Dwell calculations

[Tortfeaser]

Sorry, nuffie here. How is inductance measured? Is this possible for a punter with a multimeter? CRO? Something else? I haven't seen many coil catalogues with this value listed.

[djandruczyk]

--- Tortfeaser <marc.kelly@affa.gov.au> wrote:
> Sorry, nuffie here. How is inductance measured? Is this possible for a
> punter with a multimeter? CRO? Something else? I haven't seen many coil
> catalogues with this value listed.

The best way that I know of is with an LCR meter
(Inductance/Capacitance/Resistance) meter. A decent sized electronics tool
place would carry them. (NOT radio shack/Fry's)




Dave J. Andruczyk



__________________________________
Do you Yahoo!?
Make Yahoo! your home page
http://www.yahoo.com/r/hs


(posted by email)

[danimal]

fry's sells the Outpost.com #: 4173783

BK Precision: 878A LCR Meter $249

don't know if it's available locally at the store, tho.

[Dennis240]

Tortfeaser,

Here you go, even has warranty

http://www.used-line.com/c4847876s71-BK ... n_875A.htm

$75

[Tortfeaser]

Bargain. Thanks guys.

[randy77zt]

i installed ms&se in my 77datsun z with 81 zx turbo engine.the oem zxt efi fired a power transistor mounted to the coil bracket.my ms is firing that transistor.i tried about 1.5 ms dwell first and got a misfire at high rpm/boost.it would backfire and surge.its set at 3.7 now and i still have a minor surging feeling under high (10+ psi) boost.might try putting a little more (.5ms) dwell on it.for my application i think a msd 6a cdi box would be a safe bet but i am trying to save money right now.i would have liked to see the original wave form from the oem zxt efi system that fed the power transistor.

[VolvoPentaMan]

I've got 4 VW 1,6FSI coils, got a buddy to measure them for dwell times and energy consumption (A).

The energy consumption goes up, untill 3ms, where it dops STRAIGHT down, then consuming 20Amps. At 1,8ms consumption is about 10A, so we came to the conclusion of running dwell being 1,8ms.

But how to determine CRANKING dwell?
I've tried everything from 1,8ms to 4ms.

[The Witzl]

Lance,

A very commonly used coil, and cheaply available here in Australia, is the Bosch MEC717. It's often used in coil-per-plug aftermarket EFI systems, and is about AU$60 per coil.

Specs are:
L = 2.58mH
R = 1.0 ohm

Now there is a formula used to find the charge current, based on the spark energy you want to generate:

Code: Select all

        W = 0.5*(L)*((I)^2)

.... where:
W = energy (milli-joules)
L = inductance (milli-henrys)
I = charge current (amps)


Now, from a little bit of reading around - an ideal spark energy is about 20mJ. IS THIS CORRECT???

Using 20mJ, and the specs of the MEC717 coil above, the charge current is 4.0A.

If that spark energy is correct, it would be correct virtually across the board for most applications...... then it would then be really easy to work out the charge current required for any coil knowing only the inductance and resistance!

Using your formula above combined with this formula above, using a spark energy of 25mJ (to add a little), i got a Dwell calculated at about 1.25msec.


Hopefully this will help a lot of people stabbing in the dark to find the right dwell settings!

[Tortfeaser]

I emailed Bosch about dwell times for the MEC coils (MEC717 and MEC718 are same specs, different connector).

They replied (quoted below) suggesting dwell times of 2.6ms at 12v.

Also, the Bosch catalogue at http://apps.bosch.com.au/motorsport/dow ... ncoils.pdf quotes primary resistance of 0.45Ohms. No charge current is cited. Using 0.45ohms, your inductance value, and 4A current gives dwell of 0.93ms, so something's not right.

I've used the MEC coil in my car with 2.6ms dwell and have had no problems with spark.

-----Original Message-----
From: xxx@au.bosch.com [mailto:xxx@au.bosch.com]
Sent: Wednesday, 20 July 2005 16:47
To: xxx@tpg.com.au
Subject: Bosch Website Inquiry Reference Number: 17023

Dear Mr. Kelly

Thank you for your inquiry on Bosch Automotive Service and Technical Support, received on Wednesday, 20 July 2005.

In response to your inquiry:
I'm looking for a suitable coil or coils for your 0 227 100 200 module.
Either 2 x double ended, or something like the 0 221 503 407.

Does the 200 module do dwell control? What duty cycle to run the ignition module at?

And related, what dwell settings do the MEC717/718 coils like?

We would like to advise:
0227 100 200 does not have dwell control. Dwell is controlled in the engine ecu.
We do not have rise times for 0221 503 407 readily available.

The coil used with 0227 100 200 is 0221 500 413.

Dwell at 12 volts is 2.6ms at 13.5 volts 2.3 ms. for MEC coils.


Please do not hesitate to contact us again if we can be of further assistance.

Regards

Bob Tait
Automotive Service
Customer Service Representative
Robert Bosch (Australia) Pty Ltd
Visit our Website at http://www.bosch.com.au

[Tortfeaser]

Now I'm even more baffled. I emailed Bosch again today. They quote 2.5uH (must be mixing units up) and 6A current.

Those values give calculated dwell of 1.42ms vs their recommended 2.6ms.

Clamp at 6A

-----Original Message-----
From: xxx@daff.gov.au [mailto:xxx@daff.gov.au]
Sent: Tuesday, 16 January 2007 3:01 PM
To: Tait Robert (RBAU/ASA2)
Subject: RE: [UNCLASSIFIED]RE: Bosch Website Inquiry Reference Number:
17023

Thanks.

Sorry again.

What about primary current?

-----Original Message-----
From: Tait Robert (RBAU/ASA2) [mailto:xxx@au.bosch.com]
Sent: Tuesday, 16 January 2007 2:59 PM
To: xxx@daff.gov.au
Subject: RE: [UNCLASSIFIED]RE: Bosch Website Inquiry Reference Number:
17023

2.5uH for primary, 24 Henries for secondary.

-----Original Message-----
From: xxx@daff.gov.au [mailto:xxx@daff.gov.au]
Sent: Tuesday, 16 January 2007 2:26 PM
To: Tait Robert (RBAU/ASA2)
Subject: [UNCLASSIFIED]RE: Bosch Website Inquiry Reference Number: 17023

Dredging up an old email to you...thanks for your help then.

Have you got an inductance value for the MEC coils?

Marc

[The Witzl]

Marc,

Talking to my tuner, who deals with the MEC717/718 coils a LOT on aftermarket systems.... they say the coild can be run that low, but they are a tough coil and can happily take up to 3.0ms of dwell before starting to get into the danger zone of heat.

He recommended about 2.5-2.7ms of dwell, which matches up to what Bosch recommend.

I queried this against the calculations using the formula lance provided above, and was told that yes, thats correct - but the bosch MEC717/8 coil runs a lot better with ~2.5ms of dwell.

Changing my dwell from 1.5ms to 2.5ms made a decent improvement in my ignition system, so im happy with 2.5ms - and the coil doesnt get very hot either

[mops]

yeah, having formulas it really neet, problem it's hard to find out the indictance of a particular coil. hardly any coild have this specified either on the coil or in some documentation. even msd blaster2 coil, which I run.... no info on manufacturers website wither regarding suggested dwell or inductance...

[Quan-Time]

I have dyna DC3-1 coils, they are rated at 3ohm. Fairly common on bikes.

From the + to - terminals, its 3.6ohm on the multimeter.
From the + to the spark output is 14.24kohm
Obviously a 12v engine.
Im not sure about the L (inductance) on my system. I use DW-800 "suppression" silicone leads if thats any help.
I run 2 coils, wasted spark, on my 2cyl motorbike engine.
Can someone please help me set my dwell correctly, and I can go from there.


Incidently, the "ignition table" is a bit crazy.. sounds VERY flat while running, i thought it might be my dwell, but bike does indeed run. I plugged my bike info into the calculator in MS2, and the resulting output table was created. Ideas ?
850cc, 80hp @ 7500rpm / 62lb @ 6000rpm, 8000rpm redline. This is the "stock ECU" settings, and the bottom table is the settings ive plugged in. Seems really excessive, 103deg @ 6000rpm ? sheesh..
http://www.tr1x.org/images/TR1X-MStiming1.jpg - for those that want to see.

[MegaDave]

Dyna 3.0 ohm green coil inductance = 13.65mH
I think you can increase your dwell quite a bit more with this coil. 3ms would be too short.

[Quan-Time]

@ MegaDave
wow, smart man you are
i just got a reply email from Dyna, 12hr turn around, so im well happy.. this is what they have to say:
"The minimum dwell time would be 8 milli-seconds, and up to 12; the inductance
in mH is 13.5, which can vary from 13 to 14. I hope this helps."

So it seems my wet fart exhaust is because of underpowered coils.. Ill have a play around and see what i can come up with. All i know is these things are HUGE and im not really afraid of the heat. They are designed for 1600+cc harley "sports" engines, or highly modded engines.. So im confident they should be fine.

I dont have an Amps rating, or is that just the battery output ? Anyone wanna help calculate the "Bruce" dwell time ? Thank you so much MegaDave, big help !

[MegaDave]

Well, for the dyna coil, at 3 ohms, and a 12v battery, the most you will ever see is 4 amps. That is very low current (the ignition transistors should be able to handle that all day, especially with a heatsink), and i would just stick to a nice round 10ms. If your engine revs really fast, try 12ms.

[Quan-Time]

i have a few options here.
With the "standard dwell" option, i can only set "max dwell duration" to 8ms.
Dwell time is not editable unless i set it to "time after spark", and that means i can only put in Dwell time, everything else is not editable in that form. But i can set 10ms dwell in that way.


As you can see, thats my options.. Do you think 8ms will be enough, or should i try changing it to "time after spark" set 10ms dwell ?
Suggestions ?

[MegaDave]

I hope the MegaSquirt experts can help with the settings.
I do not understand the 'time after spark' of 10ms setting.

I only understand, you should use at least 10ms dwell, and a minimum of 0.5mS "burn time".

So, the ignition should be able to maintain 10mS of constant dwell, until the RPMs get high enough, and 10mS is to long, so you will have a 0.5ms time for the spark to occur, then the dwell begins again, and the original 10mS starts to get shorter. This sounds undesirable, but its not as bad as it sounds. I know that when this occurs, some of the magnetic field in the coil remains, and its not like starting from 'zero' or 'empty' coil.

[daniel505gti]

I have just scoped a HEC 716 Bosch coil. designed to replace older electronic ignition coils.
I found 5.5 ms entered in mega tune at 13.5 volts running was just to the end of the saturation ramp.
I will pick up a inductance meter in a few days and see if the maths shows what I saw on the scope.

[Quan-Time]

Ive tried standard dwell with 8ms. Bike seems to run much nicer at low end, but tends to die at top end. It used to idle @ 12.6v, now its 11.8v, and it maxes out at 12.6v around 4500rpm. Where as previously it was 13.8v. I suspect my charging system cant handle the new uprated coils and huge dwell times.
Possible generator replacement / rewind. My battery doesnt seem to hold much charge either. Cause or symptom ?