Parallel Battery Chargers

[d4raffy]

Recently expanded my Service battery bank and considering upgrading my existing 240v battery charger. I have an Inverter / Charger onboard also - but only used it as an Inverter at present. After researching, i was led to believe that attaching 2 battery chargers to the same battery bank, in parallel, would cause issues between the chargers, due to the intelligent 3 stage monitoring that occurs.

When looking at Sterlings Pro Charge Ultra chargers, the blurb describes thus ...

'Larger voltage / current requirements?
The Pro Charge Ultra series can be put in series or parallel with other Pro Charge Ultras. This is enabled by the chargers have dynamic charging ability.'
&
'Larger requirements?
After your final calculations are made, if you require a larger charger, then the Sterling range, because they are digital chargers can be added together. For larger requirements simply add units (2-3-4 etc) together to meet your requirements. Multiple smaller units can offer some advantages over 1 larger unit: They tend to be lower cost, have a built in redundancy, (in event of one failing) and enables you to switch one off in the event of low shore power facility.'

There doesn't appear to be any interconnection cable between multiple chargers, so they must sense manage some how....

Interested in any views or experience using this setup ?

I am also wondering if this Sterling charger will cohabitate with the inverter/charger if i parallel that up with it ?

ps .. i read the excellent compass marine article.

[a64pilot]

I parallel my Sterling with my Magnum inverter charger, they play well together, there is no interconnect and none needed. If however you turn on the Sterling first and with it on the voltage is above 12.8, the Magnum will not go into bulk mode, it will go to float as it thinks the bank is close to being full.
But if you just connect shore power, they both go into bulk, which in my case is 185 amps total, so that does cut into available power with only 30 amps shore power, however you can program the Magnum so that it cuts back when a total amp draw is reached, I have mine set to 25 amps AC draw, so at 25 amps the Magnum turns down charge to keep AC current draw at 25 amps.


Sent from my iPad Pro using Cruisers Sailing Forum

[d4raffy]

Originally Posted by a64pilot

I parallel my Sterling with my Magnum inverter charger, they play well together

Thanks - thats good to know.
I will give it a go. Not sure my inverter/charger can be limited as yours.
Im generally only thinking about using both chargers to minimise generator up time when charging..

So, i am assuming that multiple Sterling chargers don't get confused and all stay at the correct charging stage regardless. With no interconnect cable, wonder how they do this.

[a64pilot]

Originally Posted by d4raffy

So, i am assuming that multiple Sterling chargers don't get confused and all stay at the correct charging stage regardless. With no interconnect cable, wonder how they do this.

Its not just two Sterlings, it two chargers of almost any make as well as a charger and a wind generator and a Solar charger,they will all work together if correctly programmed. The key I think is being able to program one.

I have one Sterling and the Magnum, often depending on how it is programmed one will go into float before the other, so what happens if they were both supplying say 25 amps to the bank at absorption voltage, and one goes into float, the other will now supply 50 amps into the bank, cause 50 amps is below the max of 60 that the Sterling can supply, and 50 is the max that the bank can accept, due to its acceptance rate. Even if I had a 500 amp charger, 50 is all the bank will accept at this point.
Together they can supply 185 amps, and when the bank is low they will supply 185 amps, but after about 30 min., the acceptance rate of the bank begins to decline and you see the charge rate begin to drop, after maybe the first hour it's below 60 amps.
These are numbers for a 12V bank, be half that for a 24V of course, and these numbers are guesses, I have not done a study where I record the numbers, but I know as the first 30 min of generator run time, I need to keep the other big loads off so my batteries can get all they will take, after 30 min, I can start heating water or running an AC or whatever.

Having a BIG charger does not cut charging time by as much as you may think. The reason is the bank can only accept so much, and the more charged it is, of course the lower the acceptance rate is.
If I had to guess I'd guess that having a BIG charger will only reduce your charge time by about a half an hour, but having two chargers is worth while in my opinion as you know have a back up


However with some types of battery chemistry, I believe that high charge rates can be beneficial, flooded batteries for instance, high charge rates can contribute to the electrolyte being stirred, convection currents will ensure it's properly mixed, I think that AGM batteries also benefit from high charge rates, but I'm not sure why.
Gels I don't know much about

[d4raffy]

Originally Posted by a64pilot

Its not just two Sterlings, it two chargers of almost any make as well as a charger and a wind generator and a Solar charger,they will all work together if correctly programmed. The key I think is being able to program one.

thanks for the info - just to be clear ... so not confused here ..
you're saying that there is nothing special about the Sterling Charger and that all chargers will behave this way?

The fact that one charger may see a high voltage on the battery (due to the other charger) will not confuse it to switch stages incorrectly - even if the batteries are still depleted. e.g. the bank would except 100 amps but 2 x 50 amp chargers will happily work together in bulk - producing 100amps - without confusing each other ?

cheers for the help ......

[a64pilot]

Originally Posted by d4raffy

thanks for the info - just to be clear ... so not confused here ..
you're saying that there is nothing special about the Sterling Charger and that all chargers will behave this way?

The fact that one charger may see a high voltage on the battery (due to the other charger) will not confuse it to switch stages incorrectly - even if the batteries are still depleted. e.g. the bank would except 100 amps but 2 x 50 amp chargers will happily work together in bulk - producing 100amps - without confusing each other ?

cheers for the help ......

As long as they are programmable, then yes it's my experience that they will work and play well together.
But if for instance one thinks absorption voltage is 14.1 V and the other 14.3, then of course when bank voltage hits 14.2 the one that has absorption set for 14.1 will go into float, but if the voltages are set the same, the will all play well together, or that has been my experience anyway.
You do have to understand how they work though, like my Magnum will not go into bulk / absorption if bank voltage is above 12.8, so if I turn on my Sterling first and it raises bank voltage to above 12.8, the Magnum will not go into bulk / absorption.

Now I do want you to understand that if you have a good charger now, adding another large, good charger will only shorten charge time by maybe 30 min or so, that doubling your charger capacity will in no way cut your charge time in half, but you do gain redundancy

[a64pilot]

It's not uncommon at all for four charge sources charging in parallel, your generator, Solar Panels and your alternator if you happen to have your engine running, and you may have wind too.

[smac999]

with bigger battery banks you need more / bigger chargers. it's not uncommon to have 200amps of charging on out intalls with ~800ah banks. however that is maxing out small shore cords and small gens. you really want a 5k genny or 50a 240v shore plug once you get into bigger chargers.


once you get into aborbsorb or float it doesn't really matter too much if they fight as you'll won't be getting full power from them anyways. it's bulk where you want all the current. and with low batteries they will all bulk at full.