Got a bow thruster? Check your battery.

LaRea

My bow thruster battery gave me quite a scare today.  I'm lucky it didn't catch fire.  

The thruster and battery live inside a plastic cover under the v-berth.  It's a very "out of sight, out of mind" location, and I've never given it much thought -- until today.  

First symptom: I smelled a very faint odor, like maybe a problem with the toilet, but couldn't find the source.  

Second symptom:  While grabbing some tools from under the v-berth, I happened to glance at the charger, and noticed it was pushing 20 amps.  I thought it was odd because the boat had been on shore power for 24 hours, so the battery should have been fully charged.  

It was still at 20 amps an hour later, and it finally dawned on me -- oh no, could that odor be from my battery?!?

So I stuck my head down into the compartment -- sure enough, I could hear the hissing sound of water boiling off.  Then I noticed that the entire plastic cover was hot, and I got scared fast!  I shut down power and removed the cover.  The battery was so hot that I couldn't keep my hand it for more than a second.  

I pulled the battery a couple hours later after it cooled down to where I could touch it.  Luckily it didn't crack.  

What if I hadn't noticed it?  I'm pretty sure the charger would have continued happily dumping 20 amps of current into the battery.  Eventually, I guess it would have melted and/or caught fire.   

Lesson learned.  And now I'm shopping for a new charger with a remote display.  

Dream_Inn

Yes, that is very scary.  I recently changed out that battery (obviously keeping it a maintenance free AGM), but I've often thought about that charger (because I've changed the other charger a few years ago, and it's it the same brand...so, a matter of time)  I will say that I don't leave that charger on all the time.  I typically put it on after I use the thruster to get a full charge but then turn it off.  Never been a problem doing it that way and there is nothing drawing any current off of it.

Glad you found it before anything serious happened!

Ian

Not familiar with how these are wired up and the amperage when running but shouldn’t there be a lower amperage breaker from the charger?

randy56

Are thinking the charger malfunction, auto shut off, or battrie is bad? good thing you were there.

LaRea

I think the charger is okay.  After I replaced the battery, it was charging at 5 amps to top off the new battery.  I'm guessing it was a shorted battery.   

There wasn't anything that would have thrown a breaker.  The charger was running at its normal capacity.  A modern charger would include a temperature sensor to prevent this situation.  Also the software probably would not let it charge non-stop for 24 hours.  

As I've said before, chargers seem to have a duty life of 10-15 years.  So I have no heartburn about replacing my 12-year-old charger.  

reneechris14

Glad you were at the boat sniffing around. See glad I don't have a bow thruster.

Ian

LaRea said:

I think the charger is okay.  After I replaced the battery, it was charging at 5 amps to top off the new battery.  I'm guessing it was a shorted battery.   

There wasn't anything that would have thrown a breaker.  The charger was running at its normal capacity.  A modern charger would include a temperature sensor to prevent this situation.  Also the software probably would not let it charge non-stop for 24 hours.  

As I've said before, chargers seem to have a duty life of 10-15 years.  So I have no heartburn about replacing my 12-year-old charger.  

I'd say a CB for 10A would be right to allow for boost charge and top off (5A) and not allow a short to ramp up beyond that.