Don Nielson
Aluminum
- Joined
- Dec 29, 2007
- Location
- California
On a RPC does the idler motor need to be the bigger,smaller, or the same size as the motor you want to run? Don
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Rpc
- Thread starter Don Nielson
- Start date
- Replies 3
- Views 1,103
toolnut
Stainless
- Joined
- Aug 3, 2005
- Location
- Kingsport, TN
Don,
This is a hot topic of discussion among RPC builders.
Basically I can think of two or three scenarios that might help guide you.
Case 1. for an uncompensated idler design (no run caps), you need an idler at least 2X the sum of the load motors that will run at once.
Case 2. for a fully compensated idler design (run caps on both generated phases and well tuned to a plus 10% voltage balance at idle), I use an idler one size larger than the largest load motor or the sum of the load motors running at one time.
Case 3. for hard to stard loads (air compressors) you may need to go two idler motor sizes larger depending on the quality of the compressor. Compressors with unloaders will start much easier than ones without unloaders.
Examples of installations:
I have a 10 hp idler, 80 amp single phase circuit RPC operating a 7-1/2 hp blower and a 6 hp wood shaper. You can start them in any order and they work fine.
A 5 hp idler, 40 amp single phase circuit RPC, operating a one person wood shop with these tools. 5 hp x 16" table saw, 2 hp mortiser, 3 hp x 12" jointer, 3 hp x 20" wood lathe, 3 hp x 30" bandsaw and a 5 hp x 24" planer. The bandsaw is the hardest to start but the little 5 hp gets the job done.
A 5 hp idler, 30 amp single phase circuit RPC, operating a 2 hp Bridgeport mill, a 3 hp Colchester lathe and a 1 hp Harig surface grinder. This one has capacitors on one leg and can start these machines easily and it will run two of them at at time.
This is a hot topic of discussion among RPC builders.
Basically I can think of two or three scenarios that might help guide you.
Case 1. for an uncompensated idler design (no run caps), you need an idler at least 2X the sum of the load motors that will run at once.
Case 2. for a fully compensated idler design (run caps on both generated phases and well tuned to a plus 10% voltage balance at idle), I use an idler one size larger than the largest load motor or the sum of the load motors running at one time.
Case 3. for hard to stard loads (air compressors) you may need to go two idler motor sizes larger depending on the quality of the compressor. Compressors with unloaders will start much easier than ones without unloaders.
Examples of installations:
I have a 10 hp idler, 80 amp single phase circuit RPC operating a 7-1/2 hp blower and a 6 hp wood shaper. You can start them in any order and they work fine.
A 5 hp idler, 40 amp single phase circuit RPC, operating a one person wood shop with these tools. 5 hp x 16" table saw, 2 hp mortiser, 3 hp x 12" jointer, 3 hp x 20" wood lathe, 3 hp x 30" bandsaw and a 5 hp x 24" planer. The bandsaw is the hardest to start but the little 5 hp gets the job done.
A 5 hp idler, 30 amp single phase circuit RPC, operating a 2 hp Bridgeport mill, a 3 hp Colchester lathe and a 1 hp Harig surface grinder. This one has capacitors on one leg and can start these machines easily and it will run two of them at at time.
jim rozen
Diamond
- Joined
- Feb 26, 2004
- Location
- peekskill, NY
Idler motor should be larger.
My general rule is 50 percent larger than the largest
load motor, and it should be tuned with capacitors at that
size. YMMV as they say.
For a one hp b'port, a 5 hp idler won't really *have* to
be tuned.
Jim
My general rule is 50 percent larger than the largest
load motor, and it should be tuned with capacitors at that
size. YMMV as they say.
For a one hp b'port, a 5 hp idler won't really *have* to
be tuned.
Jim
gpkull
Cast Iron
- Joined
- Nov 6, 2006
- Location
- south east US
don i run a 1 hp bp off a ancient 2 hp lincoln motor. i spin start and have 25/15 mfd bal. i can plug rev all day. starting in high they both grunt a bit but nothing excessive.. motor and caps under 50.00 disconnect had laying around. wattever you do dont go static
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