Yamaha 150 TXRC: Help Understanding DC Voltage readings

[Psalm 99]

Trying to determine why engine cuts to 1600 rpm sporadically. From prior post I'm starting to look at (1) Ignition coils, (2) CDI unit, (3) Charging coil, & (4) Pulser Coil. Too sunny out to view a good spark on my spark tester so going on to CDI unit output: Left side, all three cylinders: about 20 VDC ; right side, all three cylinders, 25 VDC . Charge Coil into CDI unit: about 250 VDC. Pulse coil into CDI unit: W/Y - WBr: 71 millivolts; W/R - W/G: 20 millivolts. To get readings from the charge and pulser coils, I'm inserting a sharpened straight paper-clip wire into the back of the wiring harness, then checking ohms to see if I've got a connection. None of this makes any sense as all the data is far from the spec per manual. If these readings were right, would the engine even run? As it is, engine starts right up. Data is for engine running at about 1500 - 1600 rpm. I tried two different meters. Newer unit has max/min button to get peak voltage but all readings are much lower than the rms readings I got from my older meter. Converting from rms to peak is not difficult so I'm giving the readings from the older meter.

[99yam40]

get the proper meter for testing these motor ignition systems or get a DVA adapter to use with you regular meters

[rodbolt17]

first thing to understand is the difference between peak voltage and RMS.
if you don't wish to purchase and use the correct meters then understand what you are measuring and switch scales.
also a good understanding of a two pulser system that also uses a CPS to trigger 6 coils.

[boscoe99]

first thing to understand is the difference between peak voltage and RMS.
if you don't wish to purchase and use the correct meters then understand what you are measuring and switch scales.
also a good understanding of a two pulser system that also uses a CPS to trigger 6 coils.

Teach us how to fish please.

If measuring a coils output voltage without the use of a peak reading adapter, what setting should the meter be on? How far off will the reading typically be from what it would be if a peak adapter was used, and in what direction?

If measuring a coils output voltage with the use of a peak reading adapter, what setting should the meter be on?

What is the difference between peak voltage and RMS voltage?

How does frequency affect RMS voltage, if it does?

How is a two pulser coil system used to trigger six coils? Does one of the two coils each trigger three coils or ???

[Psalm 99]

The voltage reading surely are chaotic but I have a pretty decent understanding of peak vs rms voltage and was simply trying to determine which of the three pieces of equipment was the problem (if any). Getting relative voltages seems to be a decent direction. Going into town today and will try to get a DVA from the local auto shops. However, looking at the measured voltages, the pulse and CDI output are both way too low (much lower than the approximate 30.3% drop from peak to rms by my measuring devices). Additionally, the charge coil voltage appears to be way over the stated design in the manual. I'm guessing I have a bad pulser coil(s) which is causing the CDI unit to respond so poorly and the charge coil to not discharge but this is simply a wild guess. The question on RMS voltage vs frequency is a good one. Basically, RMS voltage is not affected by frequency but it is affected by the shape of the voltage graph (sine, square wave, triangular). The 30.3% increase in rms to peak assumes a sine wave. I have a very limited understanding of relationship between the three pieces of equipment and really appreciate the help.

[Psalm 99]

Does anyone know what the resistance (ohms) should be across both charge coils? I'm reading about 74 ohms (R wire to Br wire) and about 7.6 ohms on second coil (Br to Blue wire). From what little I can gather, the resistance should be pretty close for the two coils. Also measured resistance across the two pulser coils, both were almost identical at 364 ohms. This seems pretty close to spec from what little info is available.

[panasonic]

Do you have the service manual for your engine? What is the exact model and serial number?

[boscoe99]

Specifications are in the applicable service manual.

Here

https://www.vansoutboardparts.com/se...50c-v150c/file

[panasonic]

Specifications are in the applicable service manual.

Here

https://www.vansoutboardparts.com/se...50c-v150c/file

Thanks, hopefully that will help the OP.

[boscoe99]

[panasonic]

From CDI Electronics:

DVA stands for Direct Voltage Adapter, which is used to measure peak AC voltage. This type of measurement of AC voltage takes the absolute peak or highest value of the fluctuating AC voltage signal. Peak readings will be substantially higher than standard or RMS AC values and are typically used when testing marine CD (capacitor discharge) ignition systems due to their high variance in frequency as RPM increases and decreases.
An example would be that the typical RMS AC reading of a wall outlet in North America is 120V. However, a DVA measurement of this same AC voltage would reveal that the peak of the AC sine wave is typically between 160-170V.
Some meters are capable of reading DVA or peak voltage pulses. Many ignition system components produce short AC voltage pulses. A peak-reading analog meter or DVA adapter plugged into a digital meter captures and holds the peak value of an AC sine wave long enough for the human eye to see it displayed on the meter. A conventional meter is incapable of accurately measuring these short-duration voltage pulses. A peak-reading voltmeter has special circuits that allow the meter to capture the maximum voltage produced during these short duration pulses and display the voltage as DVA or peak voltage. Failure to measure DVA can cause good ignition components to be incorrectly diagnosed as faulty.
The only meters that have built-in peak reading capabilities are analog meters with built-in DVA. Digital meters do not have built-in peak reading capabilities. In order for a digital meter to read peak voltage, one will need a DVA adapter, such as CDI part# 511-9773 or 511-9773NL.
Using a DVA adapter, a digital meter must be set to its DC voltage scale. Peak AC voltage is the measurement, but the DVA adapter has a built-in bridge rectifier, which converts AC to DC. The DC voltage setting on a digital meter is required to accurately read DVA.
CDI part# 511-9773 has built-in test leads.
CDI part# 511-9773NL has banana jacks, which uses your meter’s test leads.

[Psalm 99]

Really want to thank you guys for all the helpful information. A DVA and winky-blink get here Saturday and with the proper equipment, I should be able to isolate the problem. Leaning toward the charge coils at this point as the resistance readings from both coils are only about 10% of design. I'll go through the entire coil and CDI procedures regardless. Hopefully, about 3.5 years of intermittent frustration will end soon.

[rodbolt17]

Capacitor Discharge Ignition. CDI.
by the very term it is a DC output. capacitors pass A/C but store/block D/C.
however as this DC output has a very rapid increase and decrease it actually acts similar to an A/C sine wave.
this particular system uses both a low and high speed charge coil.
the charge coils simply send an A/C voltage to the CDI unit.
the CDI unit rectifies and stores the voltage in a set of capacitors.
the output from the caps to the ign coils are a set of SCR's.
the SCR's are triggered by two pulser coil inputs and a CPS input.
once triggered the SCR stays ON until current falls below a threshold the the SCR turns OFF.
it is actually a pretty simple system.
if you look at the screen shot of the tune up spec guide that boscoe posted you can determine which cylinders are triggered by pulser coils and which are made up via CPS signals.
if you wish to know more google NEETS clippers,clampers and wave shaping circuits.
you can read it.
I had to pass it.

[Psalm 99]

Thanks for the clear explanation of the system. As my engine works well at low speed (1600 rpm and below), and cuts out at speeds higher than this, should I be looking first at the high speed side of the charge coil. My readings on the charge coil resistance were wrong and subsequent readings matched very closely spec on both high and low sides. The DVA and winky-blink coming tomorrow hopefully will isolate the problem.

[boscoe99]

Thanks for the clear explanation of the system. As my engine works well at low speed (1600 rpm and below), and cuts out at speeds higher than this, should I be looking first at the high speed side of the charge coil. My readings on the charge coil resistance were wrong and subsequent readings matched very closely spec on both high and low sides. The DVA and winky-blink coming tomorrow hopefully will isolate the problem.

That is exactly what happened with my Mercury EFI with a high speed and low speed charge coil. Idled just fine and ran just fine up to about 1500 RPM and then would not do more. Ran like crap above 1500. Replaced the stator and she was happy and well again.