit cheaper?

Thanks again.

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Re: Stuck building 48v battery

Post by fechter » Jul 24, 2017 4:48 pm

What I do is use some skinny solid copper wires that fit properly into the balancing connector going to the pack. You could also make a 2 pin male and cut away the shroud so it can fit into any pair of sockets on the main connector. You can use this to both measure and charge individual series sections. I try to balance them all to 4.2v to start. You need a single cell charger to do this. I use a bench power supply.

There are lots of BMS units out there on eBay, Ali Express, etc. Quality is a gamble. I always get extras and test them myself before trusting. Anything good tends to be very expensive.
Single Cell Charging Hookup 2.jpg
Single Cell Charging Hookup 2.jpg (88.98 KiB) Viewed 1938 times
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Re: Stuck building 48v battery

Post by d8veh » Jul 25, 2017 4:12 am

mcristiani wrote:

In the future, do I need to remove a bad series (two individual 18650 cells in parallel) from the whole pack to charge in the future or is there a way to target just that series?

I am going to begin repairs on a 48v 10.4ah I built. Is there a recommendation for a 48v bms that is a bit cheaper?

Thanks again.
No, you can charge a single crll-group while it's in the pack.
I can't really advise you on BMSs. I just use whatever cheap ones I can find on Aliexpress, though occasionally, I get the same as what you had: one or more cells draining down.

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Re: Stuck building 48v battery

Post by mcristiani » Jul 31, 2017 1:03 pm

I decided to cut the end off of a 5volt microsd charger.

I connected to a single "dead" cell and was able to see the voltage increase using a volt meter. On the first try I actually saw a rather quick reduction in voltage - I assume I had the wires swapped...

Then, I tried two different ways to charge a parallel set within the larger 48v battery - I will call this 'p10'.

I first soldered separate little wire with an alligator clip to the positive and negative side and connected the hacked charger for 10secs. No increase in voltage. In this scenario I tried with the bms balance wires both connected and disconnected.

I then re-read the post and saw the picture. I unplugged the balance wires and connected to two ports I saw the drain over - b10 to b9. No increase in voltage after 10 secs.

Any thoughts? Current voltage is 3.43.

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Re: Stuck building 48v battery

Post by fechter » Jul 31, 2017 1:36 pm

Maybe try it for a longer time. It's also possible the little microSD charger doesn't like the low voltage and goes into protect mode. You could get around this by placing some resistance in series between the charger and the cell. Around 10 ohms. You could use a 12v light bulb as a resistor, something like a car tail light bulb.
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Re: Stuck building 48v battery

Post by mcristiani » Jul 31, 2017 4:50 pm

10ohm resistor on the negative wire? Does it matter?

Just for reference, the setup did charge a single 18650 cell of similar voltage quite rapidly.

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Re: Stuck building 48v battery

Post by fechter » Jul 31, 2017 7:19 pm

The resistor or light bulb can go either direction. No polarity.

Charge speed depends on current. A little 5v wall wart is going to be limited to 1A at the most. Resistor will slow it down even more, so it will be a very slow process depending on pack size and cell voltage. It could take days.

By doing some math, you can pick the resistor value that will give you the most current without going over the rating of the power supply. You might be able to use 1 ohm if the supply is strong enough. I just guessed 10 ohms to be sure it's in a safe range. The resistor will get hot when it's working.

I like light bulbs because they start glowing when they pass current and gives you an indication of how much. Some guys use the 12v halogen spot lights used for accent lighting (local hardware store).
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Re: Stuck building 48v battery

Post by mcristiani » Jul 31, 2017 8:00 pm

Thanks for the continued responses. That really helps me move forward.

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Re: Stuck building 48v battery

Post by mcristiani » Aug 01, 2017 6:12 pm

I have tried to put a 10ohm resistor in between the charger and battery.

It has been running for about 10 minutes, but has maybe moved from 3.43 to 3.44v.

I included a picture this time in hopes you can look at the layout and confirm/deny anything.

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Re: Stuck building 48v battery

Post by fechter » Aug 01, 2017 6:57 pm

Does the resistor get warm? It's at least going in the right direction. You could parallel more 10 ohm resistors across the one you have to increase the current.

If you measure the voltage across the resistor, you can calculate the current.
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Re: Stuck building 48v battery

Post by mcristiani » Aug 02, 2017 12:29 pm

I put a resistor inline and then took it out and it is currently charging and getting close to the 4.12v the rest of the cells are at.

For the moment, I am just waiting to see what the end result of this will be.

Stay tuned.

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