Flash Trip Voltages

[KN4SMF]

My latest thread about my Sekonic 308 opened up a whole new can of worms about flash trip voltages. I discovered all you have to do is turn on the flash till the ready light is on and test the cord contacts with a digital voltmeter, which had about as much impedance as a VTVM. I tested my Sunpak 611, and a Vivitar 252 from the olden days and they were both upwards of 190 V. Plenty of voltage to zap a modern camera and ruin it. A little while ago I tested my Honeywell Strobonar 682S and it was only 49V. What do you think, still too high for these modern cameras? I had also tested my NikonSB-10 and it was only about 4 or 5 V.

 

[spark]

It depends on how the camera fires the flash. Old cameras used contacts, newer ones use solid state devices (transistors, SCRs, etc). Wein made an attachment, I think with an SCR (silicon controlled rectifier), that triggered a high voltage flash with only a few volts being seen by the camera hot shoe.

My Fuji GW645 manual specifically warns about high voltage so I got a more modern flash, less than 10 V.

 

[bdial]

It depends on the camera (or device), for example, Nikon specifies an upper limit of 250 volts. I don't know if that includes the most recent cameras, but it's in the manual for my D300. PocketWizard specs 300 volts max for the sync port. The manual for my Panasonic P&S just says "beware", elsewhere on the web it's reported that it can tolerate 90v and they specify 15v or less. I can't find a number for my Minolta flash meter.

According to the numbers I can find for my monolights (Calumet/Bowens), the sync voltage is 5v, but I've not measured it.

There may be a radio trigger plug-in available for your Sekonic, that would let you avoid the issue entirely.

 

[RalphLambrecht]

My latest thread about my Sekonic 308 opened up a whole new can of worms about flash trip voltages. I discovered all you have to do is turn on the flash till the ready light is on and test the cord contacts with a digital voltmeter, which had about as much impedance as a VTVM. I tested my Sunpak 611, and a Vivitar 252 from the olden days and they were both upwards of 190 V. Plenty of voltage to zap a modern camera and ruin it. A little while ago I tested my Honeywell Strobonar 682S and it was only 49V. What do you think, still too high for these modern cameras? I had also tested my NikonSB-10 and it was only about 4 or 5 V.

according to the ISO standard: flash units should require <5V to be triggered and cameras should be able to withstand >5
V of trigger gvoltage but I believe, both requirements are violated frequently.

 

[GRHazelton]

Here's a site which may be of use http://www.botzilla.com/photo/strobeVolts.html

 

[KN4SMF]

I know about that botzilla site. What astounds me is that my Nikon d7100 specs don't state the trip voltage. My entire thread probably belongs in the digital or hybrid section of this site, but there were no subcategories for flash. Thanks.

 

[wombat2go]

Some of the early electronic flash units did not have a buffer between the triggering circuit and the camera contacts.
(Contact voltage was not an issue then.)

I tested an old Pentax AF160, about the second generation of Pentax flashes from 1977 or so.
That was in 2015 after I had a hotshoe failure on an Olympus M3/4 when using this flash.

The hotshoe voltage pre trigger measured with a meter was 3.75 volt DC.

The voltage and currents during triggering depend on the impedance of the camera side contact or semiconductor.

Here are some measurements I took with oscilloscope

Camera Resistance [Ohm] , V peak [Volt] , I peak [ Amp] , Time to peak [nanosecond] , di/dt [A/usec]

AF16
3 , 15 , 6 , 800 , 7.5 ,
47 , 150 , 3.2 , ~ 100 , 300 ,

Tests with the later model AF160
3 , 4 , 1.2 , 500 , 2.4 ,
47 , 8 , 0.17 ,


So: With old flashes, the quiesecent DC "trigger voltage" measured with a meter may not be a reliable indicator of the stress on the camera.
I no longer use the AF16 on any of the digital cameras.
Edit: Sorry the tabs for the data do not line up, I should have used a spreadsheet.

 

[jim10219]

Keep in mind that measuring a flash voltage with a DMM likely won't give you an accurate reading. It will often be much higher than what the DMM reads. Most are not designed to take an accurate instantaneous reading of a quick burst like that. It depends on the DMM and the setting. An oscilloscope is a better tool, as they're designed to track fast voltage fluctuations like that. Though even then, you need a new enough one that can read peak instantaneous voltages.

 

[MattKing]

My entire thread probably belongs in the digital or hybrid section of this site, but there were no subcategories for flash. Thanks

The problem isn't limited to digital cameras. There are a lot of more recent film cameras that use electronic flash synch circuits.
I would expect that all of the auto-focus film SLRs are in that category. As an example, I won't use a direct connection between my old Bowens monolights and my Mamiya 645 Pro, whereas my older RB67 is fine.
Wein SafeSynchs or radio/IR triggers are your friend.

 

[KN4SMF]

The problem isn't limited to digital cameras. There are a lot of more recent film cameras that use electronic flash synch circuits.
I would expect that all of the auto-focus film SLRs are in that category. As an example, I won't use a direct connection between my old Bowens monolights and my Mamiya 645 Pro, whereas my older RB67 is fine.
Wein SafeSynchs or radio/IR triggers are your friend.

Always another piece of equipment you gotta buy in this racket. $40 here, $40 there... You get 40 dollared to death. At some point you have to put your foot down and make do.

 

[AgX]

Keep in mind that measuring a flash voltage with a DMM likely won't give you an accurate reading. It will often be much higher than what the DMM reads. Most are not designed to take an accurate instantaneous reading of a quick burst like that.

If you experience a burst than it already went wrong. The voltmeter must not trigger the flash. In case it does another model of meter must be chosen, or a metering circuit made up that inserts an additional resistance

 

[reddesert]

I know about that botzilla site. What astounds me is that my Nikon d7100 specs don't state the trip voltage. My entire thread probably belongs in the digital or hybrid section of this site, but there were no subcategories for flash. Thanks.

Look in the manual, not the specifications. It is probably in the Technical Notes - Speedlights section. I don't have a D7100, but the other Nikon Dxx manuals I have say in this section, "Use only Nikon Speedlights. Negative voltages or voltages over 250V applied to the accessory shoe could not only prevent normal operation, but damage the sync circuitry of the camera or flash." The use-only-Nikon part is covering their behinds, but the 250V rating has been around for a while. Some electronic film and digital cameras from other manufacturers have much lower ratings (like 10 V) so it is worth checking.

 

[bdial]

The 7100 is <250v too, if you open the PDF version of the manual from Nikon, and search for "voltage", you'll hit a paragraph with the verbiage that reddesert quotes.

 

[wiltw]

1. Back 'in the old days', metal contacts were used to close the circuit to trigger flash. These could easily tolerate high flash trigger Voltages.
2. Then (around the 1990's or so) manufacturers changed to electronic circuitry to trigger the flash -- even in film SLRs -- and the trigger circuitry would burn out when the flash being triggered was too much >12V
3. Then the dSLR was invented, and they used to same vulnerable electronic circuits to trigger the flash electronically.
4. Finally, about 2004 or so, with the launch of the Canon 20D, Canon produced an electronic trigger circuit that could tolerate 250V.

 

[pentaxpete]

I have an 'Early ' Metcablitz 45 CT-1 that I bought new in the 1970's and it burnt out the flash contacts of 2 Asahi Pentax MX Cameras due to using it so much for Local Press work -- it has a 'High Trigger Voltage' -- then I was GIVEN a load of 45 Series Mecablitzes and they are all 'safe' -- the Later 45 CT-1 units have ORANGE markings on top whereas my original has BLUE.