Magnetic reed switch in a DIY electronic ignition application.

Thread Starter

James Siebold

Joined Dec 8, 2018
8
Hello. This is my first posting. My name is James and I am into cars, electronics, computers, audio, science to name a few.

Can you use a NO magnetic reed switch in place of breaker points? Connect one lead of the switch to ground/earth and the other lead to the negative side of the coil. Then use a plastic ring with a magnet that slips over the points lobe to close the contacts. With the reed switch mounted in the same direction as the magnet. If that makes any sense. I watched a YouTube video on how to position these switches.

This sounds way too simple. With any electronic ignition system, there are usually allot of components that goes along with it. Even those systems that takes the load of the points that allows the points to last longer.

I found some reed switches that says they are good to around 1.5 amps.

https://www.ebay.com/itm/20-Pcs-14mm-Magnetic-Reed-Switch-N-O-SPST-USA-Seller/202522728698?ssPageName=STRK:MEBIDX:IT&_trksid=p2057872.m2749.l2649

I have not tested the current draw of the coil in question but I did test it on another car and it was .4 amps at 12.6 volts. The car in question uses a 6 volt electrical system. I have not tested the current draw of it's coils but I would expect it to be double that.

The car in question has a maximum speed of 5000 rpms. But has 2 cylinders so if I did the math correctly, 5000 rpms would be around 80 HZ. Could a reed switch handle that frequency?

If you are wanting to know more about this project keep reading.

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This is my Photobucket page of some of my projects.

http://s222.photobucket.com/user/turbofiat/library/?sort=2&page=0

Years ago I wanted a "dirt cheap" way of retarding the ignition timing for a turbo application without having to buy one of those MSD systems. I found a 5 pin GM HEI module. I'm currently using this on my Fiat 124 Spider and my Yugo I turbocharged. By grounding the 5th pin on the module through a pressure switch does the trick. I only need 5 degrees.

http://s222.photobucket.com/user/turbofiat/library/GM 5 PIN HEI module?sort=6&page=1

My current ignition project is for my Trabant 601. Very few people are familiar with these cars here in the United States. You guys from Germany and Eastern Europe know what I am talking about. For those who are not familiar with this car. It has a 600 cc 2 cylinder, 2 stroke air cooled engine. It uses 2 sets of points and 2 ignition coils.

Some photos of "Meine Trabbi":

http://s222.photobucket.com/user/turbofiat/library/Trabant?sort=6&page=1

I'm trying to reinvent the wheel/build a better mousetrap. I am not happy with what's on the market so I am trying to build my own electronic ignition system with some success.

Here is a photo of the breaker plate:

breaker points.jpg

Here is one of a few electronic systems on the market.

Hungarian system.jpg

This one is very hard to adjust. The plastic ring with the two magnets is oblong inside so there is not much room for adjustment. If the adjustment arches where longer it might be a better system. I had to force the plastic ring onto the points lobe and barely got the system in adjustment. Otherwise if the plastic ring is slipped on easily, the coils try to fire after top dead center.

One day I was trying to get more advance and accidentally shorted out the system that controls #2 cylinder on the board. I heard that the mosfets were bad about failing. I replaced the mosfet but it didn't fix it. I ordered another system and paid dearly for it (>$200), $50 was just in shipping and it doesn't work!

So I set out to build my own system using a points conversion kit for a Bosch distributor. Initially I tried building a "wasted spark" but I for some reason #1 cylinder was spot on, but #2 had way too much advance. I gave up on that so I purchased a second module so I could adjust both cylinders.

This board is a piece of Lexan coated with aluminum tape. It looks awful but this system I managed to get both cylinders spot on.

Trabant ignition.jpg

I removed the points lobe mechanism and used a piece of 1/4" NPT pipe, enlarged the center out with a 5/16" mm drill bit and soldered a piece of 1/2" copper pipe onto the end which the plastic ring slides onto.

https://drive.google.com/open?id=1W3UvgMc9g5Q6Ts2vEl3NsmbkuxX2j2my

This board took over an hour to make by hand using a drill press. The white mark on the plastic ring is where the magnet is located. This is for reference purposes and not to actually check the timing using a strobe light.

I removed the three other magnets and used some super glue and baking soda to fill in the gaps then sanded them down.

I can't remember if I took this photo with the engine "in time" or not but you would think that when the magnet is in the middle of the module is where it fires. But it's firing when the magnet is at the leading edge of the module.

To get both cylinders adjusted, I am controlling the advance by adjusting the air gap. The air gap is supposed to be about 1 mm. I found that by increasing the air gap, either advances or retards the timing (can't remember right off hand). That's why the board where the modules sit are slotted.

I did not like the looks of this board and decided to try again.

I had another board I had cut with longer arches so I decide to make another one. This time I have more adjustment of the timing and got #1 cylinder spot on but #2 has too much advance because I did not get the module exactly 180 degrees from the other module.

Today I tried to see if I could adjust the timing by adjusting leading edge of the module away from the magnet. It's hard to tell but using a strobe light, it seems pushing the module closer retards the timing (of course you can only adjust it inwards so far) and moving it outwards advances the timing. But once I get about 4 mm away from the magnet, the coil stops firing.

I have not tried moving the trailing edge of the module outwards to see what effect this has on the timing.
 

Alec_t

Joined Sep 17, 2013
10,597
Welcome to AAC!
I wouldn't use a reed switch in the setup you describe for the following reasons :-
1) This type of switch generally handles low currents only; much less than the coil current needed for a healthy spark.
2) Arcing at the switch contacts would soon destroy them.
3) Work-hardening of the reeds would limit the life of the switch.
4) Depending on the reed material, reeds can become permanently magnetised by the regular passing of the magnet in the same direction, leading to permanent closure of the contacts.
5) Shock and vibration in an automotive environment could cause spurious closure of the contacts and hence mis-firing of the engine.

Have you considered using a Hall Effect sensor/switch?
 

Thread Starter

James Siebold

Joined Dec 8, 2018
8
Welcome to AAC!
I wouldn't use a reed switch in the setup you describe for the following reasons :-
1) This type of switch generally handles low currents only; much less than the coil current needed for a healthy spark.
2) Arcing at the switch contacts would soon destroy them.
3) Work-hardening of the reeds would limit the life of the switch.
4) Depending on the reed material, reeds can become permanently magnetised by the regular passing of the magnet in the same direction, leading to permanent closure of the contacts.
5) Shock and vibration in an automotive environment could cause spurious closure of the contacts and hence mis-firing of the engine.

Have you considered using a Hall Effect sensor/switch?
Thanks for your reply. Yes I have considered a hall effect sensor. I just haven't found any good kits yet. These modules I got for $25 a piece from Hong Kong. I don't know their reliability.
 

shortbus

Joined Sep 30, 2009
7,236
But it's firing when the magnet is at the leading edge of the module.
Its doing that because it is using a Hall sensor. Which is also what almost every "pointless" electronic ignition uses. I agree with what Alec says about the reed switches, they aren't made for what you're doing.

Instead of moving the one module in and out to change that cylinders timing, why not make it move side to side? Is there a centrifugal advance under the point plate?
 

Thread Starter

James Siebold

Joined Dec 8, 2018
8
Its doing that because it is using a Hall sensor. Which is also what almost every "pointless" electronic ignition uses. I agree with what Alec says about the reed switches, they aren't made for what you're doing.

Instead of moving the one module in and out to change that cylinders timing, why not make it move side to side? Is there a centrifugal advance under the point plate?
Yeah, I think making the lower module (#2 cylinder) adjustable from side to side is what I'm going to do. Luckily I have a spare engine I am doing some of this work on to make it easier.

I snapped a photo of my latest board but will have to upload it later. The pic is on my phone in my locker.

I actually did away with the centrifugal mechanism. I took a piece of 1/4" NPT pipe and soldered a piece of 1/2 copper tubing onto the end for the plastic ring to slide onto.

https://drive.google.com/open?id=1W3UvgMc9g5Q6Ts2vEl3NsmbkuxX2j2my

The Trabants that used the EBZA electronic systems starting in 1984 used a fixed static timing at 4 mm BTDC. From what I have read, the reason the engine starts at TDC using points is to compensate for a weak spark in colder weather and a possible weak battery. The electronic ignition system and 12 volts introduced in 1984 made that obsolete. I stacked a bunch of O-rings underneath the points lobe to lock the advance in place and ran this car with a fixed static timing of 4mm BTDC on points and it started up just fine.

Looks like someone has already done something similar like I am doing to an old BSA motorcycle.

https://pre31.wordpress.com/2014/07/14/electronic-magneto-conversion/
 

Thread Starter

James Siebold

Joined Dec 8, 2018
8
Some photos of the current board. If you look closely to the left of the bottom module you'll see the hole I drilled. This time I ran the screws into the Lexan. With the other board I enlarged the holes to 4 mm and used the mounting plates that came with the modules on the backside of the Lexan. And the #1 cylinder adjustment arches are longer to give more adjustment.

IMG_20181208_172636122-1612x1209_crop_387x387.jpg '

This photo turned out blurry for some reason.

IMG_20181208_172753417-1612x1209.jpg
 

crutschow

Joined Mar 14, 2008
23,776
According to this reference:
upload_2018-12-9_0-35-24.png

Assuming 3000 motor revolutions per mile with a 2-stroke engine, that means the reed switch would last as little as 33 miles when switching maximum power up to 167 thousand miles for a low load.

I also suggest you go with a hall sensor for better reliability.
A reed switch will likely not last longer than standard points would.
 
Last edited:

shortbus

Joined Sep 30, 2009
7,236
So I set out to build my own system using a points conversion kit for a Bosch distributor. Initially I tried building a "wasted spark" but I for some reason #1 cylinder was spot on, but #2 had way too much advance. I gave up on that so I purchased a second module so I could adjust both cylinders.
When you did your wasted spark type how did you go about it? It should have had two magnets diametrically opposed on the rotating piece. One thing to watch with some Hall sensors is they are polarity dependent on the magnets. Also you did use a waste spark type coil didn't you?

There are also ways of doing electronic ignition using points for the switch. Standard points ignition only wear out the points because of the high amperage, take the coil away and add a transistor type amplifier and points last forever. One of my old (1957) Harley's has one of that type on it.
 
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