Charging trailer batteries while towing

[thehun54]

Towing with a '03 K3500. I can't seem to find the number of Amps available from the truck to charge the trailer batteries while running. Looked in the fuse boxes with no luck. My 5er has a 30A fuse which keeps blowing (not supprising since the trailer has 4 deep cycle batteries). Entertaining 30A breaker in place of the fuse. Any ideas?

Thanks for any help

[GBurton]

Hi

If my memory serves me correctly there is a 40-amp fuse in the fuse box that is on the driver

[HowieE]

The amps avaliable is the capicity of your alternater limited by the regulator in the alternater. As the voltage feeding back to the regulator drops do to load on the system the alternater will ramp up the meet the demand.

If your trailer has been pluged in either at home or at a campground I would assume your trailer batteries are close to full when you hook up to tow. Under this condition there should be very little current flowing from thr truck to the trailer. I would check the convertor in the trailer and make sure it is working and that the trailer batteries are charged when you start out.

If you trailer batteries are fully charged at startup and still blowing fuses the current flow may in fact be from the trailer to the truck in which case I would look at the trucks batteries or alternater.

I would not install a circuit braker until you determine why you are blowing fuses. Under normal situations you should not be blowing fuses.

[letsgo]

1st are you blowing the 30Amp fuse under load (eg. using the inverter to operate a microwave?) or on the charging cycle only?

2nd if your blowing under load then calculate the loads wattage and divide by 12 for the amperage (eg. 1500watt microwave divided by 12volts == 125Amps @ 12Vdc) that is a lot of current Poof!!!!

3rd if your blowing 30Amp fuses when charging I would not be hooking this charging circuit up to my truck period.....until you know why.

4th what I have just stated are at the extream end of the rainbow, if you want to provide more info. I am sure your problem will disappear.

5th I definately would have at least 1 solar panel installed to keep the batteries topped up and it will also reduce sulfation and increase battery life.

good luck

[richp]

Here's another possible answer.

When I got my Jayco fiver, I was intermittently blowing the 30 amp inline fuse next to the battery. Upon close examination, there were two wires (the charger's input and battery's output to the 12 volt fuse panel) coming into the 30 amp fuse, and then one wire from the fuse to the battery.

Turns out that the charger Jayco had used in the unit (an IOTA) was capable of putting out 45 amps. Every time the charger sensed the batteries were at a very low level, it hit the line to the battery with 45 amps and the fuse popped. I re-wired the unit with a straight feed from the charger to the battery (which I could safely do because the charger has a breaker in it). The fuse now is only in the circuit from the battery back to the trailer's 12 volt circuits. I haven't had any trouble since.

For what it's worth.

Rich Philips

[letsgo]

This a personal experience;

I was wedged between a motor and bulkhead on a sail boat trouble shooting a starter motor inability to crank over. All of a sudden the plastic on a #10 wire stared to melt the copper wire began to glow red, the plastic started to burn, I was stuck, the fumes from the burning plastic were so toxic I couldn't breath, I finally got out off the boat after killing the power before the fumes killed me.

After that learning experience I fuse every thing, using the right size fuses plus fast blow and slow blow. the other point I'd like to make is that the instantanious current or maximum current flow from car batteries can exceed 2000Amps I repeat 2000Amps at which point the battery will probably explode from the boiling gasses expanding so fast, or the short circuit will cause a fire, hense the need for fuse protection.

Oh well enough for the day,

good luck.

[David Utz]

Even one battery, if it's very low, can draw more than 30 amps. The current will flow as fast as it can from the truck to the trailer until the two systems are equal. You need something to limit the current flow to allow the batteries to come up at a reasonable rate. Our electronics guy suggested putting a headlight into the circuit. a 55 watt lamp will only allow 4.5 amps to travel the circuit. (55 watt / 12 volts = 4.5833 amps) As the batteries charge up, the current draw will fall and the light will start to dim. The light becomes your current limiting fuse.