Perplexed by DC thruster issue

[DonW28]

I'm scratching my head as what is going on with the DC power to my thruster. My stern thruster will only operate when I jump the negative post of the batteries that power it (isolated batteries that only power that item) to one of the other batteries in the boat. Doesn't matter if I jump it to the bow thruster battery, house batts, or gen. battery. And I do not need to jump the positive. Only the negative cable. I figure maybe I have a ground issue but not sure how to go about figuring out the problem in a smart manner.



Any recommendations are appreciated as always.


Don

 

[AlanT]

I'm scratching my head as what is going on with the DC power to my thruster. My stern thruster will only operate when I jump the negative post of the batteries that power it (isolated batteries that only power that item) to one of the other batteries in the boat. Doesn't matter if I jump it to the bow thruster battery, house batts, or gen. battery. And I do not need to jump the positive. Only the negative cable. I figure maybe I have a ground issue but not sure how to go about figuring out the problem in a smart manner.



Any recommendations are appreciated as always.


Don

Try disconnecting your charger from that stern thruster battery (and anything else). Then with only the St Th +/- connected to that battery go ahead and test, then test with the jumper you explained earlier. My guess is nothing will happen. If nothing happens it is because St Th battery is dead and is getting power from the jumper at the (-) side and your charger at the (+) side. Not an expert here at all, just an opinion. Good luck. ~A

 

[Juliet 15]

AlanT, that's some good diagnostics... Hoping to hear the outcome of this one.

 

[O C Diver]

It would help to know how that battery(s) is charged.

My initial thought would be to remove the negative cable from the battery where you put the jumper cable, clean the terminal and battery connector, inspect the battery cable for a tight crimp, and reassemble.

Ted

 

[DonW28]

Try disconnecting your charger from that stern thruster battery (and anything else). Then with only the St Th +/- connected to that battery go ahead and test, then test with the jumper you explained earlier. My guess is nothing will happen. If nothing happens it is because St Th battery is dead and is getting power from the jumper at the (-) side and your charger at the (+) side. Not an expert here at all, just an opinion. Good luck. ~A

A,
Well darn. I had hoped it was something that simple but it still works fine as long as the negative is hooked to one of my other batts. Going to check the crimp connection next. I tried it with a different battery while I was down there and it still will not operate unless it is jumped to a negative post on a different battery. Perplexed is not a strong enough word right now. LOL.


Don

 

[DonW28]

Everything is clean and tight and still no power to the thruster unless I jump a negative to another boat battery or to the main ground bus bar.



A simple solution would be to simply run a 2/0 wire from the negative to the ground bus bar but I can't grasp why I am having to do it. Something is obviously wrong or I really have no concept of DC current. I have said on here before I am not an electrical guru but I'm pretty sure in DC a battery acts as its own ground.



I'm thinking maybe corrosion inside the thruster unit could be the culprit.



Is the work around dangerous?


Don

 

[Comodave]

Let me see if I understand your post. Is the thruster system completely on its own battery? I put a stern thruster in our last boat and a bow and stern thruster in our current boat and the thrusters all have their own individual batteries. I did not hook them to any of the house or start batteries. They are standalone systems. Is this what you are saying in your first post?

If indeed they are standalone it makes no sense that you need a ground to your other batteries. If the controls are powered from the house batteries then maybe they need a ground connection.

 

[O C Diver]

How is the thruster battery(s) charged? Posting some pics of the battery and connections would also be helpful.

Ted

 

[DonW28]

Let me see if I understand your post. Is the thruster system completely on its own battery? I put a stern thruster in our last boat and a bow and stern thruster in our current boat and the thrusters all have their own individual batteries. I did not hook them to any of the house or start batteries. They are standalone systems. Is this what you are saying in your first post?

If indeed they are standalone it makes no sense that you need a ground to your other batteries. If the controls are powered from the house batteries then maybe they need a ground connection.

They are indeed stand alone. But when the batteries were replaced I wonder if the guys forgot to hook the system back up properly. My bow thruster has a separate battery as well. You may be on to something about the controls being the issue. Obviously since both thrusters work off the same control module they are only getting power from one source. At least I like to think there could be some reason for this to be happening. And the bow thruster works like a charm and is the battery I initially used to run the negative ground test.



Don

 

[Choices]

Check continuity of each cable. I once had one short out mid cable under the jacket. Took forever to track it down. Also make sure all isolation switches are closed.

 

[DonW28]

Pictures. The 8D is the bow thruster. Next to it in parallel are the stern thruster batts. Charger for the stern is mounted above. Bow thruster is charged off the main house charger.



I recall now there was a small 2 foot or so black wire with ring terminals laying the the bilge after the batteries were replaced. But it was maybe 8AWG at the most. That would have been awfully small to connect the ground to the bow thruster battery unless my DC electrical ignorance is showing again.


Wouldn't the ground still need to be the same size cable as the others even if only closing the loop for the thruster control board at the helm? Maybe that wire was more important than I thought.




Don

 

[Ka_sea_ta]

Without knowing how the thruster control is wired, what I would guess is that the controls are wired to a different voltage source then the thruster. Such that when you connect the negatives together the control + has a return path.

 

[High Wire]

All of the bank negatives ( not called grounds) should be connected together normally. Clearly they are not. It could be a control power issue where the positive (or negative) is fed from the wrong battery. You’ll have to trace the control wires back to the source.
Another issue in your pictures is that the smallest gauge ring terminals get stacked last. Heaviest terminals go on first.

 

[O C Diver]

I think the stern thruster might be running off another battery when you add the jumper cable between the 2 negative terminals.

If you follow the positive cable from the stern thruster and it goes to another battery, the thruster wouldn't run because the negative cable from the stern thruster is isolated from the other batteries, until you add the jumper cable.

The same situation could exist if the negative cable didn't go from the stern thuster to those 2 batteries.

Trace the positive and negative cables from the stern thruster.

Ted

 

[Greg S]

My bet is that the small red wire goes to the controller. Where does the yellow wire go? Probably not to the controller.

If the control panel is powered from this battery it probably is attached to a common negative buss. It won’t work until it has a negative going back to this battery bank. When you connect this bank to a common negative you are allowing the control panel to work.

Just where does that yellow wire go?
Is that black wire you found long enough to reach another negative terminal or buss?

 

[twistedtree]

Did all this happen immediately after someone worked on the boat (replaced batteries)? Or was it working fine and then spontaneously stopped working?


I suspect that the issue is the control solenoid for the stern thruster. The positive control is probably powered from the house or bow thruster bank, and the negative is wired to the stern thruster bank. Since the stern and bow thruster bank negatives aren't connected, there is no electrical path to operate the solenoid.


If the 8ga jumper cable appeared after the techs replaced your batteries, and the problem appeared at the same time, then the techs did their assigned job of breaking your boat. It seems to be what they do best. Reconnect the wire, and if you have a clamp-on DC current meter, verify how much current is running in the wire during all thruster operations, both bow and stern, and in both directions. I think you will find there is only an amp or so of current corresponding to the solenoid, and only when operating the stern thruster.

 

[Delta4242]

It sounds like you just have a ground issue. If you connect the jumper to the main DC ground and the thruster runs, this will prove it out. Most DC power problems stem from bad batteries, battery cable and connection issues, or both.
Rich

 

[DonW28]

My bet is that the small red wire goes to the controller. Where does the yellow wire go? Probably not to the controller.

If the control panel is powered from this battery it probably is attached to a common negative buss. It won’t work until it has a negative going back to this battery bank. When you connect this bank to a common negative you are allowing the control panel to work.

Just where does that yellow wire go?
Is that black wire you found long enough to reach another negative terminal or buss?

The red and yellow wires are off the battery charger mounted above the banks.


Don

 

[DonW28]

Did all this happen immediately after someone worked on the boat (replaced batteries)? Or was it working fine and then spontaneously stopped working?


I suspect that the issue is the control solenoid for the stern thruster. The positive control is probably powered from the house or bow thruster bank, and the negative is wired to the stern thruster bank. Since the stern and bow thruster bank negatives aren't connected, there is no electrical path to operate the solenoid.


If the 8ga jumper cable appeared after the techs replaced your batteries, and the problem appeared at the same time, then the techs did their assigned job of breaking your boat. It seems to be what they do best. Reconnect the wire, and if you have a clamp-on DC current meter, verify how much current is running in the wire during all thruster operations, both bow and stern, and in both directions. I think you will find there is only an amp or so of current corresponding to the solenoid, and only when operating the stern thruster.

I'm going to make another jumper today and give it a try. Sure someone in the marina is going to have a clamp-on meter I can borrow.



Don

 

[O C Diver]

Did all this happen immediately after someone worked on the boat (replaced batteries)? Or was it working fine and then spontaneously stopped working?


I suspect that the issue is the control solenoid for the stern thruster. The positive control is probably powered from the house or bow thruster bank, and the negative is wired to the stern thruster bank. Since the stern and bow thruster bank negatives aren't connected, there is no electrical path to operate the solenoid.


If the 8ga jumper cable appeared after the techs replaced your batteries, and the problem appeared at the same time, then the techs did their assigned job of breaking your boat. It seems to be what they do best. Reconnect the wire, and if you have a clamp-on DC current meter, verify how much current is running in the wire during all thruster operations, both bow and stern, and in both directions. I think you will find there is only an amp or so of current corresponding to the solenoid, and only when operating the stern thruster.

I like you analysis, but most thrusters run a control harness from the thruster to the control to eliminate that and other wiring problems. Now if there's an aftermarket wireless remote control, somebody could have wired the system differently.

Ted

 

[Comodave]

The thruster can be a completely standalone system. In other words, not connected to anything else in the boat. That is how all of the thrusters I have installed are wired. There should be no reason for needing a ground wire to the other batteries. Unless someone wired the thruster wrong in the first place and now you have to workaround that. The controls should be powered off the thruster battery, which is standalone per your reply. But I suspect that they powered the controls off some other battery. What brand thruster is it?

 

[Bmarler]

The thruster can be a completely standalone system. In other words, not connected to anything else in the boat. That is how all of the thrusters I have installed are wired. There should be no reason for needing a ground wire to the other batteries. Unless someone wired the thruster wrong in the first place and now you have to workaround that. The controls should be powered off the thruster battery, which is standalone per your reply. But I suspect that they powered the controls off some other battery. What brand thruster is it?

i have bow and stern thrusters powered by separate banks, but the control handles both. so you really can't have true standalone wiring. in reality it doesn't matter where the controller gets its power. it's the solenoid power connection that carries the high loads.
we can only speculate what the problem is, without being there to see how it's wired and controlled we're only guessing about what is most likely happening.

 

[DonW28]

Both thrusters are side power. I hooked the 8-10AWG jumper back up and of course everything works fine. We cycled the thruster several times for 3 second bursts and the wire had no warmth to it at all. A friend is bringing a clamp on meter tomorrow to confirm this is a very low amp draw for whatever reason. I know it isn't feeding the thruster motor or the wire would have melted.



I hate to give up on something but it works great with the little jumper wire feeding the negative into the boat system and appears to be perfectly safe. Why is a mystery I can't solve right now. And Key West has to rank among the worse places ever to hire marine help. Getting a good electrician over here to try and figure this out would takes me a month or two of begging.



Thanks for all the help.



Don

 

[O C Diver]

I think you will find that the power to operate the relays from the control (joy stick etc), is coming from another battery on the boat. Tying the negative batteries together provided the negative to the relay from the same battery that was feeding the positive to the relay.

Ted

 

[Comodave]

I think you will find that the power to operate the relays from the control (joy stick etc), is coming from another battery on the boat. Tying the negative batteries together provided the negative to the relay from the same battery that was feeding the positive to the relay.

Ted

+1.

 

[Roughnit]

Both thrusters are side power. I hooked the 8-10AWG jumper back up and of course everything works fine. We cycled the thruster several times for 3 second bursts and the wire had no warmth to it at all. A friend is bringing a clamp on meter tomorrow to confirm this is a very low amp draw for whatever reason. I know it isn't feeding the thruster motor or the wire would have melted.



I hate to give up on something but it works great with the little jumper wire feeding the negative into the boat system and appears to be perfectly safe. Why is a mystery I can't solve right now. And Key West has to rank among the worse places ever to hire marine help. Getting a good electrician over here to try and figure this out would takes me a month or two of begging.



Thanks for all the help.



Don

I’d contact side power for your specific controller. But I installed a side power dual control last year and the instructions required a negative jumper between battery banks when using separate battery banks bow and stern.

 

[DonW28]

I’d contact side power for your specific controller. But I installed a side power dual control last year and the instructions required a negative jumper between battery banks when using separate battery banks bow and stern.

Thanks for posting this. Makes me feel pretty good about putting the jumper wire back.


Don

 

[ronobrien]

Try disconnecting your charger from that stern thruster battery (and anything else). Then with only the St Th +/- connected to that battery go ahead and test, then test with the jumper you explained earlier. My guess is nothing will happen. If nothing happens it is because St Th battery is dead and is getting power from the jumper at the (-) side and your charger at the (+) side. Not an expert here at all, just an opinion. Good luck. ~A

That sounds like a very likely cause. A basic I was told years ago was that when diagnosing electrical problems ALWAYS verify the battery first, then verify the test equipment. Otherwise you can chase electrical ghosts for ever. Good luck.