Hi, any electrical engineering experts out there?

[Ian_Edwards]

I’m trying to understand the characteristics of a thermo magnetic switch and in particular what “IEC/EN 60204 type C curve” looks like. I’m interested because I’m in the process of adding a dedicated battery or my anchor windlass, a 1000watt Aries, which will be install up forward, to minimise the high current cable run. But this means relocating the 80amp thermo magnetic switch where it is less easy to get at (it’s currently behind the switch panel by the nav station).
What’s worrying me is that the windlass data sheet shows 80amps circuit protection (as you’d expect because it’s a 1000 watt motor running on a nominal 12volts) but it also shows a maximum current of 140amps at working load. Obviously if the thermo magnetic switch saw 140 amps for very long it would disconnect and need resetting, I’d need to get at it, perhaps quickly.
But for how long would it take the switch to disconnect and is it likely to happen?

 

[starfire]

A MCB 'C' curve, is set to trip within a few seconds on overloads of 5 to 10 times the rated current.

You will get a peak when the motor is first started, for a few milliseconds, however during normal use the windlass will draw less than it's rated power, I think you will find that if it takes the trip out, the motor is overloaded anyway. time to find another way to break the anchor out !

Has the MCB tripped while it is behind the panel ?

 

[Ian_Edwards]

No, the switch has not tripped, we anchored many time this last summer on the West Coast of Scotland and the winch has been well loaded at times, more or less to point of stalling, but the cable runs have been at least 10m each way (35 square mm cable), in the new setup the cable runs will be less than 1m each way, still with 35mm cable, so I expect it'll be able to drawn much more current.

 

[NorthUp]

The shorter cables will not make any significant difference to the current draw.

 

[Anonymous]

[ QUOTE ]
The shorter cables will not make any significant difference to the current draw.

[/ QUOTE ]Looks to me as though the old 10m leads (=20m return) would drop nearly 4V at 120A. That's one third of the emf. Hardly insignificant.

 

[whipper_snapper]

[ QUOTE ]
1000watt Aries, which will be install up forward, to minimise the high current cable run.

[/ QUOTE ]

How will you recharge the battery ?

The recharging currents will be significant. True, you won't see the initial start-up peak and true you could live with a bigger voltage drop (10%?) while charging than would be acceptable for a windlass. But I presume that in practice you will keep the existing big cables for this job, to avoid the need to run new still thick cables ?

So I wonder what you really gain by making this change ?

 

[Anonymous]

[ QUOTE ]
So I wonder what you really gain by making this change ?

[/ QUOTE ]He gains power. The windlass motor will produce considerably more power. You can't calculate it without knowing the motor characteristics but it will be significant. Very handy if you are in a deep anchorage, and your anchor is bringing something up with it.

 

[matelot]

[ QUOTE ]
[ QUOTE ]
So I wonder what you really gain by making this change ?

[/ QUOTE ]He gains power. The windlass motor will produce considerably more power. You can't calculate it without knowing the motor characteristics but it will be significant. Very handy if you are in a deep anchorage, and your anchor is bringing something up with it.

[/ QUOTE ]

Not convinced. If he does what most of us do and use the windlass with the engine running he will get a higher voltage at the windlass on the original system. Once he has the battery forward, a 100 amp draw will quickly reduce the battery voltage and this wont be held up by the lighter wires from the alternator. In addition his forward battery wont be quite as fully charged at the end of those longer wires.

Best answer is to uprate the wiring between engine and windlass - thats a fit and forget approach which another battery isnt.

 

[Anonymous]

[ QUOTE ]
Not convinced. If he does what most of us do and use the windlass with the engine running he will get a higher voltage at the windlass on the original system.

[/ QUOTE ]Firstly, let's just say that my yacht was wired as the OP's original and I have not put a new battery in! indeed, when I wanted a radio control for the windlass I put a small gel battery (small instrumentation battery to power the radio and solenoids only) with dc-dc convertor (to charge the instrumentation battery). But then I am an electrical/electronics engineer by training so it was pretty easy for me to do.

However, back to the question and comment...he will gain more power because the original wiring will still (presumably?) be in place -- i.e. nothing has reduced the power and he could remove the battery and have marginally better performance due to the short length of bigger cables from the new battery position to the windlass. So you see that he cannot lose. However, the battery near the windlass will start to deliver current when the terminal volts fall to around 12.2, tending to clamp the volts at the windlass to around 12V. At present, with the existing wiring, if the alternator can supply, say, 80A (will it, on tickover?) then there is still a deficit of 40A. If you sketch out the circuit and draw the approximate resistances, currents and emfs you'll see what I mean. He will get considerably more power -- we can't calculate how much, though.

 

[Ian_Edwards]

Hi, just logged on to see the interesting discussion. The original cabling is still in place, so I have relatively low impedance battery charging circuit (about 20m of 35mm^2), I‘ve fitted a voltage sensitive relay in the charging circuit, so that the windlass battery (100amp hr AGM) is isolated when the engine isn’t running and I’m up grading the alternator charger system with a Sterling alternator to battery charger. The alternator is rated at 115amps.
So the windlass battery looks like part of the domestic battery bank when being charged by either the alternator or the mains charger and separate system when there is no charging source present.
Why am I doing this? The boat currently has system which needs the engine running and the alternator charging before the windlass can be used. The hand book recommends running the engine at 1500rpm when operating the windlass, even then the Raymarine systems complains about low voltage when the windlass comes on load and you can’t easily use the engine to manoeuvre into the wind/tide to ease the load on the windlass. We’ve also had problems with the reliability of Volvo Penta 2D-40, the engine management system has failed, which means you can start the engine.
So I’m hoping to be able to use the windlass without the engine running if I have to, prevent low voltage alarms and possible damage to the electronics, allow the boat to be manoeuvred whilst using the windlass, and to get more power from the windlass.
The original post was to get a view on whether the original 80amp thermo electric switch was more likely to trip ..... not sure I’m much wiser ... the original reply seem to suggest it’ll be OK.

 

[Anonymous]

I think we have two issues here. A seamanship/technique issue for handling the anchor, and an electrical issue.

Generally, windlasses are not rated to fight wind or tide and bring the chain up. It is always assumed that you will be more or less over the chain when winding in. Of course, in zero wind and tide, which we often have in the Med in summer, we wind it in bit by bit letting the catenary pull the boat towards the anchor but in tidal waters or with a bit of wind, that is seldom possible. I have fitted a radio controlled up/down control to mine (it was up only with a pneumatic switch by the windlass). This allows me to control the windlass from the helm or the bow.

It can be tricky to motor the boat over the chain but it is always do-able albeit with some practice and skill. Even if you have to motor past the chain, wind up, then re-position again when the bow has fallen off the wind, or you have fallen back. You keep going like that until you are straight up and down, when you might need to break the anchor out with the engine, or the windlass might cope (often you need to motor it out if the anchor is well-set).

On the electrical side, the Sterling won't alter things at all. When the terminal volts at the alternator are down at the 12.5V level the alternator will be giving max output for the RPM regardless of a Sterling. I think that the new battery should help by providing the current you need locally.

[ QUOTE ]
We’ve also had problems with the reliability of Volvo Penta 2D-40, the engine management system has failed, which means you can start the engine.

[/ QUOTE ] Do you mean can't start the engine? I don't see how this is relevant to the design of your windlass supply. If you have dodgy engine electrics then that is a bigger priority than the windlass supply in any case (assuming that you have a manual facility on the winch or can pull it in by hand?).

[ QUOTE ]
So I’m hoping to be able to use the windlass without the engine running if I have to, prevent low voltage alarms and possible damage to the electronics, allow the boat to be manoeuvred whilst using the windlass, and to get more power from the windlass.

[/ QUOTE ] So you are sailing off the anchorage? That, in itself, is a technique that needs to be learnt....you wouldn't expect the windlass to fight against the drive of the sails, with any sort of decent breeze.

I'm not entirely sure about this, as a plan. The electrics should be fine, but the plan sounds questionable.