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-   -   Conductor size question. (http://www.cruisersforum.com/forums/f14/conductor-size-question-141847.html)

Matt sachs 25-02-2015 08:07

Conductor size question.
 
Im wiring my windlass. Its a maxwell RC12-10. Its 60 feet from the battery to the windlass and back. The manufacturers reccomends an AWG 1 wire, which is within the ABCY giudelines. ABCY recommends for 10% drop in voltage a AWG 2, and for a 3% drop an AWG 4/0. No problem so far..... The windlass is a 1200W unit (12v, 100 amps.) My concern is that they provided a 135 amp circuit breaker. Is this so I can run the windlass with low batteries and not pop the breaker? (8.8v and 136amps = 1200w). Will using the windlass with low batteries over heat my conductors rated at 100 amps? Am I over thinking this?

David M 25-02-2015 08:25

Re: Conductor size question.
 
Fuses are intended to protect the wire and not the load. Fuses are mostly intended to prevent a fire.

For a very large load like a windlass under a load, gauging it for 10% is okay but not ideal. You want a minimal voltage drop across the load in order to minimize heating of the motor. The lower the voltage drops, the more current that will be drawn. It is the amount of current drawn that will cause heating.

So between a 3% drop and a 10% drop would be okay. It is also okay to have a 135 amp fuse or breaker protecting a load of 100 amps if the wire is gauged sufficiently. If you were to fuse at 100 amps you would be popping the fuse frequently. Although more expensive, I would use a 100 amp breaker over a fuse. In addition to a quicker reset, it is easier to turn off the power to the windlass when needed.

You also want to gauge according to the run which is the distance from the battery to the load and back to the battery.http://assets.bluesea.com/files/reso...on_chartlg.jpg

So for a 120 foot run with up to a 100 amp load and a 10% drop you would want 3/0 cable. Keep in mind that the windlass will not always be drawing 100 amps...only when you are close to stopping it under a load will it draw that much current.

The alternative to buying 120 feet of 3/0 cable (very expensive and heavy) would be to put a battery close to the windlass and let that battery charge with a smaller gauge cable. The downside is the time it takes to charge the windlass battery if you are using the windlass for a long period of time. You might have to wait a while for the windlass battery to recharge.

Cheechako 25-02-2015 08:50

Re: Conductor size question.
 
He needs 60 ft not 120 ft. right?

Terra Nova 25-02-2015 09:20

Re: Conductor size question.
 
Use 4/0.

Matt sachs 25-02-2015 09:24

Re: Conductor size question.
 
Correct, its 60 feet round trip and 100 amps. Maxwell reccomends AWG1, I think I'll go with AWG 0 for peice of mind and find something else to worry about...:-) Thanks again.

svHyLyte 25-02-2015 09:25

Re: Conductor size question.
 
Quote:

Originally Posted by Matt sachs (Post 1758868)
Im wiring my windlass. Its a maxwell RC12-10. Its 60 feet from the battery to the windlass and back. The manufacturers reccomends an AWG 1 wire, which is within the ABCY giudelines. ABCY recommends for 10% drop in voltage a AWG 2, and for a 3% drop an AWG 4/0. No problem so far..... The windlass is a 1200W unit (12v, 100 amps.) My concern is that they provided a 135 amp circuit breaker. Is this so I can run the windlass with low batteries and not pop the breaker? (8.8v and 136amps = 1200w). Will using the windlass with low batteries over heat my conductors rated at 100 amps? Am I over thinking this?

You might find the following discussion useful http://www.cruisersforum.com/forums/...tion-3456.html

svlamorocha 25-02-2015 10:23

Re: Conductor size question.
 
Quote:

Originally Posted by Matt sachs (Post 1758868)
. The windlass is a 1200W unit (12v, 100 amps.) My concern is that they provided a 135 amp circuit breaker. Is this so I can run the windlass with low batteries and not pop the breaker? (8.8v and 136amps = 1200w). Will using the windlass with low batteries over heat my conductors rated at 100 amps? Am I over thinking this?

You are not. You are getting good advice about the wiring.

Now letīs clarify something else about fuses/breakers. If the voltage at the motor is too low (be it because of low batteries or too much drop in the wires) then the motor will draw disproportionately high current (more than what you assume) , run slow and burn. That is why Moorings boats have a relay that will only let you run the windlass if the alternator is charging. This willincrease voltage by at least 2 volts (say 14 volts at battery without any sag instead of 12.0-12.6 rest voltage minus the huge sag from 100 or so amps) and make your windlass motor last longer (and run better too!).

Takeaway #1: do not run windlass with low batteries without the alternator (or other charging that more than meets the windlass draw) that charging. You can hardwire this with a relay.

Takeaway #2: Make sure that between the batteries and the motor there is a fuse or breaker that meets the spec (both amps rating and curve) of the manufacturer of the windlass. What is that spec? If you go higher tan this rating you can damage the motor. It is OK that you need to fuse to protect the wire but you also need to have a fuse/breaker fuse to protect the motor. If you use the same fuse/breaker for both purposes then it needs to be upstream of the wire of course.

For example, my Lofrans Kobra 12V 1000W windlass wants to have a 100A breaker. Even if the wire has 200A ampacity there must be a 100A breaker somewhere between the battery and the windlass. Less than that and it will trip unnecessarily; more than that and the motor will burn when overloaded or voltage is low.

Maine Sail 25-02-2015 11:04

Re: Conductor size question.
 
When dealing with voltage drop for windlass or bow thrusters don't forget the battery voltage sag you may also encounter.

You would be good to consider the actual voltage at the terminals, under a 100-120A load, unless your alt is always kicking in some to help. It would not be uncommon to see 1-3 volts of drop in this type of installation, if not sized well, which can result in a shorter life for a windlass motor. If you aim closer to the 3% side, you'll be doing better.

Lets guess your batteries sagged to 10.9V under the windlass loads then you added a 10% voltage drop on top of that your windlass motor is now only at 9.7V....

Also keep in mind that the wires voltage drop is only part of the equation. Each fuse, switch and termination etc. adds a bit more so sizing for a 10% wire drop really means you are probably closer to 11-12+% on the circuit drop....

Wehn I run the numbers on 60' of wire at 11V and 110A of current I come up with 2/0 (4.8%), 3/0 (3.7%) or 4/0 wire (3%).. This is only taking wire drop into account not the fuse/breaker or any terminations. Unless your alt is always running, when using the windlass, I would not generally suggest sizing this based on 12V. This is why I run the numbers at 11V to account for voltage sag under load..... 1200W at 11V becomes 109A or 110A for round numbers...

If it were me I would be looking at a bare minimum of 2/0 but preferably 4/0....

Matt sachs 25-02-2015 12:15

Re: Conductor size question.
 
Thank you for the input. 3% drop is looking better all the time.

Wind River 25-02-2015 13:41

Re: Conductor size question.
 
I have the same length of wire run to my windlass, 60 feet round trip. My motor is a 1500 watt and I opted for the 3/0 cable. It was a little easier to run than 4/0 and still between 3% and 10% voltage drop. This cable comes from my batteries, through a 600 amp On/Off switch to a 150 amp breaker located in the V-berth next to the chain locker. On the other side of the breaker the wiring goes to 6 ga. and on to the windlass control box. From there to the windlass motor for a total round trip of about 10 feet.

When I rebuilt the windlass I had the motor rebuilt also and there was a 6 ga. ground wire attached inside of the motor casing, so I had an new wire of the same size installed at the time of the rebuild. I was not even questioning this wire size since it appears to have been what came from the manufacturer. Maybe I should have.

The moment the windlass begins to slow under load (not stop) the breaker trips very quickly. This breaker is likely 25 years old.

Can a breaker loose capacity over time or is the 6 ga. wire causing the the voltage to drop and current to spike to trip the breaker?
It is not possible to run the 3/0 all the way to the windlass motor but if need be, I could reduce the round trip of the 6 ga. by about 5 feet but that would be adding two more terminal lug connection.

Thoughts?

Just a FYI if the op decides on 3/0 cable. I had a hard time finding cable or lugs locally in 3/0. So make sure you get all you need and more before starting the project.

svlamorocha 25-02-2015 13:52

Re: Conductor size question.
 
Quote:

Originally Posted by Wind River (Post 1759143)
I have the same length of wire run to my windlass, 60 feet round trip. My motor is a 1500 watt and I opted for the 3/0 cable. It was a little easier to run than 4/0 and still between 3% and 10% voltage drop. This cable comes from my batteries, through a 600 amp On/Off switch to a 150 amp breaker located in the V-berth next to the chain locker. On the other side of the breaker the wiring goes to 6 ga. and on to the windlass control box. From there to the windlass motor for a total round trip of about 10 feet.

When I rebuilt the windlass I had the motor rebuilt also and there was a 6 ga. ground wire attached inside of the motor casing, so I had an new wire of the same size installed at the time of the rebuild. I was not even questioning this wire size since it appears to have been what came from the manufacturer. Maybe I should have.

The moment the windlass begins to slow under load (not stop) the breaker trips very quickly. This breaker is likely 25 years old.

Can a breaker loose capacity over time or is the 6 ga. wire causing the the voltage to drop and current to spike to trip the breaker?
It is not possible to run the 3/0 all the way to the windlass motor but if need be, I could reduce the round trip of the 6 ga. by about 5 feet but that would be adding two more terminal lug connection.

Thoughts?

You have about 0.5 volts drop in each of the two gauges, for a total of about 1V. That is quite a bit. .

I have never seen breakers that lose A capacity gradually over time. You can always measure with a DC clamp and see what is actually happening..

Are you saying that your problem did not exist before? Does it happen if you run the engine at charging rpm?

Wind River 25-02-2015 14:45

Re: Conductor size question.
 
Quote:

Originally Posted by svlamorocha (Post 1759156)
You have about 0.5 volts drop in each of the two gauges, for a total of about 1V. That is quite a bit.

I have never seen breakers that lose A capacity gradually over time. You can always measure with a DC clamp and see what is actually happening..

Are you saying that your problem did not exist before? Does it happen if you run the engine at charging rpm?

Even at 11 volts, that would be approx 135 amps, and it is tripping a 150 amp breaker very quickly.....


I don't know if this was a problem before as the windlass was not functional when I got the boat. It did have a separate 8D battery up in the V-berth with (if I remember correctly) 1/0 welding cable connecting the battery to the breaker, round trip maybe 15 feet of cable. Since the battery was junk and the boat was already nose heavy, I opted to remove it and wire to the house bank.

The engine is always running when I use the windlass but I have not looked at the voltage when using it. The DC amp clamp was my next course of action to try and see if it really was pulling enough current to trip the breaker.

svlamorocha 25-02-2015 15:08

Re: Conductor size question.
 
Quote:

Originally Posted by Wind River (Post 1759202)
Even at 11 volts, that would be approx 135 amps, and it is tripping a 150 amp breaker very quickly.....


I don't know if this was a problem before as the windlass was not functional when I got the boat. It did have a separate 8D battery up in the V-berth with (if I remember correctly) 1/0 welding cable connecting the battery to the breaker, round trip maybe 15 feet of cable. Since the battery was junk and the boat was already nose heavy, I opted to remove it and wire to the house bank.

The engine is always running when I use the windlass but I have not looked at the voltage when using it. The DC amp clamp was my next course of action to try and see if it really was pulling enough current to trip the breaker.

Your math is not right. When you decrease voltage by X% from rated voltage the current draw increases WAY more than X%. That is why motors burn when you give them low voltage. There are two replies about this.

I bet that you will be surprised if you measure voltage at the motor and current.

Wind River 25-02-2015 15:27

Re: Conductor size question.
 
Quote:

Originally Posted by svlamorocha (Post 1759217)
Your math is not right. When you decrease voltage by X% from rated voltage the current draw increases WAY more than X%. That is why motors burn when you give them low voltage. There are two replies about this.

I bet that you will be surprised if you measure voltage at the motor and current.

I used Amps = Watts/Volts

1500 watt motor at 11 Volts = 136.36 amps

This is not correct?

I will measure the voltage and current at the motor, just have not been able to yet. I do love factual real time data. :smitten:

svlamorocha 25-02-2015 15:34

Re: Conductor size question.
 
Quote:

Originally Posted by Wind River (Post 1759231)
I used Amps = Watts/Volts

1500 watt motor at 11 Volts = 136.36 amps

This is not correct?

I will measure the voltage and current at the motor, just have not been able to yet. I do love factual real time data. :smitten:

The power (watts) consumed by a motor does not remain constant when you change voltage.


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