In need of a neutral?

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24 Jul 2019 00:42 #140373 by Type_Zero_Design
Alright so I just realized that the original contactor on my brother that I plan to use to control mains power has a 110v coil.... Unfortunately I have 3 wire 220v 3phase with no neutral coming to the machine and from the phase converter...

Sooo short of changing the contactor to an appropriate voltage do I have any options?

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24 Jul 2019 01:10 #140376 by tommylight
Replied by tommylight on topic In need of a neutral?
A small older tramsformer that has 110 and 220V input will do just fine. Older electronic equipment has them as they were made for Europe and use and had a switch on the back. Any size will do for powering the relay.

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24 Jul 2019 02:44 #140379 by Type_Zero_Design
Tommy, dose this somehow produce a neutral? The whole concept of neutral vs ground is still a bit unclear to me.

Usually I would just use one leg of 3 phase and neutral for 110v AC So in some way would the line side transformer take 2 legs of 3 phase for 220 AC and on load side output two taps that measure 110v ac across?

If so that would be preferable to power that contactor coil along with the PC and monitor.

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24 Jul 2019 09:24 #140420 by tommylight
Replied by tommylight on topic In need of a neutral?
Those transformers have 2 of the same windings on the primary, so you would connect the two outer pins to 220 and get 110 from the center pin and any of the two other pins.
It does not matter what the secondary winding does as it is not used.
Think of it as an autotransformer.

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24 Jul 2019 18:54 #140454 by bevins
Replied by bevins on topic In need of a neutral?
Bring a 120 source in the cabinet. Most of my higher voltage machines I bring in 120vac line. You should have it near anyway with the computer and PS etc...

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24 Jul 2019 19:56 #140465 by Todd Zuercher
Replied by Todd Zuercher on topic In need of a neutral?
Why most computer power supplies are capable of running from 220? A small transformer is the best solution.

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26 Jul 2019 05:11 #140611 by Larry
Replied by Larry on topic In need of a neutral?
Hello Type_Zero:

Before I can help you, I’ll need some info. First, is the output of your phase converter, “Y”, or “DELTA” connected? If it’s delta, THERE WILL BE NO NEUTRAL. This info should be part of your documentation. If your doing a rehab of antique equipment, you may have to hunt around for this information.

Second, I’ll also need to know the amp draw of the contactor coil. This should be on the side of the unit. If not, you’ll need to power up the contactor and measure it. Since you’re dealing with a 110V coil, I’m guessing you reside on my side of the planet. Fortunately, I’ve dealt with this problem before so I should be able to help.

The really cheap way out of this mess is to get two identical surplus transformers. You don’t care what the secondary voltage is so long as they’re identical. The primary voltage can be either 120 or 240V. The important thing is the current draw of the primary winding's. They must be greater than ½ the current draw of the contractor. That said, I really wouldn’t cut this spec that close. You’re safer if the primary current draw is equal to the contactor amp draw.

You wire the transformers as follows:
Connect the primary winding's in series. Connect the secondary winding's in parallel. The second connection needs testing. You do this by connecting only one side of the secondaries together. Power the transformers up, and measure the voltage across the remaining free wires. If that voltage is nearly zero, then connect those wires as well. If that voltage is twice the value of the rated secondary voltage, than you’ll need to flip one of the secondary winding wires. Obviously, if your dealing with high voltages, power everything down then change the connections.

Once done, what you have created is a virtual auto transformer. You connect your contactor across one of the primary transformer winding's, which will show a 120V. drop across it. Your contactor will energize and you will live happily ever after.

I hope this helps.

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28 Jul 2019 18:24 #140829 by andypugh
Replied by andypugh on topic In need of a neutral?

tommylight wrote: A small older tramsformer that has 110 and 220V input will do just fine. Older electronic equipment has them as they were made for Europe and use and had a switch on the back. Any size will do for powering the relay.


A power resistor in series with the contactor coil is (probably) another option. Though it might be worth considering swapping to a 24V control voltage contactor and letting LinuxCNC control it. 24V contactors seem to run at about 15W, so with a suitable protection diode (often built-in) they are controllable by some GPIO boards.

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28 Jul 2019 18:32 #140830 by Type_Zero_Design
I ended up purchasing a 500 VA control transformer 240 primary 120 secondary. Just came in I'm in the process of hooking it up but you guys know how it works out appreciate all the insight!

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28 Jul 2019 23:04 #140849 by Larry
Replied by Larry on topic In need of a neutral?
Be Careful! In my first post I asked you if your supply is Y or Delta connected. There was a purpose to this. If your 3 phase supply is electronic, it generally does not produce true 3 phase. Rather, one leg is 240V from your commercial power company, while the second leg is an electronically generated sine wave 120 degrees leading or lagging the power company waveform. The third phase is synthesized by straddling the hot sides of the commercial and synthesized legs in a delta configuration. You must consult your manual or the manufacturer for this information. The good news is if you go across the commercial power leg, what you’re doing will usually work fine. If you span the other, you could create a system imbalance. As a clue to indicate what I’m describing to be the case, you will find one of the three legs of power to be at ground (earth) potential. Anyway, since I’m not at your side, all of this is speculation. Do proceed with caution.

Tommy, I know very well what you are talking about. As a child I remember seeing radios brought back in the late 1940s by our armed forces. They were usually purchased just prior to returning to the U.S., or Canada. In particular, the one I saw had a pin plug on the back to select 110, 220, 208, and I believe one more input voltage. They also received long wave, medium wave, as well as short wave. That, I believe was the attraction to make the purchase in the first place. A home table radio in the U.S, only received medium wave and only operated on 110V. That being the case, and assuming Type_Zero to be on my side of the Atlantic, I can tell you the appliance transformers you described are virtually non existent over here. You either do what Type_Zero did and by a step down transformer, or you go the cheap way and do the two transformer trick I described.

Buy the way, the two transformer trick works both ways. In my case I would buy surplus motors, solenoids, and contactors at deep discount simply because they were 240V. I would then drive one primary of the two transformer configuration with 120V., and run the device off of the series connected primaries at 240V. My motto, if it’s cheap and works I’m all in.

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