Converting Tractor Hydraulics from engine to Electric

by Ben N on August 10, 2021

Tractors are mechanically complicated.
Besides a transmission, there’s also the connection for the Power Take-Off (PTO) and an engine-driven pump which powers the hydraulics.

Since there’s no longer an engine, we’ll have to replace the source of power for the hydraulics. Probably the easiest way to do this is with an electric motor and pump salvaged from a forklift. The downside is that the existing pump used a flanged connection on both ends, so connecting to it is NOT as simple as just threading in a pipe.

Instead, I needed to make a custom component that was the same size and shape as the flange mount. While I COULD have cut the existing metal hydraulic lines and used that as the start of the custom component, it would still be a fair amount of work, and it would destroy a classic tractor component which I might instead be able to sell to a collector for restoration work. Even if my design for a custom part failed terribly, I could always then go back and modify the original hard lines.

The first step was simply tracing the flange and taking some measurements. Frankly, that probably would have worked just fine. This part doesn’t need extreme precision – it just has to fit over the two o-rings. However, we also have a family friend, Fred M, who happens to be a life-long machinist. I took the opportunity to visit him and ask how he would take measurements of this part and put it into CAD. We spent some time over at his place doing this, and when we were done, we had an exact copy laid out in his software. The downside was that it was an OLD CAD program, and the only output on that computer was a FLOPPY DISK. Back at home, I would have to dig up an old computer to read the file!

Once I had the CAD file on my computer, I could start playing around with it in several ways. One was to bring it into my Cameo Silhouette Vinyl-Cutter software. From there, I could load cardstock into my machine and have it precisely cut out. This gave me a real-world, 100% scale paper model, which I could use to double-check against the tractor. Sure enough, it looked good!

The other thing I could do with the CAD file is open it in a modern 3D CAD program. I’ve been learning some of the basics of Fusion 360. In that software, I opened the file, extruded the flat shape into one the thickness of the part, and added some color. I could also use a feature in the program to quickly add other existing 3D parts, including the two hydraulic fittings I would add. In just a few steps, I had a great looking 3D model of what my part would be!

Now, I just had to make it real. A trip to the local farm store got me my hydraulic fittings. For the metal itself, I simply placed an order with a local metal supplier where I could order online and pick up in person.

I then printed out a copy of my shape, including center marks for the holes, cut it out, and taped it to the hunk of metal. I headed over to Fred’s to use the mill in his garage. It was a real treat to use actual machining equipment, instead of a cordless drill! We drilled out the holes, first by marking the centers, and then using progressively larger drill bits.

To round off the corners, I simply used a grinder.

With that, the main work on the part was complete, with the exception of threading the two main holes to 1/2″ and 3/4″ National Pipe Thread. I had done a little basic work threading before, but that was always on smaller holes and with straight threads. These holes would have a taper to them. It was decided the best way to do it would be using a tapered reamer, but we didn’t have that handy. I would have to come back some other time to finish the work. I left the part there with Fred, as that’s where we would do the work anyways.

Unfortunately our schedules didn’t work out with each other, and it caused a few weeks delay. The next time I talked with Fred, he said that he had done ahead, tapped out the holes, and threaded in the hydraulic fittings. I was a little disappointed not get to try that myself (and document the steps!) but was glad to be able to continue with the project.

I bolted the part onto the tractor, and it looked good! Then I pulled it off, primed and painted it, and got ready for final assembly. That’s when I realized that one of the wrong hydraulic fittings was used! I had to pull it out and replace it with the proper 3/4″ fitting. With that done, I could install the part.

Custom component AFTER replacing with the correct fitting!

On the electric hydraulic pump, I installed a reducing bushing and right-angle adapter to get the proper 3/4″ and 1/2″ input and output to match the tractor. I already had a 1/2″ hose, but needed a trip to the store to pick up the 3/4″. Assembling the hoses to the pump was pretty straight-forward – insert the hose, hand thread the swivel, and then give it a final twist with a wrench while holding the hose in place.

I WAS a little disappointed when I went to install the 1/2″ hose, only to realize it was actually the next size smaller! Oh well, another trip to the store…

An hour later, I continued my work, installing the 1/2″ hose to the pump and then making both connections on the tractor side.

The electric hook-up for the pump motor is pretty straight-forward. I just needed a positive and negative from a 12V battery. I installed a contactor inline with that circuit. Instead of using jumper cables and having a big spark every time I would start or stop the motor, this would make a nice, safe, and simple way to do it. I didn’t even bother to hook up a switch for the contactor, instead just using an alligator clip jumper to activate it.

Of course, I would need some hydraulic fluid in the system before any of this would work. Over the process of working on the tractor, it has all been drained. I opened the fill plug, noticed the dipstick with its FULL mark, and poured in most of a 5-gallon bucket of hydraulic fluid.

I was finally ready to test the hydraulics running under battery electric power!
Since the front-end loader was removed, the main tractor component left which used hydraulics was the rear 3-Point Hitch. A single lever just raises or lowers this by allowing hydraulic fluid to flow into or out of a large cylinder.

I connected the contactor, which turned on power to motor, and it spun up to speed. I put my hand on the 3-Point lever and swung it….
And….
NOTHING!

I could see and hear the motor spinning, but moving the lever did NOT move the 3-point hitch! What was wrong? I turned off the motor and sat there trying to figure it out. It didn’t take long for me to realize that I simply had NOT primed the pump.

The pump itself, along with the hoses to and from the pump had air in them. The air-bubbles prevent the pump from working properly. It will just spin, with NOT hydraulic fluid being pumped. I cracked the seal on the output hose at the tractor end, and flipped the motor on for a second. Almost instantly, I could hear the sound of the motor and pump change, the air purge, and hydraulic fluid start spraying out of the joint. I quickly stopped the pump, and wiped up the oil that was now on top of the tractor.

So NOW I was ready to test the hydraulics!
THIS time, moving the handle DID make the 3-Point raise and lower! The speed seemed about right, and this was with the pump only running at 12V.

I also wanted to see how much power the hydraulics was using. My multimeter features a current clamp and can measure both Alternating and Direct Current. I set it to DC, and clamped it on the battery cable with the hydraulic pump motor running. The motor was drawing about 50 amps. I also measured the voltage of the battery, while it was under load. Multiplying the two numbers gives me power measured in Watts, and that was around 600 Watts or so. It didn’t seem to matter much if the hydraulic fluid was just being pumped in a loop, or if it was being used to raise or lower the hitch – the current draw stayed the same. Of course, there wasn’t much load on the hitch either.

One thing that DID cause high current draw (at least for a moment) was when I would be starting or stopping the movement of the hitch with the lever. Basically, the hydraulic control has 3 positions – Raise, OFF, and Lower. Raising and Lowering routes the hydraulic fluid in opposite directions through the cylinder. The OFF position is more interesting in how it works. It’s an “Open Center” position. In that position, hydraulic fluid simply passes straight through the control, in a loop back to the hydraulic reservoir and pump.

In the original tractor setup, the hydraulic pump was mechanically geared to the engine. As long as the engine was running, so was the pump. There was no clutch or other mechanical disconnect to stop the pump. So, when doing NOTHING with the hydraulics, the fluid still has to circulate. If it didn’t, it would actually stall the pump and kill the engine!

Now that the hydraulics are driven by an electric motor, I CAN turn the pump off when it’s not needed. Seeing as how there’s about 600 watts of power being wasted just by having the hydraulic system on, I plan to install a switch to control the hydraulics separately from the rest of the tractor systems.

Now, I just have to get back to the tricky mechanical planning of mounting the electric drive motor while retaining the clutch and PTO!

Until next time, stay charged up!
-Ben Nelson

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