? looking for 120 to 480v transformer

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Denis

Denis

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open to suggestions

looking for 120 to 480v transformer
power requirement is less than 1A
the 450v carbon-zinc battery this power supply will replace produced approx. 550mA

also, recommendations for capacitance value, .005uf seems small

200 ohm resistor should be correct to drop 480v to 450v after bridge, yes?

this unit charges capacitors

dimesnions of box power supply fits inside 3.25" wide 4.5" tall 6.5" long

30232973.jpg

AC power supply

30232974.jpg

battery schematic

30205498.jpg

complete unit
 
Besoeker

Besoeker

Senior Member
Location
UK
Denis said:
open to suggestions

looking for 120 to 480v transformer
Click to expand...
Maybe you can find a 480V 120V unit and reverse connect it?

Denis said:
also, recommendations for capacitance value, .005uf seems small
Click to expand...
I assume this is to attenuate any spikes on the supply. As a rule, I wouldn't fit anything smaller than 0.1uF.

Denis said:
200 ohm resistor should be correct to drop 480v to 450v after bridge, yes?

this unit charges capacitors
Click to expand...
The 200 ohm resistor will limit the charging current (to about 3.4A initially). It will not limit the voltage at all if the load is just a capacitor. And the capacitor would charge to almost 680Vdc.
 
G

gar

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Ann Arbor, Michigan
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EE
100110-0956 EST

Denis:

In the tube days you would have been looking for a "plate transformer" or "power transformer" and what you want would probably have been easily available. Dominate transformer manufacturers would have been Thordarson and Stancor. Stancor still exists, but listed nothing like that for which you are looking.

Your circuit diagram is incomplete if you want a well filtered output. If the device this powers has a large high voltage capacitor that is being driven by this supply, then the circuit is OK.

The transformer output voltage you want is about 450/1.414 = 318 V.

Do you need a continuous 550 MA at 450 V (250 VA)? Suppose you do, then you need about 250 VA of transformer capability. If this is a photoflash application, then the transformer capability could be less.

At Signal Transformer I found an SU-1/2, 500 VA. If the two 208 secondaries are connected in series this has an output of about 416 with paralled 120 primaries fed from 120. To reduce the output from 416 to 318 the primary input needs to be about 92 V. This you could obtain from a Variac at the input. Or a buck transformer.

Signal will also wind special transformers as well as many small transformer manufacturers.

If your 200 ohm resistor was for voltage reduction, then probably eliminate it. Depending upon the variation of load current the resistor might or might not be a good idea. You need to know or tell us more about your load.

I would use an 800 to 1000 V PIV rating on the bridge. The capacitor across the transformer secondary is probably OK for its unknown specific purpose. Probably should be a 1000 V rating ceramic.

.
 
C

Cold Fusion

Senior Member
Location
way north
Denis said:
...the 450v carbon-zinc battery this power supply will replace produced approx. 550mA

...dimesnions of box power supply fits inside 3.25" wide 4.5" tall 6.5" long...
Click to expand...
I don't think you will find a 60hz transformer that will fit in the box. As was mentioned by gar, if you need a 250VA xfm, it will be about:
5.30 x 3.75 x 3.21 (SQD 9070T250D1)
and will have an 80C rise. - that's really a lot of heat inside of your instrument.

Perhaps you could move the xfm to outside of the box, and just run the 480V to the inside where the rectifiers and rest of the circuitry is. Or put all of the power supply outside and just run the DC inside

Another alternative is to consider a switching power supply. Transformers operating at 20kHz to 50kHz are a lot smaller than 60Hz xfm.

cf
 
mxslick

mxslick

Senior Member
Location
SE Idaho
Ooops, who let the smoke out?

Ooops, who let the smoke out?

Denis said:
30232973.jpg

AC power supply

30232974.jpg

battery schematic
Click to expand...

Um, anyone else see a serious error in the two schematics pinouts? Like a serious tie-in and shorting of the primary voltage and the +450v DC out?
 
chris kennedy

chris kennedy

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Location
Miami Fla.
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60 yr old tool twisting electrician
mxslick said:
Um, anyone else see a serious error in the two schematics pinouts? Like a serious tie-in and shorting of the primary voltage and the +450v DC out?
Click to expand...

Jumper between J1 and J4? I don't see how this would create a short, but it does seem to be mixing primary and secondary voltages.
 
G

gar

Senior Member
Location
Ann Arbor, Michigan
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EE
100110-1505 EST

mxslick:

Good point.

I did not even look at the battery drawing. Quite obviously there are big problems with the labeling of the two drawings.

.
 
N

n1ist

Senior Member
Location
Massachusetts
Occupation
Principal Electrical Engineer
The device in question is a photographic strobe unit. You can either plug in the AC power supply or the DC one, but not both at once. The strobe would have a switch between pins 4 and 5 and expects 450VDC on pins 1+ and 2-.

/mike
 
G

gar

Senior Member
Location
Ann Arbor, Michigan
Occupation
EE
100110-1711 EST

The peak charging current is not a major issue. The average current required, more particularly the heating effect on the transformer of the charging current will determine the needed rating of the transformer.

Roughly speaking the the average DC current times the full charge voltage on the capacitor bank should be a more than adequate estimate of the VA rating of the transformer. Signal transformer uses this as a suggested criteria although based on an assumed moderately constant voltage on the capacitor of a capacitor input filter. Some amount of series resistance is useful to reduce the RMS/DC current level.

If this is a photoflash application, then there may be a considerably longer time between flashes than the time to charge the capacitor bank.

ColdFusion's idea of a switching supply is a good suggestion, but may be difficult to find a suitable commerical unit or to build one.

More information is needed on what the device is and the requirements of the AC to DC supply.

.
 
Besoeker

Besoeker

Senior Member
Location
UK
n1ist said:
The device in question is a photographic strobe unit. You can either plug in the AC power supply or the DC one, but not both at once. The strobe would have a switch between pins 4 and 5 and expects 450VDC on pins 1+ and 2-.

/mike
Click to expand...

If the strobe has a capacitive input then it will get a bit more than it expects if the transformer secondary is 480V.
 
G

gar

Senior Member
Location
Ann Arbor, Michigan
Occupation
EE
100110-1728 EST

Besoeker:

In post 5 I told him that he would need about 318 V for the secondary voltage, and one way to get the required voltage.

.
 
glene77is

glene77is

Senior Member
Location
Memphis, TN
gar said:
100110-1728 EST
Besoeker:
In post 5 I told him that he would need about 318 V for the secondary voltage, and one way to get the required voltage.
.
Click to expand...

And he resistor is to limit the inrush of current, into the Capacitor Load.
Initially, the Capacitor Load will appear to be a dead short.

I wonder what the .005 cap has for impedance at 120 Hz?
Wonder what is the impedance of the Xfrmr secondary?
Just, curious, since we are pulling this thing apart.
 
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