[brian_]

I still don't get what are the "buffer" and "2 small white wires" you're referring to.

The "buffer" would be the Tennant B7 floor burnisher which the motor came out of.

 

[brian_]

There is a serial number and something else engraved in the case above the label... what else does it say there?
In a quick search I found one online listing for the ME0709 (other than Motenergy's usual useless listing), and the cable with the two white wires is not in that one... and that listing says "No temperature sensor", suggesting that another version could have a temperature sensor.
So my guess is that the temperature sensor theory is correct, but it's only a guess.

 

[brian_]

Well now I feel silly. My old jumper cables are apparently broken somewhere in there. I used a different set of cables and sparks flew and the shaft spun like a champ.

Well, stuff happens.

Now to the spec label.
It says 24-72v and 104 amps continuous duty. Do you think it will pull more current in bursts? I wonder because it says 8.8hp (max) which is about 72v at 104 amps. I'm trying to figure out which controller would work well but I dont want to spend more than necessary for an overkill controller. It's for a little tractor conversion.

More complete specs are available, as noted earlier...

In a quick search I found one online listing for the ME0709 (other than Motenergy's usual useless listing)...

... including the (bolded for emphasis) short-term maximum current:

Motenergy ME1003 PMDC electric motor
Brush-Type motor.
Permanent Magnet Direct Current motor
Efficiency 92% at 48 VDC.
Rotation speed 48 RPM per Volt
Rotation speed 570 RPM at 12VDC.
Rotation speed 2300 RPM at 48VDC.
Rotation speed 3450 RPM at 72VDC.
Controller input voltage 12 à 72 VDC.
Constant torque at 0.20 Nm/Amp.
Rated power 11,5kW, peak 20kW (28hp).
Rated current 200A continuous
Rated torque 35Nm at 200A.
Max. DC current 400A during 30sec.
Max. torque 80Nm at 400A.
No temperature sensor
Output motor shaft 7/8"
Shaft key 3/16"
Recommended power cable 70mm² with 8mm lugs
Regen current in brake mode 5,6A per Nm
Brushes life about 1500 hours
Weight 17,9 Kg
Dimensions : Diam. 200mm x 188mm

The torque constant (not "constant torque") of 0.20 Nm/A implies 20.8 Nm at 104 A (approximately regardless of speed) - and a burst of 80 Nm at 400 A - with voltage requirement dependent on the speed and current. The no-load speed at 72 V is listed as 3450 RPM (the result of the motor constant of 48 RPM/V), but at 20.8 Nm the speed would be about 3000 RPM to deliver 8.8 HP.

Real motors are certainly not ideal, but the ideal model of motor constants (listed here as KV = 48 V/RPM and KT=0.2 Nm/A) is still useful, along with the basic relationship of power = torque * speed.

 

[brian_]

Ya I suppose that just because it looks like an me0709 and it's made for 24-72v, it doesn't mean that it is an me0709. I don't want to go overboard on the controller but I also don't want to limit the motor by the controller.

The motor constant can be approximately determined by applying various voltages (or even just one) and observing the resulting no-load speed. If KV is the same as an ME0709 then KT will be, too (KT is just the inverse of KV, in appropriate units of measure).

 

[brian_]

I think those specs are for the me1003.

Oops... clicked the wrong link! Sorry. But the idea is the same - just find anyone listing more useful specs. Even the Motenergy page lists "300 amps peak (1 minute) and 125 amps continuous", which may be enough information.

 

[brian_]

I don't know that I do. It was a 12hp gas tractor, so I thought I'd like to be on that ball park.
What I know I don't want to do is spend the $ for a controller that's overkill.

The engine power rating is probably at a specific speed, and the tractor may operate the engine at a lower speed, so there may never be 12 horsepower available. I do understand wanting a surge current and torque capability, so a momentary load doesn't stall the motor.