Mains Transformers - sequence to wire them up ?

[AgX]

I got many such small power supplies containing just a plain transformer, maybe added by a rectifier, but now I added one that puzzles me:

Charger Type E from Singapore Camera Factory for a Voigtländer or Rollei flash
prim. 110/220V
sec. 7.15V 5VA

3-pole connector (to the flash)
(thus I assume the transformer circuit is basically like this one (left above) https://www-user.tu-chemnitz.de/~heha/basteln/Konsumgüter/Blitzgeräte/B125-Schaltplan.gif)

The surprising thing with this one is that it got huge stickers at both sides, warning the user in 6 languages to first connect the mains cable and only then the charging cable.

What is the idea behind this warning??

Whatever I thought of makes no sense to me.

 

[AgX]

I think I got it...

So far I overlooked in the power supply circuit that transformer bypass (for direct charging of the main capacitor).
Thus the rectifyer in front of that capacitator would be more or less directly connected to the mains plug.

So, when hooking up the charging cable first to a flash with main capacitor being still charged (think of changing within a photo session from battery run to mains run), there could be the main capacitor's DC voltage at the mains plug.
But what current could run backwards through a rectifyer assembly? (Should be electronics basics, but I better ask...)
Such transformer circuit seems most common.
Why have I never come across such warning before ??

(Keep in mind, the circuit linked to is just a sample, from a different flash.)

 

[REAndy]

I'm seeing a couple of things that makes me think the schematic is not complete.
The positive side of the battery shows no connection to the circuit.
If the device in the upper left corner is the transformer, I don't see a rectifier circuit connected to it. That makes me believe that the "mains supply" is DC.

Looking at the schematic, I could see that the mains supply (upper left) being a DC input to provide power to the flash or charge the battery. But again, I see no connection to the positive side of the battery.
There is also a double pole double throw switch which seems to disconnect the mains. One pole is under lower "rounded corner triangle" (is this the connector/terminal for the mains?)... and follow the dotted line to the second pole of the switch just to the right of the negative of the battery. This switch could select connecting the battery and mains together for charging. And in the other put the battery in the circuit (turning it on).

Again, hard to tell without knowing where the positive side of the battery is connected.

Do you know:
1) Can you use the mains to not only charge the battery, but also to power the flash (like in a studio, not on batteries)?
2) Is the output of the "Charger Type E" 7.15V 5VA Direct Current output (DC) or is it AC output? (again I don't see a rectifier circuit to accept AC from the "Charger Type E"

Now off to your question about the warning. To me, it sounds like the warning is stating to plug in the "power unit" to the "mains cable" (wall plug / household electricity), and then the other cable of the "power unit" to the flash itself. Is this how you interpret the warning? In my experience, you would want to plug the "charging/power unit" to the flash first, then plug that "charging/power unit" to the flash. Because the warning says to do the opposite, and the incomplete schematic (or at least questions on the schematic), something unusual/unknown is going on.

I probably should have googled "Charger Type E" before I wrote this to see if more info is available online. When I get a chance to do this I will and come back here and write some more. But I wanted to get these questions out to you, as it might help us solve this mystery.

thanks,

REAndy

 

[REAndy]

OOPS, I should have proofread before posting. CHANGE "rounded corner rectangle" to "rounded corner triangle"
I edited my post, but leave this here for those who read it before I edited it.

 

[AgX]

"If the device in the upper left corner is the transformer, I don't see a rectifier circuit connected to it. That makes me believe that the "mains supply" is DC."

That schematic was for a 220V AC mains system. In the flash circuit there is a single diode in the main capacitator charging path.
Anyway, that circuit is from another charger/flash combo.
But two-voltages-output mains supplies are most common and I assume they are basically built like the one in that sketch.


"To me, it sounds like the warning is stating to plug in the "power unit" to the "mains cable" (wall plug / household electricity), and then the other cable of the "power unit" to the flash itself. Is this how you interpret the warning?"

Exactly! This is the warning:
Connect mains cable first! and thereafter the charging cord.

"Can you use the mains to not only charge the battery, but also to power the flash (like in a studio, not on batteries)?"
That should be the idea behind these power-supplies with 3-pole charging cable. They act both as device for charging the flash battery, but could also be used for flashing on the mains.

 

[REAndy]

But what current could run backwards through a rectifyer assembly? (Should be electronics basics, but I better ask...)

Ok, lets take that idea and run it backwards...
Assuming flash main capacitor is charged (ready light illuminated). This would put positive potential at the negative side of the diode SY361/?. If you connect the power supply up to the flash first, this would provide a path for current flow back thru the power supply to the positive side of same diode and be so much voltage from the main capacitor it could blow this diode? (you would think they would have put in a different diode that would hold this). I would think the purpose of that diode would be to stop current flow to the main capacitor as that capacitor charges. (but you would think that would happen naturally as the capacitor charges anyway). Perhaps they want the power supply to be providing power when it is plugged in (the power supply would have enough potential to prevent any back flow of current??)

 

[REAndy]

But I agree that if the flash is discharged, it shouldn't matter if you plug in the power supply to mains first or last.

 

[REAndy]

That schematic was for a 220V AC mains system. In the flash circuit there is a single diode in the main capacitator charging path.

Sorry, I should have been clearer with my question. I was asking about the "Output" of the power supply, if that was DC.
Yes, I understand that the input to the power supply is AC.

 

[AgX]

I have not metered the voltage (the unit is sealed and I would have to improvise with probe-pins, maybe I shall meter tonight.)
But as I just added to post #5 above, the 2-voltages (like in that sketch) going to the flash should be the idea behind these common 3-pole flash connectors.

 

[AgX]

But let assume it is as I think:
mains voltage going directly to the flash, there to a rectifyer and then to the main capacitator.

Under which circumstance in general could the main capacitator's DC voltage end up at critical current at the mains plug of its seperate power supply, when the capacitator is fully charged?

Or, what could have made my Rollei/Voigtländer flash different to bear that warning?

Or, maybe the warning is not even due to electrical shock...