Proper process for balancing two Dyness batteries

wingnut771 said:
Not above 55.2V.
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They will never balance even if you get it to that voltage. The first battery will hog the current and a few hours later the bank is already getting discharged. I would only believe your theory if they were left on Eskom to charge for a few days. Balancing using your method would take days of being left alone on charge.
 
denmendez65 said:
They need to be disconnected and left standing.
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left standing full voltage is nowhere near 57.6v the reason they use the peak voltage to measure full is exactly because the voltage is that flat throughout the soc curve

the only way you can hitt 57.6v is if the battery is full

if one isn't full it will be hard to hit artificial 57.6v imo unless you have a hell of a lot of current
 
denmendez65 said:
They will never balance even if you get it to that voltage. The first battery will hog the current and a few hours later the bank is already getting discharged. I would only believe your theory if they were left on Eskom to charge for a few days. Balancing using your method would take days of being left alone on charge.
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That's why I said 57.6V.
 
denmendez65 said:
They will never balance even if you get it to that voltage. The first battery will hog the current and a few hours later the bank is already getting discharged. I would only believe your theory if they were left on Eskom to charge for a few days. Balancing using your method would take days of being left alone on charge.
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And even then, use the same bank for a few months and they will drift apart again if the one is still further away compared to the other. Constantly charging and discharging will never get them balanced if the problem still exists. You would need to leave them for days again on Eskom to charge fully.
 
denmendez65 said:
And even then, use the same bank for a few months and they will drift apart again if the one is still further away compared to the other. Constantly charging and discharging will never get them balanced if the problem still exists. You would need to leave them for days again on Eskom to charge fully.
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You are wrong. They are balanced at 57.6V even if only at that voltage for 1 minute.
 
denmendez65 said:
You can't do that. You will read the average voltage across all the batteries. The only real test is to disconnect each and leave them standing for a few hours and measure.
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even this is difficult

cause the way bms's work

lets say the first battery is full early at hits cell protection voltage
the bms disconnects the cell from the charge voltage and you essentially only measuring the voltage of the second battery

have tried this before on my bike battery
set charge voltage to 16v , measure voltage before bms everything is at 16v

measure behind the bms on the cells
and the cells was resting at 3.35v with pack voltage of 13.4v

so the superficial voltage was just on the pre bms side almost like the battery is disconnected
 
leon.davibe said:
even this is difficult

cause the way bms's work

lets say the first battery is full early at hits cell protection voltage
the bms disconnects the cell from the charge voltage and you essentially only measuring the voltage of the second battery

have tried this before on my bike battery
set charge voltage to 16v , measure voltage before bms everything is at 16v

measure behind the bms on the cells
and the cells was resting at 3.35v with pack voltage of 13.4v

so the superficial voltage was just on the pre bms side almost like the battery is disconnected
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It could be that one battery (the left new one) has a cell peaking above 3.65V (because its never been top balanced properly from factory) so the bms disconnects charging while the other one carrys on therefore it never gets full. This is why I said to leave float at 57.6V overnight to give bms time to do cell balancing.
 
leon.davibe said:
left standing full voltage is nowhere near 57.6v the reason they use the peak voltage to measure full is exactly because the voltage is that flat throughout the soc curve

the only way you can hitt 57.6v is if the battery is full

if one isn't full it will be hard to hit artificial 57.6v imo unless you have a hell of a lot of current
Click to expand...
I still disagree. You don't measure batteries while they are connected in parallel. No one does that unless they are too lazy to get a spanner to separate the batteries. We test BTU units that have dozens of batteries in parallel, and they always get disconnected first before measuring.

You will find a battery in the connection that is some 3V lower when it is on its own, but it won't pull the bank down. The BTU charger will still hit the full absorption voltage and stop charging because it thinks the whole bank is full. Now, what is 1V at 50 plus volts?
 
denmendez65 said:
And even then, use the same bank for a few months and they will drift apart again if the one is still further away compared to the other. Constantly charging and discharging will never get them balanced if the problem still exists. You would need to leave them for days again on Eskom to charge fully.
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no a single charge cycle is enough to get them in balance

the days to balance is only a on small balance currents ie like the bms does
so one charge cycle they will be balanced

if something in the setup causes a drift between the two
that will happen every day
and they will meet at full every day

i have a kak setup like this
they balance every day once full and slightly drift on every discharge
been meaning to do a proper distance cable setup

but yea have to repair some batteries first (bms replacements) and do it once i install them
 
denmendez65 said:
I still disagree. You don't measure batteries while they are connected in parallel. No one does that unless they are too lazy to get a spanner to separate the batteries. We test BTU units that have dozens of batteries in parallel, and they always get disconnected first before measuring.

You will find a battery in the connection that is some 3V lower when it is on its own, but it won't pull the bank down. The BTU charger will still hit the full absorption voltage and stop charging because it thinks the whole bank is full. Now, what is 1V at 50 plus volts?
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Why not? There is no current flowing between the two at 57.6V.

Lets stick to LFP's here.
 
leon.davibe said:
lets say the first battery is full early at hits cell protection voltage
the bms disconnects the cell from the charge voltage and you essentially only measuring the voltage of the second battery
Click to expand...
Thats what I wanted to read. Since they work like that then it should be a non issue. Cable lengths etc should not matter.
 
denmendez65 said:
I still disagree. You don't measure batteries while they are connected in parallel. No one does that unless they are too lazy to get a spanner to separate the batteries. We test BTU units that have dozens of batteries in parallel, and they always get disconnected first before measuring.

You will find a battery in the connection that is some 3V lower when it is on its own, but it won't pull the bank down. The BTU charger will still hit the full absorption voltage and stop charging because it thinks the whole bank is full. Now, what is 1V at 50 plus volts?
Click to expand...
but yea that is probably lead acid which voltage lifts extremely easy

lithium soaks up charge so does not push voltage up superficially that easy i think
 
wingnut771 said:
Why not? There is no current flowing between the two at 57.6V.

Lets stick to LFP's here.
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So why bother with 57.6V if the BMS auto switches off the one battery bank and the inverter only charges the other? Its pointless.
 
denmendez65 said:
Thats what I wanted to read. Since they work like that then it should be a non issue. Cable lengths etc should not matter.
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yes they will balance out to full every time the bank charges full

now yes the one will supply more current and then less current as its voltage dips when closer to empty if none go below 20% i would not worry about it

as long as they all charge full
 
leon.davibe said:
yes they will balance out to full every time the bank charges full

now yes the one will supply more current and then less current as its voltage dips when closer to empty if none go below 20% i would not worry about it

as long as they all charge full
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It will just age the batteries differently
 
denmendez65 said:
So why bother with 57.6V if the BMS auto switches off the one battery bank and the inverter only charges the other? Its pointless.
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We don't know this is happening and no way to know either, that's why we give it overnight high voltage float time to give passive balancer time to burn off voltage of the peaking cell. It might even take longer than overnight considering some of the balancers out there.
 
leon.davibe said:
but yea that is probably lead acid which voltage lifts extremely easy

lithium soaks up charge so does not push voltage up superficially that easy i think
Click to expand...
We still disconnected the batteries for a LFP based BTU that was going into a Substation. Clearly stated in the user manual from the manufacturer.
 
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