Don't wish to put a dampener on your project but I think some maths need working on.
Your motor rating is only 3kW (4HP) assuming 100% efficiency. This seems far too small for a lawn tractor. Series motors are not constant speed, their speed being dependant on load applied which in turn increases current demand. (theoretical speed, ignoring physical restraints, at zero load is infinite) If from a fork-lift, they were probably used to drive the hydraulic systems which is only intermittent use. In a tractor they will be subject to continuous use and therefore may be prone to overheating. On basis that battery capacity is a pair of 100AH, 12volt units, with an average load of say 100A and limiting depth of discharge to 40% (too much some will say) the duration of running (or should that be crawling) will be a maximum of 24 minutes. Decent batteries are gone to weigh about 25+kg each so there will be a weight change in the tractor of +50kg for batteries and say -15kg for engine, so a net increase in weight of around 30kg.
I bought the Allegro sensors on ”breakout” boards with large double sided conductive path (looks gold-plated, not sure about that though) with 6mm bolt holes. I can´t find them on eBay anymore, so i don’t have a link. As I already have them, I’ll try them out, but if it proofs too inefficient, I’ll give you a call Docedison, thanks.
The motors are replacing a 13hp ice motor (maybe the right term is ride-on lawnmower rather than tractor). So about 4 hp for drive, which I think is more than enough, and about 4 hp for the blades which might be too little, but if it works I’ll probably be happy to cut the grass before it gets to long. With this setup, I can also eliminate some pulleys and the clutch, which hopefully will reduce the power requirements a bit. I’m going to use four 85ah marine batteries, and I’m hoping to get a couple of hours juice for just driving, and maybe 40 minutes of grass cutting.
The Arduino will try do reduce power to 130 amps per motor, and will allow 150-200 amps for max 5 seconds, and will shut of power completely if consumption is more than 200 amps for one of the motors. The Arduino also handles speed control, rpm-safety-shutdown, general safety, voltage monitoring, battery protection etc., but more on that when my code fails, and I´ll be looking for help in the programming sector
I bought an small electric forklift a while back for a different project, and the drive motor seems very similar in size and weight to the motors I'm going to use. It’s also 24 volts and series wound, but there no dataplate, so i cant be sure about the specs. I think it’s popular to use series wound motors for forklift, because its easy to reverse rotation by reversing power to either the stator or the rotor?
jackrae:
Your motor rating is only 3kW (4HP) assuming 100% efficiency. This seems far too small for a lawn tractor.
For a comparison you could look at the old GE "Elek-Trak" models -- the most popular model 12 was 1.5HP for the drive motor. They carried six batteries and ran at 36V.
MuttDriver:
The motors are replacing a 13hp ice motor (maybe the right term is ride-on lawnmower rather than tractor). So about 4 hp for drive, which I think is more than enough, and about 4 hp for the blades which might be too little, but if it works I’ll probably be happy to cut the grass before it gets to long. With this setup, I can also eliminate some pulleys and the clutch, which hopefully will reduce the power requirements a bit. I’m going to use four 85ah marine batteries, and I’m hoping to get a couple of hours juice for just driving, and maybe 40 minutes of grass cutting.
That sounds about right to me.
MuttDriver:
The Arduino will try do reduce power to 130 amps per motor, and will allow 150-200 amps for max 5 seconds, and will shut of power completely if consumption is more than 200 amps for one of the motors.
You should still use a breaker or fuse for overcurrent protection.
