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  1. #1
    Join Date
    Apr 2008
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    NSW
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    537

    Default Need advice on 12 volt dual / dual battery charging .

    I have wired up a dual battery to run a small portable fridge on a 150 amp (125 amp cont.) isolator it's running good but I also have an extra battery bank to run a winch from some old agm batteries that I have had for some years for camping . My problem is how do I get charge current across to my extra winch batteries without draining down my main battery and possibly my fridge battery once they are connected if they are in a discharged state ? I don't want to overload my alternator charging everything at once or connect the two agm batteries in parallel with the fridge battery as that might overload the isolator also. This is what I have now . Any advice would be appreciated . I don't mind a cheap solution where I have to monitor the batteries and flip a switch or two . Rub out parts of the image and put in you advice then repost the image .
    dual battery setup.jpg
    The volume of a pizza of thickness 'a' and radius 'z' is given by pi z z a.

  2. #2
    Join Date
    May 2011
    Location
    Murray Bridge S Aust.
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    71
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    5,942

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    The way that I read this, is that you want to run 4 batteries, your main battery, a fridge battery and 2 winch batteries, (we'll call these 3 the auxiliary batteries),
    is this correct?
    Your system shouldn't be overloaded unless the 3 auxiliary batteries are dead flat. If you were wanting to run the winch, you should have the engine running, to be able to keep those batteries charged any way. If you plan on being base camped for a week or two at a time, I'd look at getting a solar panel to help keep things topped up, unless you're prepared to have the vehicle running for a couple of hours per day to top up the battery. I'd also fit a battery indicator to them, just to keep an eye on the charge/discharge rate.
    I've installed quite a few dual battery setups, and the most was 3 batteries all up, and there weren't any problems.
    To grow old is mandatory, growing up is optional.

  3. #3
    Join Date
    Apr 2008
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    NSW
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    537

    Default

    Quote Originally Posted by KBs PensNmore View Post
    The way that I read this, is that you want to run 4 batteries, your main battery, a fridge battery and 2 winch batteries, (we'll call these 3 the auxiliary batteries),
    is this correct?
    Your system shouldn't be overloaded unless the 3 auxiliary batteries are dead flat. If you were wanting to run the winch, you should have the engine running, to be able to keep those batteries charged any way. If you plan on being base camped for a week or two at a time, I'd look at getting a solar panel to help keep things topped up, unless you're prepared to have the vehicle running for a couple of hours per day to top up the battery. I'd also fit a battery indicator to them, just to keep an eye on the charge/discharge rate.
    I've installed quite a few dual battery setups, and the most was 3 batteries all up, and there weren't any problems.
    Thanks for the reply . The two winch batteries are in parallel so it is one battery really . I was unsure of the best way to charge the winch battery without over loading anything . I do intend to fit battery monitors to all three batteries when I get the money . I was thinking solar trickle charger for when the vehicle is sitting about in the daytime but not sure it's good value for money . The two AGM batteries are very different to the calcium fridge battery so I am not sure it's a good idea to just parallel them . Their could be a situation where the two AGM winch batteries are discharged maybe even to 50 % so I am worried that just paralleling them could burn out the present isolator or over tax the alternator . I am after some kind of switched connection between the two circuits that I can bring in after a few hours of driving and I see that the main and fridge battery are fully charged .
    I just don't know how to wire that part , use another isolator , large relay or what ? I am not sure two isolators sensing the same main battery would work ? Solar is an option to take any load of the other system but then it takes up too much space on the roof rack . I would ask an auto electrician but the ones near me are very unhelpful so I avoid using them at all because they always want to install something that costs $500 or more plus their labour .
    The volume of a pizza of thickness 'a' and radius 'z' is given by pi z z a.

  4. #4
    Join Date
    May 2011
    Location
    Murray Bridge S Aust.
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    71
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    You could use a marine switch similar to this, in between your fridge and winch batteries. Just switch it on as required, simple and cheap.
    Heavier ones are also available.

    200A 12V 24V DISCONNECT BATTERY ISOLATOR KILL SWITCH KEY CAR MARINE BOAT CARAVAN AU $18.99 Free postage
    isoswitch.jpg

    Kryn
    To grow old is mandatory, growing up is optional.

  5. #5
    Join Date
    Apr 2008
    Location
    NSW
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    537

    Default

    Quote Originally Posted by KBs PensNmore View Post
    You could use a marine switch similar to this, in between your fridge and winch batteries. Just switch it on as required, simple and cheap.
    Heavier ones are also available.

    200A 12V 24V DISCONNECT BATTERY ISOLATOR KILL SWITCH KEY CAR MARINE BOAT CARAVAN AU $18.99 Free postage
    isoswitch.jpg

    Kryn
    I am trying to avoid drawing the charge current through the present isolator which would happen if I did that and also if the winch batteries were discharged to say 50% then they would suck all the power out of the fridge battery which could damage it . If I am going to use a switch then it has to be at the front end direct from the alternator with a blocking diode in the line . I already have a switch like that at the front end to isolate the positive terminal I connect the winch cable to , I could use that with a blocking diode . That way the alternator voltage is also in the circuit during winching .
    That gives me another idea . I could use a heavy duty relay and blocking diode and put a switch on the dash to operate it. That way I can switch it on and off as I view the battery monitors that would be far more convenient than stopping and popping the hood which I could forget more easily .
    If I can find a switch with a flashing LED in it would be good and hard to forget . I think that could work for better control of how much the alternator works . I could stop now and then and put my hand on the alternator to get an idea of how hot it normal runs . Once everything is charged it's not a big deal it's just that 310 AH of AGM battery can suck a lot of power if they are flat . What do you think ?
    The volume of a pizza of thickness 'a' and radius 'z' is given by pi z z a.

  6. #6
    Join Date
    Sep 2012
    Location
    York, North Yorkshire UK
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    6,439

    Default

    Hi,
    My two pennyworth...
    I have an arrangement with three wet lead acid batteries, one of which is the vehicle battery, 76 amp hour and two 110 amp hour leisure batteries, all in parallel . I do have a 25 amp isolator switch between the leisure and vehicle batteries which is only opened when the vehicle is serviced. A 300 watt solar panel into a charge regulator set for 14 volts is used to charge all three batteries. This system feeds all the services, fridge, TV, heating, lights etc, 24/7. Even on wet dull days, I have yet to see the battery voltages fall below 13 volts, and that is with a full load, when it has not been fit to go out of the vehicle and the heating is on. The solar panel and charge regulator can put 16 amps out if needed, although the panel can supply more than that, the charge regulator can't. It is supposed to be able to output 20 amp @ 12 volts. Since your winch is only a temporary load, I don't think that you need to worry about it too much. It's possible your fridge battery could be obsoleted without any loss.
    Best Regards:
    Baron J.

  7. #7
    Join Date
    Apr 2008
    Location
    NSW
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    Default

    Quote Originally Posted by BaronJ View Post
    Hi,
    My two pennyworth...
    I have an arrangement with three wet lead acid batteries, one of which is the vehicle battery, 76 amp hour and two 110 amp hour leisure batteries, all in parallel . I do have a 25 amp isolator switch between the leisure and vehicle batteries which is only opened when the vehicle is serviced. A 300 watt solar panel into a charge regulator set for 14 volts is used to charge all three batteries. This system feeds all the services, fridge, TV, heating, lights etc, 24/7. Even on wet dull days, I have yet to see the battery voltages fall below 13 volts, and that is with a full load, when it has not been fit to go out of the vehicle and the heating is on. The solar panel and charge regulator can put 16 amps out if needed, although the panel can supply more than that, the charge regulator can't. It is supposed to be able to output 20 amp @ 12 volts. Since your winch is only a temporary load, I don't think that you need to worry about it too much. It's possible your fridge battery could be obsoleted without any loss.
    That is not a bad idea to just dump the fridge battery and connect the two AGM's in it's place . I am sure the alternator could cope and the isolator also with normal charging . However what worries me is if I run the winch it can draw from 200 to 400 amps ! 400 amp being a very heavy load and my vehicle is not that heavy anyway so typical would be 200 amp . I am not sure what the isolator would do when it sensed a sudden 200 amp discharge on the auxiliary battery . It should isolate but how quick I does I don't know . If it's slow to isolate it may suffer excessive charging current draw .
    A 300 watt solar panel on the two AGM's would fix the problem but it's too expensive and too large . 150 watt is about as large and expensive as I can go . Does your solar charge controller block reverse current at night time ?
    The volume of a pizza of thickness 'a' and radius 'z' is given by pi z z a.

  8. #8
    Join Date
    Aug 2008
    Location
    near Rockhampton
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    6,216

    Default

    Sometimes the easiest solution is another alternator installed on the vehicle. This used to be easy in the vehicles made before power steering and air conditioning. Modern cars with so little spare room, might be next to impossible.
    Gold, the colour of choice for the discerning person.

  9. #9
    Join Date
    Jan 2011
    Location
    Far West Wimmera
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    63
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    Default

    I know next to nothing about solar, but I am keen to learn. I was interested about reverse current at night so I did a quick search. The one site I read said that reverse current protection should be built into the solar panel. They said to ask if a solar panel has “Reverse flow protected circuitry”. I have a 60w panel that I bought to keep a battery charged on an electric fence energiser. I really should do something with it.

    Dean

  10. #10
    Join Date
    Apr 2008
    Location
    NSW
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    Default

    Right I have not even looked into solar at the moment other than a few prices . I bet the ones I can afford don't have it built in but I will keep that in mind Dean . I did ask my local auto electrician about an extra alternator and it is possible on the x-trail but over a grand well the exact words were at least a grand . I can see that I would take quite a bit of time to do it . I don't want to do anything to this vehicle I can't remove easily and install on another vehicle . I could just keep the batteries fully charged as I have in the past and just take them away like that . Even after a month the AGM's would still have 90% capacity give or take age . Plenty of amp hour to get me out of trouble and it's very unlikely that I would be away more than a few days at a time as my current health at the moment is not up to long trips anyway . I just want to be able to extract us from a bog or winch off an impassible road due to rain onto the side vegetation . With road trains the way they are now getting stuck in the middle of a muddy dirt road is highly dangerous nothing stops them they just keep driving rain hail or snow and at high speeds . I once saw a bogged vehicle get slammed by a cattle truck because it was so covered in mud from the passing trucks he could not see it well . I always avoid dirt roads in rain but you can get caught sometimes . The longer your vehicle stays in the middle of the track the more dangerous it becomes and if you stay in your vehicle which you may have to due to rain it's even worse . You can put out all the triangles you like they rarely see them and just drive over them . Even a good strainer post as long as Dean never put it in would get my light vehicle off the road in an emergency .
    The volume of a pizza of thickness 'a' and radius 'z' is given by pi z z a.

  11. #11
    Join Date
    Sep 2012
    Location
    York, North Yorkshire UK
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    6,439

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    Hi Guys,

    I'll try and cover the various points made.

    Solar Panels: Since the solar cell is functionally a diode, I think that having a separate diode for reverse protection would only be needed if the back fed voltage was much higher than the panel could provide, i.e. Grid tie systems. My solar panel is a standard domestic rooftop one. It is rated at a nominal 300 watts and provides about 55 - 56 volts output. The charge controller prevents any voltage/current feed back into the panel anyway. Even on a dull wet day the panel still provides around 35 volts at several amps.

    Here in the UK these panels are available for less than £100. Mine cost me £98.00 inc VAT. I had to collect mine because they wouldn't ship less than a case of ten panels. I also bought a pair of connectors so that the panel could be disconnected and removed if required.

    Isolator Switch: Having one to separate the vehicle and domestic systems is a wise precaution for all sorts of reasons. As I mentioned, in my case it is normally only used when the vehicle is serviced. A safety issue ! A heavy duty alternator is a simple swap on mine but fitting a second one is not possible, and with the solar panel not needed. However when I was having vehicle battery problems I did isolate the two systems and when the vehicle battery was discharged enough to not be able to start the engine the 25 amp switch happily allowed the leisure batteries to charge the vehicle battery.

    I appreciate that the conditions under which you operate your RV and those that I encounter are quite different, but I hope that my experiences help you.

    I will try and get some pictures later and post them here.
    Best Regards:
    Baron J.

  12. #12
    Join Date
    Apr 2008
    Location
    NSW
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    537

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    2 x 150 watt panels would cost about $600 au 370 pounds and I would have to also buy a controller and fitting gear it would cost close to 670 pounds .
    We do live in one of the safest places in the World but we pay through the neck for the privilege . I do appreciate your input and you are obviously more experienced than me in this area . I just have all kinds of limits , space limits , money limits . Most of the stuff I am using came off another older vehicle I sold some years back and a few vehicles before that it's a kinda recycling effort . I did have to buy some stuff , cable conduit was not used much back then so I had to buy rolls of that . If I put a big solar panel on my roof it will leave no room on the roof rack for other stuff , every move I make is compromised by something . The basic dual battery system went in easy because I had that before , it's these winch batteries that have me stumped .
    The volume of a pizza of thickness 'a' and radius 'z' is given by pi z z a.

  13. #13
    Join Date
    Jan 2011
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    Far West Wimmera
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    Even a good strainer post as long as Dean never put it in would get my light vehicle off the road in an emergency .
    What are you trying to say? I resemble that remark.

    You can do it with a couple of star droppers if you know how. I got bogged with a Falcon wagon and trailer and used the mast from the jack (remember those old Ford jacks?) and I think a star dropper I found nearby to set up a winch point. I had a cable come along to winch with. I was getting firewood so I had the splitter to drive the bits in the ground.

    Dean

  14. #14
    Join Date
    Sep 2012
    Location
    York, North Yorkshire UK
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    Hi Guys,

    I'm back with a few pictures of my vehicle. Whilst I have it in mind, a power winch is very convenient, a "Trifor" manual cable puller could be used in a pinch, slow I would agree, I've seen a 38 tonner pulled back upright with one ! A single bloke yanking on the lever, mind you, me and two others were stood watching,

    20-08-2017-002.jpg 20-08-2017-003.jpg

    This is my solar panel mounted on the vehicle roof, it is a nine by six cell 300 Watt one. You can better see the connection box in the second picture. Looking down the sides there are two alloy clamps on each side that are bolted into expanding nuts. The whole of the roof rack is made from 50 X 12 x 4 mm aluminium channel. All eight mounting posts were made, six to fit the mounting points on the vehicle and two rubber mounts, designed to support the front edge of the panel. There is a wind deflector to go on as well, but I haven’t gotten around to finishing it off. The edges of the panel are black anodised, but I covered all the edges with with white PVC tape to help it blend in somewhat.

    20-08-2017-006.jpg 20-08-2017-007.jpg 20-08-2017-008.jpg

    This is the battery storage compartment with the fuse box, main terminal box and solar panel controller unit. That is in the small plastic box below the fuse box. You can see the 4mm wire connections going in on the left hand side.
    That junction box holding the main terminals is a 100 amp domestic one and was picked up as surplus from a local electrical dealer. That third picture shows the lift off lid closing off the compartment.

    20-08-2017-004.JPG 20-08-2017-005.JPG

    These last two pictures are of the control panel, housing the water gauge, LPG gas gauge, step control switch and the 25 amp isolator switch. It is shown here in the off position. Again the isolator came from a local electrical dealer.

    This is very much a work in progress, I have a lot to do to get to a finished state. However it is a very usable RV as it stands.
    Best Regards:
    Baron J.

  15. #15
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    Apr 2008
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    NSW
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    Quote Originally Posted by Oldneweng View Post
    What are you trying to say? I resemble that remark.

    You can do it with a couple of star droppers if you know how. I got bogged with a Falcon wagon and trailer and used the mast from the jack (remember those old Ford jacks?) and I think a star dropper I found nearby to set up a winch point. I had a cable come along to winch with. I was getting firewood so I had the splitter to drive the bits in the ground.

    Dean
    Just joking mate , I have built a custom stake recovery point , it's a long flat plate with holes in it at an angle and you drive bars down into it .
    I have used it once to get someone else out of trouble but never me yet. It was going quite rusty in the shed and annoying me so 2 years back I ground it all down and painted it and my sand anchor . I have seen other people use three star pickets driven in and tied together to winch out . Works ok in solid ground . I think I remember those big Ford jacks they were long like a high lift jack . Think I had one in a Falcon I owned way back .
    The volume of a pizza of thickness 'a' and radius 'z' is given by pi z z a.

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