Fuel Economy, Hypermiling, EcoModding News and Forum - EcoModder.com - View Single Post - Paul and Sabrina's Cheap 3 Phase Inverter (AC Controller) with Field Oriented Control

ecorsa · 04-08-2010, 10:21 AM

Hi, New to forum, this is a great project.
I have just read through all the posts and think i have some info to bring to the party to help clarify some of the points raised so far.
1) off the shelf 3 phase induction motors which are avalable new for cheap and 2nd hand for next to nothing are generaly available in standard frame sizes. there is a number in the size which refers to the radius from the centre line of the motor shaft to the mounting line of the feet (if the motor has them). there are 3 standard mountings, face, flange and foot, the latter can be in combination with the former 2. this link to TEC's catalog will help with this. the aluminium ones TEC-A are the most relevant. (add www to the following)
bearingboys.co.uk/uploads/Tec-cataloque.pdf
2) there are lots of benefits to running higher voltages, here is my take on it
a) less I^2xR losses (power loss is proportional to current squared) so high current is bad news all arround. anything which can reduce currents is a good thing
b) Back EMF. As RPM increases so does back EMF, which works against the applied voltage to reduce the eficiency of the motor. the higher the operating voltage, the higher the RPM can go before this becomes a show stopping problem
c) Off the shelf (cheap) motors are set up to run higher voltages as they come, basically for the above reasons.
d) there are advantages to running more batteries of a smaller size i) this makes packaging easyer (can fit in lots of nooks and crannies) ii) if one craps out its cheaper to replace a small one. iii) cheaper hook up due to smaller cables.
Safery is obviously a concern with higher voltages, but you really need to consider anything over about 30V potentially lethal anyway.

04-08-2010, 10:21 AM	#233 (permalink)
ecorsa EcoModding Lurker Join Date: Apr 2010 Location: Scotland Posts: 5 Thanks: 0 Thanked 1 Time in 1 Post	Hi, New to forum, this is a great project. I have just read through all the posts and think i have some info to bring to the party to help clarify some of the points raised so far. 1) off the shelf 3 phase induction motors which are avalable new for cheap and 2nd hand for next to nothing are generaly available in standard frame sizes. there is a number in the size which refers to the radius from the centre line of the motor shaft to the mounting line of the feet (if the motor has them). there are 3 standard mountings, face, flange and foot, the latter can be in combination with the former 2. this link to TEC's catalog will help with this. the aluminium ones TEC-A are the most relevant. (add www to the following) bearingboys.co.uk/uploads/Tec-cataloque.pdf 2) there are lots of benefits to running higher voltages, here is my take on it a) less I^2xR losses (power loss is proportional to current squared) so high current is bad news all arround. anything which can reduce currents is a good thing b) Back EMF. As RPM increases so does back EMF, which works against the applied voltage to reduce the eficiency of the motor. the higher the operating voltage, the higher the RPM can go before this becomes a show stopping problem c) Off the shelf (cheap) motors are set up to run higher voltages as they come, basically for the above reasons. d) there are advantages to running more batteries of a smaller size i) this makes packaging easyer (can fit in lots of nooks and crannies) ii) if one craps out its cheaper to replace a small one. iii) cheaper hook up due to smaller cables. Safery is obviously a concern with higher voltages, but you really need to consider anything over about 30V potentially lethal anyway.