# Can I fit two battery chargers



## Vennwood (Feb 4, 2007)

Hi All you technical wizards - can you help me here?

I have a battery bank of 480 amp/hrs (totally separate from the normal leisure batteries) that is charged by a 30 amp Sterling pro-digital charger. During the summer I use solar panels and a gennny to keep them topped up. I am concerned that during the winter, with heavier usage and little help from the solar panels, I will be needing to use the genny quite a long time. I don't want to offend neighbours with the noise so would like to shorten the time to re-charge the batteries

Is it possible to add another charger, say 50 amp Pro digital, to run in parallel with the existing set-up giving me a total of 80 amps?

Pete


----------



## DABurleigh (May 9, 2005)

Pete,

I certainly wouldn't without the express green light of Sterling. I gave them a ring about a similar charger compatibility issue some time ago and they were knowledgeable, clear and helpful.

Dave


----------



## Vennwood (Feb 4, 2007)

Thanks Dave,

I'll certainly call them - one more question - is there a maximum size for charging batteries - or is it a case of the bigger the better?

Pete


----------



## olley (May 1, 2005)

Hi Pete I have the 50amp pro-digital and I asked them the same question, they said no problem so I assume the 30amp would be the same.

Olley


----------



## DABurleigh (May 9, 2005)

No more than 1/5th capacity to maximise life. So you can go up to ~100Amps with your 480Ah bank.

I hate to think the weight of all the batteries in your van! 

Dave


----------



## Vennwood (Feb 4, 2007)

Thanks for the info Dave/Olley

Excellent help as usual

Pete


----------



## Snelly (Aug 20, 2005)

Pete

I deal in Sterling and just last week I asked Charles Sterling himself a similar question about having 2x 50A battery to battery chargers and he said its absolutely no problem. So I can only presume 2x mains chargers would be fine too.

As a previous poster said, give them a call, they are very helpful.


----------



## wobby (May 1, 2005)

An option on our Carthago was a third battery with separate charger which I opted for. 

Wobby


----------



## olley (May 1, 2005)

DABurleigh said:


> No more than 1/5th capacity to maximise life. So you can go up to ~100Amps with your 480Ah bank.
> 
> I hate to think the weight of all the batteries in your van!
> 
> Dave


Hi Dave as charging is voltage dependant, surely can you have have the biggest charger you like? unless you ramp the voltage up to silly levels the charge rate will be a max of around 1/5 of the batteries total capacity irrespective of the available output of the charger.

Olley


----------



## Vennwood (Feb 4, 2007)

Hi All,

Just spoken to Sterling (I was surprised they were back at work - nice to see they were) and they confirmed that it was ok to link two chargers in parallel - as said by others earlier - nice people to deal with.

One last question before I commit to this - Is it possible to use an alternator to battery charger that will charge this separate battery bank without upsetting the existing charging system that charges the engine and standard leisure batteries?

Pete


----------



## DABurleigh (May 9, 2005)

Pete - yes; it's just another independent load on the alternator.

Olley - I know what you mean, and I'm not arguing with Ohm's Law when the battery is simply a load/ internal resistance, but I've certainly seen my alternator, itself limited to 14.4V, dumping greater than C/4 for a time into my leisure batteries when they were heavily discharged. They don't do that now I have the Sterling b-to-b fitted, which consumes a maximum of 50A.

My usual source of battery wisdom is Victron's book "Electricity on Board", and one extract is:

Dave


> Premature aging 2. Charging too rapidly and not fully charging.
> 
> Batteries can be quickly charged and will absorb a high charge current until the gassing voltage is reached. While charging with such high current might work well a few times, this will actually shorten the service life of most batteries substantially (the exception: spiral-cell and some other AGM batteries). This is due to accelerated loss of cohesion of the active material, which results in shedding. Generally it is recommended to keep the charging current down to at most C / 5, in other words a fifth or 20 % of the rated capacity. When a battery is charged with currents exceeding C / 5, its temperature can rise steeply. Temperature compensation of the charging voltage then becomes an absolute necessity (see sect. 2.5.9). My own experience is that charging a 50 % discharged 12 V 100 Ah flooded battery at 33 A (C / 3) results in a temperature increase of 10 to 15°C. The maximum temperature is reached at the end of the bulk phase. Bigger batteries will become even hotter (because the amount of heat generated increases with volume and the dissipation of heat increases with the available surface) as well as batteries with a high internal resistance, or batteries which have been discharged more deeply.


----------

