$30 ignition

[Generatorgus]

OK, now I've got one, and a few questions.
This ignition was is obviously intended for RC models as the spark plug output is entirely shielded. As the spark plug fitting is not suited for the tiny plug on my Little Brother, I have to adapt. After I pealed back the cable shielding and removed the metal spark plug cover I found what I think is a resistor between the wire and the spring which clips to the plug tower. As this seems to be a substitute for a resistor type spark plug, do I need to include it in the circuit, or can I just toss it as I have no other use for it?

I rigged this temporary set up on the Brother, the timing will be adjusted by turning the alum. disc, rather than moving the sensor. Can I static test the hall sensor to set the timing or does it have to be hooked to the electronic module? Also the magnet in the disc is 5/16 dia., should I use something smaller?
GUS

 

[kustomkb]

I think 5/16 sounds a bit big, I think. Also the polarity of the magnet is important. I don't know anything about these ignitions except that it worked well on my "Hoglet". The Canadian distributor will include a digital tach when you order the RCEXL from him.

Here are some instructions;

http://www.hobbyking.com/hobbyking/forum/uploads/6061/RCEXL_Manual.pdf

http://www.cncengines.com/rcexelcdi.pdf

http://www.rcaer.com/userfiles/file/RC Aero - RCEXL Opto Cut off Switch - How To.pdf

 

[mu38&Bg#]

The size of the magnet impacts the RPM at which the ignition retards the timing for starting. These ignitions are designed to be timing for full advance. At very low RPM, like during setup when timing the spark, there is no delay so it can be setup properly. At hand cranking speeds, something like 300 RPM, the ignition retards the timing about 24° to make hand propping a model airplane engine easier. Then, by 4000RPM all the retard is taken out and spark occurs at the position it was set up at. When cranking it times how long the magnet is under the sensor. It needs to see something roughly equal to a 3/16" magnet passing the sensor at 1" radius at 300RPM for it to retard the spark. If the engine is running between 1000 and 4000 RPM, it will be somewhere between 24° retard and no retard.

The sensor itself can be set up without the ignition. The trigger is on the trailing edge of the signal. I noticed you've pulled back the shield on the spark lead. It is very important that this is grounded to the engine or the ignition will be damaged. These are designed to suppress noise so the lead is shielded with the ground. The resistor is there to reduce noise as well. You do not need it, nor a resistor plug, unless you find it causes interference with something.

 

[jonesie]

i also think the magnet is big i use a .125 dia. on my powerhouse and farmboy. i added a resister to my plugwire on my powerhouse but off the top of my head can not remember the size but it seemed to help, it is an ignition by jerry howell the farmboy is an s-s one, also the polarity is critical i think the south pole needs to pass by the hall sensor. good luck jonesie

 

[Lakc]

You can live without the resistor, but it does help cut down on spark plug erosion, magnetic force surrounding the wires, and the associated radio frequency interference.

Depending on the design of the ignition, and if its a copy of the ignition system I think it is, the magnet size doesn't matter. Its more then likely counting the time between pulses, so the dwell of the pulse is not important. That's entirely unlike some, and the ignition I designed, which counts the dwell time to determine rpm.

 

[picclock]

IMHO

Leave the resistor. It will cut down on radio frequency interference, decrease spark plug erosion. Its also important not to change the type of resistor as film ones break down in this type of application (the type you have looks like cracked carbon which is very similar to pencil lead - carbon and clay mix).

The magnet positioning looks wrong to me. Disc magnets are normally magnetised north on one face and south on the other. To trigger the sensor in an accurate repeatable way means that the flux change should be well defined. The way you have it mounted at the moment the flux will increase gradually as the edge of the magnet moves closer to the sensor, then decrease as the rotation carries it past. So although it will likely trigger, the position of triggering is dependent on device sensitivity, which varies widely over temperature/time. As an example if the magnet was rotated 90 degrees about the vertical axis the flux change would now take place over the width of the magnet resulting in a more accurate pulse. On some commercial systems the rotor is made of iron (magnetised) and comes to a point where the sensor is to ensure accuracy. Other systems use the sensor to detect the point at which the flux reversal takes place (the middle of the edge of you magnet shown).

A better approach may be to get one of those earing magnets and drilling a hole in the rim of the disc to carry it. At least the flux change would be concentrated over a narrow area so the timing change would be minimal.

Hope this helps a bit.

Best Regards

picclock

 

[ruzzie]

Hi
I just purchased a replacement cap to suit a 1/4" spark plug

http://www.dlenginesaustralia.com/dlshop/index.php?_a=viewProd&productId=151

Cheers
Paul

 

[Generatorgus]

That's what I love about this website. What a helpful bunch. Maybe it's the way I'm searching, I just couldn't come up with all the info you guys just gave me. :bow: Thank you all.
I'll leave the resistor in the circuit for plug erosion issue not because of radio inteference, everything imaginable disturbs the reception of the ancient stereo I have in my shop.

GUS

 

[RonGinger]

Where did you get this $30 ignition system?

 

[mu38&Bg#]

That magnet position is OK. If it doesn't trigger due to magnet polarity and turning the magnet around isn't convenient, you can turn the sensor around. All they want is a particular field orientation. Not ideal, but the engine won't notice.

Placing the magnet on edge, so the sensor sees one pole then the other is not desirable. While I don't doubt the variation in in the trigger point picclock describes, model airplane engines, some costing 5000USD use the magnet arrangement in the manual without issue. And the ignition manufacturer uses the cheapest Allegro unipolar hall sensor available, with the widest tolerances. Some ignitions do use latching bipolar hall sensors and two magnets on the crank, but these are OEM because they would be complicated to install as an aftermarket item.

Will ±5° spark timing have any influence on how this engines runs? Probably not much.

 

[Generatorgus]

Ron, This is the supplier, mine was direct shipped from China , took about 2 weeks.
http://www.hobbyking.com/hobbyking/store/uh_viewItem.asp?idProduct=13767
I haven't tested it yet, believe it or not I have to go get a 6 volt battery, I've trashed dozens of them and now I don't have one.
GUS

 

[Generatorgus]

I broke down and bought a 6 volt battery, broke my heart, cost half the price of the ignition. Did a quick rig job on a spark plug, but no spark , so I turned the alum. magnet wheel around to reverse the polarity, and hellooo... Mr. Spark. Good-bye points and hard to make fussy little cam. Electronic ignition is the best improvment the automotive industry ever made to gas engines and I already like it for models. And that's all I have to say about that.
Thanks all for the help.
Now if I can figure out why I'm not getting any fuel up...
GUS

 

[Lakc]

Odd that its 6 volts, a $.79 regulator would make it work from 6-60v. Glad you got it going.

 

[flatbelter]

Hello Generatorgus,

I've been looking at that chinese ignition system for some large RC airplane conversion engines (25-100cc). How is the durability of your system? Have you had a chance to run it yet? If so, how much run time have you had?

I'm machining a new flight weight crankcase for a 35cc echo chainsaw engine that would be just the ticket with electronic ignition.

fb

 

[Generatorgus]

fb,
I can't vouch for durabilty over a time period, but it seems to be pretty durable. I put the Hall sensor thru some hell, when I was adjusting the timing, I accidentally pushed the alum disc against it, not once but several times, didn't seem to harm it. Also, I had a brain fart and hooked it up to a 12 volt battery when I thought the little 6 volt was low on charge. I felt pretty dumb, my test spark plug just kept firing even though I wasn't spinning the engine, took me a while to figure it out. :
but apparently no harm was done.

dieselpilot,
Not to change the subject but I'm still confused about timing this thing. My engine is supposed to be set at 10 degrees BTDC, but I had to advance it to about 40 to get the engine running. Wassup with that? The engine is a Briesh, Little Brother, hit and miss. I have the governor removed because I have just made my initial start up. I don't know what RPM it was running, but it was really going. Is this ignition OK for the little guy. Then I read the Jerry Howell thing about his ignition and it added in the extra confusion about dwell and the dia. of the magnet disc, as well as the dia. of the magnet.

GUS
Confused in NE PA ??? (not unusual)

 

[Lakc]

Did you actually check with a timing light, or are you basing that on where the hall sensor is?

Some of the automatic spark advance types require the hall to be 37 btdc, which sounds like what you have.

 

[mu38&Bg#]

I understand there was a run of the RCEXL units that had a different curve than the 24° I described earlier. The airplane guys had trouble starting their engines as well.

Gus, If you need 10° advance running at some speed below 1500RPM then following the manual you'll need to set the timing, but to probably what you found at 37°, roughly 10+24°. This is because the engine never reaches a speed at which the ignition begins to advance the timing. It's always running -24° from where it's set by the manual. In practice this should have no effect on your engine, just set the timing for good running. Where you might see trouble is during starting. If you find the engine kicks back or the ignition fires much too early, reduce the size of your magnet to improve this situation. During starting this system measures dwell (it can't measure time between triggers, because if it doesn't fire on the first compression stroke of an airplane engine it simply won't start) of the magnet to determine RPM.

Greg

 

[Generatorgus]

Jeff, No, not with a timing light, I thought of it but, I lent my timing light to a "FRIEND" who hasn't done me the courtesy of returning it yet. I guess lending means you also have to make an effort to retrieve the item or it automatically becomes the property of the lendee.

I guess I just didn't/don't feel comfortable with the timing set so far advanced, just doesn't seem right.

THANKS GUYS

GUS

 

[Generatorgus]

Well I guess I was too rough on the hall sensor, it failed. My ignition still throws a spark when I turn the power on, but won't spark when I turn the engine.
I checked Ebay and there are lots listed, fairly cheap. Do I need a specific type?

 

[mu38&Bg#]

You need a unipolar open collector sensor. http://www.allegromicro.com/en/Products/Categories/Sensors/unipolar.asp