kd1yt
Cast Iron
- Joined
- Dec 6, 2013
- Location
- Vermont, USA
I thought I'd share some interesting anecdotal experience that surprises the heck out of me and that may be encouraging to anyone wondering if their situation can support a fairly large RPC.
Several years ago I was given a partially-built RPC using a big 7.5 HP old Delco industrial motor and a bunch of recycled switchgear. Bigger than I'd have "gone for" but it was free and part-built with all the needed parts.
My shop is powered via a 40 ft run of #10 UF wire, which taps off of the house's service through a 30 amp breaker. Someday I hope to run more serious power to the shop but for now it is a case of "nothing is as permanent as a temporary solution that works adequately." My home's 240V 3/4 HP shallow well jet pump causes a voltage sag enough to dim the lights for a split second when the water pump starts (my house is wired with very stiff over-spec'd wiring which I did when I rewired it from the prior rat's nest of patched and bungled wiring- but I have a long rural service drop from a not very big pole transformer that's shared with the neighboring house.
Given how my house's service responds to the 3/4 HP water pump, I never expected the 7.5 HP RPC to work in my shop without some wild and probably unacceptable dimmed lights and voltage sag when powering up the RPC. I expected it to trip breakers at least some of the time. I worried it might be so bad as to even irritate my neighbors who share the same utility pole transformer.
To my amazement, I can throw the switch and hit the start button on the 7.5 HP RPC and it whirls promptly up to speed with no detectable dimmed lights in my shop. And I can then fire up a 2 hp 3ph motor off of the RPC, again, with no detectable dimmed lights from voltage sag. Never tripped a breaker yet.
How this works so well, I do not know, other than that I expect that a lot of what the RPC pulls is reactive rather than real power. Maybe the start capacitors help considerably, too. But it still amazes me. I thought I'd pass this along in case it is of encouragement to others wondering if their situation can support an RPC. I am not suggesting that you aim to power a 7.5 HP RPC off of the tail end of a wobbly residential service with the last leg being over #10 conductor. But it should offer encouragement to people considering a moderately-sized RPC.
Several years ago I was given a partially-built RPC using a big 7.5 HP old Delco industrial motor and a bunch of recycled switchgear. Bigger than I'd have "gone for" but it was free and part-built with all the needed parts.
My shop is powered via a 40 ft run of #10 UF wire, which taps off of the house's service through a 30 amp breaker. Someday I hope to run more serious power to the shop but for now it is a case of "nothing is as permanent as a temporary solution that works adequately." My home's 240V 3/4 HP shallow well jet pump causes a voltage sag enough to dim the lights for a split second when the water pump starts (my house is wired with very stiff over-spec'd wiring which I did when I rewired it from the prior rat's nest of patched and bungled wiring- but I have a long rural service drop from a not very big pole transformer that's shared with the neighboring house.
Given how my house's service responds to the 3/4 HP water pump, I never expected the 7.5 HP RPC to work in my shop without some wild and probably unacceptable dimmed lights and voltage sag when powering up the RPC. I expected it to trip breakers at least some of the time. I worried it might be so bad as to even irritate my neighbors who share the same utility pole transformer.
To my amazement, I can throw the switch and hit the start button on the 7.5 HP RPC and it whirls promptly up to speed with no detectable dimmed lights in my shop. And I can then fire up a 2 hp 3ph motor off of the RPC, again, with no detectable dimmed lights from voltage sag. Never tripped a breaker yet.
How this works so well, I do not know, other than that I expect that a lot of what the RPC pulls is reactive rather than real power. Maybe the start capacitors help considerably, too. But it still amazes me. I thought I'd pass this along in case it is of encouragement to others wondering if their situation can support an RPC. I am not suggesting that you aim to power a 7.5 HP RPC off of the tail end of a wobbly residential service with the last leg being over #10 conductor. But it should offer encouragement to people considering a moderately-sized RPC.
