Thread: Charging an aux battery in a trailer?

yep, 50a anderson and 16mm cable, look at traxide website for elec diagrams.
david.
rumour has it they will have kits out shortly with cable, plugs and heatshrink for a kit to suit camper traillers.

Originally Posted by modman

yep, 50a anderson and 16mm cable, look at traxide website for elec diagrams.
david.
rumour has it they will have kits out shortly with cable, plugs and heatshrink for a kit to suit camper traillers.

Thanks. Luckily, this isn't on my car...I just wanted to check, as looking at a towing plug, I didn't think they looked all that substantial if you wanted decent current flow for charging....

Originally Posted by jik22

If you had a 2nd or 3rd battery in a trailer, is there a proper connector for charging it from the vehicle (Or a pin on the towing socket?), or should I just run nice thick cable from the battery controller to an Anderson somewhere near the tow hitch, and the same from the battery box in the trailer?

The easiest solution is to use Pin 7 on a standard trailer socket as a charge output - assuming you have the common type round 7 pin type socket (or use a an unused pin in the flat type socket). When wiring up the back of pin 7 on the socket use the thickest cable you can lay your hands on (ditto to the trailer battery) and wire the other end to the start battery. This way the trailer battery will get a charge when you drive. It would be prudent to add a switch in the cable as a simple isolator to prevent current backflow when you turn the engine off or otherwise if you are handy with tools, use a relay for automatic switching via the ignition.

Any other way (i.e. using electronic isolators) will cost a lot more and despite the manufacturer's claims, suffer from an insertion voltage drop (0.5-1.0V) which when added to the voltage drop of the cable (>0.5V) will more than likely prevent the trailer battery from getting a full charge.
Total voltage drop between charge source and load using electronic isolators (alternator-battery) could well be around 1.0-1.5V which when deducted from the maximum charge voltage of say 14.6 leaves you with 13.1-13.6V. The battery will need at least 13.8V to charge but upwards of 14.5-14.65V would be better. If you or any reader of this post discovers a voltage of less than 13.8V at the trailer battery, all is not lost as this can be overcome by use of “black box” electronics in the form of a DC-DC Boost converter.

If you need more info, PM me.

Originally Posted by Teks

Total voltage drop between charge source and load using electronic isolators (alternator-battery) could well be around 1.0-1.5V which when deducted from the maximum charge voltage of say 14.6 leaves you with 13.1-13.6V. The battery will need at least 13.8V to charge but upwards of 14.5-14.65V would be better.

It was the thickness of cable I'd be able to stuff into the trailer socket that had me worrying enough about voltage drop to post the question in the first place. Had a quick look tonight, and it didn't look as though I'd even be able to use 10mm let alone something of really decent thickness for a long run at potentially quite high load.

I think if you are serious about doing any mods along these lines ,,, you should try and get in touch with a Derek from ABR, over on the ExplorerOz forum.

I think Drivesafe can vouch for him








sorry I couldnt resist

Originally Posted by Teks

The easiest solution is to use Pin 7 on a standard trailer socket as a charge output - assuming you have the common type round 7 pin type socket (or use a an unused pin in the flat type socket). When wiring up the back of pin 7 on the socket use the thickest cable you can lay your hands on (ditto to the trailer battery) and wire the other end to the start battery. This way the trailer battery will get a charge when you drive. It would be prudent to add a switch in the cable as a simple isolator to prevent current backflow when you turn the engine off or otherwise if you are handy with tools, use a relay for automatic switching via the ignition.

Any other way (i.e. using electronic isolators) will cost a lot more and despite the manufacturer's claims, suffer from an insertion voltage drop (0.5-1.0V) which when added to the voltage drop of the cable (>0.5V) will more than likely prevent the trailer battery from getting a full charge.
Total voltage drop between charge source and load using electronic isolators (alternator-battery) could well be around 1.0-1.5V which when deducted from the maximum charge voltage of say 14.6 leaves you with 13.1-13.6V. The battery will need at least 13.8V to charge but upwards of 14.5-14.65V would be better. If you or any reader of this post discovers a voltage of less than 13.8V at the trailer battery, all is not lost as this can be overcome by use of “black box” electronics in the form of a DC-DC Boost converter.

If you need more info, PM me.

Don't know about this^^^

hmmm whats a trailer plug rated at, 10amps ?

i'll stick to my 50amp anderson plugs and 13sq mm cable thanks

i have less than .1volts drop at my trailer using traxide gear so i dont know where you are pulling your figures from.

but i may well be misunderstanding what you are saying...

Hi jik22, besides the fact, as Inc has pointed out, that trailer contact terminals have a continuos current rate of just 10 amps there is also another very important characteristic that everybody misses.

VERY FEW connectors are rated at a make and break current.

I use automotive type 8mm spade terminals on my gear. In a twin pin plug and socket, they are rated at 60 amps continuos current per pin and in a single pin plug and socket, they are rated at 80 amps but they are designed to be plugged together and LEFT THAT WAY.

Trailer plugs are deigned to be connected and disconnected many, many times but with NO LOAD.

Now to Anderson plugs, these are rated at 50 amps continuos current and can tolerate make and break operations under load of at least 250 times and 10,000 no load make and break operations.

Now consider the amount of times you are likely to back up to your caravan or camper trailer and couple up the battery cables while the motor is running and you have a battery that is in need of a charge. Using trailer connectors means you are going to destroy contact pins quick smart.

So best to use the correct device for the job at hand.

Cheers