What size circuit breaker for windlass?

[Brewgyver]

Originally Posted by KimSails

I'm guessing he missed the "squared" on the mm^2.

4 AWG is a bit over 21 square mm, and 5 mm diameter.

[Mike Banks]

200 amps immediate trip--180 amps working load. Use a separate ceramic-encased cartridge fuse of 200 amps and a 180 amps overload switch wired in series on the same ceramic mounting plate.

[Wotname]

Originally Posted by Cliffhanger

........

I think you are right, there must be some other problem. A dodgy circuit breaker perhaps? Bad bearings in the gearbox? Any other ideas?

Yes I have a few ideas!

First of all, you have received a few replies unthread - some of them are correct, some of them are factually incorrect and some of them are "sort of correct".

So allow me to give you my ideas (which are, by the way totally correct ).

It is unlikely (but possible) the windlass is faulty.
It is possible the circuit breaker is dodgy but probably not - so leave that to later.

More likely you have a power supply problem - batteries, cables, terminations etc.

The Muir installation manual is strangely quite on cable and circuit breaker sizes but they give us enough information to work it out. By the way, other posters have stated the purpose of the circuit breaker is protect the cable but in the case of a windlass I disagree, one circuit breaker can protect the windlass and the cable - providing the circuit breaker is less than the current carrying capacity of the cable used. In fact, Muir requires a circuit breaker for warranty purposes.

As for the working current needed, Muir tells us it is 120A for your model. The current draw of a windlass motor is determined in the main by the torque developed in the motor - more torque = more current. The available terminal voltage is only a small (but important) factor in the current draw of a windlass.

So this is the starting point, you need a suitably sized cable to ensure there is ~12V at the terminals of the windlass when it is operating at it's working capacity i.e. 120A.

I don't know what cable you have but clearly it isn't 4AWG (25mm) because such cable doesn't exist. If it simply 4AWG (21mm^2), then while it OK for the voltage drop over a total length 4m, it is too light for a 120A working load and certainly too light for 150A circuit breaker. Remember the circuit breaker won't trip at 150A, only in excess of 150A.

I don't know where Reefmagnet found the figure of 135A for the circuit breaker but I would agree it sounds exactly right!

My recommendation is to upgrade the cable to 2AWG and fit a 130A or 135A breaker but if you wish to keep the 150A circuit breaker, then upgrade the cable to 0AWG. Be aware the circuit breaker will be a little oversized and won't offer much protection as is ideal for the windlass.

Originally Posted by Reefmagnet

I think you'll find 135A is the recommended size for a 1200 watt winch on a 12VDC system.

[kenbo]

Wotname,

We don't know if the distance is 4m one way or round trip. If one way, I believe 2awg to be too light and 0awg with the 150 breaker to be correct. He could also add a 135 breaker at the windlass end of the cable run to protect the motor.

Remember it was running before he added the 150 breaker and now it trips. so that circuit is drawing somewhat more than 150A if the breaker is good. Based on Muir's spec of 120A I'm betting there's resistance in the circuit somewhere. Corrosion on the terminals, wonky foot switch or in the motor itself. It would be nice to have a clamp meter on that circuit while the windlass is running.

[Wotname]

Originally Posted by kenbo

Wotname,

We don't know if the distance is 4m one way or round trip. If one way, I believe 2awg to be too light and 0awg with the 150 breaker to be correct. He could also add a 135 breaker at the windlass end of the cable run to protect the motor.

Remember it was running before he added the 150 breaker and now it trips. so that circuit is drawing somewhat more than 150A if the breaker is good. Based on Muir's spec of 120A I'm betting there's resistance in the circuit somewhere. Corrosion on the terminals, wonky foot switch or in the motor itself. It would be nice to have a clamp meter on that circuit while the windlass is running.

I agree, we don't don't know the total wire length which is why I predicated my wire size suggestion stating a total wire length of 4m.

However after re-reading the Muir description of the this model windlass , I am in doubt of my previous analysis (i.e. I might be wrong)!

They state a working load of 624 lbs and a working current of 120A yet they also state a max load of 2,500 lbs. They don't state a max load current. They also fail to state a breaker size in the wiring diagram. If one interprets the data that 120A is required to lift 624 lbs, then a max lift of 2500 lbs is going to take quite a lot more - I don't have time to do the maths. Intuitively I believe the 120A is the max current but I will check later.

I also agree the best approach is to a clamp meter for the current and a voltmeter at the motor terminals to get a better picture of the potential issues.

And remember, the OP may just be overloading the windlass.

It has apparently being working for some time without the breaker so yes, the breaker or its installation may be dodgy.

The good thing about using some meters, they tell the real state of affairs!

[Reefmagnet]

Originally Posted by Wotname

Yes I have a few ideas!

First of all, you have received a few replies unthread - some of them are correct, some of them are factually incorrect and some of them are "sort of correct".

So allow me to give you my ideas (which are, by the way totally correct ).

It is unlikely (but possible) the windlass is faulty.
It is possible the circuit breaker is dodgy but probably not - so leave that to later.

More likely you have a power supply problem - batteries, cables, terminations etc.

The Muir installation manual is strangely quite on cable and circuit breaker sizes but they give us enough information to work it out. By the way, other posters have stated the purpose of the circuit breaker is protect the cable but in the case of a windlass I disagree, one circuit breaker can protect the windlass and the cable - providing the circuit breaker is less than the current carrying capacity of the cable used. In fact, Muir requires a circuit breaker for warranty purposes.

As for the working current needed, Muir tells us it is 120A for your model. The current draw of a windlass motor is determined in the main by the torque developed in the motor - more torque = more current. The available terminal voltage is only a small (but important) factor in the current draw of a windlass.

So this is the starting point, you need a suitably sized cable to ensure there is ~12V at the terminals of the windlass when it is operating at it's working capacity i.e. 120A.

I don't know what cable you have but clearly it isn't 4AWG (25mm) because such cable doesn't exist. If it simply 4AWG (21mm^2), then while it OK for the voltage drop over a total length 4m, it is too light for a 120A working load and certainly too light for 150A circuit breaker. Remember the circuit breaker won't trip at 150A, only in excess of 150A.

I don't know where Reefmagnet found the figure of 135A for the circuit breaker but I would agree it sounds exactly right!

My recommendation is to upgrade the cable to 2AWG and fit a 130A or 135A breaker but if you wish to keep the 150A circuit breaker, then upgrade the cable to 0AWG. Be aware the circuit breaker will be a little oversized and won't offer much protection as is ideal for the windlass.

Thanks for the mention! You prompted my to second guess where I got my rated circuit breaker value from.


The clue in the MUIR manual is in the wiring diagram. For their Storm VRC 1250 (which is a 1200w vertical winch) they identify the circuit breaker as part # "F80-RS". A bit of research indicates that this is most likely referring to their 100A rated CB, but they also have a 150A rated CB in their range, and it's difficult to tell which actual CB they're referring to.


Be that as it may, the rating of the motor is the maximum rating, and anything above this is likely to risk overheating the motor, which almost makes me suspect that the recommended breaker is 100A (1200/12). The winch motor is most likely a compound wound motor, so it will just keep increasing it's current draw as it loads up progressively more so it is important to ensure that it is protected from overloads if it jams.


The general rule of thumb with circuit breakers is 125% of maximum rated load. This is where I got the 135 value from (125A are a bit skint to source). Truth be known, I have a VRC1250 and use a 120A breaker. I can't honestly say if that works ok, because my boat is 2 weeks away from launching so I haven't yet used the winch in anger, although it's not had any problem during load testing.


Aside from voltage drop issues, other possible causes are:



1) A worn out breaker. Breakers progressively weaken, and can become extremely prone to nuisance tripping. Probably wouldn't expect an overrated breaker to trip, but if it was used as a switch over a long period of time....


2) A ground in the motor. A shorted commutator segment (cause by carbon dust) or shorted windings will cause drama for sure.


On the issue of wire selection, a rule of thumb for wires is that each 1mm2 of conductor will carry 10A for up to 10m (as a round trip to the power source). This is a safe carrying capacity without extremely excessive voltage drop, but voltage drop may be still be excessive in some applications if approaching these limits.

[Wotname]

When in doubt - ask

So I just called Muir HQ (they are up the road aways) and spoke with their technical guy. He states the Muir supplied circuit breaker for the HR2500 is 150A with trip at 187.5A. He is also happy with any normal commercial 150A breaker.

[Wotname]

Originally Posted by Reefmagnet

....... The winch motor is most likely a compound wound motor, so it will just keep increasing it's current draw as it loads up progressively more so it is important to ensure that it is protected from overloads if it jams.

.........

Maybe it is a compound wound, I have assumed (bad thing) it is series wound!

I should have asked the Muir man!!!

However, it is not critical to the OP, both types do not like being overloaded and both will overload quickly if too much load is applied.

[Reefmagnet]

Originally Posted by Wotname

When in doubt - ask

So I just called Muir HQ (they are up the road aways) and spoke with their technical guy. He states the Muir supplied circuit breaker for the HR2500 is 150A with trip at 187.5A. He is also happy with any normal commercial 150A breaker.

Actually that's sounds right. After I posted I realised my VRC1250 actually has a 1000w motor and it's more than likely the ratings assume 10V supply rather than 12 (which makes sense at high loads).


So back to square one with the OP, measure the load to see if in spec or try a new breaker!

[svJasmine]

your wire is WAY undersized.

that will bring the amperage up.

[Nicholson58]

Originally Posted by Wotname

OK, a couple of points. You have made an error with the maths.
1000W /12V = 83.3 amps (P=VxI)

Muir suggests the working current draw is 120 A (for the 12V version) - see attachment.

If you are tripping your 150A breaker, you are either overloading the winch or have some other electrical fault.

Winch motor is an induction load. If the cabling is too small, resulting in voltage drop at the motor then the motor amps will increase. Also, a stalled motor will suck a lot of amps. Add a battery near the windlass or increase the wire gage or both. Note also that a motor near the end of its life or abused also draws more.

[Frankly]

On a shunt or permanent magnet DC motor when the terminal voltage decreases the current/ available torque decreases. The torque/ current is pretty well determined by the motor load. Series or compound connected DC motors speed/ torque curves are so squirrelly that hard for me to believe that this is what the windlass has. Series motors are used to on street cars becaure they generate a lot of starting toque (although my bow thruster has a series motor).

Only disassembled two windlass motors and they were both permanent magnet. One a SL and don't recall the other mfg.


Frankly

[home_maarten]

(Very) few comments:


- the HR2500 is 1200W, whereas the one under discussion is 1000W.
- I have a 1000W Maxwell winch, which I equipped with the specified breaker, which is 80A. That works - and it doesn't trip
- I would be very reluctant to put in the size of breakers used/discussed/recommended. Especially with undersized cables, this can become a fire hazard.
- One respondend referred to having the engine running: this is a good advise (depending on the battery pack size). In my boat I have used a relais connected to the engine alternator, so that I can only operate the winch when the motor is on. This protects your battery.


Good luck!

[Nicholson58]

Circuit protection is sized to protect wire.

If you want more capacity you must install appropriate wire for the desired amps. I prefer to go larger than needed so the line loss is minimized. Once the wire is large enough you may install a breaker up to the device recommendation. Even then, the breaker protects the wire ( from short circuit).

[Group9]

It depends. But, we have a 150 amp breaker on ours. That doesn't mean that's the right size for your windless and wiring.