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Old 10-28-2013, 12:02 PM   #91
roger 04 rt OP
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Thanks for the inputs guys. If I'm correct and the Motronic is compensating dwell for battery voltage then the sticks would also need to be supplied. I think the power/voltage should look like:
Input voltage: 6 - 20V
Output voltage: 13.2V

Loads
Motronic: 0.5 A
2 Injectors: 1.5 A
2 Stick coils: 2.5 A (7200 rpm = 120 /second => 8 mS 2ms Dwell, so 25% 10 amps)

So need at least 5 amp supply. Maybe a battery and timed relay to charge is better.

Below is a chart of the starting parameters for 11.7 vs 13.6 (Motronic and injectors). One of the reasons that 11.7 works so we'll is that the sticks have 9-10 volts during cranking then 13.6 volts once running but the Motronic only sees 11.7 so calculates a long dwell.

Notice in the chart how much faster the rpm builds in the 11.7 volt case compared to the 13.6. That seems to be due to inadequate dwell at the higher voltage case.

Also note that the Motronic has no way to adaptively learn low battery voltage corrections for coils and injects during cold start.

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Old 10-28-2013, 03:43 PM   #92
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Roger, is there any evidence that the Motronic 2.4 boxer with a single plug does the same thing regarding dwell vs voltage?
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Old 10-28-2013, 05:13 PM   #93
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Quote:
Originally Posted by roger 04 rt View Post
Input voltage: 6 - 20V
Output voltage: 13.2V

Loads
Motronic: 0.5 A
2 Injectors: 1.5 A
2 Stick coils: 2.5 A (7200 rpm = 120 /second => 8 mS 2ms Dwell, so 25% 10 amps)

So need at least 5 amp supply. Maybe a battery and timed relay to charge is better.
Of course it's up to you, but I much prefer electronics to extra batteries.
Bear in mind you can't average the current unless you store energy at the regulator output, you must design for worst case current(12A Max.) or the regulator will limit.

This is great to read, thanks for posting.
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Old 10-28-2013, 07:20 PM   #94
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Quote:
Originally Posted by def View Post
Roger, is there any evidence that the Motronic 2.4 boxer with a single plug does the same thing regarding dwell vs voltage?
No evidence of that, that I'm aware of.

2004 was the first boxer model to use stick coils as you know. Since it was a wasted-spark design, the coils were each dissipating twice the power needed to produce a spark during the power stroke. That appears, based on the data, to have left them cutting corners with dwell time, keeping it as short as they could.

From the data that I have on the next model, the r1200, it seems BMW took a different approach. Without the inefficiency of wasted-spark, they set the dwell at 2 mS all time, except during the first part of cranking where they ran the dwell time to a healthy 6 mS.

Maybe what I'll do is set the alternator to 14.4 volts with a diode mod and run that directly to the coils through a relay like later 04s. Then I'll drop the voltage going to the injectors and Motronic, causing the Motronic to use a longer dwell time. Food for thought.

That reminds me that I still don't know why BMW added a relay to connect the sticks to the battery, rather than to the switched side of the key as they did in early models.
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Old 10-28-2013, 07:23 PM   #95
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Quote:
Originally Posted by MotorradMike View Post
Of course it's up to you, but I much prefer electronics to extra batteries.
Bear in mind you can't average the current unless you store energy at the regulator output, you must design for worst case current(12A Max.) or the regulator will limit.

This is great to read, thanks for posting.
Mike thanks for the reminder about total current requires. I see an 80W supply on amazon by drok for $30.
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Old 10-28-2013, 11:45 PM   #96
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Won't work. It's a boost only. You need a buck-boost combo.


Quote:
Originally Posted by mouthfulloflake View Post
Ill try and remember to order one of these up and do some testing with it with a varying input voltage.

http://www.ebay.com/itm/150W-DC-DC-B...item4aca74a505
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Old 10-28-2013, 11:51 PM   #97
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Quote:
Originally Posted by roger 04 rt View Post

Loads
Motronic: 0.5 A
2 Injectors: 1.5 A
2 Stick coils: 2.5 A (7200 rpm = 120 /second => 8 mS 2ms Dwell, so 25% 10 amps)
Is that 1.5A per injector? And at what voltage?

Quote:
Below is a chart of the starting parameters for 11.7 vs 13.6 (Motronic and injectors). One of the reasons that 11.7 works so we'll is that the sticks have 9-10 volts during cranking then 13.6 volts once running but the Motronic only sees 11.7 so calculates a long dwell.
It would be easy to set the buck/boost regulator to 11.7v and just feed the Motronic and injectors. Any idea if sustained 11.7v will hurt them?
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Old 10-29-2013, 04:51 AM   #98
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Quote:
Originally Posted by EKinOR View Post
Is that 1.5A per injector? And at what voltage?



It would be easy to set the buck/boost regulator to 11.7v and just feed the Motronic and injectors. Any idea if sustained 11.7v will hurt them?
GSAddict measured them, see below.

I don't see any reason that something between 11.7 and 12.9 shouldn't work. The biggest issue is that injector dead time increases rapidly as voltage falls so something around 12.9 V might be best.



Quote:
Originally Posted by GSAddict View Post
You would have to break into the wiring harness and power the injectors alone.

I just did some measurements and each injector draws .760A @ 12.8v so the load is 1.52A.
...
Question about a buck-boost that could go to 20-30V, how would I protect the Motronic against the regulator going to 30V out of control and damaging the Motronic, etc.?
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Old 10-29-2013, 06:26 AM   #99
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Quote:
Originally Posted by roger 04 rt View Post
Question about a buck-boost that could go to 20-30V, how would I protect the Motronic against the regulator going to 30V out of control and damaging the Motronic, etc.?
You'd have to add a fuse and crowbar circuit to protect against that peril.
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Old 10-29-2013, 07:57 AM   #100
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Quote:
Originally Posted by MotorradMike View Post
You'd have to add a fuse and crowbar circuit to protect against that peril.
At the moment, that has me favoring the second battery idea ...
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Old 10-29-2013, 08:05 AM   #101
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Originally Posted by def View Post
Roger, is there any evidence that the Motronic 2.4 boxer with a single plug does the same thing regarding dwell vs voltage?
Def, I went through the many cold-start R1150GS single-spark logs that I have. Although there are no tests of this function with data taken like I have, I've looked at what happens to dwell while the alternator comes on line.

The short story is, Dwell Time does appear to be affected by the Battery Voltage measure by the Motronic. However, the coil is very different and the compensation may be appropriate. The dwell times at idle and 13.8 volt battery, for the R1150GS single spark is about 1.6 mS (compared to 0.6 mS for the dual spark stick coils). When the battery voltage is 11.7V on the single-spark it is about 3 mS dwell.

RB
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Old 10-29-2013, 09:42 AM   #102
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Quote:
Originally Posted by roger 04 rt View Post
Def, I went through the many cold-start R1150GS single-spark logs that I have. Although there are no tests of this function with data taken like I have, I've looked at what happens to dwell while the alternator comes on line.

The short story is, Dwell Time does appear to be affected by the Battery Voltage measure by the Motronic. However, the coil is very different and the compensation may be appropriate. The dwell times at idle and 13.8 volt battery, for the R1150GS single spark is about 1.6 mS (compared to 0.6 mS for the dual spark stick coils). When the battery voltage is 11.7V on the single-spark it is about 3 mS dwell.

RB
Thank you Roger.
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Old 10-29-2013, 01:34 PM   #103
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Just another thougt (coming full circle here) - would permanently increasing the injector dwell time, though reducing the voltage going to it, provide a corresponding increase in fueling? And if so, to what effect?
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Old 10-29-2013, 08:25 PM   #104
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Quote:
Originally Posted by EKinOR View Post
Just another thougt (coming full circle here) - would permanently increasing the injector dwell time, though reducing the voltage going to it, provide a corresponding increase in fueling? And if so, to what effect?
Eric, I've been thinking about this for a couple days myself. Let's say you used a diode (or two) to reduce the supply voltage to the Motronic. Here's what should happen:

1. At first the Motronic would lengthen the injector pulses to compensate for measuring a lower voltage. Then over time the Motronic would learn through closed loop adaptation that it didn't need to.

2. There is no equivalent closed loop routine to work out optimum dwell so if the Motronic voltage was lower than the voltage at the coils, dwell time would be increased permanently--perhaps reducing coil lifetime but certainly improving starting.

Of all the things I've discovered, the Motronic likes to see a steady voltage during starting but that voltage should be steady but between high 11s and mid 12s during cold start so fuel and dwell are added.
RB
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Old 10-30-2013, 12:05 AM   #105
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Quote:
Originally Posted by roger 04 rt View Post
1. At first the Motronic would lengthen the injector pulses to compensate for measuring a lower voltage. Then over time the Motronic would learn through closed loop adaptation that it didn't need to.

2. There is no equivalent closed loop routine to work out optimum dwell so if the Motronic voltage was lower than the voltage at the coils, dwell time would be increased permanently--perhaps reducing coil lifetime but certainly improving starting.
That's kind of what I figured re: fuel. That darn Motronic adaptation again...

Quote:
Of all the things I've discovered, the Motronic likes to see a steady voltage during starting but that voltage should be steady but between high 11s and mid 12s during cold start so fuel and dwell are added.
RB
That's where a good buck/boost power regulator comes in. I think I can build one capable of 5A for around $15 or less in parts. Though I have a single spark, so I'm not sure it makes as big a difference as compared to a dual spark.
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