I am repowering an anchor winch with a 12v 1700w series wound winch motor driving a 8:1 planetary gear followed by a 4.16 : 1 chain reduction. The winch motor was advertised to run at 2100 RPM and I'm guessing this is the RPM derived with that particular winches drive train attached. My final output is about twice the 62 RPM I was expecting. I could get another reduction gear but that would still leave the gear input at around 4000 RPM which is higher than its rating. The winch doesn't have its anchor rode on it yet. This will slow it down but I expect it to race at the start of the pull when it is taking up the slack and slow to a more reasonable rate when the full load is on. There is also a brake on the winch that can slow it down.
My electrical options are a resistor in the armature circuit and I'm not sure of the value required or what kind of heat dissipation is required or a PWM control. The unit itself lives in a harsh marine enviroment and the somewhat waterproof box the motor lives in doesn't have a lot of room for extra equipment. I don't know much about PWM control . Is it possible to eliminate reduction gear and just use PWM control at that amperage.

 

The issue is being a series motor, they operate in a run-away mode , i.e, RPM is restricted by load.
Most applications using this type of motor, uses RPM detection in conjunction with the controller,

 

What do the motor specifications say about the maximum allowable speed??
WHERE did the 4000RPM come from?? Why is that assumed to be a problem?? Does the TS have access to the motor specifications??

 

You cannot predict the final RPM when using a series connected motor, every application and usage is going to be different especially with variable loads, such as a winch.
If it is an on going problem or issue in this case, then a lower voltage supply would help lower the final RPM.
Apparently this is an anchor winch.

 

1700W ÷ 12V (Assuming DC) = 141 2/3 Amps. That's 3HP.

8:1 planetary gear followed by a 4.16 : 1 chain reduction. The winch motor was advertised to run at 2100 RPM

8:1 means 3HP (whatever the torque is) equates to 24HP. Further "4.16 to 1 reduction' changes 24HP to the equivalent of nearly 100HP. There's not much meaning in those numbers without knowing the torque of the motor. Whatever the torque is you're talking a torque reading of 33 1/4 times the motor torque.

 

With the OP's original quandry, using that motor apears that using 6v would maybe solve it.?

 

Roughly calculating. Torque = Force x Radius
Giving the Armature a 50mm working radius and 1700 J (N/m) force
T= 1700 x .050 = 85 N/m
Given the 33:1 reduction would give a 2800 N/m final torque.
I roughly counted 120 revs, at 33:1 reduction equals 4000 rpm roughly
I don't think using a 6 volt battery is an option I can use as there is no room for an extra battery bank and charging would require a separate system. Reducing the 12v to 6 volt without generating a lot of heat would require some magic I'm not aware of yet. I have tried putting a rheostat in series before the armature and it slowed the motor down but also got red hot.

 

The motor specifications that I have seen show the NO LOAD RPM, since with most non-synchronous motors the speed tends to drop as the load is applied, if the motor does not have a feedback speed controller. So my suggestion is to try the motor with no load prior to installation. I have run starter motors with no load and none has ever "run away", although they do spin much faster when not cranking an engine. There is an inherent limit to no load speed for a series connected DC motor. I forget the details, that was in the motors class I took 60 years ago. My experience tends to have verified that.

 

although they do spin much faster when not cranking an engine. There is an inherent limit to no load speed for a series connected DC motor. I forget the details, that was in the motors class I took 60 years ago. My experience tends to have verified that.

Exactly' pretty much what I said !!
It characterises without getting bogged down in specific details,
Also exhibited in vacuum motors when the end of the suction tube is blocked, they 'run away' up to maximum RPM

 

The reason for 'run away' is that as the field gets weaker as rpm increases, it eventually leads to minimum torque, so friction and windage are a couple of the the limiting factors.

 

In addition to post #10, a motor driving those stages of gear reduction will slow because gearbox torque requirements increase with speed. So my response to post #1 is that in the actual application the motor will never be running no load when in the "raise-anchor" mode.The much greater concern will be overloading, if the reduction/torque multiplication is not adequate. When lowering the anchor the motor will still need to overcome the gear reduction friction when lowering the anchor, unless the system is so free that the anchor will not need a brake to stop it from lowering.

 

At the moment the motor is on the anchor winch driving reduction gear, chain drive and drum. RPM approximately 120. The winch has a clutch and a brake and will only be used for pulling anchor. I have run the motor no load and it spins REALLY fast.
At the start of a pull the line will want to come on to the drum too fast which will make it hard to manage. As it picks up the chain and anchor it will slow with the increased load hopefully enough to make it manageable. To make pulling Manageable at start of pull I could apply the brake but it is really designed to clamp the drum and lock it not run on it. Or maybe there is some kind or resistance that could be put in series with the armature. But I don't know what that looks like as it needs to carry a large current and dissipate heat. I've heard of PWM controllers but know nothing about them. Is this an option?

 

Now we have an explanation, and it makes a lot of sense. AND, CERTAINLY a cable winding on a drum is no place for hands! Braking the drum would indeed be a very poor choice, in addition to not solving the problem.
The issue with a series resistance is that as soon as the slack is taken up and the load applied, the motor might stall and the current will increase, and the resistor will produce a lot of heat in a hurry.
The best choice would be to increase the reduction ratio, probably by changing the sprocket sizes.
A second option could be a separate momentary switch to power the motor thru a resistor only to take up the slack. That circuit would also include a circuit breaker set for just a bit more than the no-load running current. Then the "raise anchor" switch could be used to apply power directly to the motor.
The problem with a PWM speed control is that it would need to safely carry at least the full load motor current, and probably also the stall current of the motor.

 

I have run the motor no load and it spins REALLY fast.

As I indicared, a 'run away condition'.
With a high current series motor. neither a resistor or PWM is a good choice, the bottom line is you need a higher reduction ratio for that motor.'

 

Today I ran the winch with a rheostat (1) between the field coils and armature (2) before the motor. At 9 volts I was happy with the speed reduction. The rheostat got very hot , more so in series with the armature I thought.
The sprocket sizes are as big and small as are physically possible. I could go to a 2 stage planetary gear reduction and hope the second stage adds enough load to slow the motor which I estimate is turning 4000 RPM which is above the recommended maximum input RPM of the reduction gear.
Searching the net to find a resistor rated for 1700w they are not a common thing and are expensive and bulky. PWM controllers with that power rating are common from Amazon ,China etc.and not that expensive. A quick search showed one rated 200 amp max with a 100amp run capacity. Would this not satisfy my requirements? Would I need a reduction gear at all?

 

Planetary gears are unusual in a typical winch application, One feature is that they are among th most efficient, which in this case, sort of works abainst you !

 

At 9 volts I was happy with the speed reduction. • • • Searching the net to find a resistor rated for 1700w they are not a common. • • • PWM controllers with that power rating are common from Amazon ,China etc.and not that expensive. A quick search showed one rated 200 amp max with a 100amp run capacity. Would this not satisfy my requirements? Would I need a reduction gear at all?

1700W ÷ 12V (Assuming DC) = 141.67 Amps. That's 3HP.

You know the math.
1700W ÷ 9V = ? ? ? Amps.
If you find that number to be within the range recommended then I'd suggest you look for something bigger. Why? Because you're running 88% over the max running capacity. Look for something that is rated at 133% to 150% HIGHER than you need. You need over 190A run capacity look for something that can handle 1 1/3 to 1 1/2 times what you need. 100A run capacity is not enough.

 

A DC motor is CERTAINLY NOT a constant power device! As the voltage is reduced the current will also drop,and the available delivered mechanical power will also drop. In addition, only the voltage across the resistor will develop the power converted to heat.
It would still be a challenge to find a place for a hot resistor on a boat of any size. I calculate the full load current at 12 volts to be about 142 amps, which is a lot of current. But the no-load current, spinning the winch drum, will be a lot less. So probably a one or two ohm resistor will slow the no-load speed quite a bit.
BUT with the loaded current being so high, any series element intended to run the motor prior to picking up the load will need to be a high capacity device. An alternative will be a separate switch to run the motor at some lower voltage to take up the slack, separate from the full voltage application circuit. That is probably quite possible, with the resistor circuit also having an automatic reset circuit breaker of some much lower current rating, probably 20 to 30amps.. That still leaves the problem of where to locate a resistor that produces several hundred watts of heat.
So now another possible scheme would be a current limited PWM driver for taking up the slack in the anchor chain only. The main control would bypass the PWM drive circuit so that it will not need to handle the full load current. Thatwill be a less chalenging design by a great deal.

 

1700W ÷ 12V (Assuming DC) = 141 2/3 Amps. That's 3HP.

I calculate the full load current at 12 volts to be about 142 amps,

Thanks for the confirmation.

That still leaves the problem of where to locate a resistor that produces several hundred watts of heat.

more like 1700 watts.

 

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