Checking trigger voltage
Some old flash units are known to have dangerously high trigger voltages. Connecting such units to modern equipment such as digital cameras or wireless trigger may damage the equiment.
The units that it is most likely to have harmful trigger voltages are vintage “generic” units that only have a centre pin on their hot-foot. Newer, dedicated flash units with multiple pins for TTL electronic flash control can generally be considered “safe”. Another clue to look for is the unit's “ready” light indicator. If this is neon, then it is very likely that the unit has a high trigger voltage. If the indicator is of the LED type, it is more likely that the unit is “safe”. But it is always best to check.
This note tells you where to find data about trigger voltages, how you yourself can measure the trigger voltage of an old flash unit, and what trigger voltages can be considered “safe”.
1. Look it up
In many cases, the trigger voltage of a flash unit is listed in the manual. If it is not, you can email the customer support department of the manufacturer of the flash unit, and ask.
Alternatively, you may find the trigger voltage of the flash listed in our product database. Note that some units have manufactured over many years, and the design of the electronics may have changed over time. For such units, we list the smallest and highest voltage reported. However, we have no way of knowing whether our data is complete.
2. Measure it
To make sure, it always best to check the voltage and the polarity of a particular unit yourself.
To check an unknown trigger voltage, you'll need a digital multimeter. For most reliable result, the input impedance of the meter should be 10 MOhm, or higher.
To measure, put fresh batteries in the flash you want to check, and charge the flash until the “ready” lamp (or equivalent) is lit. Then set the range selector on the meter to the most sensitive range (you may need to experiment to find the right one), and read the voltage from the meter's display.
You meter the voltage between the centre pin and the edge contact. Refer to the photo above if you do not know what these are. If there are more than one pin below the flash, it is the centre one you're interested in. It will make contact with the large round connector in the centre of the camera's hot-shoe. The edge contact may be a small metal square recessed in the hot-foot, or something larger. It is designed to make contact with the metal at the edge of the camera's hot-shoe. You always connect the negative probe (black on most meters) to the edge connector, and then connect the positive probe (red on most meters)to the centre pin.
The photo above shows me making this measurement on a Nissin Speedlight Di866 using a Caltek CM1100 digital multimeter. Prior to metering, I've set the meter to use the range 0 to 20 volts. I use my hands to connect the points of the positive and negative probes to the metal of the Speedlight's hot-foot. The reading of the multimeter tells me that the Di866 has a trigger voltage equal to 3.42 volts.
Note that older analog voltmeters may have a low input impedance which may result in a voltage drop inside the meter. This will result in a too low reading. For best results, use a digital meter with a impedance of 10 MOhm or more.
Sometimes, the gap between the foot of the flash and the screw for fixing it in the hot-shoe may be too narrow for the meter's probe to reach the metal of the edge connector. If the flash has a pc-socket, you can altermatively measure the trigger voltage from the pc-connector.
A typical pc-socket is shown to the right (real-life diameter is about 3.5 mm). You connect the negative probe (black on most meters) to the edge, and the positive (red on most meters) to the centre of the pc-connector.
Reverse polarity
In addition to the trigger voltage, the polarity of the flash is important. All modern cameras expects the centre pin of the flash to be positive and the edge connector to be negative.
If things are the other way around (reverse polarity), even a very low voltage may cause harm. If the unit has reverse polarity, you will see this by the voltage displayed as a negative number (a minus-sign is placed in front) on the display of a digital multimeter. Never use a flash with reverse polarity on a modern camera!
3. How much is too much?
A matter of much debate is the maximum trigger voltage that is safe for a flash that is to be used in the hot-shoe on a digital camera, wireless trigger, or other equipment you may want to connect a flash to.
Polarity is also important. The centre pin on the flash hot-foot should have a positive voltage. If it is negative, even low voltages may damage the camera.
Before connecting a third party flash unit to your camera or wireless trigger, you should always check the maximum safe trigger voltage in the manual for your particular camera.
Below is a summary of what I believe is the best information about this.
Canon
For connection through a pc-connector, Canon lists the maximum safe trigger voltage in the manual (e.g. 250 volts). However, this number does not apply to the hot-shoe. Canon does not officially give out information on the safe voltage for hot-shoe mounted flash units (beyond the obvious recommendation that you should only mount one of the Canon's own Speedlites in the hot-shoe).
However, an email from Chuck Westfall (Director, Media & Customer Relationship, Canon USA), posted in this thread in DPreview's Canon EOS 350D/300D forum in April 2005 by Doug Kerr had the following to say about trigger voltages:
The EOS Digital Rebel XT [350D] uses a modified version of the EOS 20D's shutter unit. Consequently, acceptable trigger circuit voltage for both cameras is the same, i.e., 250 volts. Except for the original Digital Rebel [300D], all current EOS digital SLRs (i.e., EOS-1Ds Mark II, EOS-1D Mark II, EOS 20D and EOS Digital Rebel XT) generate their X-sync signals electronically rather than mechanically. This is why they have higher acceptable trigger circuit voltage ratings than earlier models like the D30, D60, 10D and original Digital Rebel [300D]. These older models cannot be modified to achieve a higher trigger circuit voltage rating, since such a modification would require a different shutter mechanism as well as a complete redesign of the supporting circuitry.
I take this to mean that all Canons DSLRs newer than the 350D, as well as all the professional models, can use flash with trigger voltages up to 250 volts in their hot-shoe. However, 6 volts may be the safe limit for the D30, D60, 10D, 300D, and Canon's digital compact cameras.
Leica
In this this thread on RangeFinderForum, the following message from Stefan Staudt, Leica Camera AG is quoted:
The M9 is capable of triggering flash devices using high voltage. It is possible to use flash devices with a voltage up to 600 Volts. But it is important that the positive terminal is on the middle contact of the hot shoe and the ground terminal is on the mounting bar.
The Leica M8 and M8.2 is reported to have an identical flash triggering circuit to the M9.
Nikon
Most Nikon DSLR manuals warns against negative voltages or voltages higher than 250 volts. Here's a typical quote from the the manual for the Nikon D80 (p. 119):
Use only Nikon Speedlights. Negative voltages or voltages over 250 V applied to the accessory shoe could not only prevent normal operation, but may damage the sync circuitry of the camera or flash.
Olympus
The only verified offical notices about from Olympus I am aware of are the following note about in the EVOLT E-410 FAQ (Q #49):
Thyristor-type flash units can be used with the EVOLT E-410's Manual shooting mode as long as the sync voltage does not exceed 6 VDC. Third-party TTL flash units will not have TTL capability because the contact pins in the camera hot shoe probably won’t align with the contacts on the flash. In addition, the TTL communication with the EVOLT E-410 may damage the camera circuitry or corrupt the camera firmware.
And the following paragraph in the the Olympus Pen E-P3 manual (p. 60):
Using obsolete flash units that apply currents of more than about 24 V to the camera hot shoe X-contact will damage the camera.
However, user iROK reports in a forum message on FourThirdsPhoto.com that he has received the following information in an email from Olympus (Japan):
The E-system is designed to satisfy the ISO10330 (trigger voltage for X contact is 24V or lower). If the flash you use is manufactured under this standards, there will be no problem. The E-1 and E-300 are [designed to] withstand 500V or lower, but it is recommendable to keep 250V as a maximum level.
While I relay the above paragraph, I will add the following note: I personally do not think that 500 volts is safe with any modern camera. Flash trigger circuits are usually designed with a SCR thyristor to trigger the flash. This is an effective and low cost solution, and it will ensure a 400 volts safe trigger voltage (other electronic components may lower this). To go as high as 500 volts, a much more expensive circuit is necessary. Given that very few flashes (none of them current) have trigger voltages above 250 volts, using an expensive circuit to go to 500 volts in a modern design does not make sense.
Panasonic
On Flickr, user atmbirdie reports getting the folowing answer from Panasonic tech support:
The camera will not be damaged, even with flash units that had up to 90V on the contacts. Our spec is <= 15V.
While his question was specifically about the LX3, I believe that at least the 15 volt safe limit applies to all Panasonic digital cameras.
Pentax
Karl Schumacher sent me this message about Pentax DSLRs:
Pentax (Germany) has informed me that the maximum voltage for Pentax DSLRs *istD and *istDS is 30 volts and the maximum safe voltage for the K-series is 25 volts.
Sonia
The Sonia peanut slave trigger (can be used alone or attached to a Sonia slave attach hot shoe should not be used with flashes with a higher trigger voltage than 100 volt.
The Sonia slave with rotating hot-shoe is safe up to 400 volt.
Sony
For connection through a pc-connector, Sony lists the maximum safe trigger voltage in the manual (e.g. “Use a flash with a sync voltage of 400V or less.” Sony a700 manual, p. 77). However, this number does not apply to the hot-shoe. Sony does not officially give out information on the safe voltage for hot-shoe mounted flash units (beyond the obvious recommendation that you should only mount one of the Sony's own units in the hot-shoe).
However, user georgiaboy reports in a forum message on Dyxum.com that he has received the following information:
I spoke to a Sony tech support guy who said max voltage should not exceed 24 volts.
YongNuo
YongNuo RF-602 and RF-603 should not be connected to a flash with a trigger voltage above 12 volts.
IMPORTANT DISCLAIMER
The above information about safe trigger voltage limits is believed to be genuine and is reported here in good faith. However, I disclaim any responsibility for your camera if you hook it up with an oddball flash and it fries. If you choose to act on this information, you do so at your own risk.
The ISO 10330 (Photography - Synchronizers, ignition circuits and connectors for cameras and photoflash units - Electrical characteristics and test methods) recommendation says that cameras and flash units should be able to accept trigger voltages up to 24 volts. AFAIK all cameras and modern flashguns (from the 21st century) comply with this.
I've also noted that it as become more and more usual for DSLRs, including low-end models, to use a SCR (Silicon-Controlled Rectifier) thyristor to trigger a hot-shoe mounted flash. This type of electronic component is usually safe up to around 400 volts.
CAUTION: To avoid doing harm to the camera, you should always measure the trigger voltage before using an unknown flash on a DSLR camera to make sure it is within safe limits. Some flashes, and in particular “Made in Japan” vintage editions of the popular Vivitars, may have very high trigger voltages and can damage the camera.
As for technical protection measures, Wein sells a range of safe-sync devices (search eBay for safe-sync) to protect against excessive trigger voltages.
Please help us improve DPanswers
Once you've measured the voltage, be sure to report your results. I'll add them to out product database along with all other information you may have about the unit.
From: Brian G. — 2011-08-18 22:55
There has been an awful lot of hogwash regarding the 285 trigger voltage. I have an old one, not the 285HV.
I measured the trigger voltage on a Tectronix 100mhz storage scope, the voltage reading was 7.4 volts. There was talk that on recharge this could rise to over 14 volts, this was not the case. The risetime waveform was consistent with no additional spikes. It also seems strange that most triacs, scr's and other triggering devices usually have a high breakdown voltage (Nikon 250v) why would any camera manufacurer have a triggering device made that would flash over at anything above 6v. As far as I am aware Canon do not manufacture electronic components and the cost of having a specially manufactured trigger device doesn't make sense when there are off the shelf ready made devices. I do agree that a too higher trigger voltage can wreck the trigger circuitry on a camera but nothing above 6v is a bit silly. It could be a market ploy to get people to buy the latest generation of strobes. I have been using the 285 for a number of years, starting off on an F70 then to a D100, D200 and now the D700 with no problems. Unless it specifically states a given trigger voltage plus tolerances then most modern DSLR's should be happy up to but not maybe above the ISO 10330 regulation stated voltage. If your camera goes on the blink due to breakdown under this regulation then you should be entitled to have it repaired for free!
(I was an electronics design engineer up until my retirement)
From: admin — 2011-08-19 06:40
@Brian Gerrard,
I do not doubt that your Vivitar 285 has a trigger voltage of 7.4 volts. But this particular model was in production for almost 30 years. It was re-engineered several times during that period. As a result, some versions of the Vivitar 285 has a trigger voltage as low as 6 volts, other versions has a trigger voltage as high as 350 volts. This is why our data sheet for the Vivitar 285 lists its trigger voltage as beeing 6-350 volts. This data is based on us measuring the voltage of more than of a dozen of these devices of various vintages.
As for the 6 volts limit, I do not know what the safe limit is for various camera models and wireless trigger. I only report what is said about this topic from what I believe is reliable sources, including the FAQ posted on the official Olympus America website.