DIY Home Improvement, Remodeling & Repair Forum > Kinda electrical. Kinda plumbing.

01-29-2014, 08:36 AM
Louuuuu
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'Looks like 1" PVC going into a coupler (all pipes are iron after that) before the pressure tank.

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01-29-2014, 03:21 PM
Wuzzat?
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For a 1 HP motor with 6x inrush current @ 220VAC might give you 20A current for one second or so.

If you know the length and gauge of wire from source to pump you could temporarily splice in a short length of skinny wire, AWG to TBD, to halve the current.
The trick is so minimize the noise with shorter/longer splices while still supplying adequate power to operate your pump at the 1/2 hp power level and at normal efficiency.

A better way would have a relay temporarily cut in a series resistor for a second or so during startup.

With HP = Head x GPM/3946,
at 50% efficient you would get GPM = (1 hp/130')x(3946 x 0.5) = 15 GPM

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Last edited by Wuzzat?; 01-29-2014 at 08:23 PM.

01-29-2014, 05:47 PM
nealtw
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Quote:
 Originally Posted by Wuzzat? For a 1 HP motor with 6x inrush current @ 220VAC might give you 20A current for one second or so. If you know the length and gauge of wire from source to pump you could temporarily splice in a short length of skinny wire, AWG to TBD, to halve the current. The trick is so minimize the noise with shorter/longer splices while still supplying adequate power to operate your pump at the 1/2 hp power level and at normal efficiency. A better way would have a relay temporarily cut in a series resistor for a second or so during startup. With HP = Head x GPM/3946, at 50% efficient you would get GPM = (1/130')x(3946 x 0.5) = 15 GPM
Wait a minute, maybe I don't understand something here.
The wire size is dictated by the size of the breaker and should be big enough to handle what the motor needs. On start up the motor will draw more amps
than stated on the motor and the breaker is forgiving for a second. Motors are stupid they just take what they need, changing wire size is just asking for touble or did I miss something.
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01-29-2014, 07:43 PM
Wuzzat?
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Quote:
 Originally Posted by nealtw Wait a minute, maybe I don't understand something here. The wire size is dictated by the size of the breaker and should be big enough to handle what the motor needs. On start up the motor will draw more amps than stated on the motor and the breaker is forgiving for a second. Motors are stupid they just take what they need, changing wire size is just asking for touble or did I miss something.
Yes, normally motors want a 'stiff' (low impedance source resistance) to start up properly while under load like this pump.

The temporary high resistance switched in by an NTC thermistor or a relay/ resistor may be enough to stop the noise for one second without unduly shortening the life of the motor.

I guess another way would be to use a damped spring coupling between the motor output and the pump input shaft, with the coupling providing temporarily more acceleration difference between the motor shaft and pump shaft which then dwindles to nothing.

Try the easiest first to localize the problem and than pick the optimum long term fix.

This issue is in addition to the current vs time needs of the motor, going from high current to low within a few seconds, and the breaker current vs trip time taking perhaps a minute or more to trip at 2x rated current and maybe 0.16 sec to trip at 6x overload.
This is another messy interaction but can be solved graphically. Matching a breaker trip curve to a pump motor current vs time curve may not be that easy, but the two curves should track other with a slight offset at all places on the curves.

If the OP really only needs 1/2 hp, feed the 1 hp motor 0.707 x 220 v = ~156V [{156^2}/{220^2}= 0.5 ] and adjust to get the noise reduction and power necessary. Now we're were back to a VFD or PWM modulator or a step-down transformer.
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Last edited by Wuzzat?; 01-29-2014 at 08:21 PM.

01-29-2014, 08:44 PM
nealtw
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I didn't have to duck as most of that just went over my head anyway.
Maybe I can ask a simpler question.
Are you saying if the chart says the motor requires a wire say 10 and I run a 12 the motor will turn slower or start slower??

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01-30-2014, 06:46 AM
Speedbump
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By starving the motor of the amperage or voltage it needs to start and run, you are simply adding heat to the windings which is what kills motors.

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01-30-2014, 08:06 AM
bud16415
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I would be tempted to try teeing something like this into the line along with trying to find out if there is movement where it is and secure those pipes better. I have never used one of these maybe the pros will comment on them. They are designed to be used for rapid shutoff of flow and controlling the mass of moving water causing water hammer. I don’t see the function much different than excess incoming water needing something to slow it down.

I would not recommend a makeshift method of trying to limit inrush current to the motor. If you want to solve the problem electrically there are soft start devices on the market I’m sure I have no idea if they will work well with the type motor on a deep well pump.

http://www.cashacme.com/prod_general_plumb_waterhammer.php

I just showed the 1 inch model above they have a whole range up to 2 inch.

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01-30-2014, 08:38 AM
Louuuuu
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That's an idea. (The electrical guys a few posts back just made my head spin )

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01-30-2014, 08:52 AM
bud16415
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Everyone brings something different to the party, that’s why I like open forums. I always say there should be a header / disclaimer before every post including mine saying “Follow at your own risk.”

I haven’t ever used a water hammer suppressor but in looking on line there are a whole lot of them out there. Sears even has a selection they sell, and then there are huge industrial versions and even municipal sized units. They must sell as there are a whole line with PEX fittings and even Shark Bite’s.

Like I said in an earlier post your water tank should be doing this job, but if there is a restriction from the main flow down to the tank inlet some of the flow will be stopped or rapidly slowed down and it’s just my guess that’s what’s causing the bang.

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01-30-2014, 09:03 AM
nealtw
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They used put in a stand pipe that would go straight up and stay full of air and absorb the hammer.

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