Direct Voltage Adapter

[Schnidly]

Dear Forum,

I found on here where someone posted how to make a DVA Adapter, but I am unsure of the best size of the Capacitor, the diode and the resistor to use. I have a 1988 Mercury 90hp 3 cylinder outboard and want to make sure when I head to Radio Shack I purchase the correct materials to build the DVA. Also, I am wondering if someone knows of a box with the meter plugs on it already that will plug into my Digital multimeter, I can find a pair of plug in testing leads to use. Thank you for your input!!!

 

[Laddies]

Re: Direct Voltage Adapter

!!!

 

[Schnidly]

Re: Direct Voltage Adapter

Thank you Laddies, I did see on here where someone used a 1A 400V silicone rectifier diode, a 2.2 micro Farad capacitor rated at 400 WVDC and a resistor rated at 1Meghom 1/4 watt. Will it matter which I make for my motor? Im using a digital multimeter. When testing any voltages on the motor using this adapter do I need to have the meter on the dc setting or the ac setting, Im guessing the dc setting. Not sure however about testing the stator or trigger, aren't those ac voltages coming off of there?

 

[Dave1027]

Re: Direct Voltage Adapter

Laddie already posted the answer. DC and use the 1000 volt scale.

I'll add: The diode is why you use the meter in DC mode. The diode's job is to turn AC into DC. Actually it removes half the wave then the capacitor smooths it all out to DC.

 

[Texasmark]

Re: Direct Voltage Adapter

Thank you Laddies, I did see on here where someone used a 1A 400V silicone rectifier diode, a 2.2 micro Farad capacitor rated at 400 WVDC and a resistor rated at 1Meghom 1/4 watt. Will it matter which I make for my motor? Im using a digital multimeter. When testing any voltages on the motor using this adapter do I need to have the meter on the dc setting or the ac setting, Im guessing the dc setting. Not sure however about testing the stator or trigger, aren't those ac voltages coming off of there?

That was probably me. The values aren't all that critical as long as you stay within a reasonable area as to what's perfect. There will be some variation (tolerance in the values) but not so much as to not tell you what you need to know about the circuit in operation.

Like Dave said below, the diode makes it DC so that you can store the pulsed energy easily in the capacitor which charges up to the peaks of the narrow pulses and holds the level so that they can be read on a (dc) multimeter; they are too narrow and don't occur fast enough to be read otherwise on that type instrument; oscilloscope yes, DMM no. All the resistor does is keeps the capacitor voltage bled off (somewhat) so that if the amplitude of the input changes, the capacitor can follow it; and second purpose is to discharge the capacitor when finished. Otherwise it will just charge up and sit there.....till you get your fingers across the terminals and WHAM! BTDT on other applications of "sample and hold circuits" and it hurts!

HTH,
Mark

 

[Texasmark]

Re: Direct Voltage Adapter

This should help

Mr. Laddies Sir,

I know you are a multi-decade seasoned mechanic, but being a retired EE there is a problem with your schematic, for me anyway. Normally the inputs to circuits are on the left and outputs on the right. The schematic shown has the output on the left and input on the right.

The capacitor can't be on the pulsed input side as the average value of a sine wave is zero and the capacitor charges to the average value....just the way they work. The ac pulse has to be rectified first then applied to the capacitor for it to charge up to the peak value of the rectified input pulses and supply a readable reference voltage. Polarity of the diode as shown, then would provide positive voltages in the output (as shown) and that is the polarity of the referenced voltages in the maintenance manual under the title: "Direct Voltage Adapter (DVA) Test". May I suggest flipping it around (reversing) or labeling the left side as OUTPUT and the right side as INPUT so that a person choosing to build one could get it hooked up correctly thus providing readable outputs.

I didn't notice this until I came back to compare component values to the one I built from spare electronic parts I had around the shop.

Thank you sir.
Mark

 

[Dave1027]

Re: Direct Voltage Adapter

Good catch Mark. Lables definitely. Put the meter on the left and connect the right side to the motor.

 

[Laddies]

Re: Direct Voltage Adapter

Better yet I will just dump the schematic and you post what ever you like Texasmark

 

[Texasmark]

Re: Direct Voltage Adapter

Better yet I will just dump the schematic and you post what ever you like Texasmark

Why does this reply not surprise me? I expected such even though I was as polite as I could be!