B2B/MPPT advice to specific question please

[Dee101]

I’ve been on here asking for advice on what B2B/MPPT etc. And by chance I now see a post (by someone that has a 1996 Hymer) that says that my motorhome should only have a maximum of 100ah for leisure batteries—though the bay next to the drivers seat is big enough for 2 x 70ah, which as far as I’m aware has been there for a very very long time.
I have the Elektroblock EBL 104-2, which Undoubtedly came with the vehicle back in ‘95/96.
Is there a restriction? Only I was just about to ADD two further 70ah batteries (all same make/spec).
The original post mentioned batteries exploding, so that’s my concern.
And, if I am restricted to my current 2 batteries (140ah), is there a way around this so that I can use more battery power, as we wish yo be able to go off grid and install 400watts of solar soon
Dee

 

[Diabalo]

You can have as many as you want.

 

[SandraL]

I suspect this "restriction" comes from recharge times with original mains charger.
The original mains charger may be rated at ,say, 15amps dc output.
To put back 50ah will take about 4 hours. The larger the battery the longer the recharge time.
So a second mains charger could be the solution. But if you are rarely on mains and relying on solar the size of mains charger will not matter.
With a proposed 400 watt of solar arriving soon I would be happy to increase battery size.

Edit, as post no 5, yes its the amount of discharge that affects recharge time, although the bigger the battery the bigger the possible discharge.

 

[Lenny HB]

Hymer always recommend fitting the auxiliary mains charger when fitting a second battery which increases the charging current to 32 amps from 18 amps.

I have 3 batteries in my Hymer with just the basic charger, the only time it's lightly to cause a problem is if you constantly charge the batteries for a low state on mains.

I have 300 watts of solar and 99% of my charging is via solar or driving, sounds like you will be doing the same so it will be fine.

If you are going to fit a B2B if you want to fit a big one you need to check the size of your alternator the later Hymers normally have a 160amp alternator. If you don't know what yours is it's best to fit a 30 amp B2B.

 

[bigtwin]

The larger the battery the longer the recharge time.

This is a misleading statement.

All other things being equal, the size of the battery makes no difference to the charging time.

What makes a difference is the extent of discharge, be that from a single battery, or from a bank.

Ian

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[SandraL]

This is a misleading statement.

All other things being equal, the size of the battery makes no difference to the charging time.

What makes a difference is the extent of discharge, be that from a single battery, or from a bank.

Ian

Agreed, I have edited my post.

 

[autorouter]

Another consideration is the reason you are adding batteries. Is it because you want to use more power per day? Or are you intending to use about the same power, for more days? Although in theory the internal charger in the EBL will be OK to charge a large battery bank, some people think they are not up to the long charging times required, and will fail quite soon. I think there's something in that.

If you are intending to quadruple your battery bank, I think you should be looking at disconnecting the internal charger and getting another charger direct to the leisure batteries. Your setup dates from the days when 100W of solar and 150Ah of battery was a pipe-dream for motorhomers. A good modern multistage intelligent charger like a Victron IP65 type would do a much better job of charging and maintaining the batteries. And it's ready for any battery type if you want.

 

[autorouter]

If you are fitting a B2B then you may need to disable the split charge relay (labelled Trennschalter in the EBL140 schematic diagram).

The EBL 140 is an early model, and I think the internal wiring will take up to 30A. A B2B up to 30A could be wired into the Starter Battery input of the EBL (labelled Batt1). The split charge relay would not need to be disabled in that case, because the B2B charging amps is flowing through the relay.

Anything bigger would need to be wired direct to the batteries, and the split charge relay would have to be disabled. Unfortunately in this EBL the fridge relay is wired after the split charge relay. Probably the best thing to do is to disconnect the Batt1 input to the EBL. Then wire it through a suitable relay and fuse to the fridge 12V element feed wire. Sounds complicated, but it's not a big deal really.

Your EBL would then be just distributing the leisure battery power to the various habitation circuits as before, but all the charging would be going direct to the battery.

The EBL140 manual and diagram is available in English on the Schaudt website. If you have any difficulty downloading it (the site is in German), I can post it here.

 

[Dee101]

I seem to be having trouble replying. As my “threads” seem half lost and half appearing some 24 hours after I post them.
So this is a repeat of a reply that somehow never made it here.
Thanks everyone for your advice. It is all very illuminating.
This is what I think I can now do without any problems. But if anyone thinks otherwise, please stick your oar in.
I buy a 30ah B2B (also known as a DC to DC) combined with an MPPT, and install it.
I also ADD 2 further 70ah batteries (same make/spec as the 2 existing).
And in a couple of months time I add my 4 x 100 watt solar panels. The B2B/MPPT and the solar panels would be made by Regony.
Dee