Jump start 12 volt battery with 24 volt system (2x12v in series)

[AJ B]

I haven't had to do this yet, but if I needed to jump start my 12 volt engine battery using one of the two 12 volt trolling motor batteries wired in series, can I do this without disconnecting the TM battery terminals? I read somewhere something about using high-side or low-side but I can't find anything definitive on the internet, and don't know which is which. I'm hoping someone here knows.
I'd prefer not to have to disconnect the terminals, but I would unplug the trolling motor at the bow.
I did have to jump start once due to an electrical system fault (blown fuse on the motor) which is fixed, but I disconnected the TM battery first, and it was a real pain on the water.

[billnorman1]

Hook the negative motor battery cable to the most negative trolling battery negative side. Do NOT use the negative post of the trolling motor battery with the jumper wire attaching to the negative post of that trolling battery . If you have a 4 wire system, and no jumper, you will have to use a voltmeter to find the most negative battery. Attach the positive jumper cable to the positive post of the motor battery, and the positive side of the same battery you hooked the negative cable to. If you have a 4 wire system, disconnect the trolling motor at the front just in case.

[Marshfly]

Hook the negative motor battery cable to the most negative trolling battery negative side. Do NOT use the negative post of the trolling motor battery with the jumper wire attaching to the negative post of that trolling battery . If you have a 4 wire system, and no jumper, you will have to use a voltmeter to find the most negative battery. Attach the positive jumper cable to the positive post of the motor battery, and the positive side of the same battery you hooked the negative cable to. If you have a 4 wire system, disconnect the trolling motor at the front just in case.

Unless you plan on doing this just for a jump with a set of jumper cables, doing this will ensure that your trolling motor battery is just as dead as your starting battery and that your starting battery is being used by the trolling motor. Don't do that.

You need two things to ensure that you can actually use the combined two TM batteries as a jump battery without any problems. You need something to change the TM batteries from a 24 volt system to a 12 volt system. You need something to connect the TM batteries to the starting battery in case of needing a jump.

These two things will do that but also allow you to charge the TM batteries from the engine when you run.
http://www.yandina.com/troll24info.htm

https://www.bluesea.com/products/601...y_Switch_-_Red

I've used this combo on my last boat and have the 36 bolt setup installed on my current boat to accomplish the exact same thing. It works perfectly and simply. With the battery switch, you simply replace the accessory battery in the mix with your TM battery 1 and don't hook anything to the accessory output on the battery switch. When you turn the switch to combine, it hooks all three batteries together for a jump.

[Lou r Pitcher]

.....if I needed to jump start my 12 volt engine battery using one of the two 12 volt trolling motor batteries wired in series, can I do this without disconnecting the TM battery terminals?

Hook(Jumper) the negative motor battery cable (terminal over)to the most negative trolling battery....Attach the positive jumper cable to the positive post of the motor battery, and (to) the positive side of the same battery you hooked the negative (jumper) cable to.

[Marshfly]

The vast majority of boats will not have enough excess cable to move the wires to another battery. Especially if they were factory wired. While that would work, you're essentially changing out the battery and not jumping it. I'd check the wire length before relying on this in the field.

[AJ B]

Thanks Billnorman. Most negative trolling battery--I can remember that!

[Bradrodfish]

Take a look at this

[Marshfly]

Take a look at this

That will definitely work and does the same thing as the Blue Sea switch I linked to above. Good diagram. Add the Yandina to the mix and you can charge them at the same time.

[1bluemcm]

I am moving to this exact wiring on my boat in order to have a back up to jump/assist the start battery if needed. Not too difficult to achieve, there are places online or ebay to get pre-made battery cables with lugs properly attached, simplifies a lot.

Using this switch:
https://www.bluesea.com/products/600...Switch_-_Black

I also added color to the cables you most likely would need to add to make this setup up work. Lengths will depend on where things are and how you plan to run the cables.

[potomacbassin]

Just make sure (as the diagram shows) to hook up the jumpers to the battery on the negative side of the trolling motor circuit. Hooking it up to the other battery could result in electrolysis. I hooked my system up incorrectly the first time and started seeing corrosion on my trolling motor prop and big motor plates. Just an FYI.

[Lou r Pitcher]

The use of the permanent switch (used instead of a set of temporary jumper cables for jump starting) depends upon permanently bonding the trolling motor battery negative and cranking boating negative terminals.........a configuration which best should be avoided by boaters with trolling motors which have an internal US-2 transducer.

For some installations , the introduction of the switches circuit will introduce a path for objectionable trolling motor generated interference to reach a sonar.

[billnorman1]

Just make sure (as the diagram shows) to hook up the jumpers to the battery on the negative side of the trolling motor circuit. Hooking it up to the other battery could result in electrolysis. I hooked my system up incorrectly the first time and started seeing corrosion on my trolling motor prop and big motor plates. Just an FYI.

That and the fuel filler is sometimes grounded to the starter battery negative and that could start all kinds of wierd electrical paths plus when you jump it could burn this grounding wire.

[1bluemcm]

Getting a little off subject, but should the fuel filler be grounded? It's not on my Champ, and I figured it wasn't a bad thing to keep the fuel system separate from the electrical. Then again, I guess the gauge which extends into the tank is electrical.....never thought about grounding the filler. Filler is all plastic on some, would grounding it do anything?

[billnorman1]

Getting a little off subject, but should the fuel filler be grounded? It's not on my Champ, and I figured it wasn't a bad thing to keep the fuel system separate from the electrical. Then again, I guess the gauge which extends into the tank is electrical.....never thought about grounding the filler. Filler is all plastic on some, would grounding it do anything?

It's actually bonded. A fiberglass boat and a rubber tired trailer are not actually ground paths, fuel has been known to develop static electricity when being pumped, it just neutralizes this in the boat.

As for plastic, here's a quote: In the last two years accident investigations and research has shown that if your boat has a plastic fuel fill and you fuel your boat on the trailer at the local service station, then the fuel fill should not be grounded. See the CG link, http://www.uscgboating.org/alerts/alertsview.aspx?id=27

However if the fill fitting is metal then it should be grounded. Or if you always fuel your boat when it is in the water the fill should be grounded.

[Jonestrollingmotor]

Take a look at this

I've made this modification for customers many times. One thing to consider is to make sure the wire coming from the "one" side of the switch to the positive post of the battery is the same size as the outboard's wiring harness, usually a 4ga. Also, if you put the accessories on the "com" side, they will disconnect with the switch. I use 6ga for the connection from "two" to the trolling battery as well as the connection from the starting neg to the trolling battery. Do not try to start solely off "two" unless you use the same size cable as the outboard harness, again, usually 4ga, as the jump wires. 6ga will carry the jump but may not carry the direct start.
John

[1bluemcm]

Thanks Jones. I went with 4AWG from the TM battery because the run is about 5-6 ft, just figured worth the added expense to have that full capability.

I am rewiring so that virtually everything goes through a new fuse block - only the jack plate and maybe an automatic bilge will be connected directly to the battery. The run from "COM" on the switch to the (+) on the fuse block is about a foot, and from the negative on the battery to the fuse block is about 18 inches. Do I need a breaker in that line from COM to the fuse block? I didn't think so, but thought I'd double check. I used 6AWG to feed from COM at the switch to the fuse block, probably way overkill, but I had a bunch extra laying around and lugs to make good, solid connections so I figured why not.

[Jonestrollingmotor]

Thanks Jones. I went with 4AWG from the TM battery because the run is about 5-6 ft, just figured worth the added expense to have that full capability.

I am rewiring so that virtually everything goes through a new fuse block - only the jack plate and maybe an automatic bilge will be connected directly to the battery. The run from "COM" on the switch to the (+) on the fuse block is about a foot, and from the negative on the battery to the fuse block is about 18 inches. Do I need a breaker in that line from COM to the fuse block? I didn't think so, but thought I'd double check. I used 6AWG to feed from COM at the switch to the fuse block, probably way overkill, but I had a bunch extra laying around and lugs to make good, solid connections so I figured why not.

In the 6ga wire going to the fuse block, I would put a 50A (could use a 60A) between the battery and the fuse block. This will protect the entire fuse block, but allow the single fuses on each circuit to protect that circuit. Do you have a ground feeding the fuse block ground side also, or will all the grounds go back to the battery ground?

[1bluemcm]

Yeah, I have a 6AWG ground to the fuse block coming directly from the starting battery. Then each circuit is grounded on the (-) buss on the fuse block itself.

I'll look for a 50A breaker on your recommendation, sounds like the safest way. Thanks. Let me know if there is anything different I should do with that fuse block ground if you don't mind.

[Jonestrollingmotor]

Yeah, I have a 6AWG ground to the fuse block coming directly from the starting battery. Then each circuit is grounded on the (-) buss on the fuse block itself.

I'll look for a 50A breaker on your recommendation, sounds like the safest way. Thanks. Let me know if there is anything different I should do with that fuse block ground if you don't mind.

All should be good

[1bluemcm]

As always, you're the best. Thanks very much.