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Testing Bosch Charge circuit

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Brian UK View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Brian UK Quote  Post ReplyReply Direct Link To This Post Posted: 12 Apr 2017 at 22:32
Are you able to check diodes with a resistance meter? There are 9 diodes in the rectifier, six big ones in pairs for the three phases, and another 3 small ones to provide the current for the rotor. If one of those goes down, the light will stay on faintly as the output won't balance the battery.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Dave P. Quote  Post ReplyReply Direct Link To This Post Posted: 13 Apr 2017 at 08:15
I've mentioned this before in another thread but it's worth a mention again.Twice I have had a problem with the Bosch charging system, once on a Spada and once on an R80RT.The light stayed on, though a little dimmer than with engine stopped.In both cases, I'd lost a phase.One of the three rigid wires which are soldered to the connector for the harness, had become disconnected, but it wasn't obvious 'till I gave them a wobble.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Jerry atric Quote  Post ReplyReply Direct Link To This Post Posted: 13 Apr 2017 at 08:42
I ve just realised that I'm reading my meter wrong! Resistance check on the probes reads 0.1 and acros the slip rings 0.4, NOT 4 ohms as I had thought
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Jerry atric Quote  Post ReplyReply Direct Link To This Post Posted: 20 Apr 2017 at 20:40
Ordered a new rotor from Gutsibits who rather unhelpfully sent me a Le mans breather box instead just in time to spend the Easter holiday twiddling me thumbs. I have now fitted the new rotor. Comparing it to the old one, the old one is shot... but the warning light is still on I did the reg check and that seems OK, started the rectifier checks, they seem to say its duff but not convinced I'm doing them correctly. Guzziology is a bit vague on these checks.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Ken-Guzzibear Quote  Post ReplyReply Direct Link To This Post Posted: 21 Apr 2017 at 13:47
variable reg or German rectifier is well worth the cost from Towzatronics good advice quick service
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Jerry atric Quote  Post ReplyReply Direct Link To This Post Posted: 21 Apr 2017 at 17:16
Thanks fro that, I Just checked their website but they dont list a rectifier, just the reg. M&P on Ebay have a combined rectifier and regulator. I wonder if thats better than buying separates.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Mike H Quote  Post ReplyReply Direct Link To This Post Posted: 21 Apr 2017 at 18:10
Have you tested the diodes - NB preferably needs diode test function of a DMM...

To recap -

New brushes, yes?

Regulator earth now OK, yes? (Which I think won't affect current symptoms)

Have you checked all wires are OK and connectors OK, no corrosion or loose connections?

NB: rotor winding is 3.4 Ohms from memory; between any pair of stator terminals (3 off) is very low like 0.1 Ohms.

HOWEVER I'm sure I've mentioned before, it is typically VERY difficult to measure low resistance values accurately because surface resistance of connectors and even the probes will add to the measured value.

Ideally needs a DMM for best accuracy (moving needle meters usually have a zero adjuster, which first has to be calibrated by holding the probes together for EVERY Ohms range you want to use).

A friend of mine who is a electronics tech for a cancer charity says meter probes should be sharpened like needles, then they can penetrate surface oxidation and get a better contact on the surface and hence a more accurate reading.

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Mike H View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Mike H Quote  Post ReplyReply Direct Link To This Post Posted: 21 Apr 2017 at 18:13
PS: charge light on dash is a bulb not an LED?

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Post Options Post Options   Thanks (0) Thanks(0)   Quote Jerry atric Quote  Post ReplyReply Direct Link To This Post Posted: 21 Apr 2017 at 19:24
Thanks Mike. New brushes, all earths reading about 0.1 - 0.2. (I got a DMM from Screwfix in the end) All the other static tests seem to read as they should. I checked the rectifier readings tonight against Guzziology and they seem to be all over the place. I presume these are meant to be done with all the wires except battery connected? . If the rectifier is shot it seems a bit of a coincidence that it and the rotor should go at the same time. The charge light is the original.
An electrician mate is coming over next week to have a look so I think I had better hang on til then, I'm worried about doing more harm than good with the engine running tests. I guess 40 years for all this stuff isn't bad, perhaps i should change everything!
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Mike H Quote  Post ReplyReply Direct Link To This Post Posted: 21 Apr 2017 at 19:44
Rectifier has to be completely disconnected from everything else before testing individual diodes will make any sense.

How does Guzziology describe how to do it? Ohms (resistance range) test or other? This is why I mentioned diode test function, it's especially for diodes.



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Post Options Post Options   Thanks (0) Thanks(0)   Quote Jerry atric Quote  Post ReplyReply Direct Link To This Post Posted: 21 Apr 2017 at 20:17
He connects a probe to one terminal and the other probe to each other terminal one at a time and reads resistance . Repeat for every terminal. They include readings to earth which made me think it has to be wired in to the loom.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Brian UK Quote  Post ReplyReply Direct Link To This Post Posted: 22 Apr 2017 at 09:28
A diode is just a one way switch so very simple to test with any meter with a resistance function. It should be high resistance one way and low the other.
With a new rotor you sometime have to flash them to put in some residual magnetism.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Mike H Quote  Post ReplyReply Direct Link To This Post Posted: 22 Apr 2017 at 16:55
Yes forgot about that.

That's a wire between battery positive and the terminal for the 'live' rotor brush. Make sure you select the right one! (As the other is earthed!)

Could be a 100 Ohms resistor might do it too.

When I had a solid-state reg on mine I had to permanently install such a resistor to connect from a source from the ignition switch, to the reg input, else reg wouldn't power up and start working.



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Mike H View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Mike H Quote  Post ReplyReply Direct Link To This Post Posted: 22 Apr 2017 at 17:11
Originally posted by Jerry atric Jerry atric wrote:

He connects a probe to one terminal and the other probe to each other terminal one at a time and reads resistance . Repeat for every terminal. They include readings to earth which made me think it has to be wired in to the loom.


OK, well the rectifier negative output will be connected to earth, so I read that as, rectifier negative terminal! Big smile

Personally I would test each diode individually, probes across its pins one way, then the opposite way, this should work because the other diodes will block the current getting past by other routes, unless of course there is a short-circuit where one shouldn't be.


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Post Options Post Options   Thanks (0) Thanks(0)   Quote Jerry atric Quote  Post ReplyReply Direct Link To This Post Posted: 27 Apr 2017 at 18:04
Sorted. It was the regulator. However, the brushes were shorting due to carbon build up and a small crack in the brush holder. Thank you to all who offered advice, I have a question though: resistance between the two rotor rings should be about 3.5 ohms according to all the literature. This new rotor measured that when I got it but now measures 2.5 ohms. Will this make any difference to the charging? Any answers much appreciated, thanks.
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