PHD torque question

[beesnstuff]

Hi there,

I have a question about PHDs. When I look at Danuser F8 digger, I see 1813 ft-lbs torque in their specs:

Model F8 | PTO Auger | Danuser

but I thought HP=Torque-in-ft-lbs*rpm/5252

so if my tractor (JD5083e) suppose to have 65 HP at the PTO (540rpm).
I should have 632 ft-lbs of torque on the PTO.

How can the digger put out 1813 ft-lbs if PTO has only 632 ft-lbs of torque? Danuser magic?

where is my calculation wrong? How much torque is there on JD 5083e (65 HP on PTO) PTO?

 

[ishiboo]

No, it's pretty simple to see from that equation if RPM decreases, torque can increase... and vice versa.

The bit does not spin at 540rpm, it spins at a much slower speed. The gearbox ratio is 4.125:1, so for every 540 revolutions your PTO makes, your bit does 130. 632 ft-lb * 4.125 = over 2600, so that means your PTO output is large enough to drive it at its maximum capacity. That's what shear bolts and slip clutches are for.

In addition, the torque given is based on the maximum it can handle... if you hooked it to a 40hp PTO, you would obviously have less torque than your 65hp PTO, right?

 

[beesnstuff]

No, it's pretty simple to see from that equation if RPM decreases, torque can increase... and vice versa.

The bit does not spin at 540rpm, it spins at a much slower speed. The gearbox ratio is 4.125:1, so for every 540 revolutions your PTO makes, your bit does 130. 632 ft-lb * 4.125 = over 2600, so that means your PTO output is large enough to drive it at its maximum capacity. That's what shear bolts and slip clutches are for.

In addition, the torque given is based on the maximum it can handle... if you hooked it to a 40hp PTO, you would obviously have less torque than your 65hp PTO, right?

Thanks. It makes more sense. Gear box is what is slowing down the rotation and the torque goes up and the power cannot just disappear, it is transferred (with small losses, I guess).

With my tractor I will probably be breaking bolts if I hit something and the tractor will try to spin it at 2000 ft-lbs+.
I think my better bet will be the hydraulic drive like danuser EP15. I can transfer more power from my tractor to the bit without breaking the shear bolts. 16 GPM@2800psi should put out 2500 ft-lbs and spin it at about 50 RPM.

 

[ishiboo]

Your tractor is sized appropriately for that and will be a good match for that PHD, I wouldn't worry about it. Plus a 3-point is a lot cheaper. Only go hydraulic if you really want to loader-mount it, or if you frequently need "reverse."

 

[jenkinsph]

One big diference I find between a 3ph auger and hydraulic auger you need to consider is engine speed. Most people use idle speeds for 3ph digging not 540 rated rpms, hydraulic models require higher engine speed operation in most cases. I sold my 3ph auger and bits last year since I never use it anymore, the backhoe mounted PA30 does everything better for me.

 

[beesnstuff]

One big diference I find between a 3ph auger and hydraulic auger you need to consider is engine speed. Most people use idle speeds for 3ph digging not 540 rated rpms, hydraulic models require higher engine speed operation in most cases. I sold my 3ph auger and bits last year since I never use it anymore, the backhoe mounted PA30 does everything better for me.

Thanks. Good point. Another "pro" for hydraulic. I'm pretty sure most people drive 3pt PHDs at the slowest speed possible. I would. That means PTO is not delivering full torque (at 540rpm) that the tractor is capable of which means in the end less torque to the bit.

Let's see.

Here are pros and cons of hydraulic drives:

Pros:
-----
- higher torque because of better power delivery, all power can be delivered to the bit at LOW rpm
- no shear bolts
- more control
- slower speeds
- downpressure (loader mount)
- easier positioning
- ability to reverse

Cons:
------
- price (~4K vs 1K for 3pt PHD)

Here are pros and cons of PTO drives:

Pros:
-----
- much cheaper (1K vs 4K)
- easier setup (no hoses to the front of the tractor)
- always ready, as long as PTO spins, but it needs tractor hydraulics to work so it is not really a "pro"

Cons:
------
- lower torque
- shear bolts
- higher speeds
- no downpressure
- no ability to reverse

I've learn long time ago to buy quality tools. Pay more once rather than pay less many times. So I'm going to buy a hydraulic drive (danuser 1530 or 2035).
If I spend less time clearing post holes, breaking stones by hand, I will have more time to do other stuff around the farm.

 

[Sawyer Rob]

Many years ago I bought a cheapo PHD and yes it worked, but it didn't start digging holes easily, in anything but soft ground and would not drill worth hoot if there were any rocks below the surface. NOW, on the other hand, my brother paid much more and bought a Bush Hog brand PHD. WOW, what a joy to use compared to mine, and after seeing how my brothers started holes and worked, I was wishing BIG TIME I had spend more $$ and bought a better unit.

Well, after a few years my brother decided he didn't need his any longer and he sold it to me, AND I've been a happy camper PHD user ever since! lol

SR

 

[jenkinsph]

Thanks. Good point. Another "pro" for hydraulic. I'm pretty sure most people drive 3pt PHDs at the slowest speed possible. I would. That means PTO is not delivering full torque (at 540rpm) that the tractor is capable of which means in the end less torque to the bit.

Let's see.

Here are pros and cons of hydraulic drives:

Pros:
-----
- higher torque because of better power delivery, all power can be delivered to the bit at LOW rpm
- no shear bolts
- more control
- slower speeds
- downpressure (loader mount)
- easier positioning
- ability to reverse

Cons:
------
- price (~4K vs 1K for 3pt PHD)

Here are pros and cons of PTO drives:

Pros:
-----
- much cheaper (1K vs 4K)
- easier setup (no hoses to the front of the tractor)
- always ready, as long as PTO spins, but it needs tractor hydraulics to work so it is not really a "pro"

Cons:
------
- lower torque
- shear bolts
- higher speeds
- no downpressure
- no ability to reverse

I've learn long time ago to buy quality tools. Pay more once rather than pay less many times. So I'm going to buy a hydraulic drive (danuser 1530 or 2035).
If I spend less time clearing post holes, breaking stones by hand, I will have more time to do other stuff around the farm.

You can add down pressure kits to some of the 3ph phd models. I still prefer to have reverse though, I may encounter large boulders to gravel and everything in between. I no longer need to carry my large pipe wrenches or have helpers.