# Electrical concern:

Discussion in 'Boat Modification Journal' started by kat in the hat, Feb 2, 2008.

1. ### kat in the hatNew Member

Messages:
4,875
State:
Missouri
I was curious as to whether, or not, the length of battery leads causes any problems. I think I was reading an artical about installing a battery charger in a boat, and it mentioned not to use leads longer than what was provided. I am unclear if this pertains to the leads from the charger to the batteries, or from the motor to the charger. Does it change the impedence, or get hot, or something that I need to know about? Would like to place batteries in the bow if at all possible. Is the biggest concearn that the charger is nearest to the batteries? The instructions may explain this, but I don't have the charger yet, and wanna continue on with planning aspects until then.

2. ### Mark JNew Member

Messages:
9,407
State:
Four Oaks, NC
DC ampacity and length of run is much different then AC.
Recently we've had some threads with people talking about moving their battery to the front of the boat.
Thats no problem with the right battery but if its a cranking battery you are looking at going to a larger cable. That type cable is expensive. Its more or less a welding cable.
Your typical amerage needed from battery to engine is 50 amps.
Looking at this 12v table http://www.backwoodssolar.com/reference/wire_size.htm

You'll see a #6 gauge wire at 50 amps is good for 13 feet. From 13 feet to 22 feet requires a #4. From 22 feet to 36 feet a #2.

This is why they say leave the cable length alone. adding 2 feet may throw you into another wire size.
If it was AC wiring in a boat, you could add 100 feet and you would be OK.

I've mentioned on here before about those electric boat winches to run a properly sized conductor all the way from the truck battery to the winch or either mount a battery to the trailer at the winch because of how critical DC wire sizing is.
To answer your question, yes, if improperly sized the insulation will melt and potentially start a fire. Dont rely on a fuse to stop it. It may blow beyond the critical phase.

Do yourself a favor in this rebuild, Install a 2 bank battery switch. A turn of the switch will kill all power to the boat or you can turn on each battery independently. 30 bucks.

3. ### BKS72New Member

Messages:
3,361
State:
East of KC
If you want to put your starting batteries in the front of your boat you'll need to go with heavier leads from the batteries to the starter. You're pulling a lot of amps starting turning the starter, and the longer the run, the more resistance, so more heat. Also, (and this isn't a major concern) as voltage drops, current increases, so if you run the battery down and keep cranking, amps (and heat) go up. Coupled with a longer run already causing more heat, you need more cable to handle the add'l current/heat load.

I've never used an on-board charger, but it sounds like it's in series with your motor leads. In that case, if you're putting your starting batteries up front and running your starting current from the batteries through the charger leads to your starter there could be an issue with the internal components of the charger handling the heavier loads. If you can swap out the stock cables on the charger for heavier cables, thereby keeping the heat and resistance loads the same, you should have no issues.

If you need some heavier cable, shoot me a PM, I have a hundred feet or so of 1/0 welding lead in the garage. We could come to some sort of arrangement on cold beverages and fishing stories traded for enough lead to get you going if you need it. :wink:

That's my \$.02 from experience with electric forklifts and other assorted electrical stuff, but I'm sure someone with more detailed knowledge of onboard chargers, etc, will provide us both with more insight! Good Luck~

Mark got here before I got this posted, but after reading his response I feel better about mine :smile2: This last line is an edit after reading Mark's post.....

Branden

4. ### kat in the hatNew Member

Messages:
4,875
State:
Missouri
Thank y'all very much for the info. I kinda figured that there was an issue with it. There will be a battery switch, and Branded, thanx for the offer on the cable. I'll let ya know what we decide.:cool2:

5. ### DANZIGNew Member

Messages:
6,672
State:
West Virginia