Options for charging a large battery bank 800ah

Bassman

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I am looking for a battery charger that can charge 8 100ah numax leisure batteries that i can connect directly to the battery bank as apposed to having charge a couple at a time with a small 20a charger, one option would be to buy a few smaller 20a chargers and charge them in pairs however this is would be rather inconvenient and a charger than can do the whole lot in one go would be awesome.
 
I am looking for a battery charger that can charge 8 100ah numax leisure batteries that i can connect directly to the battery bank as apposed to having charge a couple at a time with a small 20a charger, one option would be to buy a few smaller 20a chargers and charge them in pairs however this is would be rather inconvenient and a charger than can do the whole lot in one go would be awesome.
I use a Victron Multiplus 12/3000/120 - so that features a 120A charger - to charge the 645Ah bank in my Camper.
 
I am looking for a battery charger that can charge 8 100ah numax leisure batteries that i can connect directly to the battery bank as apposed to having charge a couple at a time with a small 20a charger, one option would be to buy a few smaller 20a chargers and charge them in pairs however this is would be rather inconvenient and a charger than can do the whole lot in one go would be awesome.
Are you asking about a mains charger or in vehicle charging? assuming the former, the key part of the equation is what minimum SOC do you intend to run them down to on average!

If you can find a datasheet for your Numax Batteries they may state a recommended max bulk charge current e.g. 20A so in theory a 150A+ charger sounds ideal but in reality batteries do not pull max current for very long and this current tails off very noticeably as the SOC increases.

If you want to get the max life out of them and you don't plan run them down much below say 75-80% soc then its unlikely they will be on the bulk phase of any charge for very long before the charge switches to absorption and eventually float so you may well find a single 50A charger is perfectly adequate most of the time.

One criteria if looking at smaller 20A units might be to consider a charger with decent thermal management, fans etc as the 20A unit will be running close to at least 50% all the time even to maintain float and any parasitic loads so could get quite warm so install somewher with loads of ventilation.

You also need to take into account if/when you use the batteries heavily then recharging to a true 100% is going to take hours and hours!

This article is an excellent read re how fast batteries charge versus current over time

 

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