Leisure batteries not charging when driving

[Oldgustaf]

Any thoughts about why the leisure battery isn't charging when driving? MH is 2021 Mercedes chassis Hymer ML-T. Asking for a friend. Dealer not being very helpful. Thanks.

 

[stevec]

Probably has a smart alternator and no b2b.

 

[autorouter]

This MH is newish, and might have the older 'split charge relay' charging, or (if it has a smart alternator) a charge booster (B2B charger). Either way, the first thing to check is the fuse in the main supply from the leisure battery, probably a 50A fuse near the leisure battery. Then there will be a fuse in the supply from the starter battery/alternator, probably a 50A fuse near the starter battery.

The next step will depend on the charging method. Does it have an Electroblock (EBL) like most Hymers, if so what model number is it? Can you find out if it has a charge booster (B2B)?

 

[Scotch mist]

I had the same problem with My 1 year old pilote , it is the smart alternator , they will have to fit a B2B charger , what makes it worse is when driving as the fridge switches to 12v so depleting the battery with no charge going in , if you put the fridge on gas as opposed to A (auto) it helps a lot , this is a well known problem , the dealer will know this !

 

[Reallyretired]

My last Rapido on mercedes got negligable charge from the alternator to the leisure batteries. Normal split charge relay and long leads to leisure batteries at the rear. What current there was went to the fridge. Only real answer is a B2B. If youve already got one its not working.

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[Oldgustaf]

Thanks for the replies. He's just sent over the attached photo showing the B2B with the engine running.

 

[Oldgustaf]

This shows Power Reduct set in C3

 

[autorouter]

There is a pair of (thin) voltage sensor wires between the starter battery and the B2B, going to a 2-way connector on the B2B, with a 1A fuse near the starter battery end. Worth checking that fuse. These voltage sensor wires are required when the Power reduction curve is set to 'C3'. (This is in addition to the thick pair of wires carrying the main charging current)

Is there any way you can measure the starter battery input voltage to the B2B? The 'C3' power reduction curve means zero charge current below 12.0V, and max charge current at 12.6V and above. Maybe the input voltage is below 12.0V when the engine is ticking over.

Another thing to check is that the D+ (engine running) signal is reaching the B2B. It should be about 12V when the engine is running, and about zero volts when the engine is stopped. There is a 2A fuse on this wire, probably near the starter battery, and most likely with the other fuses for the main starter feed and the fridge feed.

 

[Scattycat]

Check the reset button on your charging unit.

 

[Oldgustaf]

Thanks for all your help, advice and suggestions. My friend is having another look but so far has not been able to pin down the problem. Odd though on no expense spared, top of the range mh.

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[Pausim]

I had the same problem with My 1 year old pilote , it is the smart alternator , they will have to fit a B2B charger , what makes it worse is when driving as the fridge switches to 12v so depleting the battery with no charge going in , if you put the fridge on gas as opposed to A (auto) it helps a lot , this is a well known problem , the dealer will know this !

The gas whilst travelling is only an option if you have both a crash sensitive regulator and rupture protection on the bottle.

 

[82125]

This MH is newish, and might have the older 'split charge relay' charging, or (if it has a smart alternator) a charge booster (B2B charger). Either way, the first thing to check is the fuse in the main supply from the leisure battery, probably a 50A fuse near the leisure battery. Then there will be a fuse in the supply from the starter battery/alternator, probably a 50A fuse near the starter battery.

The next step will depend on the charging method. Does it have an Electroblock (EBL) like most Hymers, if so what model number is it? Can you find out if it has a charge booster (B2B)?

my MH did the same thing (not charging leisures when driving), it was the fuse on the starter battery that had blown.

 

[Robert P]

Don't forget earthing straps between alternator and starter motor. We had the same problem and the garage took several hours to track the cause. He wdn't let it beat him!

 

[Gary Redfern]

I had the same problem with a 2020 Peugeot Boxer. The wire from the alternator is an earth (-12v) not a +12 feed; so called D- instead of D+. On the Electrobox there is a switch for either D+ or D-. Once I had the switch in the correct position (and the engine running), the battery charged and the fridge switched from gas to 12v when on Auto. Hope this helps.