BMS that starts balancing at a set point/different voltage?

eikido

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May 8, 2019
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Is there a BMS that can start balancing at any other voltage/setpoint than close to 100%?
I only charge my batteries to about 80% but need to charge them to 100% sometimes to balance the cells.
I want to avoid charging them unbalanced to 80%.

Is there a BMS that can solve this?
 
https://www.lithiumbatterypcb.com/product-instructionev-battery-pcb-boardev-battery-pcb-board/ev-battery-pcb-board/smart-bms-of-power-battery/

https://endless-sphere.com/forums/viewtopic.php?t=88676
 
It has some issues though, like draining the battery within 6-12 months (depends on capacity) and intermittent Bluetooth connection issues.
I myself had no problems so far.
 
"A BMS" is just functionality, you do not need to try to get everything from one monolithic gadget.

There are balancing gadgets that have no protective features, LVC HVC OCP etc. "non protective BMS"

But most important, educate yourself about pure balancing functionality rather than example gadgets.

The other issue besides start threshold voltage, is amps available to get faster balancing.

Why do you need it? How often? How much imbalance does your pack have?

Most people top-balance, fewer do bottom balancing, doing it all the time is the rarest.

Good cells need it much less, both current and timing.

With decent quality cells bought new, you should need much less. But violent high C-rates and going into the voltage shoulders at either end increases the need, besides reducing lifetimes.

 
john61ct said:
"A BMS" is just functionality, you do not need to try to get everything from one monolithic gadget.

There are balancing gadgets that have no protective features, LVC HVC OCP etc. "non protective BMS"

But most important, educate yourself about pure balancing functionality rather than example gadgets.

The other issue besides start threshold voltage, is amps available to get faster balancing.

Why do you need it? How often? How much imbalance does your pack have?

Most people top-balance, fewer do bottom balancing, doing it all the time is the rarest.

Good cells need it much less, both current and timing.

With decent quality cells bought new, you should need much less. But violent high C-rates and going into the voltage shoulders at either end increases the need, besides reducing lifetimes.

My idea with balancing the packs is to protect them since i only charge the batteries to 75-80%.
If i would only charge them to 80% without ever balancing them sporadically (fully charging the battery pack) then i could potentially kill it quickly if one or several cells laggs behind.
I don't how much my cells shifts out of sync voltage wise but would rather want to work pro-actively.
 
Then maybe look at bottom balancing instead, put more of the capacity sacrificed for longevity toward avoiding the bottom rather than staying that far from the top.

IMO it makes no sense trying to balance in the middle unless you are shunt-balancing full-time at a high rate, and that is not efficient, only necessary for cells close to EoL.
 
Balancing per se is not a protective function.

The per-cell LVC and HVC take care of that.

All balancing does is give more total bank capacity back, once imbalances get significant enough to impact usable Ah.

If the cells are well matched, you can go a long time between rebalancing, treat it as a maintenance routine like equalizing FLA.

Or, if doing the usual top-balancing, a good balancing charger can do it every cycle.

Many ways to skin that cat.
 
john61ct said:
Balancing per se is not a protective function.

The per-cell LVC and HVC take care of that.

All balancing does is give more total bank capacity back, once imbalances get significant enough to impact usable Ah.

If the cells are well matched, you can go a long time between rebalancing, treat it as a maintenance routine like equalizing FLA.

Or, if doing the usual top-balancing, a good balancing charger can do it every cycle.

Many ways to skin that cat.

So would you recommend me to do as i've done previously?
Charge to 80% to optimize capacity and lifetime of the battery pack and from time to time fully charge it to balance the pack?
I only like high quality batteries from the big names.
 
eikido said:
So would you recommend me to do as i've done previously?
Charge to 80% to optimize capacity and lifetime of the battery pack and from time to time fully charge it to balance the pack?
I only like high quality batteries from the big names.

I assume your 80% number is based on some scientific study ?
 
cricketo said:
eikido said:
So would you recommend me to do as i've done previously?
Charge to 80% to optimize capacity and lifetime of the battery pack and from time to time fully charge it to balance the pack?
I only like high quality batteries from the big names.

I assume your 80% number is based on some scientific study ?

Yes.
According to these studies:
https://batteryuniversity.com/learn/article/how_to_prolong_lithium_based_batteries

Actually around 75%.

"In terms of longevity, the optimal charge voltage is 3.92V/cell. Battery experts believe that this threshold eliminates all voltage-related stresses; going lower may not gain further benefits but induce other symptoms. "

DST-cycles-web2.jpg
 
for the normal usage here i recommend just sticking to 4.05~4.1V range. you gain a lot of lifespan by just going to 4.1v (or slighty under). going lower is not that interesting for most people here as the battery packs are too small and simply die because of being ridden too hard. lowering to 4.05~4.1v just removes the lifespan wear by enough to triple the usable lifespan.

staying below or at 4v is only interesting for long lifespan usage like solar or UPS and proper EV vechicles with big packs that need to last a decade or more.
 
flippy said:
for the normal usage here i recommend just sticking to 4.05~4.1V range. you gain a lot of lifespan by just going to 4.1v (or slighty under). going lower is not that interesting for most people here as the battery packs are too small and simply die because of being ridden too hard. lowering to 4.05~4.1v just removes the lifespan wear by enough to triple the usable lifespan.

staying below or at 4v is only interesting for long lifespan usage like solar or UPS and proper EV vechicles with big packs that need to last a decade or more.

Ok i can do that too. Both actually works as my pack is really big on my machine.
But is it better to charge it to 4.05~4.1v mostly and from time to time balance it with a full charge?
Or if i can, bet a BMS that starts balancing at 4.05~4.1v?

Also my original charger applies 67.2v (My battery is 16s).
I'm thinking of getting a smarter charger. Would it be beneficial to set a lower charging voltage such as 4.05x16=64.8v and charge at that voltage instead?
 
no, doing full charges negates the whole point of not doing them.
you need a programmable bms that can manually set the balance voltage to 4v and a charger that is set to 65-ish volt.
 
flippy said:
no, doing full charges negates the whole point of not doing them.
you need a programmable bms that can manually set the balance voltage to 4v and a charger that is set to 65-ish volt.

Ok. I will do as i've done previously. Charge to 80-90% manually and from time to time charge to 100%+ to balance.
Thanks.
I'm still considering getting a smart charger so i can automatically charge up to 80%.
 
eikido said:
Yes.
According to these studies:
https://batteryuniversity.com/learn/article/how_to_prolong_lithium_based_batteries

Actually around 75%.

Thank you!
 
eikido said:
So would you recommend me to do as i've done previously?
Charge to 80% to optimize capacity and lifetime of the battery pack and from time to time fully charge it to balance the pack?
I only like high quality batteries from the big names.
I believe longevity is best served - besides buying quality cells - by (in order of impact, and the actual values depend on the use case and chemistry, even model)

A. not discharging too deep

B not charging at too high a rate

C not discharging at too high a rate

D avoiding too-high a charge is based on resting voltage, not some guesstimate of SoC.

Some are counter to the use case here, so just take the hit

D is IMO sacrificing maybe 4-6% capacity

A is the big one, but a judgment call. Certainly 15% SoC is the lowest ** I ** would go.

 
eikido said:
Is there a BMS that can start balancing at any other voltage/setpoint than close to 100%?
I only charge my batteries to about 80% but need to charge them to 100% sometimes to balance the cells.
I want to avoid charging them unbalanced to 80%.

Is there a BMS that can solve this?

Some of the Chargery products can do balancing at set voltage points and on charge or on discharge options. Check out the BMS16T/BMS16 Pro or BMS24T/BMS24 Pro. I have both. They have a BMS16 (without the T or Pro) that does not do balancing, so get the correct one.

Here is a link. http://www.chargery.com/BMS16Pro.asp

Please NOTE: My products work perfect, however, some Chargery products other than what I recomend (such as the all in one balance chargers they have) have been known to have issues. Same with customer service. I have had good results and got all my answers within a week. Including firmware updates. So you mileage may vary,
-YS
 
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