Bowthruster Batteries

[Sailfree]

Is there an easy way of checking them?

New boat in 2005 had spiral wound bowthruster batteries fitted. They are now 13yrs old!

Bowthruster works OK but is it relying on the alternator rather than batteries?

Replace the other boat batteries some 4yrs ago so think I should replace the bowthruster ones now - any opinions?

 

[duncan99210]

If the boats in the water, try running the thruster without the engine whilst securely moored. That'll give you an indication of the health of the batteries: check the resting voltage before use and after, see how quickly they recover on resting after use.

 

[Sailfree]

manual specifically states not to run windlass or bow thruster without engine running.

i assume as load is so great it can buckle plates.

 

[lw395]

Test each battery with a hgih current tester.
Or use a clamp ammeter to see what current is coming from where.

 

[Tranona]

manual specifically states not to run windlass or bow thruster without engine running.

i assume as load is so great it can buckle plates.

This is not an absolute, just caution. At tickover your alternator puts in less than 20 amps whereas your bow thruster could be drawing as much as 140A! Your battery should be able to stand that draw on its own for the short period you operate the thruster.

 

[duncan99210]

manual specifically states not to run windlass or bow thruster without engine running.

i assume as load is so great it can buckle plates.

Do you have any means of monitoring the current flow to the thruster? I'd be amazed if the alternator would be making much difference to the current flow to the thruster batteries whilst the thruster is in use. Our windlass draws in the region of 95 amps, we have an 80 amp alternator so in theory when running the engine with the windlass is use, we should be looking at only drawing 15 amps from the batteries: this is not the case. Typically, the batteries are supplying 75 - 95 amps despite the best efforts of the alternator.

So, whilst it may be be the recommended practice to make sure the engine is running when the thruster is in use, the simplest and nearest to real world test of the batteries would be to use the thruster without running the engine. That'd give you a reasonable picture of what's going on in the batteries.

Alternatively, measure the resting voltage of the batteries, use the thruster whilst running the engine, stop the thruster and engine, measure the battery voltage as soon as you stop and then measure again after a break of say half an hour. The batteries, if they're in good health, should show some recovery. If they don't, then it may be time to replace them.

 

[Sailfree]

thanks for advice.

at 14yrs old should i just replace them or do spiral wound batteries last longer

 

[Barbican]

Without knowing what size thruster you have I'm not sure what to expect. My bow thruster (6.3kw motor) draws a little over 600amps when running (builder should've used 24v) so a reasonable proxy for a drop tester, which would be an easier way to check them. In the end I borrowed one from a friend. If your batteries are Optimas (or Odyssey) I really doubt the Alternator makes much difference to the life of the batts. My stern thruster (6kw motor) uses two 75ah Optimas with no connection to the alternator at all and they are fine after three years or so. 14 years is a good run so I hope mine are as good.

 

[Plevier]

AIUI the main benefit of running the engine is to help keep the voltage up which is kinder for the motor. Whether this is still true with modern controllers I'm not sure. It's certainly true for a direct switched windlass - for a given load, lower voltage = higher current = greater heating effect (proportional to the square of the current.)
Buckled plates should not realistically be a consideration in my experience.
As regards testing your old batteries, no easy way other than using the device itself.
Garage starter battery testers typically apply around 200A load but are only rated for a few seconds. You presumably want to know that you can get maybe 30 seconds or a minute out of it? I'm guessing a bit, never having used a thruster.
If you're in the 600A range - wow! Big kit needed to test that. That's a pretty big thruster for a yacht isn't it?
Optimas are very good batteries but 14 years? I would expect the capacity to be a fraction of what it should be, however well they have been looked after.

 

[Barbican]

If you're in the 600A range - wow! Big kit needed to test that. That's a pretty big thruster for a yacht isn't it?
Optimas are very good batteries but 14 years? I would expect the capacity to be a fraction of what it should be, however well they have been looked after.

It's a bit silly to use 12v thrusters at that rating but the builder fitted the most powerful 12v thrusters they could find, rated at 6.3 and 6kw, hence the high amps, I tried to get the batteries and cables (had to double up the 120mm jobs the builder fitted) set up so the voltage drop isn't huge, and when all is clean they are still up around that 600amp figure, and a little over 11v when running.

Normally my thrusters run just for a few seconds for maybe 3 or four bursts (when Mr Cockup visits it may be longer but no more than30secs so far). In my case it took a while to discover the battery charging circuit was wired to the wrong side of the contactor box, so charging was only happening when the thruster was energised, which is for 6 minutes in my case.

So whilst the drop tester does take out less we gave the thrusters several bursts then did the tests from which they recovered very slowly and were declared knackered - sulphated I guess (18months), so with a smaller 400amp thruster, on a pair of batts individualy tested it may be a fair reflection. The Optimas have coped well so far, and it's good to have confirmation from you that they are a good battery, thanks for posting..