Need help with a transformer

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TPA   10 kW

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Need help with a transformer

Post by TPA » Feb 04 2018 3:36pm

transformer.jpg
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With regard to the above transformer photo, it is possible to wire it 1:1, so here is what I want to do...

I have a Xantrex Prowatt SW2000 inverter. It puts out power the same way that standard household power is delivered (L1 on one prong and neutral on the other.)

These transformers are meant to wire L1 and L2 on the input side and get L1 and L2 on the output side at 1:1 or 2:1 depending on how it is wired.

What I want to know is if it is possible to take the L1 output of the inverter, run it through the transformer input, then get L2 on the output side. If so, and the output is 180 degrees out of phase with the input, then I could get 240V between L1 on the input and L2 on the output.

What I'm hoping to do is simulate the effects of the Outback FW-X240 Autotransformer. Can it be done?
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edcastrovalley   1 kW

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Re: Need help with a transformer

Post by edcastrovalley » Feb 05 2018 12:37pm

transformer 120vac to 240vac.jpg
120 VAC to 240 VAC
120 VAC to 240 VAC
transformer 120vac to 240vac.jpg (145.31 KiB) Viewed 1368 times
Are you trying to make 240 vac from your SW2000 (120 vac)? Then this should work however, you also are asking about a 1:1 setup which is different. The input and output of the transformer should be in phase with each other too.

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TPA   10 kW

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Re: Need help with a transformer

Post by TPA » Feb 05 2018 7:57pm

Thanks for the help.

When I wire L1 (the hot wire from the transformer) to H1, then the neutral wire to H2, all I get is a dead short. I've been testing with a standard household outlet which behaves the same way as the inverter.

Also, wiring this way would only end up with 240v on L1. What I need is 120v L1 plus 120v L2 in the end.

This transformer does not seem to act the same way as the Outback transformer
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edcastrovalley   1 kW

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Re: Need help with a transformer

Post by edcastrovalley » Feb 05 2018 11:43pm

Hmmm, not seeing L1 or L2 on your transformer’s diagram but before doing anything I would have your transformer checked. They sometimes go bad.

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Re: Need help with a transformer

Post by Inwo » Feb 06 2018 12:57am

It may seem like a dead short. 2kw is a pretty big surge load.
Make sure all the other jumpers are open. Primary and secondary.
If it still kicks the breaker use a high watt lamp in series.
You need to connect differently for use as an autotransformer.
Connect primary windings in series. As shown for 240vac. Jumper 2 and 3.
Connect 120vac across one winding. 1 and 2.
240 will appear at 1 and 4. While 2 and 3 are neutral.
I have no idea why you want to do that, as you can just use the 120x to 240h connection to get an output of 120-n-120 240 total on an isolated output from x, and use all 2kw.

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TPA   10 kW

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Re: Need help with a transformer

Post by TPA » Feb 06 2018 10:00pm

I didn't really want to explain why I wanted to do this because it becomes a sidetrack to getting to the answer, but you guys seem to be very helpful to my main purpose so I will gladly explain.

I have a Grundfos SQ well pump that Gets used infrequently to supply water for gardening. It has a soft start feature on it, and Grundfos is adamant that the startup current is equal to the maximum nameplate current so there should be no startup surge.

I would like to use this with a solar setup, and I already have much of the equipment to run it including this transformer that was purchased new never used. I have a Prowatt SW2000 that I'm using for another application, and if I can make it work for the well, then I'll buy a slightly larger for permanent use at the well. This well does not get used for household water and will only get used a couple of days a week for watering in the summer.

The pump has a 2 wire (L1 and L2) 240v soft start 8.4A motor (no startup surge). I should be able to get by with a 3000W inverter, but It would be much cheaper if it were a 120V inverter instead of a 240V split phase inverter if I could wire up the transformer to make a 120V inverter work.

As far as I know, it has to be 2 wire 240V, and I can't just step it up to 240V single line with the transformer to make usable power for the pump.

I could possibly wire it up 1:1 so that it phase shifts the output. Then I could use the input line as L1 and the output line as L2. The questions are 1) can this transformer phase shift, and 2) how to setup the wiring.

When I get a free moment, I will try out some of your suggestions and see how that goes. Thanks!
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Re: Need help with a transformer

Post by craneplaneguy » Feb 06 2018 11:09pm

Save up, and get a Grundfos SQ Flex well pump. And (assuming you have one) rig your solar array to pump water after your batteries reach float voltage. I hate to see off grid set ups with a dedicated water pump array and a separate array for battery charging. The Flex pumps run off AC or DC, from 30 volts to 240 (single phase)! I've supplied my rancher customers with plugs on their solar arrays, in times of excess water demand and no sun, they simply unplug the array and plug in a 120 single phase gen set, the pump electronics (not the control box, oddly enough) do all the "thinking." You can also get 120 VAC well pumps, (depending on your flow requirements) fooling with a transformer is inefficient and a hassle, but if you go that way, I'd look for an old Trace 120/240 one, should be some used ones around.

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Re: Need help with a transformer

Post by amberwolf » Feb 06 2018 11:46pm

FWIW, from the diagram I see on the transformer, wouldn't you get "two wire" 240vac with the X-output wired as specified (connecting the two center (x2 x3) wires on the output?

IIUC, you'd connect one of the 240VAC pump wires to the X1, another to the X4, and the third (neutral) to the X2+X3.

(with the 120VAC input connected to the H1+H3 (line), and the H2+H4 (neutral))

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Re: Need help with a transformer

Post by TPA » Feb 07 2018 7:54am

I am getting the dead short condition trying to apply 120V to the primary. I am sure that I am wiring it correctly.

Am I understanding right that the transformer needs to saturate (create enough impedance) to decrease the current flow in order to stop tripping the breaker?

I'm pretty sure this transformer is going to use about 50W on its own, and continuously. This certainly is not the best way to go.

I've looked at the flex pumps, they are pricey. Xantrex sells a split phase inverter for about the same price as a flex pump, and it will also take gen. input. A 120V pump is about $600. I guess I do have options.
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major   10 kW

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Re: Need help with a transformer

Post by major » Feb 07 2018 8:24am

TPA wrote:
Feb 07 2018 7:54am
...

Am I understanding right that the transformer needs to saturate (create enough impedance) to decrease the current flow in order to stop tripping the breaker?
...
No, saturation causes inductance (and impedance) to decrease and therefore is responsible for excessive current draw.

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Re: Need help with a transformer

Post by amberwolf » Feb 07 2018 11:14am

TPA wrote:
Feb 07 2018 7:54am
I am getting the dead short condition trying to apply 120V to the primary. I am sure that I am wiring it correctly.
Maybe your inverter simply can't deal with the inductive load the transformer presents? Check with the manufacturer and see what they say (some inverters can, and some can't--I blew up a 300w inverter just connecting it to a tiny 115VAC-type weedeater motor for an experiment, even with nothing connected to the motor shaft).

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TPA   10 kW

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Re: Need help with a transformer

Post by TPA » Feb 07 2018 11:46am

Well, I'm currently testing with the wall outlet in my shop. It is tripping the breaker for that circuit.

I will double check everything next time I'm working on it, and report back.
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Re: Need help with a transformer

Post by amberwolf » Feb 07 2018 11:53am

Ah...I missed that part. :oops:

Then maybe there is something wrong with the transformer?

Do you have it wired the way the diagram on the transformer states? (I know you said you're sure it's wired correctly)

Does it trip only with a load, or only with no load, or regardless of load conditions?

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TPA   10 kW

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Re: Need help with a transformer

Post by TPA » Feb 07 2018 11:57am

So, impedance stops the primary side from being a short circuit?

Does there need to be a load on the secondary to create the impedance similar to the way a generator can spin freely until a load is applied?
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fechter   100 GW

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Re: Need help with a transformer

Post by fechter » Feb 07 2018 1:03pm

If you apply 120v to the primary and leave the secondary open, it should draw near zero current.
You could try applying voltage to each section separately with no jumpers installed to see what happens. It should not be blowing the breaker on any of them.
"One test is worth a thousand opinions"

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TPA   10 kW

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Re: Need help with a transformer

Post by TPA » Feb 07 2018 7:36pm

OK, I got it working...

I wired it up by paralleling the primary and the secondary in series. I got 246V across the the ends of the secondary, and 123V one each leg relative to the center tap. I wish I had an oscilloscope so I could verify that one leg is anti-phase to the other. The well pump wires up like a water heater (2 lines and no neutral wire).

I'm not sure what was causing the trip, but I un-wired everything and carefully rewired it and it worked. I'm surprised I didn't electrocute myself.

I got quite an education thanks to you guys 8)
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fechter   100 GW

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Re: Need help with a transformer

Post by fechter » Feb 07 2018 9:22pm

The transformer output will be either 0 or 180 out of phase depending on which way you wire the taps. As long as you get the right voltage, it should be good.
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Re: Need help with a transformer

Post by amberwolf » Feb 07 2018 9:40pm

TPA wrote:
Feb 07 2018 7:36pm
I wired it up by paralleling the primary and the secondary in series.
Which is the way it indicates on the label. ;)
I got 246V across the the ends of the secondary, and 123V one each leg relative to the center tap. I wish I had an oscilloscope so I could verify that one leg is anti-phase to the other. The well pump wires up like a water heater (2 lines and no neutral wire).
Since the pump does not have a neutral, it doesn't matter what anything is relative to the center wire, only across the outside. As long as you get the voltage you need across the ends, that's all that matters. :)


I'm not sure what was causing the trip, but I un-wired everything and carefully rewired it and it worked.
Most likely something was not wired quite the way you thought it was, and was shorting across the input. :/

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TPA   10 kW

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Re: Need help with a transformer

Post by TPA » Feb 08 2018 9:22am

You know, it's strange how you get roped into thinking one way, and can't see outside that box.

I know that household current is 240V because of 2-120V lines out of phase with each other. It didn't occur to me that it would not matter if I wired a phase and neutral (one single waveform) to the pump as long as it is 240V.

Sometimes it takes a kick in the head...
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Re: Need help with a transformer

Post by major » Feb 08 2018 11:14am

TPA wrote:
Feb 08 2018 9:22am
You know, it's strange how you get roped into thinking one way, and can't see outside that box.

I know that household current is 240V because of 2-120V lines out of phase with each other. It didn't occur to me that it would not matter if I wired a phase and neutral (one single waveform) to the pump as long as it is 240V.

Sometimes it takes a kick in the head...
Hi,

Not sure how you define neutral, but the output from the transformer is isolated from the input, so household neutral is lost. Neither of the X1 or X4 is neutral. The X2-X3 connection is like a pseudo neutral but it is not connected to the household supply neutral, so cannot be considered a true functional system neutral.

Regards,

major

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TPA   10 kW

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Re: Need help with a transformer

Post by TPA » Feb 14 2018 4:41pm

I have not hooked this thing up yet and tried it out. Something keeps nagging at me. I have not been able to explain what my hangup is, so I'm hoping this diagram will make it clearer.

The top figure represents a sinewave from a single leg (L1) of typical US household power service. The RMS output is the 120V we are used to seeing on a daily basis.

The middle figure, as I understand it, is how 240V is achieved in household power by combining L1 and L2. You can see that L2 is 180 degrees out of phase with L1. The net effect is 120V RMS from L1 plus 120V RMS from L2 which produces 240V RMS. Also, the way I understand it, is that it can be used without a return (neutral) wire since one wire acts as the return for the other since the polarity is always identically opposite at every moment.

The third diagram is 240V on a single line (L1) just like the top diagram except the voltage amplitude is higher delivering 240V RMS. (side note: Is this how European power is delivered?)

I don't have an oscilloscope to check, but I think the output of my transformer is going to be like diagram 3, which causes my feeble mind to go into overload. So here are my questions:
1. The pump motor is only a 2 wire connection (no neutral wire). Does the pump expect to see power delivered on 2 lines, 180 degrees out of phase like diagram 2?
2. Is power delivered by diagram 2 and diagram 3 exactly the same thing? An electric appliance like a water heater or electric motor would not be able to tell the difference? The two sine waves in diagram 2 could be superimposed to produce diagram 3?
20180214_115114.jpg
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Re: Need help with a transformer

Post by fechter » Feb 14 2018 8:09pm

It will look like drawing 3. What you have is single phase, split phase.

A good description of it is here:
https://en.wikipedia.org/wiki/Split-pha ... tric_power
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Re: Need help with a transformer

Post by Inwo » Feb 15 2018 12:05am

Hows this?
Picture the dc equivalent.
Two 12v batteries in series. Middle connection is considered neutral if used as common or ground.
2 wires have 12v to neutral. 24v between them.
120v-0-120v.png
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