Measuring trigger voltage.

I know this is a hot topic for some, and I have a question about

measuring trigger voltage. I would like to use a Sunpak 344D flash

with a Nikon D50, but I'm having trouble getting a reading on trigger

voltage. I've tried two different multimeter/voltometers, but I can't

get a reading from them at all. I touch the two contact points, and

the flash pops, but there's no sign of any voltage. The first time, I

used a RadioShack battery tester set at 6 volts, and it didn't budge

the needle that went from "Replace" to "Good." The 2nd time, I used a

voltage tester that is used for car batteries. Again, touching the

contacts to the points on the flash popped the flash, but showed no

sign of voltage. I tried both directions (positive and negative

voltage directions), and I'm not sure what I'm doing wrong. Thanks.

 

Weldon.

Don't know about those newer multi pin models but on the older single pin in the middle model, you measure from the center pin to the outer part of the bracket(ground).

My guess is that the trigger happens too quickly for your multimeter to detect - you need an oscilloscope. Most volt/multimeters can only read "steady" voltages; a voltage that comes and goes in a flash (pun intended) is too fast to be detected by the multimeter.

 

Find a local electronics geek and ask him if he can measure it on a scope...

 

rgames

You need a high impedance voltmeter - 10 MOhms or higher. You can find instructions here by searching for "How to Check the Trigger Voltage"

 

http://www.botzilla.com/photo/g1strobe.html

Every PC terminal should have the center pole (which should be positive) and the outer pole (which should be negative). Any hotshoe should follow the ISO convention and map the positive terminal to the center contact and the negative terminal to the hotshoe outer rails (Minolta being a horrendous exception).

 

When the flash is recycled and ready to fire, there is a standing voltage at the positive terminal. The flash does not send a "trigger" signal to the camera--the flash puts a standing current in the trigger circuit and the camera closes the circuit, like a light switch simply closes a circuit which is already "live."

 

If the flash unit is a newer design (within the last 10 years) it should be less than 24 volts and should be measurable on a low-range DC voltmeter. The red lead goes to the center pole (of a PC terminal) or center contact (of a hot shoe), the black lead goes to the negative (outer) sleeve (of a PC terminal) or outer rail (of a hotshoe).

"The first time, I used a RadioShack battery tester set at 6 volts, and it didn't budge the needle that went from "Replace" to "Good." The 2nd time, I used a voltage tester that is used for car batteries"

 

"what I'm doing wrong" ? - you use wrong equipment that is not appropriate for what you are trying to measure.

 

In both cases you used wrong equipment. The battery testers have TOO LOW internal resistance to measure voltage of an electronic equipment.

 

Battery testers are not DC voltmeters. Battery testers draw too much current from your flash, and cause significant voltage drop during the measurement, that is detected as a trigger circuit short that fires the flash.

 

Basically, battery testers are not appropriate to measure voltage in electronic equipment, or the flash synchronization circuit voltage.

 

The car battery tester allows on purpose too much current flow from the battery to test the battery voltage at certain battery load, or at certain current flow. This provides a masure of battery strength more than the exact voltage.

 

The device you need is one that does not draw much current, or practically operates on the voltage levels, and not on the current flows.

 

What you should do: get a DC voltmeter that has at least 100 Kilo Ohms per Volt internal resistance, or get the a new type digital voltmeter that has about 1 Mega Ohms per Volt internal resistance.

 

Putting it differently: use a DC Voltmeter that was designed for electronic labs to measure voltages in electronic equipment.

Hi Weldon,<BR><BR> An O'scope is the way to properly measure the worst case voltage spike, the ringing of the waveform. In a lab one would use a storage O'scope and set the the trigger so one gets a waveform, the storage scope has a different type of phosphor that lasts for awhile. With a non storage scope one can use a polaroid scope camera to capture the spike; or turn up the scope abit and watch carefully to see it the peaks vary. In tests like this one wants to use a 10x probe, or better High Voltage 100 or 100x probe. One can blow the scopes front end too if you send too high a voltage to it.A more modern settup is to use a digital scope that captures the waveform in memory.<BR><BR>In measurements like this, the cord type and length, plus the load, the camera, will scatter the highest peaks one measures.<BR><BR> A few advanced new mulitmeters by fluke have features to detect voltage peaks, but these are not the common ones folks are use to using in everyday repair and service work.<BR><BR> In testing of 5KV Laser High Voltage power supplies,here I use a 1000X speicalized scope probe, so 5000 volts becomes 5 volts at the O'scope's BNC. With a laser supply, the capacitive loading of the HV probe is nill. With a dinky flash's trigger circuit, one needs to consider the loading effects of ones probes. With a "mulitmeter" type meter with a qlich capture feature, too narrow a pulse width will fake off the meter, and give low readings. Here one might get a false reading, and the true volatge spike might be 1000 volts. With an inductive trigger circuit, the snap can be many hundreds of volts to thousands of volts. This didnt matter much with a pure mechanical sync contact, but can compromise an electronic trigger of a modern camera.<BR><BR> With a grey area "it works" test, the repeated high voltage stress of each flash firing can break down a semiconductors junctions, such that a failure occurs soon, or abit later down the road. <BR><BR>Not to be too negative, the equipment you have capture the true peak voltage of the spike.

There are digital type "scope" affairs that cost about 150 bucks, heck even radio shack might have them now. The Velleman HPS10 what I got for the local high school. It has a 128 by 64 pixels display. <a href="http://www.electronickits.com/gold/HPS10.pdf"><b>The owners manual is here</b></a> One still needs to use a 10x probe to buffer the input.

Weldon stated that he only had a Radio Shack battery tester, and a tester for car battery.

 

So, I am a bit suprised with Kelly's statement: "the equipment you have capture the true peak voltage of the spike" ?

<i>Not to be too negative, the equipment you have <b>Cannot</b> capture the true peak voltage of the spike.</i><BR><BR>When I was in 5 grade; I was a marginal 3 grade in english, and at college level in math and science. I guess the engineering stuff crowds out the English!

An interesting experiment would be to see if a fast acting MOV, Zenar diode, or just dinky Neon bulb would clamp the spike, but still allow the camera-flash rig to fire.

You need an AVO (amps/volts/ohms) meter with a high input impedance which draws virtually no current (or at least only a fraction of a microampere). I tested my trigger voltage with one of these. Mind you, it's tricky getting the probe to touch the centre pin of the PC plug without shorting across and discharging the flash.

One can use a meter with a standard 10 megaohms and the meter still might not respond to a spike. By respond I mean faithfully measure its peak. Most common meters are not made to record a sub millisecond spike that goes to several hundred volts. IF a meter does respond, it still often measures just a fraction of the actual peak voltage. This is why folks blow up their cameras, they use the wrong tools, make the wrong assumptions, them cry when their device breaks. It like using a reflective meter in a coal mine or snow, and getting the wrong reading. A voltage spike needs to be recorded with a O'scope, so one isnt froging around guessing and doing a cheesy amateur have baked guess. Most common meters dont have a super high "crest factor" ; and also many dont respond to a sub millisecond spike faithfully. If this was a doctors office, it would be like going back to the stone age, trying to measure a spike with a dumb meter. Using the proper tools is what one should do to actually measure a voltage spike. O'scopes have been around for many decades.

In photo terms; using an O'scope versus a multimeter to measure a fast voltage spike would be like saying to use a incident lightmeter, versus a film box or extinction meter for a major motion picture shoot.

Frankly, the above posts on techniques for measuring higher voltage spikes are irrelevant given that IIRC the Nikon shoe limitation is 12V.

 

The Botzilla listing shows the 344D as 4V, so it should be fine:

 

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

Kelly - you're full of it regarding the oscilloscope requirement for this purpose. The voltage that is important to measure is a static DC voltage from the flash unit. There's no waveform to be concerned about.

 

Any halfway decent digital voltmeter will provide the necessary information.

 

If the flash in question is a hotshoe type of flash unit, measure from the center pin to the "common" terminals at the side of the hotshoe.

 

If the flash in question connects to the camera via a cable (typically with a PC plug on the end), merely measure across the two connector terminals - whatever the format of the plug.

Kelly, Skip,

 

I was puzzled with possibility of spikes when shutting down (closing) the flash sync circuit with a camera, or with a tip of a screwdriver.

 

When I was designing and prototyping photo flashes, many years ago, I noticed that clumping down (closing) the circuit with a screwdrive manually sometime caused a pretty long distance spark, that would indicate the voltage spike could have been much higher than the static electricity level on the sync trigger circuit.

 

I had more time on my hands so I did test is with a Hewlett-Packard storage scope.

 

When I connected a camera, and the scope, and triggerred the flash via camera action (non-digital camera), eliminataing possibility of adding static voltage from my hand, there was firm clumping down action and the short wave produced some decaying oscilations that never peaked above the voltage level. That was manual camera, do not remember the flash or it could have been my own prototype. Then I stopped worrying about it. Since there were no digital cameras to blow, my only concern was human reaction to possible too high (static like - minimal current harmless) voltage shock, e.g. like dropping the camera in panic.

Before you run out and get an oscilliscope, give this a try:

 

It could be that you are having a hard time NOT shorting out the connections when you try to take the measurement. It is really hard to hit that little pin in the middle of a PC cord, and sometimes all you have to do is come close and it will spark across (though that shouldn't happen with the low-voltage units).

 

What I use is an old PC extension cord that I have cut off and exposed the wires of. I use this as a continuity tester and to check trigger voltage. I hook up the male end to the flash cord, then touch the bare wires together to make sure the flash is firing. Then, if I need to check the voltage, I hook up the VOM probes to those wires.

 

I have never had a VOM trigger a flash. The internal resistance is usually too high for that to happen.

 

Happy shooting. -BC-

Skip; Heck you can be go out and use your simple tools and get the wonky pseudo low results and feel cool. If your camera then breaks then you are fool, for ignoring the spikes that happen with some flash trigger circuits. The lay public is always doing dumb pseudo engineering stuff like this, and then blaming device makers when their stuff breaks. This is why folks get hurt when their simpleton model doesnt match reality. Simplifying what is going on might be good for a grade school class, but hell has a place for folks who frost over safety issues, and folks lives get taken. Some electronic strobes have a 1000 + volt spike on the pc cord for a short dwell, that has little real energy, and thus doesnt hurt a robust 1950's flash sync. The same spike can with time compromise a semiconductor junction with repeated zaps. In a good way all this dumbness of the general public helps the sales pipeline, as goods get broken by invalid jackass simpleton assumptions.<BR><BR>Just because Strobe model #1 has no high voltage spike is no reason to assume that Strobe model #2 doesnt. Yes go ahead and ignore the proper tools, be a fool and feel good in your simpleton world. In a professional electrical engineering environment your comments would be regarded as lay, naive, reckless, amateur, dangerous. An O'scope will allow the full spike/pulse voltage to be measured. A simpleton meter will work with some flashes that have no spike and a steady state voltage, but be a jackass tool to use for a flash that has a nasty spike. Why fart around with a whusy amateur tool that may give a bogus result? Wrong assumptions just drive up warranty costs for all. <BR><BR>Long ago the 1950's giant strobes would often fry a weaker dumb flash contact, and some makers just like today had some taboo cameras to avoid, or where an extra buffer circuit was required.<BR><BR>Even if you measure the max voltage from your flash, their is no bet that the camera maker knows the voltage level well, or understands the repeated firing breakdown problem. Often spineless marketing chaps just ignore engineering data, and use bigger numbers to cook the books, ie make the data sheets look good.

In the 1960's some of us used 510 volt DC batteries with our Potatoe :) masher strobes. Some of these units had the 510 volts on the PC cord, but it appeared at a high impedance. Some of these units would fire sometimes when connected to a long trigger cord settup, due to static etc. The design of strobes sometimes then was to PURPOSELY has abit of current and voltage to the sync socket, so the mechanical contact was self cleaning. A super low current would not self clean the contact, unless it was a more expensive contact material. <BR><BR>In a concert settup with alot of cords, just moving the cords on the ground /floor can sometimes create voltage spikes on the cords which can cause a false trigger. In todays weak electronic trigger circuits of cameras, one can blow the trigger with just the cords,and NO strobe connected yet.

You can measure the voltage with a DVM, which typically has a 10MOhm input impedance. The static voltage is the highest voltage your shutter contacts will see. Once the contacts, mechanical or electronic, close, the voltage drops. I don't understand all this talk about ringing with regard to the trigger circuit - a lot of techno-babble IMO. Let's have just the facts, ma'am.

 

The flash circuits in a Nikon DSLRs require tip-positive voltage, and are rated to withstand +250 VDC. You must not use tip-negative sync. (q.v. http://support.nikontech.com/cgi-bin/nikonusa.cfg/php/enduser/std_adp.php?p_faqid=7349&p_created=1064859643&p_sid=nJmtPn6i&p_accessibility=0&p_lva=&p_sp=cF9zcmNoPTEmcF9zb3J0X2J5PSZwX2dyaWRzb3J0PSZwX3Jvd19jbnQ9MTImcF9wcm9kcz0wJnBfY2F0cz0wJnBfcHY9JnBfY3Y9JnBfc2VhcmNoX3R5cGU9YW5zd2Vycy5zZWFyY2hfbmwmcF9wYWdlPTEmcF9zZWFyY2hfdGV4dD12b2x0YWdl&p_li=&p_topview=1

The impedance of a DVM is so high, the the voltage is often exaggerated on open circuits. A more accurate test would be to load the circuit with a resistance equal to the open-contact impedance of the camera shoe, using a DVM test voltage of at least 1.7 VDC (to overcome any diode threshhold).

One has to consider the reason for making this measurement - it is simply to determine if the trigger voltage (from the flash) is below or above the stated maximum for a given camera's switching circuits. A typical modern DVM is the appropriate tool.

 

A camera owner attempting to make the decision about whether or not to use a particular flash or possibly to employ a device like a Wein SafeSync does not care about engineering-level detail. This is strictly a go/no-go type of measurement. If the voltage is even close to the limit for the camera, the choice should be no-go.

Not sure if many will read this as the post is pretty old, but I got my Sunpak 344D measured today. It measured a fairly constant +10.20V. Upon firing the flash, the voltage dropped to 0.00V, but climbed back up to the +10.20V mark within about 3 seconds. I got it measured at my university's physics department using a fairly expensive, professional looking voltmeter/multimeter. I asked about the oscilloscope, and the gentleman running the lab said that unless it was a fairly pricy, digital oscilloscope it would still have trouble reading a very quick voltage spike. He also stated that he thought that a flash running off 4 AA batteries would have very little possiblility of creating a huge voltage spike like the ones people are worried about. (aka 100+ volts). I have no idea about a studio strobe that runs off 120V wall mounts... So, for what it's worth, my Sunpak 344D has a trigger voltage roughly 2.5 times higher than the Botzilla website lists, but that said, it still should be pretty safe if Nikon DSLR's can take up to 250V. I'm going to contact them this afternoon just to get verbal confirmation of that fact. I know the website says it, but it would make my mind easier just to hear a Nikon rep say it's true also.

 

PS: For a quick reference, Nikon's newest SB-600 measured a pretty steady trigger voltage of +4.0V. So, my old flash is again 2.5 times that...

Sounds like you've taken the correct path, Weldon.

 

The only other consideration is whether there are extra pins on the flash that might contact pins on the camera when they shouldn't. The center pin on a hotshoe is the trigger switching contact. Any other pins surrounding the center pin are for communication between camera and flash. If you are using a non-Nikon flash on a Nikon and there are extra pins that touch between the flash and the camera, you may have a problem.

 

If the flash only has the center pin (and if the trigger voltage isn't a problem), then you can use the flash - with the camera in manual exposure mode.