Fuses for a bow thruster

[Ian_Edwards]

The bow thruster on Eynhallow is a 12 volt Lewmar TSL150, dating from 2007, it's not a current model, so I'm having difficulty finding out if it's a 5kw or 6kw unit.

It's currently powered by the 500 amp hr domestic battery bank, which is located about mid ships and it has some really heavy duty cables running about 5m to the thruster.

if it's 6kw then it'll draw 500 amps at 12volts, if it's 5kwatt then it'll draw 417 amps. Hefty currents.

The system works OK when the batteries are fully charged ( the engine is always running when I use the thruster), but when the batteries are part discharged after a days sailing, the voltage drops when I use the thruster, to the point where the Raymarine kit drops out. When the Raymarine kit comes back to life it isn't always in good health, it kind of works, but some function aren't fully operational. I have to switch the system off and on to reset everything to get back in full working order.

The obvious solution is to put some additional battery capacity nearer the thruster and there is space to do that in the thruster compartment.

My current plan is to wire the new batteries in parallel with the existing domestic bank, so the new and the old share the load. However, because the new batteries will be very close to the thruster and connected with short heavy duty cable (about 1m long) I expect the new batteries to take the lions share of the thruster load. The 5m cable to the existing domestic bank will have a significantly higher voltage drop at high current than the short cables to new batteries.

I think the combined banks will still charge OK, The voltage drop at charging currents will be small and given time the two battery banks will balance out.

I'm obviously going to have to fuse the cables from the new battery bank to the thruster. Lewmar recommend a 500amp fuse for the 6kw motor and a 400amp fuse for the 5kw motor. However, these fuses will be up forward under the chain locker and not readily accessible. So I was thinking of using a circuit breaker which can be remotely reset.

Having set the scene:
1) are there any potential problems with this proposed set-up?
2) does anyone have any info on the TSL 150? I've emailed an inquiry to Lewmar, but I'm yet to get a reply.
3) does anyone know where I can source 500 amp (at 12volts) circuit breaker with a remote reset.

 

[pvb]

I think the TSL150 has a 6kW motor, and that would certainly be a fair assumption for you to work on.

Using the existing cables to provide charge (and additional current) to the new batteries would be fine. For safety, you need to fuse the cables at both ends, to prevent a fire if the cables were damaged and shorted. I'd use 500A MegaFuse or ANL fuses for this.

I'd also use MegaFuse or ANL fuses for the short cables to the thruster. The blow characteristics of these fuses are fairly generous - they should tolerate a 20% overload for some time. Whilst it's possible to get remotely resettable circuit breakers, you're into industrial equipment territory and the cost will probably be horrendous. If you're really concerned about an operational problem if the fuse to the thruster blows, you could simply have a relay across the fuse terminals, operated from somewhere convenient. There are lots of cheap 500A relays about for automotive use.

 

[William_H]

The thing about high current fuses is that being big they are more robust. I would think that if you fitted 500amp fuse you could assume it will have a very long life and if it blows you have got real problems. I think a single fuse at the new battery terminal will protect both the wiring forward to the thruster and back to the other batteries. How ever make sure the other batteries have a fuse as well.
Re the failure of electronics at low voltage it is far better to operate all the elctronics from asource (battery) isolated from engine start anchor winch and thruster. ie fed witha VSR so that low voltage siolates these services. good luck olewill

 

[Ian_Edwards]

Thanks for the input, there is already a 500amp fuse at the domestic battery end of the of the thruster power cables, and I haven't managed to blow that yet, so I guess fitting a 500amp fuse in the new supply will be reliable enough.

I have considered a separate battery for the instruments, but that is very hard to do in practice. The boat works on an EMPIRBUS, which is (i think) is a CANbus system, so the power cables are all in parallel to each of the 7 EMPIRBUS nodes. The instruments are switched from different nodes, and I don't have a full circuit diagram for the wiring. I've asked Southerly (in there various forms) if they can supply me with one, but they haven't been able to find one. I guess there's little chance of getting one now. Southerlies only made six 46 RS's the last one in 2008 or 2009, so it's not a common design.

 

[philip_stevens]

I have a similar set-up to what you are quoting.

I have 3 x 105amp service batteries, and 1 x 80amp bow thruster battery. All can be paralleled to operate the bow thruster and anchor windlass, and the 80amp battery can be isolated to supply just the b/t and a/w.

Cables are circuit breaker protected at both ends, and the b/t and a/w also have a 300amp fuse.

The reason for the 80amp battery, is that the original heavy duty cable was just for the anchor windlass, and was not quite big enough for when I fitted the bow thruster - hence the 80amp battery to reduce the load on the original a/w cable.

The engine start battery is just that alone - nothing else is run from it, and it is a proper start battery, and not a leisure battery.