View Full Version : Powering flash from the mains?

22nd January 2008, 07:42 PM
What's the easiest way I could rig up my flash unit (the STF-22) to use mains electricity for power? (obviously some sort of transformer - 6v presumably?).

I presume I need some sort of 'fake' batteries to wire the transformer power to? Has anyone done this sort of thing?

I understand the STF-22 is basically an FL-50 bottom half with a different head on it, so anything which would work for an FL-40/50 should also work for this flash...

Any tips appreciated! :)

23rd January 2008, 08:17 PM
What's the easiest way I could rig up my flash unit (the STF-22) to use mains electricity for power? (obviously some sort of transformer - 6v presumably?).

I presume I need some sort of 'fake' batteries to wire the transformer power to? Has anyone done this sort of thing?

I understand the STF-22 is basically an FL-50 bottom half with a different head on it, so anything which would work for an FL-40/50 should also work for this flash...

Any tips appreciated! :)Hi lauriek,

Personally, I have no idea why one would want to do that, because if you do it properly, it won't be cheap. I would buy a few set of extra batteries instead. The only reason I can think of is if you want to rig up your set and let the camera work on itself for a long time, not having a chance to change batteries. Anyway...

I don't know much about the STF-22, but it looks like the FL-50 with two external flash heads. Just an idea or two...

Assuming it is indeed, like the FL-50...

If it is the way it is with the FL-50, then there is an external connector on the front, behind the rubber cover, under the red focus assist LEDs. Assuming that is the case, that connector is used for external power. Remove the rubber cover. Note that it can be a bit hard, but don't worry. The left two (seen from the front of the flash) of the four contacts you see inside is with 99% probability the external power connector for low power feed. I measure the same voltage on those two pins as the battery voltage, so my assumption is that it is connected in parallel with the batteries. I have just checked this out. Measuring my batteries at this moment shows 5.24 V when connected in series on the table and the same voltage when inside the flash, with the flash turned off, can be measured on the two pins sticking out mostly. My interpretation is that there is nothing in between the batteries and those two contacts. On the FL-50, the left most contact is of + (plus) and the one to the right of that is of - (minus) polarity. So, my assumption is that that is where I would connect external power. The problem is to find or make a connector, but maybe you can solve that part somehow.

My only problem with my theory is that if that is the case, i.e. no protection diode or anything in between the batteries and the external power in the flash, than you should build one outside the flash to prevent the current rush which will occur if you have batteries inside the flash when you plug in the external power. Without that protection, I would recommend you to remove the batteries before connecting to external power.

My second proposal or idea is to make a kind of a battery simulator out of two pieces of wood. You need to connect two wires, one two the bottom contact point, nearest the camera, one to the top, nearest the flash head (of the FL-50). The bottom one is the + (plus) the top one is the - (minus) battery contact. The two wooden pieces are used to keep the contacts pressed against the wires. Connect your external power supply to those contacts with the correct polarity. The two middle contacts you see in the battery bay are just there to create series connection when batteries are used, you don't have to bother about them, in fact, watch out, not to connect them to anything because it may cause short circuit. This DIY project would work with 100% certainty, if done the right way.

In both cases, watch out for the followings. Use at least 0.75 mm2 wires because the current is high. Use regulated, high quality power supply. I would not use anything else than 6 V supply and with an ability to deliver at least 2, but preferably 3 A current at 6 V. The power supply MUST be short circuit protected. And most of all, be very careful. Even at this voltage there are risks involved. One of them is that if anything happens, warranty is void. Everything you, or anybody else do is at your own risk, don't ever try to blame it on me or on the forum. I can only stand for that none of the above is lie, everything is according to the best of my knowledge and measurements. I would gladly post some images to illustrate, but currently I am in conflict with the forum rules, so I will not post images until that is cleared out.

Good luck, and tell us how it goes.

23rd January 2008, 09:45 PM
I hereby release you and the forum from any legal obligations you may think you have with regards my safety with regards to flash modifications! ;)

Much appreciated!

Anyhow, there is a power connector, I never knew that was there!! (slightly embarrassing!). Presumably that's where the mega-expensive li-po flash power unit plugs in? Meaning there's no chance in hell of me getting one of those connectors.....

I was thinking along the lines of some fake wooden batteries - but I prefer the idea of plugging power straight into that power connector. Shame the connector looks like a proprietary Olympus one...

Re the transformer - 3A, crikey, no wonder these flashes eat batteries!!

23rd January 2008, 10:04 PM
I think making a connector should not be too difficult. I'll get back if I come up with something.

24th January 2008, 07:53 AM
Hi again Lauriek,

I have some seemingly bad news for you regarding the FL-50 external power contacts. Looking at my PM lists on another forum (ClubSNAP) I found the following old message from a fellow member. I had no time at that time (and still have not), so we did not continue with this one, and I actually forgot all about it.


I see you're interested in the pin-out specs for the FL-50. I have some information you might be interested in. I think if we put our heads together we can figure this out. I did some experimenting with my unit. I was able to power up the control via the port using the two long pins. the inner pin is negative and the outer is positive. However it won't charge the caps. Max current draw is only about 82mA. Then the yellow and green leds begin to blink after one minute of trying. I thought I was throught but then I found some specs on the SHV-1. Here's a link


You'll notice there are two voltage outputs. 6v and 330v.
That means to me, that the two longer pins power the control part of the FL-50 and the two short pins only charge the caps. What I don't know is how to convert low voltages into high voltages.

One other point to think about, the FP-1 grip helps power the flash too but it uses only four C batteries. I'm not sure how it helps power the flash yet or which pins it connects to.

Please give it some thought as I know you like to tinker as much as I do.

Xxxxxxxx Yyyyyyyyyy

That means my assumption is wrong assumin he is right. It is also possible that he did not had the right power supply connected to the 6 V input, connecting a too weak power supply may result in the battery warning indicator activating he experienced. Anyway, don't waste time on clicking on the link, it leads to nowhere. To convert 6 V to 300 V is not a big deal, but it needs too much work to be an interesting alternative.

Sorry for bringing some bad news...

2nd February 2008, 08:38 PM
It's not the end of the earth - there's still the "fake batteries connected to a transformer" method, which should be do-able... I've almost certainly got a suitable transformer, so I just need to whittle some little fake wooden batteries!! :)

Jim Ford
3rd February 2008, 11:08 AM
It's just occurred to me that if you go down the 'fake batteries' road, perhaps you need to have a fairly well smoothed dc supply to them. There may well be a capacitor in the flash in parallel with the batteries, to reduce the power supply source impedance. This helps compensate for batteries that have a high internal resistance - eg that are getting low.
Because it expects batteries to be connected, this capacitor may not expect any ripple on the voltage. If such a capacitor is connected to an unsmoothed 'rough' dc supply with a lot of ripple, it can overheat to an extent that it could explode.

If you inspect capacitors that are designed for smoothing the rectifier output of a AC power supply, you'll find that they have a maximum ripple rating.

What this means is that instead of choosing just an 'ordinary' plugtop dc supply for the fake batteries, perhaps you should go for one that has some sort of smoothing built in.

Jim Ford

3rd February 2008, 05:19 PM
Definitely agree with Jim. The supply used must be of a high quality, regulated one not a chepo one can find anywhere.

9th February 2008, 12:30 AM
Thanks for that guys, I'll certainly bear that in mind!