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Charging Problems (did read the faq's)

Yes, sorry I forgot to mention that...the first thing I do on the Guzzi when there is an electrical problem is pull the spade terminals, clean them and reassemble with some sort of lubricant. Then I always check the fuse contacts, well actually I do the fuse contacts first. In 25 years of ownership I think I can safely say that this is the first problem I've had which has really got me puzzled.
I have cut off and resoldered the spade terminal on the G1 wire into the rectifier, I suppose the next thing is to work my way round the other wires in that circuit...cutting and resoldering spade terminals...but first....does the 1.2w bulb limit the current flowing in the G1 blue wire when the engine is not turning over??
 
levoz said:
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 this was done with the engine running logically the charging system should be working ..... normal right?

levoz said:
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?

The bulbs should light up when you have ignition without engine running and its normal not to have voltage to the brushes because its the 3 yellow wires rectified that will give you the + voltage.(G1)
For this the engine has to be spinning. (Stator)

Another continuity to check is between the blue wire from the rectifier or the alternator labeled (T)
and the yellow wire one by one with an ohm meter.
Should be shorted (Almost 0 ohms) ..... and not to ground

These windings have to be a very low resistance for to generate a voltage with enough current to supply the 3.5 ohms field winding.

Edit: Stator example for LM3 Bosch 0 120 340 002, 105mm, 0.6 Ohm with Y, 14V, 20A.... otherwords its able to drive a 20 amp load when it spins and gives out 14V.
That 14v output is (G1) that feeds the regulator and in turn feeds back to the 3.5 ohm rotor. (While spinning of course)
 
I have rechecked resistance across (new) rotor slip rings and across yellow wires/T connection as per the previous post from Dan. Values seem to be in line with what you suggest. Still getting 12v at the DF brown wire terminal when disconnected going down to approx 1v when connected to the brushes. Charge light staying on rotor not being magnetised enough.
Is there a possibility that a poor connection in the ignition switch might affect the current in this circuit?
Everything else works fine, starts immediately all lights working perfectly...
 
The stator generates an AC voltage to the 3 yellow wires …3 phase voltage.
This AC voltage is “Rectified” by the 3 diodes on the Rectifier board that supply a positive voltage to (G1 and D+)
If DF is 12v when you do not have the brushes connected ….you should also have a 12v or higher on (G1 and D+)

If you connect the brushes and the voltage on DF goes to 1v …… check to see if G1 and D+ also drops to 1v or so.
- If G1 and D+ stays a 12v or higher the problem is the regulator under load cannot supply voltage (check connectors, ground wires or regulator itself)
- If G1 and D+ drops at the same time as DF the problem is either stator or the rectifier board (Diodes, connectors, ground)

Stator ……
The same above test can be done to the 3 yellow wires one by one.
Check the voltage per yellow wires before connecting the brush and after
Depending how accurate / sophisticated your multimeter (voltmeter) is …. …… (its a high frequency AC voltage) and if you see it drop also it is definitely the stator that can’t supply the current. (connectors, ground wire or ultimately the stator)

Hope this can help

Edit:
Forgot to answer the question :blush: Is there a possibility that a poor connection in the ignition switch might affect the current in this circuit?
The wire to the ignition is on a separate connector from the rectifier board directly to the battery,
That connection is also what charges the battery ... when the stator give out full voltage 14V. (Other accessories wouldn't work)
 
Is there a possibility that a poor connection in the ignition switch might affect the current in this circuit?
Everything else works fine, starts immediately all lights working perfectly...

Levoz I think john might have already given you the answer to this ;)
Yes you can get 12V without a load, then when you put demand on it drops away.
As a test try to run a brake or indicator light globe off the main switch ...hook it up direct off the end of your brown brush lead...if it wont light up you have a definite answer.
You could try to run a new wire from the charge light through to the regulator take off (G1?) point. in fact if you use this jump wire to check all the various wire sections in the circuit. It's quite likely it is just a bad wire and not the switch as you say once you get it charging the lights are working etc etc

These older keyed main/ignition switches can get a bit reluctant to run a decent amount of current.

The main switch is a little bit fiddly to pull apart but I've done two of them over the years and the result is great tho' I always run everything through a relay nowadays as that way you are only running a small amount of current (enough to trigger the relay)through the main switch.
 
Thanks again to all of you for your suggestions.
I have tried applying a load by connecting a bulb across various circuits and I found this very useful, however it has not solved my problem.

I am certain there is nothing wrong with the regulator. All diodes and earths in rectifier appear to be working correctly.

What is puzzling me, in spite of everything that has been said here, is amount of current flow in the blue G1 wire and from there through the red wire via the regulator to the brown wire to the the DF terminal.

I am talking here about the current flow when the engine is stopped. As I have said before when the DF terminal is disconnected I get a reading of 12v. When it is connected to the brush the voltage falls to 1volt (engine stopped). If I connect a 5w bulb to the end of the brown DF wire (instead) of the brush the same thing happens, there is not enough current to light a 5w bulb. This is entirely logical - when the engine is stopped, the blue wire leading from the generator bulb to the G1 terminal is acting as an earth, that is why the gen bulb lights when the engine is stopped. It is effectively being earthed through the brushes. The red wire leading to the gen (and oil and neutral) is the live circuit - so if I connect a 5w bulb across the live (red) side of the gen bulb and earth it, then the 5W bulb lights up. If, however I connect it across the blue (G1) side then it does not light because this is effectively the earth side of a 1.4w circuit, so it seems to me that the maximum amount of current flowing through the G1 circuit is minimal (engine stopped). There is a 12v potential difference when you disconnect the DF wire because the circuit is no longer complete but once you connect up the brush (engine stopped) that pd disappears from the earth side of the circuit.

Do any of you get 12v DC measured between the DF brush and earth when the engine is stopped (ignition on DF wire connected)...I can't see how you can?
 
Having my LM3 in parts I was able to measure the voltages.
Measured the battery at 12.07v

When the engine is stopped, in normal situation with the DF wire connected to the rotor, DF should be 0.6v or so and the battery charging idiot light should be “on” …… the reason is that a continuity is present between the 12v from the fuse#3…. through the battery idiot light to (G1 or D+ at 1.48v) ….. through the voltage regulator (DF at 0.62v) ….. going through the 3.5 ohm to ground of the rotor.

When the engine is stopped and the DF wire is removed, DF should be 10.7v or so and the battery charging idiot light should be “off” ….. the reason is that NO continuity is present …..”floating voltage” …. coming from the fuse#3 …..through the battery idiot light to (G1 or D+ at 10.93v) ….. through the voltage regulator (DF at 10.7v) ….. and NOT going to any ground.
 
Thanks very much for doing that Daniel.
That has cleared up my suspicion that there was in fact nothing wrong with the gen light/G1/DF circuit. I thought there was because I have (here) about the fact that there should be 12v at the brushes and that there should be a strong static magnetic field.

Your values are very similar to the results I am getting. I thought that the voltage at my DF terminal was supposed to be 12v when the engine was stopped and that the fault with mine was that it was unable to generate a magnetic field because of the low (less than 1volt static ) value at the brushes. I will have to start looking elsewhere for the fault.
The fact remains that when the thing is static, the magnetic field at the rotor is very weak, certainly not enough to make an allen bolt stick to it.

What I am also puzzled about is if I attach a 12v positive lead directly to the DF terminal and start it up then the whole thing works properly. I mean by this that I can measure 13+ v AC across the yellow leads and there is a very strong field at the rotor when static. Surely if there was a fault in the stator I would not get the 13+v AC?
 
levoz said:
What I am also puzzled about is if I attach a 12v positive lead directly to the DF terminal and start it up then the whole thing works properly. I mean by this that I can measure 13+ v AC across the yellow leads and there is a very strong field at the rotor when static. Surely if there was a fault in the stator I would not get the 13+v AC?

When you do attach the 12v directly to the DF wire (field of the rotor) you are inducing more current and producing a larger magnetic field on the rotor windings therefore when the rotor is spinning inside the stator the “flux” being sliced is larger generating a greater transfer of magnetic field on the stator ….. in turn producing a voltage on (G1 or D+).

The 0.62v DF from the VR with the 3.5 ohm load should be enough to create a small current (going to ground) to produce a magnetic field on the rotor.
Note: The current is limited by the idiot light 1.2w and the VR circuit impedance. (Calculated and measured is approx 0.1 to 0.2 amps)......(And any bad contacts between these points)

As John mentioned....clean and re-assemble all those connectors? 12 volts will flow through a "dirty" connector, but you may not get the amperage you need
Or Kym's comment ….. the ignition switch may not be making a good contact!

When the rotor spins (with 0.1amps of field current) this change in magnetic field should be enough to start generating voltage on the stator windings to (G1, D+) faster you spin more voltage is generated.
The voltage output is governed by the amount of current in the field, and is controlled by the Voltage Regulator.

Edit: Just a comment .... placing 12V from the battery on the field windings directly (DF) may damage the 3.5 ohm winding .... your drawing 3.4 amps from a battery that can supply +100amps or so. :pinch:
 
hi
I've had several charging problems over the years and found that most of my problems have been earth(ground) related. it might be worth just double checking these. I now add earth wires to nearly everything which I think helps.
failing that just go back to the basics and work methodically through the system.
sounds a bit obvious but sometimes it works.

Hope you get sorted soon.
 
I just signed up for the forum after finding this string on the web. I fitted a new rotor and voltage controller after my 76 850-T3 let me down one night. When I ran the bike I was only getting 11.56v no matter the revs.

I found and followed Jono's comment about touching the DF with a wire from battery +ve. Afterwards I started the bike and low and behold 13+ volts at about 3500 rpm where I couldn't get better than 12.5v no matter the revs on the old rotor.

Thanks guys you saved what little hair I have left. I hope the original poster managed to get things sorted out.
 
I also have a 1975 T3. I kept on having problems with the Bosch alternator which is, after all, 44 years old. I replaced it with one of these. I have had no problems since
It arrived in New Zealand in just over a week from England and was very easy to fit. Being hidden under covers it is invisible from the outside so nobody knows. It was worth every cent spent!

Google Gutsibits.

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