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 Post subject: Charging caravan battery
PostPosted: Sat Oct 14, 2017 12:05 pm 
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I have tried relays and split chargers over the years and the only way I got them to work was with second battery in the car not caravan and taking three phase from the alternator. Since then things have moved on, with cars which switch off the alternator when accelerating for example.

So today it would seem DC/DC inverters are the answer, Ring do one at £200 with 30 amp output which is likely bigger than required, and Sterling do a range but designed for boats with a price tag to match. It also leaves the question where should it be mounted, in car or caravan, in caravan it monitors the battery voltage better less volt drop between inverter and battery, in the car less likely it will cut out because of supply volt drop.

However caravan already has a good battery charger, from 230 volt mains supply, so is a DC/DC inverter best option? Or would it be better to use a 12 volt to 230 volt inverter in the car and take the power to caravan as 230 volt AC reducing cable sizes and volt drop problems. It would need some method to switch the inverter on/off in car and some connector that can handle 230 volt between caravan and car, they cost around £50 per 500W so that should power a charger up to around 30A. I would think any less than 10A charge not worth doing, consider a 2 hour time between camp sites that's only 20 Ah with no losses, and over 30A need to question if car can supply that much, however there is one big question.

If such a good idea why is it not already done? Or is it?


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PostPosted: Sat Oct 14, 2017 12:57 pm 
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I don't recognise a problem.

If your caravan is at home you charge the battery via an extension.
If your caravan is at a park you're on a hook up and charging the battery anyway.
If you're on the move, why would you want to charge the battery?

Inverter? What for? Most stuff in a caravan can be 12V (LED lighting, TV, Sat receiver etc) and cooking/heating is gas.

I think you're over thinking this matter.

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PostPosted: Sat Oct 14, 2017 4:02 pm 
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well its a leisure battery designed for deep cycle, long and slow charge cycle it doesn't need a high current

modern cars usually have a can bus black box when setup for towing, so variable charge rates arnt a issue

As K_E says your trying to solve a problem that doesn't really exist, a bit like a banana slicer when you have a knife, but the slicer takes twice as long to clean, it doesn't save you any time cutting a banana


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PostPosted: Sat Oct 14, 2017 5:50 pm 
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What about this
https://www.practicalcaravan.com/review ... ry-charger


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PostPosted: Sat Oct 14, 2017 7:50 pm 
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boxedin wrote:

It does seem CTek range is the battery chargers that others seem to want to emulate. And as said 7 amp is ample to maintain a battery in fact even 3.8 amp is likely good enough. However although using a battery for just the essentials one light, the water pump, and ignition plus fans for heating it will likely last a week, at the end it is unlikely to have enough to work the motor mover to get it back up the drive, and this is the major problem.

Before having a motor mover we had a smaller caravan which I could with help from wife telling me if I was going to hit anything reverse into the drive. However with the longer caravan it really does need the motor mover to get into the drive, and until in the drive no way to put on charge without removing the battery.

So as it stands we are limited to using sites with hook up which in the main is OK, I like having induction hob etc in the caravan. But height of summer finding sites with hook up is not always easy, so having the option is nice.


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PostPosted: Sun Oct 15, 2017 7:01 pm 
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ericmark wrote:
at the end it is unlikely to have enough to work the motor mover to get it back up the drive, and this is the major problem.



Would a Starter Pack have sufficient 'grunt' to work the motor mover?

http://www.toolstop.co.uk/index.php?opt ... gIzUvD_BwE

Keep the Starter Pack at home and then have some sort of changeover switch to the supply side of the motor mover.


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PostPosted: Sun Oct 15, 2017 8:00 pm 
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If you're on a hook up right until you leave and drive home how can there not be enough charge in the battery to move the caravan?

Surely this is all down to 'planning' and nothing to do with execution?

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PostPosted: Mon Oct 16, 2017 12:26 am 
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kellys_eye wrote:
If you're on a hook up right until you leave and drive home how can there not be enough charge in the battery to move the caravan?

Surely this is all down to 'planning' and nothing to do with execution?

80% of the time we have a hook up, but in the summer months we have found when we get to a site there are non available, up to now if the battery did go flat no worries we could charge it when we got home, but now with larger caravan I would have a hard job reversing it into the drive, so need the motor mover when we get home.

For me reasonably easy, keep a spare battery in garage and just swap batteries, however my wife can't lift the batteries and whole idea of motor mover is she can now get caravan in and out on her own. As it was she would have to watch me reverse it around a corner into the drive, the angle between car and caravan means I could not see where it was going and needed her to ensure no one went behind it while reversing.

I have been directed to this DC to DC inverter this is a far better price, seems a worth while project to use these to charge battery. What I really need to do is measure how much power needs putting back in the battery after the caravan is parked, not a clue if I need 5 Ah or 55 Ah of power left in the battery.


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PostPosted: Mon Oct 16, 2017 9:45 am 
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I don't know about modern cars with multiplex wiring, but in days gone past we had a few options, bearing in mind hook ups were a novelty, put another battery in the caravan wired to the existing one, you will double your Amp/H, put one in the boot/back of the car, charge by relay or the cigarette lighter, install a solar panel on the roof of the van, or do as I did and buy a small leisure generator, In my days I had a "Yamaha 1000 EF", one of the club members had a small "Honda" it was rated at 250Wt it was light enough to be picked up by his wife, it was very quiet and economical, and on long rallies kept his batteries fully charged. Nos



For this message the author Nos has received gratitude : ericmark
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PostPosted: Tue Oct 17, 2017 7:47 am 
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Nos wrote:
I don't know about modern cars with multiplex wiring, but in days gone past we had a few options, bearing in mind hook ups were a novelty, put another battery in the caravan wired to the existing one, you will double your Amp/H, put one in the boot/back of the car, charge by relay or the cigarette lighter, install a solar panel on the roof of the van, or do as I did and buy a small leisure generator, In my days I had a "Yamaha 1000 EF", one of the club members had a small "Honda" it was rated at 250Wt it was light enough to be picked up by his wife, it was very quiet and economical, and on long rallies kept his batteries fully charged. Nos

This is the major consideration, generators have come down in price, size, weight, and noise. So if split charging is going to cost more than a generator then hardly worth it.


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PostPosted: Tue Oct 17, 2017 12:43 pm 
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This may be oversimplifying things, or the weight may be an objection, but why not carry a separate battery solely for the motor mover?
Charge it up separately each time after use. Don't use it for anything else. If the motor mover has to be connected to the "normal" caravan wiring then either a plug and socket or changeover switch arrangement of some sort.


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PostPosted: Wed Oct 18, 2017 8:41 am 
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If I was with caravan every time easy option is spare battery at where we store it. However an 88 Ah battery is heavy and my wife would not be able to get it into battery box, she may be able to lift and carry although that would be hard, but would not get it into box.

Some of the modern inverter generators are small and that may be the way to go, not measured battery charger yet but would be unlikely over 750W so next job is to actually use energy meter on caravan. Also need to see how much fridge uses as advantage with generator it could also power fridge.


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PostPosted: Wed Oct 18, 2017 11:09 am 
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ericmark wrote:
If I was with caravan every time easy option is spare battery at where we store it. However an 88 Ah battery is heavy and my wife would not be able to get it into battery box, she may be able to lift and carry although that would be hard, but would not get it into box.

So why not, as I suggested but perhaps didn't make quite clear, actually carry the extra battery onboard the caravan?


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PostPosted: Thu Oct 19, 2017 7:41 am 
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If you want you can run the fridge off the genny, just plug it in as normal through your "Blue" socket, the only problem is that, and again talking in the past, is that the onboard distribution system will only trickle charge the battery, if you use the gennys 12vlt output direct to a battery it will get more Amps ie faster charge. One last point buy a proper named genny, not a diy store model, it will cost more, but could be a lot cheaper in the long run, caravan electrics are getting more and more complicated, a cheap genny could and possibly will end up frying them. Many years ago it happened to me, I needed a new TV new DVD player and a new distribution system, not cheap ::b ::b Nos


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PostPosted: Thu Oct 19, 2017 9:43 am 
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My wife claims generators are anti-social so it seems that idea is shelved, she says no one on holiday wants the hear a generator, OK Wispergen does not make much noise, however the price and size kind of rules them out.

So it seems she has spoken so things will stay as they are, she says if there is no hook up then it's no holiday I'm not roughing it so we simply will not use that site. She even got electric hook up last time we used a tent.

So new battery in caravan and I also have one out of old caravan which has been on charge for a week now and charger has still not dropped into final stage. Not sure on caravans built in charger, when they first started to be put in caravans they were normally around 8A however the modern ones can have up to and including 35A stage chargers, not sure about the whole idea of a stage charger with a caravan?

We would likely discharge the battery on leaving home and arriving on camp site using motor mover, although most camp sites are large enough to reverse caravan into place with the car. However this will mean on connecting to mains supply the voltage will likely rise to 14.8 volt, using caravan G5.3 MR16 lamps LED these are rated at 10 - 30 volt DC so not a problem, but cheaper lamps would not like this voltage. It is hoped before lights are used the charger has dropped into float mode and battery is around 13.4 volt.

Yes BS7671:2008 would not allow the use of stage chargers A721.55.4.1 give us a range 11 - 14 volt so since stage chargers exceed this they should not be used, however they are used.

The old caravan had the charger built into the consumer unit, which also had all the blade fuses for 12 volt as well as MCB's and RCD for 230 volt, not found the charger yet in the new caravan, there is a relay box which has clearly had a problem at some time and in line fuse holders and fuses by-pass some of the relays. This needs sorting and is on my to do list.

Reading BS7671:2008 it would seem to comply with A721.55.5 you need relays, both fridge and battery charging should only work with ignition switch on in tow vehicle and they should not be on the same supply so on 7 pin S socket pins 9 and 13 are continuous power supply and 10 and 11 power supply controlled by ignition switch, so a relay needs to use the supply from 9 and 13 to either charge or run fridge, Pin 12 is used to tell car trailer is OK this has been a problem even with the single 7 pin plug.

For trailers with air or vacuum brakes there has always been a need to have a warning light in the tow vehicle, this was pin 2 on old single 7 pin plug, however people wanted a battery light in caravan so they also used this pin for power, needed a fuse just in case a trailer was ever fitted with vacuum brakes as it would be direct short with no vacuum. Latter the pin was used for rear guard fog lamps, which were in early days illegal, now it's other way around, you must have them.

The S 7pin socket came around to give more connections as caravans were getting electric reversing hitches so reversing light, vacuum warning, ignition supply, and continuous supply all moved to new plug, but still it was not enough people wanted a second ignition supply so tried stealing the coding for coupled trailer pin 2 which does not exist on the 13 pin sockets.

I was tempted to use that pin 2 for a second ignition feed, saves using relays, but if we don't want to use fridge when travelling and don't want reversing camera on caravan and other such odd things then the S plug is not needed and neither are most of the relays. So first step was to find out what was needed then decide what to do about the extra fuses and faulty relay box. If I have to build one then want it to include all I need.

Years ago we towed a caravan to south of France and then with those distance suppose we did need fridge to be powered, but today 100 miles would seem to be tops, so if cold when we leave and plugged in when we arrive no real need to give it a supply when towing.


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