MinnKota killin my battery? update…

Ok, so here’s the latest.
I went out and ohmed out the 4 wires heading up to my front trolling motor, no problems there at all. But then I took the head apart on the MinnKota, and as the pictures show (not very well), I ohmed out the two wires coming out of the shaft that lead down to the motor. You might be able to see on the meter that I have 026 for resistance. The master electrician that I work with told me that was ok, there should be some resistance built into it. I figured the opposite. Plus, if I did have a problem with the coil, I would think it would affect both batteries, not just the one.
Any suggestions on this? I think I’ll contact MK too and see if they’re able to give any info out about their motors.

I’ve never had this much of a problem with a 24v system in a boat. It is truly driving me crazy trying to figure this out. I can’t just keep going thru batteries all the time.

Are you getting 24 volts at the head?

NK, talk about frustrating!! So, how often are the batteries going dead and when is it happening (after use with trolling motor or after charging over a period of time)? Some things I would check and maybe you have already done these:

1) With the plug and wires connected to the battery, check for 24V at the trolling motor.

2) Disconnect from batteries, check for short on the red/black at the trolling motor.

3) Check for short between any of the 4 wires after disconnecting wires from battery leads. This would be a resistance/connectivity test on the MultiM. And perhaps do this with the 4 plug bars and wires connected. This should debug any issues with shorts on the wires and/or plug.

4) Check the connections on the plug.

5) Not a battery expert, but could perhaps the battery that you are not replacing be draining the other batteries (the bad one is the one you are keeping). I know to promote battery health it has been recommended to me to use the same type of batteries. Preferrably the same age, size, brand, etc.

6) When your batteries are fully charged, test each bank by putting the multimeter in series to measure the current.

Just some ideas, but I don’t know if they will help.

Raap

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Are you getting 24 volts at the head?

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Yup, at speed 10.

You will need to take a more scientific approach to figuring out why one of the batteries is failing.

When wiring batteries in series, your batteries need to be matched. Same capacity.. which generally means using cells from the same manufacturer and age. Of course one would expect the older cell to degrade and fail each time, but it seems from your description that perhaps it is always one cell that survives.

Be careful not to mix capacities of batteries. Batteries have a cold cranking amp rating, but also a continuous discharge rating. I would suspect that the continuous discharge rating is more pertinent to this kind of problem.

When the system is drawing current, the same amount of current is being passed through all the cells. (Each 12V battery has 6 cells). If any cells are weak, then they will appear resistive and actually develop a voltage in the reverse direction. If you monitor the voltage on the battery as you run your trolling motor, you may see the voltage drop off on the weaker battery at a faster rate than the strong battery.

Were I going to figure this out, I would choose to wire in two voltmeters, one across each 12V battery, and then monitor the discharge of each battery on the next outing. What you are looking for is for one battery to drop to around 10V or lower with a load applied, while the other maintains a 12V charge.

If you run batteries for a period of time with one of the cells is weak and becomes reversed, it ruins the cell… essentially, it becomes charged in the reverse direction which causes the two plates to become similar in composition and no longer functions as a galvanic pile.

The other point made in a post by another member was to check the charge rate. Measure the voltage across the cells during charging. Check to see that both your batteries are getting the same voltage (around 13.8V like your car’s voltage regulator). If one of your chargers is outputting above 14V, then it can overcharge that battery and shorten the useful life.

Personally, I would suspect that your charger might be overcharging the cell and boiling off water causing the same battery to be observed to fail repeatedly.

Yup, very frustrating. I can’t even tell you the rage it causes.
The batteries aren’t going dead; it just blows a cell or something, but it’s just dead, and you can tell immediately while you’re trying to use it. I’ve been checking the voltage with the meter before and after charges, and everything seems to be cool.
1. Did it, got it. No problems there.
2. I did not do that one yet, but in that instance I would think that the short would affect performance immediately, and affect both batteries. It’s taking 3-4 weeks of use to kill the battery.
3. Did it, no problems there. All wires are good.
4. Did it, no problems there.
5. Yup, have discussed this with my coworker, and he says that could be the case too. But I’m doubtful of that because I’ve never had this kind of problem before with batteries in worse shape than these. These were new in Sept, both the same exact battery. I don’t get it.
6. Haven’t done that one yet, but might check it out.

This is a 4 wire system to both the front and rear trolling motor. I found the red wire (not the orange) coming from the trolling motor to the battery in question had a loose connection to the circuit breaker. Surely this could not have been causing all these problems, but for whatever reason, I soldered the circuit breaker connections from the rear motor, but did not from the front. They are all soldered now, so I guess we’ll see what happens tomorrow.
Thanks for the suggestions…I gotta whip this thing somehow!

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Personally, I would suspect that your charger might be overcharging the cell and boiling off water causing the same battery to be observed to fail repeatedly.

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This is something that worries me too, and I need to look further into this. My charger seems to be working fine, but I still have my suspicions about it, but who knows at this point. I did change the leads to the other battery just to see what happens. Hey, it’s under warranty.

The 4 wires are hooked to each lead of each battery, so the 24v is made at the plug, as there’s a jumper in there. I really don’t wanna pull all the wires to make it a 2 wire system either. I just want this one to work. I just can’t figure out what the problem is.

If you have an on board charger, they do go sometimes and they can have one bad bank or a worn through wire to your battery. I hate battery problems. I once replaced a board in my cota and the problem was a bad hot wire now I have an extra board.

Here’s what I did: I switched the leads from the battery charger over to the other battery that’s still under warranty, so if it is the battery charger, I guess I’ll find out.
I’m also refraining from using my front trolling motor until I can call them tomorrow and ask about the resistance in the windings.
If the girl at cabela’s wants to grouch at me if I bring two dead batteries in, she will get an earful. Batteries are still under plenty of warranty, and my battery charger? Also cabela’s pro sport. She can eat it.

Here’s the latest-
I got to thinking today: I started having problems with all this when I went to this trolling motor, which came on the boat when I got it in July. I had this charger in a previous Crestliner, and I had no problems. Hmmmm….

I talked to MinnKota yesterday, and he said I should “probably have either zero or infinite with my ohmmeter while ohming out the motor coil leads that come up from the motor in the shaft. Having a reading doesn’t necessarily mean there’s a problem”, which makes no sense to me. I’m at the point where I think it’s probably a problem.
He did say one test to do was to run 24v directly to those leads with no controls connected, and read the amps it’s drawing under no load (not in the water). It should be 10-15a at the most. I’ll try to do that today and we’ll see what I come up with.

The point that he would be making is that when the motor’s commutator is contacting the windings, then the resistance would be low. If the commutator was open (between windings) then the resistance should be infinite or a few mega ohms (ie million ohms).

So, then one asks… “How low?” If I simply make contact to anything that I measure the resistance of, I get 0.3 ohms typically due to the resistance of the contact, so you will not get “zero”. If the no load current is around 10-15 Amps, then your effective resistance would be around 1.6 to 2.4 ohms for the windings, which sounds more reasonable than 26 ohms that you had measured.

Although the 26 ohms that you measured previously might show up if the commutator and brushes had some wear and there might be particulates bridging between brushes and commutator causing the measurement to look resistive. This would not mean that the motor was bad.

If your motor was bad, I could see you complain that it runs down quickly, but I don’t see it destroying your battery, but this is along the lines of why I suggested wiring in the two voltmeters to monitor the individual batteries while they are cycled as this will give you a reference to understand your system behavior and a means to monitor it’s performance.

I noted that you are located in Nebraska which makes it a bit difficult to share equipment (I am in Minnesotoa), but were I closer, I would loan you my oscilloscope so that you could see what the charger is outputting during your charging cycle. I remain suspicious of the charging cycle being the source of the problem.

I would love to know if you have gotten any further? I have a minnkota 24v system that I am lucky if I get 4 hours of trolling out of before it eats the batteries… . Wiring is new, battieries are new and all I can think of is the motor is doing something funny!… ug I feel your pain!

Ya Burr, it’s very frustrating. I will tell you what I’ve done the last couple of times out though, and that is that I’m using just the rear motor, and I’ve demanded quite a bit out of it lately, and nothing bad has happened yet. I know 9 outta 10 times it’ll be the battery charger that’s the problem and not the motor, but we’ll see what happens. I switched the charging leads to the other battery and it hasn’t blown yet either. It needs a little time yet, but I sure hope it’s the motor and not the charger. Gives me a great excuse to get a newer motor, too.

Well guys, here it is, I hope….think I’ve found the problem. I guess it has to be the charger. I switched the leads around on the two batteries, and did not use the front trolling motor at all. Was using the rear Vector today and not 5 minutes into the trip, the battery that had the leads switched over to it blew. I guess if the chic at cabela’s wants to yell at me again, I can tell her it’s their battery charger, too.

So, here’s what I’m thinking….the one good lead that’s left….can I splice another set of leads onto it and charge both batteries with one lead? I guess it would take twice the time, but I’m not really concerned with that so much. I’m sure it’ll still charge em up overnight, and if it doesn’t, it’ll be close. Interested to see if that would work or not.

You can charge both at once as you describe, with the batteries wired in parallel But when you do this, if one battery has a problem, like a shorted cell, then it be a lower impedance load on the charger and take all the current, leaving your other battery weakly charged. Better to get a new charger so you can quit fooling with it and get back to fishing!