isolation transformers constant power usage?

Discussion in 'General Electronics Chat' started by sdowney717, Mar 11, 2015.

  1. sdowney717

    Thread Starter Member

    Jul 18, 2012
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    So you have a primary and secondary say a 1:1 ratio. It runs at 120vac.
    Imagine it is a 30 amp in and 30 amp out.

    To get power out the secondary, you have to energize the primary.
    When you turn on the primary how many amps are used? Is it using full 30 amps all the time flowing on the primary windings?

    If you want power from the secondary, do you have to turn on some kind of primary switch, then turn on the secondaries switch to a device?
     
    koibhi likes this.
  2. Reloadron

    Active Member

    Jan 15, 2015
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    The primary current will be a what the output current is plus any losses. Plug in an isolation transformer, apply no load, feel the transformer. Do you feel heat? That heat is power being used on the primary without a secondary load at all. So if I have a 30 Amp isolation transformer and I place a 10 amp oad on the secondary my primary current will be 10 amps plus any loss.

    Introduction to Transformer Losses. Give the link a read as it covers things well.

    As to switching? You can switch the primary, the secondary or both. The transformer won't care but keep in mind, a transformer with an always on primary is always drawing current and thus using power.

    Ron
     
    Last edited: Mar 11, 2015
  3. sdowney717

    Thread Starter Member

    Jul 18, 2012
    386
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    If I wanted to wind my own high power isolation transformer say for 30 amps 120 vac, do you have a link to that?
     
  4. #12

    Expert

    Nov 30, 2010
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    3600 watts is the size of more than 3 microwave oven transformers. (Be sure to include a handle to lift it with.)
    Start by finding someplace to buy the core and they will probably be a lot of help. There are web pages that help explain this. I'll see if I have any listed.

    Oops. Family business. Gotta go.
     
    Last edited: Mar 11, 2015
  5. shortbus

    AAC Fanatic!

    Sep 30, 2009
    4,015
    1,531
    Transformer core laminations are not cheap. I bought some last year for a project and was surprised at how expensive they were. and your limited to what they stock, unless you want to pay for special tooling to make your size $$$. Then you need a way to vacuum impregnate them after they are put together to insulate between each layer of the core.

    I bought from these guys, but be prepared for sticker shock - http://www.tempel.com/products/transformer/

    And this doesn't even count the copper wire prices, another big shock.
     
  6. Reloadron

    Active Member

    Jan 15, 2015
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    With a margin you are looking at a 4 or 5 KVA isolation transformer. You are looking at as a minimum AWG 10 wire. While not real big this is a big transformer and like #12 mentions you will need a heck of a handle to lift this thing. This is not as easy as winding a few turns of magnet wire around a nail a few times. You can likely buy a 3 to 5 KVA isolation transformer for $150 to $200 (maybe less). While I can't immagine why you would want such a transformer outside of industrial use this would be much, much easier bought than built and likely the same cost or less to buy when all is said and done.

    Oh yeah, I just saw the post by shortbus. The laminations alone will be a challenge. Been there and done that. :)

    Ron
     
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  7. #12

    Expert

    Nov 30, 2010
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    I have seen a 100 watt transformer idle at 0.05 amps in the primary.
     
  8. sdowney717

    Thread Starter Member

    Jul 18, 2012
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    http://www.instructables.com/id/Microwave-isolation-transformer/?ALLSTEPS
    Modifying a microwave oven transformer to make an isolation transformer.
    Can these then be paralleled to increase the power?

    Could one modded transformer be enough to power an MSW 1500 watt inverter? So that you could have a grounded neutral in the output.

    Would a transformer even work with an MSW inverter.
     
  9. Reloadron

    Active Member

    Jan 15, 2015
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    MSW Inverter, I assume to be (Modified Sine Wave) Inverter. What exactly are you trying to do? Exactly means in detail. MSW inverters typically convert 12 / 24 VDC to 120 or 240 VAC at 50 or 60 Hz. A 1500 watt MSW inverter under full load will draw about 125 Amps on the 12 Volt DC input and about half that with a 24 Volt DC input. Also if I power a 1500 watt inverter from a DC source why would I want to place an isolation transformer on the output? Finally I am not sure what would happen since a MSW is far from a regular sine wave and much more closely resembles a square wave. So again, what exactly is the goal here, what exactly are you trying to do?

    Ron
     
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