There are a lot of posts regarding grain motor sizes. It seems the consensus is that a 1/4 HP, 1720 rpm motor will do the job (geared down by a ratio of around 8). This pulls the rpms down to around 215 and pushes up the torque to about
73 in-pounds (assuming no energy loss)
1/4 HP = (torque in ft-lbs)*RPM/5252
Without gear reduction, 1720 rpms and about 9 in-lbs torque (0.75 ft-lbs)
My first question is does anyone know if these rpm ratings are the max they can run? I have a barley crusher malt mill and they say don't go over 500 rpms. I have no idea the resistance to crushing grain to back calculate the required torque but have seen people crush with about 40 in-lbs. If I have more torque than I need, will it run at higher RPMs? For example, say I take this 1/4 HP and 1720 rpm rated motor and gear it down to 215 RPMs. This can generate 73 in-lbs of torque at this speed. If I am only drawing 24 in-lbs of torque to grind the grain, will the rpms triple to 645? Or do they max at the rating and actually go at the same speed for variable torque requirements (draw less power)?
My second question pertains to the type of motors. There are AC, DC, single phase, triple phase etc. Sometimes they aren't listed in HP, but are listed in VAC. I noticed DC motors are much more expensive. When someone says they bought a 1/4 HP 1720 RPM motor, should it be obvious that it is one of these styles?
My third question is when motors are given in VAC, my conversion to HP is far off. 1 HP ~= 747 Watts, 1 Watt = 1 Amp * 1 Volt,
This McMaster-Carr AC Gearmotor states 10 rpms, 1 full load amp, 40 in-lbs torque, with a single phase 115 VAC @50/60 Hz
1 amp*115 Volts = 115 Watts; 115 Watts/747 = 0.154 HP;
0.154 HP*5252/(10 rpms) = 80.9 ft-lbs torque = 970 in-lbs torque>> 40 in-lbs.
I am obviously fundamentally flawed and think it has to do with the VAC.
That was a lot, thanks for any input!
73 in-pounds (assuming no energy loss)
1/4 HP = (torque in ft-lbs)*RPM/5252
Without gear reduction, 1720 rpms and about 9 in-lbs torque (0.75 ft-lbs)
My first question is does anyone know if these rpm ratings are the max they can run? I have a barley crusher malt mill and they say don't go over 500 rpms. I have no idea the resistance to crushing grain to back calculate the required torque but have seen people crush with about 40 in-lbs. If I have more torque than I need, will it run at higher RPMs? For example, say I take this 1/4 HP and 1720 rpm rated motor and gear it down to 215 RPMs. This can generate 73 in-lbs of torque at this speed. If I am only drawing 24 in-lbs of torque to grind the grain, will the rpms triple to 645? Or do they max at the rating and actually go at the same speed for variable torque requirements (draw less power)?
My second question pertains to the type of motors. There are AC, DC, single phase, triple phase etc. Sometimes they aren't listed in HP, but are listed in VAC. I noticed DC motors are much more expensive. When someone says they bought a 1/4 HP 1720 RPM motor, should it be obvious that it is one of these styles?
My third question is when motors are given in VAC, my conversion to HP is far off. 1 HP ~= 747 Watts, 1 Watt = 1 Amp * 1 Volt,
This McMaster-Carr AC Gearmotor states 10 rpms, 1 full load amp, 40 in-lbs torque, with a single phase 115 VAC @50/60 Hz
1 amp*115 Volts = 115 Watts; 115 Watts/747 = 0.154 HP;
0.154 HP*5252/(10 rpms) = 80.9 ft-lbs torque = 970 in-lbs torque>> 40 in-lbs.
I am obviously fundamentally flawed and think it has to do with the VAC.
That was a lot, thanks for any input!
