# Battery charging - do I have a problem?



## Vennwood (Feb 4, 2007)

I deliberately drained around 100amps out of our battery bank and then proceeded to re-charge them up.

Immediately we got a flow of +80amps - terrific

After a couple of minutes this started to drop to around 40amps and settled there until I got tired of watching it.

So the question is - is this normal given that there was "room" for around 100amps? Why have a 80a charger if it is only going to charge at 40a

I could have sworn that last year when I did this exercise it wacked it in at 75 - 80a intil the battery was within 25 amps of being charged

Do I have an impending problem here?

Pete


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## Mrplodd (Mar 4, 2008)

Charging your battery at 75 - 80 amps, Thats enough to melt VERY large cables !! 

I suspect that whatever meter you are using is either duff OR you have mis-read it !! Could it be 7.5 - 8.0 ????


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## raynipper (Aug 4, 2008)

Yes it is usual for any charger to input close to it's maximum at first and then progressively drop to a more modest charge as the battery becomes topped up.

Ray.


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## CliveMott (Mar 10, 2008)

Sounds normal to me. What charger does your Flair 8000 have? Is it the Mastervolt combined charger and inverter lump?

C.


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## safariboy (May 1, 2005)

The usual rule is about 1/8th of the A-Hr rating for 10 Hours. More than that might overheat the plates. So 80A seems far too much. It is not a good idea to flatten lead acid batteries anyway like this. You should not go below about 11.6V I seem to remember
Modern battery chargers usually detect the state of charge and adjust accordingly but I am not sure how effective this is.

Car alternators usually can charge at higher currents because they need to charge while lights fans heated windscreens etc. are on and it is important to get the battery fully charged again even after a short run.


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## bevdrew (Aug 30, 2009)

Why did you drain your batteries down anyway? Not good to go below 12v


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## Vennwood (Feb 4, 2007)

Thanks one and all.

There are 3 x 180AH AGM batteries and they are charged by one Sterling 30A and one 50A Pro digital chargers both through a 400A shunt, monitored by a Sterling Battery Management system.

The intent was to be able to charge the batteries quickly if I had to use a genny or use an electric point at an Aire or Stellplatz. I drained 100 amps off to help stop shadowing of the batteries and give them a good cycle.

From what Clive and others have said and my own research this afternoon I guess the chargers are just doing their job. Pitty in a way as it kinda defeats the original objective - i.e. to charge the batteries quickly

Thanks again


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## Kees (Jan 15, 2009)

It might be worthwhile repeating the exercise with just one charger turned on and the other off, then repeat again with the first off and the second on. If the Sterling (on its own) then charges at 30A and the Pro Digital (on its own) charges at 50A then they are both working correctly.

I believe they are both 3-stage chargers and my guess is that one of them has tripped into float mode early on. This one is then not able to contribute to the charging until the second charger also drops into float mode. This is always a problem with 3-stage chargers in parallel. If nothing else, by having the two chargers you have a back-up in case one fails.

Hope this helps

Kees


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## CliveMott (Mar 10, 2008)

If you have two different chargers both mains powered then its quite likely that only one will provide most of the charging. This is because the cutback voltages for both units are unlikely to be identical. Close but not identical. Its better to have one BIG charger than several small ones in parallel. 
The chargers will cut back anyway to stop excessive battery voltage.

How long did you discharge the batteries at 100 amps first for?

C.


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## Vennwood (Feb 4, 2007)

CliveMott said:


> If you have two different chargers both mains powered then its quite likely that only one will provide most of the charging. This is because the cutback voltages for both units are unlikely to be identical. Close but not identical. Its better to have one BIG charger than several small ones in parallel.
> The chargers will cut back anyway to stop excessive battery voltage.
> 
> How long did you discharge the batteries at 100 amps first for?
> ...


Hi Clive,

I discharged the batteries over a 5 hour period. As I said originally it hasn't been a problem in the past, when I first fitted these chargers all was well and they both charged at their respective rates and cut back in the later stages as I expected them to.

I think Kees may have a point in that one of the chargers may have gone into float mode so I'll look in the instruction manual and see if its possible to reset them or something.


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