Electric Drive Motor Retrofit

[ptsg]

Yes, forklift batteries are definitely heavy! My electric forklift that can lift 3300 lbs has a 1700 lbs 24V battery. I've restored it in the past but I can't remember the HP of the motors. The one for the drive is a 3 speed big one.

The batteries are way too expensive to replace. The forklift doesn't really worth that much. Once the batteries die, I might just convert it to diesel. It doesn't get the use it used to get a couple years a ago.

 

[MossRoad]

If you can get your hands on a Baldor motor book, you will see that the torque increased as more load is applied. The torque can increase to 2 to 3 time痴 more than running torque. Baldor shows what they call "break-down torque". The torque can increase to 3 times or more than running torque. A motor produces it maximum torque at stall speed, and this is called "locked rotor torque". The motor torque does not fall off as the load increases. This is very simple. Gas engines only produce power every other revolution of the crankshaft. Electric motors produce power every single revolution. That is why a 10 hp electric is same as the 20 hp gas this being said, a 20 HP electric motor will need some VERY high capacity batteries, and be VERY expensive to buy, then there's the recurring replacement cost.. think LARGE rechargeable lithium batteries!..

By that logic, a 2 cylinder 2 stroke gas engine rated at 20 HP should need a 40HP electric motor to replace it, because it produces power every 180 degrees. It just doesn't work that way.

 

[MossRoad]

Agreed. To have any chance of working you need to throw away the hydraulic drive motors and use electric wheel motors. I don稚 think this is a feasible project the way it is. I really doubt the wind and rolling resistance of electric car is as high as load on a powertrac and they have way bigger batteries than will be possible for this project. The electric forklifts use massive batteries. I had to take my backhoe to go unload a forklift battery and it weighed 50 percent more than the whole PT does. And probably doesn稚 use as much energy. The electric forklifts only drive around on on flat ground which with a deep gear ratio doesn稚 take much power and lift the mast. Depending on the load that could take quite a bit of power but it痴 only momentary.

I agree that electric forklift batteries are very heavy. I helped maintain electric clamp trucks at a newspaper for about 30 years. Ours were rated at 10,000# lift. We used them to stack 2000+ pound rolls of newsprint in our warehouses, and unload rail cars. The batteries were not that large, maybe 3' x 2' x 2'. The area under the hood of a PT425 is about 2.5' x 2.5' x 18", the gas engine, battery and fuel tank taking up the most room. The PT425 only weighs about 1500#. I do not know the weight of our forklifts, or the weight of our battery packs. I suspect that batteries needed to power a motor large enough to supply adequate power to the PT4255's hydraulics for any amount of time might weigh quite a bit, but nowhere near as much in our 10,000# forklifts.

I think determining the size of the electric motor needed would be the first step. Then determining how long of a run-time at load is desired. Then determining how big a battery pack would be next. After that, you could determine the weight of the batteries, then decide if the PT wheel motors could handle that much weight squatting on them, and if the center link in the articulation could handle that weight as well.

 

[MossRoad]

Yes, forklift batteries are definitely heavy! My electric forklift that can lift 3300 lbs has a 1700 lbs 24V battery. I've restored it in the past but I can't remember the HP of the motors. The one for the drive is a 3 speed big one.

The batteries are way too expensive to replace. The forklift doesn't really worth that much. Once the batteries die, I might just convert it to diesel. It doesn't get the use it used to get a couple years a ago.

View attachment 592293

I agree that batteries, purchased new, would be ridiculously expensive. I can remember 3 of our electric clamp trucks that had batteries die on them, and they sat in the basement and/or warehouse for decades before they were scrapped, because the replacement batteries cost about as much as leasing a propane powered clamp truck for several years.

 

[4570Man]

I agree that electric forklift batteries are very heavy. I helped maintain electric clamp trucks at a newspaper for about 30 years. Ours were rated at 10,000# lift. We used them to stack 2000+ pound rolls of newsprint in our warehouses, and unload rail cars. The batteries were not that large, maybe 3' x 2' x 2'. The area under the hood of a PT425 is about 2.5' x 2.5' x 18", the gas engine, battery and fuel tank taking up the most room. The PT425 only weighs about 1500#. I do not know the weight of our forklifts, or the weight of our battery packs. I suspect that batteries needed to power a motor large enough to supply adequate power to the PT4255's hydraulics for any amount of time might weigh quite a bit, but nowhere near as much in our 10,000# forklifts.

I think determining the size of the electric motor needed would be the first step. Then determining how long of a run-time at load is desired. Then determining how big a battery pack would be next. After that, you could determine the weight of the batteries, then decide if the PT wheel motors could handle that much weight squatting on them, and if the center link in the articulation could handle that weight as well.

The battery I had to move was out of a 3600 pound capacity lift and it was about 18” thick and 3’ tall and 4’ wide and weighed 2200 pounds. This battery was lead acid. A lithium battery would be better but I still doubt it would be anything close to enough. I imagine the gas motor and fuel tank and battery isn’t over 300 pounds. The electric motor would make most of that back up. How much weight do you think you could add without adverse affects? But not to worry. Just add a solar panel to the hood and then add a canopy with another solar panel on top. If that’s not enough you could put a wind mill on the top. I’ve heard people claim both of the above for electric cars. Heck, those solutions are way too complicated. Just put generators on the blade spindles.

 

[4570Man]

By that logic, a 2 cylinder 2 stroke gas engine rated at 20 HP should need a 40HP electric motor to replace it, because it produces power every 180 degrees. It just doesn't work that way.

Agreed. That’s a foolish way of rating motors that doesn’t even work. A 3600 rpm 20 hp gas motor would in theory be equal to a 3600 rpm 20 hp electric motor. The 20 hp gas motor can’t make much more than 20 hp before it stalls and the electric motor can probably produce double that much for a brief period but it couldn’t do it very long.

 

[MossRoad]

The battery I had to move was out of a 3600 pound capacity lift and it was about 18 thick and 3 tall and 4 wide and weighed 2200 pounds. This battery was lead acid. A lithium battery would be better but I still doubt it would be anything close to enough. I imagine the gas motor and fuel tank and battery isn稚 over 300 pounds. The electric motor would make most of that back up. How much weight do you think you could add without adverse affects? But not to worry. Just add a solar panel to the hood and then add a canopy with another solar panel on top. If that痴 not enough you could put a wind mill on the top. I致e heard people claim both of the above for electric cars. Heck, those solutions are way too complicated. Just put generators on the blade spindles.

Perpetual motion! :laughing:

I have no idea how much weight the PT425 chassis can handle. I know several people have or condsidered either flipping the wheels inside out to gain width for hillside stability, or adding duals to that model and found that the factory doesn't recommend it because the wheel motors aren't made to withstand that type of side load, and will develop seal leaks and quickly wear the shafts, seals and bearings. So that's one thing... will the wheel motors be able to handle the additional weight of adequate batteries.

Lead acid batteries are what we used in our clamp trucks, bulldogs, and pallet jacks. Does anyone know the cost difference between those and lithium ion? I see there are Prius battery packs out there for a little over $1000. That includes shipping, but you have to add $750 for a core deposit. No core? That means $1750 for a Prius battery pack. And I have no idea of the dimensions of that battery pack.

Toyota Prius Gen 2 Hybrid Battery Replacement | Greentec Auto

 

[SpringHollow]

The rule of thumb though is that you need twice the size gas motor as an electric motor. And that held true when I converted my log splitter to be able to use electric or gas.

Ken

 

[radios1]

By that logic, a 2 cylinder 2 stroke gas engine rated at 20 HP should need a 40HP electric motor to replace it, because it produces power every 180 degrees. It just doesn't work that way.

no, By that logic, a 2 cylinder 2 stroke gas engine rated at 20 HP should need a 10HP electric motor to replace it!..

 

[MossRoad]

no, By that logic, a 2 cylinder 2 stroke gas engine rated at 20 HP should need a 10HP electric motor to replace it!..

In all reality, a 20hp engine and a 20hp electric motor both make 20hp. Horsepower is horsepower is horsepower.

 

[MossRoad]

 

[4570Man]

no, By that logic, a 2 cylinder 2 stroke gas engine rated at 20 HP should need a 10HP electric motor to replace it!..

In either case it’s a stupid logic that doesn’t work. If you were converting something like a wood splitter that only sees occasional and brief high load the undersized electric motor will probably work. If it’s a continuous duty load there’s no reason why a considerable amount smaller equal rpm electric motor could do the work. If it can then one the ratings was flawed.

 

[radios1]

In all reality, a 20hp engine and a 20hp electric motor both make 20hp. Horsepower is horsepower is horsepower.

the DC electric brushed motor makes power during the full rotation, each time the commutator aligns with a brush, torque is produced so you get more torque than a gas engine, which relies on a flywheel to keep the engine turning.. it's only single phase AC induction motors that only make torque each 180 degrees, and three phase AC induction motors make torque each 120 degrees. I did not yet correct my original post on this.

 

[4570Man]

the DC electric brushed motor makes power during the full rotation, each time the commutator aligns with a brush, torque is produced so you get more torque than a gas engine, which relies on a flywheel to keep the engine turning.. it's only single phase AC induction motors that only make torque each 180 degrees, and three phase AC induction motors make torque each 120 degrees. I did not yet correct my original post on this.

A 1750 rpm electric obviously has more toque than a gas motor. The 3600 rpm electric shouldn’t be much difference. Your logic is stupid and flawed. Does a 50 hp 2 cylinder gas do less work than a 50 hp 4 cylinder gas? If so where does the 50 hp 6 cylinder stand? The toque rise of the electric is much greater than the gas motor but it’s continuous duty load shouldn’t be any different. If a 20 hp electric motor could continuously do twice the work of a 20 hp gas motor than the rating is flawed. The gas motor either less than 20 hp or the electric was more then 20 hp probably both. Don’t confuse brief power rise with higher power.

 

[MossRoad]

the DC electric brushed motor makes power during the full rotation, each time the commutator aligns with a brush, torque is produced so you get more torque than a gas engine, which relies on a flywheel to keep the engine turning.. it's only single phase AC induction motors that only make torque each 180 degrees, and three phase AC induction motors make torque each 120 degrees. I did not yet correct my original post on this.

Now you're talking torque and that's different than HP. HP is HP and if they are both rated at 20, they'll both make 20. No way around it.

How bout we stop poking each other and get back to the OP's project.... :thumbsup:

 

[SpringHollow]

For an electric motor, the power it produces is a function of rotational speed relative to its rated speed. But the torque is the same throughout its speed range. I have seen the plots online before. (At near stall conditions, I do believe torque might increase as the motor draws more power.) So an electric motor can respond to an instantaneous heavy torque load rather well. That is the advantage of an electric motor. In the same situation, a gas motor would have to be oversized in order to respond as well. So in applications like a log splitter, the rule of thumb applies. For a constant load at rated speed, one is concerned with HP and you need the same size motors (or so I would believe).

Ken

 

[MossRoad]

Yep. That's the way I understand it, too.

 

[JD-Beach]

Thanks for all the responses, ideas, and links.

Yes, Moss, I'm the one who had Tazewell install the bigger wheels. I've been out of touch for a while running a business, marrying off children and enjoying grandchildren. I used my PT-425 to move migrating sand off of the beach every spring but then we had a seawall installed, so my tractor use decreased. I ended up selling my PT to my business partner with the condition that I could borrow it any time I wanted. Kinda like owning a machine without the maintenance or storage issues.

I've been thinking about buying a used machine for this project. … perhaps a ground-up restoration of a used machine.

I'll continue the research and report the progress.

JD

 

[JD-Beach]

Yes, current as in time. :laughing:

One thing I was thinking about. Since the PT425 is all hydraulic, and the gas motor only turns one-way, all you'd need is an electric drive motor and an on-off switch. No reversing circuit would be needed and no speed control would be needed. You could put in speed control for the electric motor, but would it really help anything? You need full flow to create enough pressure to do the steering/FEL functions well. The AUX PTO wouldn't need full pressure, but since it's fed from the same valve bank as the FEL, which is fed from the power beyond on the steering valve, it's gonna get the same pressure anyway.

I suppose you could put in some sort of sensors to only apply the motor when the forward are reverse pedals are pushed, but I think response would be awful. And then you'd have to figure out circuitry to do the same for the FEL and steering. That's why I'd think you always want the electric motor on at speed all the time.

Just some thoughts.

Moss, my thoughts exactly.... I understand that converting electrical energy to rotational to hydraulics back to rotational is not very efficient, however, replacing the wheel motors with electric motors introduces a whole new level of complexity. This would require speed and direction control and you would still need to run a pump for the steering and FEL. Plus consider a tight turn where the outside wheels turn faster than the inside wheels. The present hydraulic system has this all under control.

 

[JD-Beach]

There is a company in Ohio, “Mean Green Mowers”, that use small electric wheel motors on a zero-turn-mower. I called them to discuss this project. In short it appears that it would be much easier to use electric drive motors in a skid steer version of the project. Each wheel motor could be quite small and each side would require an independent controller. The articulated steering aspect and four-wheel drive of our PT’s adds much complexity to an electric drive motor conversion. For this reason, I should like to keep all of the hydraulics in place and overcome the resulting inefficiencies with more battery.

My thoughts are to focus on the single engine to motor conversion with an arrangement of batteries located around the motor. … and leave the remainder of the tractor intact. I understand that the PT tub will need modification. I’m prepared to hire out a welding shop to handle those mods.