Author Topic: Hall Sensors  (Read 11342 times)

Offline Alan Haisley

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Re: Hall Sensors
« Reply #30 on: January 20, 2014, 02:32:43 AM »
Mosey,

Your picture of the circuit board looks like the circuit board is between the transistor and the heat sink. If so you won't get much heat sink value.

Also it looks like your heat sink is screwed to something which makes me wonder if the heat sink is electrically isolated from the engine and everything else. Assuming the engine frame is in the circuit somewhere the heat sink needs electrical isolation.

Alan
Near Raleigh, NC, USA

Offline Bezalel

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Re: Hall Sensors
« Reply #31 on: January 20, 2014, 03:13:49 AM »
Hi Mosey
 
Alan,
 
I just visited Jerry's web page
 
well knock me over with a feather!   Jerry bolts the semiconductor directly to the circuit board.

 I guess he doesn't get daily ambient temperatures in the thirties and forties oC at his place.



 
The designer says it works and there are plenty of them out there so I guess history shows it is ok with this circuit.

Still not good practice in my view.

Bez
Queensland - wet one day, humid the next

Offline Don1966

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Re: Hall Sensors
« Reply #32 on: January 20, 2014, 03:44:18 AM »
Mosey,

Your picture of the circuit board looks like the circuit board is between the transistor and the heat sink. If so you won't get much heat sink value.

Also it looks like your heat sink is screwed to something which makes me wonder if the heat sink is electrically isolated from the engine and everything else. Assuming the engine frame is in the circuit somewhere the heat sink needs electrical isolation.

Alan
Allen your point is well taken, the collector of the transistor is usually the part attached to the transistor tab. In this circuit the collector is tied to the coil lead and the emitter is tied to positive lead this would short out the transistor.
Mosey I suggest you make sure the transistor tab is not connected to the heat sink and the engine. I can send you a mica isolator and a screw insulator insert if you want it.

Don

Offline Mosey

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Re: Hall Sensors
« Reply #33 on: January 20, 2014, 02:03:27 PM »
Don, I'm a little befuddled. Yes the heat sink is connected to the tab with a 2-56 brass screw, with the PCB in the middle, and then the engine frame. If not connected to the tab, it is no longer a heat sink. I can certainly isolate the HS from the engine with nylon bolts and washers, as I intended to use the HS as my mounting for the PCB. But, is the tab really connected to the circuitry of the transistor? Strange, as it is there for HS purposes. I only included the HS because it makes a nice mount and it looks cool.
To recap: Isolate the transistor and the HS from the engine, but connect them mechanically to each other for heat transmission.
I will use the Cap furnished by Roy Sholl on his coil.
New transistor is coming and will be used.
Retest as per Don.
Then, we'll see some sparks? Maybe? Hope so.
Thanks guys, really appreciate all the help.
Mosey ( out here in the darkest jungles of New Jersey) :happyreader:
             
« Last Edit: January 20, 2014, 02:08:43 PM by Mosey »

Offline Alan Haisley

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Re: Hall Sensors
« Reply #34 on: January 20, 2014, 03:48:52 PM »
Mosey,

I think that the tab is bonded to the transistor substrate to provide the heat sinking properties. That makes it an electrical bond as well as a thermal bond.

If it were I doing this, I would move the heat sink out. Right now it is the “third layer”: (1) transistor; (2) PC board; (3) heat sink. Make the heat sink first layer, then the transistor, etc. Also if you really want the heat sink to be effective, go to your local Radio Shack or similar store and get a small tube of thermal grease to put between the heat sink and the tab.

You may need a thicker nylon spacer to make the circuit board stand off far enough to not short anything.

Alan
Near Raleigh, NC, USA

fcheslop

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Re: Hall Sensors
« Reply #35 on: January 20, 2014, 04:06:55 PM »
Thanks for the cap info.
cheers

Offline Mosey

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Re: Hall Sensors
« Reply #36 on: January 20, 2014, 07:01:31 PM »
The Cap supplied by Roy and in my circuit is a 104K, 400v.
Mosey

Offline Don1966

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Re: Hall Sensors
« Reply #37 on: January 20, 2014, 07:48:03 PM »
Yes! the collecter is connected to the transistor tab and is there for heat transfer to the heat sink if one is used or just as a heat sink itself. You can mount the heat sink and the transistor together as long as you isolate it from the frame you should be ok. This explains way you blew your transistor.

Regards Don

Offline Bezalel

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Re: Hall Sensors
« Reply #38 on: January 20, 2014, 09:08:09 PM »
Hi Mosey
 
Isolating the transistor from the engine can be done in two places,
 
 
              a.  a mica insulator between hestsink and transistor, with insulated bolting hardware
              b.  insulate the heatsink from the engine with insulated bolting hardware
 
you can do both, but if you chose to do one only, use the first method so you don't have a live heat sink, the circuit will still work but not a good thing
 
If you use option b. only, any conducting object that touches the engine and heatsink at the , same time will short out the transistor again. 
 
Bez
Queensland - wet one day, humid the next

Offline Mosey

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Re: Hall Sensors
« Reply #39 on: January 20, 2014, 10:07:36 PM »
I think I understand this now, I will insulate the PCB from the Heat Sink with a non-conducting fastener, nylon washer, using proper thermal grease, and the Heat sink from the engine via non-conducting stand-offs (make em from nylon)  and fasteners (nylon).
See pictures below which mayt shed light on what I have. The existing brass standoffs and fasteners will be replaced.
Mosey




By the way, the blue plastic binding strips only allow a #16 wire, so that limits the ground wire back to the engine/coil.

« Last Edit: January 20, 2014, 10:24:07 PM by Mosey »

Offline Don1966

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Re: Hall Sensors
« Reply #40 on: January 20, 2014, 10:38:31 PM »
Look good Mosey, I suggest you buy some nylon fastners to go with your new insulators. You wouldn't want to put the screws back into in unless your insulators had isolators to isolate the screws with.

regards Don

Offline Mosey

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Re: Hall Sensors
« Reply #41 on: January 20, 2014, 10:39:50 PM »
Don,
Absotutely!
Mosey

Offline Bezalel

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Re: Hall Sensors
« Reply #42 on: January 20, 2014, 10:50:38 PM »
Great Mosey
 
Don't forget the mica insulator between Transistor and heatsink.
 
The heatsink grease is non-conductive sure but it is also a poor dielectric.
 
Which means any voltage between Transistor and heatsink will break down the very thin layer of grease. This will cause a short out between Transistor and heatsink.
 
The voltage refered to will occurr any time a tool  touches both heatsink and engine at the same time, even though the heat sink is normally isolated from the engine.

you don't wan't the engine stopping ... just coz you dropped your screwdriver on the heatsink. 
 
Bez
 
« Last Edit: January 20, 2014, 11:00:59 PM by Bezalel »
Queensland - wet one day, humid the next

Offline Mosey

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Re: Hall Sensors
« Reply #43 on: January 20, 2014, 11:14:15 PM »
Would a nylon washer be acceptable between HS and PCB? I don't have any mica.

Funny you should mention contact with the system, as I ponder the practicality of the exposed ignition. Is it a problem to leave it hanging out in the open, exposed to fingers or bumping into? Consider housing the ignition PCB in a plastic shield? Cooling?
Or is this overthink?
You know I hate those ignitions buried in a wooden coffin underneath the engines.
Mosey

Offline Don1966

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Re: Hall Sensors
« Reply #44 on: January 20, 2014, 11:28:46 PM »
Mosey you need something like this. The top slides open and all the connections are on the box.  :stickpoke:

Don