240V AC Motor Fail to Start counter/ 120V lacks N wire

[TheRocketScientist]

I have an AC motor of about 1.5HP, run with 240V AC single phase. The motor is about 300 ft from the controller, which switches only one leg of the 240V. At the motor, then, I have a ground wire, one leg always hot, and one switched line. Typically on/off abut 60/40% on a 5-minute total cycle.

I'd like to fabricate a "fail to run" counter. Increments a counter if after oh 15 seconds of power applied, the motor is not drawing the expected amperage. Maybe there's a better way to do this.

I have a current sensor time delay cube relay and another time delay relay - to ignore the startup and shutdown portions of the cycle. And a totalizer that takes any voltage [in this scenario] or a contact closing. Easy enough.

BUT... the TD relays/ current sensor work on 120V AC, not 240. At the motor, I have two "120V" wires... but no N wire to serves as the other line. I understand using the ground wire, though it would work, is not to be done.

It'd be a major expense to have a N wire brought from the panel. What about tapping a fairly nearby lighting or similar circuit for an N wire? The only other option seems to be go shopping for 240V versions of the TD Relay/ Current Sensor. Was hoping to avoid a huge outlay of $ in these tight times, since I have the components... they just require a different power supply.

Suggestions for bringing in an N wire, or an alternate method to count Fails To Start [PLC?] ???

Thanks!

 

[TurbineGen]

If the motor hasn't started after 15 seconds I would hope your protection scheme would have taken that motor offline. If you are going to push the motor to start until a breaker takes it offline, then why not use that as your motor failure to start indication. You could put some type of voltage sensing on the line and if it drops below 50 volts or something volts, then the motor has tripped offline and therefore has not started.

Or were you planning on using this as part of your protection scheme?


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If it is broken, fix it. If it isn't broken, I'll soon fix that.

 

[jraef]

You must not "mix" your neutrals from another source with the power from this panel.

Simplest solution using what you already have, just add a small 240-120V Control Power Transformer to give you 120V in this box.

I would rather just find a current monitor that has a built-in time delay and runs on 240V, they are out there.


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[ScottyUK]

How big is the motor? Assuming you are using the motor with the two windings connected in series you can probably get away with using the mid-point of the windings as a source of 120V AC. It's rough & ready but the rest of the system sounds like it falls in that category too.

A book full of all kinds of malpractice and general tricks for using 3-phase motors where there is only single phase, using 120V motors on 240V supplies, and things of that ilk is called Electric Motors written by Jim Cox. It's intended for the home workshop user, not the professional engineer, and some of the things he describes might be ok in a home workshop but couldn't be used in a commercial product. Might be worth spending a few pounds / dollars / etc on a copy from Amazon.


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If we learn from our mistakes I'm getting a great education!

 

[waross]

Scotty beat me to it. Pick 115V from the series connection of the windings. Most NEMA 115:230V motors use a 115V start winding and get 115V from the series connection. No problem with powering a timer. Tip. Connect the timer to the same leg that powers the start winding.
Note: Motors for use on 120:240V supplies are rated 115:230V

Bill
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Jimmy Carter