What happens when a winch reaches it's limit

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What happens when a winch reaches it's limit

Post by Khan » 14 Nov 2016, 12:59 pm

Following the other topic on winching.

As mentioned, it makes sense to not exceed your bull bar / mounting rating with an overly powerful winch.

e.g.

9,500lb rated bull bar + 9,500lb winch = Good

9,500lb rated bull bar + 12,000lb winch = Possibly very bad.

Say you go with a 9,500 / 9,500 pair though. What happens if you're so stuck the winch hits its limit?

Does the winch have some sort of safety cut out at the weight or is it just the winch will fail/break before damaging the vehicle?
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Re: What happens when a winch reaches it's limit

Post by albat » 14 Nov 2016, 2:05 pm

You might never get to know the answer to that question!!!
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Re: What happens when a winch reaches it's limit

Post by AusTac » 14 Nov 2016, 2:32 pm

Weakest link goes first, be it a cheap winch that ramps the current right up and melts your master switch/wiring/relay control box, or if you have a cheap bar with poorly engineered mounts it may depart the vehicle, my bets would be on the winch electrics failing before anything mechanical starts coming off the car
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Re: What happens when a winch reaches it's limit

Post by Wes » 15 Nov 2016, 12:51 pm

Khan wrote:Does the winch have some sort of safety cut out at the weight or is it just the winch will fail/break before damaging the vehicle?


I've been doing a fair bit of reading on winches lately and none have an auto-cut off or limiter that I've seen.

The limit is just what they're telling you not to exceed.
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Re: What happens when a winch reaches it's limit

Post by Baronvonrort » 15 Nov 2016, 2:32 pm

Khan wrote:Following the other topic on winching.

As mentioned, it makes sense to not exceed your bull bar / mounting rating with an overly powerful winch.

e.g.

9,500lb rated bull bar + 9,500lb winch = Good

9,500lb rated bull bar + 12,000lb winch = Possibly very bad.

Say you go with a 9,500 / 9,500 pair though. What happens if you're so stuck the winch hits its limit?

Does the winch have some sort of safety cut out at the weight or is it just the winch will fail/break before damaging the vehicle?


With engineering we have something called a "Factor of Safety"

If the winch is rated to pull 9500 Lb then that is a working load, if it has a factor of safety of 2 then it should start to self destruct around 19,000 lbs, if it has a factor of safety of 3 then is should self destruct around 28,500 lbs.

The factor of safety is calculated with breaking loads not the Youngs Modulus which is where it starts to go through inelastic deformation when it exceeds this figure, up to there it should spring back when load is removed.

When designing this sort of thing an engineer might say winch should break before bulbar therefore the bulbar should only have elastic deformation possible which means stress levels have to be below the Youngs Modulus of the materials used when subject to double the working load of the winch assuming the winch working load is subject to a factor of safety of 2.

The reality is vey few bullbars are engineered for any and all winches so your guess is as good as mine
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Re: What happens when a winch reaches it's limit

Post by brett1868 » 15 Nov 2016, 10:26 pm

I recall the early Warn winches used a shear pin but having just looked at the parts list for my current model xdc9500 and no sign of one. Apparently mine has a thermal cutout so I can't cook the motor.
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Re: What happens when a winch reaches it's limit

Post by Varmtr » 16 Nov 2016, 9:34 am

Now this may have been changed, but vehicle recover winches didn't come under lifting equipment regulations hence no 2:1 safety factor. The only winch that did was made in Melbourne by Banford and Smith but haven't seen one in years.
A normal low mount recover winch when getting to its max can do a number of things. Besides the amps going through the roof and burning out the motor or wiring. They can snap cable, hook, gearbox, mountings, housing etc all depending on the quality of the winch. The best way to reduce winch damage is if you can do double line pull it might be slower recovery but you effectivily reduce loan on the winch and winch mounting.
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Re: What happens when a winch reaches it's limit

Post by Baronvonrort » 16 Nov 2016, 9:48 am

Varmtr wrote:Now this may have been changed, but vehicle recover winches didn't come under lifting equipment regulations hence no 2:1 safety factor.



As far as I know Factor of Safety is not regulated it's something the engineer and manufacturer decide on when designing something, as a general rule I find comparable equipment with a FOS of 3 tends to last much longer than something with a FOS of 2.
A FOS of 2 seems a little low for lifting equipment I would use at least 3-4 because consequences of failure could be really bad.

Thermal overload switches are common the missus triggered the one in our vacum cleaner recently, I told her it would be OK just wait for it to cool down and it will work again.
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Re: What happens when a winch reaches it's limit

Post by Varmtr » 16 Nov 2016, 12:33 pm

Most of the lifting gear I have seen at my work run a 4:1 or even 5:1 safety margin. The only other recovery winch I have seen rated for lifting is the Tirfor hand winch rated 2.5t pulling but derated to 1.6t lifting and these do have a shear pin when overloaded.
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Re: What happens when a winch reaches it's limit

Post by <<Genesis93>> » 17 Nov 2016, 10:25 am

Baronvonrort wrote:
Khan wrote:Following the other topic on winching.

As mentioned, it makes sense to not exceed your bull bar / mounting rating with an overly powerful winch.

e.g.

9,500lb rated bull bar + 9,500lb winch = Good

9,500lb rated bull bar + 12,000lb winch = Possibly very bad.

Say you go with a 9,500 / 9,500 pair though. What happens if you're so stuck the winch hits its limit?

Does the winch have some sort of safety cut out at the weight or is it just the winch will fail/break before damaging the vehicle?


With engineering we have something called a "Factor of Safety"

If the winch is rated to pull 9500 Lb then that is a working load, if it has a factor of safety of 2 then it should start to self destruct around 19,000 lbs, if it has a factor of safety of 3 then is should self destruct around 28,500 lbs.

The factor of safety is calculated with breaking loads not the Youngs Modulus which is where it starts to go through inelastic deformation when it exceeds this figure, up to there it should spring back when load is removed.

When designing this sort of thing an engineer might say winch should break before bulbar therefore the bulbar should only have elastic deformation possible which means stress levels have to be below the Youngs Modulus of the materials used when subject to double the working load of the winch assuming the winch working load is subject to a factor of safety of 2.

The reality is vey few bullbars are engineered for any and all winches so your guess is as good as mine


Factor of safety would apply to the cable, which may have an ultimate tensile capacity of 2, 3 or 4x the winch rating, though the weak points would be the connections rope crimps/joints etc

As far as the Winch rating; it would have more to do with the TORQUE its able to generate to turn the drum (causing tension in the cable)...

So the winch would simply not be able to 'rotate' once it get to the limit (heating/thermal cutout ensues) the motor is trying to turn but cant do it...

a 9,500lb winch would probably have a capacity to do a smidge more, maybe 10% (guess) simply because you would never design and specify any product then market it at its absolute limit..... a chinesey product, probably less.

Also consider the Same torque generated at the drum, would create MORE tension in the cable (pull) with an unraveled cable (less layers of rolled up cable, torque acting on a smaller radius/lever arm) so if working at the limit, have the least amount of line rolled on.....
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Re: What happens when a winch reaches it's limit

Post by Ken » 17 Nov 2016, 11:02 am

brett1868 wrote:I recall the early Warn winches used a shear pin but having just looked at the parts list for my current model xdc9500 and no sign of one. Apparently mine has a thermal cutout so I can't cook the motor.


I'm assuming a shear pin does as the name implies and snaps to release the strange before something breaks?

It lets go of the wire/rope I guess?
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Re: What happens when a winch reaches it's limit

Post by Baronvonrort » 17 Nov 2016, 11:22 am

FOS would apply to all the parts of the winch- drum, mounting bolts ,cable,hook,etc, by putting a lower factor of safety on certain components you can design which parts fail first.

If 9500 Lbs is the maximum working load specified then that has a factor of safety applied to it ,with working loads nothing is engineered to operate with no factor of safety at max working loads, if it can only do a smidge more it isn't engineered.
Aircraft probably have the lowest FOS (around 1.5) because they need to be lightweight, a larger FOS will make it heavier and cost more for materials making it more expensive to produce.

For a winch the cable and swage fitting/hook is probably the weakest point designed in due to being easiest to replace, they would probably use a 7x19 cable so it could roll around a drum.
If you knew diameter and material then cable manufacturers specify breaking loads for their cable.
7x19 304 Stainless steel-
8mm = 4,082 kg breaking load, weight 25.8kg/100m
10mm = 5,980 kg breaking load, weight 40.0 kg/100m
11mm = 12,591 kg bl, weight 69.3 kg/100m
316 stainless isn't as strong with 5,310 kg breaking load for 10mm.

So with 9500lbs max working load there isn't much FOS with 10mm 7x19 304 SS cable yet it would be cheaper for material cost than using 11mm which would put FOS in the ballpark for proper engineering.
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Re: What happens when a winch reaches it's limit

Post by Wobble » 18 Nov 2016, 11:12 am

Ken wrote:I'm assuming a shear pin does as the name implies and snaps to release the strange before something breaks?


Yes, it's designed to break first and be easily replaced after.
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