Modern Vespa

Hi ModVespa,

I have a '79 P200E that I've restored from the heap. Recently, I have had a problem with the battery charge being depleted after a few rides. I can tell when the voltage dips below 9V because the horn weakens, the signals stop working, etc. New battery, with a good initial charge, along with a replacement rectifier/regulator, has got me baffled as to the source of the problem.

Right now the battery has been depleted to about 1.5V (scooter off) and when you put a multimeter on the terminals with the scooter running, it doesn't get above 0.8V, throttle or not.

I suspect the regulator/rectifier may be the culprit, and it isn't replenishing the battery with the proper 12V charge during riding. But this is a new part replacement, and I am suspitious if it actually is the problem.

Is there a way to test the regulator with a multimeter directly on the regulator terminals, or is the only way to test it through the battery while it's on? Also, can anyone suggest any other tests to run to determine if this part is at fault or not.

Thanks,
-Peter

If your fuses are good, and you don't have a short somewhere else in the frame ( which would likely result in your lights not working, battery charged or not )

then there's a very high chance it's your rectifier.

You can get replacement ones ...but they're not cheap ( unless you buy [redacted] knockoff ones )


I'd guess that you can hold a multimeter ( set to volts DC ) up to the tab on the rectifier that puts out 12v DC juice, run your bike and see if it's getting 12v DC .....and then check at what current.

Thanks, Eric. I'm having trouble figuring out on the attached wiring diagram which terminal fuels the battery with 12V DC juice. Perhaps the black wire, but that looks like a simple ground.

Well, that diagram confuses me a bit, as it looks like the battery positive side hooks directly up to the stator, which i didn't think was possible.

Trace your own wire ...how does the red lead off of the battery wire hook up to everything ?

Is this possibly a problem with either the stator or wires going to the battery? The stator powers the spark, and the headlamp. The other electrics are charged separately from the stator. If that wire or portion of the stator is failing, you might still have a running bike with a working headlamp, but not power being replenished into the battery.

I'd be inclined to pop the wire of the rectifier when the engine is running and see if you're getting any power at all. You might just be running all your lamps off the battery with no recharge going on.

Mike

Eric - The red wire from the positive end of the battery follows what we see in the diagram: through the fuse, then splits to the key ignition and the stator.

Hojo - The stator could be the source of the problem too, I agree. But I don't follow your logic about popping the wire of the rectifier to determine if the any power is on. Could you rephrase that? And just so we are on the same page, you are talking about removing the yellow (see diagram in previous attachment) wire from the rectifier right?

It sounds like the problem could either be with the (1) rectifier/regulator device or the (2) stator portion which interacts with the regulator. I guess what I'm looking for is advice on how to test the health of (1) and the health of (2). [/img]

Sorry, in a rush and don't have time to look at the diagram. I'm suggesting removing the wire from the stator to the rectifier that would/should provide power to the battery system, and attaching that wire to a voltage meter to see if any juice is coming in to the rectifier. If there's no power on the wire, then perhaps the wire or stator are faulty. If there IS power, then it's probably the rectifier. that's faulty.

Mike

I would not trust this diagram. Using a clock face the coil @ 5 has an earth at the inner end but no o/p from outer end. Coil @ 3 has no connection at inner end. I have both versions of the Haynes book #707 complete with their wiring bloopers.
I had a PX wiring short out in the terrminal block on the fan housing.
All seemed ok but the battery was not charging. Eventually only the ignition was working ( separate circuit ).
Had to remove the stator & wiring to block to replace said wiring. Insulation was like plasticene.

Mick

I have the same problem, replaced rectifier, wasn't the problem. waiting for tools to remove fan plate and stator.

watching this thread with baited breath

Only marginally related to the charging problem, but...

Has anyone else faced the problem of the green wires on P200's decomposing?

On the resto I am doing, I plan to replace all the green wires or buy a new harness.

Jim

almost every old p i'v seen has what looks like heat rot on the green

when its so bad you never know where the break is

some use the old neutral wire(brown) from the selector box and others try to run new

either one is work

Hey everyone, I did some testing of the issue over the weekend. Here are the results around the rectifier without the battery attached, but the engine running:

1) B+ pole on the rectifier shows ~17VDC at idle, up to around 100VDC at high acceleration
2) Turn signal pole (C) shows no voltage output
3) Two yellow cables from the stator show 12VAC, up to around 50VAC at high acceleration

Some odd results:
4) Once the pink wire is attached to the B+ pole, no VDC is recorded at all from the pink wire

Also, I erroneously attached the "red and yellow" wiring diagram for the P200 earlier. The correct wiring diagram for my P200 is the "2 yellow wire" one and is attached here.

Do these results eliminate the stator as the source of the problem?

If that is your wiring diagram, you have a rectifier/regulator with two AC wires in (yellow) and two DC wires out. Your tests seem to show the stator is providing AC, but the regulator is not providing the DC output. It changes the AC to DC and bleeds excess voltage to ground simultaneously.

Another way to test it is to use a lamp such as a brake/tail light fixture with the typical 1157 bulb and first attach one stator yellow wire to the fixture ground and the other yellow to one of the other lamp wires, run the engine, and see if the lamp glows. If it glows, the stator can provide load and should be okay. It may blow the lamp when you rev it up. Oh well, sometimes sacrifices have to be made.

Then unhook the regular wires to the regulator DC terminals, hook up the test fixture and see if it glows while running. If not, faulty rectifier. If it glows, but your voltmeter shows low or no DC when hooked back up, possible short somewhere on + wire.

Another test is to hook a diode bridge rectifier's AC inputs to the yellow wires, and hook the lamp to the + and - and see if the lamp glows and/or blows while running. If so, bad regulator.

Make sure there is no short on the DC out wire before buying a regulator.

Thanks, Blackbart! I ran your bulb test suggestion on the yellow AC wires and got a glowing bulb (didn't want to rev it and blow it up, because i'd near to re-solder wires to another bulb).

I then put the positive wire from the bulb onto the B+ pole and the negative onto the vespa body. No glow. I then put the + wire on the C pole; no glow.

What I can tell is that these tests show that my rectifier is no producing DC power out of either the B+ or the C poles, and is fried. I'm glad to have found the source of the problem, however upset that I bought this Ducati rectifier from Scooterworks about 2 years ago and it is already pooped.

Thank you to all who helped me diagnose the source of the problem; hopefully others will see this thread and gain some knowledge on how to do the same with their vespa.

Side Note: Does anyone have a suggestion for a replacement rectifier? I don't want to shell out ~$150 again for a genuine Ducati...

Best,
-Peter

How high should the AC voltage be between the two yellow wires? I have the same problem as mentioned above, and with the multi-tester I measure 15 V AC between the wires. I replaced the rectifier, but still don't get 12V DC on the B+ exit of that rectifier. Is 15V AC ok, or should it be more. The engine turns ok, but the battery of my 1978 PX drains without recharging. The test with the two yellow wires on a bulb gives a positive result, glowing like the sun.

Hi Lomax,

I think that voltage you are seeing between the yellows is expected, however that only confirms that the electrical supply to the rectifier is correct. The voltage shoots up (or the bulb gets brighter) when you rev the throttle right?

Between my broken rectifier and my working rectifier, I couldn't get any voltage coming from the B+ pole either, so I wouldn't use that as an indicator of working order (contrary to what people have said on this thread earlier). The only conclusive test I could do with my working rectifier to confirm it was operational, was hooking it properly to the battery and testing the battery terminals with the multimeter. At rest, it was about 12V and shot up a couple volts when I rev'd it (14V).

-Peter

Peter, Yes, the bulb gets much brighter when revving the throttle. At rest, the battery gives a good 12,5V, but with the engine running it does not gets any higher, even when turning up the rpm a lot.

When I check the rectifier itself, should there be a connection between a yellow (G) plug and the B+plug in one direction, but not in the other direction? Because that is what I learned about diodes, the main components of a rectifier, they let electricity flow in only one direction.

I can't really comment on the specifics of the rectifier connections themselves, but the fact that the voltage doesn't increase from 12.5V on the battery when you throttle is strong evidence that the rectifier is broken.

I was able to replace my broken rectifier with a used one on eBay for much less than retail. Consider checking it out!

I bought a new one on Ebay, in Germany. And I think it was broke before it came out of the box. I'll try to find one that is working, just to swap for a few minutes. That way I can find out if its the rectifier or not.
Thanks for the advise.

The lamp bulb glowing brightly is the true test of the stator's AC output. If there are bad connections or corroded stator wires, sometimes a voltmeter won't detect it under no load conditions. The lamp loads the circuit and replicates more real life conditions and requires no in-depth meter knowledge.

You can also test the regulator DC output with the lamp. It should glow normally on the DC outputs with the engine running.

It seems the regulator is for battery charging, and provides no headlamp voltage regulation. 4 wire.

This next statement won't go well with some purists, and I would only try it on a scoot where originality is of no concern. There are lots of 4 wire stator based regulators available. Some of the 125-150cc overseas scooters with the GY6 engine have 4 wire regulators that are inexpensive and all over the internet. Some snowmobiles also.

Blackbart, thanks for the low-budget advise, I was also thinking in that direction. This rectifier should, as you said, only feed the battery. I found out that the headlights got AC directly from the stators purple wire whit the engine running and the battery disconnected. With the battery connected, and once the ignition key turned on, the headlight also got DC from the battery. Looking at the electrical diagrams, my Vespa's electricity is a mix of two different scoots. Too many wires and bad improvised connenctions. I disconnected the AC wire to the headlight, and it glows just as good as before. That way, I will not kill the next regulator/rectifier.
Next step will be finding an aftermarket regulator that transforms the 15V AC from the two yellow wires into 12-13V DC to the battery. So a 3wire regulator could do the job.
Results will follow..

Yes, possibly, as long as it's a regulator/rectifier.

My bet is that you've been sold a newer AC/DC type reg/rec rather than the total DC type that you need. Both of these have the same marked connections but are different internally.
Try lighting the test lamp off of the two yellows while they are connected to the reg/rec. If it doesn't light when they are connected to it but will if you disconnect one then you have been sold the wrong one.
Kev.

The two yellows, comming from the stator, have AC, between 15 and 40 Volt, that should be converted to 12 (13,5) Volt DC. Where is the difference between a AC/DC and a total DC type?
I will do the test, and let you know the result.
And I keep looking for a basic, low budget rectifier that will do the job, while I already lost 40 dollar on the 'real' thing, with no result at all.

I just developed similar issues, proper AC power coming into the regulator, no DC coming out, and I noticed on the mulit-meter, I have continuity between my positive and negative battery terminals meaning I have a short somewhere, I think this is causing me to burn out regulators/rectifiers

On the AC/DC type, one of the G's is for a single wire from the stator the other G is the AC output to the loom. These two G's are connected together inside the unit and a tapping goes through a half wave rectifier to the B+.
On the DC type the two G's are the AC feeds into a bridge rectifier which gives full wave rectification to the B+.
If you connect the Two AC feeds onto the AC/DC type they will be shorted together and therefore can have no voltage between them.

The 2 G's are connected, in both directions, that should be the reason why things don't function. And it seems that the good rectifier/regulator is hard to find. Will be continued..

That will definitely be the reason why things don't function.
It will be worth trying whether half wave will be enough output to keep your battery charged using the reg/rec that you have. You can do this, simply, by disconnecting one of the yellows from the reg/rec and connecting it to earth.

I disconnected one of the yellow wires from the regulator, with no result. When I connected that wire to earth (frame), it gave a lot of sparks, but no extra power on the battery. Next option will be finding a bridge rectifier that can handle the voltage from the stator, and when/if I can get this to work, I must look for a regulator to keep voltage under 14V DC.
Another solution is:
http://www.sip-scootershop.com/EN/Products/50005000/CDI+Ignition+VESPATRONIC+Vespa.aspx
But that one is only an option when nothing else will work. LoMax stands for Low cost, Maximum pleasure

If it was sparking it wasn't connected to earth properly and as such I would expect it to spark as current is flowing through it. As the connection was high resistance (it wouldn't spark otherwise) the voltage output could never be right as all the volts are dropped across the poor connection.
Kev

I have interesting setup, Keep burning out regulators it seems. Mine is the 5 pole purple,purple, gray, yellow, black
a, a, +b, ground, g

Seems I have continuity between red battery cable, and frame & black negative cable, but only when key is turned on. no voltage out on +b, ground or g on the regulator. If I plug in an older regulator I get proper DC and AC out, but AC isn't regulated (its why I put in a new regulator.)

Anyways, I can't figure out where my red is grounding out at as it all looks solid as far as I can tell, head set is clean, nothing touching so assuming it must be inside my key unit?

1. Help me find my short

if this needs to be its own thread, MODs please let me know.

Shawn, if your wiring is the same as the first diagram posted, then your reg/rec is different again, so it is probably best to start a new thread. Otherwise it is going to get confusing as to which reg people are talking about and which diagram to look at.
Kev.

When the key is turnded on, you also make a connection to the head- and taillight, or dashboard lights. Trough the bulbs, you make contact with the earth side of the circuit (with just a small resistance from the bulb itself). Therefor it is normal to have continuity. I did the test, with the same result on my p125x. Why not keeping the old regulator, and regulate the AC behind it, with a separate regulator. I know it is possible, I just don't know how. If you want to regulate the AC, because the bulbs keep blowing, you could try to put a second bulb in the circuit, in a serial connection, so each bulb will get half the voltage. Measure the AC voltage under load, and make sure you don't have 6volt bulb on a 15V circuit.

Lots of Chinese scooter rectifier/regulators here:

http://motors.shop.ebay.com/i.html?_nkw=scooter+voltage&_sacat=&_odkw=gy6+parts&_osacat=0&bkBtn=&_trksid=p4506.m270.l1313#item3ca32ed4ea

The key to retrofitting on a Vespa P with a four wire regulator is to get a four wire type, and then figure out which two terminals are for AC in and which two are DC out.

They serve double duty on a china scoot, most have the headlight AC tapped off the incoming stator wires, and the regulator clamps the AC to about 13 volts AC for the headlight.

They also rectify stator AC to DC, and regulate it to about 14 volts DC for battery charging.

An internet search will find lots of parts suppliers.

I did the test again, this time with good connection between the second yellow wire and earth, but with the same result. The voltage even drops a little with the engine running (12,50V to 12,20V).

This could be a solution, I'll try to find them in Belgium, because the shipping cost is 3 times the items value. Thanks for the link.
Fixing a Vespa with Chinese parts, it's like making a Harley running better with Honda-parts

Most 4 pin AC/DC regs are not too different to the reg he has now - although it has two seperate stator inputs, one half wave DC output and earth. So it would need to be wired exactly as I mentioned before with one yellow earthed. The difference in the cheaper alternative is it's missing the other input and as such will not charge as efficiently as the one he has now.
If you're going to get a replacement get a full wave rectifier/regulator.

The yellow one that should be earthed, does it has to go in the rectifier at the same time? Because I did put it directly from the stator to ground, without going to the second G of the regulator.
And I am afraid a full wave rectifier/regulator is 5 times more expensive. If I am sure to buy the right one, that would be no problem, but in this case it would allready be the 3rd one.

One stator yellow should go to the reg the other needs a good contact to a clean earth. The other G on the reg will remain unconnected. As you said you had sparks, then you were probably just holding the connector against earth which obviously wasn't good enough. Make up a link wire with a male spade one end and a ring on the other so that you can bolt the yellow temporarily to a good earth connection and try again.
As for buying the wrong types, that is easy to do and is why I wouldn't recommend any other type, without seeing a diagram of it's connections or of the machine it was intended for.

Sorry missed the post where you said that you had made a good connection. Was that reading just done at idle. Did it not increase with revs?