Need help sourcing a relay for Durst TRA450

Eric Rose · Mar 2, 2018

Yes I know this is an ancient piece of gear but my enlarger which I use all the time depends on it. The unit is a very old one, I suspect looking at the interior probably a 1960's vintage. Below are some photos of the unit in question. I have temporarily repaired the relay but it won't last much longer. If someone could provide me with a part number for the relay in the lower left so I could order a new one that would be awesome!

Eric G. Rose

AgX · Mar 2, 2018

Once you found out its way of switching, the respective voltages and the load current you could use any respective relais off the shelf. You only would have to make a custom fix. And maybe you would have to solder the contacts.

Where would you order the original part?

Eric Rose · Mar 2, 2018

I tried Durst US but got no reply.

ic-racer · Mar 3, 2018

I have had good results polishing relay contacts with metal polish, if you can take it apart.

ic-racer · Mar 3, 2018

Also, this may help, V23009 and V23008 are shown in various schematics:

Svenedin · Mar 3, 2018

ic-racer said:
I have had good results polishing relay contacts with metal polish, if you can take it apart. View attachment 196316

+1. I have an ancient motor car that has a number of relays. They were always playing up so I would keep some very fine emery paper in the glove box to clean the "points" (contacts). "Switch cleaner" (isopropyl alcohol) on a cotton bud is a less aggressive way of doing it. These were electromechanical control boxes and the electric fuel pump. Lucas and SU stuff.

From your photo Eric those contacts look really dirty and also misaligned. They can become pitted with arcing when the gap is incorrect. If the contacts are beyond salvage you may even be able to source just the contacts rather than the whole relay.

AgX · Mar 3, 2018

ic-racer said:
I have had good results polishing relay contacts with metal polish, if you can take it apart.

No need to take them apart, one can custom make a thin grinding tool.

AgX · Mar 3, 2018

A likely apt relay would be around 5-10€. (solder-in versions are cheaper than free standing ones with connectors)
Establish the necessary data and then go through some online-catalogs.

I would not know where to obtain lose contacts. I better not imagine the hassle to insert them into the springs...

Svenedin · Mar 3, 2018

AgX said:
A likely apt relay would be around 5-10€.
I would not know where to obtain lose contacts. I better not imagine the hassle to insert them into the springs...

They would be already mounted on new springs but if a new relay is that cheap not worth the hassle.

Eric Rose · Mar 3, 2018

I already tried polishing the contacts. They are beyond repair. Thanks for all the help so far. I have no idea how to look up relays but I can measure the voltages on the various contacts.

4season · Mar 3, 2018

Was there some sort of outer housing to that relay, and if so, can you post a photo showing the markings, if any? Mostly need to see electrical specifications. Relay itself looks like a fairly standard double pole, double-throw device, but I can't determine the appropriate voltage and current requirements just by looking at the photos you've posted.

Eric Rose · Mar 3, 2018

No outer case. I am going to use my DVM to measure the voltages and post results.

AgX · Mar 3, 2018

Here just as reference of what kind of mechanical relays you have to look for:

solder-in models (scroll down)
https://www.reichelt.de/Print-Steckrelais/2/index.html?ACTION=2&LA=2&GROUPID=7621

free standing;
https://www.reichelt.de/Industriere...ob7dd424fd53861494adee821b745eb82&LANGUAGE=EN

AgX · Mar 3, 2018

You have to know:

-) what switching the relay does: opening/closing at the very pair(s)
-) the voltage of the load
-) the current of the load
-) voltage of the operating circuit
[-) current of the operating circuit, is likely of less interest]

Sirius Glass · Mar 3, 2018

Remove the relay.
Tell us the specifications that you can read off it.
Post a photograph of its connectors and any symbols.
Post a photograph of its diagram [showing contacts open or closed]
Then we can help you find a replacement.

bdial · Mar 3, 2018

This may help (scroll down to the "Relays" link under "Other Electrical Controls" https://www.mcmaster.com/#electrical-controls/=1btdp3b
Basically you need to know whether you have a single pole or double pole, the operating voltage and how much current it needs to handle.

Chan Tran · Mar 3, 2018

bdial said:
This may help (scroll down to the "Relays" link under "Other Electrical Controls" https://www.mcmaster.com/#electrical-controls/=1btdp3b
Basically you need to know whether you have a single pole or double pole, the operating voltage and how much current it needs to handle.

The original relay is a double pole double throw but only single throw is needed. The current rating isn't that important because you can simply oversize and it's not higher than the outlet. What is most important is the voltage for the coil. It could be 220V but could be a lower voltage.

AgX · Mar 3, 2018

Well, there are relays that take the same load current, but different load voltages, let's say 12V versus 230V.
If you run the 12V version on the mains you may have an isolating issue. So the load voltage is of importance too.
That is why I was detailed above. Of course one may chose on oversized relay concerning the load.

davidmasek · Mar 5, 2018

From looking at the schematics, there are 3 different versions of TRA450. The oldest one uses an AC relay, the later two a DC relay, the coil voltage seems to be in both cases 110V. On the other side - one contact switches 25V voltage for the lamp, the other 220V (for the fan maybe?)

Need help sourcing a relay for Durst TRA450

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