Hello again, I used your guys help a couple of years ago to put together a RPC based on a 7.5 idler and it runs great. I am buying a house next month and need to upsize my RPC to accommodate some larger machines which will following me there. The largest machine motors I have right now is a power hacksaw, mill and a lathe with 5 hp each. I went with a friend to buy a shaper last week and saw a converter there which I bought. It's a shop made balanced converter with a 30hp idler. The shop I am moving to has 200 amp service. Will this be enough for the startup pull of the 30hp motor?
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Amp pull at startup
- Thread starter Phils69
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Barely. Be sure the water heater and oven aren't on when you start it. Are you sure you need that much? What's the biggest motor you intend to run?
I probaly wont need one that big but knowing me I might one day. It's a detached garage and it has its own 200 amp panel and the house has its own as well. Not sure how that works exactly but shouldn't the garage panel be able to supply 200 amps on its on?
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Yes. I suggest that you reserve the existing panel for single phase loads. Add a 100 amp breaker fed directly from the service to supply the RPC and then install a three-phase panel supplied by it for your three-phase loads. Put a 100 amp main in the exisitng panel.
Sounds like a plan. I have a big 3 phase panel I'll be using for all the 3 phase machines. I'll try to remember and post a pic once it's installed. Now the question would be should I use the 30hp RPC for everything or only the larger motors and the 7.5hp RPC for everything else? I could run the 7.5 to supply the big 3 phase panel to meet most of my needs and the 30 to a small panel just for the larger motors? Would there be enough difference in operating cost to justify doing it that way?
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Figure 2x running amperage to start
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There might be. The no-load current for a 30HP motor @ 240V is 27 Amps, that's about 6.5 KW at idle, but that is running on 3 Phase. I have no idea how to calculate the no-load current in a RCP configration. Nor am I sure what the power meter would actually see as "real" power, due to the regeneration effects.
Once the system is operational, it would be interesting to take some power measurements (with an actual power meter) to see what is really happening.
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Right, but the startup transient won't trip a 100 amp breaker.
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I just upgraded my 3hp RPC to a 15hp RPC. I can run the smaller 1 1/2 and 2 hp machines on it without a problem. The 15hp RPC does put out some heat compared to the little 3hp that I had. I agree with putting the 3 ph output to a seperate 3 phase panel.
At idle with no load on the RPC, the only difference will be the extra friction encountered in the larger RPC, so that would be the difference for extra draw at idle.
As far as amp draw goes, Lets say that the amp draw from a machine is 30 amps, It'll be roughly the same whether its single phase or 3 phase. The only difference is that in 1 phase circuit the amperage gets divided between 2 legs (15 amps per leg),and on a 3 phase circuit the amp draw would be divided up by 3 legs (10 amps per leg), assuming the voltage is the same. which means that you can run a smaller wire theoretically to the machine on the 3 phase side. The 3 phase jolt on startup of the large motor does draw quite a bit more than running load, for this reason I ran some 8 guage wire (mainly because I had it laying around) to my 10hp lathe. The previous owner only had 12 guage running to the machine and on startup, especially when put into high gear, the machine struggled to ramp up. At my house with the 8 Guage wire it ramps right up with no struggle.
If it was my place, I'd just run the 30hp RPC for simplicity sake, though it might cost you a little bit more in electricity. I have no idea how much, but there's the overcoming inertia on startup on the larger RPC plus the additional friction.
Marcel
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Hmmmm... 30 HP is a lot.
1 HP is 746 Watts and I usually use 750 to round-up the numbers. Also, Watts (power) is equal to Voltage x Amps.
30 x 750 = 22,500 Watts
22,500 = 240 x Amps; therefore, Amps = 93.75. ... That's a lot of current and for reference is about 2.5 times as much as a central air conditioning unit in a typical 3 bedroom house. 1 Watt is equal to 3.4 BTU so, that's the equivalent of a 76,500 BTU heating or cooling device.
Those Amps are when the motor is pulling the full 30 HP -which hopefully doesn't happen all that often.
Anyhow, under full load the power from the meter going into the RPC will be at least this much plus any inefficiencies from the PRC itself. The best quality motors are about 95% efficient and typical values range anywhere from 75 to 85%. I would roughly estimate a 10-15% loss in the RPC so, the actual power coming out of the meter is right around 100 Amps (give/take a little).
The startup current on a motor can be quite high -especially if there's a load. An unloaded motor has a very brief draw of about 1.5 x the rated current and something like a compressor motor (which usually has a high load) can be upward of 3 to 4 times the rated current...
In your shoes, yes, I'd get a dedicated panel box for this and depending on how much you load the machine, you may need to look into "slow-blow" type breakers or possibly a VFD to use as a "slow-start" device if at all possible.
Ray
1 HP is 746 Watts and I usually use 750 to round-up the numbers. Also, Watts (power) is equal to Voltage x Amps.
30 x 750 = 22,500 Watts
22,500 = 240 x Amps; therefore, Amps = 93.75. ... That's a lot of current and for reference is about 2.5 times as much as a central air conditioning unit in a typical 3 bedroom house. 1 Watt is equal to 3.4 BTU so, that's the equivalent of a 76,500 BTU heating or cooling device.
Those Amps are when the motor is pulling the full 30 HP -which hopefully doesn't happen all that often.
Anyhow, under full load the power from the meter going into the RPC will be at least this much plus any inefficiencies from the PRC itself. The best quality motors are about 95% efficient and typical values range anywhere from 75 to 85%. I would roughly estimate a 10-15% loss in the RPC so, the actual power coming out of the meter is right around 100 Amps (give/take a little).
The startup current on a motor can be quite high -especially if there's a load. An unloaded motor has a very brief draw of about 1.5 x the rated current and something like a compressor motor (which usually has a high load) can be upward of 3 to 4 times the rated current...
In your shoes, yes, I'd get a dedicated panel box for this and depending on how much you load the machine, you may need to look into "slow-blow" type breakers or possibly a VFD to use as a "slow-start" device if at all possible.
Ray