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Charging Problems (did read the faq's)

levoz

Just got it firing!
Joined
Apr 26, 2011
Messages
11
I have a 1975 850 T3 which I have owned for 25 +years. I thought I knew my way round it pretty well but have encountered a charging problem which I can't seem to sort out. Here is what I have checked so far:
Note I am using a decent meter (one of those one with a reference cell in it)...
Battery is good and holds it's charge.
Charge light is working correctly when used with the Bosch rectifier but is staying on when revs are increased.
resistance across slip rings seems to be correct (used the value in the Haynes manual) definitely not infinite!
Resistance across the 3 yellow wires seems to be approx correct as in Haynes manual
I know that one of the diodes on my rectifier went a few years ago (20!!) and I replaced it and the thing seems to have worked reasonably well since then.
This time round I Initially tried replacing the rectifier with a used Newtronics unit bought off e bay. No difference with this except that the idiot light does not function but in both cases (Bosch and Newtronics) I can only detect a very small AC output across the yellow wires when the engine is running..
Both the Newtronics and the original Bosch unit give the same symptoms ie that I cannot measure 12 volts across the slip rings when the ignition is switched on and then engine is stationary and also that I can only measure a very small AC voltage with the engine running.

Surely I should be able to detect 12 v DC at the terminal where the brush is labelled DF (brown wire) and also at the blue stator connection before the thing will start to produce 12-14V AC across the yellow wires.
I have checked the red current carrying wire from the ignition switch and can measure 12 v at the input to the voltage regulator with the ignition on and obviously also at the rectifier.

So...why is there no 12v at the alternator (+) brush terminal (brown wire)...is this a regulator fault? How can I test it?
Any help gratefully appreciated.
 
I too have a T3. Nine times out of 10 on these old Guzzis with the Bosch charging system its the alternator rotor, the wires get fried. If I recall correctly the resistance across the slip rings with the brushes raised goes infinite, at which point no amount of reving will get you any more voltage than what is already in the battery. Since your charging light clearly works, that is not the fault. Believe it or not, if the bulb blows on these old bikes they can't charge. Not sure what to make of the idiot light not working with the used Newtronics rectifier, that may or may not mean something. I would probably reinstall the Bosch, perhaps test the diodes first, though I hear they sometimes test good even when bad. No doubt there are threads here & at other sites about how to go about checking things. If you don't already, you should really, really pick up a copy of Guzziology which will aid you in so many ways on so many subjects, well worth many times its cost. In the 165k miles & 33 years I've had my T3, I've replaced the rectifier once, voltage regulator once, had an issue with the charging light bulb socket once, & replaced the rotor maybe 4-5 times. In fact I installed a voltmeter so the next time it takes a dump I know to shut off my headlight, so I can get up to 200 miles before I have to recharge the battery or start walking if I'm on the road & have to. Most likely you will have to rewind the rotor at your local automotive charging shop, or replace it from a number of sources. I've run in to a number of Guzzi folk on the road over the years with charging issues, & like I said if its the Bosch system, it way more often than not turns out to be the rotor.
 
thanks for that Bob. I did read your previous posts on the LeMans charging issues. However, the resistance readings across the slip rings are near enough what it says in the Haynes manual as are the readings across the yellow wires which would surely rule out the rotor?.
:( Also, surely a knackered rotor would not explain why there is no DC input voltage to any part of the alternator.....
 
The yellow wires have nothing to do with the rotor. They are the pickups for AC voltage from the stator to go to the rectifier. It sounds like the voltage regulator has failed. The Bosch system controlls output by controlling volatage supplied to the rotor. If you have the old mechanical type, you can remove the cover and dress up the contacts. You can even increase the output voltage a little by bending the tab down so it takes more magnetic pull to open the charging contacts. It is possible to jump the regulator at the plug, but it has been many years since I worked on a Bosch system and can't remember which two connections at the plug should be jumped. One will be B+, the other is the lead to the rotor. You can probably use your meter to figure out which is the rotor lead.
Good luck,
 
thanks for that John...that sounds like my kind of repair...maybe I will even fork out for a new regulator.

While we are discussing this, does anyone know how to wire up the system so that I can use the Newtronics component and, since that is an integrated regulator/rectifier, bypass the regulator but still get a live feed to the alternator?
 
The regulator earths, (The black wire from the three pin connector.) with a little loop that bolts to the, by now inevitably rusty, framework to which the reg is mounted. It in turn is bolted to the frame by several other by now rusty bolts. with out a decent earth refference the Reg can't work.

Pull the earth spade out of the block and insert another wire with a spade on it but long enough that the other end can be connected directly to the battery's negative terminal and see if that improves things.

If it doesn't? Toss the reg and use a Bosch RE55/56 or 57. 55 has two pins and earths through the case (Add an extra earth direct to the battery.), either the 56 or 57 has three pins and one of the last two has a resistor hanging off the bottom that if you snip it off will give you an extra volt.

Pete
 
Googled Newtronic and took a quick look, and suspect that it is useless with the Bosch system. I think it' intended for systems with permanent magnet rotors and simply dumps unused current to ground, dissipating the energy as heat. In older Guzzi's with bosch alternators, the regulator (is supposed to) vary the current to the field winding on the rotor to hold the voltage constant. Once generating, the field circuit is fed from a set of three smaller exciter diodes on the rectifier board. The only battery current available to the field comes through the alternator warning light when the ignition is on and the alternator isn't charging. The field winding should read 3.5 ohms through the slip rings with brushes disconnected. Some old ones were 7 ohms. It all sorta points to a bad regulator or rectifier board. One thing to try is to monitor the battery volts with a meter, and jumper 12V straight to the hot side rotor brush. If the voltage starts rising when you rev the engine, the rotor and stator are probably OK.
 
Thanks to all of you for your suggestions.....I have now replaced all three major components and am at my wits' end:
Replacement (used but good) bosch rectifier...no change
New voltage regulator (Bosch) ....no change
New Rotor...no change
Brushes are good

Charge light is still staying on and measuring voltage across battery terminals still shows :S no voltage increase when the engine is revvved.

I've seen some things here about 'flashing' the rotor via the DF brush but I'm not sure what this will achieve...

Apart from measuring resistance across slip rings and the yellow AC connectors, what voltages should I be able to detect when the ignition is on (engine not running) at the following points:
The brown wire at the DF terminal of the alternator
The blue wire which connects to the coils on the stator
There is no measurable DC voltage at the blue wire where it outputs from the rectifier (this is the one that connects to the stator)...should there be a voltage here?
Any suggestions gatefully appreciated... :S
 
As for "flashing" that is only when installing a new voltage regulator for a generator. Not a technique for alternators as the rectifier takes care of correct current flow.

At this point about the only thing you haven't checked is the continuity of all your wires. You may have an open circuit.
 
You know you have to have 12V at the brushes, right? Follow that wire backwards until you find the reason it doesn't have 12V.
 
With reference to the charging light when used with the rectifier but stays on when revs are increased ........

The 3 yellow wires, from the generator, generates an AC voltage going to the rectifier board ...... when revving the engine the diodes convert this voltage to +DC (identified as G1on the schematic) wire going to one connector (terminal) of the idiot light.
The light has already a + voltage on the other connector (terminal) coming from a fuse.

When you turn on the ignition ….without running the engine does the generator light come on?
If off the fuse may be blown …..because no voltage is present on one side of the connector (idiot light).
If on the fuse is good ….. you should have a 12v on one side of the idiot light terminal. (With respect to ground)

When you run the engine (idle) the DC voltage from the rectifier board (G1) should increase …. Not the same potential voltage as coming from the fuse (Battery) but should not be 0 volts. (Measured always with one lead of voltmeter to ground)
The light should be "on" because you still have a difference in voltage between both terminals. (of the light bulb)

When you rev the engine the rectifier’s job is to give more of a + DC voltage on (G1) wire going to the bulb ..… doing so the voltage difference between the light bulb terminals will decrease turning off the light.

Hope this helps ......
 
Dan,

What would be the ground path for the idiot light if the fuse is blown? In normal operation the ground path is though the rectifier. When the system is charging, there is 12 VDC on both contacts so the bulb goes out. If the fuse is blown, all you have is an open circuit and no light at all.
 
john zibell said:
What would be the ground path for the idiot light if the fuse is blown?
If the fuse is blown, all you have is an open circuit and no light at all.

With reference to the circuit diagram
http://www.thisoldtractor.com/guzzi007/schematics/1974_850T_USA.gif
or any other diagram for that matter..... :lol:
Pin 12 of the 15 pin connector ..... goes to the fuse#3 but fuse #3 also supplies voltage to the Light switch (dimmer, city light, parking light)

So depending where the light switch position is located the bulbs are a source to ground.
Edit: Forgot to add ... definite ground source through the bulb when in neutral and probable ground source (bulb) if oil pressure switch is defective.

So to answer your question .... Yes ......if you had the fuse blown and that fuse was suppling ONLY that idiot light you'd have is an open circuit and no light at all. (But not in this case)
 
Armed with a new rotor, a new old rectifier and a new Bosch voltage regulator I have narrowed it down to the 12v feed to the DF brush. If I disconnect this wire and put a voltmeter across it, it shows 12v DC when the ignition is on. However if I connect it to the DF terminal on the alternator it does not produce sufficient current to energise the rotor (if that is the right word) ie generate a decent magnetic field. The 12v signal disappears when I connect the brown wire to the brush.
If I replace the DF feed with a direct connection to the battery positive terminal, the rotor becomes strongly magnetised and if I start the engine up like this, the charge system works properly, ie the charge light goes out and I can measure 13 plus volts AC across the yellow wires (dependent on revs).

So, why so little current in the brown DF wire? It is measurable as 12v DC but is not enough to magnetise the rotor,
Presumably the current in this wire comes from the blue charge light circuit wire which feeds the red output wire at the rectifier...this goes to the voltage regulator and the brown DF wire. I have replaced the voltage regulator and I have also tried bypassing the regulator (ie connecting together the red and brown VR wires) to see if that makes any difference...no to both
I have taken all the instrument panel (charge light circuit) bulbs and connections out and checked them...no apparent problems there.
any more ideas :blink:
 
You have voltage but not enough current to magnetize. In that case I'd check every connector between the rotor and the 12 volt supply. There is a corroded connector/contact somewhere that is impeding current flow.
 
Touch a wire from your postive battery post to the DF field of your alternator, it will throw a tiny spark and thereafter work they way it should. That's what worked for me a couple weeks ago when I was in the same boat.
 
The battery is capable of giving a huge amount of current ..... whereas the voltage regulator limits the current all depending on the winding resistance.
(Guzziology) V7 and early 850T the impedance of the field windings are +/-6 ohms therefore draws +/-2 amps from the regulator. Later models 3.5 ohms draw 3.4 amps

The + voltage comes from the rectifier board (G1 and D+) supplying voltage to the regulator (connector D+).
When you rev the engine the D+ voltage should get higher.

If you disconnect the DF wire from the VR and measure on the terminal it should stay at 12v ..... it should to drive the field windings. (If it drops in voltage, when you connect it back, you may have a bad ground on the regulator or the field windings may have a short to ground).
 
Thanks for your suggestions again.
I have already tried "flashing" the DF terminal using a direct connection from the battery.

I have been exploring the possibility that there must be a poor connection somewhere upstream from the DF connection to the brushes.
Since I have just bought a new rotor, it must be one of the 3.5 ohm variety, however, surely the current in the DF connector to the brush at standstill must be limited by the 1.2w generator bulb ...?

I cannot find any problems with connectors upstream...the problem is difficult to deal with because I am getting 12v so measuring continuity is not going to show up the problem.
I have tried inserting direct 12v DC at various points and then monitoring the voltage at the brushes - for example if I insert a direct connection to a 12v battery at the (blue) rectifier feed G1, I can see that it gets through to the brushes. If I insert 12v dc further upstream, where the (blue G1)generator wire splits by the steering, again I can see that 12v is getting through to the brushes.

If I attach the same direct 12v feed to the other side of the generator bulb circuit, eg at fuse f3 or fuse f1, then the bulbs all light but there is no 12v showing at the brush...surely this means that current flowing to the brush is limited by the bulbs...or maybe the problem is in that side of the circuit?
 
Did you disconnect, clean and re-assemble all those connectors? 12 volts will flow through a "dirty" connector, but you may not get the amperage you need.
 
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