Leisure battery discharging

[RobPeel]

Morning Funsters & Happy Fathers Day!

When I switch my Dometic fridge over from mains to leisure battery, it shows 14.6 amp discharge, which can’t be right. Over a couple of hours travelling, (new)/leisure battery drops rapidly from say 13.5 to 12.4v.

Fridge is maintaining temp but icing up - I switched on last night & icing up already.

Could it be fridge? Or alternator?

Regards,

Rob

 

[Diabalo]

It shouldn't run off the hab battery something is wrong. Traveling it should run off the alternator.

 

[poppycamper]

Morning Funsters & Happy Fathers Day!

When I switch my Dometic fridge over from mains to leisure battery, it shows 14.6 amp discharge, which can’t be right. Over a couple of hours travelling, (new)/leisure battery drops rapidly from say 13.5 to 12.4v.

Fridge is maintaining temp but icing up - I switched on last night & icing up already.

Could it be fridge? Or alternator?

Regards,

Rob

Our fridge RMD 8555 draws circa 15a when running on 12v with engine running

 

[RobPeel]

Thanks both. My understanding was that the ‘smart’ alternator should charge both batteries?

 

[Tombola]

Is it running via inverter from leisure batteries and yes the alternator can charge both if it is setup that way.

Does it have a b2b installed do you know
Even if it doesn't it can still charge the leisure...just not as regulated.

The fridge can draw 14 amps then cut out and in as required

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[Derbyshire wanderer]

Mine is similar as the split charger from the smart alternator isn’t giving enough to charge the leisure batteries and run the fridge properly together.
I am going to fit a B2B charger to sort it but until then drive with the fridge switched off

 

[Dave101]

It sounds like your lesuire battery is not receiving charge from the alternator.
If you have a B2B charger check that it is operating correctly, if no b2b charger then it will have a split charge relay somewhere in the system.

 

[RobPeel]

It sounds like your lesuire battery is not receiving charge from the alternator.
If you have a B2B charger check that it is operating correctly, if no b2b charger then it will have a split charge relay somewhere in the system.

Thanks Dave101. Agree leisure battery not receiving charge. If I switch fridge off, or over to gas (I know but just to isolate problem),:then battery is fine. Have solar panel also. Will look into B2B charger?

 

[Dave101]

Does your system use a CBE distribution fuse board? (I know some Hobby's do..) It is possible that the D+ circuit has failed, the CBE does usually have a fuse for the D+ circuit denoted by two batteries joined together icon.. check if that fuse is OK..
Fridge is generally wired to the habitation electrics / lesuire battery but only "allowed" to run on 12v when the engine is running, if the D+ circuit fails the fridge may still operate on 12v from the leisure battery but the charging relay which relies on the D+ will not activate.... hence no charge to lesuire battery.
There are many other possibilities but that is a fairly common one, whether it is pertinent to your system I don't know.

 

[RobPeel]

Does your system use a CBE distribution fuse board? (I know some Hobby's do..) It is possible that the D+ circuit has failed, the CBE does usually have a fuse for the D+ circuit denoted by two batteries joined together icon.. check if that fuse is OK..
Fridge is generally wired to the habitation electrics / lesuire battery but only "allowed" to run on 12v when the engine is running, if the D+ circuit fails the fridge may still operate on 12v from the leisure battery but the charging relay which relies on the D+ will not activate.... hence no charge to lesuire battery.
There are many other possibilities but that is a fairly common one, whether it is pertinent to your system I don't know.

Apologies Dave for delay. Forgive my ignorance - what is a CBE fuse board. I have the leisure battery & fuse board under drivers seat - a beggar to get at. Is this it? regards, Rob

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[autorouter]

Thanks both. My understanding was that the ‘smart’ alternator should charge both batteries?

Yes that's correct, in theory. But it's not simple.

A smart alternator is designed to reduce fuel consumption. It does this by delaying the recharging of the starter battery. When the engine is under load or cruising the engine control unit (ECU) dials back the charging so the load on the engine is less, so less fuel consumption. When you lift off the pedal, or apply the brakes, the ECU turns the alternator on so that it charges the battery, and applies a load to the engine to slow down. This uses otherwise wasted energy. But to do this, the ECU and smart alternator keep the starter battery at much less than full charge, so there is always space for more charge into the battery.

If you simply connect the leisure battery in parallel with the starter battery with a relay while driving, then the leisure battery will get the same treatment, which is probably not what you want. To avoid this it is usual to fit a Battery-to-Battery (B2B) charger, also called a DC-DC charger. It takes power from the alternator in the same way that the lights, wipers etc take power from the alternator. Then it boosts the alternator voltage to whatever is required to charge the leisure battery.