Solar - 2 x Leisure Batteries & 1 x Engine crank battery?

[StitchUp]

Yesterday I spent all day sorting the wiring in our van - it was in a dreadful state with cables not crimped properly, a cheapo solar controller (Perfect Suitor) buzzing like mad and a myriad of other issues! So, I stripped out the lot and started from scratch.

I fitted a new controller a Victron with bluetooth and made good all the wiring. So, presently I have 2 identical 124ah linked, all fused and the Victron working nicely. Now what to do with the engine crank/starter battery? I'd like to make use of the alternator charging all batteries when the engine is running but I'm aware one shouldn't connect leisure batteries and crank starter batteries together as they have different characteristics.

Any learned people out there who can suggest if I can bring the crank battery into the game and if so, how?

Thanks

 

[LesW]

Battery Master.

 

[XxAnthxX]

I’d imagine just about every leisure vehicle these days will have a split charge relay or battery to battery device fitted to link the hab and cab battery’s to allow alternator charging of both battery sets when on the move.
Maybe consider a battery master or CBE device for linking the charge to both battery sets from solar or when on EHU.

 

[StitchUp]

Thanks very grateful

 

[Burgo]

+1 For Battery Master. Keep it all as simple as possible so there's less to go wrong.

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[donkey]

Hi

Not sure a battery master is what the OP requires. He wants to charge the leisure batteries when driving. The battery master , as far as I understand, charges the starter battery from the leisure batteries.
I would suggest some form of split charge relay device.

Geoff

 

[GeoffnDee]

I would expect it to already have one fitted , but if there is not ,what is needed is a split charge relay this will allow the alternator to charge the starter battery and the leisure batteries when driving, as donkey says the battery master, when fitted , transfers a small amount of battery charge from the leisure battery into the starter battery to keep it topped up , when parked up , using solar or charger power that is being fed into the leisure battery.

 

[StitchUp]

I read some of the blurb on the Battery Master and it doesn't appear to what I need. I want to be able to charge the leisure batteries while the engine is running. It seems the previous owner(s) disconnected an isolation switch connected to the engine battery - not sure why. I'd prefer an automatic cut-off as I'm sure to forget throwing a switch

 

[XxAnthxX]

As mentioned earlier, you should be looking to a split charge relay or battery to battery charger to charge from the alternantor.

 

[GeoffnDee]

Split charge relay it is then ,as that it is what it is designed to do automatically when the engine is started , the battery master is not what you need at the moment although you may want to fit one in the future if the starter battery looses power , which most do, due ECU drain etc when parked up long term.

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[TerryL]

I fitted a Sterling B2B charger years ago, fools the alternator into maxing out it's output to recharge the leisure batteries. Very simple connections and for our pattern of use is ideal. I also have a 100w solar panel connected directly to the 2 leisure batteries and a battery master that trickles the engine battery. The whole system has only let me down once - last year when lockdown meant a six month gap where I couldn't recharge anything and there was simply not enough solar to keep up. Jump start and the B2B had everything sorted although one L/B eventually failed so I replaced them both, just in case.

 

[StitchUp]

I would expect it to already have one fitted ,

Our van, a Lunar Roadstar 720, it's 20 years old so is it still something you'd expect to be fitted?

Thanks to everyone for your comments.

 

[GeoffnDee]

Yes, I would expect a spit charge relay to be be fitted to much older Motorhomes as normal ,perhaps it is there but not working or a fuse has blown.
Have you confirmed , with a meter , that when the engine is running there is no charge going to the leisure batteries from the alternator.?
The relay is often fitted near to the starter battery ,possibly along with another one for 12v fridge operation.

 

[TerryL]

No split-charge relay on our 2007 Swift Bolero - which is why I fitted the B2B.

 

[GeoffnDee]

Was there not one inside the PSU ? (Nordelettronica ? )

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[Itsmcb]

There almost certainly is a relay near the starter battery. Usually two, one split charge and one for the fridge when driving. Both have fuses and both are prone to fail at that age. I've recently swapped both my relays. Also any connections need to be checked for corrosion.

 

[StitchUp]

I just found this in the depths of the door pocket still in it's box

 

[GeoffnDee]

I do not think that type of relay (voltage sensing) is correct for a motorhome set up which includes solar ,someone else may be able confirm this , and say why , but a normal heavy duty split charge relay would not be expensive anyway.

 

[autorouter]

There's basically two ways to charge a leisure battery from the alternator. The usual way is a split charge relay to connect the starter battery to the leisure batteries while the engine is running, and disconnect when it stops. The other way is to use a battery-to-battery (B2B) charger, sometimes called a charge booster or DC-DC charger.

As you say, the split charge relay has a bit of a problem if the batteries have different charging characteristics, but it's usually tolerable, especially if you have solar to ensure a full charge every few days. A B2B is especially useful in the winter months because it usually charges faster than a direct alternator connection. You can get B2Bs of different powers, 20A, 30A, 60A for example.

The next question is, how do you tell the split charge relay/B2B that the engine is running? There are two ways to do this. The simple way is to notice that the starter battery voltage rises above about 13.5V when the engine is running, so you can use a voltage sensitive relay (VSR) like that Durite one. The B2B will probably have a voltage-sensitive mode too.

The problem is, when you have solar and/or mains charging, the starter battery voltage can rise when the engine is not running, triggering the relay/B2B. The alternative is to use the 'D+' signal from the alternator to trigger the relay/B2B.

This is not the same as the ignition signal. When you first turn the key, the dash lights come on - that's the ignition. When the engine has started, the alternator light goes out - that's the D+ signal. You want to use the D+, otherwise the relay connects while the starter motor is running, which draws a a massive current for a few seconds. You don't want the leisure batteries connected while that is happening.

A BatteryMaster is the opposite of a B2B, it charges the starter battery from the leisure battery. This is useful if parked up for a few weeks, with the leisure battery charged by solar. It stops the starter battery going flat.

 

[royw]

There's basically two ways to charge a leisure battery from the alternator. The usual way is a split charge relay to connect the starter battery to the leisure batteries while the engine is running, and disconnect when it stops. The other way is to use a battery-to-battery (B2B) charger, sometimes called a charge booster or DC-DC charger.

As you say, the split charge relay has a bit of a problem if the batteries have different charging characteristics, but it's usually tolerable, especially if you have solar to ensure a full charge every few days. A B2B is especially useful in the winter months because it usually charges faster than a direct alternator connection. You can get B2Bs of different powers, 20A, 30A, 60A for example.

The next question is, how do you tell the split charge relay/B2B that the engine is running? There are two ways to do this. The simple way is to notice that the starter battery voltage rises above about 13.5V when the engine is running, so you can use a voltage sensitive relay (VSR) like that Durite one. The B2B will probably have a voltage-sensitive mode too.

The problem is, when you have solar and/or mains charging, the starter battery voltage can rise when the engine is not running, triggering the relay/B2B. The alternative is to use the 'D+' signal from the alternator to trigger the relay/B2B.

This is not the same as the ignition signal. When you first turn the key, the dash lights come on - that's the ignition. When the engine has started, the alternator light goes out - that's the D+ signal. You want to use the D+, otherwise the relay connects while the starter motor is running, which draws a a massive current for a few seconds. You don't want the leisure batteries connected while that is happening.

A BatteryMaster is the opposite of a B2B, it charges the starter battery from the leisure battery. This is useful if parked up for a few weeks, with the leisure battery charged by solar. It stops the starter battery going flat.

I wonder why a b2b/master all in one has not been developed ?

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[68c]

Autorouter....That is one of the best description I have seen about leisure batt charging. Simple and direct. Perhaps you could add a little more adding the modern 'smart alternators'.

 

[Revolvor]

I wonder why a b2b/master all in one has not been developed ?

It has!

I have CTEK D250 which is a combined MPPT Solar charger and B2B charger. In addition, when the leisure batteries are full charged from solar, power is transferred to trickle charge the vehicle Battery.

https://www.ctek.com/uk/battery-chargers-12v-24v/d250se

If the SMARTPASS module is added, the B2B can supply 140Amps!

 

[jp11]

There's basically two ways to charge a leisure battery from the alternator. The usual way is a split charge relay to connect the starter battery to the leisure batteries while the engine is running, and disconnect when it stops. The other way is to use a battery-to-battery (B2B) charger, sometimes called a charge booster or DC-DC charger.

As you say, the split charge relay has a bit of a problem if the batteries have different charging characteristics, but it's usually tolerable, especially if you have solar to ensure a full charge every few days. A B2B is especially useful in the winter months because it usually charges faster than a direct alternator connection. You can get B2Bs of different powers, 20A, 30A, 60A for example.

The next question is, how do you tell the split charge relay/B2B that the engine is running? There are two ways to do this. The simple way is to notice that the starter battery voltage rises above about 13.5V when the engine is running, so you can use a voltage sensitive relay (VSR) like that Durite one. The B2B will probably have a voltage-sensitive mode too.

The problem is, when you have solar and/or mains charging, the starter battery voltage can rise when the engine is not running, triggering the relay/B2B. The alternative is to use the 'D+' signal from the alternator to trigger the relay/B2B.

This is not the same as the ignition signal. When you first turn the key, the dash lights come on - that's the ignition. When the engine has started, the alternator light goes out - that's the D+ signal. You want to use the D+, otherwise the relay connects while the starter motor is running, which draws a a massive current for a few seconds. You don't want the leisure batteries connected while that is happening.

A BatteryMaster is the opposite of a B2B, it charges the starter battery from the leisure battery. This is useful if parked up for a few weeks, with the leisure battery charged by solar. It stops the starter battery going flat.

You've got me worried now. I've got the signal wire of my 50A Renogy B2B connected to an ignition live. It seems to be working well. You say "the relay connects while the starter motor is running, which draws a a massive current for a few seconds". Does that mean the leisure batteries and their wiring are providing the starter current? Why would it not be just the starter battery?
I have a Mk8 Transit and don't know where the D+ is.

 

[autorouter]

You've got me worried now. I've got the signal wire of my 50A Renogy B2B connected to an ignition live. It seems to be working well. You say "the relay connects while the starter motor is running, which draws a a massive current for a few seconds". Does that mean the leisure batteries and their wiring are providing the starter current? Why would it not be just the starter battery?
I have a Mk8 Transit and don't know where the D+ is.

No need to worry with a B2B. A split charge relay is a direct metal connection between the batteries, so current can easily flow both ways. A B2B has diodes in it, that only allow flow one way. It won't allow any flow back to the starter battery. Best to use the D+ if available, but no big deal if it's not.

 

[jp11]

That's a relief! Do you think the signal wire I connected to an ignition live from the van fuse box is OK?
Of course, with the Renogy B2B the control panel will send solar current back to the van battery when the leisure battery is full. But then, it' just changing the direction, instead of normally to the leisure battery....

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[autorouter]

That's a relief! Do you think the signal wire I connected to an ignition live from the van fuse box is OK?
Of course, with the Renogy B2B the control panel will send solar current back to the van battery when the leisure battery is full. But then, it' just changing the direction, instead of normally to the leisure battery....

The wire from the ignition live to trigger the B2B should be fine. The tech spec says it has reverse current protection. The Solar Controller built into it is designed to charge both batteries while ensuring no unwanted backflows anywhere. Looks like a neat all-in-one unit.