24v Trolling Motor Wiring

[BobP]

My TM battery connections were corroded so my buddy removed the batteries to clean them up but mixed up the battery positions or connectors afterward and we couldn’t get it to work.  After several tries, I realized the system didn’t have a jumper between the batteries so the 24V jumper had to be either in the TM plug receptacle or the TM plug itself.  It was in the plug.  Progress!  But we were getting only 12V.  So we reversed the + battery connectors and finally got 24V running to the TM. My question is what is the electrical advantage to running 4 12V wires from the batteries and jumping them at the plug to create 24V versus jumping the batteries themselves and running 24V on 2 wires to the front of the boat? 

[J Francho]

Smaller gauge wires?

[BobP]

Mine are gauge 6 or 4 Diameter.  Pretty large.

[Angry John]

You have twice the volume of wire.  You could check a 24v wiring table to see if the Guage is large enough to carry the load at that length

[J Francho]

6 is plenty.

[BobP]

If I remember, the better size is 6 gauge, and that’s what they are.  I bought the boat used and the TM might have been installed by the first owner after the original purchase.  But my question remains, basically is there enough drop in amperage on a 24V 6 gauge cable over 19 feet that it is advantageous to run twice as many 12V 6 gauge cables instead?  I ask because I may want to change TMs in the future and it would be simpler to jump the batteries and use a single pair of cables up to a new TM.

[J Francho]

I've never seen a boat rigged the way yours is.  I been around a few.

[junyer357]

Thats the way our hydrasport came. It had the origional omc tm til about 3 years ago when we upgraded to a fortrex. The omc had a 12/24 switch on the foot pedal. It had all 4 wires on the plug and converted as needed inside the foot pedal to give you 12 or 24. 

I rewired it at the plug and the batteries and did away with the 12v option and only use 2 of the 4 wires. 

 

[J Francho]

54 minutes ago, junyer357 said:

The omc had a 12/24 switch on the foot pedal.

Now it makes sense.  Though I'd never want to use 12 if I had 24v.

[PAbasser927]

1 hour ago, junyer357 said:

Thats the way our hydrasport came. It had the origional omc tm til about 3 years ago when we upgraded to a fortrex. The omc had a 12/24 switch on the foot pedal. It had all 4 wires on the plug and converted as needed inside the foot pedal to give you 12 or 24. 

I rewired it at the plug and the batteries and did away with the 12v option and only use 2 of the 4 wires. 

 

 

Same exact scenario when we picked up our Stratos.  We did the same thing with the wiring when we upgraded to a Terrova.  There were two sets of 6 gauge wires running from the bow back to the battery compartment.  Now one set is no longer in use at all.

[junyer357]

59 minutes ago, J Francho said:

Now it makes sense.  Though I'd never want to use 12 if I had 24v.

Yea. It was pointless. Occasionally the switch would get flipped and it would barely move the boat. 

[BobP]

Yeah, the TM is an old OMC unit.  The mount is getting a little wonky now but has run reliably for 20 years.  The danged thing just won’t die!  I’m a “not broke, don’t toss it” guy but if it ever breaks, I’ll be upgrading and was just wondering how a new unit would best be wired since I have two alternatives with 4 wires in place now.

[WRB]

The more connections you have the more problems. I would change out the old 6 gage wire also and run 1 pair with 24 volts. The circuit breakers should be changed to 50 amp during the rewire.

Tom

[mattkenzer]

2 hours ago, BobP said:

Yeah, the TM is an old OMC unit.  The mount is getting a little wonky now but has run reliably for 20 years.  The danged thing just won’t die!  I’m a “not broke, don’t toss it” guy but if it ever breaks, I’ll be upgrading and was just wondering how a new unit would best be wired since I have two alternatives with 4 wires in place now.

At the batteries, if you join the two Reds together at the start of your 24V System and the two Blacks together at the end of your 24 Volt System then do the same at the plug in, it is now straight 24V. Just bring power through two wires instead of one.

[junyer357]

3 hours ago, BobP said:

Yeah, the TM is an old OMC unit.  The mount is getting a little wonky now but has run reliably for 20 years.  The danged thing just won’t die!  I’m a “not broke, don’t toss it” guy but if it ever breaks, I’ll be upgrading and was just wondering how a new unit would best be wired since I have two alternatives with 4 wires in place now.

Ours still ran well too when we replaced it. The pins on the foot pedal it hinged on to turn the head were wore slap out and made it hard to turn and made a grinding sound. Went to an fortrex and recessed tray and havent looked back. Much more power, never between speeds anymore, and much more comfortable all day recessed. 

I added a jumper between neg on bat1 and pos on bat2 and used an existing red cable on bat1 pos and black cable on bat 2 neg. On the plug end i verified my 24v with a meter and wired to those terminals on the male end of plug. Left the other pair abandoned in place after i cut exposed ends off and taped them up. Never know if i may need them again. 

[BobP]

37 minutes ago, mattkenzer said:

At the batteries, if you join the two Reds together at the start of your 24V System and the two Blacks together at the end of your 24 Volt System then do the same at the plug in, it is now straight 24V. Just bring power through two wires instead of one.

Ok, now I have 3 options.  Nice!  Thanks for the comments guys.

[StratDude]

To double the voltage of 2 batteries, you must connect them in series. You only need 2 wires from the batteries to the plug. One wire from the Pos of battery number 1 and one wire from Neg of battery number 2. Then connect a jumper wire from the unused Pos and Neg on both batteries. 

 

The reason the OP has 4 wires from his batteries to the plug is due to the type of system (variable 12V/24V) used with his original trolling motor and plug.  

[J Francho]

1 minute ago, StratDude said:

WRONG!!!

He still has the jumper at the plug.

[StratDude]

If he switches to another trolling motor, the plug may not work.. Better to install jumper at the batteries. The jumper in the plug is a smaller gauge and can "blow" like a fuse if overheated. Seen it happen several times from oversized wiring and upgraded trolling motor sizes.

[J Francho]

Agreed, just pointing out that it's not in parallel.  Personally, I've seen or heard of such thing, but I've only had two boats with 24v set ups.

[BobP]

My basic question was whether there was an electrical advantage (I.e., a voltage advantage) in using 4 ea 6 gauge cables carrying 2 pairs of 12v current from 2 separate batteries over 20/ft of wires versus a single pair of 6 gauge wires carrying 24v from a jumped pair of batteries.  I think the answer is yes since the impedance would be half as much on the 12v wires as on the 24v wires.  I know the simplest wiring would be to jumper the batteries and run a single 24v pair to the front of the boat.  But since I already have 2 pairs in place, it would seem the most practical solution with the best electrical efficiency would be to continue with a jumper on the TM plug as there would be less voltage loss.  I can go either way and am sure any TM would run ok with either wiring scheme, so if I’m getting my electrical theory wrong, there’s probably no use in beating knots in my head cause I’m done here.  Thanks to all for their advice.