WHAT WILL HAPPEN TO WINDLASS DRAW

[MARC D]

Hi All,

I have a question regarding a windlass current draw when the voltage applied is going down:

Is the current draw will rise in respect to the formula P=E x I ?

or

the motor speed will go down (with the current draw down as well) ?

Thanks!!

[donradcliffe]

A bit of both. I had a windlass start to trip its breaker. I took apart and cleaned every connection from the battery to the windlass motor. End of problem.

[Jammer]

It depends on how the windlass motor is wound. Most windlass motors are series wound. They can be identified by the use of three motor terminals: up, down, and common.


Series wound motors draw current proportional to the square root of torque. Speed is a function of voltage and torque. There are a number of articles on DC series wound motor theory that explain the reasons for this in detail, see for example: https://www.electrical4u.com/series-...-series-motor/


Therefore, if you do indeed have a series wound motor, the current will stay about the same regardless of voltage, and the speed will be reduced when the voltage is reduced.


In a shunt wound (typically four terminal) motor, the current will increase if the voltage is reduced, because the back EMF in the armature is reduced due to the lower magnetic flux from the reduced field voltage. The speed will stay about the same.



In a permanent magnet (typically two terminal) motor, the current will stay about the same if the voltage is reduced, and the speed will go down, much as with a series wound motor.

[MARC D]

Thanks Jammer!

Now I need to find out what type of motor I deal with!!

[SailingHarmonie]

It's WAY more complex than P=EI with a motor. Everything is inter-related in complex ways, and not in the way the typical description of things is given. The following generalizations are true for relatively small changes, things change in more complex ways if you make big changes, but here goes:

In a brushed DC motor:

• speed increases with increase in voltage.
• Current increases with change in torque.

The result of this is that changing the voltage with no change in load will change the speed of the motor, but NOT THE CURRENT.

Let's imagine we have a 100% perfect power supply that can keep a constant voltage no matter how much current we draw. We turn our motor on at zero load, and it spins up to it's "no-load" speed.

If we now apply torque to the motor, the current increases, the voltage and the speed stay the same (because we have that magic power supply that can deliver constant voltage to the motor windings).

Now in the REAL world where we all live, we have batteries, not magic power supplies. If we apply torque to our motor, the current draw goes up, and the voltage goes DOWN because that's the way batteries and wires work. It follows then that the motor slows down because the voltage has decreased.

It LOOKS like the current has increased BECAUSE the voltage has gone down, but that is not really true. The voltage has gone down because the current has gone UP! Probably not a difference that matters to the sailor running the windlass, but to the engineer designing the system it DOES matter.

Now things get more complicated because past a certain point, the motor efficiency drops as the speed decreases. At speeds much below design, the efficiency is lower, and more of the amperage is wasted as heat. So if the voltage (and hence the speed) drop far enough, you start to stress the motor.

The end result from a motor running from a battery is that the current increases, and the voltage drops. Past a certain point, the slower the motor turns the less efficient it is, and the more power is wasted as heat.

If you have a system with low voltage drop (short, large diameter wires, and batteries with low internal resistance), the voltage stays up higher as the current increases under load, the speed stays higher, and the motor stays operating in its most efficient speed range. It works better, runs cooler and lasts longer.

[MARC D]

Thanks SailingHarmonie for your explanation. I'm getting there (I think!).

Anyone knows what type of DC motor windlass manufacturers are using?

From Jammer info, I read that Shunt motor are kind of self-speed regulated. That may be the type preferred for windlass??

[rslifkin]

My Maxwell HRC10-8 has a series wound motor.

[Jammer]

Originally Posted by MARC D

Anyone knows what type of DC motor windlass manufacturers are using?

From Jammer info, I read that Shunt motor are kind of self-speed regulated. That may be the type preferred for windlass??

It varies from one model to the next.


As just one example, Lofrans uses permanent magnet motors on their Dorado windlass and series-wound motors on their Project 1000 and Cayman windlass. Older Lofrans Kobra were permanent magnet but as some point they switched to series wound.


The advantage of series-wound motors is that the starting current and starting torque are lower. The starting torque in a permanent magnet motor can be, in practice, dozens of times the design operating torque which can put excessive strain on the gearbox components. Similarly the extraordinarily large starting current (well over 1000 amps for a fraction of a second) can put excessive strain on the contactor and electrical system.


These problems become more unmanagable as the motors get larger, so series-wound motors are more common in larger size winches and windlasses. As an example, my boat has Harken electric winches. The comparatively small halyard winch has a permanent-magnet motor. The primaries have series-wound motors.

[Wotname]

Originally Posted by MARC D

..... I read that Shunt motor are kind of self-speed regulated. That may be the type preferred for windlass??

I have not seen a shunt wound motor on any windlass but I guess they might exist.

All the windlass motors I have seen are either series wound or permanent magnet for the reasons given up thread.

As stated earlier by Jammer, the current characteristics of these two motors are similar.

[Jammer]

Originally Posted by Wotname

I have not seen a shunt wound motor on any windlass but I guess they might exist.

See for example the Lewmar V4 and V6.


https://www.lewmar.com/sites/default...11-English.pdf - pp. 14-15

[Wotname]

^^ Thanks.

[MARC D]

Top notch information, thank you all!