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11-08-2009, 06:38 PM #1
Need 220v to 110v transformer and help
I would like to use a transformer to step 220 single phase power down to 110 so I can use the 110 to power a control relay for a 5 hp motor. I have a 220v 10 2 wired circuit already and I don't want to pull new 10 3 wire so I thought I could just add in a transformer to get the 110v. I already have a 110v relay. Does this make sense? Can anyone help me to get the right transformer? Or maybe have a used one for sale?
11-08-2009, 07:05 PM #2I have a 220v 10 2 wired circuit already and I don't want to pull new 10 3 wire so I thought I could just add in a transformer to get the 110v.
An electrician could tell you more exactly, but I think that is the case.
Edit to add: If you did re-pull that 220 with 3 conductors, then you should be able to split one leg (and of course the neutral) off for your 110 device.
11-08-2009, 07:29 PM #3
It may well be much easier and cheaper to get a control relay with a 220v coil or perhaps change the coil on the relay. Mouser or Digikey can supply you with transformers and relays. And BTW you can get 110v with a step down transformer with no neutral. You could use ground to get your 110v but not code and not safe (I do hope you have a grounded circuit).
11-08-2009, 07:51 PM #4
You are on exactly the right track.
You would wire the transformer primary to the 220 (with suitable fuse), and the secondary you would connect one wire as a neutral, connecting (bonding) it to the chassis, and then carrying it on as the neutral, the other would be the 120V hot wire.
That is 100% code.
What you want is a control transformer, which is one with the "oomph" to close relays.
How big a transformer you need depends on the power the relay requires. It should be marked on the relay (contactor), given as "VA".
Add up the contactor coil VA (the pull-in VA) and the VA for any other power needs, like lights, other relays, etc that will be on or pulling in at the same time. The control transformer must have a VA rating at least as large as, and preferably larger than, that.
They do tend to be expensive. DigiKey carries some, you might try them. otherwise, teh local industrial electric supply place will have or be able to get one.
Check in the "wanted" section here also.
11-08-2009, 08:02 PM #5
I would also look at replacing the coil first if this is the only requirement for 120vac.
It should be cheaper and easier.
You don't have to set up a grounded neutral but if you do make sure there is a positive bond to the service ground.
If you chose not to set up a grounded neutral, then both legs of the secondary should be fused instead of just the 'live' conductor.
11-08-2009, 08:48 PM #6
Yep, control transformers are expensive...
Control transformers are DEFINATELY expensive.
Pretty much figure that a control transformer off the major auction site will set you back $15... But if you MUST have a transformer, shop around- you can probably do a little better. I bought four of 'em for about $5 each, shipped to my doorstep.
Bein's there so expensive, I think it'd be better to just spend the $45 and replace the relay with something made for 240v, that way all your control circuits will be unisolated, unprotected, and free, ready, and willing to shock the crap out of unsuspecting users. Those silly control engineers really know how to take the 'fun' out of industrial workshop environments with all their nonesense 'safety' stuff. (sigh)
By the way- a 'clean' power feed has no neutral, so there's lesser issue of 'zero sequence' currents... the load is inherantly balanced, and with the machine chassis bonded only to ground. Many industrial machines are wired for 3-phase Delta so that there's no need whatsoever to have a 'neutral'. They're generally all equipped with a control transformer (with taps for 208/230/277/480) so that when the machine needs to be reconfigured, it's simply a matter of selecting the appropriate motor wiring, transformer tap, and overload heater coils.
11-08-2009, 09:43 PM #7
You will find plenty of transformers at www.digikey.com. They aren't the cheapest by any means but it is easier to find stuff there and easy to make small orders.
If 0.22A@117V is enough, here is one for $15:
Price of a transformer will vary a lot depending on how much power you need.
If you are just driving a relay and don't need much current, you probably don't need a full transformer, you can use an autotransformer (non isolated).
Any transformer with sufficient wattage and a split 110V/220V primary can be wired as an autotransformer. If you have any surplus transformers around, this is worth considering. Just insulate over the secondary leads and connect the two windings of the primary in series and wire the relay across one. The voltage won't be exactly half, but it may be close enough (you can even use the secondary for boost/buck if necessary).
Radioshack has a $50 step down transformer (not in stores, though):
Depending on your relay specs, a replacement 220V relay might be cheaper, but probably not (220V coil relays are a bit expensive).
It is also possible to rewind a relay coil for 220V or 110/220V operation if the relay is easy to disassemble. Unwind the old coil, counting the turns and measure the diameter of the bare wire with a micrometer. Order a spool of magnet wire with 0.707 times the diameter (look up in a wire gauge table) and wind twice as many turns as were originally present for 220V. For 110/220V, wind two coils with the original number of turns and connect them in series for 220V and in parallel for 110V. Use sandpaper to strip the insulation off the ends. A piece of 1/8" or 1/4" threaded rod (if that is a suitable size to fit through the bobbin) with some nuts to hold the bobbin in place run through a hole in a piece of wood (clamped in a vice) as a bearing and bent into a crank shape will do for a coil winder. A pair of nuts on each side of the bobbin and a pair with washer on each side of the block of wood. It doesn't hurt to wrap a little tape around the threaded rod to match the inner diameter of the bobbin. Here is another DIY coil winder from a hand cranked drill with a pedometer modified as a turns counter:
There are a bunch of coil winding videos on youtube, etc.
Wind the coil evenly so you can fit the same amount of wire in the same space. First layer right to left, second layer left to right, third layer right to left, etc. If you hold the wire slightly to the left when winding right and slightly to the right when winding left it will automatically wind each turn next to the previous one without a gap. It helps to put the spool of wire on a horizontal shaft so it can unwind as needed and you can tension and guide the wire between your finger and thumb. Note that for a 220V coil you may be using rather fine wire which will snap with too much tension; don't let the wire tangle coming off the spool.
One of many sources of magnet wire (ebay/froogle for more).
Table of wire gages including feet per pound for magnet wire:
with recomended tension:
Polarity matters when connecting series/parallel windings.
11-09-2009, 07:44 AM #8
Maybe I'm making this more complicated than I need to. I have 110 power about 10 feet from where I am installing the 5hp 220 motor. Why don't I just power the relay coil off the 110 circuit with a normal old light switch to activate the coil and skip the whole transformer idea? Sounds kinda simple now that I've slept on it for a night.
Yes both circuits have a ground wire in them.
11-09-2009, 12:47 PM #9
Do it right like JST said. Check out ebay item # 300363289894 or # 170402612607 Lloyd H
11-10-2009, 07:39 AM #10
A transformer will probably be as epensive as a new relay, a lot of transformers are 240/120 witch means it may be center tapped and you may get 120 between 1 leg and your new center. This may have odd voltages to ground, and should be deemed like live, and fused on both wires.
11-10-2009, 07:01 PM #11
the 240 input will need two fuses, as both leads are "hot", but the secondary should just have one wire ground bonded as the "neutral, and the other remains the hot lead.
You can follow NEC requirements for transformer VA and fuse sizing. if you do, there may be no need for a secondary side fuse, but normally they are good to have even so.
A small control transformer may be fairly cheap...... but watch out for some of the cheap made-in china ones....... they may have faston tab connections, and I know from personal experience that those from china have a habit of pulling out of the bobbin, causing many bad words. Specifically the small power ones from Digi-key.
I don't know the power you need. And I don't know if you can get a trade discount at a supplier..... that helps a lot on new ones.
A second source of power is a bad idea. The controls will remain "on" even if machine power drops. Then teh machine may start up unexpectedly if the problem with machine power is fixed. Not good. With one source, the machine will "safe" itself if power drops.
11-10-2009, 08:00 PM #12
Ok I'll start looking more seriously for a 220 / 110 control transformer. The relay that came with my motor is a FASCO H230B Definite Purpose Contactor, 2 pole, 30 FLA 40A Res, Coil 120 VAC. Anyone know what transformer I need?
11-10-2009, 09:29 PM #13
It still seems to me you ought to just change the contactor if the only purpose of the transformer is to operate the contactor. Here's a link to the same one with a 220v coil for a bit over $10. You could pick it up locally at a refrigeration supply for very little more.
11-11-2009, 07:05 AM #14
11-11-2009, 07:48 AM #15
11-11-2009, 08:07 AM #16
How many conductors+ ground are in the wire supplying power to your 220 5HP motor? If you have just 2 wires you need a transformer or a 220V coil, if you have 3 or 4 wires you have everything you need.
Your household power service simply consists of two conductors that each make 110V to ground or 220V between them. If you have 220V wiring to a machine you will typically have everything needed to get 110V.
A switch that will work on 120 will work on 220.
11-11-2009, 08:24 AM #17
If you want to go the simple toggle switch route, you can get one rated for 240v from any electrical supplier and may be even H.D. just sub the PB's for the switch.
Is this a 1 phase motor?
I would tend to go with the push button set up for that size of motor, your choice.
What is the application?
11-11-2009, 08:42 AM #18
It's a 1 phase 5 hp motor for a dust collector. I have a 10ga 2 conductor plus ground to the machine, I'm trying to avoid running a new 10/3 plus ground just to switch the coil. The dust collector came with the Fasco relay, so I've been trying to use it.
So it looks like I have a couple of options: Transformer to get the 110v for the Fasco relay, or get a new relay with a 240v coil. Either option is probably cheaper than pulling 70 ft of new 10/3 cable.
I'll avoid my idea of powering the coil off a different circuit so I don't have problems with the motor restarting unexpectedly.
11-11-2009, 09:06 AM #19
Check out Surplus Center every once in a while. They also have oiled filled capacitors, cabinets, switches, and other parts. You may also try your local air conditioning repair shop and see if they have any used contactors that will work. Joe
This contactor has three poles @ 135 Amps and two sets of aux contacts at 5 Amps. Although it is an overkill for a 5HP single phase motor.
11-11-2009, 07:35 PM #20
I have a small control transformer I'd part with.
It's got windings on one side for 208, 230, and 460v, which are supposed to be the secondary. The side that's supposed to the the primary is 115. You should be able to wire it backwards to do what you need. It's only rated @ 50va, but that should be plenty for a contactor. If you want it, drop me a PM, been sitting here for years, so I'll part with it cheap.