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Help Needed to Estimate Holding Voltage for Electric Clutch

05/23/2015 7:56 AM

I have a Countax Westwood ride-on mower (and lots of long grass because it is not working) It has a Warner electric clutch that runs on 12 vdc. I am rewiring the entire electrical system.

The alternator regulator has failed so the battery does not get charged and runs down during use. The only real current draw is the clutch.

I would like to reduce the current drawn by the clutch coil whilst running (without losing friction power) by using a resistor in series with the coil. I just happen to have a 1.1 ohm 25 watt resistor that I can use.

The stated design current is 3.5 amps at 12 volts (which gives 3.43 ohms) so when working with 1.1 ohm in series will reduce the current to 2.65 amps.

I do not know the magnetic forces, but the initial force is 3.5n amp-turns to overcome the distance (air gap) that once engaged with zero gap, so hopefully the friction will not be lost if the amp-turns reduce - which at 2.65n amp-turns relates to about 76%.

Warner says a 'voltage' reduction has the effect of causing the clutch to slip and wear out quickly - which is true if the clutch cant deliver the torque (as happens when the battery runs down) but in my case I only want to reduce the voltage until just before it slips - hence a 1.1 ohm series resistor.

Apart from my mower, I do not have any experience of working with electric clutches - so I might be wrong - any suggestions please..

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#1

Re: Help needed to estimate holding voltage for electric clutch

05/23/2015 10:43 AM

I don't know for sure, but I'd have thought reducing the voltage would risk clutch slippage and burnout, so you'd end up with a bigger problem than you have now. If it would work with lower current it would be designed like that, for economy.

I think you'd be better off replacing the alternator regulator. Is it built in to the alternator, like on a car? Are you sure it's the regulator? Brush wear (if any) is a more common problem. At a pinch, like if you can't get the right regulator, you might be able to do a lash-up using a regulator from a car alternator, mounted externally and running some wires.

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#6
In reply to #1

Re: Help needed to estimate holding voltage for electric clutch

05/24/2015 4:00 AM

GA

Thats the sensible way to go......

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#7
In reply to #1

Re: Help needed to estimate holding voltage for electric clutch

05/25/2015 7:01 AM

Thanks to everybody for all the help. I wanted to avoid spending money on replacement parts that I did not need. As it happens, the Briggs engine just blew up. I lost a conrod. So a new engine has been obtained, that (it appears) does not need a regulator - it just has a single diode with no regulator.

I read somewhere in the Warner guides that voltage control can be used to regulate the max torque delivered by brakes and clutches.

I assumed, in my case, that the voltage needed to 'pull' the clutch to engage, was much higher than needed to hold against slippage, and that a resistor in series would be a simple way to lower the voltage. ie, the clutch would not slip during grass cutting.

But as advised - get the electrics working!

In the meantime the grass is growing.

I will spray it with dilute whisky- it doesn't stop it growing - but it comes up half cut!

Thanks for the help.

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#2

Re: Help needed to estimate holding voltage for electric clutch

05/23/2015 12:55 PM

I would be searching the local mower repair shops for a regulator....or just add another battery...or a larger battery....I hear a honda regulator might work....

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#3

Re: Help needed to estimate holding voltage for electric clutch

05/23/2015 2:27 PM

It will be easier and more cost effective to charge your battery more often or add a second one dedicated to the clutch. While it's true that the holding current on an electric clutch is usually lower than the pull-in current to engage it, depending upon the exact type you will be risking clutch slipping or drop out during many types of sudden changes in load due to high/clumping grass, hitting an obstruction, or engine speed.

Unfortunately you won't know this unless you notice poorer cutting action, or smell the clutch burning. You'll probably find that replacing the regulator is cheaper and easier than another battery and/or replacing the clutch.

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#4

Re: Help needed to estimate holding voltage for electric clutch

05/23/2015 6:43 PM

Maybe you could convert it to manual....this seems the hardest way to go, but it is a possibility...

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#5

Re: Help Needed to Estimate Holding Voltage for Electric Clutch

05/24/2015 1:12 AM

I had a similar problem with a Honda powered mower. Changed the rectifier/regulator. The OEM part was $A180. Went online to AliExpress.

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