Electric tractor

[SPYDERLK]

Sorry to inform you, but prime time has passed you by. In the industrial world, electric forklifts far out produce their IC powered brothers. Just take a look at this manufacturer. Crown Forklift | Electric Forklift | Crown Equipment. Electric forklifts move far more goods than their IC counterparts. I guarantee that every morsel of food you but from the store was move far more by Electric trucks than IC ones.

That is because they dont produce fumes and are cleaner to maintain. The problem is that they have to carry the better part of a ton of batteries to do the miniscule total work they are required to do in comparison to even a lawn tractor. It is wonderful that they or any electric vehicle can produce tremendous torque and power by drawing the stored energy quickly. The problem is they cant draw it for long w/o being dead. Driving around on on flat hard surfaces takes only a little more than nothing. Continuous up and down inclines will eat them up. Regen braking would improve this at the cost of complexity, but battery, motor/gen heating problems will shorten component lives. Making an electric tractor would be fun. If you dont have low expectations for the actual real world work it has to do tho you will ultimately be disappointed.
larry

 

[FlaDon]

That is because they dont produce fumes and are cleaner to maintain. The problem is that they have to carry the better part of a ton of batteries to do the miniscule total work they are required to do in comparison to even a lawn tractor. It is wonderful that they or any electric vehicle can produce tremendous torque and power by drawing the stored energy quickly. The problem is they cant draw it for long w/o being dead. Driving around on on flat hard surfaces takes only a little more than nothing. Continuous up and down inclines will eat them up. Regen braking would improve this at the cost of complexity, but battery, motor/gen heating problems will shorten component lives. Making an electric tractor would be fun. If you dont have low expectations for the actual real world work it has to do tho you will ultimately be disappointed.
larry

GE sold a lot of electric tractors and with more modern battery tech, the weight is becoming less of a problem.

 

[varmint]

This has been real interesting, like so much stuff that gets chewed around this site! Some years ago, I worked part time for the Electric Launch Company (ELCO) helping make one-off boats. The larger ones were 33', driven by 48 volts, if I remember, really heavy, large batteries, and not cheap. The charge/discharge cycles were pretty well thought out, and everything was optimized via' knowledge and experience. The boats would run all day on a charge, carrying 20+ people at a cruise speed of around 6 knots. The weight of the batteries was a plus, since they needed ballast anyway. Of course, moving thru water is different than moving over terrain, but they were (are?) great boats for their application. Electricity is not without environmental costs, but it should be a lot cleaner, with stack scrubbers and such, than burning diesel in your backyard. Plus, the batteries are very recyclable.

 

[Nat]

SPYDERLK, I am not going to try to tell anyone about something they know more about than I do, but here is a link to a man who truck gardens with a battery powered G Allis Chalmers tractor that he converted to an electric moter. He can tell you if it has enough power and if it will do actual tillage, and you can look at his website and see pics of him doing it. HTH, later, Nat
Allis Chalmers "G" Electric Cultivating and Seeding Tractor Conversion Project

 

[Wayne County Hose]

That is because they dont produce fumes and are cleaner to maintain. The problem is that they have to carry the better part of a ton of batteries to do the miniscule total work they are required to do in comparison to even a lawn tractor. It is wonderful that they or any electric vehicle can produce tremendous torque and power by drawing the stored energy quickly. The problem is they cant draw it for long w/o being dead. Driving around on on flat hard surfaces takes only a little more than nothing. Continuous up and down inclines will eat them up. Regen braking would improve this at the cost of complexity, but battery, motor/gen heating problems will shorten component lives. Making an electric tractor would be fun. If you dont have low expectations for the actual real world work it has to do tho you will ultimately be disappointed.
larry

The large batteries in an electric forklift are a plus. They act as the counterweight. "Miniscule amount of work?" The modern electric forklifts routinely outperform their IC counterparts. Inclines are nothing in amp draw compared to lifting 3,000 lbs. 40 feet and higher. I have been an electric forklift mechanic for 22 years. I have worked in engine rebuilding shops and built race engines. Apples to apples, a modern electric system smokes IC stuff. Just look at locomotives and submarines, and your largest earth moving equipment, all electric. I guess earth moving equipment never climbs grades, after all, the earth is flat, isn't it?

 

[IanH]

Ian,,, is there a formula where we could take the horsepower, torque, and rpm of an I/C engine and convert it to tell us what we would need component wise for a conversion?

Hi, I'm afraid when replacing an IC engine with an electric drive there isn't really a quick formula. There might be if all that was needed was to replace the engine with a motor of the same nominal power - but that would over specify the motor in many applications.

For the two wheelers we might be able to say that if the original IC engine was well matched to the machine and was often used near it's max power output then an electric motor with the same continuous power rating might be needed. If the machine is mainly used at power output levels well less than the IC engine peak output then such an electric motor may well be over specified. Figuring out just what would be needed gets a bit involved.

A quick note to say that the actual power drawn by the machine is duty dependent - fitting a motor that has more torque capacity than is needed doesn't mean that it will deliver that higher torque - it will only deliver what the machine asks for. So there is a argument for saying that so long as the extra cost doesn't bother you, fitting a motor with a bigger power output capacity than is actually needed won't hurt for normal operations - it will only deliver what the machine asks for. If stalls are likely to be a frequent occurrence then that argument changes.

Generally stalling can also be an issue - however with the two wheelers the limited download on the wheels should act a bit like a mechanical fuse - ie the wheels should slip if too much torque is applied.

The basic power unit conversions are easy enough though - 1 HP is approx 3/4 kW.

Don't know if this helps.

Ian

 

[IanH]

Maybe some more detail will help. I have an old sales brochure that lists the shipping weight of the basic David Bradley tractor with the tires on it and a 1 3/4 gas engine at 238 pounds. The claw tread tires were 6.00 x 16.

42 lb wheel weights were an option for each wheel plus the tires could be filled with liquid ballast. The engines were 1 3/4 hp up to what may have been about 7 or 8 hp in the last years of sales, but most were 2-5 hp machines, I suspect. Most I've seen had Briggs & Stratton engines.

The pulley visible in the photo above the tire that Nat posted is the clutch pulley. Power is transmitted to this clutch pulley and then internally this drives the differential. On the basic models, the speed was adjusted by changing the size of the pulley on the engine. The ground travel speed was advertised as being changable from a top speed of 2.4 mph to 2.1 mph at 3200 rpm by changing the engine pulley. Minimum speed was .7 mph. On some later models, the speed was adjusted by moving a lever that controlled a variable size pulley on the clutch. Also, on some later models, there was a reverse feature and a differential lock.

There was a front mounted 24" inch rotary mower attachment and a 24" reel mower attachment offered. I saw a picture of a wider attachment on another website that appears to be a 3 blade unit, but couldn't find the specs.

The plow, disk, etc. mounted to the rear. The plow had a shipping weight of 58 lbs. The front mounted snow plow had a shipping weight of 53 lbs.

It's not a very wide machine. The tires can be shifted in to 16 1/2 inch on center of the tread to 24 inches on center of the tread. Clearance under the tractor was 11 inches. The claw tread tires were advertised as having a height of 28 inches.

I'm guessing that Nat's model may be the basic model because I didn't see the levers for the variable pulley, the reverse or the cable control for the differential lock.

It shouldn't be too hard to mount an electric motor to the DB just because it's so open and it's belt drive. They also had a ride on cart that connected to a hitch on the drawbar on the rear of the tractor. So you could put the batteries in the cart.

Although I was thinking I'd like to see a Gravely converted to electric power, the DB should be easier to convert.

Thanks for the info.

The 238 lbs is a good deal less than the 350 lbs I used for the motor power estimate. If I go with the same traction coefficient of 0.6 and 2 mph speed the ideal wheel power consumed with the machine at the limit of slip would drop to a tentative 840 watts x 238/350 = 570 Watts. This would still need to be factored up to cover any loses in the mechanical transmission to get an indicative motor power output. So a 750 W motor might do it rather than a 1000W unit, it's easier to get 24V motors at the lower powers and a 24V system, needing 2 x 12V batteries might be wee bit easier to package than a 36V 3 battery arrangement but there's not much in it. I'd look at how much cost I'd save with a smaller motor and if it wasn't much I would still be tempted to try the bigger one - more capacity to play with if the sums are wrong.

The availability of weights and wheel ballast confirms traction was an issue, and the availability at the time of 7 or 8 Hp machines makes me wonder how all that power was used - and if I'm missing something, it has been known!

On the +ve side a lighter machine should mean lower current draw as the wheel torques can't rise so high, and this will prolong the duration of the batteries.

If the IC engine speed was 3200 rpm, then this is helpful because the max speed of many electric motors isn't going to be much different from this and perhaps the existing transmission elements might be used as is. This would need to be checked once a motor was selected and its actual specs known. Strictly speaking an electric drive wouldn't need a clutch as the controller could take it from zero to full speed and reverse without mechanically disengaging the drive. But it may be too much trouble to muck about with.

Hmm... who's going to have a shot? I guess we would never really be sure until one was converted and set to work.

Ian

 

[FlaDon]

Thanks for the info.

The 238 lbs is a good deal less than the 350 lbs I used for the motor power estimate. If I go with the same traction coefficient of 0.6 and 2 mph speed the ideal wheel power consumed with the machine at the limit of slip would drop to a tentative 840 watts x 238/350 = 570 Watts. This would still need to be factored up to cover any loses in the mechanical transmission to get an indicative motor power output. So a 750 W motor might do it rather than a 1000W unit, it's easier to get 24V motors at the lower powers and a 24V system, needing 2 x 12V batteries might be wee bit easier to package than a 36V 3 battery arrangement but there's not much in it. I'd look at how much cost I'd save with a smaller motor and if it wasn't much I would still be tempted to try the bigger one - more capacity to play with if the sums are wrong.

The availability of weights and wheel ballast confirms traction was an issue, and the availability at the time of 7 or 8 Hp machines makes me wonder how all that power was used - and if I'm missing something, it has been known!

On the +ve side a lighter machine should mean lower current draw as the wheel torques can't rise so high, and this will prolong the duration of the batteries.

If the IC engine speed was 3200 rpm, then this is helpful because the max speed of many electric motors isn't going to be much different from this and perhaps the existing transmission elements might be used as is. This would need to be checked once a motor was selected and its actual specs known. Strictly speaking an electric drive wouldn't need a clutch as the controller could take it from zero to full speed and reverse without mechanically disengaging the drive. But it may be too much trouble to muck about with.

Hmm... who's going to have a shot? I guess we would never really be sure until one was converted and set to work.

Ian

Well I was going to do a 2-wheel Gravely but dad has other ideas. So a 4 wheel one is what will end up being built. As I already have a 24V motor, that also sets what the voltage will be. The motor for the tractor is aircraft quality and is rated at 9.5 HP at 3600 RPM. As for a controller, way back in the 70's we used an electronic controller for controlling 4 .55HP motors on model locomotives. These weren't small ones like you have inside, but ones that weighed in the 500 to 800+ lb range. The overload capacity of an aircraft quality motor is up to 100% for X amount of time. Railroad locomotives ( full size) also have an overload rating and depended on time vs overload to get the trains moving.

To get a rough figure of what an electric motor can do vs an ICE figure 1 electric HP = 2 ICE HP.

 

[SPYDERLK]

The large batteries in an electric forklift are a plus. They act as the counterweight. "Miniscule amount of work?" The modern electric forklifts routinely outperform their IC counterparts. Inclines are nothing in amp draw compared to lifting 3,000 lbs. 40 feet and higher. I have been an electric forklift mechanic for 22 years. I have worked in engine rebuilding shops and built race engines. [[[Apples to apples]]], a modern electric system smokes IC stuff. Just look at locomotives and submarines, and your largest earth moving equipment, all electric. I guess earth moving equipment never climbs grades, after all, the earth is flat, isn't it?

[[[Apples to apples]]] - electric is wonderful for fine control and hi torque, actually rising as it stalls-like a diesel except electric can do it all the way to zero rpm. But apples to apples about battery power being able to compete with IC power in the tractor world is a different story. All things are parasitic to the engine. In the case of your examples, the sub has a nuclear engine and the train a diesel. These engines are providing the electric power. The conversion from heat to electricity has losses unfortunately, but in these cases the power loss is allowed for in the design because the parasitic electric drive simplifies final transmission of the mechanical drive power. In all cases of electric drive somewhere there is an engine making it possible. The A/C mains rely on an engine. This engine provides the power to charge the battery with the small amt of energy it will store. In doing this it provides to the battery about 1.5 times as much energy as it can store. This is necessary to fully charge the battery - - and it is necessary to fully charge the battery both for its health and to give the parasitic vehicle the best possible chance of doing a reasonable amount of work and still being able to get back to the engine. Because of this energy storage limitation the energy must be used carefully, in planned ways -- efficiently. A locomotive would go a long way if filled with batteries - rolling friction of steel on steel is close to the ultimate efficiency. Unforfunately to do something useful it must pull a payload that is not batteries up long hills. Better take an engine along and just leave the batteries. Rolling friction of hard rubber on concrete is pretty efficient too, so most of the energy used on the level by a forklift is used for acceleration and lifting. But if the plan doesnt hold up just perfect you find that that 10000# forklift that will lift 3000# 40' high may need to take the whole 13000# up a couple of 5' inclines. This more than doubles the energy use of the 40' lift and in the case of lower lift heights the incline energy use becomes proportionately greater. Now start dragging things around on the ground like is normal with a tractor. Dont get far from the engine.
larry

 

[FlaDon]

Straight battery locos and hybrid locos are being built today. Both are being used to move the source point of pollution away from places such as LA/Long Beach. Also, as the hybrids use the engines only to keep the batteries charged, they can be set to run at their peak power to fuel point.