K100 Alternator choices

[LSkrabut]

My K100LT '88 alternator appears to be giving up after 20 years of giving :)

I am only getting about 13.8 vdc at the battery. When I check the battery, still only getting that 13.8vdc when rev’ing the motor around 4k. Running per my voltage gage is normally around 13.3vdc, dropping under 12vdc at idle. Runninglights will also drop my running voltage to 12vdc.

My question is about which alternator can I put in this bike?

I think I found a 60amp K1200RS '02 alternator. Per the fiches a K1100 appears to be the same as the k1200RS other then the fact of 50 amps version vs the 60 amp version. All the part numbers are the same other then the alternator itself between these 2 bikes, even the regulator (50 amp).

Will this work in my K100 after changing the spade connectors for lug connectors? The alternator comes with the clutch housing and rubber bumpers.

Also I have read that my battery should be a 18-20AH battery, or should it be a 25-30AH? Will either one work in this case of a bigger producing alternator?

I think I read somewhere the main fuse should be increase? Should a bigger ground wire added to the motor? What about the wiring harness itself, will it be ok going to more amperage output on the charging circuit?

Read many times going to a 50 amp alternator is a common upgrade for the K75/K100 bricks. Just not sure if a 60 amp alternator is possible and if it is, safe?

Thoughts, Warnings, Guidance anyone TIA

[LSkrabut]

I was mislead about the 60 amp unit, it is a different size. :(

Guess I will be getting the 50amp K1100 alternator after all.

Still any issues I should be aware of adding 20 more amps to the existing wiring and fuses? Battery?

[MotorradMike]

Are you sure it's the alternator that's not working?

If the field coil isn't being driven hard enough by the voltage regulator, the same symptom will show.

[LSkrabut]

No I am not sure the alternator is not working properly.

But if I throw a load on it (2x55w driving light), shouldn't this be a heavy enought load? plus head light and taillight with 2 rear running lights. Also at times heated handgrips. The bikes voltage goes down with added load.

Where is this "Field Coil" located at? Part of the alternator isn't it?

[deilenberger]

I was mislead about the 60 amp unit, it is a different size. :(

Guess I will be getting the 50amp K1100 alternator after all.

Still any issues I should be aware of adding 20 more amps to the existing wiring and fuses? Battery?Nope. Pretty much plug and play. There is no "main fuse" on a BMW that I know of (the reason their wiring harnesses occasionally suffer from meltdown..) and the battery has no idea what size alternator you are running, the battery will draw what it needs to charge itself. The wiring should be of adequate size to the alternator - it's a short run to the common terminal that connects it to the battery. I've put them on K75's with no problem at all.

[MotorradMike]

Where is this "Field Coil" located at? Part of the alternator isn't it?

Alternators in general have 3 connections.
GND
Output
Field

The GND is usually the case.
The Output is a big terminal with a heavy wire on it.
The Field input is a smaller terminal with a thin wire on it.

The spinning alternator makes electricity proportionally to the (small)amount of field current supplied to it by the regulator. If your alt. is capable of 13.8V it might be OK.

I'm just suggesting you test it thoroughly before changing it and having the same issue with the new one.

[Paul_F]

When we switched my 33 amp alternator to a 50 amp, there was an electrical connector that was different on the 50 amp, so we took the electrical connector off the 33 and put it on the 50. It was easier to attach the old connector to the amp than put a new connector onto the bike's wiring. Also as I recall, there was a clamp that from the 33 amp alternator that would not fit on the 55 because of proximity to the frame with the 55 being a bit larger. Just used a different type of device to lock it into place. Been running fine for a year now and I don't worry about shutting off the electric clothing when slowing down for small towns and villages with the additional lights running.

[PGlaves]

When we switched my 33 amp alternator to a 50 amp, there was an electrical connector that was different on the 50 amp, so we took the electrical connector off the 33 and put it on the 50. It was easier to attach the old connector to the amp than put a new connector onto the bike's wiring. Also as I recall, there was a clamp that from the 33 amp alternator that would not fit on the 55 because of proximity to the frame with the 55 being a bit larger. Just used a different type of device to lock it into place. Been running fine for a year now and I don't worry about shutting off the electric clothing when slowing down for small towns and villages with the additional lights running.

The 33 amp has a two-pole, L arranged, plug that goes straight onto spade lugs recessed into the back of the alternator. The 50 amp unit has two posts - one large, one small, that take two different sized spade lugs, or in the alternative, two ring terminals. This is on the left side near the back of the alternator.

So just exactly what parts did you swap from alternator to alternator?? The spade lugs??

When I did the swap I cut the connector off the wiring and installed one large and one small ring terminal to fit the 50 amp model's posts.

[Paul_F]

The 33 amp has a two-pole, L arranged, plug that goes straight onto spade lugs recessed into the back of the alternator. The 50 amp unit has two posts - one large, one small, that take two different sized spade lugs, or in the alternative, two ring terminals. This is on the left side near the back of the alternator.

So just exactly what parts did you swap from alternator to alternator?? The spade lugs??

To be truthful Paul, my much more experience friend did most of the work while I watched. I remember that he decided that it would be easier to change the plug on the alternator on the bench to match what was already on the bike's wiring harness. The exact part, don't know, but a switch was made.

[LSkrabut]

In my digging around on this possible swap, I have read where one person added a connector to lug jumper from both of the spaded connectors to the corresponding poles on the 50 amp alternator. Issue there is adding points of possible failure or resistance to the current path. Good point, easy to go back to old setup of the 33 amp alternator.

Well I got one coming in by US Mail. When I get it I will investigate the best way for my case to connect or change the wiring.

Keep on adding thoughts here, I like to think things out before jumping. I also feel I need more juice for the running lamps I have on or like to have on. Normal RPM's I am only showing about 13.2 volts once warmed up, to me that is low.

[PGlaves]

To be truthful Paul, my much more experience friend did most of the work while I watched. I remember that he decided that it would be easier to change the plug on the alternator on the bench to match what was already on the bike's wiring harness. The exact part, don't know, but a switch was made.

OK - he must have just switched the spade connectors so the old L plug would engage them. I on the other hand cut off the plug and put on ring terminals, when I could have just put on push on connectors and spade terminals. I didn't think of that at the time.

There is "always more than one way to skin a cat." Disclaimer - that is a quote of an old saying. No harm came to any cats. No offense to anybody who has a cat was intended. There is no need to notify either the ASPCA or PETA.

In any event - the 33 has two spade terminals and a plug. The 50 has two round posts. In OEM configuration the 50 has two separate push on connectors on spades. Ring terminals work too on the 50.

[Kayseventyfive]

My own preference, whenever possible, is connectors that I can tension myself. They stay tighter and cleaner, and are easier to clean when necessary. I have been irritated too often by push-on connectors.

[breyfogle]

My K100LT '88 alternator appears to be giving up after 20 years of giving :) Guidance anyone TIA

My guess is all you need is a new set of brushes and maybe new slip rings. The OEM alternator is a standard Bosch unit that can be rebuilt just about anywhere. BTDT

[LSkrabut]

Any input on the battery?

I seen the Odyssey PC925L which is called for on the K100 series. Sort of expensive, but lots of CA.
http://www.odysseybatteries.com/battery/pc925l.htm

As stated, this bike when purchased only has a 16AH battery in it now. I think BMW calls for a 19AH flavor of a power source.

Another apparent popular power source is the Odyssey PC680.
http://www.odysseybatteries.com/battery/pc680.htm

Still more power then stock, lighter then stock and the PC925L.

Again from my reading on this, some ppl and charts call for a 25AH or stronger battery?

How about the Westco 12V30 from BeemerBoneyard with charger? The CCA is alot lower then the Odyssey's?

What is really needed on these K100LT with all the heating elements and self added lights?

[LSkrabut]

I have taken the alternator apart. Cleaned it up, insure the brushes are long enough for good contact. Use a ohm meter and diode checker and from what I could tell, stator and rectifer appeared to be ok. I also check and cleaned most of the connections I could easily get to. Ohm out most of them that I could to somewhat insure that there were making good contact. Again .001 ohm does not mean that will carry current, but it is a good indicator.

Just not enought output voltage, the 13.8 is only when cold and for a very short time. Ususally drops to 13.3 within 3-4 minutes of running. But it tends to stay there no matter if high beam is used or high heat on the grips. If it is hot outside, then voltage drops to 13.0 even. This is at 5k running speeds.

Thanks for the thoughts and path of T/S'ing. I now hope it is nothing more than a meak/weak alternator and maybe an old battery. I am planning on riding this beast of pleasure till the real cold sets in (freezing temps). I ride it as a daily rider 120 round trip a day. I place about 10k on it since I got it this June.

http://www.tubarks.com/Aurora/K100LT_SV.jpg

[barryg]

I'm a dummy on electrics. I use to see everyone writing about useing the K police bike alternator when U needed to update to a alternator with more juice for your K. I ssume that what your talking about now.

[PGlaves]

I'm a dummy on electrics. I use to see everyone writing about useing the K police bike alternator when U needed to update to a alternator with more juice for your K. I ssume that what your talking about now.

BMW used two different alternators in the K75/K100/K1100 bikes.

The original was a 33 amp (450 watt) Bosch unit.

On the early police bikes they installed a 50 amp (700watt) Bosch unit.

Starting with the ABS1 bikes they installed the 50 amp unit as standard. Non ABS bikes still got the 33 amp for a while.

Any of the 50 amp alternators are ALMOST a direct bolt-in swap.

This thread has discussed one of two differences. The wiring attachment to the two types differs.

The other critical difference is that they take two different couplers on the alternator shaft. The 33 amp unit has a shaft with a Woodruff key and the coupler is slotted for the key.

The 50 amp unit has a shaft that is not slotted for the key. The coupler from a 33 amp unit is a loose fit on the shaft of a 50 amp unit and the coupler slips no matter how tight you try to tighten the nut.

So - when swapping from a 33 amp to a 50 amp alternator in your early bike so equipped - get a new coupler for the 50 amp unit too.

See - "Monkey Nutz" in Benchwrenching, BMW ON - April, 2008

[barryg]

Gotcha, thax Paul. Gotta a 87 KRT, now I know the deal.

[PGlaves]

Gotcha, thax Paul. Gotta a 87 KRT, now I know the deal.

For the curious: If you look at the exposed side of the alternator - under the little black cover - just ahead of the coolant overflow tank - you will see a sticker. If it says 33 that is what you've got. If it says 50 that is what you've got.

Or if the wires attach on the back that is a 33 amp unit.
If the wires attach on the left side that is a 50 amp unit.

[Kayseventyfive]

Just not enought output voltage, the 13.8 is only when cold and for a very short time. Ususally drops to 13.3 within 3-4 minutes of running. But it tends to stay there no matter if high beam is used or high heat on the grips. If it is hot outside, then voltage drops to 13.0 even. This is at 5k running speeds.



Doesn't sound all that bad. Right after the discharge of starting, the alternator is charging 13.8, which replaces what was expended. Once the battery is charged, the 13.2 or 13.3 is a proper float voltage. With a full load, the alternator is still charging the battery.

As long as the alternator charges up the battery after a discharge and then carries the load, you should be all right.

Maybe I should hook up a meter and check mine.

[bmwmick]

No I am not sure the alternator is not working properly.

But if I throw a load on it (2x55w driving light), shouldn't this be a heavy enought load? plus head light and taillight with 2 rear running lights. Also at times heated handgrips. The bikes voltage goes down with added load.

Where is this "Field Coil" located at? Part of the alternator isn't it?

Here is some info:
http://www.seatrider.org/techntips/upgrade%20your%20early%20k%20bike%20alternator.htm

I think there is more on this forum too, search on +alternator and my userid.

Mick

[LSkrabut]

Here is some info:
http://www.seatrider.org/techntips/upgrade%20your%20early%20k%20bike%20alternator.htm

I think there is more on this forum too, search on +alternator and my userid.

Mick

Thanks Mick, Already done that and seen your page in this quest of mine.

I got a 50 amper with the right clutch housing and the bumpers are in good shape (so are the bumpers in my 33amp unit) coming in next week, slow but cheap shipping. :)

I just don't like my running voltage going below 13 volts if I turn on my running lights and it appears to be getting worse. Got to turn off some lights till I get it installed I guess.

[bmwmick]

Even with my 50A alternator and a 14.2V regulator, my voltage at idle 'can' go as low as 11.9V. Just depends on how many loads you have on. As soon as I'm above 1,500RPM, it sits at 13.8V unless I had just started the engine.

[HFbmw]

Has anyone talked of the low voltage that BMW puts out?
We are used to the 14.6 volts that the cars put out. I think most of the japenesse machines run the higher voltage.
Took me a few years to realize that BMW machines are made to use the lower voltage.

Use to have the R65. Tweaked the regulator in that so I could use a home made vest and not find a dead battery.

Now these gel batteries like the lower voltage... hmmm

So yes your bike is supposed to only charge at 13.8 volts.


tim lindstrom
95 k1100RS
minnesota

[LSkrabut]

Ok, I now got a 50 amp alternator in. My charging voltage was about 13.5 now. BTW the voltmeter now shows 13.5 volts at about 1500 to 1800 rpm, where before it had to be around 3k before it started to get near 13.volts. Also the voltage stay more constant with the newer alternator.

I have now replaced my battery negative ground wire, guessing it was a 10 gauge wire with a homemade soldered lug 6 gauge cable (black). $3 for the 2 lugs, $2 for the wire from Home Depot. That brought my voltage up to 13.7. Per Tim's response, I might be where I should be on charging voltage.

I am thinking about placing in parallel another homemade 6 gauge lugged (red) wire from the alternator to battery. Per the wiring diagram it appears to be a straight shot. Is this a fact? I did not want to undo the wiring harness to verify this or to remove the existing 10 gauge wire.

Per a wiring diagram I got it appears that there might be 2 common collection grounding points. Anyone know where these might be hidden? The both appear to be tied together and then grounded someplace, anyone know where that place might be? I like to clean all 3 points of contact. K100-Electrical_Ground.pdf (http://www.tubarks.com/Aurora/K100-Electrical_Ground.pdf)

I do know having or insuring ground is an excellent way to insure one charging and electrical load is in tip top shape. By using a slightly larger ground and initial charging wires help also.

TIA

[bmwmick]

LS,
The ground points are under the tank. Remove it and you will see them.
As for the #6 wire, I would not waste my time. 10Ga wire will carry 55Amps and you can't even get there from the Alternator output.
The major points to beef up are the Plus and minus cables from the battery to ground (which you have done). I believe the red wire going to the starter relay is also 8Ga or better.

[deilenberger]

LS - for sure clean the central ground points. As BMWMick said - they're under the tank. Located on bolts coming off the central frame section. Remove the nuts, use some fine (400 grit) sandpaper on each ring connector going to ground, and put it all back together. I found on one of my K's that someone had thought putting grease on the ground connections were a good idea - it wasn't. The grease was partly insulating the grounds and dropped my system voltage.

Clean and tight is just fine for these.

[Dennie]

:ear:lurk

[LSkrabut]

Putting on another 23K miles this season, the 50 amp alternator voltage stayed the same, about 13.7-ish cold and 13.2-ish once warmed up.

Checked all connectors and they all were tight and clean, I cleaned them up anyway.

I am guessing since the bike's voltmeter and my Fluke DVM are reading the same, the regulator is putting out what it is putting out. Never did the bike have a real issue with voltage or battery power. I even ran it this fall with a heated jacket liner, again not a single issue with the voltage showing around 13.2 volts after the bike warmed up.

It really does not seem to make any difference running a safety light in the rear, added more bulbs in the rear tail light (4 total now), 2 - 55w running lights and a heated jacket and handlebar grips on high. still the same old 13.2-ish voltage.

I now just figure it is the way it is. Be happy it all works ;)