Timing light voltage

[Walt Fricke]

Does anyone know what the voltage is that comes out of, so to speak, the inductive clamp used over a spark plug wire?

I need to know this so I can figure out how to reduce it to 3-5VDC for data recording. Yes, there might be other places to get such a signal, but this one is what I am going to use. I'm going to buy a cheap timing light just to get the inductive clamp and its wire, and go from there to make a circuit to drop the voltage and clean it up, if needed, into nice square waves.

I suspect it is kind of high, as the typical timing light uses this to make a xenon or other bulb strobe. But I don't know, and haven't been able to find a reference. I've got a scope, but it is old and large and is going to be hard to use on a running engine.

Walt

[HawgRyder]

A neon lamp needs at least 67.5 volts to fire.
I suspect that's the voltage of most of the inductive pickups...67 or more.
Bob

[Trackrash]

Why do you want to do this? To measure RPM? Seems like there would be an easier way. But I'm no expert.

Most timing lights use a 12v hookup. I'm guessing that it is used to amplify whatever signal comes from the pickup.

Since you have a scope why not use that to measure the voltage from a pickup.

Keep up informed of your project.

[wwest]

The timing light sensor clamp will produce just enough of a voltage pulse to trigger the electronics in the light, probably about the same voltage level you get from the magnetic PU in the distributor.

[Chuck.H]

Sounds like a good item to get at a flea market for $5 just to get the pickup. I suspect the pulse spike is quite high and noisy, and probably why the Innovative data logger has trouble reading it reliably.

Despite you saying you knew of alternatives, I'm going to give you one anyway :-) The 3.2 engines, if that's what you have Walt, have an extra, unused speed (or reference, I can't remember) sensor on the top of the motor, that comes out to a connector under the ICV.

Best,
Chuck.H
'89 TurboLookTarga, 369k miles

[Walt Fricke]

Well, I warned you.

I want to be able to get one or more (six would be better) ~5 volt pulses per two engine revolutions with no more effort than opening a lid and clamping onto something which is right there.

I am not interested in reading RPM as such, but with correlating engine revolutions with something else. In this case, rear wheel revolutions. That allows determining gear ratios.

In another life I do technical inspections on race cars which must have the right gears to meet the rules. Currently I do these measurements mechanically, manually turning over the engine one revolution and using a digital level on a rear wheel to determine how many degrees the wheel has turned, which I check against a table. Historically a degree wheel has been used on the tire, but same theory. Works quite well, but is a bit time consuming.

I want to automate this so I can check dozens of cars at an event rather than just a few at random. I can use optical sensing to see how often wheels turn with rear jacked up. Engine can idle, no need to try to crank manually (not easy on the new cars anyway - can't get at the crank pulley nut the way you can on a good old SC). Combining the wheel and crank counts will give the ratio.

Here is a schematic for a timing light. My electronics knowledge stops short of being able to tell what voltages are where in this circuit, but I see transformers in there stepping some current up I think. The 12VDC part ends up applying a voltage (stepped up, I suppose) to the ends of the tube, and whatever comes from the inductive clamp is then applied right outside the glass of the tube, and that is enough to cause it to flash.



67V is a starting point, though - more than I knew.

I recently bought a digital, dial back to zero, timing light, so I'm going to sacrifice the flashlight battery powered, perfectly fine regular timing light I have been using so I can use its inductive clamp. Cheaper than purchasing a replacement clamp from the usual sources.

[KTL]

Hey Walt, I recently bought an Equus timing light to replace the one I toasted. The Equus lights come with a removable/plug-in harness for the 12 V leads and the inductive clamp. Point being is since I toasted one light, I now have two harnesses. You are welcome to have the spare at no cost. Merry Christmas to you for all your support/participation here over the years.