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#7121 - 01/22/02 11:24 AM Sprinkler Pump Hookup
bobss10 Offline
Junior Member
Registered: 01/22/02
Posts: 2
Loc: Miramar, FL
I have a question regarding a hook-up for a sprinkler pump. I recently replaced a 1 1/2 hp pump for my sprinkler system. The old pump was running via 120. I hooked up the new pump to run on 220 and verfied that I indeed have 220 at the timer and 220 is being supplied to the pump. My reasoning for upgrading to 220 was that the pump would use less amps (9.6 vs 19.2) and run cooler, thus lasting longer. The pump runs fine, but it doesn't seem to run any cooler at all, it very warm to touch after running just 15-20 minutes. The power is being supplied from the main panel via 30 amp cbs. I was under the understanding that the pump would only draw 9.6 amps. Is something wrong here or am I just overly concerned. Thanks in advance for your assistance amd time.
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#7122 - 01/22/02 01:13 PM Re: Sprinkler Pump Hookup
sparky Offline
Registered: 10/18/00
Posts: 5303
volts x amps are inversely propotional to the load served
Simplified formula is here....
#7123 - 01/22/02 08:06 PM Re: Sprinkler Pump Hookup
maintenanceguy Offline
Registered: 12/02/01
Posts: 300
Loc: Southern NJ, USA
If you're doing the same amount of work, it will take the same amount of work. so it stands to reason that two different motors under the same load would produce the same amount of heat.

whether low voltage and high amps or high voltage or low amps, the work done stays the same.
#7124 - 01/22/02 11:40 PM Re: Sprinkler Pump Hookup
Elzappr Offline
Registered: 12/20/01
Posts: 270
Loc: Oregon
I've never noticed any higher voltage motor connection running any cooler than at a lower voltage, tho it sort of makes sense that lower current should mean lower resistance losses, so less heat. But motors aren't designed that way. If you had a dual voltage motor, you would be running the same amount of current in each winding, whether in series (higher voltage hook-up) or in parallel (lower voltage hook-up). Taking a que from that understanding, you might reasonably expect that a motor will be designed to run at its "normal" temperature (too hot to keep your hand resting on it), regardless of the operating voltage. My advice is to just make sure the amp draw is less than the nameplate figure, provide adequate ventilation, and install it so there is some metal to metal heat sink (if available).
#7125 - 01/23/02 09:29 AM Re: Sprinkler Pump Hookup
George Corron Offline
Registered: 05/16/01
Posts: 717
Loc: Lorton, Va USA
I have a way to at least make my students puzzle over that problem.

What is cheaper to run, a 4kw heater connected to 120V, or a 4kw heater connected to 240V?

The answer is their both the same. First for that answer, the PoCo measures in watts, so 4kw is 4kw, no matter the voltage.

But the same answer applies to your motor Xhp is Xhp no matter the voltage, it ain't gonna run cooler, or cheaper for that matter. It doesn't pump faster or harder, it's the same, you just save a little (usually negligible) on the intitial installation costs but that's about it.
#7126 - 01/23/02 09:43 AM Re: Sprinkler Pump Hookup
bobss10 Offline
Junior Member
Registered: 01/22/02
Posts: 2
Loc: Miramar, FL
Well, Thanks to all for your replies. This is a great site and many thanks to you pros out there willing to help a DIY'r like myself.
#7127 - 01/23/02 11:50 AM Re: Sprinkler Pump Hookup
Registered: 12/24/01
Posts: 28
Loc: Omak, WA, USA
I build combat robots [Battlebots] and we get into all kinds of things with current vs volts and such. Also, in the dim reaches of my memory are some electrical formulas I learned in college. I seem to remember the formula for heating as I squared X R. So I am reasonably sure that you should get half the heating with twice the voltage. However, as Elzappr pointed out, the way a motor is wired you really still have the same amount of applied voltage per winding which would cause the same amount of current to flow which would produce the same heating.

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