What voltage do darkroom timers usually use? I need to replace a fried transformer on a GraLab 600

[Kresado]

Long story short I forgot to use my step down adapter and plugged it into a 220v outlet, didn’t realize my mistake until 15 seconds later I noticed a weird smell and the lights on the display went off. Took it to a local place but they just stripped down the transformer and said they couldn’t do anything.

GraLab 600 specs; 110-125 Volts at 50/60Hz, 9 Amps
Outlet B - 700w
Outlet A - 300w

My estimates and understanding is that the transformer and the board runs likely around 12-12.6v so my question is, once I have found the voltage, would I be able to just re solder a new transformer on with the same voltage but with a higher ampage (finding transformers for 9 Amps seems to be pretty tough so could i use a 10 Amp one instead?) I will then use it through a step down outlet plug

Also this may be a dumb question but if I were to find an AC adapter that matched the needed specifications (something like the one pictured below) would I be able to open it up and use the transformer unit from that, taking it out and then soldering it to replace the one on the timer.
Thanks heaps for any advice

 

[AgX]

Where did you get that 9A from? At best it is the rating of the switches for controlling outside circuits. The transformer is only to feed the electronics of the timer and to control those two switches.
You better do nothing yourself in this case! Find another electronics expert who might work on it.
In your preceeding thread on your issue you already got a hint at the isssue being more complicated than you think.

 

[AgX]

Transformers are built with standard materials concerning voltage, within the household range. Thus I assume your transformer to be able to be fed with twice the designated voltage. Problem rather seems to be the electronics behind it, notwithstanding the higher voltage, failing and as result putting much higher drain on the transformer, making it overheat.
In the best case the transformer indeed itself did not stand the voltage and shortcircuted in itself, without further damage. But I doubt it. Thus my advice to give the thing into competent hands.

 

[Kresado]

Got the 9A rating on the back of the timer, I do plan on having someone more well versed look at it as soon as Covid allows me to do so.

 

[DWThomas]

Also this may be a dumb question but if I were to find an AC adapter that matched the needed specifications (something like the one pictured below) would I be able to open it up and use the transformer unit from that, taking it out and then soldering it to replace the one on the timer.
Thanks heaps for any advice

The short answer is 'no', that adapter, as with most recent technology, uses a switching power supply and does not contain anything likely to be a drop-in replacement for the transformer in that timer. I also agree with Agx that at least the power supply rectifiers and such will have seen double voltage and there is likely damage there.

 

[RalphLambrecht]

I operated both, 110 and 220V, darkroom s, both with mixed equipment and transformers. For timers ,the frequency, either 50 or 60Hz is also important as they may use it to count time.

 

[Nicholas Lindan]

There should be printing on the transformer, somewhere, giving the input and output voltages. The logic in the timer works on 5 volts. It is possible the timer uses 12V for the relay coils.

The 9A on the timer nameplate is the power plug current - it includes the maximum current for the enlarger and safelight. The transformer only consumes a few hundredths of an amp, if that.

A 120V transformer plugged into 220V will overheat and fail. The higher voltage will result in saturation of the iron core (the transformer core can no longer support a magnetic field - it's all fielded out) and large currents will flow through the transformer's primary causing overheating. However, it takes some time to destroy a transformer this way. The picture doesn't show a melted-down transformer so it probably survived.

The transformer in the power supply module you show will NOT work in this application.

Plugging your timer into 220v resulted in twice the output voltage. The transformer feeds a rectifier and capacitor and then a voltage regulator. My guess is the voltage regulator worked for a brief period of time and then failed. If the voltage regulator failed shorted and overvoltaged (er, fried) the logic circuitry then you should think of getting a new timer. If it failed open, and the logic circuits (IC's) didn't get destroyed, then replacing the voltage regulator may restore function.

This is a typical voltage regulator: https://www.digikey.com/en/products/detail/on-semiconductor/LM7805CT/458698 These are commonly available most everywhere. It is possible your timer has a switching regulator, then the above part will not be on the circuit board.

If you have a voltmeter measure the voltages between the metal tab on the regulator and the two outside leads. Ideally the voltages will be 8-12VDC and zero. If you measure 8-12V on both legs then toss the timer in the trash. If you measure 8-12 and 5 volts then the regulator is OK and something else gave way.

P.S.: You did check the timer's fuse... There may be a smaller fuse soldered to the circuit board.

 

[Nicholas Lindan]

I also agree with Agx that at least the power supply rectifiers and such will have seen double voltage and there is likely damage there.

Well, probably not. The standard rectifier diode will survive (and thrive) with several hundred volts - a 500V rectifier costs just as much as a 50V rectifier. Most all manufacturers use the high voltage units and don't worry anymore about voltage ratings.

 

[DWThomas]

The standard rectifier diode will survive (and thrive) with several hundred volts - a 500V rectifier costs just as much as a 50V rectifier.

Yes, perhaps, but any filter capacitors down the line are far less likely to be anywhere near that robustly spec'd. Also, decades back (not sure how old that timer may be) a lot of consumer electronic gear was not as reliable as we might wish it were to begin with.

Anyway, it is said that once the smoke is allowed to leak from some components, they no longer work.

 

[AgX]

A 120V transformer plugged into 220V will overheat and fail. The higher voltage will result in saturation of the iron core (the transformer core can no longer support a magnetic field - it's all fielded out) and large currents will flow through the transformer's primary causing overheating. However, it takes some time to destroy a transformer this way.

I did not consider transformer saturation happening. For unknown reason I always linked this with frequency, but voltage plays its part too.

 

[snusmumriken]

I don't know what the market for such stuff is like in Vietnam. Here in Europe it would be far easier to buy another timer on eBay, and generally safer. I tinker with low-voltage electronics myself, but mains electricity has the potential to cause serious fires...

 

[Chan Tran]

Well you're in Vietnam. I think it may be better to ask someone there to build you a timer.

 

[wiltw]

Probably best to simply buy a replacement, rather than to guess as to what has fried! Plenty of Gralabs on eBay.