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Caravan battery charging from wheels

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Old Apr 23rd, 2018, 21:59   #11
SwissXC90
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Originally Posted by canis View Post
Haha! You're quite right, energy is not free. But the energy has to be paid for in fuel no matter how it gets there, and you'd be suprised how much drag an alternator working hard puts on an engine. I've no figures on the subject
Super easy to calculate.

14V x 160A = 2240 Watts or 2.24 kW

A Volvo 185hp D5 engine is 136kW

So the alternator running at full output is using 2.24/136 = 1.6% of the maximum engine power

But the engine is not at maximum power all the time, at idle it uses around 4kW to 8kW, so at just above idle the alternator is easily around 20% of the engine load.

Not insignficant at all

And remember the downside of charging a caravan using a trailer-wheel driver generator: the energy to pull the caravan comes from the vehicle engine.
You incurr losses through the vehicle transmission and drive system.
So charging the caravan directly from the car alternator is the most efficient as you don't have the drive train losses being added into the equation.

If the caravan battery is not charging to 100%, consider increasing the diameter of the charge wire coming from the trailer plug to the caravan battery.
The larger the wire, the less voltage drop and thus more charge voltage available.
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Old Apr 24th, 2018, 11:14   #12
canis
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Thanks, some really informed replies there.
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Old Apr 25th, 2018, 14:19   #13
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Charging a 12 v flooded cell battery to 100% of it's capacity takes a long time. From 50% capacity to 80% might take several hours. To get it to 100% might well take a further 6 or more hours. As someone said earlier volt drop in the cable from alternator to battery will have an impact but even with no drop it's still a lengthy process.
If anyone really wants to get their head around the issue can I suggest they look on a site such as www.canalworld.net you can go on as a guest. Use the search facility and you will find enough information to keep you reading until doomsday. Like most forums you will find a range of opinions but also many absolute facts

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Old Jun 29th, 2018, 23:09   #14
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Start by saying I'm not a caravaner (so shoot me if you want I just browse here occasionally to broaden my mind), however I do drive an articulated truck with a big trailer.
Trucks do use a 24v system so dragging up elementary electrical formulae from my school days, twice the voltage means half the current which would be 1/4 of the power lost due to resistance, but with a 40ft long trailer we still get lots of power to the rear lights, I'd suspect that losses due to length of wire is minimal unless the builders have really cheaped out and used very thin wires. What I find is more often a problem with an artic is the quality of the connection of the plug/socket on the front of the trailer, often one can observe that with the taillights and fog lights on adding the hazard flashers will cause the other lights to pulsate due to the earth return not being able to carry all that current, usually on the truck that is down to damage and wear in the plug/socket, on a caravan I would also consider the possibility of corrosion in the plug/socket reducing the efficiency of the connection.

Batteries on truck trailers are not so common but with more and more electical gizmos on the trailer they're not so rare either. The charging methods are perhaps a little behind caravans given that it's not so established. Early trailer batteries were often only charged when the side lights were turned on, in a crude sense it ensured the truck was up and running before putting extra load on the electrical systems but it did lead to one company I worked for having to make a ruling that sidelights were to be kept on at all times as over the summer the batteries for the security systems would go flat leaving the trailer 'insecure'. My present job involves some double decker trailers with a moving deck which is done by an electrical hydraulic system, these are generally powered from mains electric at the hub but use their onboard batteries at the outbase depots, usually there's no problem but if we need to we can take power directly from the tractor unit but that uses what we call an Anderson Lead which has wires like jumper cables and a chunky plug with large electrical contacts.
As others have suggested the 80% charge figure may be more related to the way a battery charges combined with the level of sophistication of the systems in the car and caravan to manage when the battery is actually being charged. Bear in mind that on a car we don't tend to do a deep discharge of the battery very often, usually just enough to start the car, whereas with a caravan one would be discharging the battery all evening to have light, watch telly etc and then need to put back all that charge while driving.
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Last edited by DaveNP; Jun 29th, 2018 at 23:15.
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Old Jul 7th, 2018, 08:39   #15
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I simplify matters by booking electric hook up on the pitch.
Van comes home for washing/ loading before a trip so gets connected to fully charge battery before trip, electric hook up means battery full at end of stay, wash unload before return to storage means battery full when it goes in and I fortunately have facility to charge in storage occasionally.

Landrover doesn't have S plug and no idea if volvo 13 pin has split charge facility as never tried to charge battery on the run.

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Old Aug 15th, 2018, 14:02   #16
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Morning Canis, ref.charging caravan batteries,does any body use Solar panels? also any boat/barge owners 'on board'? what are the wind driven charging units all about?? could they be utilised for van use?

Sorry,more questions than answers, regards,Keith.
I have a 100 watt solar panel on my caravan roof that keeps my battery charged up all year round, When on sites and using my van we only use site electric, the battery is used for the motor mover for putting it in and out of storage or on my drive to pack things up and to postion on site.
While in storage the solar panel maintains the leisure battery charge, even through winter, and ensures it is charged for next time I need to hitch up with motor mover, the van is too big and heavy to pull by hand and not enough space to get car to the front to hitch up, and the leisure battery keeps the alarm/tracker battery topped up. Many new caravans now come with solar panel charging as standard.
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Old Aug 15th, 2018, 15:14   #17
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It's a solution looking for a problem. My leisure battery holds a charge all winter and will still drive a motor-mover no problem. The only charging it gets is when it's hooked up to my car, or via electric hookup, or occasionally from a solar panel when there is no hookup. It simply doesn't need to be charged via the caravan itself. If you have a decent leisure battery charging from the van itself simply isn't required in my experience.
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Old Aug 15th, 2018, 18:08   #18
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It's a solution looking for a problem. My leisure battery holds a charge all winter and will still drive a motor-mover no problem. The only charging it gets is when it's hooked up to my car, or via electric hookup, or occasionally from a solar panel when there is no hookup. It simply doesn't need to be charged via the caravan itself. If you have a decent leisure battery charging from the van itself simply isn't required in my experience.
While I agree with most of what you say, last winter in the very cold weather my caravan battery was far less efficient and the load of the movers was evidently making it struggle.
I like to move the van during storage to help prevent pitting of the wheel bearings, just half a revolution makes a difference. Without a reffresher charge my van battery would not of lasted the winter. I have no solar panel and it's a case of self discharge over time, cold weather inefficiency combining to result in a van that will not move on the movers at the end of the winter.

Paul.
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Old Aug 15th, 2018, 18:35   #19
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While I agree with most of what you say, last winter in the very cold weather my caravan battery was far less efficient and the load of the movers was evidently making it struggle.
I like to move the van during storage to help prevent pitting of the wheel bearings, just half a revolution makes a difference. Without a reffresher charge my van battery would not of lasted the winter. I have no solar panel and it's a case of self discharge over time, cold weather inefficiency combining to result in a van that will not move on the movers at the end of the winter.

Paul.
Sure, your battery may be less than it was, but charging from the caravan wheels won't change that. I'm fortunate, we now have power points in the storage yard so if I really needed to I could charge from them, though I haven't had to yet.
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Old Feb 17th, 2019, 11:56   #20
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Originally Posted by green van man View Post

Landrover doesn't have S plug and no idea if volvo 13 pin has split charge facility as never tried to charge battery on the run.

Paul.
When daughter acquired her XC70 she had tow hitch and electrics fitted by an independant specialist. Van has twin plugs but much to my annoyance he fitted 13 pin electrics to the car. Discovered this too late and daughter wasn’t of a mind to change things. Later found that there is no charge to the van battery as there is no connection via the 13 pin socket as the wiring simply isn’t there. Another thread somewhere suggests that this is now standard practice and 13 pin does not support charging the van battery. Info. I’ve found seems to show that only pin 10 is switched 12 volt and can be used for fridge or battery Is this correct? Looking at the gauge of the wiring to the socket it doesn’t look heavy enough for either and definitely not to have both by creating an internal connection somewhere in the 13 pin to twin 7 pin adapter, which I had thought of doing.
I fitted the hitch to my 940 myself with twin 7pin plug electrics and there is charge to the van battery.

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