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

Peter Barry peter_g_barry at hotmail.com
Fri Apr 8 14:09:45 EDT 2005


Many thanks Michael - the Durst repairers did indicate that the problem was 
with the relay, which continually blows the fuse and sometimes the enlarger 
bulb!  I will start with replacing the relay as you suggest and then 
graduate to the transformer if that doesn't work.

...Pete

>From: Michael Briggs <MichaelBriggs at Earthlink.net>
>Reply-To: f32 Large Format Photography Mail List <largeformat at f32.net>
>To: f32 Large Format Photography Mail List <largeformat at f32.net>
>Subject: Re: [LargeFormat] Power supply for a Durst 450 CLS head.
>Date: Fri, 08 Apr 2005 01:55:20 -0500 (CDT)
>
>
>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
>
>
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