Windlass safety thermal cut out switch

[ICENI]

On my last boat I fitted a thermal overload cut out switch in the windlass supply wiring near the battery to avoid overloading the windlass motor and also provide a safety facility to avoid overheating the windlass wiring supply cables.

On my Bavaria which did not have a windlass, last year I installed a Lofrans Tigres windlass on a platform I bonded into the anchor locker and once more, in the supply wiring I fitted a 100amp rated thermal cut out.

Whilst last at my boat I drew up the chain into the anchor locker and was dissappointed to find that the cut out tripped continually when running the windlass to draw the chain up.

Obviously thie cut out I fitted was not up to the job and needs replacing with a more reliable one because the weight of a 3 metres of 8mm chain should not be too much to cause continual tripping!

Looking on the internet I found one make of switch that seems to be suitable.   It is available from Force 4 and is made by Osculati.

Please can you nice people comment on  this problem for I do not want to spend another £70.00 only to find the switch is not up to the job?   Also any other make of switch cut outs that perform satisfactory results.

[elias]

Hi,
Since you have a Tigress , I guess 1200watt , means that you draw 1200w/12volt = 100 amp . Actually , since you will have a drop of voltage ( you can see when you put a heavy load to your battery the voltage drops, sometimes in my case drops to 10-11 volts ) , meaning that is 1200w / 10 volts = 120amps . I think that’s the reason for the cut off. Also are you sure your bank is big enough for that ? Do you have your engine on and RPM to around 1200-1500 so the alternator supports the energy needs ? Look at mine that was with 2*140ah batteries and a tigress windlass

[Yngmar]

According to the Lofrans manual, the Tigres has a 1500W motor, which at 12V will draw up to 125A in optimal conditions. As conditions are never optimal (voltage drops under such loads), you breaker should probably be a bit higher. The 135A one from Elias sounds about right and 130A (a common size) would probably work too. 100A is too small, which is why it's tripping all the time. That's the right size for the smaller Cayman model.

The breakers Lofrans sells appear to be E-T-A breakers, which you can find plentiful online. No matter the brand, you should go for a thermal-magnetic one rather than just a thermal breaker. Magnetic ones will switch off immediately in case of short circuit while offering a delayed profile on overload (which is what you want for a windlass).

[Markus]

I've currently got a 125 A blade fuse (Quick windlass) and have also been thinking of switching to circuit breaker so had a few links ready for this.

Lofrans Tigress (12 V) recommended circuit breaker is 100 A magnetic:
https://www.lofrans.com/product/71-horizontal-windlasses/5017-tigres
https://www.lofrans.com/product/77-circuit-breakers/5033-circuit-breaker

However, the website does not give out much details of the magnetic circuit breaker. With all probability the tripping curve (trip current as a function of time) is such that it is quite slow to trip in overload situation allowing higher currents to pass for some seconds to a few tens of seconds. I am attaching here Quick magnetic-hydraulic circuit breaker curve for reference.

I believe windlass motors are normally just simple DC-motors without any fancy electronics. If there's some additional voltage drop (meaning additional resistance) in the circuit, it should decrease the total current in the circuit and thus be not the cause for tripping the circuit breaker. Reasoning: current I = U / R_tot; in which U equals battery terminal voltage and R_tot is a sum of cabling, contact resistances and the windlass motor circuit resistance.

What should also be noted is that if you have a thermal breaker, it will trip at lower current (probably around 10% lower) at higher ambient temperatures compared to normal room temperatures.

Edit: added also the curves for Eaton 187-series MRCB thermal circuit breaker which I have been considering => as you can see, it would need to be rated for around 130% higher nominal current compared to Quick magnetic-hydraulic circuit breaker to provide roughly same characteristics, so perhaps for your case +30% would also be a good assumption if you end up using thermal breaker.

[ICENI]

Very many thanks people.

As I said in my original post, on my old boat I had and used for some thirty years a Lofrans Tigres.   I used a 100amp thermal cut out but not the same make.   Obviously the one I sourced is too sensitive.

As someone with considerable electronic knowledge (It was my job) I realise that running it ashore with no alternator charging was pushing things!   

I will take the above advice and go for something in the 120-135amp range.

Thanks again.