Flash trigger voltage

Big Mike · Jun 9, 2005

I though I asked this before but I can't find it.

How do I go about testing the trigger voltage of my third party flash units? I've got a bunch of them and I don't want to use them with my 20D until I know that they are within the safe voltage allowance.

I know, I know...get a Canon flash....I'm working on it.

paul rond · Jun 11, 2005

Here is a site that has done the measuring for you. Just look up your flash unit.

http://www.botzilla.com/photo/strobeVolts.html

Good luck....

ThatCameraThingy · Jun 11, 2005

Hey Big Mike

Actually it is a very easy thing to do.

1. Switch flash on , and wait for it it charge up.
2. Take your Volt meter.
3. if one of the old analouge or cheap ones where you need to set the voltage scale , make sure that it is set to above 300v to begin with ( a word of caution : Some of the old studio flashes can have trigger voltages of up to 400V !!!!!! , handle with care)
4. on a studio flash place one probe on the outer contact of the sync cable , and the other on the inner probe.
5. measuer the voltage.

on hot shoe flashes the trigger voltage is measured between the centre point on the hotshoe and the little contact that is on the side of the hotshoe. I have found that the probe can not always get to the contact on the side , I use a paper clip wound around the probe to get in there.

on the newer flashes i find the trigger voltages typically under 10volts.

I have a few older (1980s) flashes that have vltages between 10 - 40 volts

and our studio flashes at work are about 150V.

under 10v your 20D should be safe. A techincian told me that typically the voltage should be safe if it is under 16V.

look ath the manual though

hope this helps.

Best yet - Get yourself a Speedlite 580ex - awesome!!!!

paul rond · Jun 11, 2005

To read the voltage spike, a meter reacts too slow and it won't be able to capture the peak. You may be able to see the spike deflection of the needle or the running numbers on your digital meter but you'll not get a reading. An ociliscope set up with a synch trigger to capture is the way to go.

Oh BTW there is an isolation cable you can buy or even build if you are handy that can isolate any voltage safely from your camera. I believe I saw it for around $15.

ksmattfish · Jun 11, 2005

I can't remember my source now, but I heard that the problem became enough of an issue with the 10D, which had a rating of 10 or 12 volts or so, that they dealt with it in the 20D, which has an external pc socket rated up to 250v.

I seem to remember thinking the source was reliable, but since I can't remember, I guess you better go with your test.

Let us know what you find out.

Christie Photo · Jun 11, 2005

When I bought my 10D, I also bought something called a safe-sync by Wein. It slides into the hotshoe and you can plug a pc cord into it. Two years later, and I've yet to plug ANY sync cord directly into my camera.

ThatCameraThingy · Jun 12, 2005

paul rond said:
To read the voltage spike, a meter reacts too slow and it won't be able to capture the peak. You may be able to see the spike deflection of the needle or the running numbers on your digital meter but you'll not get a reading. An ociliscope set up with a synch trigger to capture is the way to go.

Oh BTW there is an isolation cable you can buy or even build if you are handy that can isolate any voltage safely from your camera. I believe I saw it for around $15.

Paul,
if you opened the flash and tried to measure the trigger voltage over the flash tube you would have a tough time doing it.

To measure the voltage acros the contacts of the flash is as easy as i described before.

Go and try it, you will see that there is a continious voltage over the two poles that is 'waiting' to be shorted. On my Canon 550ex this is 6.45V . on some of the others it is it is up to 40V.

enjoy the day

paul rond · Jun 12, 2005

You never measure the trigger voltage at the tube, that is the firing voltage and is generall 1KV to 4KV which will give you one heck of a shock.

Measuring trigger voltage is at the pc connection and as soon as you put the meter on it the flash fires. I just put my Vivitar 283 on a Fluke and it gave me a fast burst of number rolling to 50V but never gave me a reading... or should I assume 50V is the peak? I put my flash on my Simpson analog meter and it deflected the needle to just over 150V but never hit the actual voltage I captured on my Techtronics scope at 600V.

Part of the problem is the very low amperage and the burst if too fast, milliseconds, which is much too fast for your meters.

The chart is very complete and fairly accurate... http://www.botzilla.com/photo/strobeVolts.html

ThatCameraThingy · Jun 12, 2005

Hey Paul

Heck , I'm gonna back out of this one. Looks like you have far more experience and better equipment to measure this kind of thing than I do. I was quite happy thinking that the 50V you measured was the peak voltage.

guess i am just luky I havn't blown anything up yet ??

any way , how come you know so much ? Electronics your field , or are you playing with flashes and trigger systems etc. I know they say the 283 is a nice flash to use for high speed stuff since you can pull the output (and hence the exposure time ) way down.

thanx for the comeback

Big Mike · Jun 13, 2005

Thanks.

Yes, the manual for the 20D says to keep it under 250v so most units are safe. Although, according to that list, one or two of the Braun units I have...are over 300v...so I'm not going to be connecting those to my camera.

*edit* Actually, all the units I have are under 250v so they should all be safe on my 20D. Although, 'should' in not a very strong word when dealing with a $2000 camera.

A safe-sync would be the way to go. I'll put it on the wish list.

Christie Photo · Jun 13, 2005

This is what the little guy lools like:

http://www.bhphotovideo.com/bnh/controller/home?O=productlist&A=details&Q=&sku=245292&is=REG

paul rond · Jun 13, 2005

I've been playing with electronics since I was 11 yrs old, since the tube days and was a ham operator once upon a time... too many hobbies.

It can be dangerous to think the voltage is so little cause of the equipment used to measure it. That is how accidents happen and digital accidents are expensive. What it seems is not always what it is. I blew up a brand new Cannon with a flash and that was what tipped me off something was going on and thus the reason I found so much information on teh net about it. Once upon a time it didn't make any difference what teh trigger voltage was since it was just a mechanical switch jumpering a contact. Now it's all about electronics. Get an isolator, it's the safest way to go and cheap enough when compared to the equipment it is saving.

The hot shoe gizmo is perfect. I wish I knew about it sooner. I have the cable isolator which is nice but built into a hot shoe is really nice.

The Vivitar is a great flash, very popular in it's day. You can find em for $30 these days for high speed strobe fun. I posted a link somewhere for triggers and mods to play with if you are into electronics projects.