Looking for a DVA Genius

[ckraker]

I've been trying to build my own DVA for a Digital Multimeter, I've seen the post on this forum, and was pretty sure I had it figured out. Well I tried to test it out by tapping the leads on a 9 volt battery to see if I could get a solid 9 Volt reading. Is this a good way to test it? I can't seem to get it to work. I'm pretty sure I have the correct resistor and Diode, but my Capacitor is a 2200 +- 5%, and I'm not sure what that means. Any Help would be appreciated.

Also--- I realize they are only 35 bucks but I'm stubborn and want to figure this out.

 

[bktheking]

Re: Looking for a DVA Genius

I've been trying to build my own DVA for a Digital Multimeter, I've seen the post on this forum, and was pretty sure I had it figured out. Well I tried to test it out by tapping the leads on a 9 volt battery to see if I could get a solid 9 Volt reading. Is this a good way to test it? I can't seem to get it to work. I'm pretty sure I have the correct resistor and Diode, but my Capacitor is a 2200 +- 5%, and I'm not sure what that means. Any Help would be appreciated.

Also--- I realize they are only 35 bucks but I'm stubborn and want to figure this out.

Read the thread again, I've since updated it. The CAP is supposed to be 2.2 micro farad @ 450 V, it was my bad and I apologize if it's screwed up because of this. I posted a new pic of how it's supposed to look, I just got back in from the garage from swapping the diode around, I tested mine on a car battery and it worked.

http://forums.iboats.com/showthread.php?t=371144

The first pic is the new one, my thought is if it weren't wired right in the pic that I posted it wouldn't work but it does.

 

[F_R]

Re: Looking for a DVA Genius

I've been trying to build my own DVA for a Digital Multimeter, I've seen the post on this forum, and was pretty sure I had it figured out. Well I tried to test it out by tapping the leads on a 9 volt battery to see if I could get a solid 9 Volt reading. Is this a good way to test it? I can't seem to get it to work. I'm pretty sure I have the correct resistor and Diode, but my Capacitor is a 2200 +- 5%, and I'm not sure what that means. Any Help would be appreciated.

Also--- I realize they are only 35 bucks but I'm stubborn and want to figure this out.

Your capacitor is way off. 2200 indicates it is 2200 picofarads. That is the same as saying .002200 microfarads. You are looking for 2.2 microfarads. A picofarad is one millionth of a microfarad.

 

[ckraker]

Re: Looking for a DVA Genius

Wow- I'm not a circuit kind of guy so I gave the list to someone that I thought was, guess he wasn't. See Pic.
Where can I get a cap. Radio Shack?

Do the Diode and resistor look okay?

 

[bktheking]

Re: Looking for a DVA Genius

Wow- I'm not a circuit kind of guy so I gave the list to someone that I thought was, guess he wasn't. See Pic.
Where can I get a cap. Radio Shack?

Do the Diode and resistor look okay?

Have a look at the thread I posted, the proper cap is listed (pic) as well as the wiring of the circuit, your diode looks reversed as was mine in the original pic, it's now flipped around, that's if i'm looking at your pic properly. As far as radio shack, maybe, here is Canada it's now the Source and 3/4 of their electronics parts aren't there anymore. If you can't find one I can mail you one, I bought 2 extra.

 

[ckraker]

Re: Looking for a DVA Genius

I already flipped the Diode--- I promise it looked a lot better the first time I made it. Sort of emberassing looking now

 

[bktheking]

Re: Looking for a DVA Genius

I already flipped the Diode--- I promise it looked a lot better the first time I made it. Sort of emberassing looking now

It's awesome! Who cares, I made mine with a dremel tool, soldering iron and the same colour wire and if you notice the banana clips are held on with electrical tape, I plan on crazy gluing it on.

 

[F_R]

Re: Looking for a DVA Genius

Hello again, I came back to say that I may have jumped to conclusions. You might actually have a 2200 microfarad capacitor, not picofarad. My electronic training dates back to the stone age and 2200 mfd is a mighty big capacitor to my brain's way of thinking. Nevertheless, it still is way off from what you want. 1000 times too much capacity in fact. Note that when I refer to "big", I am speaking in terms of capacitance, not necessarily physical size.

I just now went to the Radio Shack website and did a search for capacitor and did not find a suitable one. But the dummies did show me all their resistors. (?!!!)

 

[bruceb58]

Re: Looking for a DVA Genius

That is a 2200 pF cap.

Look for electrolytic caps. Also note that these are polarized so you need to know which side the positive side is.

That resistor in the picture above is a 2.0 Meg Ohm if the color bands are red black green like I think they look like they are.

Color code is

0=black
1=brown
2=red
3=orange
4=yellow
5=green
6=blue
7=violet
8=grey
9=white

for a red black green you get 20 x 10^5 = 2.0 x 10^6 = 2 meg ohm

I am curious, what voltages are you trying to read. I am not familiar with an outboard ignition. If I knew what you are tryimg to measure including the voltage and the duty cycle. I could probably help you with what size components are actually critical.

 

[F_R]

Re: Looking for a DVA Genius

That is a 2200 pF cap.

I am curious, what voltages are you trying to read. I am not familiar with an outboard ignition. If I knew what you are tryimg to measure including the voltage and the duty cycle. I could probably help you with what size components are actually critical.

The charge coils produce up to around 400VAC which is rectified and stored in a capacitor in the power pack.

The trigger coils produce up to around a couple of VAC

The power pack output is a series of DC discharges from the power pack's storage capacitor, fed to the ignition coil's primary winding.

It can also be used to check the AC output from the alternator's windings. If working properly that is around 12-18 VAC. If open circuit, can go way up over 100VAC

All AC frequencies (Hertz as politically correct called these days) depend among other things on the RPM of the motor, which can be anything from cranking speed to several thousand RPM. Multiply by the number of poles and number of cylinders, etc. Same thing for the capacitor discharges from the power pack

Hope I got it right.

 

[Vic.S]

Re: Looking for a DVA Genius

Hello again, I came back to say that I may have jumped to conclusions. You might actually have a 2200 microfarad capacitor, not picofarad.

No you were right first time . That is definitely 2200 pf.

a 2200mfd one would be huge!

 

[daselbee]

Re: Looking for a DVA Genius

I don't know why you guys are bothering to test on DC battery sources.
That is an invalid test.
The circuit will always read 0.7V less than the DC voltage source.
12V DC battery will read 11.3V.

This is a device for measuring the DC peak voltage value of an AC input signal, and you can only "test" it that way.


And, correct, a 2200 uF, 400VDC cap is about the size of a large coffee can, IF the cap even exists.....it'll be huge....

 

[bktheking]

Re: Looking for a DVA Genius

So what household item can be tested if "any", or something else that doesn't require being placed in a barrel of water at -30C

 

[daselbee]

Re: Looking for a DVA Genius

Stick to boat motor advice...you do that well.

Stay away from electronics....not too good there.

As we have seen...that "missed decimal point" actually does make a difference. Just as using VALID testing methods for circuits does.

Just my .02.

(Decimal point in the correct place...)

 

[bktheking]

Re: Looking for a DVA Genius

...

 

[daselbee]

Re: Looking for a DVA Genius

A better test would be to measure house voltage.
Just plug it into the wall socket. Convenient AC source signal.

That is a better test, but still not truly valid. Differences when using it on an engine will occur due to the fact that the house voltage is at 60HZ, but the engine is producing pulses, spikes, of very high rise and fall times, not a sine wave as is the case with house voltage. Well, let me clarify...the stator is outputting some kind of AC waveform that probably closely resembles the house current...but the PP is outputting to the coils high voltage pulses that have very fast rise and fall times. Probably does not resemble a sine wave at all. And, the frequency is constantly changing with engine RPM.

A GREAT test would be to put an oscilloscope on the input signal, read the peak DC voltage exactly, then measure with our homemade device and compare the 'scope with the device. That is the cadillac of the test to determine if it "works" or not. I really wish I had a scope so I could post real actual values here....

Not practical (for almost all of us) to use a scope....but if you use house voltage at least you are testing AC, verifying that the diode is actually rectifying, etc.

You know, this whole thing is kinda like when some ppl test batteries. They throw a voltmeter across the terminals, measure 12 volts, and think the batt is good. Maybe so, maybe not. A VALID battery test must include loading the battery to be absolutely sure.

My background? 20 years as a test engineer with IBM.
(I sure hope the above info is accurate...):redface:

 

[bktheking]

Re: Looking for a DVA Genius

Huh, International Business Machine's , very cool. The first server's I started working on were IBM's. I almost had a scope, went to a friends house and he had one sitting in his closet. When I asked him what he was doing with it he said nothing, it just sits and collects dust. He is coming down for a visit in the spring, maybe I can get him to bring it then I can do a comparison. He told me I could have it and the next day when I went to leave he changed his mind. And yes in order to check a battery you need a load tester and to input the CCA into the tester to test accurately. Batteries swell, then plates short out and then no more battery, they show 12 but don't have the amp output to turn a starter.

 

[daselbee]

Re: Looking for a DVA Genius

Yes exactly. Testing validity has been beat into my head for the past 20 yrs.
Get that scope...would really be interested in knowing what the waveforms look like. One guy posted some pics of the output of a 4000 dollar Fluke meter that had a LCD display showing the exact waveforms. I think that was over on marineengine.com, and it was a while back...

I also posted here once that the measurements will vary. My rig (when I get it built) will almost assuredly read differently than yours, because of the differences in meters. Analog, good digital, cheap digital, we all have different test equip. I will exclusively use an analog meter for these measurements. That's why I suggest taking some readings from your motor when it is running right. Get those "stake in the ground reference" readings so you can compare in the future.

Hey, also, it really is very impractical to try to calculate mathematically what voltages you should be reading, because we don't know the waveform....
Math calcs are generally for sine wave signals.

 

[JustJason]

Re: Looking for a DVA Genius

I am curious, what voltages are you trying to read. I am not familiar with an outboard ignition

Stator and Pack output peak voltages. The stator is permanant magnet and the RPMS vary but it's still to quick for a regular meter to read the peak voltage correctly. You need to slow down the voltage pulse so the meter can see it.

On a side note. If I were building a DVA (which i'm not because I own a few brand name ones). Build it for 500+ volts. I've seen some J/Rudes with broken mags on the flywheel put out over 450 volts. And please be careful, voltages this high will light you up like a christmas tree.

 

[Texasmark]

Re: Looking for a DVA Genius

That is a 2200 pF cap.

Look for electrolytic caps. Also note that these are polarized so you need to know which side the positive side is.

That resistor in the picture above is a 2.0 Meg Ohm if the color bands are red black green like I think they look like they are.

Color code is

0=black
1=brown
2=red
3=orange
4=yellow
5=green
6=blue
7=violet
8=grey
9=white

for a red black green you get 20 x 10^5 = 2.0 x 10^6 = 2 meg ohm

I am curious, what voltages are you trying to read. I am not familiar with an outboard ignition. If I knew what you are tryimg to measure including the voltage and the duty cycle. I could probably help you with what size components are actually critical.

Bruce, think pulsed radar! Pulse ampl 300v, pw 50 usec give or take 50%, prf 17 pps. Trying to peak detect and store for a DCVM to read it. I am currently working the bugs out of the other current post on this topic on this same forum. He has one more tweak and should be there except for his selected values. To me the 2.2 uf is overkill but that doesn't really matter. Also the pulse amplitude should be constant so the size of the bleeder isn't all that critical either.

On the color code, you know that you got it right but I'll never forget my short cut: Bad boys rape our young girls but violet gives willingly....compliments USAF basic electronics 101, day 1. Grin Still remember my instructor, name Mrs. Goff, Black, middle aged, and heavy set civilian. She did like her colored chalk, very artistic person. Caught me off guard being I was entering a military tech school but she knew her stuff and knew how to get it to you. That's what mattered.

Mark