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Old 11-25-2012, 08:36 PM   #1
roger 04 rt OP
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Eh? R1150 Alternator Start-Up Fix & AFR

The other day while taking some AFR data on cold start and warm up I noticed that my alternator light was on. I haven't noticed it before but after going back through a year's worth of data I can see that it has happened several times in the past. After a couple minutes the alternator started on its own and the light went out. Or if I blipped the throttle the alternator came on-line and the Batt light went out. So I might have lived with it by blipping the throttle. However:

During the time the light was on, there was no alternator output and the battery voltage was at the Motronic was about 12V. When the alternator came on-line the voltage jumps to 14V.

Then I noticed something very interesting. During warm-up when the voltage was at 12V, the mixture was about 8% leaner than a moment later when the voltage jumped to 14V. Thats too lean and i could feel it in a slightly rough idle. The Motronic sensed the lower voltage and lengthened the injector pulses, trying to compensate but in Open Loop it didn't compensate enough. If the alternator stayed off line until the bike went closed loop, the AFR was at the correct level before and after the step up in voltage. This means that the Motronic closed loop algorithm could fully compensate for the low voltage. That was lesson 1 for me.

So then I tried to understand why the alternator wasn't self starting. I for some feedback that many bikes do this. The starting current for the alternator flows though the Batt bulb on the Instrument Panel. I decided to try a resistor across that bulb and found that with a 220 ohm resistor across the bulb, the alternator aways starts.

The bulb is 1.7W and let's about 140 mA through the alternator rotor to start it. Adding the 220 resistor boosted the start-up current by a mere 50 mA for a total of 190 mA. BTW if the Batt bulb burns out the alternator may not start, it depends how much residual magnetism is in the rotor. Lesson 2.

Looking at the parts list, it originally specified a 1.7W bulb. But that is crossed-out now and a 3W bulb is now called for. So to get at the Batt bulb I first had to pull the High Beam bulb (they're both in a knuckle-busting location). As luck would have it, the High Beam was 3W even though the Batt bulb was only 1.7 W. So all I had to do was swap the bulbs, its hard to tell the difference of brightness. I plan to carry a 3W spare (Toshiba A14V3W).

Running the numbers, the magnetizing power with the 1.7W bulb was about 75 mW. The 3W bulb boosts that to 225 mW--a big jump

So if your alternator doesn't start on its own you might want to check the Batt bulb and see what it's power is.

RB
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Old 11-25-2012, 09:37 PM   #2
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Thanks for that roger 04 RT,
That reminds me of my old R80. No bulb =no charge. On my 1150gs I just changed some of my indicator bulbs
to LED type and wondered what would happen on that circuit so I left the batt. light alone, will check to see what watt. is in there now.
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Old 11-26-2012, 03:40 AM   #3
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Interesting.

My 1150's alternator light doesn't extinguish on a cold start until I give the throttle half a blip. Bumping it maybe 200rpm does the job and the motor runs a tad stronger afterward. Now that its cold enough to require the enrichment lever, the lamp extinguishes immediately on startup.
A warm start, such as you'd might do after a fuel stop, extinguishes the lamp immediately.

It has behaved like this for years.
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Old 11-26-2012, 06:25 AM   #4
roger 04 rt OP
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Originally Posted by Mike Ryder View Post
Thanks for that roger 04 RT,
That reminds me of my old R80. No bulb =no charge. On my 1150gs I just changed some of my indicator bulbs
to LED type and wondered what would happen on that circuit so I left the batt. light alone, will check to see what watt. is in there now.
You could but an LED in that location as long as you found a place for a 56 ohm or 68 ohm 5 watt resistor from switched B+ to the D+ terminal on the alternator. Both those wires are at the Diagnostic connector. You could also put the resistor across the two wires at the bulb but they're hard to get to there. Some think the resistor better because the alternator will still start is the bulb burns out. I'm just going to carry a spare 3W bulb.

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Interesting.

My 1150's alternator light doesn't extinguish on a cold start until I give the throttle half a blip. Bumping it maybe 200rpm does the job and the motor runs a tad stronger afterward. Now that its cold enough to require the enrichment lever, the lamp extinguishes immediately on startup.
A warm start, such as you'd might do after a fuel stop, extinguishes the lamp immediately.

It has behaved like this for years.
Since it appears that BMW changed the part from 1.7W to 3W you probably have the low power bulb. If the Hi-Beam bulb has a 3W you could just switch them and see what happens.
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Old 11-27-2012, 03:28 AM   #5
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Thanks

Thank you for your tip, it´s very useful and instructive. Trying to understand the work of the alternator, I´ve found that there´s news electronics voltage regulators like BOSCH F00M http://www.wai-wetherill.com/images/...Sell_Sheet.pdf . They´re not cheap, but I think it solves the same problem, and enhance the features of the system. Has anyone try one of these?

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Old 11-27-2012, 09:22 AM   #6
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Originally Posted by Blasterwizard View Post
Thank you for your tip, it´s very useful and instructive. Trying to understand the work of the alternator, I´ve found that there´s news electronics voltage regulators like BOSCH F00M http://www.wai-wetherill.com/images/...Sell_Sheet.pdf . They´re not cheap, but I think it solves the same problem, and enhance the features of the system. Has anyone try one of these?
Make sure your BMW is fitted with the Bosch alternator and not the Denso unit.

I understand there are not many Denso alternators fitted here in the US but other countries may be different.

We're power hungry, energy wastin' folks here in America so we demand the higher output alternators. I have 200amp electrical service in my garage just for lights and a few battery chargers...what a waste.

Roger, I understand (well, not really understand but have knoledge that) part of the electrical system (Load Shedding Relay circuit?)is grounded through the starter solenoid contacts (sounds almost like some of the Joe Lucas genes leaked through to the BMW engineers).

Am I correct, if the instrument cluster lamp that signifies alternator output is burned out, no charging takes place?

Also, is there any way to slightly increase bus voltage on our bikes to accommodate AGM battery charging profiles? I understand the AGMs like a bit more charging voltage (maybe an additional 1/2 volt DC) than is currently delivered by the alternator.

Note everyone, new avitar photo...the flowers are gone...replaced by my friend Ginger. Careful, she'll chew your leg off...

def screwed with this post 11-27-2012 at 10:16 AM
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Old 11-27-2012, 10:04 AM   #7
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Originally Posted by def View Post
...

Roger, I understand (well, not really understand but have knoledge that) part of the electrical system (Load Shedding Relay circuit?)is grounded through the starter solenoid contacts (sounds almost like some of the Joe Lucas genes leaked through to the BMW engineers).

Am I correct, if the instrument cluster lamp that signifies alternator output is burned out, no charging takes place?

Also, is there any way to slightly increase bus voltage on our bikes to accommodate AGM battery charging profiles? I understand the AGMs like a bit more charging voltage (maybe an additional 1/2 volt DC) than is currently delivered by the alternator.

...
Hi Def, You're correct that the LR relay is grounded through the starter solenoid--a bit of 1960s engineering if you ask me. That is because the solenoid is either low resistance with no starter switch voltage so the relay is energized. Or, you press the starter button, lifting the voltage to +12 and then there is no drop across the LR relay coil and the relay is NOT energized. Wow! Today it would be in a line of code that read something like:

IF(StartSW=1) then LR relay = OFF

Else If RPM < 800 RPM LR relay = OFF (would keep the lights from draining the battery while the key was on but engine not running)

Else LR Relay = ON

If the bulb burns out it is harder to energize the Altenator. I'm told there is some residual magnetism (most of the time) and that IF you spin it fast enough it USUALLY starts. But you're correct, the lamp is there to provide some power for start-up magnetism.

If got some neat curves that show just how much slower the Injectors are at 12V than they are at 14V. It is really quite astounding. At 12V on a cold day here the injector pulse was 5 mS and the AFR was 13.8:1. And on the same cold day at 14V the injector pulse was a little under 4 mS and the mixture was 11.8:1. That is because the injectors get slow as the voltage drops. I had not expected to see that amount of sensitivity.

I don't really know about how to change the alternator's voltage characteristics so I hope they are compatible with the Odyssey that I installed last year.
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Old 11-27-2012, 10:26 AM   #8
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If got some neat curves that show just how much slower the Injectors are at 12V than they are at 14V. It is really quite astounding. At 12V on a cold day here the injector pulse was 5 mS and the AFR was 13.8:1. And on the same cold day at 14V the injector pulse was a little under 4 mS and the mixture was 11.8:1. That is because the injectors get slow as the voltage drops. I had not expected to see that amount of sensitivity.
Roger, I observe some momentary lumpy running at cold start even with the cold start throttle lever advanced. So, this lumpiness is due to momentary low voltage and cold fuel injector coils. If I am understanding correctly, this cold condition produces a lower AFR (richer) which is desirable at cold start? Wow...if this is true, we have an automatic choke on our BMWs and didn't even know it until now.
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Old 11-27-2012, 11:51 AM   #9
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I may have not explained the effect well but the Motronic delivers a lot of fuel in order to produce the rich mixture needed to start and warm up. As you know, when cold, the fuel being sprayed condenses on the TB, intake system and back of valves, so it doesn't make it into the combustion chamber to be burned. Also the colder fuel doesn't vaporize as well. So the Motronic is doing its best to get that rich mixture.

I don't think that injector coil temperature is an issue but if you see the red Batt indicator light glowing after start-up for a while, you can be pretty sure the battery voltage at the injectors is lower that it's normal (13.7V on my bike) level. On my RT, the headlight is on as soon as it starts and without the alternator charging the battery, it's about 12V

When powered by 12V, the injectors have a lot more dead-time, or said another way they turn on more slowly than at 13.7 volts. The Motronic measures the lower voltage and lengthens the pulse, but not enough to fully account for the slower turn on time. (Once the bike goes closed loop though, the Motronic doesn't just measure the voltage and make an adjustment, it keeps adjusting until it makes the mixture rich enough to get to the O2 sensor transition point, which is 14.7:1 on stock bikes and 13.8:1 on mine.)

So when it's cold, you've just started, and it's idling and if the Batt instrument light is on, your bike is probably running leaner than it should and may run rougher due to that, mine does.

One last point:

For the first 25 seconds, the Motronic is making the mixture very rich like about 3X as much fuel. After the first 25 seconds and until the engine warms up, it runs open loop with 3-15% extra fuel, slowly decreasing the fuel as the oil sensor indicates warmer temperatures. So yes, it has a well hidden choke function.
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Old 11-27-2012, 12:28 PM   #10
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One last point:

For the first 25 seconds, the Motronic is making the mixture very rich like about 3X as much fuel. After the first 25 seconds and until the engine warms up, it runs open loop with 3-15% extra fuel, slowly decreasing the fuel as the oil sensor indicates warmer temperatures. So yes, it has a well hidden choke function.
Yipee. Now I know why my plugs soot during cold start.

Thanks Roger.

You GS BMW folks need to listen to this fellow and read this thread about the Motronic engine management. He has done considerable testing and has documented much regarding the inner workings of the Motronic and how to improve the engine fueling. Oh, and he lives right next door to MIT, an impressive place in itself.

I have been in the Rad Lab at MIT where dad and his team worked to develop US RADAR during WWII. I recall seeing the 10cm RADAR cavity there (I was unimpressed at the time inasmuch as I was only 4 years old).
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Old 11-27-2012, 12:35 PM   #11
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Here's a good example of the alternator coming on late. It was before I figured out what was going on.

Looking at the curve below from 40 seconds to 60 seconds you can see the START-UP enrichment program being run. In that period, the Motronic is gradually reducing the enrichment.

At the 60 mark, until about the 2 minute mark, the Motronic is holding the length of the fuel pulses fairly steady, but it looks as if the mixture is getting richer. This is because as the engine warms up, more of the fuel gets burned and there is less oxygen in the exhaust. And what the O2 sensor is measuring is oxygen which effectively means mixture.

The from the 2 minute mark until about 5:10, the Motronic is gradually reducing the fuel as the engine warms further. But you can see at 3:20, the mixture steps down. This is exactly when my alternator started charging. The injector pulses didn't get longer (in fact they got a little shorter as the Motronic uncompensated for the low voltage) but the Battery Voltage got higher and the injector turn-on time got shorter and they squirted a bit more fuel--roughy 7% more.

Had the alternator been running from the beginning, the first 3:20 of the graph would be shifted down by about 7% richer. When I get a minute I'll post a normal start.

Finally just before 5:20, the Motronic goes Closed Loop and settles on +- 13.8:1.

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Old 11-27-2012, 12:48 PM   #12
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Here is a clean start of my R1150RT with everything working as it should on a day when my garage was about 45 degrees. You can compare it to the previous slide where the is the step down due to the alternator coming on late at 3:20 on that graph.

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Old 11-27-2012, 04:23 PM   #13
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Amazing what a little voltage will do....impressive.
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Old 11-27-2012, 07:32 PM   #14
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That makes me want to find the power, and ground connections to the motronic unit, and make sure they are clean and tight!
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Old 11-27-2012, 08:58 PM   #15
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That makes me want to find the power, and ground connections to the motronic unit, and make sure they are clean and tight!
Good idea...me too.
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