Home Model Engine Machinist > Building Them > Questions and Answers > Multi cylinder CDI
Reply
 
Thread Tools Display Modes
Old 07-04-2013, 06:24 PM   #1
Leucetius
 
Join Date: Nov 2010
Posts: 29
Liked 2 Times on 2 Posts

Default Multi cylinder CDI

Good evening guys.

A friend of mine and I have a question regarding CDI on multi cylinder engines. More exactly if it is possible to realize this (in our world) without the usage of a distributor to direct the discharge of the coil to the correct spark plug?

Greeting from Germany
Kevin



__________________
Leucetius is offline  
 
Reply With Quote Quick reply to this message
Old 07-04-2013, 06:41 PM   #2
Lakc
 
Join Date: Aug 2009
Location: Detroit
Posts: 967
Liked 54 Times on 51 Posts
Likes Given: 17

Default

To direct the discharge of a coil without a distributor is probably not going to happen. Multiple CDI units with multiple coils are generally the way its done.



__________________

Jeff

Lakc is offline  
 
Reply With Quote Quick reply to this message
Old 07-04-2013, 07:03 PM   #3
Jasonb
Project of the Month Winner!!!
 
Jasonb's Avatar
 
Join Date: Mar 2008
Location: Surrey, UK
Posts: 1,900
Liked 318 Times on 189 Posts
Likes Given: 11

Default

Depends on how many cylinders you have, if not many then the lost spark method is common. eg when the CDI is tripped usually by a hall sensor it will send a charge to each sparkplug only one of which will actually fire.

On say a V8 you could get away with two CDIs and loose the sparks.

J

__________________
Jasonb is offline  
 
Reply With Quote Quick reply to this message
Old 07-04-2013, 09:09 PM   #4
el gringo
 
Join Date: Aug 2010
Posts: 66
Liked 7 Times on 5 Posts

Default

Roy Scholl at S/S engineering set me up with a two coil CDI for one of my
two cyl engines at a minimal extra charge that allowed me two wire both spark plugs from the same CDI although they were both triggered by the same hall sensor.

__________________
el gringo is offline  
 
Reply With Quote Quick reply to this message
Old 07-04-2013, 09:38 PM   #5
Leucetius
 
Join Date: Nov 2010
Posts: 29
Liked 2 Times on 2 Posts

Default

The engine at stake can be seen at the attached pictures. It's from the magazin 'Model Engineer' and my friend is in the planning phase of making it. I've done the CAD files for him and now he wants to change the engine from it's original glow plug system to spark ignited. As you can see on the rear view, a hall sensor can be attached at the camshaft without destroying the overall look. Imagine this beauty with a distributor...

Quote:
it will send a charge to each sparkplug only one of which will actually fire
So on the 4-cycle, 4-cylinder engine shown, this means all spark plugs fire together every cycle/90° camshaft rotation? Doesn't this especially leads to problems at the end of the intake/begin of compression?

We thought that maybe it's possible with 4 hall sensors but just one magnet. In the manner that there's just one coil which is triggered by each sensor and somehow the circuit routes the discharge to the corresponding spark plug.




__________________
Leucetius is offline  
 
Reply With Quote Quick reply to this message
Old 07-05-2013, 03:53 AM   #6
dieselpilot
 
Join Date: Jan 2009
Location: Chicagoland
Posts: 1,188
Liked 87 Times on 79 Posts
Likes Given: 1

Default

Switching high voltage electronically is not easy or practical. A pair of twin ignitions is the simple answer if you want CDI and no distributor.

Seeing that you're in Germany you may look at http://www.power-spark.de/

Greg

__________________
dieselpilot is offline  
 
Reply With Quote Quick reply to this message
Old 07-05-2013, 07:30 AM   #7
Jasonb
Project of the Month Winner!!!
 
Jasonb's Avatar
 
Join Date: Mar 2008
Location: Surrey, UK
Posts: 1,900
Liked 318 Times on 189 Posts
Likes Given: 11

Default

It will depend on your timing and crank layout but taking a twin or one side of your engine as an example with two magnets on teh end of the cam shaft and one hall sensor.

As one sparkplug fires at the top of the compression stroke the other will get a spark at the top of the exhuast stroke which will have no effect.

The problem starts as you get more cylinders and the sparks get closer together to a stage where you get an early spark in one of the cylinders that tries to make the engine backfire.

J

__________________
Jasonb is offline  
 
Reply With Quote Quick reply to this message
Old 07-05-2013, 10:05 AM   #8
Leucetius
 
Join Date: Nov 2010
Posts: 29
Liked 2 Times on 2 Posts

Default

Thanks for your answers. We think the lost spark method is interesting as such but he won't use it. My friend will buy
a) one RC-i 400 from Power Spark and
b) two RCexl Twin cylinder from RCXp
when the engine is ready for testing - I will post results and videos.

Greetings and happy weekend
Kevin

__________________
Leucetius is offline  
 
Reply With Quote Quick reply to this message
Old 07-05-2013, 11:15 AM   #9
Niceonetidy
Colin D
 
Niceonetidy's Avatar
 
Join Date: Jul 2012
Location: Dixie land UK
Posts: 115
Liked 33 Times on 20 Posts
Likes Given: 53

Default

BTW,

You can buy these single and Twin Rcxel units at an amazingly low price from Hobby King, Search engine accesories

__________________

Life long modeller, www.bailey-steam.com

Niceonetidy is offline  
 
Reply With Quote Quick reply to this message
Old 07-05-2013, 06:05 PM   #10
Leucetius
 
Join Date: Nov 2010
Posts: 29
Liked 2 Times on 2 Posts

Default

That's a nice information! I know HK from my days I was flying several Helicopter and Airplanes, main source of LiPos in this time and scene



__________________
Leucetius is offline  
 
Reply With Quote Quick reply to this message
Reply


Quick Reply
Message:
Options

Thread Tools
Display Modes

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off

Forum Jump

Similar Threads
Thread Thread Starter Forum Replies Last Post
Multi page thread Draw-Tech Questions and Answers 2 03-22-2013 12:02 AM
A multi-cylinder crankshaft machining tutorial gbritnell A Work In Progress 26 05-30-2011 10:06 PM
Multi-lead threads joeby Tips and Tricks 13 03-11-2010 05:10 PM
Making Multi Cylinder Engines Philjoe5 Questions and Answers 7 11-26-2008 04:54 AM
Smithy Multi-Function machines Graybeard Questions and Answers 12 01-04-2008 05:55 PM

Newest Threads




- Top - Member List