Starter or Leisure Batteries

[dpsuk999]

I currently have a separate battery bank running my inverter and intend on fitting a B2B to charge that battery bank and just wondered which battery to link it to, the starter battery or the leisure battery?

 

[Geo]

That would depend on what will give the greater output to your Inverter battery bank
Eng battery will almost always be fully charge by the alternator and pass on any surplus
when eng is running
House battery's will drop the min you start using them, and if solar cant keep up with usage there will be little or no
spare to pass on from them so B2B may well not work as well
Its a hard call but you know best your battery usage solar inputs and driving times better than anyone on here

 

[Geo]

Personally I would go for Eng batt as, when and if Inverter bank drops below good
you can always start eng and top up without moving

 

[Pausim]

I would not run an inverter from the engine battery, discharge that and you may not get started again. I assume you are asking about how to connect the B2B, it should be connected to both starter and leisure. It is fed from the starter battery (but only when the engine is running) and charges the leisure battery, in effect using the excess power from the alternator.

I have a Votronic VCC1212-45 B2B and it does a great job, leaving both leisure and starter batteries fully charged after every journey. There are 2 ways the B2B can tell if the engine is running, either by sensing a voltage increase or by a trigger wire from the alternator which is known as D+. Motorhomes use the D+ signal for other purposes such as switching the fridge to 12v. I favour the D+ because some people say that the B2B can switch on when it shouldn’t if something else, such as a mains charger or solar system starts trying to charge the engine battery. I think some cheaper B2Bs leave out the D+ method of switching and for me that would be a no no.

I hope I have understood the question properly but no doubt there will be knowledgeable people along shortly to offer a range of advice.

 

[Pausim]

Oops perhaps I have misunderstood your question, do you have 2 leisure banks, one for usual stuff and one just for the inverter? If so I agree with @Geo, connect to the engine bank not the other leisure bank.

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[dpsuk999]

Oops perhaps I have misunderstood your question, do you have 2 leisure banks, one for usual stuff and one just for the inverter? If so I agree with @Geo, connect to the engine bank not the other leisure bank.

Hi, yes I have 2 leisure banks, one for habitation and one for the inverter and then the starter battery. Both the starter and habitation leisure banks are charged via alternator (Schaudt EBL220) and want to fit a Schaudt WA121545 to charge my inverter bank while driving so I did originally think using the starter battery as I thought the same as @Geo that it would pass more onto the inverter bank as will be more charged than he leisure bank

 

[Pausim]

Hi, yes I have 2 leisure banks, one for habitation and one for the inverter and then the starter battery. Both the starter and habitation leisure banks are charged via alternator (Schaudt EBL220) and want to fit a Schaudt WA121545 to charge my inverter bank while driving so I did originally think using the starter battery as I thought the same as @Geo that it would pass more onto the inverter bank as will be more charged than he leisure bank

Yes, if you connect to the other leisure bank I suspect you might be asking a bit much of the existing wiring and perhaps leave it a bit starved. Probably safer to have separate wiring and fuses.

 

[Jamsdb]

I thought about having two battery banks for inverter and domestic use on my MH but after reasoning it out I decided to just have one large domestic bank made of four Trojan T105s giving 450 amp hours at 12 volts. Normally I don't think a deep cycle domestic bank can support an inverter for serious work i.e. a microwave but by the time you have a large bank of batteries the accumulated available amp draw will support some heavy use. I can draw 120 amps using a 2000w inverter driving a micowave and it still won't sag below a voltage of over 11.5 volts. ( The inverter cuts out at I think 10.5 volts). As for draining the batteries just monitor it as you would any battery bank and you should not run into any trouble.

 

[hilldweller]

I thought the idea of B2B was the B2B loaded the engine battery so much the alternator kept giving maximum output which it can transfer to the leisure battery.

The leisure battery is only trickle charged by the alternator due to thin(ish) cables connecting to that would achieve nothing.

I may be wrong.

 

[dpsuk999]

I thought about having two battery banks for inverter and domestic use on my MH but after reasoning it out I decided to just have one large domestic bank made of four Trojan T105s giving 450 amp hours at 12 volts. Normally I don't think a deep cycle domestic bank can support an inverter for serious work i.e. a microwave but by the time you have a large bank of batteries the accumulated available amp draw will support some heavy use. I can draw 120 amps using a 2000w inverter driving a micowave and it still won't sag below a voltage of over 11.5 volts. ( The inverter cuts out at I think 10.5 volts). As for draining the batteries just monitor it as you would any battery bank and you should not run into any trouble.

My inverter bank are victron lithium’s which are fantastic if you are drawing big amps out. I’ve always kept them separate from the habitation batteries (victron gels) as the schaudt panel can get confused so Udo Lang at Schaudt advised having a separate bank of batteries for the inverter

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[dpsuk999]

I thought the idea of B2B was the B2B loaded the engine battery so much the alternator kept giving maximum output which it can transfer to the leisure battery.

The leisure battery is only trickle charged by the alternator due to thin(ish) cables connecting to that would achieve nothing.

I may be wrong.

I agree, the cabling used these days by the manufacturers is sometimes not adequate but my van been of an era when manufacturers were not run by accountants did the job right and very adequate cable size so I think ill use the engine battery as the link

 

[hilldweller]

I agree, the cabling used these days by the manufacturers is sometimes not adequate but my van been of an era when manufacturers were not run by accountants did the job right and very adequate cable size so I think ill use the engine battery as the link

I did not explain properly.

The "normal" MH split charge relay system links the engine battery to the leisure battery as soon as the alternator starts charging. They deliberately wire in thinner wire to limit current flow for when the engine battery if full and the leisure battery is low which would result in a massive current if wired with heavy duty wire and relay. This is the poor man's B2B.

As I understand B2B you will wire that with proper job cable to pass 50A or so from the alternator via the starter battery across to the leisure battery. It's all electronically regulated so the current will never get out of control.

 

[Pausim]

Are you sure the Schaudt 121545 has the right charging profile for Victron lithiums? I believe it has a constant 14.4v LiFePO4 charge rate. My Votronic 121245 instructions suggest a 14.2v charge rate with a 13.6v float level for Victron LFP-BMS 12.8 (if this is what you have). I chose Votronic because it has a wide range of lithium profiles, my Relion lithium is given as 14.6v/13.8v which is within the parameters specified by Relion. I was surprised by how different the charging profiles are for various makes.