Edit: Just realized there will be a delay needed so the direction relays don't release before the contactor opens, since that's when the major arcing occurs.

And now we're back to the diodes.

 

And now we're back to the diodes.

Is there something wrong with using four diodes (bridge) to suppress the contact arcing and increase their lifetime?
Seems like low-cost protection to me.

 

Also in place of those shown in the OP, I would rather use a couple (or one) of a automotive starter relay!

 

Is there some wrong with using four diodes (bridge) to suppress the contact arcing and increase their lifetime?
Seems like low-cost protection to me.

YES!! There IS something wrong with protecting the contacts of a high current relay MADE TO NOT BE PROTECTED by diodes. First the load is a MOTOR, not an inductor. Second, a diode that would be suitable to absorb the energy from opening a circuit with about 50 amps flowing will cost a whole lot, (times 4), and third,the relay I suggested already has a double break contacts arrangement and a moving contact that is heavy. It weighs almost an ounce. (3cm diameter and at least 3mm thick!!

 

There IS something wrong with protecting the contacts of a high current relay MADE TO NOT BE PROTECTED by diodes.

What type of contact is MADE TO NOT BE PROTECTED by diodes?
I don't see how the diodes could possibly damage contacts, as they protect them from arcing.

First the load is a MOTOR, not an inductor.

I didn't know that.
But motors have inductance and will generate inductive type current until they stop.

Second, a diode that would be suitable to absorb the energy from opening a circuit with about 50 amps flowing will cost a whole lot

It doesn't have to absorb all the energy, it just carries the current for the short time it takes the motor stops.
The rotational impedance of the motor absorbs most of the energy.
The bridge diode I posted in post #9 has a 300A surge rating, and costs less than U$3.

the relay I suggested already has a double break contacts arrangement and a moving contact that is heavy.

So an expensive relay with large contacts is better than a cheaper relay protected by cheap diodes?

 

I used a couple of 16A G2R relays in an H-bridge to switch a DC motor. Even with a diode bridge, it could still strike an arc and destroy the relays.
Putting a second set of relay contacts in series substantially reduced failures (a much bigger improvement than the diode)

 

What type if contact is MADE TO NOT BE PROTECTED by diodes?
I don't see how the diodes could possibly damage contacts, as they protect them from arcing.
I didn't know that.
But motors have inductance and will generate inductive type current until they stop.
It doesn't have to absorb all the energy, it just carries the current for the short time it takes the motor stops.
The rotational impedance of the motor absorbs most of the energy.
The bridge diode I posted in post #9 has a 300A surge rating, and costs less than U$3.
So an expensive relay with large contacts is better than a cheaper relay protected by cheap diodes?

The relay I suggested, the one being discussed, has been used by FORD to power the starter motor on a whole lot of their products, although I have not looked at any of the more recent ones. The starter motor is a very high current device and so that relay is intended to last thru thousands of starts with no problems. AND that relay design is also used in similar relays for other applications.
Consider that MAX, a person rather familiar with such relays, has also suggested using one, with no demand for protection diodes. Then, also, consider that winch motors, usually under load, do not coast very much.

 

Even with a diode bridge, it could still strike an arc and destroy the relays.

Don't see how the small forward drop of a diode can strike an arc if the diodes were directly across the contacts.

 

CONSIDER ALSO the physical challenge of adding mechanically adequate diodes to a circuit wired with #8 wire. All to protect a relay designed for the exact application and having a great service record of over 30 years.

 

$15.00 on Amazon, probably never need to replace it again!

 

$15.00 on Amazon, probably never need to replace it again!

View attachment 331271

And how would you provide the reversing signal to the motor which is now done by two SPDT relays?

 

$15.00 on Amazon, probably never need to replace it again!

View attachment 331271

THAT looks like what I was talking about!!
As for the directional control, we did say that the other relays would select the direction, but would not be switching any live power. So first the direction selection, and then the power switches on. OR, it could be done using four of these in an "H BRIDGE" arrangement.
I can visualize how a normally closed section could be added to allow two relays of this style to be wired as an SPDT set and do it with only two of them. The mechanical design would not be that bad, I can explain that idea to a good mechanical designer.

 

Don't see how the small forward drop of a diode can strike an arc if the diodes were directly across the contacts.

I've never really thought about the mechanism as to how it happened. I just know it did. The arc struck between the contacts that were trying to open. The whole relay lit up bright green and the entire moving contact burned away.

 

as mentioned, currently used relays also have NC contacts. so to make that work with high current DC relays, one would need 4 of the high current relays. but this would be also prone to failures since no inherent interlocking exists and there are no monitoring contacts.

one could and should use winch relay/contactor like this or this. some come with remote controls too.

 

I've never really thought about the mechanism as to how it happened. I just know it did. The arc struck between the contacts that were trying to open. The whole relay lit up bright green and the entire moving contact burned away.

Then I suspect the diodes weren't connected properly or were underrated, since it takes in the neighborhood of 30V to maintain an arc.

 

Automotive Starter-Solenoids are not a good plan,
they are NOT rated for "Continuous-Duty",
and, it is very likely that the Coil will burn-up under Winch-Duty.
I've burned-up quite a few before figuring this out in the school of hard knocks.

SPDT 12-Volt-Contactors are readily available.

This would eliminate the need for ~3-Relays/Contactors for providing reverse.

They are normally rated for "Continuous-Duty" usage.

They are usually rated in excess of 100-Amps.

SPDT Relays/Contactors do not require Diodes, but may benefit from having them added-on.

SPDT Relays/Contactors can be operated by the same smaller Relays that are switching the Motor now,
thus eliminating any worries about smoking the Wireless-Controller with a heavy Coil-Load.

They're not cheap, but You will have the bonus of never having to replace them.
.
.
.

 

Most winch operation is not continuous duty. Esp pulling a mower up a ramp. But you do make a good point with it. There are similar relays made for longer duty cycles.

 

Don't see how the small forward drop of a diode can strike an arc if the diodes were directly across the contacts.

If you consider the simplest version being an SPST relay supplying a motor with a diode across the motor, when the relay opens, the inductance of the motor requires that the current continues to flow, so the voltage at the motor terminal goes immediately to -0.6V. That puts V+0.6V across the opening contact (where V is the supply voltage). That might be enough to cause an arc, and obviously in the case I observed, it was enough to cause an arc.
If there were no diode, then there must be an arc for the current to flow, so only the contact gap limits the voltage. The diode improves it by limiting the voltage across the contacts to the supply voltage, in which case there might be an arc.
I think a snubber might be better.

 

That puts V+0.6V across the opening contact (where V is the supply voltage)

What was the supply voltage for when you got the arcing with a diode?

 

What was the supply voltage for when you got the arcing with a diode?

24V - which makes it rather more likely to happen than 12V.