B2B - if size matters, what is too big/overkill? (1 Viewer)

[MisterB]

good morning, is there a max size of B2B that above that size would be just wasting money?

i have 2 x 130A AGMs and will be fittng 260w of solar (if it fits on the roof lol) - we do tend to drive a lot and previously had a 50A B2B on a previous motorhome that worked perfectly well with 2 x 95A batteries.

i am looking at B2B's but unsure of what size would be adequate and what would be overkill

thanks

 

[funflair]

You must also bear in mind the size of your alternator as you don't want to run at it's max.

EDIT just to add I would most likely go for 60A but you could possibly go higher if you need a faster charge.

 

[Kannon Fodda]

Three issues to set the maximum B2B size
Alternator size
Wiring size (and any fuse rating)
Battery max charge rate

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[MisterB]

Thanks Martin (as always !!) and Rob, we have a Fiat Ducato based Adria - 2.3 multijet - so looks like its around 150A - not looking to go anywhere near that maybe 60-90A B2B?

 

[Googlebot]

I am sure the max charging for a lead acid is about 10% to 20% of the capacity. Anymore and you get excessive gassing which means you bugger them quickly.

Lithium will take much more, 50% of the capacity at least.

A 50 amp B2B is quite large. With that and the solar you could see 70 amps in summer. I think that’s too much for lead acid.

If it was me, I would stick with the 50 amp one. As others have said, your alternator might not handle much more either.

 

[MisterB]

Battery to Battery Charger w/ Solar Regulator 12V to 12V - BBS1230 9 Months Warranty

The present series of BBS1230 does not have the starter battery solar trickle feed function enabled. For the starter battery trickle feed we advise fitting a BM12123 battery maintainer. New to 2020 12V to 12V Battery to Battery Charger w/ 350W Solar Charge Controller BBS1230 12V to 12V 30A DC to...

sterling-power.com

this one seems to be a good price but is only 30A - however it also controls solar input, so saves buying an MPPT controller.

has anyone any experience of using one of these?

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[Lenny HB]

30 to 40 amps max if you want your batteries to last, but AGM's don't last long anyway.

 

[eddie]

I have just fitted a Sterling 120 amp buck boost unit, removing the factory fitted 160 amp B2B

 

[Lenny HB]

I have just fitted a Sterling 120 amp buck boost unit, removing the factory fitted 160 amp B2B

That would kill his batteries.

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[MisterB]

That would kill his batteries.

I think I'm going to go with a 30Amp B2B to prevent that, thanks, not what I originally intended but it will be erring on the safe side.