I'm working on a project to use a three-phase motor on an electric = tractor.=20 As a proof-of-concept, I have replaced a 10 HP B&S gas engine on a = Craftsman=20 riding mower, with a 2 HP 3450 RPM three-phase motor, and I was able to=20 drive a short distance on an extension cord to single phase 240 VAC and = a 2=20 HP Fuji/GE motor controller. I have some youtube movies that show some = of my=20 progress, but they don't show my more recent better results.
My next step was to power it from batteries. A previous post about using = an=20 iron-core toroid to generate 350 VDC at 1.5 kVA or more was to be the = DC-DC=20 converter for this, and I still may build a more practical version. But = for=20 now, I wanted something simple, so I decided to use an ordinary = automotive=20 inverter. I used a full wave bridge to a pair of 3300 uF 400 V = capacitors in=20 series, with the common to one side of the AC, which generated about 320 =
VDC. It was able to power the VF drive, but the 175 watt inverter was = not=20 enough to run a 1.5 HP 1725 RPM motor. A 300 watt inverter worked for a=20 short time, but the 6 amp power supply kept tripping. So I replaced it = with=20 a 12 year old 17 A-H SLA battery and it was able to run the motor under = no=20 load, with only an occasional complaint from the inverter. Here are the=20 results:
RPM Vbatt Ibatt Freq Imotor Vmotor
0 12.4 1.0 0 0 0 300 12.1 7.0 10.0 2.41 42 450 12.1 7.0 15.0 2.32 62 900 11.8 8.0 30.0 2.35 121 1200 11.9 9.5 40.0 2.22 152 1930 12.1 7.0 61.0 1.35 164 2500 12.0 7.0 83.3 1.00 164The RPM values are based on synchronous speed. The motor seemed to have = good=20 torque, but I didn=E2=80=99t have a way to load it properly, and I = didn't want to=20 load the inverter too much. It seemed to complain when the battery = current=20 reached about 10-12 amps during start-up, especially at 1200 RPM.
I plan to buy a larger inverter for the last phase of this project. The = best=20 deals at Harbor Freight are as follows:
750W $50 $0.067/watt 1000W $80 $0.08/watt 1200W $100 $0.083/watt 2000W $160 $0.08/wattBut I found some much cheaper on eBay
3000W $100 $0.033/watt 1000W $55 $0.055/watt 1000W (220V) $43 $0.043/wattThose prices include shipping and are "buy it now" prices. If these will = do=20 the job, there's no way I can build one myself for anywhere near that = unless=20 I don't count my time and use surplus/junk box parts. And one facet of = my=20 project is to make the system modular and easily built anywhere in the=20 world.
But I want to use at least two batteries to get reasonable run time. = This=20 proof-of-concept phase is only for a utility cart which will probably = need=20 only about 1 HP average, so a single 100 A-H deep cycle battery should = give=20 at least one hour, which is fine. Even my 17 A-H SLA might give me 15=20 minutes, and I have another small battery I could add. But since these = are=20
12V inverters, I need to consider what is the best way to get the needed =link voltage. My best guess is to use one inverter for each battery, = connect=20 the AC through a FWB to get 160V, and then connect two in series for =
320V.=20 The batteries will be "hot", however, since the inverters are not = isolated.=20 So I just need to put them in plastic containers and use isolation=20 techniques to monitor voltage and current.I plan to make a datalogger to keep track of the power and energy used = under=20 various load conditions (mostly going up and down hills), to get an idea = of=20 efficiency. I want to compare my results to other electric tractors = which=20 usually use brushed DC motors or BLDCs, and relatively simple controls.
OK, enough of a "brain dump" for now. I'll post more when I have more to =
tell. Please feel free to comment and make suggestions.
Thanks,
Paul=20