Qbatteries

[martin007]

Hello!

A friend has recommended some AGM batteries that give very good results.

https://qbatteries.co.uk/images/motive/ ... AGM-76.pdf

Charging Method:
Charge the batteries at least once every six months, if they are stored at 25°C
Constant Voltage (V) -0.2C x 2h + 2.4–2.45V/Cell x 24h, max. Current 0.3CA
Constant Current (A) -0.2C x 2h + 0.1CA x 12h
Fast -0.2C x 2h + 0.3CA x 4.0h

2.4 (at 25º) x 12 cells = 28.8v ?

[steves1977uk]

Those 67Ah+ batteries are too wide for powerchairs. The specs don't give enough info like internal resistance. They'd be ok for the bigger scooters.

Steve

[Burgerman]

Charging Method:
Charge the batteries at least once every six months, if they are stored at 25°C

Means if not connected to a powerchair. If they are stored and connected do it every few weeks 24 hours even if the chair is turned off.

So ignore this charge info.

For moderate normal cyclic use, set the ZXD Shirley charger to say 12A max if XLR connector, or 25A if connected via Anderson connector, and set volts to 28.80V. Set it to transition to FLOAT at a lower voltage of 27.2V when the current drops to 0.2 to 0.3Amps. And then allow it to charge for 24h to several days now and again. And overnight every night until you must disconnect it to get up.

The idea is that it will spend around 8 hours at 28.8V and then drop to 27.2V.

And top up during the day for 30 mins, 1 hour, or whatever, whenever you get chance as well.

[martin007]

For moderate normal cyclic use, set the ZXD Shirley charger to say 12A max if XLR connector, or 25A if connected via Anderson connector, and set volts to 28.80V. Set it to transition to FLOAT at a lower voltage of 27.2V when the current drops to 0.2 to 0.3Amps. And then allow it to charge for 24h to several days now and again. And overnight every night until you must disconnect it to get up.

28.8v at 25º or 20º?

[Burgerman]

Its similar. But at 25C I would use 28.8V according to the usual rules...

Its not that critical on AGMs. Thats why many specs say charge at 14.4 to 14.7V at 20/25C.

If its really hot like 30C or more then drop it to 28.4V. Remember that the battery may be warmer than your air temperature. You live in spain. In my country I would just charge at 28.8 summer to 29.2V winter as its around 20C ish in my house all the time.

If you want to calculate it and be super accurate then its easy. Most AGMs need 4 mV extra per 1 degrees C temp drop. Or -0.004V for every 1C rise in temp. PER CELL.

So if its 12 cells, on a 24V system thats 0.004V x 12 = 0.048V per 1 degree. Or if its 5C colder, you would increase voltage by 5x 0.048V so 0.24V.
So at 15C, instead of 20C you increase from 28.80V to 29.04V.

Easier to look it up...

MAX is highest you should use = fastest charge and what we need for cyclic use.
OPTIMUM is best for say a solar system that has days to charge and gives longest service life.

[martin007]

OK.

28.8 at 20º and 28.5 at 25º

Are all AGM batteries charged at the same voltage?
There is no different (manufacturer) brand?

[Burgerman]

Pretty much. 14.4 to 14.7 volts typically t room temp. Theres some variation. But unlike gel it is not so critical.

Too much volts with gel = shrunk or cracked gel or empty voids. Because as the electrolyte which contains water splits and produces gas at higher voltages it pushes the gel away from the lead plates and dries it out... That causes voids or bubbles in the thick gel mix that doesent recover. Not enough volts or not enough time = sulfation long term is also bad as it allows sulfation to remain each charge. So gel is quite voltage and time critical.

Too much volts with AGM isnt that big a problem. Thats why they are charged at a higher 14.4 to 14.7V. Which is much faster. Because any small amount of gas produced is recombined back into water faster. And that just mixes back into the acid/water electrolyte. So AGMs charge faster. And can charge faster because of the higher volts. They will still charge full at a lower 14.1V, but they then suffer from sulfation in cyclic use, and slow charging means that this is just then exhadurated. So its best to charge at 14.4 to 14.7V. In deep cycle use, typically 8 to 12 hours CV. Overcharge in time or voltage is less of a problem on AGM. If you overdo do it however then you still lose electrolyte, and cause grid corrosion. Hence float after 8 hours CV.

[martin007]

I understand.

Thanks Burgerman.

[martin007]

What is the recommended float voltage for AGM batteries?

[Burgerman]

AGM.
To complete a charge after the CV part for 1 to 2 days max, 13.7V to 13.8V. Not longer.
To complete a carge more slowly, and maintain for up to 14 days to a month, 13.5 to 13.6V.
To store, after a complete charge, for long periods like over winter, to indefinitely 13.35 to 13.4V

Double for 2 batts in series.

[martin007]

To complete a charge after the CV part for 1 to 2 days max, 13.7V to 13.8V. Not longer.
To complete a carge more slowly, and maintain for up to 14 days to a month, 13.5 to 13.6V.
To store, after a complete charge, for long periods like over winter, to indefinitely 13.35 to 13.4V

Double for 2 batts in series.

OK, at 20ª
Could you give me the equivalent values for gel batteries at 20º?


P.S. I can't go 14 days without using the powerchair.

[Burgerman]

You may not. But people have 2 or more. And also store batteries not in a chair. And use for solar or UPS or for off grid backup like generator startup batteries.

Gel float is almost the same.

To complete a charge after the CV part for 1 to 2 days max, 13.6V to 13.7V. Not longer.
To complete a carge more slowly, and maintain for up to 14 days to a month, 13.5V.
To store, after a complete charge, for long periods like over winter, to indefinitely 13.35 to 13.4V (same)

[martin007]

OK.
I'll print the information.