Bow Thruster - Would another battery in parallel make much difference to the amount of thrust?

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therowans

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Volvo Penta BP800 with a Exide EM1000 AGM close by and wiring looks good and thick.

Voltage starts after charge at 14.7v and during about 45 seconds of bursts of thrusts goes from 10.6V to 10.2V, and back to 13.7 when stopped.

Any thoughts would be very much appreciated.
 
therowans said:
Volvo Penta BP800 with a Exide EM1000 AGM close by and wiring looks good and thick.

Voltage starts after charge at 14.7v and during about 45 seconds of bursts of thrusts goes from 10.6V to 10.2V, and back to 13.7 when stopped.

Any thoughts would be very much appreciated.
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Measured at the battery or at the thruster?
 
That. And it may also be sha**ed.

Remove the underspecced one completely and install one properly sized battery. Also, check the cable size used. If the battery is 1/6th of the recommended capacity it may also have thin cheap cabling.

Also, make sure your crimps and connectors are 100% solid.

I’ve had a load of pain with a similar problem; turned out in my case that in addition to a charging problem, the connectors were badly terminated. Now it’s fixed, the BT has become fantastically better.

EDIT I don’t think the battery is undersized.
 
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I fitted a battery bank dedicated to the thruster. Specialist high energy surge batteries. Very short very heavy cables. It did make the thruster more lively for sure but that was a side benefit. The principal reason was to get the huge voltage-drop-inducing 600A load off the domestic bank. The nav kit was rebooting because of the 10v trough when the thruster was used.
 
westernman said:
You don't need much capacity (Ah).
You do need the possibility to draw a large amount of current 300A or so - but not for an hour.

You will be better off with a truck starter battery.
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That's not what the manual says. And why is a "truck starter battery" any better than a correctly rated AGM?

Since a 300A/Hr battery is going to be heavy, it may be better to fit a couple of 150s in parallel as Beneteau did as original equipment for my Quick bow thruster. If the OPs thruster is factory fit, what does the battery tray look like? Is the current battery already a replacement and obviously too small for the space allowed?
 
Sticky Fingers said:
Just noticed something. The OP says ‘50A’ the spec sheet says ‘300 Ah’. Not the same. Which is it?
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I think it's an error, probably Chinglish translation since the first two start off referring to AHr and to add to this, you don't get double the current by putting the batteries in series for the 24v versions they also refer to in that sheet, so I'm certain it's referring to AHr.

The motor current drain is not mentioned in the manual but Google/AI suggests it's a 5kw motor which means a current drain of 500 amps at start up. Assuming safe discharge of a lead acid battery to 50% capacity, the OPs 50AHr will give 3 minutes of useful life before crapping out (as it seems to be given his voltage readings).

Edited to say, yes it is a 5Kw (7HP) motor as mentioned in this thread:

VandKoala

Thread 'Bow propeller only works one side'

Hi, last weekend our old 5kw bow prop started only working to one side (of course while blowing 20knots from the “wrong” side) :)
To starboard - only trickling sound and almost no trust. To port gives ok trust. You can hear the difference in the video.

Where do I start looking?

Thanks!

800.jpeg
 
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House batteries need low amps (A) for a long time and a decent capacity (Ah).
Bow thruster and windlass batteries need high amps for a short time. Like starter batteries. You don't need much capacity (Ah).

Trucks need large CCA (cold cranking amps) for a short time and therefore their starter batteries are good candidates for powering a windlass or bow thruster.
 
Sticky Fingers said:
300Ah would need six batteries which can’t be right.

I’ve got a Sleipner SE100 24v thruster, it pulls 340A at 24v, needs a battery with CCA of c. 760, max 3 minute duty cycle. The ‘Ah’ of the battery isn’t specified.
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Needs 6 only if you used 50AHr. Or two 150AHr.

Re battery capacity, your manual says :

Use an appropriate dimensioned battery with Cold Cranking Amps (CCA) according to recommendations given in the Electrical Reference Guide chapter. Battery voltage must be compliant with the voltage rating of the thruster motor and control circuitry.

The capacity and rated discharge current of the battery should be according to the rated nominal current drawn and the typical duty cycle for thruster operation. The nominal current drawn is listed in the Electrical Reference Guide chapter.
The actual voltage at the motor while running the thruster determines the motor RPM and thrust. Using a smaller cross-section than recommended or a low-capacity battery could reduce performance.

Installing a battery close to the thruster reduces the length of the power cables and potentially increases the performance, due to lower voltage drop in the power cables. For installations on large vessels with bow and stern thrusters or catamarans a dedicated battery for each thruster should be considered.

An installer could work out a reasonable battery to use ie current drain of 740A (12v) 340A (24v) and a duty cycle of 3 mins means a min battery capacity of 80AHr to use 50% capacity in 3 mins. (Actual figures are 37AHr drain in 3 mins). It would be reasonable to double that to avoid caning the batteries on a windy docking day, so 160AHr would be reasonable in my view.
 
Sticky Fingers said:
That. And it may also be sha**ed.

Remove the underspecced one completely and install one properly sized battery. Also, check the cable size used. If the battery is 1/6th of the recommended capacity it may also have thin cheap cabling.

Also, make sure your crimps and connectors are 100% solid.

I’ve had a load of pain with a similar problem; turned out in my case that in addition to a charging problem, the connectors were badly terminated. Now it’s fixed, the BT has become fantastically better.

EDIT I don’t think the battery is undersized.
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If it’s measured at the battery it can’t be the crimps or the cables. It seems the CCA of the battery is too low.
 
I’d put an additional battery across the bow thruster battery with jump leads. If the voltage doesn’t drop to the 10s I reckon it proves the battery is not up to it whatever the numbers say.
 
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