Hybrid Power Trac

[woodlandfarms]

So what would be more efficient. Electric wheel motors and pto pump, or on big motor driving the master hydraulic pump? Could you get motors small enough to be wheel motors yet strong enough to move 2000 lbs.

I assume the consensus is the 425 would be the ideal platform given use times vs size?

 

[ponytug]

If you don't do mowing, I think you might have a shot at it, although 3 hours of run time is a long time for battery power, especially if you are trying not to deep discharge your battery pack.

You would have a great shot at really really lowering your center of gravity.

I can put you in touch with people that I know who have done everything from electric shopping carts to electric couches (big hit at Burning Man) and cars.

I am sure that quiet would be worth something to some of your customers. Let us know how much extra they were willing to pay.

All the best,

Peter

Pony,
I have done a little reading on some of the EV conversion sites and I think, for some, an electric Power Trac could work. I use mine commercially and , except for field mowing, I don't think I actually put more than 2 or 3 hours of run time on it during the day most of the time. It seems that the electric motors are very compact so after removing the engine and fuel tank, there would be lots of room for batteries. And unlike a road vehicle, where weight is a negative, it would be good in the tractor. I sure like the idea of a quiet PT. Might be a fun experiment if someone came across an old PT with a blown engine.

 

[ponytug]

Electric motor hands down. And it would be worth it to you to replace your hydraulic power attachments in favor of electric motor driven attachments. Large digital controlled motors have efficiencies in the high 90s. See Electric Motors and Guide to buying electric motors

In the horsepower range that we are talking about efficiencies are in the 90% efficiency range, against 72% for hydraulics (85% pump x 85% motor).

Motors are no problem. Most electric cars use two, one on each wheel. With four, you would be ripping.

Now you are going to keep this clean, and dry, right?

Given your slopes, you might want to consider sealed AGM batteries for the 45 degree side slopes.

I think that green or red doesn't matter, it just changes the cost and the resulting performance.

All the best,

Peter

So what would be more efficient. Electric wheel motors and pto pump, or on big motor driving the master hydraulic pump? Could you get motors small enough to be wheel motors yet strong enough to move 2000 lbs.

I assume the consensus is the 425 would be the ideal platform given use times vs size?

 

[SnowRidge]

So what would be more efficient. Electric wheel motors and pto pump, or on big motor driving the master hydraulic pump? Could you get motors small enough to be wheel motors yet strong enough to move 2000 lbs.

I assume the consensus is the 425 would be the ideal platform given use times vs size?

The trouble with electric wheel motors is the needed controller. To be efficient, it would have to be some sort of chopper or pulse width modulator. (I'm assuming a bit here. I haven't looked into it.) That would let you get rid of the complicated drive pump, so it would be a trade-off.

You would probably want to keep the hydraulic steering, but you wouldn't want the pump running unnecessarily. That might require some tricky engineering. An accumulator with a pressure switch might work.

The more I think about it, the more I would like to see someone give it a try. Just not me.

 

[KentT]

Since you guys are talking in the theoretical, over my head, I thought I'd post this example of a gas-generator powered, electrically driven garden tractor conversion. Note, however, that it was done by a guy who designs/builds the controls for a living. This is not a "shade-tree engineering" type of mod, IMO. So, that leaves me out, for sure...

Simply Shocking?

 

[woodlandfarms]

So you both brought something up that I had not considered...

How do you keep the controls and motors clean in such an environment? If you seal a motor the housing would have to be huge to dissipate the heat, and reostats really hate dirt of any kind...

You guys think the hypothetical electric PT platform would be best suited to the 425 chasis?

 

[MossRoad]

The PT uses four hydraulic motors, one at each corner, in a series/parallel configuration. As you all know, standing still, if you turn the steering wheel right, the front right wheel rolls backwards while the rear right wheel rolls forwards. While that is going on, the left front wheel is rolling forwards while the left rear wheel is rolling backwards. How are you going to replace the hydraulic motors with electric motors and achieve that same motion and not spend a gazillion dollars doing it? It would require some very expensive controls.

 

[SnowRidge]

The PT uses four hydraulic motors, one at each corner, in a series/parallel configuration. As you all know, standing still, if you turn the steering wheel right, the front right wheel rolls backwards while the rear right wheel rolls forwards. While that is going on, the left front wheel is rolling forwards while the left rear wheel is rolling backwards. How are you going to replace the hydraulic motors with electric motors and achieve that same motion and not spend a gazillion dollars doing it? It would require some very expensive controls.

More to the point, how are you going to brake it? When the PT is still, the tram pum is centered, and I think there is a bit of a fluid path from one motor to another, which allows the wheels to move in your above scenario. You could do the same thing with electric motors, just by open circuiting them, but you would then have a roll away issue. You could also short circuit them and get considerable rolling resistance. It would not, I think, prevent the static turning scenario, so I think I just answered the question as I typed.

The real problem is braking. You could brake electrically, but it would complicate things. Drum or disc brakes could be added, but the PT's treadle control system does not lend itself to a foot brake, except for those among us with three feet.

 

[ponytug]

Guys, it really isn't that bad.

Rheostats are so last century. More to the point, they are horribly inefficient. Use a PWM controller, so, "Yes", you need one of those pulse width modulated controllers. In the same vein, you use the electric motors to brake and reverse, which is trivial, plus you get all of that energy back. Good news is that the controllers are widely available for car conversions. (I was amazed when my electric car buddy showed me his home brew design for his race car; it was a one million watt controller, but if you do the math, that would be what you need. A PT is just slightly ahead of golf cart power, way behind cars. And yes, Virginia, the controller is totally water proof and sealed. Ditto the motors, but I don't think that they are submersible in the normal configuration. With a little engineering, anything is possible.

As MR brings up, you will need to have a computer controlled differential, or wire the motors diagonally, but, again, the commercial car controllers do allow for it. You will need a new steering controller. (If you raid it off of a Prius, you would get some snazzy on wheel controls.)

Seriously, it might be a step above grandpa's shade tree engineering, but not much. There are lots of sites devoted to electric conversion.

There are even members amongst us with race records for electric vehicles... (No, not me.)

And no from an efficiency perspective, you don't want to have a hydraulically driven tractor power by an electric pump, although it might be the low cost solution and the easiest to implement. If you aren't religious about it, it is by far the simplest. The motor could easily be activated and governed by the hydraulic pressure in the various circuits. This is definitely something grandpa could do.

All the best,

Peter

The PT uses four hydraulic motors, one at each corner, in a series/parallel configuration. As you all know, standing still, if you turn the steering wheel right, the front right wheel rolls backwards while the rear right wheel rolls forwards. While that is going on, the left front wheel is rolling forwards while the left rear wheel is rolling backwards. How are you going to replace the hydraulic motors with electric motors and achieve that same motion and not spend a gazillion dollars doing it? It would require some very expensive controls.

 

[Bob999]

Dear Bob999,

Your numbers are accurate for the older generation of plants, but the current (80's onward) plants have efficiencies well over 35%, approaching 50+% in the best coal fired plants.

Peter,

I would be interested in the source of your information about current producing power plants.

The following quote is taken from the Department of Energy web site:
Department of Energy - Electric Power

"Research is also underway to increase the fuel efficiency of coal-fueled power plants. Today痴 plants convert only a third of coal痴 energy potential to electricity. New technologies in Energy痴 Fossil Energy program could nearly double efficiency levels in the next 10-15 years. Higher efficiencies mean even more affordable electricity and fewer greenhouse gases."