Powering Attachments

liteblue · Mar 13, 2006

Newbie question: I can easily understand that all tractors have a horsepower loss at the pto (vs. gross engine HP), especially those with hydrostatic transmssions. But for powering in-place/stationary attachments like log splitters or chippers, the power loss should be less (i.e. there is no other draw on the engine). In fact, wouldn't the power loss be much less significant? What am I missing here? /forums/images/graemlins/confused.gif

crazymike · Mar 13, 2006

most stationary attachments don't require much in the way of HP.

A log splitter is hydraulic which is based on the hydraulic system output.

A generator or water pump uses minimal engine power.

The things that require high HP from the PTO such as bailers and spreaders require you to be moving to function.

The few items that do require HP such as chippers, etc... still require small amounts of HP

LarryD · Mar 13, 2006

Are you looking to buy an attachment that is marginal for you machine?

I would suspect that manf. published PTO HP numbers are determined on a stationary unit to provide the highest values and in fact my be lower depending on any other loads.

Of course I haven't slept in a Holiday Inn Express in a while so I could be wrong. /forums/images/graemlins/grin.gif

BB_TX · Mar 14, 2006

I think what you are referring to is the mechanical losses due to gearing etc. from the engine to the PTO shaft. If there is a 10% mechanical loss from the engine to the PTO, then that loss is there whether you are moving or stationary. What you are confusing is the total available power. If your tractor has 30 HP and it is stationary, then the power available to the PTO would be 30 HP minus the losses. If you are in motion, then the power available to the PTO would be 30 HP minus the losses associated with the PTO mechanics AND minus the power required to put the tractor in motion. So, yes, you will always have more power to the PTO when stationary.

EdKing · Mar 14, 2006

The power loss is due to the coupling through the transmission. Same as in a automobile, you have engine HP, then you have HP available at the rear wheel. The measurement of the PTO is done with the tractor stationary. At the local Long dealer where I worked as a mechanic, we had a dyno to measure PTO HP, and it was a stationary unit. On the very early tractors, which used a large flywheel and a belt, the PTO was coupled to the engine rather than the transmission, and the PTO HP was rated higher than the HP at the wheel.

Soundguy · Mar 14, 2006

( horsepower loss at the pto (vs. gross engine HP), especially those with hydrostatic transmssions )

To be fair.. you'd probably have to look at the actual tranny setup. If the pto is run off a counter shaft, and is tied to engine rpm.. then the hp loss at the pto is not based on the hydrostats hp loss to the wheels.. etc. if it was a full hydro pto.. (?? not sure who has that? powertrak? ).. then thet hyd loss would need to be factored in ).

( wouldn't the power loss be much less significant? What am I missing here? )

I'd expect to see pto hp.. no more even when stationary.. as the others said. pto hp is figured on a dyno.. and the tractor aint moving when that is going on..

Most log splitters i see, use a pto powered pump... and the size pump you can run will depend on your tractor's pto hp.. etc..

Soundguy

liteblue · Mar 14, 2006

Thank you Ed/BB/Soundguy! I now understand the difference. The way you guys explained it makes perfect sense. Once again TBN'ers to the rescue.

Joe /forums/images/graemlins/laugh.gif