Minn Kota not running with weird voltage drop

[YeOldeRusty]

Using 2017 Minn Kota Maxxum 55lb with variable speed control

 

About a month ago my Minn Kota started working intermittently then quit all together. Every so often when I pressed the button I would here it click and then nothing. I replaced the control board and got nothing. 
I took it in to a shop last week and $150 in labor later we still had no answer. When unplugged the outlet gets about 13.5V. When plugged in, the input wires to control board drop to around 4v and there is nothing on the output wires. 
If I use jumper cables and attach from battery to output wires from control board leading to motor, the motor starts going fine. Yet if I connect the input and output wires directly and skip the control board, nothing. Even putting output wires directly on outlet yields nothing. 
One guy at the shop said it had to be a bad armature. I called a parts shop to order a new armature and the guy told me over the phone that if the armature was bad then it wouldn’t spin at all when using jumper cables. 
 

Does anyone have any suggestions on what might be wrong? I really don’t feel like spending $200 at a shop just for them to tell me it’s a switch or something minor. Thanks

[Tennessee Boy]

It sounds like you know what you’re doing.

I’m not sure I’m following exactly what all your doing.  You have power at the plug but you can’t confirm you are getting 12V at the control board.  Have you tried bypassing the plug and wire by providing power directly to the control board from a battery using different wiring?

 

[Jig Man]

There is an other major site with a trolling motor forum that might help.  The site censor won’t let me show it.

[YeOldeRusty]

1 hour ago, Tennessee Boy said:

It sounds like you know what you’re doing.

I’m not sure I’m following exactly what all your doing.  You have power at the plug but you can’t confirm you are getting 12V at the control board.  Have you tried bypassing the plug and wire by providing power directly to the control board from a battery using different wiring?

 

I just tried going directly into control board. No luck. 
 

It’s strange that I’m getting 12v at the input wires, but as soon as they’re connected to the board it drops to 4v. Then nothing at the output

[cyclops2]

badly corroded battery cable wires in the squeezed on lugs & battery clamps / lugs .could be BOTH cables.

[YeOldeRusty]

6 minutes ago, cyclops2 said:

badly corroded battery cable wires in the squeezed on lugs & battery clamps / lugs .could be BOTH cables.

But if the battery cables are corroded, why would I still be getting full voltage at the outlet?

[Way2slow]

If you know how to use a voltmeter, you could have saved yourself a few hundred dollars.

Using a voltmeter, just follow the cable back toward the battery, every place there is a connection, check both sides of the connection.  If both sides have the voltage drop, follow it on back to the next connection, again check both sides.  Keep following it back to the battery.  A prime culprit for this are crimped on connectors and dirty connections. 

Also, remember it takes two wires to make a circuit.  I don't know how many times I've seen people think it has good voltage, but forget it also has to have good connections on the negative leads also, so make sure you troubleshoot the negative cable.  

If the voltage going to a circuit is dropping, most likely the power source is the problem, not the circuit, unless there is a major short and that usually causes tripped breakers, blow fuses or smoke.

 

[MN Fisher]

11 minutes ago, Way2slow said:

If you know how to use a voltmeter, you could have saved yourself a few hundred dollars.

Using a voltmeter,

Can't stress this enough - the one I bought years ago when I was doing hobby electronics has saved my butt more times than I can remember.

 

[YeOldeRusty]

Mystery solved. Found an inline fuse I didn’t know about that the shop guys said they checked. Thing was absolutely melted and had to install new fuse holder. Coulda saved about $140 

[casts_by_fly]

Any chance they checked it and it was fine but then melted after?  I’d want to know why it melted in the first place so that it didn’t happen again 

[Way2slow]

It probably melted simply because it was most likely too small.  That motor can draw 50 amps on max and should be on a 60 amp circuit breaker, not a fuse.  I can't say I've ever seen a 60 amp inline fuse, it would need 6ga wire going to it.

 

[WRB]

5 hours ago, YeOldeRusty said:

Mystery solved. Found an inline fuse I didn’t know about that the shop guys said they checked. Thing was absolutely melted and had to install new fuse holder. Coulda saved about $140 

Was the repair shop a certified Minn Kota service and did the repair shop service the motor brushes? If so you didn’t waste too much money. To melt a inline fuse holder means a direct short and the fuse malfunctioned. Maybe the fuse was wet?

Tom

[Way2slow]

A short usually vaporizes the fuse.  A melted fuse is from more current than it's rated for.  However, the only fuses I've dealt with large enough to handle that kind of a load are sand filled ceramic housings and you can't see the element to know if it melted or vaporized.   

[YeOldeRusty]

13 hours ago, WRB said:

Was the repair shop a certified Minn Kota service and did the repair shop service the motor brushes? If so you didn’t waste too much money. To melt a inline fuse holder means a direct short and the fuse malfunctioned. Maybe the fuse was wet?

Tom

I found them through the Minn Kota website on list of certified techs. They took apart the foot and took out armature, brushes, etc. but never replaced anything. Just put it back together

Here’s the fuse 

I’ve had that trolling motor on there since 2017 and this is the first issue. Wasn’t even the motor and that fuse lasted almost 5 years so I just replaced it

[WRB]

Replace the fuse with a 50 amp marine circuit breaker.

Can’t see how a qualified service tech didn’t replace a 30 amp TM fuse with a 50 amp marine circuit breaker?

Tom

[Way2slow]

It's not my boat so I shouldn't care, so I deleted what I posted.

I will say, if you've thought about upgrading to a larger TM, all you need to do is upgrade the wiring on what you have and you will think you have a new TM twice the size.  That's how much performance loss you have with what you have.

Also, Minnkota recommends a 60 amp breaker, 

 

[Tennessee Boy]

Someone replaced the trolling motor and didn’t replace the factory wiring.   From the Maximum manual.

 

 

[WRB]

I always used a 50 amp breaker per battery and have no issue with upgrading to 60 amp. Also used 6 gage wire.

At a minimum use what the TM mfr recommends. Marine environment use marine parts.

Tom