Effective PTO HP on a JD 4520 with E-PTO

[eepete]

I have a JD 4520 with E-PTO. The tractor has 50 HP on the PTO at the rated engine speed. My questions is what is the HP of the PTO when I have the E-PTO engaged and am at the lower (and correct) engine speed?

Years (decades?) ago, you could get torque curves for engines (torque vs. RPM). As you gear up the PTO for the economy mode, it would have less torque. Combined with reduced engine speed that should mean less power. I suspect the answer to my question will involve wrestling with concepts of torque and horse power.

The event that has triggered this questions is I purchased a SpeeCo PHD that is rated at max PTO of 40 HP. While I normally get good quality and well matched attachments all from my JD dealer, I only need to make 36 6" holes for my next project. I'm sure there will be more holes in the future, seems like every time I use my manual post hole digger I swear it's the last time and it's not. So the PHD decision was a mix of a fit of frugality tempered with the local clay soil and not too big rocks. I am hoping that careful use will make it work and the $600 I saved will be good in the long run.

I've also used my MX6 mower with the e-PTO. It really bogs down the tractor when I engage the PTO, but my dealer says it's OK. I use it like this when I'm effectively "mowing the lawn" and it's all level surface with grass where I'm taking off 4" or so. I've also used the sickle bar in this mode and it seems to have all the power it needs. I use the MX6 in "normal" PTO mode in areas that get cut once a year, and it's great. One pass at 5 MPH and I'm done.

So there's my questions and circumstances that brought it up. TIA.

Pete

 

[jenkinsph]

Pete,
I have wondered about this too and don't have an answer for you. I have an older Deere 31B phd and have sheared the bolt that holds the auger in place with no damage done to the gearbox or pto driveline. I think that using the e pto setting is a good way to limit the chance of damage though, I would go for it.

I know that Cummins has torque and horsepower curves for most of their industrial engines, don't know about Deere.


Steve

 

[radman1]

If your 4520 has HST, it is rated at 50 hp. I rarely (ok, never) run a pto driven PHD, at pto speed. I don't use a pto PHD any more, but when I did I typically ran them a low engine rpm and they seemed to dig better, less wobble, can control how fast they dig easier and probably safer to operate. I would rather kill the tractor engine, then break the PHD or replace a shear bolt. Just throttle back your 4520 and you will save your shear bolts, be below your max 40hp for the PHD and it should work good. I don't think e-pto is the solution to reducing power for a PHD.

 

[jenkinsph]

If your 4520 has HST, it is rated at 50 hp. I rarely (ok, never) run a pto driven PHD, at pto speed. I don't use a pto PHD any more, but when I did I typically ran them a low engine rpm and they seemed to dig better, less wobble, can control how fast they dig easier and probably safer to operate. I would rather kill the tractor engine, then break the PHD or replace a shear bolt. Just throttle back your 4520 and you will save your shear bolts, be below your max 40hp for the PHD and it should work good. I don't think e-pto is the solution to reducing power for a PHD.

I agree with using lower engine speeds and find the auger is easier to control.

If he uses the e pto at a low engine speed he will definately lower the torque available to the phd. This is just simple gearing and simple math.


Steve

 

[eepete]

The normal RPM for the PTO is 2300 (i think) the RPM when using the e-PTO is 1750. The little bit I've been on the tractor, it seems that power seems to drop of fast around 1400 RPM. So the mix of using the e-PTO and running at 1400 to 1500 RPM seems like it will work. And the RPM could go lower if I needed to reduce power more. The fact that both of you run PHD at less than PTO speed is good to know. The lower RPM combined with the e-PTO gearing and I think I'm good to go.

Just for fun I'll ask my dealer to contact Deere Central and get the PTO rating for the PTO when in e-PTO mode. When/if I hear back I'll post the number here.

radman1: I'm curious why you think that the e-PTO is not a good solution to reducing the power to the PHD? I agree with Steve that it seems like a good way to reduce torque/power to the PHD.

Pete

 

[radman1]

radman1: I'm curious why you think that the e-PTO is not a good solution to reducing the power to the PHD? I agree with Steve that it seems like a good way to reduce torque/power to the PHD.

Pete

The e-pto will increase your pto rpm more than you need. I prefer the slower turning auger on the PHD. Say you run the tractor at 1400-1500 rpm engine speed. The e-pto will give you a much faster auger rpm on the PHD than I feel you need. At 1400-1500 engine rpm and in normal pto, you will run the auger slower, and yet be under the max pto hp of 40 recommended by the PHD company.

Most diesel tractors have max pto hp in the 1700-1900 range, depending on the size of the motor. Look at the NE tractor tests. Hp ratings are given at pto speeds of 540 or 1000, depending on the pto shaft/output. However, the max engine hp is at the lower rpms because of the torque/hp curves. This is how the diesel engine can power through tough conditions. Now if the e-pto operates the engine at 1740 rpm, it is probably very near the peak engine/pto hp. I feel it is best to run the PHD at a normal pto setting and at a lower rpm of 1400-1500, get below the hp peak and still have a slow auger rpm on the PHD. However, with lighter duty mowing, run the e-pto to get the 540 rpm for best cut for the mower, and yet save fuel, engine wear, less noise etc.

 

[jenkinsph]

Some good points by all so far, my idea of low speed is throttled down all the way which on my tractor is around 1250 to 1300 rpm. Next week I should be ready to start a fence project with about 250 to 260 post holes, I will try both the standard and e pto settings to see what works best. I am also looking forward to utilizing the tilt function on my hitch to help plumb the auger.


Steve

 

[orlo]

Just a note that everybody is already aware of but I'll mention it anyway.

With EPTO being the exception (A mechanical increase in the PTO shaft speed compared to engine speed which reduces torque to the PTO shaft compared to normal PTO operation).

Also, I'm not talking about a dead stop situation where 'kinetic' (my term) horsepower (flywheel/mass effect) can shear things, I'm talking about loading the implement without stopping it.

Reducing the speed doesn't necessarily reduce the ability to shear pins. HP isn't what shears pins, bends tillers, etc. it's torque. The reason we can use HP to rate implements is that they are always rated at 540RPM which means only the torque varies with HP variation. Every 1hp of rating equals about 9.72 ft/lbs of torque. So if you have 10 pto hp available (again, at 540) you have 97.2 ft/lbs of torque at the shaft. go to something like 56 on the 4720 and you have 544 ft/lbs of torque (a sh##load in technical terms) - That's a lot of torque. And realize that will INCREASE slightly as engine speed decreases (Remember the governer will increase the throttle to maintain speed so it shouldn't matter what speed you have the throttle set at).

Most diesel engines actually have more torque when you slow them down a bit from operating speed (Deeres are like this also). If you slow it way down of course you'll reduce the torque, but if you slow it down a little you can actually INCREASE the torque
when it's under load.

This is why as somebody already mentioned a torque curve is helpful for determining the PTO HP and torque at any given RPM.

 

[eepete]

I heard back from the dealer. He said no one has ever asked that question before. He called Deere and they said that:

"The 540/'540 economy' PTO allows operators to select the engine rpm needed for their PTO application. The economy position provides 540 rpm to the PTO at approximately 70 percent of the engine's normal rated speed. Effective PTO HP in the 540E mode is 65% of the rated PTO HP. The 4520 is 50PTO HP times 65%. The effective HP rating is 32.50PTO HP."

This would also explain why the MX6 _really_ lugs down the tractor, and I have to be at 1900 RPM to start it. The PTO range on that cutter is 30 to 70 HP. So getting back to the PHD the e-PTO at 1500 RPM will probably be perfect for 6" and 9" holes. Sounds like I could use my 15 to 30 HP tiller too (width constraint is the big problem there). Because of it's name, the e-PTO sounds like a fuel saving device but in fact it can let you use a broader range of implements and let you play with PTO speed, much like the PTO speed selector on other tractor brands. The name (e-PTO) might be how you market an old trick to a the new dogs.

Steve: I remember in another post your saying that your idle speed was 1250 to 1300. Mine is 1100. The operator and service manual state it's 1100, and advises that at 600 hours you should "check low engine idle speed". Later, in the service engine section the action to take if it's off is to "see your John Deere dealer. Wonder if this ties in with your computer problems. Just FYI

I'm getting a hydraulic top link top link (ordering it today). That should leave me with only one axis to worry about.... I should be drilling my holes this weekend if the weather co-operates. Look forward to hearing how things work for you.

Pete

 

[jimgerken]

You can't run the PHD slow enough, in my opinion. I run mine on a 540 PTO with the engine at idle (44 HP tractor). If I hit something like a root, I get in less trouble this way.