The most effective way of getting 90-100 watt of 82 regulated VDC

[alexandru_voicu]

Hi everyone,

As I'm still a novice in electronics, I would like to ask for your advice. Here is the shorty story. One of my other hobbies is film photography. I have a beseler photo enlarger that I bought from the US and I use it with a stepdown transformer. The lamp inside needs 82VDC. I opened the head some time ago and I remember I saw a diode and a resistor before the lamp. That would make sense. 120VAC * 0.707 gives around 84 VDC with half-wave rectification. Given that I would like to get rid of the stepdown transformer, do you think of other simple ways (preferably with a very limited number of parts, so I can fit them in the enlarger head) to get the same results from 230-240VAC (I live in Europe)?

If there is no solution, I am willing to build a separate power supply (regulated, well-filtered, etc.). I guess I would need a transformer with a 60VAC / 2A secondary, but I have no idea how to regulate it at 82VDC.

Any comment would be greatly appreciated.

Thank you,
W.S.

[FYL]

Suitable 230/240V lamps aren't available?

[alexandru_voicu]

Hi,

Thank you for your answer. I actually thought of that, but I don't know enough about optics in order to take such a decision. The head is a diffusion type - in case you are familiar with enlargers - and I don't know what kind a substitute I should be looking for. There are issues with the temperature color, too many variables for my limited knowledge.

W.S.

[FYL]

Just ask Beseler...

http://www.beselerphoto.com/

[PRR]

A 230:115 step-down AUTOtransformer IS the most obvious solution (other than a Euro-market lamp from Bessler). This could be a 50VA-75VA transformer with dual 115V/230V primary.

A custom power supply uses at least as much iron, probably twice as much since it probably won't use an autotransformer. Full-transformer plus an AC/DC conversion suggests three times the total iron.

It is not clear to me why Bessler fed 82V. Is it perhaps a 120V lamp run on 82V for ultra-long life?

Are you printing color or BW? Lamp voltage affects lamp color which will mean re-calibrating your process for any voltage shift.

However since it apparently has no regulation now, I don't see why it needs regulation.

[alexandru_voicu]

Hi and thank you for your comments.

The enlarger uses a quartz-halogen lamp which does work at 82 volt, according to the specs. Its life is rather short - estimated at 40 hours. Why 82 volt, I don't know, but this is the recommended voltage for the lamp.

Coming back to my initial question, I see the possibilities. One is two get 82 volt inside the head of the enlarger and get rid of the awful stepdown transformer I'm using now. The other is to build a regulated power supply which will replace the present stepdown transformer. Even if it is heavier, at least it's regulated, something that matters both for lamp's life and for the consistency of exposure.

I don't know, however, how to get 82 volt @ 1.1A regulated.

Thanks,
Alex

[PRR]

> I don't know, however, how to get 82 volt @ 1.1A regulated.

All the ways that I know how to design 230VAC to 82V regulated are very ugly.

An additional problem is that the lamp will pull 3 to 10 times more current at start-up. We'd like to reduce this, for lamp-life and because the 3A-10A surge is extra work for the regulator.

The most efficient version that I could think of dissipated over 700 Watts peak 200 Watts average in a resistor (which could be an electric tea-pot) plus 160 Watts in a MOSFET (which means several MOSFETs on a very large heatsink).

More efficient would be seven 12VDC 2A switching regulators in series.
www.jameco.com
GS25A12-P1JU
AC/DC Power Supply Single- Output 12 Volt 2.08A
$18.95 each ($134 for seven) (plus shipping and import taxes in your country)

A 230:115 autotransformer (or dual-primary 75VA transformer) is even more efficient and cheaper, though not regulated.

> the awful stepdown transformer

What is so awful about the stepdown transformer? You only need 100VA. It can hide under the bench.

Have you contacted Beseler to see if there is a Euro-Market lamp?

http://www.beselerphoto.com/international.html
http://www.beselerphoto.com/reachus.html
http://www.donsbulbs.com/cgi-bin/r/t.pl?searche=enlarger

> life is rather short - estimated at 40 hours.

As I recall, you turn-off an enlarger when not exposing(?). Take 10 second exposures, that's 14,400 prints, maybe less if thousands of on-surges shorten life. In a high-volume commercial shop doing long runs of identical prints, that's a couple of high-profit weeks. In hobbyist use, 10,000 prints is more than a lifetime.

[sluckey]

I would keep it simple and just use a stepdown transformer. There's no requirement to regulate the voltage to that incandescant lamp. Beseler didn't do it.

[alexandru_voicu]

Thank you very much for your comments and suggestions. It seems that the only way to go is to find a European substitute for the lamp. As for the power supply, actually Beseler used to build regulated power supplies for their enlargers for decades (but using 12 volt lamps, I think). This is the latest development, probably to cut costs in a business that unfortunately is dieing.

W.S.

[DummyLoad]

It is not clear to me why Bessler fed 82V. Is it perhaps a 120V lamp run on 82V for ultra-long life?

perhaps for spectral output tuning?