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Quote: Originally posted by shocker on 29/6/2010

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so what is my split charge battery feed to the caravan actually doing?I have an alternator triggered 40a relay with heavy gauge wiring running to the battery charging pin of my 12S socket.

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It is charging your caravan battery but, I repeat, NOT at tickover speed, only when the engine is revving.

An alternator actually has to work quite hard to put power into a battery and there are many electronic firms around these days producing very specialised relays for multi-battery charging but these can cost a few hundred pounds each.

The alternator on your car is not meant to charge any more than the car's battery so asking it to charge two batteries plus run the 12v side of a fridge is pushing it.

If I was able to fully recharge my caravan battery by connecting it to the car and leaving the car on tickover speed for half an hour, as suggested in an earlier letter, I would be in heaven.
On the downside, a lot of electronic engineers would be out of a job.

I am, at the moment, trying to rig a system whereby I can charge a second battery in the boot of the car when I am not towing. I know that even on a full day out I will not be able to fully charge this battery but hopefully I can get enough of a charge into it to negate what I do use from the caravan battery each evening.

I have heard of others using heavy duty cable to a spare battery in the vehicle boot but if that battery needs heavy duty cable, why does the caravan battery not need equally heavy cable?

Afterall, the cable that charges the caravan battery is the same gauge as all the other wires in the 7-core cable.

If, when you say heavy duty cable, you mean a wire like the one that supplies your starter motor, that's not necessary at all.  What you do need is a wire that will take up to about 30 amps from the alternator.

Wiring on modern cars seems to be getting thinner all the time, and I would certainly be happier with something a bit thicker, especially as the cable run is from the front of the car right to the back.

No doubt someone will be along shortly with the exact cable specification.  Best answer is to get the proper spec and buy a length of wire for the purpose.  If in doubt, the thicker the better, but it doesn't need to be starter cable.

Jim

From Rune Caster;- Lobey, you can run a wire off this relay, from the redundant van battery charging terminal to a charging point in your boot.

Yes, I was thinking of doing this.

Then I would run a +pos to pin 2 (spare) and a -neg to pin 5 (spare) in the 12S socket from the Boot Battery. This would couple with a another 12s plug that was only wired to these two pins. I would then use this cable to transfer power from the car boot battery directly to whatever unit I required it to power in the caravan.

By necessity, this would be a long lead as it would have to run from wherever the car was parked to the van.

I have used this set up before when I had a TT although in that set up the car battery itself was used.

I find it rather sad that the cost of the electronics that are required to get maximum power out of vehicle batteries is far greater than the price of a generator, yet the advantages of using the silent battery far outweighs the noise and polution caused by these gastly machines on an otherwise tranquill campsite.

If it was the other way around, we would all be on 12v and generators would only be found where they were originally designed to be, on a building site.

Hi Rune Caster, I live on the banks of the Clyde Estuary and so I am surrounded by Boat Builders, Marinas and Yacht Anchorages. Many of the yachts use wind turbines to keep their batteries topped up and out on a yacht, the wind turbine is ideal.

However, in a caravan situation they are not ideal. Firstly they are noisey. They whine or buzz and they also vibrate. So if you were using one near a caravan, it would need to be mounted on its own pole and that pole guyed in such a way that it did not touch any part of the van.

A solar panel during the day and a wind turbine at night sounds like the perfect set up but in practise, I am afraid that it is not.

Like I have said elswhere, hopefully in the next 20 years or so, Fuel Cells will become affordable to all and batteries, generators, solar panels and wind turbines will be consigned to the history books for ever.

Quote: Originally posted by Rune Caster on 01/7/2010

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erm... weren't the first generators used in the traveling fairs? - Wonder if I'd be more popular on a camp site with a traction engine ticking away supplying me with electricity?

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you may laugh, but I do have a friend who does just that, OK its mainly at steam rallies etc, its a small stationary steam engine, an alternator (or is it dynmo, cant remember right now) running from it, re-charges his bateries during the day, then in the eve powers TV etc, and suprisingly quiet, just a gentle phut-phut

hmm, wonder how well a parrafin steam genny would go down??