Thruster Problem

[henningbuus]

Both thrusters respond very weakly and eventually completely stop. I noticed that the voltmeter showed 12 volt for the thruster battery and 13 volt for the other batteries, so I thought I had a bad thruster battery. I then used my multi-tester to check the voltage directly at the battery, and it showed 13volts. Even when engaging the thrusters, the voltage at the battery only dropped to 12.8.
I engaged the parallel power switch, and nothing changed the boat voltmeter stayed at 12 volt.
My ranger tug 31CB also has a generator. It is powered through the stern thruster main switch. When I tried to start the generator, the voltmeter stayed at 12 volt for a few seconds, and then totally dropped to the bottom of the scale. The generator starter motor didn’t crank.
The mystery is why does the battery show 13 volt at the battery but only 12 volt on the boat voltmeter? And whatever the problem is, why does it affect both thrusters?

 

[Ralf H]

Hi there!

I hope I'm following you correctly. But to answer the question on why this is happening to both thrusters, it's because they both operate off the same battery. There is only one thruster battery. The symptoms that you are getting from the thruster battery - both when trying to use the thruster and when starting the generator - may be confirming that you have an issue with the battery, as it looks like it can no longer handle the load. It's not unusual for a battery to be able to charge to a nominal voltage but still not be able to produce any power when the battery is put to use. This usually indicates a battery that is at the end of its service life. The other issue could be loose connections, most likely at the battery terminals. Make sure those are tight and that all cables and connectors are serviceable. If everything appears right, then it's probably time to replace the battery. Hope this helps.

Cheers,

Ralf

 

[henningbuus]

Thank you for your input, Ralf. I agree that the problem has to be with the Thruster battery. I am more inclined to believe that the problem is with the battery terminal as you mentioned, because the battery voltage did not drop much when the thrusters were activated. I will try and clean the battery terminals, and hope that will take care of the problem.

 

[NorthernFocus]

Thank you for your input, Ralf. I agree that the problem has to be with the Thruster battery. I am more inclined to believe that the problem is with the battery terminal as you mentioned, because the battery voltage did not drop much when the thrusters were activated. I will try and clean the battery terminals, and hope that will take care of the problem.

If I understand what you wrote voltage measured directly at the battery does not drop when you activate the thrusters or try starting the generator? If that's the case then it sounds like an issue with loose/dirty connection somewhere in the circuit. Don't forget to check the ground side as well as the positive. If the battery terminals aren't the culprit then continue checking all of the connections between battery and load. The isolation switch is common to all loads so is a likely suspect.