Jumping cranking battery from trolling motor battery?

[Lookin4Bass]

I'm sure there's a thread or two on this but I couldn't locate them.

I was told that jumping your cranking battery from the TM batteries could fry your starter if you have a 24v TM system.

I have a Minn Kota Maxxum 74 24v motor. I put a volt meter on each of the batteries and got a reading of 12v from each individually.

When I put the pick ups on the positive terminal of battery 1 and the negative of battery 2 I get over 24v.

That said I assume I can safely jump from either TM battery (alone) to the cranking battery?

[ash]

What you want to do is detach the bridge on 24volt system (ie take all of the cables off. Then jump from battery to battery, I was told by my mechanic its BAD to not detach the bridge as it could fry the outboard ECU (computer)

[TritonBrent]

I believe as long as you only hook the cables up to the Positve and Negative on one of your TM batteries you should be just fine,you are only going to get 12 volts. I've done it this way a few times and have never had a issue.

[SHAFT]

Everything I have read , and it makes sense, is you can jump off any one of the TM batteries with out disconnecting it from the series circuit , just make sure its one battery and the pos. and neg. from that one battery

[L.Hackney]

I have done it more than once and my starter is fine. I'm not saying it's ok to do but it worked for me...

[mark poulson]

A question.
Would pulling the trolling motor fuse, or throwing the breaker, before you jump separate the batteries and protect your big motor?

[ash]

I wish Frank or one of the mechanics would get on this thread. I am not saying that you cant jump with the bridge connected. What I am saying is I was told speciflly with my Evinrude NOT to do it as there could be a voltage spike introduced to the system that could damage that ECU (that guys is over a grand) so the recommend is to temporarily take the battery out of the circut then jump. (really all you have to do is disconnect one terminal and it is off the circut) Safe insurance if you ask me.

[201Pro]

Guys,

I think the problem is when you pick a ground (black wire) from somewhere other than THAT particular battery and then put the positive onto the WRONG battery, i.e. in a 24V system, from ground one battery is 12V while the other batter is 24V referenced to ground. So if you pick the wrong battery, i.e. the 24V one, then you'll stand a chance to fry your electronics on the motor.

As had been mentioned in previous posts, if you pick one of the trolling motor batteries and use those exact terminals (both positive and negative), you should be pretty safe.

[chf8500]

Be safe|||||||||||||||||| disconnect the bat you are going to use to jump from. no question about it 24v or 36v does't matter not only do you stand a chance of frying the starter, ecu or any other elec component, one big mistep spark and just the right amt of fume in the bilge = one major bang that if you are still with us you can have the insurance co buy you a new boat or if you love your wife she can be a rich widow. always connect the 12v pos 1st then hook up the grnd. one can only imagine how big explosion is if you screw up and short cut. BE SAFE

[Smile_n_Jax]

I'll agree with what chf said. Better to be safe than sorry. Yes, you can jumper series wired trolling batteries to your starting battery, but one mistake could be devastating. Better to disconnect the series cable so you know you're going 12V to 12V. I had occasion to do that a while back. I'm a retired automotive technician and I knew I could jump 12V to 12V, but I still disconnected the series jumper just to be on the safe side.

[Jason Milligan]

I was stupid enough to try and jump my outboard without disconnecting the trolling motor batteries from eachother. I fried my ECM! My advice, buy a new cranking battery and keep it charged. Much cheaper than the 1,600 dollar bill for replacing the ECM...

[biteme]

When you jump the starter from the cranking battery you are taking a gamble. For those of you that have got away with it odds are your trolling batteries are low enough that they wont hurt anything. As the trolling batteries run down on a 24volt system they go towards the 14 volts you need. I promise you if you have 25 volts(full charge) or 36 volts and try to jump the starter is will burn up the starter and ECM.