Hall sensor again

[Gordon]

I have just completed putting a transistor ignition system on one of my engines (Duclos six cycle) I seem to be burning out hall sensors. I am using a TIM-6 ignition which I have assembled from components but it is the fourth one I have completed. I have the magnet mounted in the brass timing gear. There is a steel cam mounted on the back of this gear also and the high lobe of the cam clears the end of the sensor by about 1/16". I burned out the first one because I assumed that the ground was not good enough so I moved the ground wire to the aluminum bracket which holds the sensor. I got the engine running for about one minute then it died. There is a LED in the circuit so I can see when the sensor is activated. After some playing around I discovered that I was not actually getting spark at the plug in spite of the LED. I can get a good spark by jumping the base and signal on the hall sensor but not through the LED. I have been turning it over with a cordless drill because it takes a rather high RPM to get it started. While turning it over I could see the LED flashing and then fading until the LED would not light and the sensor was burned out. I can still get a good spark by jumping base/signal. I have looked at all solder joints and see no bad joints. Is it possible that having the cam running next to the sensor or the magnet passing a steel spur gear (90° from firing position) the sensor is being effected? Any other ideas?

Gordon

 

[canadianhorsepower]

Gordon
I have my doubt about any parts beeing to close
but usualy a LED will fry like your descrption goes
Hi then fading then nothing. Can't help you much without a diagram
but I would check the resistor value, this would drive more current
then needed and fry stuff. If you have diagram please post

have a look at this diagram it's solid as a rock
http://www.homemodelenginemachinist.com/showthread.php?t=20415&highlight=sage

 

[tornitore45]

Make sure you have two wires from the engine to the ignition board in the following configuration:

From the ignition board ground point to the engine frame on any point that has a good metal path to the head where the plug is.

A second wire from the ignition board ground point to the common of the Hall Sensor.

The Hall Sensor common is NOT grounded at the engine but is grounded at the ignition board.

Doing so it eliminate a common GND path between the spark current and the weak Hall sensor current. The ground lead from the engine frame carries ONLY the spark return current and it easily has a drop of a few V due to the fast wavefront. If the sensor was grounded at the engine frame, this voltage drop would appear in series with the Hall sensor and zap it.

I have built the same engine this summer and had some difficulties in sustaining the run, no ignition problems.

The governor weights seems too heavy or the spring too weak because it cut off at too low an RPM.

When I disabled the governor it run consistently but would die at the slight manual application of the "miss" control, in other words it seemed that it has just enough power to keep running full throttle but not enough to stand a few misses.

I like to hear your experience once you get you ignition issues resolved.

 

[Gordon]

Thanks Canadian. That may be the problem. My electronic savvy is not too good so I basically just copied the Howell. I bought some LEDs and they came with a resistor so I just used that. The original circuit used a 270 ohm and the one which came with the LED is 200 ohm. I think that I will probably just take the LED out of the circuit since I can get close by eyeball and then tweak from there. I have build a couple of others from components and they seem to be working OK. Maybe just dumb luck.

Mauro: I had the engine running well until I started monkeying around with it again. I changed the carburetor to a Fellows design and that worked much better. I do have two separate grounds wires.

View attachment TIM-6A.PDF

 

[Gordon]

So I replaced the sensor and changed the resistor on the LED and also modified it like the other circuit so there is a jumper wire to disable the LED. Engine started and ran for about one minute with the LED disconnected until it faded and died just like before. Sensor burned out. Plug still fires with a connection between where the ground and the signal go on the board but the Hall will not fire it. I have built three others using this same circuit and same components and they work just fine. I think that I will try replacing the sensor with a switch and see what happens.

Some of us just cannot let well enough alone. I have 23 engines (steam and IC) so I hesitate to start a new one so I have been going back to previous engines and modifying carburetors and ignition. My tendency in the past has been to build an engine and quickly move on to the next one without some of the refinements to make it a final finished project.

 

[Gordon]

It may be time to confuse my already confused brain even further and look at reed switches. At this point I do not know what to look for to size a reed switch but they are relatively cheap. Amazon has them from under $1 and up.

 

[canadianhorsepower]

It may be time to confuse my already confused brain even further and look at reed switches. At this point I do not know what to look for to size a reed switch but they are relatively cheap. Amazon has them from under $1 and up.

try replacing R5 and the LED with a reverse bias diode
1n4007 will do

I think reed switch will float

good luck

 

[Gordon]

LUC: I will try but I doubt that will help because the LED was not connected while the engine was running. On the other circuit it showed a jumper on the LED and I thought that was a good idea. You do not need blinking lights. I just put in the jumper to make sure that the sensor was working and removed it to run. Still burned out the sensor. I still have not figured out why this unit is acting different than the other three I have assembled from components and the two I assemble from the Howell kit.

 

[canadianhorsepower]

LUC: I will try but I doubt that will help because the LED was not connected while the engine was running. On the other circuit it showed a jumper on the LED and I thought that was a good idea. You do not need blinking lights. I just put in the jumper to make sure that the sensor was working and removed it to run. Still burned out the sensor. I still have not figured out why this unit is acting different than the other three I have assembled from components and the two I assemble from the Howell kit.

Gordon: you don't want to put a jumper in place of the LED and resistor this will fry your all sensor. The output of that sensor is an output
btw what is the part number of that sensor

cheers
Luc

 

[Gordon]

I did not jumper across the sensor. I just put in some terminals so that I could eliminate the LED from the circuit and put in a jumper to put the LED back in the circuit. The Hall sensor is #A3144. It is the same one I have been using on the other units. I may just use a micro switch on this engine instead of the Hall but I certainly would like to know what makes this one different than the other units all wired the same.