Im in the process of building a 10 HP RPC. The problem I'm having is the idler motor starts but rotates slowly. I will try to attach my schematic (Im new here so if I have issues I'm sorry but hello everyone.) I think the issue may be with my start capacitance. I'm using approx.700MFD. I read a few threads and some say 100 MFD per HP and as low as 35 MFD per hp. I have about 85 MFD running cap across L1-L2 and L2-L3. My potential relay is a Supco apr 5. Also I do not have the 15k resistor across the starter cap. (because I don't have one yet but I believe the circuit should run without it.) Any recommendations would be greatly appreciated. Also everything is wired with 10 gauge wire.
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Rotary phase converter issue starts and runs slow.
- Thread starter tink123
- Start date
- Replies 11
- Views 4,223
Joe Miranda
Titanium
- Joined
- Oct 19, 2004
- Location
- Elyria Ohio
Are you sure you have the motor wired for low voltage?
From your drawing, looks like you are using a delta wound motor.
These can work, but are a bad choice for RPC's.
Normal RPC designs are for Y wound motors, cap values are based on Y wound.
Delta wound only energizes one phase winding internally.
Y wound energizes two windings internally.
With delta motors you need a converter 3X the size of your load.
With Y motors you need a converter 1.5X the size of your load.
SAF Ω
These can work, but are a bad choice for RPC's.
Normal RPC designs are for Y wound motors, cap values are based on Y wound.
Delta wound only energizes one phase winding internally.
Y wound energizes two windings internally.
With delta motors you need a converter 3X the size of your load.
With Y motors you need a converter 1.5X the size of your load.
SAF Ω
The motor is a Leland Faraday model LFI-3100B. Is their a way to verify how the motor is wound. When I received the motor it was setup like the schematic above with T3,T5, and T9 tied together and etc. It doesn't have a drawing on the motor. Is there anything on the plate that would designate that it is delta wound?
The connections indicated are consistent with it being delta, and some make no sense as a wye, such as the 1, 6, 7 connection in low volts.
johansen
Stainless
- Joined
- Aug 16, 2014
- Location
- silverdale wa
electrically delta and wye are identical, but thermally they are not.
Something like 75% of the heat is in one winding, with 25% of the heat in the other two windings, when run on single phase as a motor.
wye motors split the heat between two windings evenly. this is why you can run a wye motor up to 57% of its nameplate hp as a single phase motor, delta is limited to 50% or less, i can't recall.
(you can find on google images of burned out "single phased" motors and delta is one winding destroyed, wye is two windings destroyed, but those images are not proof that all of the current was only flowing through the single winding for a delta connected motor, but it has become common knowledge one way or another that delta connected motors cannot be run from single phase)
anyhow if that motor isn't worth anything to you, you can make a synchronous motor from it and use that as an rpc, it will need a pony motor to start it up and some additional fail safe electrical interlocks. but it will generate better three phase than an induction motor rpc. (it would be less work to use a 3 phase generator head as an rpc if you can get one cheaper than the time required to cut slots in the induction motor's rotor and wind a field coil..)
Something like 75% of the heat is in one winding, with 25% of the heat in the other two windings, when run on single phase as a motor.
wye motors split the heat between two windings evenly. this is why you can run a wye motor up to 57% of its nameplate hp as a single phase motor, delta is limited to 50% or less, i can't recall.
(you can find on google images of burned out "single phased" motors and delta is one winding destroyed, wye is two windings destroyed, but those images are not proof that all of the current was only flowing through the single winding for a delta connected motor, but it has become common knowledge one way or another that delta connected motors cannot be run from single phase)
anyhow if that motor isn't worth anything to you, you can make a synchronous motor from it and use that as an rpc, it will need a pony motor to start it up and some additional fail safe electrical interlocks. but it will generate better three phase than an induction motor rpc. (it would be less work to use a 3 phase generator head as an rpc if you can get one cheaper than the time required to cut slots in the induction motor's rotor and wind a field coil..)
rons
Diamond
- Joined
- Mar 5, 2009
- Location
- California, USA
For a start: 
You don't need to disconnect C1 from P1 when the motor is starting. You should be using both points on K2 for the start capacitor.
Wire it so that L1 --> P1, L2 --> P2, P3 is the generator. The terminology is usually to call the Px lines Tx, T1, T2, and T3.
What rpm is the 10hp motor plate say?
You don't need to disconnect C1 from P1 when the motor is starting. You should be using both points on K2 for the start capacitor.
Wire it so that L1 --> P1, L2 --> P2, P3 is the generator. The terminology is usually to call the Px lines Tx, T1, T2, and T3.
What rpm is the 10hp motor plate say?
rons
Diamond
- Joined
- Mar 5, 2009
- Location
- California, USA
No, my suggestion means to connect the start capacitor to T3 through TWO of the relay contacts. That distributes the current across two paths.
Learn how to attach pics, just one, not three.
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