Suitability of PWM for marine Winch Motors?

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MikeAqua

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#237865 21-Jun-2018 13:48

Question: -

Would a PWM motor controller be suitable for controlling speed of a 12V or 24V DC boat winch?

This would be a 60A - 100A load, with a run time of several minutes.

They aren't (widely) used to control boat winches, yet there is a case for doing so. I'm wondering why - limitations etc?

Background: -

Winches on small boats are 12V or 24V DC.

A popular form of winch is the drum winch in which rope is wound on/off a spool with horizontal axis (not unlike a hose reel). They are popular because they don't require anyone to go up front to drop the anchor or to control the rope as it comes off the winch whel th anchor is retrieved.

A limitation of drum winches is the effective circumference of the spool increases as rope is stored, increasing retrieve speed. If the anchor hits the fair-lead at speed it can fly up and damage the front deck or windscreen. You have to be on the ball and see the anchor coming. This can be difficult if you are also focusing on controlling the boat or watching the kids or ...

Despite this issue, no/few manufacturers offer any form of speed control. They just advise marking the rope a few meters above the anchor and pulsing the winch from their. Base don my internet research this seem a sensible application for a PWM motor controller.

Mike

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#2041763 21-Jun-2018 15:34

Wouldnt you still need a sensor to determine the position of the fair lead in order to control the motor speed, PWM or not ?

Stall current could be quite a bit higher, though good engineering can mitigate destructive currents thru the PWM circuits.

I'd be looking at a sensor-type arrangement on the chain / fair-lead junction - reflector / RF tag ?

I use a 1 HP (human power) motor to uplift the anchor, but the bearings are a bit stuffed, brushes worn to the nub, and is generally pretty inefficient ..

kryptonjohn

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#2041781 21-Jun-2018 15:58

Those drum type winches seem popular with work boats, commercial fishing boats etc, but I've always wondered why as they take up deck space and put the considerable weight of chain rode up high instead of down low?

What's the benefit over the common horizontal or vertical windlass with chain gypsy and chain pipe to a below deck locker? They're also self feeding and tailing so able to be operated remotely.

1eStar

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#2042025 21-Jun-2018 21:45

Drum winch is a step up from a selftailing rope/chain winch, because: the transition from rope to chain is often unreliable, and freefall/power out anchoring also often troublesome.

My father just upgraded from a self tailing to drum winch recently on his 20' fishing boat.

But the biggest upgrade which nearly negates the need for a rope/chain/anchor completely is his new Minn kota GPS enabled trolling motor.

Forget your pwm speed controller, get a Minn kota or motorguard!

There is a drum winch supplier in Oz which does a variable speed controller.

gumboot19

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#2042100 22-Jun-2018 06:36

Electric drum winches are quite common in Aus. the variable speed and ease of use is great.

Pacific Seven in Tauranga have fitted quite a few.

Batman

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#2042107 22-Jun-2018 07:25

is PWM pulse wave modulation?

kryptonjohn

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#2042118 22-Jun-2018 08:02

I'm used to all-chain rode which never seems to be a problem with conventional windlasses - due to the weight of the chain it always feeds in and out perfect.

MikeAqua

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#2042492 22-Jun-2018 15:34

Usually small boats (<7m) havge the type of caspstan where you wrap the rope around three times and as the winch runs you pull the rope.

Self-tailing type winches that you can remotely operate need a larger and well designed rode locker, other wise the rode can pile up under the winch and cause jams. My father had this issue with an all chain rode on his ~40ft launch.

Mike

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kryptonjohn

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#2042495 22-Jun-2018 15:39

Ah now I'm with you. Frankly it surprises me that those chain gypsies that grab both rope then chain and feed down a chain pipe work at all with rope - as there's not enough weight in the rope to carry it down and stack it in the locker. Plus the eye splice onto the chain has to make its way through as well!

Never really had a problem with the chain piling up too high - I guess it just has to be deep enough to not happen.

MikeAqua

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#2042499 22-Jun-2018 15:49

SepticSceptic:

Wouldn't you still need a sensor to determine the position of the fair lead in order to control the motor speed, PWM or not ?

Speed control doesn't need to be automated. Most controllers can be remote controlled via an analog input of some kind. You could do this from the helm. Mark the rope 5m above the shackle and when I see the mark reduce the speed. One might even bypass the PWM somehow for most of the retrieve, and only use it for the last 5m or so.

In principal though, as the rope builds up on the drum and it has to work harder there should be an electrical change of some kind on the circuit. Possibly this could be used to automate speed.

But .... generally things on boats should be simple. A rugged analog control on the helm is simple.

Mike

MikeAqua

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#2042501 22-Jun-2018 15:52

kryptonjohn:

Ah now I'm with you. Frankly it surprises me that those chain gypsies that grab both rope then chain and feed down a chain pipe work at all with rope - as there's not enough weight in the rope to carry it down and stack it in the locker. Plus the eye splice onto the chain has to make its way through as well!

Never really had a problem with the chain piling up too high - I guess it just has to be deep enough to not happen.

Wet rope is heavier. If you try hauling in new rope (dry), it can be a bit of an issue.

Locker depth and slope are crucial, chain needs to be able to slide away from the winch. Shiny new chain helps too.

Mike

SepticSceptic

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#2042536 22-Jun-2018 17:09

MikeAqua:

SepticSceptic:

Wouldn't you still need a sensor to determine the position of the fair lead in order to control the motor speed, PWM or not ?

Speed control doesn't need to be automated. Most controllers can be remote controlled via an analog input of some kind. You could do this from the helm. Mark the rope 5m above the shackle and when I see the mark reduce the speed. One might even bypass the PWM somehow for most of the retrieve, and only use it for the last 5m or so.

In principal though, as the rope builds up on the drum and it has to work harder there should be an electrical change of some kind on the circuit. Possibly this could be used to automate speed.

But .... generally things on boats should be simple. A rugged analog control on the helm is simple.

If the rope builds up on the drum, there is less rope / weight to pull out of the water, so effectively the motor works less ?

Yep, chain is heavy, rope is heavy. Try to avoid doing more than twice on any fishing trip.

Or get an electric winch. Which are really not that cheap.

Hmm, maybe time to repurpose a windscreen washer motor, or car starter motor.

Aredwood

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#2043018 24-Jun-2018 00:23

There was another thread on this exact same subject. And the best answer was to switch in a whole heap of car headlight bulbs as a current limiting / speed control resistor. As halogen lights are effectively a non linear resistor.

Biggest problem will be that slowing down the motor, won't reduce the load much. So make sure that you don't overheat the motor due to the speed control.

MikeAqua

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#2044640 27-Jun-2018 10:51

SepticSceptic:

If the rope builds up on the drum, there is less rope / weight to pull out of the water, so effectively the motor works less ?

The weight is relatively constant as the rope weighs very little in the water, it's really just a few metres chain and the anchor.

But as the rope builds up on the drum the retrieve rate (metre per second) of that weight is increasing, so I assume more energy is required?

Mike

MikeAqua

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#2044656 27-Jun-2018 10:58

Aredwood: There was another thread on this exact same subject. And the best answer was to switch in a whole heap of car headlight bulbs as a current limiting / speed control resistor. As halogen lights are effectively a non linear resistor.

Biggest problem will be that slowing down the motor, won't reduce the load much. So make sure that you don't overheat the motor due to the speed control.

I've seen a similar solution - using a bunch of resistors to dump excess energy as heat. I don't see that as a very practical idea on a small boat.

Hence my interest in a PWM unit. I've seen 12v 100A units, which would easily handle the type of winch I'm looking at (60A)

If I went down this path, I'd wire things up so that I can bypass the PWM most of the time. When I'm getting close to the shackle I would switch to the PWM circuit and go slowly for the last 5 metres.

Reverting back to my original question: is there any reason a PWM won't work?

(noting that I would have to be careful not to overwork the motor at slower speeds).

Mike

Aredwood

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#2045116 28-Jun-2018 00:43

Calculate how much current the motor would consume if it is jammed. As that is the worst case scenario current that the PWM controller needs to be able to handle. (measure the resistance through the motor when cold and use ohms law) The answer will be way higher than 60A.

PWM would work for what you want to do. But you would likely need a controller that can handle way more than 100A.

How the motor behaves under different voltage / speed / load combinations also depends on wether it is series wound, shunt wound, or permanent magnet.

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