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Toxic_Avenger
20th November 2014, 08:54 AM
Looking for some advice from the tech heads who are electrically astute. Question is in regards to winch wiring on a defender, electrical cable selection, and voltage drop.

My winch at max load 9500lb, first row, can draw approx 360A, and I'm looking to run cables approx 6m from battery to winch solenoid> winch motor> negative battery terminal. This is 6m conductor length.

Warn winches recommend a voltage drop of less than 1v, which using a voltage drop calculator suggests I'd need 50mm squared cable to take full current with a 0.75v drop.

Now comes the interesting part. The winch has a thermometric cut out, which is not specified, but will cut in under periods of excessive load, so it's possible that I'll never exceed the duty cycle of the cable before that of the winch. ISO 50mm2 welding cable is good for 527A at 30% duty cycle in welding applications, so there should be plenty of head room there.

For the sake of over engineering, the primary battery cables will be sufficient.
I will be mounting the solenoid box in the engine bay, probably under the wing. Naturally the supplied winch motor to solenoid box cables are to short.
Would it be worth upgrading the solenoid to winch cables to a similar gauge? Or would the resistance within the solenoids themselves be the bottleneck? Shorter cable runs would not have as much voltage drop but not sure if this would be a half done job, not upgrading the whole way...

All advice appreciated,
Mitch

Toxic_Avenger
20th November 2014, 09:01 PM
https://www.aulro.com/afvb/images/imported/2014/11/290.jpg

Surely someone wants to discuss the finer points of Ohms Law?

Vern
20th November 2014, 09:10 PM
I think everyone is scared to post after the last winch isolator debacle.

6m you say? For that distance bigger is always better, I'd go 70mm2. Then between the solenoids to winch motor, you could drop back to 50mm2, but I'm no expert, I'm just a dopey electrical contractor:(:)

drivesafe
20th November 2014, 11:17 PM
Hi Mitch, your 50mm2 cable will be fine and if you want to increase the size of the solenoid to winch cable, you can either replace it with a thicker cable, or just add another cable based on the original and the new cable having a total square of 50mm2, and this will give you the same current carrying capacity.

BTW, if you have not bought the 50mm2 cable yet, then it does not have to be welding cable.

0B&S ( 49.5mm2 ) or ordinary ( thick stranded ) 50mm2 cable has the same operating characteristics as welding cable, the only difference between ordinary cable and welding cable is that welding cable is more flexible but if you cabling is installed correctly, it should not be flexing anyway, so it may be a lot cheaper to use ordinary 50mm2 cables.

One word of caution, under no circumstance should you use a solid state type solenoid in a winch type wiring setup. They are not designed for this type of use and are too dangerous.

Conventional electromechanical solenoids are far safer and more efficient.

For the type of currents your winch circuit will be handling, a solid state solenoid will add voltage drop to the setup and the amount of voltage drop increases as the current increases.

Plus solid state solenoids generate large amounts of heat and will need to have a large heat sink fitted, to allow this heat to dissipate.

But the more dangerous aspect of using a solid state solenoid is that if they fail, which is rare when used in the correct type of use, but when the fail, they almost always fail in a shorted state and the only way to brake the circuit is just that, you have to disconnect the cabling from the device.

The opposite is the case when using an electromechanical solenoid.

As the current rises across the contacts, the resistance reduces, which means the voltage drop reduces.

While electromechanical solenoids also produce large amounts of heat, their case is designed to tolerate and disipate the heat and this makes them much smaller for the same current carrying capacity.

But the biggest benefit of using an electromechanical solenoid, while again also rare, but if they fail, they almost always fail in an OPEN CIRCUIT state, making them much safer for winch use.

drivesafe
21st November 2014, 12:36 AM
I don’t care whether solid state solenoids are used in comp trucks, as these are specialised vehicles, where the operators also run their winches so hard they destroy batteries after only a couple of uses, so once again, not what is likely to be happening with the average winch user.

As stated, they add an unnecessary level of danger and introduce additional voltage drop, for no gain what so ever.

An electromechanical solenoid is still by far a better and safer choice.

And it is safety that should be paramount, and not the use of unnecessary gadgets.

BTW Mitch, if it is just security that you are after, a cheaper alternative is to get a 10mm Distribution Stud.

This is an insulated M10 bolt, and you then permanently secure the positive cable coming from your battery to the base of the stud and then fix the positive cable coming from your winch to the top of the stud.

When the winch is not in use, just undo the top nut and remove the cable coming from your winch, job done.

drivesafe
21st November 2014, 09:11 AM
Hi again Mitch, if you want to go up market, here is the 500 amp battery switch I supply to the marine trade.

It is both a standard On/Off switch and it has a keyed lock that allows you to lock the switch in the OFF position.

https://www.aulro.com/afvb/images/imported/2014/11/285.jpg

Toxic_Avenger
21st November 2014, 06:04 PM
BTW, if you have not bought the 50mm2 cable yet, then it does not have to be welding cable.

I work in sales, and can get good rates on welding cable, so I'll probably stick to that. Quick search on ebay shows my rate is cheaper than the 0B&S ex china... so I guess that's a hidden perk of the job :p



One word of caution, under no circumstance should you use a solid state type solenoid in a winch type wiring setup. They are not designed for this type of use and are too dangerous.

The solenoid pack i've got is electromechanical (factory Warn issue, p/n 36729BO). The contactors rattle when I shake it, so definately not solid state.

The distribution stud is an elegant and simple fix for the isolation problem, but so is that marine switch. Just need to get an idea of where something of that size could be stashed inside a puma engine bay.

My initial plan was to wire the winch back down the passenger side (LHS) chassis rail (most direct route), but looks like most people are sending it down the driver's side rail, than crossing it over the gearbox, or across the front of the bulk head?

Might need to do some reading, but as it stands, the winch rope needs to spool off the bottom of the drum, and as it is wired / positioned, this puts the winch motor side of the winch on the driver's side.
I'm guessing it will be a matter of changing the motor polarity and re-feeding the rope back on the spool?

drivesafe
22nd November 2014, 12:26 PM
Hi again Mitch, I just put up the info on the Distribution stud and the switch to show there are a number of other options open to you.

Using either the switch or the Distribution stud have their own advantage in that if you do draw the voltage down a fair bit, solenoids can drop out or even oscillate, but these two do not.