Tachometer for DC motor in electric tractor

I just put a basic magnetic pickup tachometer on the tailshaft of this 13" DC forklift motor.
I wanted to know how many RPM it would spin at 12V.
Turns out that it's around 1200 RPM, or about 100 RPM/Volt.
An old tractor like this is designed to run at 1800 RPM or so for the PTO to spin at the correct speed. If I wanted to use this motor and get the PTO speed right, in theory, I could run it at 36V and 50% PWM.
When NOT using the PTO, it could be run faster.
This is the tachometer I'm testing out: amzn.to/3uR16qs

[@raymondeldred977]

I've never in my life heard of a forklift running on a (single) 12 VOLT battery... So he just replaced the gas motor with a wrist watch motor..

[@BenjaminNelsonX]

This is just for testing.
You never want to run a DC Series Wound motor unloaded at higher voltages.
By testing at 12v, I can just multiply to see what the RPM would be at 36 or 48v.

[@kylekleman]

Any update on project? Cool tractor!

[@AKIOTV]

And it just keeps speeding up haha. I assume it's a series motor, which without load will spin up to infinite rpm, although the friction in the bearings will limit the rpm at some point, if by then it hasn't torn itself apart. But on only 12v it may be pretty safe, what rpm did you end up reaching?

[@BenjaminNelsonX]

Just a little over 1200. Yes, it’s a series-wound motor, so I was only testing it at 12v. No need to spin it up crazy!

[@rickway2039]

Im super excited to see this one come along. Any idea on the HP of that motor? These old 450s pushed about 50hp. As long as you can get the input shaft spinning at the right rpm for the pto to turn 500 rpm, should be good

[@BenjaminNelsonX]

This tractor was rated at about 38HP.
I should have plenty of RPMs at 36 or 48v, and can throttle it down to the appropriate speed through the motor controller. I don’t have a great way to test the torque of this motor, other than to use it. But it’s a 13” diameter series-wound. It should have MASSIVE torque!

[@bromdulasta]

So 12 miles per hour??

[@BenjaminNelsonX]

No. We are just talking RPM at the motor here. Nothing to do with the transmission or tire size.
The stock tractor is designed to go up to about 15 mph, but in theory could actually go much faster than that, not that you would want to!
Most tractor work is about torque, not speed.

[@bromdulasta]

@@BenjaminNelsonX ah got it, thanks for clarifying