Charging batteries while driving?

[R_Lefebvre]

The problem here is that it will not lower the amps. It will only lower the volts and the difference is simply made into heat. This is a wast of power. Amps is a mater of how much the devise pulls. You need the volts to charge the bat. If you try to charge a bat at to low a voltage it is hard on it. Aside from cost and with the proper fuse/breaker, bigger wire is always better.

That said there can be a problem charging a bat too fast. If it gets too hot it can be damaged. I wonder if there is a heat sensing charging regulator on the market. I know the later XJs (and other new cars) have a temp sensor under the bat for this reason.

Yes, it does lower the amps. V=IR. A long run of 10g is reasonably high resistance, so it lowers the amps in the circuit. As the battery comes up to full charge, the amps drop, and the voltage drop across the wire decreases as well. When the trailer battery is fully charged, the current goes to zero, as does the voltage drop.

 

[dawsonc61]

I've got "tired head" now.

 

[Mashurst]

I guess the question that needs an answer is how many amps are we trying to move?
I got off my lazy butt and did some calcs and it looks like 10g is really fine. I used a run of 16 ft, so that is from the alternator to the bat in the trailer.
@2amps voltage drop is .03v
@5amps voltage drop is .08v
@15amps voltage drop is .24v
So I don't think you are going to have any problem with 10 gage. If your bat is pulling 15 amps you have got real problems to worry about.
...on the other hand 8g would be better.
Fit were me I would run a buss to the back with 4g or bigger and go from there.

 

[robert j. yates]

How many amps can you run through your 7 pin connector...I would say 20 max unless you have made some upgrade to it.

If you don't plan on having to jump start your vehicle from the batteries in the trailer than that would work fine.

I have as I mentioned, a dual battery kit underhood along with dual batteries in my trailer so I already have a backup for vehicle starting. I don't ever intend to jumpstart my vehicle through the 7 pin and frankly until this discussion, that had not even occured to me. My solution would definately not support vehicle jump starting.

I had 2 reasons for wanting dual batteries in the trailer...first so I had enough power for the fridge/freezer and secondly so that I had access to batteries outside of the Jeep in case I needed to rig up my Ready Welder for a repair. The dual kit in the TJ is kind of a PITA in order to remove them and rig up the welder. Having a dual set up in the trailer nosebox makes them much easier to get at.

 

[joedude]

Hey guys,
I'm a total NOOB on here too (in Fact is my first post on this forum! :wings.

Here's what I was thinking.
Couldn't you just hard wire a trickle charger under the hood. Complete with a plug that leads to the trailer and perhaps a relay to isolate the whole system from the vehicle battery when its not in use? I figure that using a trickle charger may not completely top up a low battery on a short charge, but in the longer hauls wouldn't you get a better charge and perhaps extend battery life?


I came accross this great forum by doing a Google search for something else for my Hilux and it turns out I'll be tackeling this perticular topic in the near future so I'm getting two birds with one stone! :victory:

 

[Mashurst]

Couldn't you just hard wire a trickle charger under the hood.

Don't trickle chargers run on wall/shore power?

 

[dawsonc61]

Don't trickle chargers run on wall/shore power?

If they make a DC trickle charger I haven't seen it.

 

[joedude]

If they make a DC trickle charger I haven't seen it.

Some have prices listed. So not too bad. And they seem pretty straight forward to install.

http://www.dyersonline.com/Products/Tekonsha-DC-DC-Trickle-Charger__18216.aspx

http://www.shoprvparts.com/product.do?no=13496F

http://www.redarc.com.au/dc_battery_chargers_BCDC1206.htm

 

[joedude]

Don't trickle chargers run on wall/shore power?

I suppose you could use an AC power inverter and then plug that to a common wall plug AC to DC battery charger. You would loose some efficiency in the transfer from DC to AC and then back to DC. But it would a pretty easy and simple setup.