HOW TO BUILD A D.V.A. (DIRECT VOLTAGE ADAPTER)

[JUSTINTIME]

u need this for checking ALL! ignition voltage, like coil input, triggers, pulsers,exciters, etc

 

[50alive]

Re: HOW TO BUILD A D.V.A. (DIRECT VOLTAGE ADAPTER)

i have followed this board the a few years now and it is good entertainment.
this is the first time i have relied

From what I see you are trying to measure the peak voltage on short duration spike

we always called it a pulse stretcher
But their are a few problems with your circuit

1.as soon as the input voltage goes away the cap will start to discharge so the actual voltage measured will always be less then the peak. the rate of decay would depend on the RC time constant and the loading effect of you meter

2.the instantaneous charge current in a cap is limited only by the circuit impedance and then decrease as the charge builds up.
This can cause several problems, if the driver is an electronic circuit with a transistor output it could destroy the circuit. An instantaneous over current on the transistor. It could also destroy the input diode. If the input impedance is very low the inrush current to the cap could cause it explode. i have seen this happen a few times. not something you want to be holding in your hand when it happens



A better way to check for an ignition pulse or any pulse would be an old style analog meter you will see the needle jump up for every pulse the hight it jumps the biger the pulse and not danger of damaging the driver. or the best option would be an O scope then you will be able to see the pulse with out loading the circuit this would also give you the ability to measure the pulse to be sure it meets spec.

 

[j_martin]

Re: HOW TO BUILD A D.V.A. (DIRECT VOLTAGE ADAPTER)

Not everybody that wants to troubleshoot an outboard carries around an O-scope. I do, but I'm wierd.

I have heard that a DVA is a peak reading adapter. The diagram above will work for that. Any filtering circuit, which is what this is, has a leak down characteristic like 50alive says. What he doesn't say is that the rc time constant would be long, and the loading effect of the meter (unless it's really cheap junk) would be minimal.

I think I would add about a 100 ohm resistor in series with the input, to limit inrush, but that is also limited by the characteristics of the diode.

hope it helps.
John

 

[JUSTINTIME]

Re: HOW TO BUILD A D.V.A. (DIRECT VOLTAGE ADAPTER)

it works fine, most of the guys use it at school
i use an analog meter because u get a better reading
the digital meters jump around too much

 

[Texasmark]

Re: HOW TO BUILD A D.V.A. (DIRECT VOLTAGE ADAPTER)

In my ex line of work, interference was always a problem and we too had the old Simpsons. But as time progressed, the folks at the calibration shop quit calibrating them over and above our protests. Did miss them.

I also vaguely remember a peak reading detector meter we had that would tell you, without seeing it on a scope, the peak value of a short pulse, repetetive signal. Had to give it time to pulse up.

Agree with all of 50's comments. Lots of electronic circuits are injured by just such spikes caused by normal inrush (in poorly designed circuits) and by unsuspecting ESD. That's why proper ESD procedures are so important, especially in today's microcircuit world.

Some co-worked laughed at using ESD procedures till they went to ESD prevention class and saw just what happens and how minute it seems at first.

Mark

 

[Paul Moir]

Re: HOW TO BUILD A D.V.A. (DIRECT VOLTAGE ADAPTER)

But for the vast majority of testing on an outboard, the circuit will work just fine. Specifically for determining if stators and triggers are operating within their performance parameters. These rarely fail with intermittents, instead shorted or open coils push the running peak output voltage outside the operational parameters.

Some triggers operate at very low voltages (~1v), and for those the circuit will not suit due to the diode drop. It's important to understand the limitations on it. But it is nevertheless a helpful and useful diagram, and I for one would like to thank JUSTINTIME for providing it.

The alternative (as far as I see) is to construct a full out peak detector, which is an entirely more complicated circuit since it needs range switches and protection in addition to the peak detector amplifiers.

 

[bonitasprings]

Re: HOW TO BUILD A D.V.A. (DIRECT VOLTAGE ADAPTER)

I would very much like to make one of these and need it now but it appears the instructions have been moved or deleted. Can someone direct me as to where it might be?

thanks

 

[Barnacle_Bill]

Re: HOW TO BUILD A D.V.A. (DIRECT VOLTAGE ADAPTER)

Here you go