Trolling for info...or wiring again?

[NBE]

OK, I've searched but not lucky enough to find the exact thing so here goes:

- Replaced a 24V Motor Guide Tour 767 (67# thrust) with a MinnKota Terrova 80# thrust
- Wiring coming from the two batteries are two seperate hots and two blacks going to the front of the boat. These are 6AWG.
- No selector switch. It's straight 24V with two individual 12V being jumpered to 24V at the plug.
- I currently have a 40A circuit breaker at the battery on each of the two positives that are going up front. MinnKota. of course, recommends 60A breakers for this trolling motor.

So my question is, with the two seperate 12V wires going to the front of the boat, wouldn't the amp draw be halfed? In other words, if the total amp draw is 50A and you have two wires supplying the power would that equate to 25A per wire?

I'm trying to decide if my current 40A breakers are good enough (if it truly is 25A per wire) or do I need to go ahead and chage over to 60A ones? I have new 60A ones already but I do wonder if 60A breakers are ok for that setup and 6AWG wire. I certainly do not want to put breakers on that are too big for the wire size etc. I did look at some charts but they all differed somewhat so I wanted to ask here too.

Thanks!!
Brad

 

[wifisher]

Re: Trolling for info...or wiring again?

Sorry, you need full amps from each battery.
Your motor requires 60A at 24V.

Which can be shown as:
60A*24V=1440 watts


So therefore:
60A*12V=720 watts
+
60A*12V=720 watts

720 watts *2=1440 watts

 

[fishrdan]

Re: Trolling for info...or wiring again?

^ Agree, you need 60 amp breakers if that's what MK recommends. I didn't look up the specs, but it's believable. If you leave the 40 amp breakers it will work at low speeds. BUT! When you are in a pinch and need to go WOT on the TM or stall the on something, you could easily pop one of the breakers. Not something you want happening while you are being blown into a rocky shoreline......

I think you are fine with the 6ga wire, but how long is the total wire run, + and - . There are several DC wire calculators available (Blue Seas) that will show you the correct wire size needed.

 

[NBE]

Re: Trolling for info...or wiring again?

Thanks to you both for your input. I was pretty sure I was going to have to change them out and as I said, I do have them already. I was mostly not sure about using the 60A with the 6 AWG wire. I didn't want to overprotect the wire and have bigger problems.

Thanks for the chart...Blue Sea info that is. That one makes better sense but I am looking to be borderline. My total run per wire is about 18 - 20 feet and at 50A (what the max for the motor is supposed to be) that puts me kind of borderline between 6 and 4 AWG according to that chart?

I do not run the trolling motor on high for extended periods of time very often so I'm thinking that I will be fine. I will just remove the 40A ones and install the 60A ones and go test everything out to see how it works.

Thanks again!


Brad

 

[wifisher]

Re: Trolling for info...or wiring again?

I don't really feel like figuring it out right now, but I think you will be OK with the 6ga. I would suggest running the motor on high for a little while, and then grab your wires and make sure they are not heating up. If they are heating up enough to notice, you are wasting energy there, and will get better performance with larger wires.

Remember that when figuring wire length, you need the total length, not the length of each side.

 

[fishrdan]

Re: Trolling for info...or wiring again?

My total run per wire is about 18 - 20 feet and at 50A (what the max for the motor is supposed to be) that puts me kind of borderline between 6 and 4 AWG according to that chart?

Try this wizard and see how it comes out. Couple of tips on the calculator, use 10% voltage drop and a fixed load (even though the load will be variable most of the time). I play with the voltage drop (9%, 8%, 7%, etc.) to see where it jumps to the next size of wire

With that calculator, it's looking for the total wire length, + and - for both batteries. As I understand your configuration, the battery wire runs are (about) 20' from the receptacle, and both batteries have + and - cables run to the receptacle. That would equal 80' of wire. Since you are running 4 conductors, the length can add up quickly, and if you don't measure correctly it can come out skewed. (IE: my 18' boat has a 23' wire run from the transom to the bow receptacle, but only a 7' run from the bow battery to the bow receptacle, 60' of wire.)