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Charging Battery


Len

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Electrics do cause me some confusion but on a recent trip I had to make a lot of use of the movers to negotiate to my car. The end result was that by battery charge dropped to a reading of 10. 8v. We then did a five hour journey with the fridge powered on 12v. At the end of the journey I noticed no increase in the battery charge.

Everything charged up fine when on EHU.

I have read somewhere that the charge from the car is only a "trickle" charge and wonder if I was expecting too much.

Would be glad of your thoughts.

 

Len

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Test the feed from the car by connecting the 12s and meter check the battery posts with the engine on a fast tickover.

 

You should get 14volts approx. No increase in volts means you may have blown a fuse in the 12s feed from car.

 

The engine revs make a split charge relay operate and the car supplies the caravan instead of the car battery.

 

The supply comes from the alternator.

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I have read somewhere that the charge from the car is only a "trickle" charge and wonder if I was expecting too much.

 

Len

 

Far from it. In most cases its the highest level of charge your battery will get.

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The feed to the caravan battery is entirely separate from the feed to the fridge when connected to the car via the 12S socket. In addition the former is always live but the feed to the fridge is only live when the engine is running. Each feed should also be protected by its own fuse. The fridge 12V is not run at all from the caravan electrics so would not discharge the battery.

 

Both of these feeds come directly from the car battery so as Alan says can be the higest rate of charge as the car will in most cases be at a higher voltage than the PSU on EHU.

 

A simple test tool is a small 12v bulb with two leads. If wired correctly in the 12 s socket one pin should be live with the engine off and two should be live with the engine running although the extra one may need the engine a little above idle to make it come live.

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Agree with above. A car alternator will charge the battery in your caravan fully after a fairly short journey and keep it topped up. The relay to your fridge should ensure fridge is only taking power when the engine is running at faster than tick over to ensure your batterys are not flattened by the fridge, which with no charge going to battery would not take long!

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Hello Len,

 

Whilst I entirely agree with the advice given by those above, even if you do have a healthy voltage present on pin-7 (battery charging circuit) of the 12S socket when the car alternator is charging, this unfortunately does not mean that the battery will be receiving a healthy charging current. The reason for this is that a test meter or a small bulb will only take a tiny fraction of the current (amps) that a discharged battery would require to re-charge it relatively quickly. It all depends upon the size of the cables that run from the car battery to the split charge relay and 12S socket at the rear of the car, as an insufficiently sized cable will cause a considerable voltage drop to occur over its length when a higher current is taken or required by the caravan battery.

 

Do check (or get an auto electrician to check for you) that the cables are at least 2. 5mm2, as this could be the cause of your problem.

 

Regards,

David

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Electrics do cause me some confusion but on a recent trip I had to make a lot of use of the movers to negotiate to my car. The end result was that by battery charge dropped to a reading of 10. 8v. We then did a five hour journey with the fridge powered on 12v. At the end of the journey I noticed no increase in the battery charge.

Everything charged up fine when on EHU.

I have read somewhere that the charge from the car is only a "trickle" charge and wonder if I was expecting too much.

Would be glad of your thoughts.

 

Len

It would be beneficial to check the system through from car to van battery.

Measure voltage across van battery

Plug van into car.

Measure voltage across van battery.

Start car engine

Measure voltage across van battery

If voltage does not increase then try increasing the revs of the car engine as you measure the van voltage.

The van voltage should have increased as the car starts to charge the van battery.

 

It may also depend on what type of van you have, my Lunar has a PDU (power distribution unit) and Lunar do say that this only allows the battery to trickle charge when on the road. So if the van battery was low then it may not fully charge it up but only hold it where it is.

It becomes fully charged when on ehu and even then the charging voltage is limited by the PDU, I presume to aviod damage to electronic components.

Brian

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