'67 911 with 55 amp Bosch Alternator overcharging

[red911]

Hello all,

I replaced the original 35 Amp Bosch alternator with a 55 Amp Bosch alternator.

Two years ago, the battery (Yellow Optima) discharged with both the headlights and wipers on for hours as we were driving to Maine. I got towed and purchased a battery charger at Wal*Mart. The car ran well the rest of the weekend. But, I did decide to see what the charging system was doing, so I sent the gauges to Palo Alto that winter (2012 - 2013) and had them put in LED gauge lights.

They installed a voltmeter and I also purchased a voltmeter for the cigarette lighter.

This year when I started up the car, at 3,000 RPM it charged at 18 V. So, I thought the Voltage Regulator failed, so I ordered another one from Zim's based upon posts here.

Today I installed the new VR for a '67 and it charged at 18 V too. The car has an MSD box that required some rewiring. As an aside, I have noted that the distributor cap is wearing prematurely as I only have 3,000 miles on the car since a total restoration. So this is two new VR and it is overcharging which will lead to a battery failure.

Do I need the variable VR from a later car to dial in the voltage? Is the 35 A VR not able to keep up with the 55 A alternator? Did the MSD box change the charging system, or what else should I review?

Thanks, Tom

[edmayo]

Did you order a V.R. for a 55 amp alt.? Is it a Bosch regulator? Is it one with a removable cover that can be removed for possible adjustment? What did you 'rewire'?

[red911]

Did you order a V.R. for a 55 amp alt.? Is it a Bosch regulator? Is it one with a removable cover that can be removed for possible adjustment? What did you 'rewire'?

Thanks Ed for your reply.

I did not find a VR for a 55 amp alternator, which is why I asked if an adjustable VR might work. Do you know of the Porsche Part number for the 55 amp Bosch Alternator, as I could not find it.

The rewiring was for the MSD box.

Tom

[1968DT]

Tom,

The P/N #'s are the following:

Voltage Regulator - Bosch,
Brand: Genuine Porsche
Part #: 901-603-206-02-OEM

Alternator - Bosch #0120 400 665 here's one on ebay...

The VR are not cheap, at least $200.00 for a new one. I paid $220.00 for one last year.

Dan

[304065]

Tom LOL you're running around like a Circle Track racer running off the battery only, then charging with 18V full field all the time.

You've got the wiring connected incorrectly I think. For some reason you are sending "full field" current to DF instead of the reduced current from D+/61 terminal.

Reviewing:

Connections at VR: Cannon plug into VR with DF, B+ and D- in the plug. Here is the pinout to verify:



And of course your B+ wire, red with white stripe, goes to the terminal block. Does yours have a broken fin?

All right that's on the console end. Do you know that if you disconnect the negative terminal if your battery so you don't kill yourself or burn the car down,,,,then remove two M6 self-tapping screws and one M6x12 threaded screw (at six o'clock position) and undo the clamp for the starboard heat tube,,,, you can stick your cell phone behind the alternator and snap a photo (put it in selfie mode) of the connections on the back of the alternator. That way you can see what you have without having to remove the alternator itself (which is time consuming).

Now, here's where it gets interesting. The difference between a 64-68 35A and a 69- 55A is the brush holder on the back and the wire harness. The early cars have an engine end with an M5 (8mm Across the Flats nut) D+/61 stud, a 1/4 (6.3mm) male faston for DF and a pair of M6 studs for D- and B+. The later ones combine the DF and D- into a white plastic cannon plug with the connections at right angles like this: (please forgive the sepia tone, I took this without a flash 10 years ago)



Now somehow you have +12V, like what's supposed to be on B+ (alternator output to battery) flowing to DF. I don't know how, but that is what is happening.

Take that Optima battery out in front of the neighbor kids, put on some safety goggles, tell the kids to stand back and hit it with a ten pound sledgehammer as hard as you can. AGM batteries like that require a 15V charging voltage to get started-- they are properly charged with off-board "interacter" battery chargers. "But the guys on the Pelican Board swear by them" yeah I've been hearing that for 15 years and also hearing about how occasionally some chap's Paris-Rhone burst into flames like a Tesla with a hangover when it tried to accomplish the 15V specified by Optima to begin charging. And those are the guys who completed project #69, windshield wiper reversal, "to move the wipers out of the driver's line of sight." Try a phone book to sit on instead. . . don't get me started.

Seriously now, a Group 51 or 51R (I'm forgetting which) lead- acid battery is more than adequate to turn over a two liter motor-- it can be charged by a VR with a 14.4V set-point will be fine.

For street use you do not need anything more than a Bosch Solid-State external VR. Bosch doesn't make these anymore, I think they are actually made by Transpo: the last one I ordered had no identifying marks of any kind on the case and looked exactly like the image I posted above with the yellow noise supression tape. Google up Transpo IB305, this is a solid state regulator with regulation in the B- circuit, 14.4v set-point. This will run you about $35.

There is no such thing in 2016 as a regulator for a different wattage-- it's all about the set-point in terms of voltage supplied to DF. In 1968 when Porsche introduced the Motorola alternator this became an issue, because the solid state buzz box regulators in those days were incompatible between brands. This is why the alternator decal all the way to the left is not present on my '66 or your '67, but is properly present on a '68-- because of the different alternators available. But in modern practice, the solid-state version as above is the best replacement.

Don't even get me started on what is right for concours. An original VR is right up there with an original muffler in terms of unobtanium.

Anyway sorry for the long-winded answer but I hope it helps. If you will post up here some good clear photos of (a) your connections at the electrical console and (b) the connections behind the alternator I'll do my level best to help you through this. But there is only one possible answer and that your alternator is running full-field, hence some connection somewhere must be sending +12V into the DF terminal.

Good luck!

[red911]

Thank you #304065,

Actually, your first quote on the circle track racer is close to home. I used to race a FV with a gutted generator and then I took off the fan belt for a few more horsepower too!

I appreciate your comments and here are the instructions that I used to hook up the 55 amp alternator, so that may be helpful diagnosing my issue, other than the Optima battery of course. I'll deal with that later.

Just put the wire as is on the B+ terminal.


On Mar 20, 2012, at 5:59 AM, Tom Gentz wrote:

Sorry to be such as pest, but there is only one red/white wire. My question was do I want to put a pigtail on the end to make two B+ wires, or can I keep the original single terminal wire going to B+?

-----Original Message----- From:XXXXX
Sent: Monday, March 19, 2012 9:04 PM
To: Tom Gentz
Subject: Re: Porsche 911, 55 Amp Bosch Alternator Wiring

If there two wires, then one on each.

On Mar 19, 2012, at 9:09 AM, Tom Gentz wrote:

Thank you,

Should I split the B+ (battery) and put it on both B+ terminals, or is hooking it up to one ok?

Tom

-----Original Message----- From:XXXXX
Sent: Monday, March 19, 2012 11:31 AM
To: Tom Gentz
Subject: Re: Porsche 911, 55 Amp Bosch Alternator Wiring

Hi Tom,

When viewing the alt. from the rear with brush holder toward the top, the two spade connectors will be 90 degrees apart. The upper spade is ground and the bottom goes to the DF of the regulator. The small
5 mm lug is the D+. The two 6 mm lugs are for the B+ (battery). The ground wire (brown) goes to any of the six alt. studs.

[red911]

Hello #304065,

I have a diagram, but I need your email to send it to you, unless there is a way to post a scanned image, which I have tried.

My email is: tbgentz@cox.net

Thanks in advance, Tom

[red911]

Hello all,

If indeed, I have DF and D- (ground) reversed, will that cause full voltage (18 V) to go to the battery?

I want to fix this today, but if I reverse those two connections, will the alternator and voltage regulator work in concert with each other?

Thanks, Tom

[red911]

Hello all,

I have posted two photos. Seems like I have everything wired correctly.

[red911]

second photo