Build your own peak voltage adapter

[jnk]

First of all, I don't want to take credit for this. This is an idea from a guy named Michael Henderson over at youtube. His video is

.

So, as some of you might already know, in order to perform all the tests in the service manual you need something called a peak voltage adapter. Honda recommends either a special tool with part number 07HGJ-0020100 or a product called IgnitionMate. I searched for both of them online and they both seem to cost upward of 100 dollars. Ouch. That is the price of a used stator ! Well, the good news is you don't have to spend that kind of money since you can build a simple circuit to measure peak voltages for less than a buck. This is the diagram:

The idea is quite simple. You apply the waveform to be tested to a capacitor through a one way diode. This way the voltage across the capacitor terminals can only be increased and so it asymptotically approaches the peak voltage of the waveform. To take a measurement you read the DC voltage on the capacitor. Important point: the multimeter must be switched to DC. Never mind that you are dealing with AC waveforms, what you you are measuring is the constant voltage across the capacitor.

The third part in the diagram is a hefty one megaohm resistance slowly discharging the capacitor. This is for safety reasons. No need to zap yourself if you accidentally touch the leads 5 minutes after you took a measurement.

This is my finished product:

OK, I am the first to acknowledge that the quality of craftsmanship leaves something to be desired. I am not that good with a soldiering gun as I am with a bike (and I am not that good with a bike to start with).

So how can we test if the adapter works ? No use taking it to the bike if we can't trust its readings. Well, the simple thing to do is just plug it in a socket. The usual caveats apply here: don't try this if you are not comfortable with high currents, electrolytic capacitors are known to explode, you may electrocute yourself or set your house on fire, etc, etc...

So what is it that we are expecting to read ? If you are in US the mains electricity is at 110 volts rms and so at 155 maximum. In Europe it is 220 volts rms, 310 maximum. Remember to switch you multimeter to DC.

This is what I got:

So my adapter works. It's time to take it to my bike. This is a video of me measuring the ignition pulse generator:

The video shows an important point. You can't infer the peak voltage from the rms voltage as you can, for example, on mains electricity. The AC reading is nowhere near 0.707*maximum. This is because this is not a sine waveform. So you have to use the adapter.

So what can you measure with the adapter on your CRF450X ? Basically two things: ignition coil peak voltage and ignition pulse generator peak voltage. The first is the input to the primary coil from the exciter coil in the stator. It should be minimum 100 volts. The second is the signal to the ICM from the stator that it should fire up the spark (the ICM will also take into account the engine rpms and the throttle position for the exact timing). This should be minimum 0.7 volts.

This is where to put the leads to measure the exciter coil:

Then you just crank the engine with the electric starter and wait for the measurement to reach a peak.

This is where to measure the ignition pulse:

You must disconnect the six wire connector from the ICM. Similarly you crank the engine with the electric starter and wait for the measurement to reach a peak.

This is it I guess. Hope someone else finds it useful.

Edited July 7, 2013 by jnk

[Jim Dettman]

Nice write-up. I've bookmarked this one.

Thanks!

Jim.

[HondaRider-26]

First of all, I don't want to take credit for this. This is an idea from a guy named Michael Henderson over at youtube. His video is

.

So, as some of you might already know, in order to perform all the tests in the service manual you need something called a peak voltage adapter. Honda recommends either a special tool with part number 07HGJ-0020100 or a product called IgnitionMate. I searched for both of them online and they both seem to cost upward of 100 dollars. Ouch. That is the price of a used stator ! Well, the good news is you don't have to spend that kind of money since you can build a simple circuit to measure peak voltages for less than a buck. This is the diagram:

The idea is quite simple. You apply the waveform to be tested to a capacitor through a one way diode. This way the voltage across the capacitor terminals can only be increased and so it asymptotically approaches the peak voltage of the waveform. To take a measurement you read the DC voltage on the capacitor. Important point: the multimeter must be switched to DC. Never mind that you are dealing with AC waveforms, what you you are measuring is the constant voltage across the capacitor.

The third part in the diagram is a hefty one megaohm resistance slowly discharging the capacitor. This is for safety reasons. No need to zap yourself if you accidentally touch the leads 5 minutes after you took a measurement.

This is my finished product:

OK, I am the first to acknowledge that the quality of craftsmanship leaves something to be desired. I am not that good with a soldiering gun as I am with a bike (and I am not that good with a bike to start with).

So how can we test if the adapter works ? No use taking it to the bike if we can't trust its readings. Well, the simple thing to do is just plug it in a socket. The usual caveats apply here: don't try this if you are not comfortable with high currents, electrolytic capacitors are known to explode, you may electrocute yourself or set your house on fire, etc, etc...

So what is it that we are expecting to read ? If you are in US the mains electricity is at 110 volts rms and so at 155 maximum. In Europe it is 220 volts rms, 310 maximum. Remember to switch you multimeter to DC.

This is what I got:

So my adapter works. It's time to take it to my bike. This is a video of me measuring the ignition pulse generator:

The video shows an important point. You can't infer the peak voltage from the rms voltage as you can, for example, on mains electricity. The AC reading is nowhere near 0.707*maximum. This is because this is not a sine waveform. So you have to use the adapter.

So what can you measure with the adapter on your CRF450X ? Basically two things: ignition coil peak voltage and ignition pulse generator peak voltage. The first is the input to the primary coil from the exciter coil in the stator. It should be minimum 100 volts. The second is the signal to the ICM from the stator that it should fire up the spark (the ICM will also take into account the engine rpms and the throttle position for the exact timing). This should be minimum 0.7 volts.

This is where to put the leads to measure the exciter coil:

Then you just crank the engine with the electric starter and wait for the measurement to reach a peak.

This is where to measure the ignition pulse:

You must disconnect the six wire connector from the ICM. Similarly you crank the engine with the electric starter and wait for the measurement to reach a peak.

This is it I guess. Hope someone else finds it useful.

This is great info in not sure what I did wrong when I tested min at the outlet it piped my house circuit breaker

[harkon]

This is great info in not sure what I did wrong when I tested min at the outlet it piped my house circuit breaker

 

If you popped the breaker you either had the wrong resistor or you had the wrong capcitor. Make sure you get the appropriate voltage rating on the capcitor for wall current if you are going to test this way. It should be rated for 170VDC (North America) or higher at the minimum. The 400VDC cap JNK spec'd should not create a problem. Also make ure the diode has a PIV rating of at least double what the capacitor is, otherwise you'll let the smoke out of that as well. If you had any incorrect parts, it's likely they are damaged and will need replacing anyway.

 

Lastly, be aware that a silicon diode will drop 0.7 volts at a minimum. Whatever the voltage drop needs to be added to the final reading. The missing ~1VDC generally is not an issue for large signal testing, but if you were looking at a small trigger voltage on a different bike, it could play a factor. For most of what you'll need this for on the CRF, this will not be a factor.

Edited December 30, 2014 by harkon

[mossman77]

If you popped the breaker you either had the wrong resistor or you had the wrong capcitor. Make sure you get the appropriate voltage rating on the capcitor for wall current if you are going to test this way. It should be rated for 170VDC (North America) or higher at the minimum. The 400VDC cap JNK spec'd should not create a problem. Also make ure the diode has a PIV rating of at least double what the capacitor is, otherwise you'll let the smoke out of that as well. If you had any incorrect parts, it's likely they are damaged and will need replacing anyway.

 

Lastly, be aware that a silicon diode will drop 0.7 volts at a minimum. Whatever the voltage drop needs to be added to the final reading. The missing ~1VDC generally is not an issue for large signal testing, but if you were looking at a small trigger voltage on a different bike, it could play a factor. For most of what you'll need this for on the CRF, this will not be a factor.

 

A couple things to add...This circuit should have a current limiting resistor in series with the capacitor to limit the initial current.  This will protect the diode and keep the initial current draw to an acceptable level.  The capacitor acts like a short circuit when it is depleted of all charge and connecting a short to 200V+ will result in a huge spike, which can damage the diode.  A 330 ohm 1/4W resistor in series with the diode should suffice.  This will keep the maximum current down to less than an amp and satisfy the maximum operating conditions of the diode.  The capacitor will take longer to charge with the addition of this resistor, but it will be negligible.  If using a 22µF capacitor (you don't have to use this exact value), the capacitor will fully charge (thereby giving you your peak voltage reading) in about 36 millseconds (0.036 seconds).  As you can see, adding the 330 ohm resistor will have no perceivable effect, but will keep the charging current down to a safe level, which will minimize the risk of damaging your diode.

 

Edited January 29, 2015 by mossman77

[CRF DOC]

  The capacitor will take longer to charge with the addition of this resistor, but it will be negligible.  If using a 22µF capacitor (you don't have to use this exact value), the capacitor will fully charge (thereby giving you your peak voltage reading) in about 36 millseconds (0.036 seconds).  As you can see, adding the 330 ohm resistor will have no perceivable effect, but will keep the charging current down to a safe level, which will minimize the risk of damaging your diode.

 

 

What do you mean "no perceivable effect..." ??? If I have to wait 36 millseconds for each test...I will only be able to perform 806,400 tests in a standard workday...talk about lost productivity...

[Tony Johanzzon]

Thank you, I will definitely build this one...

[Sam400]

Thanks for this, I’ve just made one to diagnose some an ignition problem works great!

[Nikler]

Hi,

Built this yesterday, with the original config, without the 330 ohm resistor. Got a reading of 178 volts.

Scrolled all the way down... and found the post about adding the 330 resistor to spare the diode.

Then I got a value of 8 volts!

Removed the 330 resistor and was then back to the original reading.

So, something happens when you add this, don't know what, but that's what I'm hoping someone can answer.

Yes, I did double check the circuit and solderings.

Also the remark about 36 milliseconds, I don't get that, no matter what configuration I use I have to "pump up" the voltage using the kickstarter repeatedly and with force.

Another question, my manual (Suzuki RM85) says it should be above 200 V, I got 178, how correct is the reading using this tool?

I have replaced ignition coil, CDI and stator, do I need to consider replacing the magnetic rotor?

[Al Salva]

On 3/24/2022 at 1:23 PM, Nikler said:

Hi,

Built this yesterday, with the original config, without the 330 ohm resistor. Got a reading of 178 volts.

Scrolled all the way down... and found the post about adding the 330 resistor to spare the diode.

Then I got a value of 8 volts!

Removed the 330 resistor and was then back to the original reading.

So, something happens when you add this, don't know what, but that's what I'm hoping someone can answer.

Yes, I did double check the circuit and solderings.

Also the remark about 36 milliseconds, I don't get that, no matter what configuration I use I have to "pump up" the voltage using the kickstarter repeatedly and with force.

Another question, my manual (Suzuki RM85) says it should be above 200 V, I got 178, how correct is the reading using this tool?

I have replaced ignition coil, CDI and stator, do I need to consider replacing the magnetic rotor?

yes  indeed, you need to bypass300ohms resistance to test ignition coils 

The capacitor is a 22uF 400V, R1 is 300 ohms and R2 is 1M ohm. !!! UPDATE !!! For testing ignition coils R1 needs to be by passed.