Voltage drop

[sailaboutvic]

Did put this else where in another posting but didn't get a reply .
What is an acceptable voltage drop over 22 mts ( 11 mts V- and 11 mts V+ ) 35sq cable 1000 w motor ?

 

[matthewriches]

Is your ship supply 12v or 24v?

 

[macd]

Hi Vic. I presume that's for a windlass. On-line calculators show drop at full rating (1000W/83A) is around 8% (giving a fraction over 11V at the motor for a nominal 12V at the battery).

That's quite a lot. 1/0 AWG (53.5 sq.mm) gives 5%, 2/0 AWG (67mm) gives 3.88%. To get the 3% which is probably recommended but arguably a bit over the top, you'd need 3/0 AWG (85sq.mm). Now you know why many windlasses have their own battery (although I prefer to suffer the larger cable size on the grounds that it's a simpler set-up).

When we bought our boat, the wiring was about the same size as yours for a slightly longer run and the drop measured well over 1V. The windlass was decidedly sluggish. I installed some much heavier stuff, but combined the circuits to windlass and bow-thruster (which was also under-rated), on the grounds that I'd be unlikely to use both at the same time.

Edit: re Matt's post, I'm assuming 12V system because I seem to remember that's what you have. 24V makes a significant difference: just 3.9% drop.

 

[mikegunn]

Hi Vic,
Assuming you have a 12V system you should expect to see a voltage drop of approximately 7.5%. If you are driving an electric motor, as opposed to sensitive electronics, it is generally considered that a drop of 5% or less would be acceptable. To achieve that you will need to double your cable size to 70 mm.sq.
Mike.

 

[savageseadog]

A 0.5V drop on a 12V system is what I work with. Can be difficult to achieve. The OP should remember that the initial current will be very high indeed and the initial current and operating current will be higher if loaded. There would be a danger of a stall if heavily loaded with undersize cable.

 

[sailaboutvic]

Hi Mac and other
Yes Mac for my windless and it 12v I should had said , although the boat is 13 mts I would say the run is more like 10 mts each way if that , now and then it still throw the breaker ,
Although it's 12v with the engine running as we do it more like 13 plus V , we getting 0.5 drop on each cable and at 13v I would had tho it was acceptable, tell me other wise , it needleing me , one of our other friend got same size boat with 10mm chain same as our and same windless but there anchor is 35 kg where are is just 25 kg and their never trip .

Before anyone make suggestions on motor this is a new windlass and the problem had happen for the start ,
The old windlass was also 1000w with a smaller breaker and that never trip .
In the pass I also taken smaller run from the bow/T Witch have very large cable (90 mm ) and used the 35mm cable on a run of a few mts adding the breaker just to check and it also tripped . Very puzzling .

 

[lw395]

Is the breaker the correct slow-blow type for motor loads?

Does the breaker trip with no load on the windlass, e.g. lowering the hook?

More voltage drop, i.e. more resistance in the cables will lower the peak inrush current, reducing the tendency for the breaker to trip. Up to the point where the motor starts slowly in a current-limited mode and the inrush is prolonged, or the motor even stalls and burns out.

Windlasses for yachts are normally designed around the idea that there will be a voltage drop.
Any info from the manufacturer?

 

[sailaboutvic]

Is the breaker the correct slow-blow type for motor loads?

Does the breaker trip with no load on the windlass, e.g. lowering the hook?

More voltage drop, i.e. more resistance in the cables will lower the peak inrush current, reducing the tendency for the breaker to trip. Up to the point where the motor starts slowly in a current-limited mode and the inrush is prolonged, or the motor even stalls and burns out.

Windlasses for yachts are normally designed around the idea that there will be a voltage drop.
Any info from the manufacturer?

Breaker is the right type , I also experimented with another breaker still the same.
It tent to trip with the slight resistance on the chain as it coming up , but there been times when we tested it and been tight back and you can almost snap the lines they where so tight and it does trip , that's the problem it don't trip all the time .
But sod law tell me there be a time when it trip at the wrong time , any way what ever the case I like to get it sorted .
Last year I give up and had two diefferent engineers out , one that fits lots of windless but off. Course while they are out it doesn't trip but both said they put much bigger breakers on then I got , although mine is already larger then lorans say that windlass Needs,
I am a bit worried about putting any bigger breaker on .

Lofans have been helpful but as what you expect they say it's not their windlass that's the problem but it some where else and to get it checked out , which I have twice . But not to put a bigger breaker on .
So I just can't win .

 

[halcyon]

Hi Mac and other
Yes Mac for my windless and it 12v I should had said , although the boat is 13 mts I would say the run is more like 10 mts each way if that , now and then it still throw the breaker ,
Although it's 12v with the engine running as we do it more like 13 plus V , we getting 0.5 drop on each cable and at 13v I would had tho it was acceptable, tell me other wise , it needleing me , one of our other friend got same size boat with 10mm chain same as our and same windless but there anchor is 35 kg where are is just 25 kg and their never trip .

Before anyone make suggestions on motor this is a new windlass and the problem had happen for the start ,
The old windlass was also 1000w with a smaller breaker and that never trip .
In the pass I also taken smaller run from the bow/T Witch have very large cable (90 mm ) and used the 35mm cable on a run of a few mts adding the breaker just to check and it also tripped . Very puzzling .

Are we talking 1000 watt motor output rating or 1000 watt motor input load ?

Brian