# Charging and electrical testing questions



## Waleem (Nov 1, 2006)

Hi Guys
Need to sort the charging problem with my Dethleffs. The split charging now only works when it feels like it, although the mains charger is working fine. This is great as long as I have mains hookup, but we intend to stay on Aires in France when we go in August, and I need split charging I can depend on ! I am also wondering if the fridge 12V is working as I have no indicator light on my van. The charging system on the van is an all integrated type, similar, I think, to the Hymer electroblock system. So, on to the questions...

1. What level of charge would the leisure battery normally receive whilst driving, and does it vary or is it a set level?

2. Whilst reading through other posts, I came across fuse problems being a cause for similar symptoms. How do I test a fuse for continuity ? I have a multimeter, but I must be honest-it confuses me ! If someone could give me step by step, I would be grateful!

Many thanks in advance!


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## trevorf (May 16, 2005)

Hi 

Your vehicle should charge the battery at about 14.2 volts when driving. The amount of charge the battery receives depends on how long you drive for.

To test a fuse, set your meter to ohms (resistance) on the lowest scale setting and connect the red and black leads to each end of the fuse. The reading should be zero ie no resistance.

Trevor


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## trevorf (May 16, 2005)

Hi again

Thought this may help


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## gromett (May 9, 2005)

The voltage of a charger split or otherwise is irrelevent (sorry) the bit that matters is the current that is put in. They do have a relevence to each other but are not always directly related.

The alternator of a vehicle via the split charger will not put an awful lt into a battery especially when within 80% of full charge. 

What I would personally recommend is either a solar panel with a decent solar controler module (MPTT) and/or a small generator.

If you want me to I can give you details of my setup and requirements to guide you on an optimal solution but it will only be a guide as everyone is different.

Cheers
Karl


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## Waleem (Nov 1, 2006)

Thanks guys-very helpful comments. I will set to testing the fuses.
Karl-so do I understand correctly ? The voltage supplied by the alternator through the split charge system to the leisure battery varies according to how well charged the battery is? If that IS the case, I probably need to run the battery down a bit in order to test the system correctly. Or have I got hold of the wrong end of the stick? (Quite possible!!  )


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## gromett (May 9, 2005)

If a battery is very low then when charging it will pull down the voltage of the output from the split charger. Even though the charge current will be maxed out the voltage can be a lot lower than would otherwise be expected.

The best way to test that the split charger is working fully is to disconnect the positive from the split charger and put your multimeter in series with the cable. Ensure that it is on the Amps setting and has a high enough capacity to cope with the charge current. ie don't do it if your multimeters maximum current rating is 20Amp and your split charger can whack out 50amps.

Also a split charger will only charge the battery to around 85%. So if you have only used the battery a little and then drive it is unlikely to put any charge into the battery and this may be why it appears to work intermittently.

Regards


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## Boff (May 10, 2005)

Waleem said:


> The voltage supplied by the alternator through the split charge system to the leisure battery varies according to how well charged the battery is?


Nope.

Unless you have a special battery-to-battery or alternator-to-battery charging system, which is not standard in a Dethleffs, the charging regime is controlled by the alternator regulator. The job of the alternator regulator is to compensate for varying engine revs and provide a constant voltage of about 14.2 volts to the _engine battery_.

The only thing the split-charging relay does is that it connects the leisure battery in parallel to the engine battery while the engine is running. So there will be a constant voltage of 14.2 v at the split charge outlet while driving.

From here normally two separate cables branch off: One goes to the 12v input of the fridge, and the other to the leisure battery. The charge status of the battery determines the _current_ that flows in the cable. And as the cable usually has a significant lenght (and many motorhome makers don't use too thick cables for cost reasons), this cable will provide a certain resistance and therefore a voltage drop. So the voltage that you measure directly at the leisure battery will be a bit lower than at the split charge relay (resp. the engine battery).

This resistance is not entirely a bad thing, because it limits the charging current if the battery level is really low. And as the battery is charged the voltage goes up.

The split-charge will however never charge to 100%. For that the battery would have to be charged at up to 14.4 volts, and this the alternator simply cannot deliver. So the leisure battery will be charged up to about 80-90%.

Which is, as long as the battery is in good condition, normally fully sufficient while travelling. However, to extend battery life it should from time to time be fully charged, so it is not a bad idea to hook up on mains from time to time.

Best Regards,
Gerhard

P.S: A similar voltage drop of course also occurs on the cable to the fridge. And most problems with fridges not properly working on 12v are actually caused by this voltage drop.


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## Waleem (Nov 1, 2006)

Thanks again guys-more to think about! In some ways, I wish my Dethleffs just had a normal split charge relay, but it is all integrated into the charger and thus harder to test! Can I just run my current situation past you just to make sure I am getting it right?

My leisure battery is charged (From hookup) at present to 12.6V When I start the van's engine, I get 14.2V at the battery for a few seconds, then back to 12.6V From what has been said, I am assuming that because the battery is well charged, the split charge is not putting a constant charge to the battery. If I partially discharge the battery and then try, I should get a more consistant 14.2V at the battery when running. Is that right ?
Many thanks again for all the advice-I find electrics VERY confusing!!


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## Boff (May 10, 2005)

Waleem said:


> ...I get 14.2V at the battery for a few seconds, then back to 12.6V


Then there is something wrong!

Maybe the split-charge relay is defective, and drops out after a few seconds.

Or maybe your split-charge only activates when the voltage from the alternator exceeds a certain value? Check if the voltage on the battery goes up again to 14.2 when revving up the engine in idle.

Or your van has been (improperly) retrofitted with one of these blooming cutoff relays, that some people think(imagine?) are required according to UK standards.

Best Regards,
Gerhard


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## Waleem (Nov 1, 2006)

Thanks Gerhard
I'm pretty sure that revving it makes no difference to the charging input, so suspect an internal fault with the charger system. I am going to test the fuses etc and if that fails, I suppose I will have to buy a new charger from Dethleffs (No doubt at huge cost) unless I can find someone capable of repairing it.
One further question that has just occurred to me-is the split charge feed always connected directly to the alternator, or can it be fixed to any other point on the vehicle's wiring ? I am going to try to trace the connection just to ensure that it isnt a loose wire or something. I have asked Dethleffs for a wiring diagram, but they sent me a schematic only which doesnt give any details of charger wiring. I have asked them if they can help with more specifics, but havent had a reply yet.
Thanks again.


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## Boff (May 10, 2005)

Waleem said:


> One further question that has just occurred to me-is the split charge feed always connected directly to the alternator, or can it be fixed to any other point on the vehicle's wiring ?


Normally it is connected directly to the engine battery, not to the alternator.

Best Regards,
Gerhard


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## Waleem (Nov 1, 2006)

Gerhard
Again, many thanks. There seems to be only one wire to the vehicle battery from the charger, so I am assuming it fulfils all the seperate functions. I will remake this connection, just in case!


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## ksebruce (Nov 5, 2006)

Not an electrician but on mine (Burstner) the engine battery takes priority when engine running. Does this not mean that as the engine battery is drawing from the alternator the liesure battery will not show as charging? Will this have a bearing on what is happening?


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## Boff (May 10, 2005)

ksebruce said:


> Not an electrician but on mine (Burstner) the engine battery takes priority when engine running.


There are several different ways of giving priority to the engine battery:

The simplest one, which is used in by far the most vans, is the "long-cable method" :wink: : Simply because the split-charge relay is connected to the engine battery, not directly to the alternator, the way from alternator to leisure battery is considerably longer than from alternator to engine battery. Hence as long as the leisure battery draws from the alternator the voltage at the leisure battery will always be a bit lower than at the engine battery. This is a primitive but effective way of prioritizing the engine battery.

Some more clever split-charge units also cut off the leisure battery should the voltage from the alternator drop below a certain value. This should however not happen too often during normal engine operation, as long engine battery and alternator are in good condition. Maybe if the engine is in idle and many consumers from the vehicle side (headlights, fan, radio) are switched on.

A real prioritizing, including independent status monitoring of both batteries, requires a B2B charger and/or a special alternator regulator. I am not aware of any vans (at least not in the price range I consider as reasonable) that have such ex-factory.

Best Regards,
Gerhard


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