Bosch alternator repair

I have a '72 R75/5. It had an old mechanical reg (still excited field type - same as used in most cars and your RS)

I replaced it with a solid state one I found/adapted from an auto manual. Two transistors, 5 fixed resistors, one variable (so I can set the limit) one zener diode and a couple of rectifier diodes.

I'm not aware of anyone marketing a TO3 style regulator for lead acid batteries but I seem to remember GM alternators had one that fit on the brush housing (so it would be three connections, ala TO-3)

My homemade one uses four wires - one to ignition (but it works with that tied to the alternator output - used it on a Toyota Land Cruiser in that mode), one to ground, one to the alternator diodes (diode board in the R75 with a set of 3 diodes that only fed the regulator), and an wire for the slip rings.

My bike has a "charge" indicating lamp on it. When the alternator is just starting - the current to excite the field comes through the idiot light - when the alternator is spinning, and generating voltage, the power for the slip rings comes from the diodes, turning the idiot light off.

I can supply the schematic of what I used.. You'd need a modicum of electronics knowledge (ability to observe polarity of the diodes, connect the semiconductors, solder and package it (no heat sink necessary if you use a TO-3 or TO-220 or TO-66 or similar transistor for the output. I used a pair of 2N3054 transistors and heat-sinked the pass transistor - but it never got mildly warm.

Mine has worked since 1973 - the transistors are exposed and I've been varnishing them to slow the rust. I have a 81 Honda 750 and it uses the same type alternator - I rewound the rotor when it shorted - that's a lot harder than building a simple regulator.

I can scan and send the schematic if you want to try building one, remove capital Xs and treat like an email ady.

XganethX(at)movemail(dot)com

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I also would like a scan of schematic if you would. Can send direct to hiviewNOSPAM@ bresnan.net Of course leave out the no spam TIA Warren

I suggest you ask this question on sci.electronics.design.

They will design a new one for you...

Mark

Are you in England? If you were in the states, I'd suggest calling National Automotive Lines in Shelbyville, Indiana. They do not have a website. They sell car parts, but the link you provided suggests that the brush-regulator assembly is used in a variety of automotive alternators, not just bike regulators.

The toll-free number is 1-800-428-4300. The toll-free fax number is

1-888-442-9222. It's a great outfit to do business with.

Have you looked online? Volvo and Saab both use a very similar Bosch alternator with the onboard regulator, the last time I needed one it was only about $30 online though the dealer charges around $170.

If it's a modular unit it's a simple matter of buying a new one. Usually around 20-30 bucks US.(unless you purchase direct from the dealer then of course it may cost more.)

Hi...

Your use of the word "chap" leads me to believe you're probably somewhere in the UK, so don't know how helpful this might be.... but...

Here we can buy rebuild kits for virtually any alternator for about 20 dollars cdn. They come with everything, the regulator of course, as well as new brushes, springs, bearings, etc.

Our most "famous" source is Canadian Tire, perhaps you have something equivalent over there?

Take care.

Ken

I have english background, but I live in the States. I have checked Kragen's and the part retails for $110. Amazing as I bought a whole rebuit alternator for my experimental plane for $20 (with core). Probably some generic american brand would be quite cheaper. I can get the actual BMW part for $85 so I will probably just do that vs run around on an experiment I soldered together. A new BMW alternator costs $575, talk about bending over.

Check out

it crosses to the same site I get Volvo and Saab parts from. I don't know what model your BMW is but they list the same Bosch regulator/brushpack that many other European cars use and it's $26 aftermarket or $44 OEM. That place has great service too, I've ordered items several times and had them show up within 48 hours with standard shipping.

Not that it's relevant, but I used to own a BMW, a 1970 1600. I eventually installed a Bosch alternator from an Opel in the BMW. The only difference was in the mounting ears on the exterior of the alternator. The internals were identical.

I suspect that interchangeability is still the rule, and that if you order the Bosch alternator as a Volkswagen part or an Opel part, for example, you will pay less for it than you would had you ordered from the BMW dealer.

Or get an exchange unit from a Bosch dealer. Or indeed an exchange unit from any reputable source.

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    Dave Plowman        dave@davenoise.co.uk           London SW
                  To e-mail, change noise into sound.

Try any import parts dealer for an aftermarket. Beck/Arnley specializes in high quality aftermarket electronic/electrics for imports. In the US there is also Standard electrics who manufactures all sorts of crossable aftermarket part for auto electrics. You can usually get Standard brand at NAPA or any good speed shop. Bosch also should have that component, I've used Bosch parts in alot of the competitive racers I helped build.(I especially liked their "blue coils" and the adjustable brain boxes they offered. very easy to adjust top performance and super tough.)

If you can find an old part man who really knows his stuff he'll most likely have a cross-parts manual, something that's very hard to come by. I had a fellow who had a cross manual for all things British/Italian to Most American electrics.( Used him alot to clean out all the bad electrics that came on British cars. When I'd finished that MG or Jaguar would be running on a Ford/autolite altenator/regulator and a good marine grade all copper wiring harness.)

NEVER buy from the dealer. Go to any decent import parts store and get the beck/Arnley aftermarket part. Or Bosch.

;-) What problems did you have with the actual wire?

Lucas got the blame for the poor quality components but in reality it was the penny pinching car makers demanding the lowest prices. The original Jaguar company being notorious for this. If Lucas didn't make them down to their price they'd have bought elsewhere. But Lucas also made very high quality stuff for Rolls Royce - and of course aerospace work. Funnily the vehicle which sticks in my mind with the very worst electrics I've owned was a small Bedford van - made by GM in the UK. With mainly Delco electrics. It was a miracle to have all the basic stuff working at any one time...

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    Dave Plowman        dave@davenoise.co.uk           London SW
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Re: the Lucas to Autolite conversion.

If the OP can find a way to adapt a GM three-wire alternator to his BMW bike, he will never have to worry about finding Bosch alternator parts again. That's a bit of a modification though, I suspect.

Three wire alternators are usually just a battery sensing device so not difficult to modify the wiring for - unless I've got it wrong?

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    Dave Plowman        dave@davenoise.co.uk           London SW
                  To e-mail, change noise into sound.

He's referring to the old style with a 3 wire cable going to an external regulator. Bosch made those too, but when I encounter them I usually swap to the later style alternator with an onboard regulator, one less cable stringing around the engine bay.

Well... GM electronics have allways been notoriously bad. Had a brother in law who was a designer for Delco at one time and later Packard electric. He was always complaining about GM and how crappy they could be in regards to design standards.

As for the Lucas wiring harnesses, aluminum wire and incredibly cheap grade vinyl insulation. Or have you never seen a TR4 that'd gone up in smoke from harness fire? In the very last years of production at British Leyland that damn aluminum wire would find it's way into just about everything they rolled off the line. And what with the poorly designed electronics in the late models any resistance load variances over the harness could make for some very wonky functions. Never have liked anything turned out by Lucas. ( I'd have a constant stream of customers who'd need new rectifiers for their Lucas altenators. Those things tended to burn out every few months or so and many customers insisted on keeping their British import authentic. Even when I tried to tell then that not all MG's had Lucas under the hood and that it'd be ok to replace with more reliable electrics. Take for example the v8 mgb's with the 3.2 litre v8 from buick. Very rare state side but very popular back across the pond. All quality Delco, at least compared to what Lucas stuck in 'em.)

I've had countless cars with Lucas electrics dating back to the early '50s and never ever come across aluminium cable. I still own an '85 SD1 Rover.

Why they should have used this stuff for export defeats me.

Aluminium household wire was around for a very short time when there was the copper crisis in the UK caused by UDI in Rhoadesia -the UK main supplier.

IMHO electrical fires in older UK cars was caused by inadequate individual fusing of circuits - indeed those most likely to be accident damaged like the lighting ones had often no fusing at all. But the cable was pretty well common to all cars - in the UK at least. I'll do some more research.

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    Dave Plowman        dave@davenoise.co.uk           London SW
                  To e-mail, change noise into sound.