Adaptive charging

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ProperCharging
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Adaptive charging

Postby ProperCharging » Tue Nov 02, 2010 7:00 pm

I’m searching a 72V lead acid charger with “adaptive charging algorithm” in order to get longest possible battery life. Chargers with “adaptive charging algorithm” have variable absorption time depending on SOC at charger switch on.
Does anyone know whether the Zivan NG3 perform this way?

GregsGarage
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Re: Adaptive charging

Postby GregsGarage » Tue Nov 02, 2010 8:40 pm

You can get the the NG3 configured pretty much anyway you like. The UK distributor is Electrofit Zapi. They will work with you to get a charge profile for your battery pack. They will want to know the exact batteries you are using. You also can get the charger configured to compensate for battery temperature.

Correct charging is important to cell life, but correct discharging is probably even more important. For lead acids try not to go below 50% dod and also look the batteries ability to deliver the current required. Trying to pull to many amps from a battery will also shorten its life.
Greg Fordyce

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dillond666
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Re: Adaptive charging

Postby dillond666 » Wed Nov 03, 2010 11:42 am

I was under the impression that most lead acid smart chargers vary the absorbtion time depending on the state of charge. My zivan gives constant current up till a certain voltage is reached (2.4v per cell) then gives constant voltage while the current reduces. As this is done by voltage / current measurement the state of charge when you switch the charger on doesn't matter.

What type of battery are you charging? The charge curve for flooded is very different to gell / agm.

ProperCharging
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Re: Adaptive charging

Postby ProperCharging » Thu Nov 04, 2010 11:15 am

I’m charging “pbq” brand Agm batteries. Two12V 80Ah in parallel, and six in series to give 72V.
As you might already know charging agm’s in series strings very often result in short battery life due to overcharging. Although batteries come from same batch, they differ in performance and hence reach critical charge voltage randomly. Those batteries getting charge voltage beyond the specified max voltage will gradually loose capacity and eventually “kill the whole package”.

Overcharge (over voltage) is more eminent when charge start at high SOC, say 70 % and over, but with a charger utilising variable absorption time, there’s fewer problems with overcharge.

In addition to use a charger with variable absorption time, I plan to us “battery clampers” in order to protect any battery from getting over voltage.
Anyway, I won’t use the NG3 unless I’m certain of its performance regarding variable absorption time.

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Re: Adaptive charging

Postby GregsGarage » Thu Nov 04, 2010 11:37 am

dillond666 is the person you want to talk to, he is working on an almost identical setup using a management system based on the BMS project on this forum. I am sure he will be along shortly.

Another option is to just use the Zivan (or large charger of your choice) for the constant current phase and finish off with 6 individual smart chargers of say 2 to 4 amp capacity. This means each battery is finished off without overcharging.
Greg Fordyce

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dillond666
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Re: Adaptive charging

Postby dillond666 » Sat Nov 06, 2010 6:10 pm

The Zivan should do for your requirements. Just ask for an AGM curve and send them (electrofit zapi) a copy of your battery datasheet. The charger doesn't just rely on dumb timers, it measures voltage and current as it charges.
Regarding BMS, If the parallel strings are only connected together at the ends you should be able to achieve reasonable balance. If they are paralleled at every 12v step in the series string (buddy pairs?) I would imagine proper balance being rather harder to achieve.
I am using a derivative of Peters BMS for my 160aH 156v AGMs, it clamps the voltage for each battery at 14.4v as well as starting and stopping the charger and sending data to the display unit. I consider this version to be experimental and will be redesigning it when I get the car on the road. FYI undercharging is just as detrimental to battery life as overcharging and it's the issue that gives me the most worry as I refine the BMS. Greg pointed out correctly that you should try not to discharge your battery too deeply if you want to get a good cycle life.

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Re: Adaptive charging

Postby GregsGarage » Sun Nov 07, 2010 10:32 pm

dillond666 wrote:If the parallel strings are only connected together at the ends you should be able to achieve reasonable balance. If they are paralleled at every 12v step in the series string (buddy pairs?) I would imagine proper balance being rather harder to achieve.


I would recommend connecting as buddy pairs.Each pair of cells will be automatically balanced to it's buddy, so you only have to worry about 6 batteries instead of all 12.
Greg Fordyce

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dillond666
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Re: Adaptive charging

Postby dillond666 » Mon Nov 08, 2010 9:43 am

Each pair of cells will be automatically balanced to it's buddy


I had thought about that but I figured if the two batteries in the buddy pair have different impedances they would accept and deliver charge at different rates. This would mean for charging, the one with the highest impedance would hit the clamping voltage first and when the BMS was clamping it would prevent the buddy from receiving full charge as the clamp bypasses current round both batteries.
It would also mean the battery with the lower impedance would become exhausted more quickly on discharge thus compounding the battery balance issue.
Maybe :)

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Re: Adaptive charging

Postby GregsGarage » Mon Nov 08, 2010 8:22 pm

Because the buddies are in parallel, they will be at the same voltage. A high discharge may cause a temporary imbalance, but they will always return to the same voltage. Currents in the two batteries may be different but voltage will be the same.
Greg Fordyce

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