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-   -   Voltage reg/Rectifier (http://www.horizonsunlimited.com/hubb/other-bikes-tech/voltage-reg-rectifier-23758)

simmo 21 Oct 2006 13:04

Voltage reg/Rectifier
OK here goes travelling genius's...sss

Now I have an aircooled Italian 900cc twin that is only testing at 12 volts across the battery terminals at 3,000 or there abouts revs. I believe I should expect 14.5 volts if everything is functioning normally.

As the bike was running rough on three quarter to full throttle when I got it and had been sitting for a while, I assumed blocked up carb jets. I can say categorically that this is not the case anymore! My italianised hands now understand the Mikuni CV carb with oil line heaters very well.

The bike still runs poorly, breaking down (poping, backfiring, running on one cylinder etc) when the throttle is openned wide. I suppose I am trying to find out how to determine wether its the Reg Rec thats clapped out, the coils under load or the stator/alternator itself. Fuses all look good, and I have fiddled with the conectors.

Tips on how I might go about resucitating the Crapati welcomed.....and all you schwinhundt lovers, the G/S has been parked. The new one handles and has brakes but clearly reliablilty is yet to improve....



beddhist 21 Oct 2006 16:32

Have you checked the connectors?

With everything still connected measure the voltage into the RR unit. Voltage should increase as revs go up from idle. Set the V meter to AC for this. There will be three wires (assuming it does have a three-phase alternator...) and you should have the same voltage the three ways. You can also disconnect these wires and measure resistance, should be about equal the three ways and no connection to ground. Any other measurement and it's the alternator winding. If this checks out OK try another RR.

mollydog 21 Oct 2006 18:16

A simple question first.....How's the battery? :smartass:
So many times guys over look this simple element!

Is this a Ducati?

I would get hold of a service manual so you can go through all the
electrical trouble shooting steps.

There are always several resistance tests you can do to find the fault,
sometimes they show where it lies and sometimes not.....I've seen
bad stators that show resistance within spec....so who knows.

The batt may test at 12.5 volts but could have a bad cell and causing

But your system should be putting out about 14 volts as you've pointed out.
So who knows. But a good battery is very important so that the other
components can operate at spec.

Also look for any corrosion, clean all connections, tighten all connections,
look for frayed or abraided wiring looms, split sections, bad kinks, missing
or unplugged or bodged plugs or wires.

Good luck!


Dodger 21 Oct 2006 20:17

You haven't said what make and model bike you have so any help can only be very generalised .
If the bike has a manual ignition advance system ,you should check this for correct operation as it may not be advancing enough [ or even at all ] at higher revs.
Bad spark plugs can also cause a high end misfire on one cylinder .
But ,as you have pointed out .the alternator may not be charging so put a known good battery on the bike and ride it a short distance to find out if that's the cause of your misfire and then check alternator as suggested .
Weak or stiff carb diaphragms can also be the culprit but you 've already checked them .

simmo 22 Oct 2006 01:29

Thanks guys, Beddhist thats the clue I was seeking, I'll have a go and let you know.

Yes it is a Ducati, a 900 Monster and once running properly will be my regular transport, I am sick of fixing the old BMW. I even have a spare tank to modify for a decent touring range.

It has a good Batt, new spark plugs, filters, belts and oil, new emulsion tubes and lovelly clean carby jets. Caps, fuses and connectors checked. I am just trying to isolate the problem before I waste more money on unnecessary expensive replacement parts.


Frank Warner 23 Oct 2006 02:44

Your first gess at the rectifier/regulator is a good one - that is the 'normal' failure mode .. much like the airhead rotor on the bm.

One test - does the ret/reg get warm/hot? If cold then it is not doing much work. If hot it is doing too much .. may be not working the right way. I suspect the ret/reg may be passing AC to the battery .. and the battery won't like it .. err if the battery is hot .. it is the ret/reg !!!!!

Certainly a battery voltage that is not over 13 when the motor is running so revs is not good ... fix it before riding anywheres ..

Checking the 'alternator' - Measure the AC output from the alternator .. should go up and down with engine revs .. umm how many volts .. errr that will depend on if it is loaded or not .. ie if the retifier reg is working .. but it should be around the 10 to 20 volts ac level. If my theory is working...

lecap 24 Oct 2006 12:35

Battery check:

Check for fluid level and top up with destilled water to max. (the Ducati pobably has a sealed maintenance free batt - skip)

Charge your battery with a good quality charger. While charging the battery voltage should go up to 14.4 volts max. after 12 hours or so depending on state of the battery and type of charger used.

Disconnect the charger. Battery voltage should be some 13.5 volts dropping slowly (you will need a good digital voltmeter, if you have something else throw it away and buy a good one, they ain't expensive).

After the battery has been standing for at least a couple of hours (best one day) the voltage should have settled to 12.8 Volts. If it is lower the battery is old. If it's below 12V you should get a new battery. A battery with a bad cell will always drop down clearly below 12V within a day. A typical voltage for this would be 10.5v approx for a battery with a broken plate (cell shortcut, this one will never exceed 12V even if freshly off the charger). You often have a combination of a bad cell and a weak battery which will show a voltage of less than 10V one day after charging.

You can shorten this procedure by visiting a reliable battery shop with your battery. They have testers but they might also want to sell a new battery :-/

Alternator check:

Once charged you put the battery into the bike and start the engine. Your voltage should be above 12.8 volts with the engine idling. Most charging systems will feed some 14+ volts into the battery without revving the engine high (at 2000 to 3000 rpm). The voltage should modulate a bit from idle when reving the engine up and should reach more than 14V fairly quickly.
12 volts at 3000 rpm is IMHO a clear indication of one faulty coil in the alternator. Note that measuring the resistance of the three coils will give correct readings in most cases and even against ground the coils will not "leak" if tested with a resistance meter / diode tester.
Besides testing the voltage output of the three phases of the alternator, which is often tricky without making new cable connectors or stripping insulation off the bike's wiring, only applying high voltage to the coils will reveal an earth leakage of one of the coils past the insulation against ground. A good automotive electrics shop will be able to perform this test and they will also be able to rewind the coils or give you an address to get the problem fixed.
Rewinds are usually superior in quality and often also provide higher power output of the generator. A rewind often only costs a fraction of a new replacement part.

In your case:
The battery is permanently low on charge and whilst the battery will for some time provide enough power for the starter it will not have enough voltage for the ignition causing backfire and rough engine run. Sooner or later the battery will also fail prematurely.

Regulator / rectifier:

Within 20 years of working on motorcycles (the last 12 professionally) I never had a regulator / rectifier malfunctioning except an old selen plate model on a Black Bomber and a similar piece of shite on an also otherwise very sorry Duc 350 twin. The modern 3 phase rectifier / regulator units usually don't break.

Alternator coil problems are relatively common on older bikes (10 years+) and seem to happen more often on "vibey" bikes as mechanical stress is a contributing factor to break the insulation of the coil. The problem can also occur on fairly new bikes (in my case a KLR 650, 1 year / 15000 km) The symptoms were identical to your bike.

Frank Warner 25 Oct 2006 00:54

Rec/reg failures.

Originally Posted by lecap
Regulator / rectifier:

Within 20 years of working on motorcycles (the last 12 professionally) I never had a regulator / rectifier malfunctioning except an old selen plate model on a Black Bomber and a similar piece of shite on an also otherwise very sorry Duc 350 twin. The modern 3 phase rectifier / regulator units usually don't break.

You have never seen a VFR then .. they do the rec/reg all the time!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!! !!!!!! Do a web search ..

And it is fairly common on ducks too....

I've had two fail on a honda 250 twin ... personal experience.

------------------- Techincal - One of the three SCRs in the Rec/reg fail short circuit ... usual cause is a 'hot spot' in the junction ...

simmo 28 Oct 2006 21:09

An update...well the stator windings in the alternator have checked out OK. The regulator rectifier had failed. A new one has been put in and I am now getting a between 13 and a heady 14 volts at the battery with the bike running. Stopped the Battery is steady at 12.7 volts.

Pleased with the result I then set out for a ride expecting my back firing to have vanished and Ducati ownership to be one of reliability and noise...well umm..should have known better....

I still have the problem..as it is occuring on both cylinders I doubt it is a coil, lead or plug cap. Having two fail at the same time seems unlikely unless the failed reg/rec has damaged them both.

Another check of the plugs revealed carbon deposits which brings me back to poor ignition or an overly rich mixture.

I will have a play with the needle and urrg float settings and see if that makes a significant diferrence and change the leads and caps.

The bike runs fine at idle and when its not under load, all farts and bother on 3/4 to full throttle...screams main jet doesn't it?

cheers and thanks for your help guys its been very helpful even if I haven't solved the problem yet.

simmo 29 Oct 2006 15:04

Well, I am going to have to do plug reading lessons...The bikes electrics are fine and the black carbon on the plugs wasn't on the electrodes, they were very clean this time around almost no staining at all, combined with flaming backfires a guru supected the bike was way to lean.

Taping up one of the snorkles on the airbox proved this to be a reasonable assumption as the thing went significantly better.

Next step is to take the tops of the carbs and raise the needles to richen up the mixture and begin to enjoy this thing.

Exactly why this worked so well when you would think carbs would suck what air they needed and the mixing would take place inside them... completely escapes me..

looks like mysterious backfiring and rough running was at least two problems with potentially similar effects..tomorrow we should have the second and last sorted...

fatboyfraser 1 Dec 2006 09:50

Italian reliability; an oxymoron?
Now I’m just going for a wild stab in the dark here but there’s no chance that the choke could be stuck on is there?
I just hope that its sorted in time for me to play with it at Christmas ;)

simmo 6 Dec 2006 16:31

Got me to work today smarty pants!

fatboyfraser 8 Dec 2006 03:09

When they said that 24 hours of reliability was something only the Japanese could manage they didn't know what they were talking about :)

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