Upgrading my simple RPC, questions

Investigator said:
Will this do it?

https://www.ebay.com/itm/7-5HP-Rota...134475?hash=item264360300b:g:rzQAAOSwo4pYNIuX
Click to expand...
it will do but you can do it for a lot less money

there are many ways of doing it, but it doesn't get much cheaper than this...

www.hobby-machinist.com

Rpc simple design unbalanced

Rpc simple design Here's a simple plan for an unbalanced 220/240 v single to 3 phase converter. this design will start ANY 3 phase motor of ANY horsepower with a change of start capacitors! keep in mind,the contactor coil is 220v in this design, adjust coil voltage for high voltage use(480v)...
www.hobby-machinist.com www.hobby-machinist.com
 
Last edited:
Ulma Doctor said:
it will do but you can do it for a lot less money

there are many ways of doing it, but ti doesn't get much cheaper than this...

www.hobby-machinist.com

Rpc simple design unbalanced

Rpc simple design Here's a simple plan for an unbalanced 220/240 v single to 3 phase converter. this design will start ANY 3 phase motor of ANY horsepower with a change of start capacitors! keep in mind,the contactor coil is 220v in this design, adjust coil voltage for high voltage use(480v)...
www.hobby-machinist.com www.hobby-machinist.com
Click to expand...

My question/concern is having to use 2 switches basically at the same time to get things started; 1 to power the assembly and 1 momentary to start the motor. Is there a single switch that functions the key ignition on a car in that turning it 'on' is a half turn with a momentary on in position 2 that will automatically turn it back to position 1 when released?
 
the normally closed stop in combination with a normally open start is a common motor starting latching circuit.
the capacitor in my design is operated by the start switch, once the idler is started, the capacitor is out of the circuit.

there are ways of using a toggle switch or using a maintained contact switch, but those may require the use of a secondary relay.

the control system runs many types of equipment with electrical latching.
there is safety to consider, the latching circuit will not start without operator input in the event of a power outage.
a maintained circuit will not have the same safety without the use of other devises to otherwise prevent operation without operator input
 
Ulma Doctor said:
the normally closed stop in combination with a normally open start is a common motor starting latching circuit.
the capacitor in my design is operated by the start switch, once the idler is started, the capacitor is out of the circuit.

there are ways of using a toggle switch or using a maintained contact switch, but those may require the use of a secondary relay.

the control system runs many types of equipment with electrical latching.
there is safety to consider, the latching circuit will not start without operator input in the event of a power outage.
a maintained circuit will not have the same safety without the use of other devises to otherwise prevent operation without operator input
Click to expand...

When buying switches or the 3 pole contactor coil, is there any problem buying oversized? For instance this one:
https://www.amazon.com/Definite-Pur...BH5JXTK8WKS&psc=1&refRID=XVVVSWE2EBH5JXTK8WKS
 
i always oversize, when in doubt!
it would not be overkill to use a 50 amp contactor.

i might be tempted to seek 60 amp gear like this...

www.ebay.com

Fuji SC35AA Magnetic CONTACOTR 3 Pole 600 Volts 220 V Coil W/ Overload Realy for sale online | eBay

Find many great new & used options and get the best deals for Fuji SC35AA Magnetic CONTACOTR 3 Pole 600 Volts 220 V Coil W/ Overload Realy at the best online prices at eBay! Free shipping for many products!
www.ebay.com


note that it has a 220v coil.
( if you were to follow my design, you'll need 220v coil)

if you were to use a 120v coil, you would need to add a step down transformer
 
I understand not wanting the complexity of a VFD but, for the record, it is possible to use one with a two speed motor and use the lathe controls normally. It requires an LC filter (Sine wave filter) on the VFD output and running the VFD at a constant output voltage and frequency by twiddling with the settings. Some VFD's allow this. That is my present setup with a 2 speed motorized 16" lathe. It doesn't take advantage of speed control of the VFD at all but for me I stubbed my toe by buying an RPC that was too small for the lathe and rigged up the VFD instead. Moral of the story, don't cheap out on an RPC that is just barely big enough to deal with the inertia of the lathe because you will tire of the loooong spin up times. My VFD setup works great though. At some point I will likely replace the motor with a larger HP single speed and take advantage of the speed control. Have not missed that capability yet though.
 
Some VFD's have setting for 2 separate motors, so you can setup the VFD to operate at both motor speed settings. One can use 3 way changeover switch 1 0 2 to switch the motor wiring and activate a VFD input that changes the motor parameters. The flip side, is in most cases no functionality of using this approach (I have tried it several times). Two speed motors come in a number of different configurations, but typically you loose Hp on the lower speed setting. In this case you use only the high speed wiring configuration directly wired to the VFD. If you you have a constant Hp motor (typically 4P and 2P), then you wire the motor for 4P (low speed) and run the VFD to 120 Hz which double the torque on the 4P setting and Hp is constant from 60-120Hz). Use the same parameters for both low speed and high speed motor setting, I would not recommend it. The VFD settings such as amps, RPM, poles, and the autotune data is very different and likely to result in sub optimal performance.

As a general note, I have had a number of poor performance issues of matching a VFD to multiple speed motors, the exception being constant Hp motors. I have done several VFD conversions with constant torque (variable Hp) motors and in all the cases I ended up replacing the motor with a single speed. The motors would run rough and we saw cogging at the lower speeds. I have also seen this infrequently on a few single speed 3 phase motors.
 
Ulma Doctor said:
the normally closed stop in combination with a normally open start is a common motor starting latching circuit.
the capacitor in my design is operated by the start switch, once the idler is started, the capacitor is out of the circuit.

there are ways of using a toggle switch or using a maintained contact switch, but those may require the use of a secondary relay.

the control system runs many types of equipment with electrical latching.
there is safety to consider, the latching circuit will not start without operator input in the event of a power outage.
a maintained circuit will not have the same safety without the use of other devises to otherwise prevent operation without operator input
Click to expand...

How about these:
https://www.amazon.com/Motor-Start-...arting+capacitor+250vac&qid=1599185012&sr=8-9
https://www.amazon.com/gp/product/B07DYKX5TD/ref=ox_sc_act_title_1?smid=A1LH3TFU4S09BS&psc=1
https://www.amazon.com/gp/product/B07MC1QGKZ/ref=ox_sc_act_title_2?smid=AFOU01QSKEAT5&psc=1
 
the cap and switches are fine, the contactor needs to have a 220v coil , unless you plan on utilizing a step down transformer.


the 40 amp would suffice, if a 50 amp can't be easily located
 
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