what is Hall effect?

[zeusrekning]

I've seen alot about hall effect ignitions while looking at some small engines. Could someone explain in laymans terms how this works. I'm familiar how ignition works on the small go kart engines. How is this different than Hall effect ignition?

 

[RonC]

Ignition points are a switch. So is a transistor. A "Hall effect" transistor uses a magnetic field instead of a bias current to turn the device on. So instead of a cam, you have a disk with a magnet on it, and instead of mechanical points, you have a Hall effect transistor, usually driving another transistor (or two) capable of switching higher currents. This assembly can be rotated to provide advance/retard, just like normal points.

 

[1Kenny]

It is how Ronc explained it. To add to it a hall effect sensor can be used for many things including driving a tachometer. The Delphi site has lots of information on it about voltages and applications that may help you out. Auto wrecking yards are an inexpencive way to get a hold of sensors.

Kenny

 

[cfellows]

One difference between points and hall effect is that a hall effect transistor can only switch small currents. You have to use a transistorized ignition module in addition to handle the heavy current required by the primary of the ignition coil.

Points, as you know, will drive a coil directly although you can also use points (or even a microswitch) with a transistorized ignition module.

Chuck

 

[Bogstandard]

If you go to Jerry Howells site here
http://www.jerry-howell.com/IgnitionMenu.html
He shows what the components that are required to make a basic and very reliable system. Plus he also shows how they are set up for dwell angle etc. I actually made half a dozen of them for the same price by etching my own boards and buying the components.


Here is a setup on one of my engines.

The rotor disc on mine is mounted on the end of the camshaft. I embedded the hall sensor into epoxy in a groove machined into an ali holder that can be rotated around the camshaft drive to give advance and retard. For multi cylinder work, for two cylinder you can get a twin fire coil that fire both plugs at the same time and uses a 'lost spark' method of firing the plugs. For more cylinders you can use a distributor with an interrupter plate, so one magnet and one sensor can be used to fire say up to eight cylinders.
The main advantage of hall sensors is the ability to work under very harsh conditions (if sealed correctly), as you can see on my engine, it is covered in oil and grime after a half hour running in session, which with a normal points system could lead to loss of operation. Also they don't suffer from points bounce or wear on the cam follower (no cam needed) as it is purely non contact and usually is a more compact setup.

Hope this helps

John

 

[zeusrekning]

Thanks John , the pic helped alot. It looks like it works the same way as the points-less ignition on go karts. It just hit me typing this that when I said ignition on go-karts that most people think points type ignition. My kart engines always had the magneto with out points. I'll check out the link before asking anymore questions. Again thanks guys.

(Edited after following above link)

Is the spark plug firing as long as the magnet is in the path of the hall sensor?
I am still not understanding the dwell angle completely. It seems like the plug would be firing through the entire ignition stroke. Also, how is battery life. I understand the guys whom John linked to states that his parts are intended to be used on models. I would be using this on soon to be mobile projects. I'm assuming I would need a 6volt charging system.

 

[mklotz]

Probably more than you want to know but it's interesting to know what's going on inside a Hall effect device.

Physicists have long been aware of something called the Lorentz force. If a charged particle moves across a magnetic field, it's path will be curved by the field. This principle is what makes a mass spectrometer work.

In the late 1800s, Edwin Hall noticed that the motion of these charges generated a voltage difference perpendicular to the field and nominal direction of motion of the particles.

Imagine a magnetic field along the Z direction passing through a plate of material lying in the X-Y plane. If I pass a current (negatively charged electrons) through the material in the Y direction, I will be able to measure a voltage across the X direction of the material.

In the Hall effect sensor of which we speak here, the material is a semiconductor through which we pass a current. When an (properly oriented) external magnet comes close to the material, the orthogonal voltage is sensed and that voltage is used to turn a transistor switch on.

An interesting aside here. Submarines (and probably other ships) use a Hall effect log to measure their speed through the water. A probe is poked through a water-tight seal in the hull of the ship. Inside the probe is an electromagnet that generates a magnetic field. Sea water flowing past the probe contains ions - particles with a residual charge (this is why sea water is a reasonable conductor of electricity). The motion of the ship then generates a voltage, via the Hall effect, which is sensed by two small contacts on the side of the probe. This voltage is proportional to the speed of the ship through the water and can be used as a relative speedometer.

 

[Powder keg]

Great Marv!!! More useless info stuffed into my brain:O) I'll be able to remember this in 30 years but not where I live:O)

Wes

 

[Lew Hartswick]

Thanks Marv. I was contemplating a treatise on the Hall effect but decided it would
be "over kill" for the O P and gave it up. But on the other hand maybe it was intresting
for some of the others. The use of such in the computer fans to generate the
rotating field in brushless DC motors etc I'm sure would be inappropiate here.
...lew...

 

[zeusrekning]

Is the dwell time charging the coil. When does spark occur? Is it as the last magnet passes?

 

[Bogstandard]

Hi Z,
My engine shown below runs to a max of about 6.5-7k rpm.
The disc diameter as far as I can remember is either 5/8" or 3/4" and uses one 1/8" magnet. If you have trouble calculating things out, Jerry Howells is a very helpful person, and I am sure he will be able to sort out things like disc sizes vs RPM.

When the magnet starts to pass the hall sensor, the sensor is switched on, and thru the tim6 circuit the coil charges up, and as the magnet finishes passing, the sensor is turned off and the coil then fires. This is what Jerry explains about when he talks about dwell angle. Too long a dwell angle (too many magnets) give a long charge time and causes overheating of the coil and wastage of the battery power. Basically, if you have a large rotor (say maybe a big flywheel) that your magnets are mounted in, you will require more magnets, smaller rotors (like mine) would only require one 1/8" magnet, and any smaller would require maybe the 2mm one.
I use a small 3amp hour 6volt gel cell for running mine, and that should give at least a couple of hours running. A pack of four or five NiCad or NiMh AA cells of say 1.5 to 2AH cells should give you well over an hours running.

I hope this has helped to explain it a bit better, all these wiggly amp things baffle me at times as well.

John

 

[zeusrekning]

I think I get it now. I have looked the internet over for a 12volt system similar to jerry howells with little luck.

The project I am working on is a 1969 Rotax 320cc two stroke. I know it's not a model but I hope to use this engine on future engine designs I want to work on. The engine will moe than likely not be used for anything other than maybey a future gokart project. I need a 12volt system mostly because the engine has a 12volt starter on it and I would like to retain this along with a 12volt charging system.

The best thing I have found is John Clarke's CDI ignition plans http://www.not2fast.com/ignition/cap-dis-ignit-cdi.pdf.
But it looks complex for me being I am not an electronics guru.

Is there a way to use the Jerry Howells TIM-6 system on a 12v system?

 

[Bogstandard]

Hi Z,
Have a look here, you might have to use a 12volt auto coil.

http://www.5bears.com/tim4.htm


John

 

[Ripcrow]

Why not a simple reed switch instead of a hall sensor

 

[cidrontmg]

I think a reed switch works ok, unless the frequency is rather slow. 5 sparks/sec is only 300 rpm. There's no way to run a F1 motor at <10000 rpm with a reed. At 50 sparks/sec, that's 3000 rpm - no way. But you could try

 

[canadianhorsepower]

or this circuit

http://www.homemodelenginemachinist.com/f31/new-ignition-circuit-20415/index7.html

 

[stevehuckss396]

Could someone explain in laymans terms how this works.

There is a sensor called a hall sensor that replaces the points. When you expose the hall sensor to a magnet it turns on which is the same as the points being closed. When the magnet is removed it turns off which is the same as the points opening. Using the signal from the hall sensor the coil is turned on and off creating the spark.

Thats about as simple as I can make it.

 

[stevehuckss396]

Why not a simple reed switch instead of a hall sensor

Size and speed. The hall sensor can turn on and off faster and it is only 3/16 of an inch square.