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Checking trigger voltage

Here's how you find out whether your old flash is safe
by Gisle Hannemyr
Published: 2011-03-31.

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.

Hot-foot.
Trigger voltage is measured between centre pin and edge contact on the flash's hot-foot.

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 DC range. To find the right range, start with the highest DC range and go downwards until the meter indicates you are out of range. Then back up one step. This is the most sensitive range. You should now be able to read the flash's trigger 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 contact 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 of the mounting bar on the edge of the camera's hot-shoe. You always connect the negative probe (black on most meters) to the edge contact, and then connect the positive probe (red on most meters) to the centre pin.

Measuring.
Measuring voltage with a digital multimeter. Black probe on edge contact, red probe on 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.

pc.
Alternatively, you can measure the voltage between the centre (+) and edge (-) of the pc-socket.

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 contact. If the flash has a pc-socket, you can altermatively measure the trigger voltage from the pc-socket.

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-socket.

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 contact 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 list of what I believe is the best information about this, however, make sure you read the disclaimer before acting in this information.

Cameras

Canon

For connection through a pc-socket, 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.

In a 2007 interview with The Digital Journalist, Westfall confirms the above and adds some older film SLRs to the list.

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 is the safe limit for the D30, D60, 10D, 300D, and Canon's digital compact cameras.

Leica

In 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.

Caveat: While I relay the above paragraph, I will add the following note: I personally do not think that 600 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 600 volts, a much more expensive circuit is necessary. Given the cost of Leicas, it may of course use a more expensive circuit, but given that very few flashes (none of them current) have trigger voltages above 250 volts, using an expensive circuit to go to 600 volts in a modern design does not make economic sense.

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.

As for 500 volts being safe, see my caveat under the Leica entry.

Panasonic

On Flickr, user atmbirdie reports getting the following 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 volts 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.

Sony

For connection through a pc-socket, 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.

Flash triggers

Cactus

For Cactus brand radio triggers, the maximum trigger voltage is listed in the manual.

For Cactus V4 and V5, the maximum safe voltage is listed as 300 volts.

Pixel

Pixel does not list trigger voltage as part of its specifications, but Pixel King vendor DSLRkit.com lists 36 volts as maximum trigger voltage under the heading “Additional information”.

Pocket Wizard

Pocket Wizard lists maximum voltage in the owner's manual.

For the dedicated hot-shoe (e.g. the MiniTT1, FlexTT5), voltages should be less than 50 volts. For the 3.5 mm jack flash interface, the MiniTT1, FlexTT5 and Plus II models are listed as being able to handle up to 200 volts. The Plus III is listed as being able to handle up to 300 volts.

Seagull

According to vendor CowboyStudio, the Seagull SYK range of optical triggers is only guaranteed to work with flashes with a trigger voltage less than 12 volts.

Rebranded version of these triggers are sold as Hama 6967 and Kaiser K1501.

Sonia

The following information is from UK-based vendor Colinsfoto:

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.

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.

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20 responses:

avatar
Vivitar 285 Flash unit.

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)

avatar

@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.

avatar
Pinout?

What about other contacts on the hot shoe?

Canon and Nikon have different pinout for transferring digital data and other stuff, should we worry about that? Some say to isolate those pins. Any photo of that?

avatar
Nikon D3000 and high trigger voltage

I use Nikon SB-16 with 4.7 volts and National PE-201M with 147 volts. I've been using these for more than a year with my Nikon D3000 without any problems.

avatar
Fujifilm Flashgun EF-20 to work on Nikon D3200

I have a Fujifilm EF-20 Flashgun which I use on my X10 camera.

I have new Nikon D3200 DSLR camera and was wondering if this will work on the Nikon?

Can anyone tell if it will work without damaging the D3200! Or is there an adaptor I could buy! If you could email me back asap.

avatar

@steve b.,
the Fujifilm EF-20 is dedicated for TTL exposure control with selected Fujifilm cameras. There are no manual controls, so if it works on the Nikon D3200 at all, it will be as a manual flash firing at full power (GN 20, meters @ ISO 100).

However, it is has a low trigger voltage and will not damage the Nikon D3200 – so you can test it if you want to.

There is no adaptor to make Fujifilm TTL work on Nikon (or anything else non-Fujifilm).

avatar
Used wrong polarity on Nikon D5100! Could it be harmed?

I happened to use my Metz 36 AF-5 (one time on my D5100) while the batteries were unintentionnally mounted the wrong way around. The flash didn't work then, but from that moment the flash doesn't function properly anymore on my Nikon D5100 and my Nikon D50. I have to adjust the aperture every time I have to focus to a different distance. It seems it only acts like a manual flash.

Now I have measured the voltage and it shows 4.21 V. I also measured the voltage again with the batteries mounted in the wrong way. It show 0.0 V (zero, so NO negative/minus [-] value!).

I guess I wrecked my flash but my greatest concern is, could it have damaged my camera? In what way? And how can I check that?

The camera still functions as intended, also with the built in flash.

Apreciate your comment, Hans

avatar
Wrong polarity on batteries in flash

@Hans N.
I do not think inserting the batteries the wrong way in the flash and connecting to the camera should damage the camera electronics. The batteries are used to power the electronics of the flash. The voltage from batteries is not applied directly to the hot-shoe. So your camera should never “see” the reverse voltage.

To test that your camera is still OK, borrow a good, dedicated flash for Nikon i-TTL, and just test that everything (TTL control, power zoom, etc.) works OK.

However, putting the batteries in the wrong way may damage the circuits in the flash itself.

avatar
Image MBZ 1500

This flash isn't listed in the "product database" link. Also, I don't have a digital meter to measure the voltage.

Clues:

  • it is a generic flash;
  • the hot shoe has three pins;
  • it has 90 degrees tilt, no swivel;
  • there's an LCD indicator;
  • there's a ready indicator unit light;

I intend to use this flash on film cameras (Pentax K1000, Canon AT-1, Konicas).

Thanks for reading my message.

avatar
Cactus V4 & 5 Metz 60CT1/2

Excellent thread with nice information. I have above two flashes which now using with CTR 301 P with Wein safe sync. As mentioned above Cactus V4/5 is safe up to 300V. Will my above combination work fine without any damage to the camera. Metz have 20 to 30V sync. Thanks.

avatar
Image MBZ 1500

Hi again,

I went to a photo store to get the measurement of flash Image MBZ 1500. I was given a number, which is 1,95.

What does it mean??

And again, who could give me info about this flash?

avatar
Contax TLA140

The Contax TLA140 has two pins on either side – no central pin on the hot foot. How do I go about measuring its voltage and whether it's safe as regards positive/negative voltage? I want to mount it on a Ricoh grd iii and the manufacturer suggests the following:

"Use only flash units with one signal terminal, which must be an X-contact with a positive voltage of no more than 20 V."

I know from Contax that the flash is an x-contact but don't know if it's one signal terminal or if it is positive voltage.

Please help me to measure properly the voltage of this unit so as to not fry my camera.

avatar
Contax TLA140

@Chris,
the Contax TLA140 has a centre pin, see diagram below:

Contax TLA140
Measure the voltage between the centre pin and edge contact.

I expect the voltage to be well below 20 volts and the centre pin positive. When you measure it, please report it here, so I can add it to the voltage database.

The second pin on the hot-foot is a TTL pin for the Contax G-series OTF TTL system. On a non G-series camera, the Contax TLA140 will only be a manual flash.

avatar
Contax Tla 140

Measurements made as instructed above with a helix dt-830b are as follows: When switched off it read 2.51 stable. Switched on at 4.72. When fired it dropped and then back to 4,72.

Mounted on a Ricoh gr d iii (directly on hot shoe), it is apparently working at full power on manual. Quite strong but a solution when wg 2 is attached (Tla 140 stands high hence no shadow cast).

Thanks for helping me. Spread the word.

avatar
Don't trust single trigger voltage measurements

Trigger voltages cannot be measured with a single instrument like a multi-meter or even an oscilloscope. Becuase they consist of a capacitor of unknown source impedance discharging into an unknown load, all single measurements will be inaccurate, sometimes over 100% out.

To accurately determine the open circuit voltage of a flash, you need to make at least two measurements with known load impedances and use simultaneous equations and Kirchof's Law to determine the open circuit voltage.

This is partially explained at the electronics magazine Silicon Chip: A Safe Flash Trigger For Your Digital SLR Camera. However, you need to pay for the full article.

avatar
Vivitar 16M flash unit and Nikon D3200

Hi gentlemen,

Is there anybody who knows if it is OK to use the VIVITAR 16M flash on the Nikon D3200? I measured the trigger voltage using a multimeter and it registers over 60V but not above 70V. Would appreciate it very much for the info.

avatar
Vashika TF-103

Vashika TF-103 old flash

measured 249volts

(5 measurements using extech ex330 meter)

avatar

@shockey,
what would you expect someone trying to sell a product to say?

avatar
Some measured flashes

FLASH TRIGGER VOLTAGES [18OCT13]

Measured with a Fluke 8060A DVM, Cal Date 07MAR13

5 flashes each with fresh internal batteries where applicable and with external battery packs where applicable, then averaged

Flash Unit Average Trigger Voltage [VDC]

Yongnou YN565 EX TTL Speedlite 4.9

Yongnou YN560-III Manual Speedlite 4.9

Polaroid PL144AZ-C TTL Flash 5.2

Trigger Voltage [VDC]: 5.7

Vivitar 285HV Flash 8.1

Metz 32CT3 Flash 16.4

Norman P500M Power Pack 28.1

Vivitar 2800 Flash 146.9

Vivitar 283 Flash 250.2

Vivitar 283 Flash 249.9

avatar
Metz 36 AF-5 for Pentax on Sigma dp2M

I wanted to use a more powerful flash on the Sigma dp2M and I purchased used Metz 36 AF-5.

The flash didn't fire properly, the camera didn't recognise there is a flash on the hot shoe, but when I press the trigger - flash was firing very low, like pre flash. Later I open the flash and removed all the pins except the central pin. Now the flash works at full power in manual mode. I was thinking if there is a way to put back some of the pins to make it work in TTL mode.

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