PTO HP numbers

[Ken45101]

I've noticed that some manufactures specify their PTO HP at full rpms which are 25% above what you run the engine at for standard 540 PTO rpm. IOW, the published PTO hp spec is totally unrelated to the speed you would use the engine at.

For example, NH TT series gives the pto HP at 2600 rpm, but for 540 PTO attachments, you run at under 2000 rpm. Kubota is the same way with the M series, (although the MX series has to run flat out to get 540, so those specs would be meaningful.)

I don't suppose there is any way to figure out the PTO hp at 540, is there?

The reason I'm looking at this is that I'm looking for a larger rotary cutter than the 6' I currently have. The rule of thumb I've heard here is 5 hp per foot of cutter.

 

[art]

Ken, there are various ways of running equipment and the RPM's needed to run it well. Just like with many numbers, we wonder how did you get there?

I'd say either of your tractors would do it well although if you bought a mower that would cut 4 to 5" stock you would be way to low of horsepower.

 

[Ken45101]

I'd say either of your tractors would do it well although if you bought a mower that would cut 4 to 5" stock you would be way to low of horsepower.

But I'm looking at buying a 12 or 15' mower.

12' times 5 hp/ft would require 60 pto HP. The New Holland is only 43 hp at 2600 rpm, but for 540 pto, you are supposed to run it at 1940 rpm, which would obviously have a lot less than 43 hp.

I'm debating on trading the New Holland (only 30 hours) on a Kubota M7040 or 8540.

Ken

 

[sandman2234]

I hate to think of the beating your going to take, trading in a tractor with only 30 hours on it.
As far as the run of 5hp per foot of bush hog, that rule is subject to a lot of interpetation. Not that I disagree with it, as we have to have a baseline, but just how much tractor it takes to turn a 12 or 15 foot bush hog really depends on several things, such as what your mowing (seasonally maintained pasture or right of ways, etc?)
If I were completely sure I was going to have to spend a lot of money trading up, I think I would go ahead with the bush hog purchase, getting the one that I needed. Then hook it up to the tractor I have and go give it a whirl. However the drawback to that is, once you clear an area, and keep it cleared, it takes less hp to maintain it, rather than that first cutting, so consider that also. You might want to clear an area with your 6' hog, and wait till it needs mowing again before trying out the larger mower with the existing tractor.
Just a few thoughts to consider,
David from jax

 

[MESSMAKER]

I would think you should be in the market for a 8' or 10' model. I can't imagine you could do a 15' model.

 

[Ken45101]

I hate to think of the beating your going to take, trading in a tractor with only 30 hours on it.

Better to trade it now than wait a year. Actually I was offered a better trade in than I expected.

One problem with giving it a try with what I have is that I'd have to add an additional remote. No sense spending that money if I'm pretty sure it's not going to have enough horsepower.

Yes, I realize that if I'm cutting pasture that's under control, it will be easier than one that's overgrown. My hope is that with a larger mower, I'll be able to get it done fast enough to keep it under control, LOL.

Ken

 

[piller]

I've got an M8540HD. One of the reasons I stepped up to the 8540 was that it would allow me to make round bales or pull a batwing mower.

Presently I have a Woods 10' pull type rotary cutter. I was mowing some thick stuff yesterday in a pasture that had not been cut in 1.5 years. The 8540 barely knew the bush hog was back there, in the thickest stuff the digital PTO speed readout dipped less than 10 rpm.

Believe it or not but I actually use my 8540 with R1 tires pulling the 10' bush hog to mow around the house, the result is very good, the maneuverability is not however. This works well for my soil conditions as long as it has not rained in a couple of days. I wish though that I had either bought the 9540 or upgraded my wheels/tires to the 9540 size, in radials.

From your sig it appears you have an M5040HD, I would think that having an M5040HD and also an M8540/9540 would be a very nice setup indeed.

I agree that it makes sense that the manufacturers should provide PTO HP and torque data at the PTO 540 rpm engine speed.

 

[schmism]

For example, NH TT series gives the pto HP at 2600 rpm, but for 540 PTO attachments, you run at under 2000 rpm. Kubota is the same way with the M series, (although the MX series has to run flat out to get 540, so those specs would be meaningful.)

you know this to be a fact?

if so i guess the NH TT series is significantly diffrent than my TC. 540rpm on my tractor (as indicated by the dash light) occurs at about 2500 rpm.

 

[ampsucker]

i think what you need is the horsepower and torque curves for the actual engine you are considering.

often peak horsepower and peak torque occur far from max rpms.

a good engineer will design pto speed to coincide with engine rpm at the point where the engine gives max torque AND max horsepower.

for example, here is the info for the kubota bx24 engine, the d902.

Kubota Diesel Engine Super Mini series - Model D902

take a minute to study the charts and get your bearings. a lot of information is presented here.

while horsepower continues to climb up to the rpm limiter, peak torque actually occurs near 2800 rpms. pto speed on these motors is around 31-3200 rpms essentially splitting the difference between peak hp and peak torque.

also note that minimum fuel usage occurs around 1800-1900 rpms, not at idle like most would assume.

every engine is different. for your own tractor and engine, you might want to take that into consideration instead of just blindly assuming that peak horsepower and peak torque occur at maximum rated engine rpm and drop down linearly from there the lower rpms go. this is almost never the case.

amp

 

[chh]

Part of what you are seeing on the numbers is that the manufacter is listing the rated hp at the 1000 rpm pto setting. This is getting to be more common to use this number instead of the 540 pto rpm number on larger tractor models. The 540 rpm pto hp is listed in the specs(somewhere)

Here is a link to the Nebraska Test reports which will gives all the tested rating info that at least is standardized. The new TT series is included as well as the Kubota models.

NE Tractor Test Publications