permanently installed jumper cables - gauge size?

[KRS62]

Hello all. Even though I now religiously use an on-board charger and haven't had a dead main battery in years, I would like to install permanent "jumper cables" from the trolling motor battery to the main battery. If the main battery ever dies, I would like to flip a switch to have the TM battery help out the main just enough to get the motor started. (If I get a dead battery now, I move TM battery to the back and it's a pain to get out and move!)

My charger is up front as well, and I currently charge the main battery through a cigarette lighter, so I will incorporate hard wiring this as well. So I bought a 3 way battery switch that would control flow back to main battery. (Off, Charge or Jump.)

So my question is about minimum wire gauge. I know that "the bigger the better" is the case here, but the wire port that I plan to use has limited space. Originally I bought 10ga, but I am beginning to question if I should go bigger. (I don't think I could get bigger than 8ga to fit in the port.) So the smaller the gauge, the longer I will have to wait for the main battery to charge. (I don't need an instant start like you get with true jumper cable gauge wire.) I am fine sitting there for a few minutes while the TM battery charges charges the main.

So am I on track here? 10ga okay for this purpose? 8ga?

thanks!

KRS

 

[Frogman Ladue]

If your running any kind of distance with the "jumpers" I'd say at least 6 ga.

 

[KRS62]

If your running any kind of distance with the "jumpers" I'd say at least 6 ga.

I'd say it would be about a 10-11ft run

 

[Jonboat Jerry]

Here is a link to a 12V automotive chart which should answer that.
6ga would work.
https://www.offroaders.com/tech/12-volt-wire-gauge-amps.htm

 

[Frogman Ladue]

...what he said.

 

[KRS62]

Well, my latest thought is to run another PVC pipe just under the gunwale (topside, as I don't any other place below deck) and run proper gauge cables from the TM battery to the back. I can also run the charger wire back to the main through there as well. I can also get a 2 battery switch, such that I can use either battery or both to start. I will get into it this weekend and see what will work best. Thank you for the responses.

KRS

 

[Bob Landry]

For a tin boat, I would keep it as simple as possible. I would run a 6ga wire between the two battery pos posts with a simple off/on switch located in an inconpicuous place. If you ever need to start off the trolling battery(unlikely), the switch will combine both batterys when needed.

 

[PSG-1]

What would work really well would be to have a female TM plug wired to the battery, then make up an adapter with a male plug. But I think TM plugs are AWG 8, that's a little small for jumping....you really need AWG 6. But if you could rig up some type of plug like this, it would work great, and keep the live terminals covered when not in use.

 

[KRS62]

I picked up some 6ga today (black and red) and also a Battery 1/Battery 2/off/both battery switch. I will post some pics later.

KRS

 

[Bob Landry]

I'm not understanding the need for the 1-2-Both switch. With it installed, you are going to be tempted to connect the batteries together to run the TM longer and that's something you don't want to do. The start battery should be dedicated to nothing but starting the motor. You cn always limp home without lights and a stereo, but you want to be able to start the motor.

 

[Hanr3]

When you connect the TM to the starting battery you should start the motor right away. Don't wait for the starting battery to drain teh TM battery. With both batteries connected they will equalize power. It would be better to use the TM to start the motor and skip the starting battery all together. You hook your truck battery to teh other vehicles battery because there is no port on the alternator to connect the jumper cables too.

I think the real question here is: What is draining your starting battery so you can't start teh motor? You need to fix that issue first. You should never need your TM to start your motor.

 

[KRS62]

I'm not understanding the need for the 1-2-Both switch. With it installed, you are going to be tempted to connect the batteries together to run the TM longer and that's something you don't want to do. The start battery should be dedicated to nothing but starting the motor. You cn always limp home without lights and a stereo, but you want to be able to start the motor.

The way I am installing it will only allow for the outboard motor to access both batteries. The trolling motor will only have a connection to the TM battery. That said, if I had that option, I doubt that I would be tempted to use the main battery for trolling. I would much rather start the motor and head home versus fishing longer and possible getting stranded (or having to hand start.)

I hope to have it complete by the end of next weekend. Some work travel has put a damper on working on the boat.

KRS

 

[Hanr3]

Good, you completed the first step, identifying the problem.

Some work travel has put a damper on working on the boat.

KRS

Now comes the hard part, what are you going to do about it. :mrgreen:

 

[Bob Landry]

I'm not understanding the need for the 1-2-Both switch. With it installed, you are going to be tempted to connect the batteries together to run the TM longer and that's something you don't want to do. The start battery should be dedicated to nothing but starting the motor. You cn always limp home without lights and a stereo, but you want to be able to start the motor.

The way I am installing it will only allow for the outboard motor to access both batteries. The trolling motor will only have a connection to the TM battery. That said, if I had that option, I doubt that I would be tempted to use the main battery for trolling. I would much rather start the motor and head home versus fishing longer and possible getting stranded (or having to hand start.)

I hope to have it complete by the end of next weekend. Some work travel has put a damper on working on the boat.

KRS

Regardless of how you THINK you are installing it, when it is set to both, anything fed by the common terminal of that switch is running on both batteries. I'm just saying be really careful. You are going to be tempted to switch it over to both so you can troll "just a little while longer" and it's going to be very easy to get yourself in touble doing that.

 

[KRS62]

I am close to completing this project and here are some pics. I still need to finish painting my conduit and should have it all wrapped up by Saturday. (Looks like the pics posted in backwards order.)

Also - you can see the new bilge I put in. The old one looked to be on its last leg and I didn't trust it anymore.