Advice on battery charging

[lorrieandjas]

Hi Guys,

OK - I am confused. There seems to be two schools of thought on batteries and charging options. Bit of background - have a 2012 GU Patrol with stock battery. Have a camper-trailer with 2x75Ah AGM batteries in it. Have an Anderson plug on the trailer. In the past I have always just run an Anderson from the alternator via a relay (solenoid) to charge the rear batteries. I know several people with this kind of setup.

Now - in comes DC-DC chargers, battery management systems, etc. The question I have is this really needed? Basically the issues I see - under-charging - ie the alternator not putting out enough charge to charge the house batteries. The other issue is potentially over-charging/over-heating. The third issue (potentially) is not getting the house batteries to full charge?

I've been doing a little bit of looking into all this and the way I am thinking is to run an Anderson on the back of the Patrol with a bi-directional Voltage Sensing Relay inline and fuse. Then on the camper another fuse near the house batteries. I'll use 6 B&S (13.5sq.mm) cabling. I'll also use the portable solar panels (with regulator) when camping.

Thoughts?

[megatexture]

If you put a ctek 250s dual on the trailer or in place of the relay it will boost the amps from the alternator and can double as a solar regulator and will monitor both inputs at the same time.
I couldn't tell you if there will be a loss in performance by mounting the unit to the camper but it would be ideal as they have a temp monitor so it won't cook the batteries.

You can't rely on the alternator to fully charge agm batteries it won't happen.

I've done the voltage sensitive relay before and won't go back as that method was not maintaining my batteries properly redarc make a similar product also that might be worth looking at also but if you consider ctek then you won't get cheaper then on eBay

Also having a multistage charger will maintain the batteries when not in use at home.

[the evil twin]

This subject could easily run to a 100 pages alone but in as short a version as possible...

Alternators are "dumb" chargers IE they just sit there happily spinning away and produce a regulated voltage at up to their max current at whatever RPM they are spinning at and after that the voltage falls away.
Therefore an Alternator source relys totally on the battery/ies charge acceptance rate/s on how much charge goes back in over how much time. The higher the charge in a battery the lower the charge acceptance rate.

That is no biggee on an SLI battery (cranker) as all they do is a momentary large draw on start then sit there happily sucking up whatever small amount they need...
but...
can be a major issue on House batteries esp if there is a longer cable run and therefore voltage drop to the house battery such as in a camper.

I use dual sensing VSR's in my setup (two of them, one in the vehicle and one in the camper) and I have no issues whatsover BUT all four batteries are of roughly equal capacity and same technology. I can plug in any charging source (solar, smart charger, alternator) at any point and it will charge any battery that is "low". The way my useage pattern works out the lowest battery out of my four is usually the vehicle Aux

IMHO the bottom line is this...
If your useage is such that your house batteries consistently need to be charged from the vehicle OR you wish to use differing technolgy esp Calcium, Calcium hybrid OR you only want to run lighter gauge cable to the Caravan/Camper then you should opt for a DC/DC solution.
You can then get away with some voltage drop and also tailor the charge voltage to suit the application
otherwise...
If your house batteries are traditional lead acids and usually well charged from Solar/Mains or whatever then VSR's are absolutely OK IF the cable run is sufficient gauge.

In my case my camper batteries are always either;
on Solar so only needs it's morning top up for a couple of hours after overnight drain (approx 12 AH)
on Mains IE CTEK battery charger
or under tow so charging from the Alt

[lorrieandjas]

Thanks guys - now I am looking at the Redarc BCDC1240 DC-DC chargers but have been told because I have two AGMs hooked up in parallel in the camper I need two of them? Does this sound right to you guys??

Jas

[lorrieandjas]

Actually - disregard that - just called Redarc who confirmed in parallel you only need one! Bloody distributors don't know what they're talking about!

Jas

[the evil twin]

Thanks guys - now I am looking at the Redarc BCDC1240 DC-DC chargers but have been told because I have two AGMs hooked up in parallel in the camper I need two of them? Does this sound right to you guys??

Jas

If they are hard wired in parallel then No, you only need one as they appear as one battery to the device
If they can be selected one or the other then No you only need one just put it upstream of the selector switch
If they can be used independantly then, technically, yes you could use two

EDIT... DOH.... you beat me by one second ROFL

[the evil twin]

... I should add that I use a Cole Hersey switch in my rig and put it to both when towing but only normally run on one battery at Camp so there is one "on line" and the other is fully charged and off line.

[megatexture]

Mine is doing 3 batteries aux under the bonnet and two on the camper I have only ever had one issue and that was that the charger wouldn't charge due to the temps under the bonnet as it was 46 deg in the shade and flipping hot under the hood out at longreach.I disconnected the battery and just charged it via solar when we parked. If a ctek can do my 3 putting out 20amp I'm sure the redarc will cope with 2 Agm batts putting out 40amp

[threedogs]

There is a real danger of batteries exploded with high under bonnet temps,
My AUX is Trojan wet cell 105 AH with water kit.
they would not sell me a sealed one. well they would but would not install it
Worth thinking about, Evil Twin or Yendor may know more on this.

[lorrieandjas]

OK - so the setup I'm thinking now is the 40A DC-DC Redarc - the only thing I don't like about the Redarc is she isn't bi-directional - so the cranker technically can't be topped up if I throw a cell on the house batts - but not a huge issue - can always just connect the panels to the cranker if I need it.....

Now - in terms of fuses - 100A fuse near the cranker and near the house batteries?

Jas