The 'diodes' are not actually diodes, but SCR's in the old products and MOSFET's in the newer aftermarket designs. So forward bias tests are not showing any except that the parts are there.

Best suggestion IMHO is to get a used OEM VR.

As for tests, put the voltmeter across the AC circuit to the bulbs. It should limit at some value at some moderate RPM level. The actual voltage is impossible the predict with a standard voltmeter. The actual AC is nothing close to a sine wave,neither regulated or not. An old style true RMS voltmeter is needed.

Another key area to check is to see if the VR is actually connected. It is connected in parallel with the stator's lighting coil. (Connected 'in shunt' across the stator is another way to say this.) So check continuity from the VR connector to the bulb sockets on each side, which are probably yellow and yellow/black.

 

thanks so much for quick response and I will let you know the outcome tonight

-Fallflight

 

So I checked for continuity at the bulb connector and VR connector and and both the yellow and Yellow/black have continuity at the VR with the headlight wires. When I rev the engine past idle, i can take the Voltage to 16.7 volts so I stop. No sense in blowing more bulbs. Added an extra ground between engine and chassis before this test. Everything points to both VRs being bad. Any other ideas?

-Thanks

 

I went back to the older VR where the ground wasnt a separate wire going to the grounding bolt. Black wire goes inside the potting. Seems to work but when I test this black wire to the VR aluminum shell...there is no ground. This doesnt make sense. Any ideas? maybe I don't have the concept as to how the extra voltage shunts to ground

Anyways, thanks for your help

-Fallflight

 

Interesting.... The schematics show this black wire going inside the VRR and making a connection to the case. So I would also expect what you seem to have been expecting. There is another point at which the black wire gets grounded to chassis, through the harness.

The black is the - side of the DC output. The AC system typically the floats, i.e. has no direct connection to chassis. The regulation is between the yellow and yellow/black, where the regulation is shunting across the floating AC portion of the system to limit the AC voltage.

So are you getting a reasonably limited voltage at the light sockets now?

 

Interesting.... The schematics show this black wire going inside the VRR and making a connection to the case. So I would also expect what you seem to have been expecting. There is another point at which the black wire gets grounded to chassis, through the harness.

Despite how the wiring diagram appears, the black wires are connected to the case externally, and never internally. You may remember that I tested this two or three years back with several voltage regulators. That was when I misplaced them after putting them away lol

 

I have been using a new MOSFET VRR for a few years now on my vintage sled and it work well, you simply connect the two yellow wire the two of the three input connectors and use the DC output for your DC circuit.
I got a aftermarket one but a new BRP one off of any modern sled will doo.

 

Yes , you have it right. The limited current output of the stator along with the battery acting as a sort of 'current sink' also limits the voltage out of the DC port.

Glad it is working now. The issue with MOSFET VRR's is that the so-called 'design engineers' are just copiers of application notes and don't really know how these systems work.


Do you happen to remember the PN and brand of the aftermarket one?

 

hi guys

I am now getting about 14.3 volts regulated now with the VR that has the internal ground. When using the VR with the external ground, it wouldn't regulate at all. Maybe a bad regulator from new as I just bought it. Why would this not work with the external ground (Grounded to frame via a bolt.)?

so that I better understand, this VR is regulating the AC volts and limiting them, before AC voltage is rectified to DC?

Thanks

 

I am now getting about 14.3 volts regulated now with the VR that has the internal ground.

Did the old one just start working properly?

 

Funny how things work out that way! Tnx

 

Yes, but seems the voltage goes down as I rev the snowmobile. These are my brother in laws sleds ans they dont run them much. so Idle is 14,5 volts and works for me as it will charge battery at that RPM

That is good news. How low does it go, mid 13s?

It would be cool to get a measure of both AC and DC at various rpm. The experiment could be repeated with one headlight disconnected, and then with both of them disconnected. And of course like you have already done, avoid going over 16Vdc, and maybe limit to less to provide an allowance in case it does jump high and burns a bulb.

This kind of testing can be fun and inspire thought. I love this stuff lol I find the testing like this is the enjoyable part of the electrical. Over my time on DooTalk, I must have spent hundreds of hours between measuring my own stuff and assisting others to take the measurements. When I find someone who is intimidated with the electrical, that gives me the incentive that change that. I bet you are good with the electrical, probably a lot better than me.

I changed the regulator as the system wasn't making any voltage. When I found a bad terminal at the engine harness, I should have kept the old regulator

Who knows, maybe we can make the new one work and you would have a spare for your BIL.

 

The sleds are put away for now, but I am sure that I will do some preseason testing and will report back at that time. I still don't understand all of it. I get that the engine makes AC and the lighting system and engine spark use this, and that the only DC circuit is for charging the battery. What I don't understand is how the VR regulates both DC and AC at the same time. You would think that this is done separately with different components within the VR but must do it together, before the voltage is rectified to DC

-Fallflight

 

The AC is regulated, and since the DC is derived from the regulated AC, then the DC is automatically regulated. Plus the battery is a 'ballast' on the DC charging voltage, which is another form of regulation. (But not a good one....)

 

That is a pretty cool explanation. Will you remember this in six to eight months? That will be the approximate time before the sled gets taken out of storage. This has been a great season that has lasted longer than usual. Within a few weeks DooTalk will begin to peter down until it stabilizes for the remaining months. Maybe by then we will have a VRR depotted.

 

A other way of seeing it, think of it as a series of events, so take it one step after the other, the VRR first regulates the AC voltage from a varying 12-55VAC to a constant 14.5VAC then it will rectify this 14.5VAC into constant 14.5VDC voltage.

To clarify things the stator has two different sections one for the ignition and one for the AC voltage to the lighting and battery charging circuit, so the AC produced on the ignition section has nothing to doo with the lighting section, you could have a burnt stator winding on the lighting and still be able to use your sled.

 

Important to note that the DC is a pulsating DC on the half wave. Most multimeters can't measure that very well and will most likely read lower than the AC.
The diode or mosfet on the DC side can only handle 5 amps. If the battery drops down to 9 volt or lower, it can blow the regulator.

 

Important to note that the DC is a pulsating DC on the half wave. Most multimeters can't measure that very well and will most likely read lower than the AC.
The diode or mosfet on the DC side can only handle 5 amps. If the battery drops down to 9 volt or lower, it can blow the regulator.

And this is how it works for the older VR's: The voltage out of the lighting coil is something like a sine wave. The regulating parts (SCR's, MOSFET's or thyristors) are connected across the coil, and when they turn on , they electrically short the output. The sketch below shows the parts turning on during each half cycle at the points in time marked with the asterisks. When the output polarity reverses, then the circuit 'resets' and the voltage starts to rise in the reverse polarity until the next firing time.

The timing of when these parts are fired during each half cycle is set by a circuit which detects the average output voltage and adjusts the timing. For example, if the output voltage rises (like when the engine RPM's increase), then the timing will turn on the regulating parts earlier in each half cycle, to keep the average output regulated.

The above sketch shows the pulsating nature like TheBearAk describes. A standard meter does not measure this 'spikey' waveform properly; most are set up to give accurate readings only for a sine wave. Even most True RMS voltmeters will be off.

The idea of shorting the stator (lighting coil) output may seem crazy but 2 things actually make it a good design:

• The design of the coils, magnets, and air gaps causes the current to limit when the VR shorts the output. So this prevents the winding from being burned out.
• With the a hard short in the regulating parts when they fire, the voltage across the part when shorted is almost zero. Power dissipation is voltage times current so this design actually keeps the power (the heat) in the regulating devices to a low level.