How to measure trigger voltage of a flash unit

I am aware that older flash guns can damage your camera electronics as they have

higher trigger voltage. My question is how do you measure this voltage. I have

some older manual flash units that I would like to try for fun but not if there

is a risk of killing my camera.

 

Any suggestions?

Just use a DC Voltmeter, set it to the 200V range. (The meter should have at least 10KOhm/V in that range, so that the load to the flash is small).

 

Charge the flash, and measure the voltage between the two contacts

at the flashshoe. If this voltage is below 20V (repeat measure in 50V range setting of the meter), the flash is save, if it exceeds 20V it is potentially dangerous.

 

That said, I use an old Metz 30BCT flash with my 300D. This flash has over 150V at the flashshoe (measured as described above).

So far, it has caused no damage.

 

Some older Metz 45 units are said to have up to 400V at the shoe.

 

Rainer

Thank you Rainer - I shall play sparky and see what happens.

I've also used the table at this site in the past to get an idea of the strobe's design voltage before further testing - http://www.botzilla.com/photo/strobeVolts.html.

Some units will measure low or zero with a simple dumb slow responding VOM. But when the flash fires there is a big kick of many hundreds of volts, sometimes a thousand plus. <BR><BR>In proper Electrical work folks usually use a capture device that will grab/record the voltage waveform/pulse; and not load the circuit.<BR><BR> A lessor device can often give a low reading; ie false security. <BR><BR>Imagine old Jethro checking you parachute, ammo, and hand granades before you jump into enemy lines with jackleg testing. :)<BR><BR> With a high impedance VOM one can measure DC voltages and not load most circuits down. The pickle is whether your flash has a trigger circuit that sends/kicks back a high voltage pulse that your VOM wont measure. Then you get a dead 300D.<BR><BR> Most camera repairs in the flash PC socket/hotshoe area are due to folks blasting out the ciruit with older strobes.<BR><BR> Imagine going outside and trying to measure lightning with a VOM! :)<BR><BR> With a storage O-scope I have seen voltages that spike over a thousand volts; such that a 100X high voltage divider probe was required. I have seen folks ruin a O-scopes channel with tests using just a 10X probe. <BR><BR>All it takes is one quick spike and alot of semiconductor junctions get ruined. Thus playing "sparky and see what happens" is a good way to learn electrical stuff if one learns from ones mistakes. The question is what the mistake costs.

If somebody recommends a VOM and it "works" with chap #1; then chap #2 might have its work too. Then Chap 3# tries and his camera gets fried and things get evil; as jackleg test fails.

If you have one near you, take the flash to a Radio Shack. They'll test it for you.

What camera? All of the recent Canon bodies are rated for 250V sync and pretty universally

safe. Conversely, if you've got one of the older 6v sync bodies (300d, 10d, d60, d30) very,

very few old flashes are acceptable. (Sorry, no clue about Nikon sync specs).

 

Even the 6v-sync Canons will generally survive a low-current high-voltage sync--these

cameras are all mechanical sync, not electronic. It's just that the sync switch is small and

delicate, high voltages at high currents will pit the switch into uselessness or even weld it

together. Getting away with it once is not a guarantee that you're safe. They also very

likely have no protection on the TTL circuits. Again, mostly you're not going to have the

high-voltage sync in contact with the TTL circuits, so you can get away with it for a while.

But twist a charged flash wrong taking it out of the shoe and you have a problem.

 

I'd love to know what flashes Kelly says are kicking back 1,000 volts at the sync circuit

when fired. Since the voltage at the sync terminal in a high-voltage sync circuit is merely

from a small capacitor waiting to be dumped into a step-up coil, I don't see how the spike

upon firng is generated. Maybe some sort of extremely low current bleed-through from

circuit board traces too close together? In any event this spike is very unlikely to cause

trouble in a mechanical sync camera--high voltage sync is only dangerous to a

mechanical switch by causing arcing at the moment of opening or closing. A transient

spike would have to be very precisely timed to cause a problem.

 

Anyway, I've certainly used 200v Vivitar 283s on a Sony DSC-770, an Oly E-10 and a

Canon 1dsII with no ill effects.

 

Kelly's remark about "Most camera repairs in the flash PC socket/hotshoe area are due to

folks blasting out the ciruit with older strobes." makes it sound like this kind of damage is

common. Funny how you NEVER see an "it happened to me" report amongst all the vocal

forum folks. In fact, the only reports I've ever heard of someone frying a camera with a

high sync voltage were from the first generation of consumer Nikons with TTL flash

metering. The sync circuit was safe, but the TTL circuits weren't. Twist a charged flash

wrong taking it off and poof!

I use a cheap analog multi-meter to measure a number of manual flashs before I use them on my 5D. you can do that by measuring it between the pc terminal conector or the hot shot center contact to ground (at the side of the shoe or pc plug). If it is less then 100V, I use them. My assumpion is that (I hope) the switching overshoot/undershoot voltage (as post above) under load won't have enough energy to trigger transitors latch up (aka: chip in camera fried). Most ICs have input protection diode that has 250V spec, more under real world condition (quantum physic?). Knock on wood, so far I never had any issues.

 

My 2 cents: Like UV filter, if it brother you, get a hot shoe safe sync adapter and save some sleep.

<p>I ran a few tests on various speedlite I have and the results are shown below. I did these tests because I was interested in what current range the PC sync connector had to handle. You can see the current ranged from 0.18mA to 11mA for the flashes that I tested. From ohms law I = V/R<br>

Flash sync PC port open circuit voltage & current sink tests for various speedlites Rodney M Letts Oct 2015<br>

Voltage was measured with a precision 5 ½ Digital Multimeter (HP 3478A)<br>

Resistance substitution using a 1% precision Decade Box (RS Components Ltd type RM6)<br>

Make Model O/C Voltage Maximum resistance that<br>

still triggered flash <br>

Canon 533G 4.60v 880 ohms <br>

*Canon ML-1 Macro 6.03v 540 ohms<br>

Yongnuo 560II 4.30v 6600 ohms<br>

Yongnuo YN-14EX Macro 2.56v 14200 ohms<br>

*Amarand AHL-C60 LED Aputure macro light 3.312v 1410 ohms<br>

* As the Canon ML-1 macro speedlight and the Amarand Aputure AHL-60C don’t not have PC sync connectors, they each had a HD-N3 hotshoe adapter (Ebay) fitted as this hotshoe adapter has a PC sync connector. The HD-N3 is a hotshoe adapter for the Sony NEX7 camera and converts the non-standard Sony hot shoe to a generic hotshoe, as the adapter is passive it was not necessary to have it connected to the camera for the tests. I would guess that a 20% range variation may occur for the same units other than mine and would be wary about using the Canon ML-1 macro flash light on Sony Camera even with the adapter. The only info I have that Sony cameras don't like sync voltages greater than 5 volts. As the ML-1 is slit quite low and does not have a high voltage trigger requirement I would still be careful. <br>

rodletts@gmail.com</p>

<p>I ran a few tests on various speedlite I have and the results are shown below. I did these tests because I was interested in what current range the PC sync connector had to handle. You can see the current ranged from 0.18mA to 11mA for the flashes that I tested. From ohms law I = V/R<br>

Flash sync PC port open circuit voltage & current sink tests for various speedlites Rodney M Letts Oct 2015<br>

Voltage was measured with a precision 5 ½ Digital Multimeter (HP 3478A)<br>

Resistance substitution using a 1% precision Decade Box (RS Components Ltd type RM6)<br>

Make Model O/C Voltage Maximum resistance that<br>

still triggered flash <br>

Canon 533G 4.60v 880 ohms <br>

*Canon ML-1 Macro 6.03v 540 ohms<br>

Yongnuo 560II 4.30v 6600 ohms<br>

Yongnuo YN-14EX Macro 2.56v 14200 ohms<br>

*Amarand AHL-C60 LED Aputure macro light 3.312v 1410 ohms<br>

* As the Canon ML-1 macro speedlight and the Amarand Aputure AHL-60C don’t not have PC sync connectors, they each had a HD-N3 hotshoe adapter (Ebay) fitted as this hotshoe adapter has a PC sync connector. The HD-N3 is a hotshoe adapter for the Sony NEX7 camera and converts the non-standard Sony hot shoe to a generic hotshoe, as the adapter is passive it was not necessary to have it connected to the camera for the tests. I would guess that a 20% range variation may occur for the same units other than mine and would be wary about using the Canon ML-1 macro flash light on Sony Camera even with the adapter. The only info I have that Sony cameras don't like sync voltages greater than 5 volts. As the ML-1 is slit quite low and does not have a high voltage trigger requirement I would still be careful. <br>

rodletts@gmail.com</p>