Once the green light comes on, no more current flows into the battery, it is no longer balancing. The BMS disconnects the charger from the battery, hence the green light.

The voltage is held on at 42v while the green light is on. That's what provides the charge to balance the cells. The BMS switches off the charging if it uses a separate charge control mosfet, but the bleed resistors will be open, which drains the battery down and switches back on the charge mosfet.

The voltage is held on at 42v while the green light is on. That's what provides the charge to balance the cells. The BMS switches off the charging if it uses a separate charge control mosfet, but the bleed resistors will be open, which drains the battery down and switches back on the charge mosfet.

 

 

Hmmm, I'm not convinced about that. To do the balance as you say would still require current from the charger. Even if some excess charge is being bled off through resistors from cells at a higher state of charge, power from the charger would be needed to charge the cells at a lower state of charge. However, once the green light is on, no more current is flowing from the charger.

 

Have you got a datasheet for a BMS explaining the mode of operation you describe?

Vfr400 is correct, but be aware some packs balance at less than 100%. It will all depend on the BMS that your battery pack has.

 

Mine balances from 50% plus, so I never need to charge to 100% to activate the balancing feature.

 

 

Can you give some info on this BMS that balances from 50%? Sounds interesting.

Hmmm, I'm not convinced about that. To do the balance as you say would still require current from the charger. Even if some excess charge is being bled off through resistors from cells at a higher state of charge, power from the charger would be needed to charge the cells at a lower state of charge. However, once the green light is on, no more current is flowing from the charger.

 

Have you got a datasheet for a BMS explaining the mode of operation you describe?

You don't need a data sheet. Put your fingers on the bleed resistors to see how hot they get.

If you check the voltage from time to time, any reduction from that 41.8v will show how much imbalance there is. You only need to leave it on charge for a long time after the green light if the battery is unbalanced.

Are you saying that any unbalanced battery can be recovered by prolonged charging?

Are you saying that any unbalanced battery can be recovered by prolonged charging?

Yes, that's why in many instruction manuals it says to leave the battery on charge for a long time for the first charge.

Yes, that's why in many instruction manuals it says to leave the battery on charge for a long time for the first charge.

Thanks,

I have wondered exactly what freezing temperatures could do to a battery, so I placed an 18350 that I use in my vaping pipe in the freezer for a few days.

When I took it out I did not wish to measure any voltage in case it caused damage but let it warm up.

I am now using it as before with no signs of degradation.

Can you give some info on this BMS that balances from 50%? Sounds interesting.

This is the link to the battery I purchased:

 

https://em3ev.com/shop/em3ev-48v-13s5p-jumbo-shark-ebike-battery/

 

The blurb about the balancing is in the description, but if you don't fancy scrolling through to find it, here is the specific paragraph reference the BMS:

 

'We use a high tech, fully programmable Smart BMS, which is rated for genuine 40A continuous plus, with a programmable over-current trip set to >60A (which is ample for the intended application). With our BMS you can view various battery data, such as: cell voltage levels, temperature, instantaneous charge/discharge current, capacity (genuine SOC, measured Ah and remaining Ah), data log, error indication (on matching LED panel) and it all links to your phone with a continually updated and improved App. Our BMS balances during charging (when charging and when at >50% charge) and therefore doesn’t require a full charge in order to balance. Auto power off function, auto power on and with a pre-charge function (no sparks, so long as the battery is powered off when linked to the controller)'

Blue tooth or smart BMS are widely available on AliExp and one can fit them to any generic battery pack, on can set the final balance charge limit to which ever voltage they wish. Likewise one can use the dearer Neptune BMS.

This is the link to the battery I purchased:

 

https://em3ev.com/shop/em3ev-48v-13s5p-jumbo-shark-ebike-battery/

 

The blurb about the balancing is in the description, but if you don't fancy scrolling through to find it, here is the specific paragraph reference the BMS:

 

'We use a high tech, fully programmable Smart BMS, which is rated for genuine 40A continuous plus, with a programmable over-current trip set to >60A (which is ample for the intended application). With our BMS you can view various battery data, such as: cell voltage levels, temperature, instantaneous charge/discharge current, capacity (genuine SOC, measured Ah and remaining Ah), data log, error indication (on matching LED panel) and it all links to your phone with a continually updated and improved App. Our BMS balances during charging (when charging and when at >50% charge) and therefore doesn’t require a full charge in order to balance. Auto power off function, auto power on and with a pre-charge function (no sparks, so long as the battery is powered off when linked to the controller)'

 

Thanks for that, and for Nealh's info.

 

I'm currently running a long term experiment looking at how long it takes for cells to go out of balance if charging to 41V (see my thread in the Technical section of the forum):

 

https://www.pedelecs.co.uk/forum/threads/charging-pack-to-41v-experiment.38470/

 

After >60 cycles, the cells show no sign of going out of balance. It had occurred to me that perhaps the BMS was balancing even at a lower voltage, but according to the spec sheet, it should only balance at 4.18V and above:

 

 

However, can this be trusted? It isn't a smart BMS, or programmable. I suppose the only way of being sure is to monitor current flow in the balance wires during charging.

Thanks for that, and for Nealh's info.

 

I'm currently running a long term experiment looking at how long it takes for cells to go out of balance if charging to 41V (see my thread in the Technical section of the forum):

 

https://www.pedelecs.co.uk/forum/threads/charging-pack-to-41v-experiment.38470/

 

After >60 cycles, the cells show no sign of going out of balance. It had occurred to me that perhaps the BMS was balancing even at a lower voltage, but according to the spec sheet, it should only balance at 4.18V and above:

 

[ATTACH=full]39610[/ATTACH]

 

However, can this be trusted? It isn't a smart BMS, or programmable. I suppose the only way of being sure is to monitor current flow in the balance wires during charging.

Interesting thread, although you probably spend more time testing your batteries, than actually enjoying riding. Tongue in cheek of course

 

I'm a firm believer in buying a pack with quality cells and not cheap out in this area. It makes financial sense in the long run, even if a quality pack can add quite a bit more to the budget.

 

I think once quality cells have had an initial balance, then there's no reason for them to go out of balance, unless there's some duff cells in the pack.

 

My last 29E pack wasn't in such good shape after 2 years and the voltage sag was horrendous. I put this down to me fully charging after every ride and leaving it for long periods fully charged.

 

My latest pack with HG2 cells appears to be going stronger with the same usage, but the difference is, that I don't charge after a ride and only fully charge just before my next ride.

Thanks for that, and for Nealh's info.

 

I'm currently running a long term experiment looking at how long it takes for cells to go out of balance if charging to 41V (see my thread in the Technical section of the forum):

 

https://www.pedelecs.co.uk/forum/threads/charging-pack-to-41v-experiment.38470/

 

After >60 cycles, the cells show no sign of going out of balance. It had occurred to me that perhaps the BMS was balancing even at a lower voltage, but according to the spec sheet, it should only balance at 4.18V and above:

 

[ATTACH type=full" alt="39610]39610[/ATTACH]

 

However, can this be trusted? It isn't a smart BMS, or programmable. I suppose the only way of being sure is to monitor current flow in the balance wires during charging.

As I said, you can feel the temperature on the bleed resistors when the bleed transistors are open. You don't need a meter.

Your charge voltage is very close to when the bleed resistors are open, like within the margin of measurement error, so it could be that they are in fact doing some balancing.

As I said, you can feel the temperature on the bleed resistors when the bleed transistors are open. You don't need a meter.

Your charge voltage is very close to when the bleed resistors are open, like within the margin of measurement error, so it could be that they are in fact doing some balancing.

 

Unfortunately, it's a sealed unit, so you can't touch the resistors:

 

 

If 41V is too close to 41.8V, perhaps only charging to 40.5V will be better.

 

Maybe I'll do that once I've done 100 to 150 cycles at 41V

Edited December 3, 20205 yr by WheezyRider