Step-down transformer backward?

  • Thread starter Fester Bestertester
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Fester Bestertester

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I have this transformer:

http://www.signaltransformer.com/sites/all/pdf/M4L.pdf

model M4L-2-10, 210/230/250 primary with 115 secondary.

Is it safe to use it in reverse to get 230v from 115 mains?

This is in N. America.

Thanks.
 
Fester Bestertester <fbt@fbt.net> wrote in
news:0001HW.D01EC97C00C0F566B02919BF@news.eternal-september.org:

I have this transformer:

http://www.signaltransformer.com/sites/all/pdf/M4L.pdf

model M4L-2-10, 210/230/250 primary with 115 secondary.

Is it safe to use it in reverse to get 230v from 115 mains?

This is in N. America.

Thanks.
Click to expand...

Should be no problem. A transformer can be used in both directions.

BTW 1000VA is quite a heavy signal :)

petrus bitbyter
 
On Sat, 23 Aug 2014 22:43:08 -0700, Fester Bestertester <fbt@fbt.net>
wrote:

I have this transformer:

http://www.signaltransformer.com/sites/all/pdf/M4L.pdf

model M4L-2-10, 210/230/250 primary with 115 secondary.

Is it safe to use it in reverse to get 230v from 115 mains?

This is in N. America.

Thanks.
Click to expand...

Be ready for the voltage out to be around 90 - 92% of expected.

I found out the hard way once when I wanted to make an 'isolation
transformer. I had two 'bell' transformers so thought aha! put them
together 115 down to 24 V then 24 v back up to 115! WRONG! only got 100V,
why? seems the transformer companies add some turns, some oomph, to make
up for the losses. Draw out the model and you'll see.

So conclusion is may work may not. but is safe to do. The 'shell' of the
transformer is referenced more to the secondary, so just watch your
isolation.
 
On 8/24/2014 5:23 AM, petrus bitbyter wrote:
Fester Bestertester <fbt@fbt.net> wrote in
news:0001HW.D01EC97C00C0F566B02919BF@news.eternal-september.org:

I have this transformer:

http://www.signaltransformer.com/sites/all/pdf/M4L.pdf

model M4L-2-10, 210/230/250 primary with 115 secondary.

Is it safe to use it in reverse to get 230v from 115 mains?

This is in N. America.

Thanks.



Should be no problem. A transformer can be used in both directions.

BTW 1000VA is quite a heavy signal :)

petrus bitbyter
Click to expand...

I once described a setup using a transformer backwards,
Phil Allison, said it was a bad idea, something regarding
magnetizing current is specified and wound for the primary.
The secondary may not have the turns needed for the proper
magnetizing current.
My setup worked short term, that's all we needed,
might have been a problem if we tried to run it 24/7.
I am accepting Phil's input, even though I always thought
transformers were reciprocal.
One caveat, my setup was using two transformers for isolation and
looked like this 120//12 to 12//120 driving a many, many section
Cockcroft–Walton generator. I think we were up near 10kV.

Mikek
 
On Sun, 24 Aug 2014 09:05:58 -0500, amdx wrote:

On 8/24/2014 5:23 AM, petrus bitbyter wrote:
Fester Bestertester <fbt@fbt.net> wrote in
news:0001HW.D01EC97C00C0F566B02919BF@news.eternal-september.org:

I have this transformer:

http://www.signaltransformer.com/sites/all/pdf/M4L.pdf

model M4L-2-10, 210/230/250 primary with 115 secondary.

Is it safe to use it in reverse to get 230v from 115 mains?

This is in N. America.

Thanks.



Should be no problem. A transformer can be used in both directions.

BTW 1000VA is quite a heavy signal :)

petrus bitbyter


I once described a setup using a transformer backwards,
Phil Allison, said it was a bad idea, something regarding magnetizing
current is specified and wound for the primary.
The secondary may not have the turns needed for the proper magnetizing
current.
My setup worked short term, that's all we needed,
might have been a problem if we tried to run it 24/7.
I am accepting Phil's input, even though I always thought
transformers were reciprocal.
Click to expand...

This sort of thing was done in amateur radio applications all the time.

AFAIK the only real caviat is that with losses going the "wrong way" you
may not get a full 2:1 step-up ratio, and you may not be able to run it at
full rated power. If it's operating in a satisfactory manner and not
getting too hot, then you're OK.

Phil knows a lot of things. He just thinks that he knows a lot more.

--

Tim Wescott
Wescott Design Services
http://www.wescottdesign.com
 
In article <0001HW.D01EC97C00C0F566B02919BF@news.eternal-september.org>,
fbt@fbt.net says...
I have this transformer:

http://www.signaltransformer.com/sites/all/pdf/M4L.pdf

model M4L-2-10, 210/230/250 primary with 115 secondary.

Is it safe to use it in reverse to get 230v from 115 mains?

This is in N. America.

Thanks.
Click to expand...

One item on the list to watch out for is the L value
on the secondary side.

Transformers do not need to worry a lot about the L on the
secondary side since it isn't being connected to a source.

The gage of the wire will be larger of course..

Most of the time they don't put a lot of copper on the
secondary side and when you reverse it
the coil may saturate to a higher no load current than expected.

What I would do if you have one handy, is put a LCR meter on the
secondary to measure the X and then apply that to basic ohms law to
find out what the no load current is going to be.

It'll most likely work for you but be less efficient power
usage wise.

Jamie
 
On Sun, 24 Aug 2014 07:03:10 -0700, RobertMacy
<robert.a.macy@gmail.com> wrote:

On Sat, 23 Aug 2014 22:43:08 -0700, Fester Bestertester <fbt@fbt.net
wrote:

I have this transformer:

http://www.signaltransformer.com/sites/all/pdf/M4L.pdf

model M4L-2-10, 210/230/250 primary with 115 secondary.

Is it safe to use it in reverse to get 230v from 115 mains?

This is in N. America.

Thanks.



Be ready for the voltage out to be around 90 - 92% of expected.
Click to expand...

That tranny has several sec taps, including 250, so he can probably
get close to 230.

Should work fine.
 
One item on the list to watch out for is the L value
on the secondary side.

Transformers do not need to worry a lot about the L on the
secondary side since it isn't being connected to a source.

The gage of the wire will be larger of course..

Most of the time they don't put a lot of copper on the
secondary side and when you reverse it
the coil may saturate to a higher no load current than expected.

What I would do if you have one handy, is put a LCR meter on the
secondary to measure the X and then apply that to basic ohms law to
find out what the no load current is going to be.

It'll most likely work for you but be less efficient power
usage wise.

Jamie
Click to expand...

1.2 H. Which works out to 450 K-ohms, 2 mA. Seems pretty small...
 
On Sat, 23 Aug 2014 22:43:08 -0700, Fester Bestertester <fbt@fbt.net>
wrote:

I have this transformer:

http://www.signaltransformer.com/sites/all/pdf/M4L.pdf

model M4L-2-10, 210/230/250 primary with 115 secondary.

Is it safe to use it in reverse to get 230v from 115 mains?

This is in N. America.

Thanks.
Click to expand...

Yes you can.
Select the right tap under load.
If used unloaded, the voltage will be higher.
Take care not to select a too high secondary under no-load conditions.
Under full load the voltage will decrease.

w.
 
Yes you can.
Select the right tap under load.
If used unloaded, the voltage will be higher.
Take care not to select a too high secondary under no-load conditions.
Under full load the voltage will decrease.

w.
Click to expand...

So: higher voltage unloaded; lower voltage loaded; less total watts
available.

Sounds like it will work for me within these limitations.

Thanks to all.
 
On Sun, 24 Aug 2014 09:15:27 -0700, Maynard A. Philbrook Jr.
<jamie_ka1lpa@charter.net> wrote:

..snip...

What I would do if you have one handy, is put a LCR meter on the
secondary to measure the X and then apply that to basic ohms law to
find out what the no load current is going to be.

It'll most likely work for you but be less efficient power
usage wise.

Jamie
Click to expand...

If you use an LCR meter on an AC power transformer you may get inductor
values MUCH lower than expected.

Why? because these transformers are designed for a lot of voltage on them
so they don't care about using highly coercive material, translates to
....the material does NOT come 'on' magnetically unless driven much harder
than most LCR meters are capable of. So, down in the lower permeability
region the inductance can look even 1/10th what it really will be when
properly driven.
 
ctuallly why don't you just take whatever transformers, piut the primaries in parallel and the secndaries in series ?
 
In article <op.xk3636dq2cx0wh@ajm>, robert.a.macy@gmail.com says...
On Sun, 24 Aug 2014 09:15:27 -0700, Maynard A. Philbrook Jr.
jamie_ka1lpa@charter.net> wrote:

..snip...

What I would do if you have one handy, is put a LCR meter on the
secondary to measure the X and then apply that to basic ohms law to
find out what the no load current is going to be.

It'll most likely work for you but be less efficient power
usage wise.

Jamie



If you use an LCR meter on an AC power transformer you may get inductor
values MUCH lower than expected.

Why? because these transformers are designed for a lot of voltage on them
so they don't care about using highly coercive material, translates to
...the material does NOT come 'on' magnetically unless driven much harder
than most LCR meters are capable of. So, down in the lower permeability
region the inductance can look even 1/10th what it really will be when
properly driven.
Click to expand...

on most LCR the larger scales are in the 1Khz, i have one that will use
100Hz. take your pick.

Hasn't failed me for looking for defective or just measuring the value,
yet.

Jamie
 
on most LCR the larger scales are in the 1Khz, i have one that will use
100Hz. take your pick.

Hasn't failed me for looking for defective or just measuring the value,
yet.

Jamie
Click to expand...

I (OP) think i'll just use an in-line amp meter.
 
On Sunday, August 24, 2014 3:43:08 PM UTC+10, Fester Bestertester wrote:
I have this transformer:



http://www.signaltransformer.com/sites/all/pdf/M4L.pdf



model M4L-2-10, 210/230/250 primary with 115 secondary.



Is it safe to use it in reverse to get 230v from 115 mains?



This is in N. America.
Click to expand...

** So you have about 120V AC at 60Hz available.

Problems regularly occur with such trannys wired in reverse if the turns ratio is wrong or the AC frequency is too low.

Luckily, linked tranny is speced for 50Hz as well as 60Hz with a 115V rated secondary. Using it at 60Hz implies the input voltage can be increased by 20% for the same magnetising current when used at 50Hz. It is rated at 1kW so regulation is gonna be close to 5%.

The turns ratio you need is exactly 2:1 so 120V becomes 240V at no load, dropping to 230 or so under full load.

The ratios available are 1:1.9 and 1:2.08 for the 230V and 250V windings respectively.

It should work OK with the 230V winding giving about 220V under load and the 250V winding giving about 240V under load.


..... Phil
 
On 8/24/2014 3:56 PM, RobertMacy wrote:
On Sun, 24 Aug 2014 09:15:27 -0700, Maynard A. Philbrook Jr.
jamie_ka1lpa@charter.net> wrote:

..snip...

What I would do if you have one handy, is put a LCR meter on the
secondary to measure the X and then apply that to basic ohms law to
find out what the no load current is going to be.

It'll most likely work for you but be less efficient power
usage wise.

Jamie



If you use an LCR meter on an AC power transformer you may get inductor
values MUCH lower than expected.

Why? because these transformers are designed for a lot of voltage on
them so they don't care about using highly coercive material, translates
to ...the material does NOT come 'on' magnetically unless driven much
harder than most LCR meters are capable of. So, down in the lower
permeability region the inductance can look even 1/10th what it really
will be when properly driven.
Click to expand...

This was one of my early conundrums while in a first years electronics
class lab. Everyone was given a 0.5 Henry choke and told to measure it
using (been a long time) but, as I recall, a sig gen, a big resistor and
meters. The class all wrote up their reports with some silly results
like 0.017 Henries. No one cared that the chokes were labeled 0.5
Henries. Of course the TA who spoke very poor English cared even less.
I went on a mission to figure this out, and learned about B/H curves
and initial permittivity. I also learned how low the current was for our
class experiment. It was an exiting time for me. :)
40 years later this pops up when I think of the 4 times rule for
winding transformers, specifically for the input to a radio. A radio
signal of 1uv barely excites the transformer core, I suspect we are way
below the signal level where any relative permeability specs were made.
I have never seen any allowance for that fact when winding transformers.
Mikek



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Thinking of this, wouldn't it seem logical that the primary is outside the secondary ? You are trying to achieve a desired output. That is al that matters.
 
Fester Bestertester wrote:
1.2 H. Which works out to 450 K-ohms, 2 mA. Seems pretty small...
Click to expand...

** Wanna try that again ?

1.2 x 2 x pi x 60 = 452

120 / 452 = 0.265


..... Phil
 
On Sun, 24 Aug 2014 18:40:37 -0700, <jurb6006@gmail.com> wrote:

ctuallly why don't you just take whatever transformers, piut the
primaries in parallel and the secndaries in series ?
Click to expand...

Good one! ...Hanging head in the shame of NOT THINKING OF THAT! In
defense, was used to working with 120/24 transformers where two wouldn't
do it.

But, as you so rightly pinted out, 240/120 takes two to do it, and done.
As long as the secondary can take that voltage. And most transformers are
rated, for what? 3kV? or at least 2kV isolation so should work safely.
 
Fester Bestertester wrote:


** Wanna try that again ?

1.2 x 2 x pi x 60 = 452

120 / 452 = 0.265

.... Phil



Yes, that's correct.



One should remember that H does not invert, which

would give the answer of 2 mA, if one did. :)






The quiescent primary (115 V) current is not measurable on a 6-digit HP bench

DMM.


Why would this be so?
Click to expand...

** A tranny with no magnetising current is simply not possible.

For the ML4-2-10 ( 1 KVA e-core) expect to see around 0.5amps rms when the 115V winding is energised.


...... Phil
 
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