posted 05-21-2007 12:06 PM ET (US)        

Background information-
I’ve recently moved up to a 24v Minn kota and installed a 3-blank onboard charger. The 24 volt is 2 12v-batteries connected (+) to (-) with the trolling motor hooked to the respected vacant battery posts for the 24volt system.

The onboard charger is a minnkota 3-blank 15amp (5amp to each battery if three batteries were connected) mounted near the counsel. Cords that connect to the batteries are fused on the positive ends. These cords need to be extended to reach both the starting battery and the 12/24 volt near located in the back of the boat.

I’ve ran my wiring (insulated) and match the wire gauge as recommended from the battery posts to a terminal block and installed an additional 30amp fuse on the positives connectors. The terminal block is a 6-gang seachoice (http://www.seachoice.com/productdetail/ProdDetail.asp?pid=32482), identical to this but with 6 on each side instead of 4. I mounted the terminal block onto a wood block prior to mounting on the boat.

Connecting to the terminal block is where I need help and I've been able to find diagrams.

At the terminal block, I’ve hooked all the positives to one side and the negatives to the other side . I’ve labeled the batteries (1-starter, 2&3-trolling motor) along with the wires respectively. According to the Minnkota charger guide book, I don’t have to unhook the 24 volt system to charge.

Last night I started to hook up the batteries to the post and started with the 24volt connections, the first battery on the 24volt hooked up fine…but when I hooked up the second battery (-) neg. connector it caught on fire and toasted the wire for about 6 inches.

If anyone can offer up some assistance on getting this connected correctly, I would be greatly appreciated as I don’t want my boat to catch on fire.

I've also posted this on the main page in addtion to the small boat electrical, just incase someone may have some input from that area also.

posted 05-21-2007 01:26 PM ET (US)            

Dude, you created a dead short on each of the two batteries for your 24v trolling motor. Draw yourself a diagram on paper, and it is real obvious. You NEVER want to directly wire the positive and negative terminals of a battery together, which is exactly what I think you did.

Minnkota does indeed say that you can hook the batteries in a 24v series up to their chargers without breaking the 24v connection, but that is because the circuits are isolated inside the charger. By using a bus instead of a terminal block, you un-isolated them.

posted 05-21-2007 04:06 PM ET (US)            

Ok, so I need to get a different kind of Terminal block, like the one you've shown. Will do at lunch.

After it sparked and caught flame, I did disconnect everything. Prior to the spark I had the trolling motor wires connected but the trolling motor was not plugged in.

Could I have ruined anything like the charger? Or the trolling motor wires? Batteries? Is there anything I should look at because of the wiring [mistake]

And again Thank you, obviously my speciality is not electrical.

posted 05-22-2007 12:00 AM ET (US)            

If you did not connect the charger wiring to the buss bars, then the charger is probably OK.

The 24-volt battery consists of two 12-volt batteries connected in series. When you began to connect the batteries in parallel by connecting them to your bus bars, you directly shorted the plus and minus terminals of one of the batteries together. The short circuit current of the battery is very substantial. It immediately turned the connecting wiring into a very effective heating element and started melting the wire.

If that is all that happened then you just have melted some wiring and insulation, and probably put a healthy dent in the battery's charge. You can replace the wiring. The battery can be recharged. So far the damage is not too bad.

If you had the charger connected, there should be fuses in the charger leads. If there were excessive current, the fuses should have blown. It is typical on chargers which are intended to be used with 24-volt series-connected battery banks that BOTH leads have fuses. The fuses are there to protect against just this sort of mistake in wiring or other current short circuits. Check the fuses and replace any that are blow. Check the charger operation again, before re-wiring the system. See if it produces the proper voltage output from all three sets of outputs.

posted 05-30-2007 07:30 PM ET (US)            

You hit it on the money. The charger was connected on the short circut. I've retested it and it works fine. The one thing I will need to do is replace the wiring. It looks good after about a foot but I think I'll just replace it for good measure.

posted 05-30-2007 11:49 PM ET (US)            

Many people are complacent when working with low voltage circuits because they do feel there is much risk of electrocution from 12-volts of direct current. They are right about that, but, as this discussion has shown, the short circuit current can be very high in low voltage circuitry. The instantaneous heating effects from very high short circuit currents can be as dangerous as the electro-shock effects from higher voltage circuits.