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Gotway Msuper v3s warm battery


danw872

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Whilst I was checking the motor wires on my Msuper V3s today I noticed a warm spot on both batteries and was wonder if anyone else has noticed this.

Will be getting a temp gun on it soon just to confirm its not in my head.

I noticed it in this area on both batteries (see pic) maybe the balance board is there but i have no way of telling. The area was pretty warm after charging but after 5 hours after charging I noticed its still warm to the touch in this area. Does anyone have any info on this.

Thanks Dan

20170210_173557_zps5mkndhll.jpg

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Thank you most of my experience is with Lipo cells and as you know only get warm when charging at high amps or discharging at high amps but once charged/discharged cool down.

Think it's time to do some research on these 18650 cells.

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If you are saying that it's warm 5 hours after you charged it (and the charger is unplugged), then it's just a false impression on your brain that it's warm. However, if in reality it is warmer than the rest of the wheel that would mean the battery is discharging for some reason, and you would clearly see the battery charge level dropping.

If the battery level is not dropping (and the charger is disconnected), the battery can't be warm - unless the first law of thermodynamics is not in affect in your part of London ;)

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9 hours ago, Marty Backe said:

If the battery level is not dropping (and the charger is disconnected), the battery can't be warm - unless the first law of thermodynamics is not in affect in your part of London

there is a third possibility though: the battery level is dropping so slowly that one wouldn't see the difference in a day or two. This is happening with most EUCs anyway, because after turning them off they are usually in stand-by modus and not really entirely turned off.

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I believe it is just the BMS doing its job creating heat (resistor bleeding I believe) to use up any over charging in the cells. To what I have read this is normal and can take a while in the larger size batteries mine being the 1300wh. 

I will be grabbing my temp gun tomorrow and doing some tests.

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32 minutes ago, Mono said:

there is a third possibility though: the battery level is dropping so slowly that one wouldn't see the difference in a day or two. This is happening with most EUCs anyway, because after turning them off they are usually in stand-by modus and not really entirely turned off.

I really doubt this. I've had a fully charged EUC sitting for over a month in the back of a car and it was still essentially fully charged when I turned it on. The batteries may lose ~2% per month and if there's a standby current being drawn it's probably on the order of micro-amps.

If a battery pack is warm then there's a non-trivial amount of current flowing thru the battery and you would see a measurable drop in the battery level over a period of hours.

34 minutes ago, danw872 said:

I believe it is just the BMS doing its job creating heat (resistor bleeding I believe) to use up any over charging in the cells. To what I have read this is normal and can take a while in the larger size batteries mine being the 1300wh. 

I will be grabbing my temp gun tomorrow and doing some tests.

I can't believe the BMS is doing any work when the charger is not plugged in. 5 hours is a huge amount of time to be generating heat. I guess I should try and find an engineering description of exactly how BMS's are designed because I admit I'm only speculating based on my engineering background - I have no direct knowledge.

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10 minutes ago, Marty Backe said:

I really doubt this. I've had a fully charged EUC sitting for over a month in the back of a car and it was still essentially fully charged when I turned it on. The batteries may lose ~2% per month and if there's a standby current being drawn it's probably on the order of micro-amps.

If a battery pack is warm then there's a non-trivial amount of current flowing thru the battery and you would see a measurable drop in the battery level over a period of hours.

I can't believe the BMS is doing any work when the charger is not plugged in. 5 hours is a huge amount of time to be generating heat. I guess I should try and find an engineering description of exactly how BMS's are designed because I admit I'm only speculating based on my engineering background - I have no direct knowledge.

That makes 2 of us and I stumbled across the heat when I was checking the motor connectors.

But when I find heat on batteries it always gets me thinking. I repaired DJI drones for 3 years and did a lot of work with lipo batteries.

Heat gets me a little worried when its happening after charging but BMS boards are new to me. With lipos the charger does the balancing hence why I asked about the heat.

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Found this information to be very helpful.

How a BMS Balances the Pack

If your charger shows a green light (indicating that its full), our theoretical 13S pack will read 54.6V when its hooked up, but if…as soon as you unplug it from the charger, the battery pack plug reads 53.0V on a voltage meter? This means that one or more of your sub-packs is not taking and holding the full charge.

The way that a BMS works is that it allows a simple bulk charge to pass through it to the battery until it reaches the programmed “full” charge. Then it stops the charge and takes a moment to sense what each of the sub-packs’ voltage is at. Most sub-packs will be at 4.20V, but one cell might be at 4.15V

Most BMS’s then drain the other sub-packs to the voltage of the lowest pack (in this example, 4.15V). and then the BMS allows the bulk charger to send another full charge to all the cells. This drain and charge happens several times until the BMS senses that all the sub-packs are all close enough in voltage to be considered “balanced”.

Due to the varied cells’ resistances, when the LVC cuts power at the end of a ride cycle, each of the sub-packs will be at a slightly different voltage (which is natural), but…as long as they are not too far away from each other, the BMS can then manage getting them to a balanced charge state without it taking so many drain/charge cycles that…it seems like it takes forever for the pack to finish charging.

Out of all the different ways that a piece of electronics could fail, the sub-pack “drain” function (as part of the drain/charge cycles at the top of the charge for balancing) can fail, and completely drain that sub pack down to zero. If you have a 13S / 48V pack, and the packs highest voltage is 4.2V less (50.4V instead of 54.6V), you have a dead sub-pack that will no longer take any charge. If a BMS uses the “drain the high cells” method to get the pack balanced, that is called a “resistor bleed”.

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7 minutes ago, danw872 said:

Found this information to be very helpful.

How a BMS Balances the Pack

If your charger shows a green light (indicating that its full), our theoretical 13S pack will read 54.6V when its hooked up, but if…as soon as you unplug it from the charger, the battery pack plug reads 53.0V on a voltage meter? This means that one or more of your sub-packs is not taking and holding the full charge.

The way that a BMS works is that it allows a simple bulk charge to pass through it to the battery until it reaches the programmed “full” charge. Then it stops the charge and takes a moment to sense what each of the sub-packs’ voltage is at. Most sub-packs will be at 4.20V, but one cell might be at 4.15V

Most BMS’s then drain the other sub-packs to the voltage of the lowest pack (in this example, 4.15V). and then the BMS allows the bulk charger to send another full charge to all the cells. This drain and charge happens several times until the BMS senses that all the sub-packs are all close enough in voltage to be considered “balanced”.

Due to the varied cells’ resistances, when the LVC cuts power at the end of a ride cycle, each of the sub-packs will be at a slightly different voltage (which is natural), but…as long as they are not too far away from each other, the BMS can then manage getting them to a balanced charge state without it taking so many drain/charge cycles that…it seems like it takes forever for the pack to finish charging.

Out of all the different ways that a piece of electronics could fail, the sub-pack “drain” function (as part of the drain/charge cycles at the top of the charge for balancing) can fail, and completely drain that sub pack down to zero. If you have a 13S / 48V pack, and the packs highest voltage is 4.2V less (50.4V instead of 54.6V), you have a dead sub-pack that will no longer take any charge. If a BMS uses the “drain the high cells” method to get the pack balanced, that is called a “resistor bleed”.

Very interesting. But note that this is all happening while plugged into the charger.

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To what I can work out the BMS is working even after charging.

Depending on what board gotway have used the BMS will drop all the cells voltage to the lowest cell voltage even after charging is complete. If a BMS uses the “drain the high cells” method to get the pack balanced, that is called a “resistor bleed”. I think this is happening after charging is completed. I could be wrong though.

It's still a little over my head but I am still looking in to it.

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