BMW alternator output...mods?

Jon,
I wouldnt worry about the charging system. you have a 280W alt.
I have a'73 /5 dresser, with the R100RS engine and 280 W. I run a windjammer with 60 W hl, plus 2 sidelights, 2 saddlebags with 3 running lights each, a trunk on my rack with 2 running lights, plus the SC with tail/brake and 4 more running lights on rear, and a driving light in front.
also the standard bike tail light/brake light and turn signals.
Then I hook up my cargo trailer, with 2 more tail/ brake lights, and 6 more running lights.
I used the stock battery with this system for many years with no problems, even when I had the 750 engine and 180 W alt.
recently I removed the bike battery,and added a car battery in my right saddlebag, for more power at campgrounds to run camp lights ETC.
The alt charges the car battery fine with no additional help. I put a battery tender in place where the original battery went , but have not used it at all this summer. lot of low speed in-town stop and go riding..to PO, Bank, ETC, plus occaisional highway riding, no problems.

I've tought about the car battery addition but just haven't done it. Putting a battery tender where original battery goes is a good idea, too.
Haynes shows R100S to have 250w 18A alternator, the same for all 1000cc units. So, I guess I need to not watch the volt meter so much. But, if you add up the total amp draw as if all lights etc are on at the same time, the result should not exceed the amp output lest a voltage drop will occur and drain the battery. Maybe the car battery has enough reserve amps to compensate as compared to a little bike battery. I've got more lights to put on like you have so the car battery seems right. That EnduraLast alternator would be nice but it costs too much for me. Jon

Jon,
I ran the bike and all the lights with my /5 solo[no sidecar] for many years, with the stock 28 AH battery. what might help is putting a switch on all the extra lights like I have.
during the day all I have on is the bike headlight, and brake and signal lights working when necessary.
the bike tailight, SC tailights,trailer tail lights, all the running lights do not go on during the day..not needed then. At dusk I flip the switch on and the taillights, running lights and the SC driving light goes on.
Im not too much for night riding any way...just when I need to get home.

the car battery is a plus, giving you extra starting power , reserve if needed, and if you put it in the SC trunk, more ballast.
The Alt has no problem keeping it charged in normal use. it will NOT charge it if the batterey is way down. you can burn out your alt this way.
thats where the battery tender comes in handy. at times if needed just plug it in at home or on the road in a campground, motel, whatever, and in the AM you will have a fresh battery, ready to go.
my tender is permanently hard wired right in to the old batt terminals under the seat, where the old battery was. I also wired in a auto-fused wiring terminal under there to hook up all the extra wires from lights and and a power take off for a air compressor.

Jon,
There are two different alternators that were put in the R100's (not counting the police alternator). The only way to tell for sure which you have is to open the front chest and check the rating label on your stator.

**Be sure to disconnect your battery negative lead before you open the front cover so you don't short out the diode board!!!!!**

As far as upping the output of the stock system, there are a few things that you can do which I have found helped me in the past.

First: Go through every single connection in the charging circuit and make sure that they are clean shiny metal on the contact surfaces and tight contact. Use a good quality dialectric grease on all connections to keep out moisture/corrosion and to prevent current leakage.

Second: Yes, a electronic voltage regulator set at a slightly higher voltage will give you slightly more wattage at lower RMP's, but if the voltage is set too high, it will be at the expense of some shortened battery life due to higher charging/more heat.

Third: Upgrage the size of wires used in the charging system. One thing I did that made a noticable difference was simply replacing the stock wire between the diode board and starter with a heavier gage one that bolted directly to the frame of the diode board rather than relying on the large spade connector on the end of the board. I can provide more detailed instructions/photos of this if you or anyone else is interested.
Basically, all charging/power from the alternator goes through that wire, through the terminal on the starter solenoid, and back through the starter cable back to the battery and then the rest of the bike.
If you check that wire and the insulation is stiff/cracked/etc. It means that it has been overheating from the load it has been asked to carry. Especially bad from my point of view as an engineer is the connection of this wire to the diode board with a spade terminal. That means all the charging energy of your bike is relying on a connector that uses spring tension to maintain contact... in a vibrational environment....

I also upgraded the ground wiring from the battery to the chassis and the replaced the three wires from the stator to the diode board with slightly heavier gage to reduce resistance loses.

Also, make sure that your diode board is properly grounded!!! If you have a black timing chest and/or rubber diode board mountings contact me for details on what to do to improve your diode board ground.

Of course, I would be remiss if I didn't say... that if you really want usable electrical power/wattage in city traffic, idling, etc... there is no substitute for the EnDuraLast charging system.

I have it installed on both of my Airheads now, and there is just no comparison with the stock system, even with all the tweaks that I mentioned.

I got one of the first kits and helped test the output and wrote the installation instructions that John is now sending with the kits. And it has several real world advantages.

It puts out usable wattage at just off of idle. We are talking about over 200 watts at 2000rpm by my own measurements!!! And with no brushes there will be less maintenance with the system, no fear of not charging if your dash light is burnt out, etc... (you did know that if your charge warning light doesn't come on when you first turn your key on that no excitation energy goes to the rotor to initiate charging, right?) (burnt out charge warning light = no charging)

One other thing is that it eliminates the diode board and moves that part out of the heat of the engine, so you don't get a fall-off of charging as the engine heats up. And, you don't have to disconnect the battery to get into the front cover anymore because there is nothing in there exposed to shorting out.

Yes, it is a bit pricey. But how much have you got invested in your rig so far? And how much would it cost to be stranded with a dead battery?

YMMV

Thanks riders. All good info. My unit is unmolested yet, except for Windjammer and big seat. Being '78 R100S w/ only 17,855 miles on it means that likely a good go over of the connection points and retro fit the baynbet connector is what I'll do first. Charge lamp works. Upgrade to large mil wire is always good for current flow, so I'll do that too. I have 3 brake lights and two headlights along w/ blinkers and running lights. I am also going to try the enduralast solid state regulator, and install a heafty car battery in the sidecar boot. The high dollar alternator may be in the future but to rich for me now. I do all my own work, so it will be a while, but I will post results. Thanks ya'll, keep the right wheel down.

I do not know the skinny on the "rubber" diode board mounts. What's the issue?

Re: rubber diode board mounts...
I don't remember when they went to them, but BMW tried to fix a problem with the diode boards that didn't really exist (vibration) by going to rubber mounting studs similar to those holding the battery box in the /7 models.
The real problem was that the early Wherle manufactured boards were crap, and were simply failing at a higher rate than the earlier and much better Bosch boards.

What BMW did was replace the solid aluminum studs on the timing cover with the rubber studs and then added a grounding strap from the post of the diode board mount to the engine cover. The ground they provided was inadequate. AND many of the early black painted timing covers did not ground out well to the engine block because of the paint.

The diode ground wire has to carry just as much current as the positive charge wire. (energy in = energy out [neglecting losses]) And the original provided was just too light for the job. There was a retrofit kit that was done on most bikes when they were brought in for service with a "spider" wire, but in my opinion, even that is too wimpy for the job.

What I did was actually use 6mm bolts passed from the inside to the outside of the diode board buss-bars to create terminal studs for connecting my positive and negative leads to the diode board. That way you have a securely clamped connection right to the same bar that the diodes mount in. Best possible electrical connection!

Just be sure that the bolts used are short enough that they don't get close to shorting out against the timing cover when you remount the diode board! (the positive buss-bar is the lower one, the upper is the negative buss-bar)

I tried to attach a photo to show you what I am talking about, but it didn't work...
I can email it to anyone who is interested...

Hey, I just posted photos of my modified diode board in the albums section. Think this link should work, otherwise just look for the album titled "BMWzenRider's Stuff".

http://www.sidecar.com/megabbs/photos/photo-thumbnails.asp?albumid=253

Feel free to ask questions...

Very nice, zenrider. You are a gold mine of information . Album pics clear and easy to get.

How about going to my post on "R100 trans" and do me up a comparison of 32/10 and 34/11 rear drive for my '78 R100S . It has 32/11 stock now. Maybe 32/10 is too radical a change? I just have to down shift to maintain 55mph on small hills. I've located a good -spline 32/10 but purchase is one way, no trades back. Jon

Glad I could help. For reference, the wire I used in the photos is #10 gage. #12 gage would probably have been adequate, but there was room for the heavier gage, and it is just that much less resistance...

Also, when installing the bolts I wire brushed them and the buss-bars to get good shiny metal surfaces before assembling and coated with dielectric grease when the harnesses were bolted on to prevent corrosion. You will notice that the lower screw IS shorter and I used a jam nut to give more effective stud there to deal with clearance issues with the timing case.

Also, all the connectors on the wires were crimped with a good quality tool, and then soldered, putting enough heat on to allow the solder to wick fully into the joint. The crimp gives it vibrational strength, the solder gives better electrical properties. Soldering alone may be vunerable to cracking from vibration.

Oh, btw, I have been commenting on the transmission thread. And I am currently running a 32/10 final drive on a R100RT of the same vintage, and think it is a good compromise between gearing and fuel economy. The 3.09 will not be that much different than the stock gearing to really notice with the extra weight of the car tagging along...