240v to 120v transformer question

[GlennWest]

I see these fairly cheap and costly. If I step down 240 to 120 for a low amp use, what would I need to get. I want to use a 120v mini split interior head on a 240v outside unit. Already have it and be hundreds saving. The wires are small like speaker wire.

[rpsinc]

I would check with manufacturer to see if they offer what you are looking for.  Transformers, while useful, also have a certain amount of lost efficiency in their function.

[Mark and Dale Bruss]

Since the mini-splits use phased start up on their motors and fans, I would believe the interior heads are not just simple AC voltage.  In fact I would suspect the interior units are DC. 

So there might be no difference  in the interior units.  If the interior units are 240 or 120 specific, I would believe that a transformer will not work.

[GlennWest]

We think alike in this. The units are specific to the voltage of the compressor. Different item number also. I am going to check the voltage on those small wires tomorrow. Simple. Just pull cover on compressor unit. The compressor is DC. 

[Fulltimer51]

Just a reminder that 240/2=120.

[GlennWest]

1 hour ago, Fulltimer51 said:

Just a reminder that 240/2=120.

Just run one hot wire? Could it be that simple?

[Darryl&Rita]

47 minutes ago, GlennWest said:

Just run one hot wire? Could it be that simple?

Work as well as a welder with one wire.

[GlennWest]

Ok. 

[Al F]

For house hold service, the only 240V power I know of is, is a pair of 120V wires, phased 180 degrees apart.  So if you want 120V you just tap into one of the 120V wires supplying the 240V power.  It is just that simple, or am I not understanding the question?

Of course you do need more than ONE wire.  You also need the neutral and ground wires, but only one hot wire

[GlennWest]

Yes, I just had a brain fart yesterday. I know this stuff. Got hung up on transformers. Thanks

[oldjohnt]

Glenn, it sounds like you're coming around and have this under control, but for those who may not I will offer a few bits of information:

1) Of course if for whatever reason a person wanted to use a transformer to convert  240 VAC Single Phase to 120 VAC Single Phase that's fairly simple. In addition to the In and Out Voltages you need to size the transformer to handle the Watts or Volt Amps the unit will draw. Voltage and Power ratings and selections are straight forward and simple.

2) The next consideration would be whether to use an Isolation Transformer orrrrrrrrrrrr or an Auto Transformer ???

3) The next consideration would be how to configure the transformers output. Floating, Bonded, Separate Derived Source etc.  

4) Next if you want to spend more money but only if its a necessity, you may need to consider a ferro resonant  transformer that stores energy in its magnetic field which can help reduced  brownout (excessive low voltage) when for example a compressor starts up.

 As I'm sure you're already well aware, typical home residential electrical service is 120/240 volt single phase three wire in which you have two legs of 120 VAC (Either leg with respect to Neutral) plus 240 VAC Single Phase L1 to L2. A typical 240 VAC circuit would consist of three wires, Two Hots L1 & L2 plus a Safety Equipment Grounding conductor. A Typical 120 VAC circuit would also consist of three wires, One Hot, One Neutral, One Equipment Grounding Conductor 

 

Best wishes

John T

[GlennWest]

Don't believe it will work. Both 120v and 240v unit has same wires going to unit. I checked mine and 120v, neutral, signal, ground. Installation manual doesn't list voltage. think I will call Highseer about this.

[Darryl&Rita]

My understanding of what he wants to do, is to re-use an existing inside evap core as a daughter of a new condenser. The existing unit is 120, while the new condenser is 240, and all daughter evaps get power from the condenser. A transformer should be able to be sized to accomplish this. It could run either bonded or floating, as long as stickers were made to identify this on the junction box.

[GlennWest]

Called highseer. He states the unit supplies 240v to evaporator unit with a single line. So a transformer would have to be used but checked and unit only $195. Wall units are very inexpensive. I also don't have to order lines with it.  Cassettes are $600 and $690 due to different line lengths.

[Darryl&Rita]

Just remember, a single line doesn't always mean a single wire.

With that price difference, you'd probably be ahead to replace your whole system, and sell as a complete package, minus lines. Then install the wall unit, and cassettes to match the new condensor.

[Al F]

3 hours ago, GlennWest said:

Called highseer. He states the unit supplies 240v to evaporator unit with a single line. So a transformer would have to be used but checked and unit only $195. Wall units are very inexpensive. I also don't have to order lines with it.  Cassettes are $600 and $690 due to different line lengths.

I would want to measure the voltage at the evaporator to verify it really is 240V on 1 wire.   It seems to me that they would have to have extra circuitry to take the 240v from two wires and put it on a single wire.  Extra circuitry equals extra money to make the product.

[GlennWest]

Well, I will when I do this. I don't have a 240V unit to test currently. All I can do is trust that they telling the truth.  I don't know of anyone in this area that I could ask about this. But like stated, not expensive to change out. Had not priced a separate wall unit price. I was pleasantly surprised.

[oldjohnt]

Glenn, All this talk about "one wire" ??? This mean TWO conductors inside a single jacket (could be called a "wire") or ONLY a single conductor or just what?? Obviously in a 120/240 volt single phase three wire service the 240 VAC exists across TWO wires, L1 & L2, voltage is the potential difference between TWO wires/terminals/lugs wherever. Single wire Neutral versus one for each 120 VAC leg ??? see below. There's no 240 Volt potential difference on ONE WIRE ALONE !!! Its 240 volts POTENTIAL DIFFERENCE from one wire to another.

That being said, there exist what are called in the trade Multi Wire Branch Circuits. That's where ONE Neutral WIRE serves as the return current path for TWO Hots, L1 & L2. IE you could have a 240 volt L1 & L2 circuit with a single Neutral serving BOTH L1 & L2 individual 120 VAC legs. 120 L1 or L2 to Neutral but 240 VAC L1 to L2.

While Multi Wire Branch Circuits are NEC approved it was never my first choice especially where heavy inductive loads (say a motor or compressor etc) or other inductive loads like ballasted fluorescent lighting or transformer power supplies etc are in use as its possible to overheat the single Neutral.  

I'm confident you are on the right track and will get this dern thing figured out

Best wishes, take care do it safe.

John T

[Al F]

7 hours ago, oldjohnt said:

Glenn, All this talk about "one wire" ??? This mean TWO conductors inside a single jacket (could be called a "wire") or ONLY a single conductor or just what?? Obviously in a 120/240 volt single phase three wire service the 240 VAC exists across TWO wires, L1 & L2, voltage is the potential difference between TWO wires/terminals/lugs wherever. Single wire Neutral versus one for each 120 VAC leg ??? see below. There's no 240 Volt potential difference on ONE WIRE ALONE !!! Its 240 volts POTENTIAL DIFFERENCE from one wire to another.

That being said, there exist what are called in the trade Multi Wire Branch Circuits. That's where ONE Neutral WIRE serves as the return current path for TWO Hots, L1 & L2. IE you could have a 240 volt L1 & L2 circuit with a single Neutral serving BOTH L1 & L2 individual 120 VAC legs. 120 L1 or L2 to Neutral but 240 VAC L1 to L2.

While Multi Wire Branch Circuits are NEC approved it was never my first choice especially where heavy inductive loads (say a motor or compressor etc) or other inductive loads like ballasted fluorescent lighting or transformer power supplies etc are in use as its possible to overheat the single Neutral.  

I'm confident you are on the right track and will get this dern thing figured out

Best wishes, take care do it safe.

John T

John T,

I am kind of confused about exactly what you are explaining.

My reading of what the mfg is saying about the evaporator being 240V is that they have a single load wire (L1), a single neutral wire and a ground wire.  You would now, suposedly be able to measure 240V from L1 to neutral or 240v from L1 to ground. 

If what I suspect that they really have is the standard 240v circuit with L1, L2, Neutral, and ground then it is a simple matter of just picking off either L1 or L2 and wiring a standard 120V outlet. 

What I am keying on is this quote of what the mfg told Glen in an earlier posting:

Quote

Called highseer. He states the unit supplies 240v to evaporator unit with a single line. So a transformer would have to be used

I just didn't make sense to me that they would set up a circuit with just L1, Neutral and ground.

On edit, I should have made the statement just above "a 240V circuit with just L1, Neutral and ground.

[GlennWest]

L1, nuetral, signal, ground

[rpsinc]

I think that is the bundle that comes with the line set in mini splits.  Power is the line voltage which is L1, Neutral and Ground.  The signal is what controls the cassette unit, fan speed etc.  This is DC I think.  

[GlennWest]

L1 on mine is 120v. So 120v going to evaporator unit. So 240v should be on the 36k unit.

[rpsinc]

I think you are right, but likely would have 2 hot wires, L1 & L2, usually no neutral on 240VAC, and ground, then the control wire for each cassette.

[GlennWest]

5 minutes ago, rpsinc said:

I think you are right, but likely would have 2 hot wires, L1 & L2, usually no neutral on 240VAC, and ground, then the control wire for each cassette.

Believe you are right and I really don't see why a single wire and tie in a neutral wouldn't work. But as I stated earlier it not expensive. 

[oldjohnt]

22 hours ago, Al F said:

John T,

I am kind of confused about exactly what you are explaining.

My reading of what the mfg is saying about the evaporator being 240V is that they have a single load wire (L1), a single neutral wire and a ground wire.  You would now, suposedly be able to measure 240V from L1 to neutral or 240v from L1 to ground. 

If what I suspect that they really have is the standard 240v circuit with L1, L2, Neutral, and ground then it is a simple matter of just picking off either L1 or L2 and wiring a standard 120V outlet. 

What I am keying on is this quote of what the mfg told Glen in an earlier posting:

I just didn't make sense to me that they would set up a circuit with just L1, Neutral and ground.

Hey there Al, good questions, let me try this again..........I think you're on the right page and get this, but for any who don't, here goes.............

A single load wire (L1) in a standard 120/240 volt single phase three wire system, with Hots L1 & L2, Neutral and Ground, WOULD MEASURE 120 L1 (or L2) to Neutral,,,,,,,,,,,,,,,Would measure 120 L1 (or L2) to Ground,,,,,,,,,,,,but the 240 is ONLY across L1 & L2 (but they didn't run an L2 right???).  It's NOTTTTTTT 240 from L1 to Ground or Neutral, its only 120. You need L1 and L2 for 240 !!!!!!!!!!!

Also the safety equipment grounding conductor is ONLY for fault current NEVER !!!!!!!!!!!!!!!!! normal return current.

Ifffffffffffff they ran a single load wire (L1),,,,,,,,,,a single Neutral wire and a ground wire, they can ONLY get 120 from that L1 to Neutral... 

A typical 240 ONLY circuit would have THREE WIRES, Two Hots L1 & L2, and a Ground NO NEUTRAL REQUIRED FOR 240 ONLY.

A typical 120 ONLY circuit would also have THREE wires, One Hot (L1 or L2), One Neutral, One Ground

If they run a FOUR wire circuit L1,,,,,L2,,,,,,,Neutral,,,,,,Ground its possible to get 120 or 240

It is possible to use a SINGLE Neutral for BOTH L1 & L2 120 volt circuits.

The pole or pad mounted transformer used for residential 120/240 volt single phase three wire LV secondary service IS 240 VOLTS END TO END ACROSS IT. The way you get TWO legs of only 1/2 half that (120) is to tap that transformer winding in the center.  That center tap point (Neutral) is attached to a No 4 bare coper wire which runs down the pole to a ground rod. Then 3 wires, L1 L2 Neutral, are ran to the homes main panel where the Neutral is again (there or riser etc) attached to all readily available Grounding Electrodes.  Typically in the main distribution panel (but NEVER again downstream) the Neutral Buss is BONDED to the safety Equipment Ground Buss. From there on out downstream you carry L1   OR   L2  plus Neutral and Ground for 120 branch circuits or L1 & L2 and Ground for 240 circuits. 

 That help any at all lol

Fun chat yall, hope this helps but absent the schematic I just cant say from here what is going on. I can ONLY explain the basic theory

John T