DC to DC Battery Chargers
Submitted: Sunday, Mar 13, 2011 at 13:35
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Member - Kevin S (QLD)
In searching for 12 volt information I came upon member
John and Val's blog of a couple of years ago on Electricity for Camping. The detail, together with the discussion at the end, makes for a very interesting read.
The material on DC to DC battery charging caught my attention as I have realised that the only reason that my caravan batteries are near to fully charged at the end of a day's towing is that they have been on 240V charge the night before and I have used nothing out of them during the day because the three way fridge has its own system through an Anderson Plug and motion switch.
Material about the Redarc BCDC 1206 and Ctek D205S on the 'net suggest that they are mainly designed for the charging of caravan and trailer batteries.
So I have a question. Is the type of electrical wiring installed by car dealers to a 7 pin plug and by caravan manufacturers from the plug to the van likely to be sufficiently robust to allow a DC to DC charger to recharge two 70 AH batteries after a road side over night stop?
I am trying to see weather the cost passes the "caravan park"
test. That is, how many nights out of a caravan park would it take to pay for the cost of installing a DC to DC charger. Obviously any rewiring of tug or van will raise the bar.
I would appreciate comments.
Kevin
Reply By: oldtrack123 - Sunday, Mar 13, 2011 at 14:58
Sunday, Mar 13, 2011 at 14:58
Hi Kevin
RE:'So I have a question. Is the type of electrical wiring installed by car dealers to a 7 pin plug and by caravan manufacturers from the plug to the van likely to be sufficiently robust to allow a DC to DC charger to recharge two 70 AH batteries after a road side over night stop?"
The best way to
check the whole system IS,after the van battery has had some heavy use & Before starting the car [in the morning after o/n ]:-
[a]With no load on the van battery
check it's voltage @ IT's terminals
[b] connect voltmeter direct to car battery , start engine & run@fast idle for say 5mins
[c]Read voltage then immediately read van battery voltage as before.
If the differance is more than about 0.25v max the wiring is inadequate.
[e]If there is any other 12v items which may run, turn them on & repeat tests [c]
again if differance between van bat & car bat exceeds 0.25volts the system should be checked for undersized cables, poor connections etc
Peter
AnswerID:
448087
Reply By: Mike DiD - Sunday, Mar 13, 2011 at 18:02
Sunday, Mar 13, 2011 at 18:02
The type of electrical wiring installed by car dealers to a 7 pin plug and by caravan manufacturers from the plug to the van is suited for running the lights on the rear end - and only just !
AnswerID:
448102
Reply By: Dennis Ellery - Sunday, Mar 13, 2011 at 18:10
Sunday, Mar 13, 2011 at 18:10
Standard vehicle wiring is not likely to be sufficient but that depends on the size of the charger.
I have a 20amp DC to DC battery charger supplying a 100ah deep cycle in the caravan.
When the deep cycle battery is low the charger draws about 30 amps and charges at full load of 20 amp.
I use a 9mm pair but probably could get away with a 6mm pair, but if you drop too much voltage on the input line, the charger becomes less efficient of course.
AnswerID:
448106
Reply By: Ray - Monday, Mar 14, 2011 at 12:26
Monday, Mar 14, 2011 at 12:26
I would forget the 12v to 12v charger and install heavy cable. I have used 4asg cable via a 175 amp Anderson plug. Fused at both ends and a relay, ignition connected, close to the primary battery in the car. There is nothing to go wrong except possibly the relay. Forget all those fancy relays and 12 to 12 transformers and you can't go wrong.
AnswerID:
448171
Reply By: Member - Kevin S (QLD) - Tuesday, Mar 15, 2011 at 15:07
Tuesday, Mar 15, 2011 at 15:07
Thanks to those who have posted comments. Quite a variety of suggestions for me to sift through.
Kevin
AnswerID:
448323
Follow Up By: Dennis Ellery - Tuesday, Mar 15, 2011 at 23:11
Tuesday, Mar 15, 2011 at 23:11
It’s good to see an acknowledgement of appreciation for those who responded to your post.
Thanks for the effort, its a pity more didn't do it.
FollowupID:
720682
Reply By: Nomadic Navara - Tuesday, Mar 15, 2011 at 23:50
Tuesday, Mar 15, 2011 at 23:50
Kevin
As you are a Queenslander you probably have the 7 pin flat socket on your tug. The current rating of these is only about 5 - 7 A. If you have the large round 7 pin set-up then it will be good for 30 - 35 A.
If you attempt to run your 3 way fridge through the small pins you will burn it the pins out if the fridge wiring is heavy enough to supply sufficient current to the fridge. Same will happen if you have heavy enough cable to run your intended battery booster.
If you have other trailers that plug into your trailer socket then fit a 12 pin socket to the tug and a 12 pin lug to the van. The 5 extra pins will carry 30 A. The 7 pin trailer plugs will mate with the 7 small connectors in your 12 pin socket on the tug.
This will be OK for a booster with up to a 25 A output. If you purchase a larger one then you will need to go the Anderson plug way.
AnswerID:
448385
Follow Up By: Member - Kevin S (QLD) - Thursday, Mar 17, 2011 at 20:45
Thursday, Mar 17, 2011 at 20:45
Thanks Nomadic Navara. The fridge is not the issue. It is on a separate circuit through an Anderson plug with a motion switch and works really
well. The issue is how much power is getting to the battery when the van is under tow. The responses, including yours, will help me to sort it out I am sure.
Kevin
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Reply By: Member - John and Val - Friday, Mar 18, 2011 at 08:48
Friday, Mar 18, 2011 at 08:48
Hi Kevin,
Glad you find the blog useful. It's had so many extra bits tacked on over time that it's really in need of a comprehensive re-write, but that will have to wait.......
As others have said, the standard wiring and connectors in your vehicle really aren't up to the job, especially if you fit a decent dc-dc charger. (The charger increases the charging voltage so that the battery receives extra current. To generate that extra voltage the charger itself draws current adding to what's flowing in the supply wires. Losses are proportional to current so it's a losing battle unless you have heavy cables to minimise losses.) I'd run a pair of 6mm or bigger wires from engine bay to van with an anderson plug for coupling tug to van. Why a pair? You need heavy cable for both the positive and the negative sides. I in fact use 2 sets, one to run the 3 way fridge when the alternator is running, the other for battery charging. You may find that simply installing heavy cable will be adequate for your needs, but for a really good job I'd suggest heavy cable plus a dc-dc charger.
HTH
John | J and V
"Not everything that can be counted counts, and not everything that counts can be counted."
- Albert Einstein
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Follow Up By: Member - Kevin S (QLD) - Saturday, Mar 19, 2011 at 15:00
Saturday, Mar 19, 2011 at 15:00
Thanks
John. More good advice. I think I will start with heavier cables and see how that works. If not enough charge then add a DC charger. My 3 way fridge already is on a separate circuit through an Anderson plug and there is already some charging occurring to the battery.
A question if I may? If I don't fit a DC to DC charger in the van and I use a 120 watt solar panel to extend stationery periods do I need anything between the regulator on the panels and my 2x70AH batteries?
Thanks,
Kevin
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Follow Up By: Member - John and Val - Saturday, Mar 19, 2011 at 16:48
Saturday, Mar 19, 2011 at 16:48
Hi Kevin,
I think you are going the right way - put in some heavy cable and if that doesn't quite do what you want, add a dc-dc charger.
re solar connections - having the solar regulator on the panels is not ideal as the regulator can't then compensate for losses in the cable leading to the battery. Better to have the solar regulator close to the battery if that's possible, especially if it's an MPPT type of controller.
Depending on your usage patterns and how often you want to visit caravan parks, an option might be to increase your solar capacity and forgo the dc-dc charger. Another option if you do go up the dc-dc charger path would be to use a CTEK DC250S Dual charger, which incorporates both a 20A multistage DC>DC charger and an MPPT solar controller. With one of these, you could bypass the present solar regulator and have a really nice system. This path would cost several hundred dollars, and more if you added more solar capacity. This stuff is a quick way of spending money!
The straight answer to your question is that you do not need anything between the solar regulator and the batteries apart from a good sized cable, and of course an inline fuse close to the batteries.
Cheers
John | J and V
"Not everything that can be counted counts, and not everything that counts can be counted."
- Albert Einstein
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Follow Up By: Member - Kevin S (QLD) - Saturday, Mar 19, 2011 at 16:57
Saturday, Mar 19, 2011 at 16:57
John,
You are not wrong about spending money. I visited a nation wide battery franchise to ask questions and they had me up to $1,500 in no time at all. That's a lot of nights in a caravan park.
We mostly stay in caravan parks but want the flexibility to do a few nights in national parks at times. There is a dream spot in
Cape Le Grand NP near
Esperance that I just can't wait to spend a few nights at.
Tanks for your response. Very helpful.
Kevin
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Reply By: Member - Kevin S (QLD) - Saturday, Apr 02, 2011 at 16:11
Saturday, Apr 02, 2011 at 16:11
Having considered the
feedback from
forum members and done some other research, I have decided to put a 120W solar panel on top of the van with a regulator in the boot of the van. The challenge here is that the van is a pop top so methods of bringing the wires to the regulator are not all that obvious.
I think I can take the wire to the back of the van and bring it down the sleeve that carries the wiring for the lights and then take it to the wires under the van and follow them into the boot and back out again to the batteries on the A frame.
If anyone else has met this challenge and found a different method, I would love to hear about it. My main concern about following the existing ceiling wiring is that it is a fairly long run and even with large wires I could still get a voltage drop.
Kevin
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