backup battery connection

Aurelia · Posted: Mon Nov 23, 2009 12:26 am Post subject: backup battery connection

I am carrying an extra 55ah battery for a trolling motor on my dinghy. If I was to have trouble with the main boat batteries, and wanted to put the spare into the main system to boost voltage, how would it be best to temporarily connect it? I know in a car, you can plug portable power into the cigarette lighter socket and jump start the car. Could you do something similar on a CD25? I am guessing it would be smarter to simply jump with cables to one of the other batteries on board and get an engine started. I am interested in having whatever connection materials I need on board to do this so I am open to suggestions.

Greg

Sea Wolf · Posted: Mon Nov 23, 2009 1:50 am Post subject:

Greg-

The battery cables are your best bet.

The ~100-150 amps or so required to start the outboard shouldn't be run through the small diameter wires that connect your cigarette lighter/accessory outlet to the battery. They are probably only sized for 20 amps or so, and would be woefully overloaded with 100 amps or more if your battery were well discharged.

Also, there's probably a fuse in that circuit that would blow if you tried it. What is more, it's a long way back to the motor, and the small diameter wire would put up a lot of resistance going that distance. Better to use the jumper cables right at the battery next to the motor!

Another alternative for some is an emergency starter battery pack that can be used expressly for that purpose. I keep one under the helm floorboard that's plugged into the shore power circuit, so that it gets charged every time we plug in ashore or use the generator.

For another alternative, Thataway Bob keeps a small lawn tractor battery aboard with some jumper cables, which is probably similar to what you have.

Cheers!

Joe. Teeth

Doryman · Posted: Mon Nov 23, 2009 6:33 am Post subject:

Those emergency starter battery packs are not powerful enough to jump-start a 150. Been there, done that. They might be strong enough to slowly charge up the boat starting battery enough to start but it would take quite a while -- I did not find out. I am going to make up a set of jumper cables that will reach from my house battery (separate circuit) to the starting batteries.

Warren

BrentB · Posted: Mon Nov 23, 2009 12:39 pm Post subject:

Anyone use a low battery alarm and LED light like the ones used in smoke alarms?

thataway · Posted: Mon Nov 23, 2009 9:34 pm Post subject:

There are both low voltage alarms and low voltage disconnects.

Warren, you should be able to connect the house and engine start batteries, through the switchs on the boat.

I do carry a short set of cables to go from the lawn tractor/pwc battery (which will start a 150 hp), but only once. I have been able to start a 150 with a jumper pack--so it depends on the specific jumper pack. Some are more powerful than others.