[LargeFormat] Power supply for a Durst 450 CLS head.

[Michael Briggs]

On 07-Apr-2005 Peter Barry wrote:
> Hi to all,
> 
> The transformer which powers the 450 CLS head on my ageing Durst L1200 
> enlarger has just had the last rites pronounced on it.  Replacement 
> transformer units seem to be a little rare on the second hand market, so 
> does anyone know how to rig up an alternative 24 V 450 W power supply?
>

Do you know that the transformer is the part of the power supply that failed?
The TRA450 that I have failed due to the internal switch.  Durst initially
designed the power to be switched by a relay.  The relay must have frequently
failed because Durst retrofitted a triac to control the 24 V power, with the
triac switched by the original relay.  On mine, the triac failed twice, so I
replaced it with a a heavy-duty contactor relay.  Probably both the original
relay and the later triac were unable to cope with the heavy surge current of
turning on the lamp.  If the relay or triac is the problem on your power
supply, upgrading to a heavier-duty relay should be cheaper than replacing the
transformer.  But you will need to understand electronics and know how to work
safely on electrical apparatus.

The lamp in the CLS 450 is an ELC, which is 250W, not 450 W.  But to keep from
operating the transformer near its limit, which may mean a reduced lifetime, it
is best to get a transformer of a somewhat higher rating.  Also, a higher rating
means that the brief but large turn on surge current is less likely to damage
the transformer.   The "industrial control transformers" are designed to cope
with transient overloads, and so are probably an excellent choice.

--Michael