$30 ignition

[tornitore45]

Generatorgus, did your ignition come with the Hall sensor?

 

[flatbelter]

Well I guess I was too rough on the hall sensor, it failed.

I've got two ignition kits coming in the mail. The distributor made it a point to note that anything over 6.0 Volts would toast the electronics. To the point that a fresh battery pack could be trouble. You would think if it was that sensitive they would put in a voltage regulator, but I guess you get what you pay for...sometimes.

So, should I glue the magnet down for the initial setup?

 

[Generatorgus]

Wow, Christmas day, already. I got kind of vacuumed up in the real world of work and also complicated by some other things I don't need to bore you guys with.

tornitore, yes the ingnition came with the sensor. When I damaged mine I checked a replacment from the company, I think 7 or 8 bucks plus shipping. Being quite frugal (CHEAP ;D), I decided to try ebay for parts. I refound MBs post on the Upshur engine
http://www.homemodelenginemachinist.com/index.php?topic=11257.300, and searched out the components.
Results were :10 sensors for $6.45, free shipping
: 10 Fubata connectors with leads $10 free shipping Both direct shipped from China, took a couple weeks.
Also: 5 pair EC3 connector, $4.99 plus 1.75 shipping.
Not bad, 10 sensors with connectors $16.45, do the math. Now I have to brush up on my small parts soldering.

Now I have to get busy and try to get my engine ready for Cabin Fever in a few weeks. ;D

More to follow.

GUS

 

[lee9966]

For whatever it's worth, I had a lot of trouble with killing hall effect sensors using the S&S ignition until I learned to not only have the ground from the sensor wired to the ignition unit as usual but also to ground it to the engine. I have never had a hall effect sensor die since then in my limited newbie usage on a couple of engines.

Lee

 

[Generatorgus]

Lee, I had mine grounded, I just kind of beat the hell out of it trying to get it running. I think my magnet disc wore thru the casing, I haven't taken it off the engine yet.
GUS

 

[flatbelter]

Well I got around to installing one of the electronic ignitions on a modified 26cc Homelite engine.

Had to cut the plug wire and solder on a new boot to fit a standard spark plug. That made the braided shield wire a little short. I soldered a bit of copper wire to the shield, ran it around the plug wire, then bolted the free end to the engine jug as a ground. I suppose I should have cut the plug wire back further so the shield wire would have covered it. (next time) It still needs some kind of shield/ground, perhaps something could be fabbed from sheet aluminum or steel later to make it look nice.

Since the motor is for airplane use, I milled/lathed off as much excess metal from the engine as possible. Next time I'll leave more meat around the front bearing so I can drill and tap for sensor hold down screws. For now a few wraps of 1/2" masking tape hold the sensor in place.

Long story short I killed the first hall sensor when the engine flooded out. Amazing how well oil and gas work as insulators. Apparently if the plug can't fire, the voltage back feeds and wipes out the sensor. I ended up flipping the motor back upright (plug on top) but still couldn't get it to fire after changing the sensor. Then I noticed that the prop adapter was moving and realized that I had sheared the half moon key that I had fabricated to replace the one that ran away on the garage floor. Note to self, don't make keys from soft metals like copper anymore.

Once I get the carb to quit p*ss*ng gas into the engine and lock the prop adapter to the crank, then perhaps I can get this motor to fire up. Looks like I should stock op on sensors too.

On the bright side, I'm picking up lots of experience....

 

[mu38&Bg#]

Long story short I killed the first hall sensor when the engine flooded out. Amazing how well oil and gas work as insulators. Apparently if the plug can't fire, the voltage back feeds and wipes out the sensor.

Yes, that's normal with these. Sometimes it will take out the ignition itself.

 

[Lakc]

The spark is gonna find ground, the trick is to give it something easier then the sensor to find it through.

 

[jpeter]

Don't leave out the supressor resistor. That resistor plays a roll in protecting the hall effect sensor. I've never played with an HK unit but I like the idea of the automatic advance. Seems like what my v8 should have. I wonder if it can spark fast enough. Let see, at 4000 rpm I'd need 32,000 sparks per minute. Anyone know if it can manage that.

 

[mu38&Bg#]

Not sure. Most are only rated for single cylinder use I've run RCEXL at 12kRPM or so. I can see it doing 15k, but not much more. At 4K wouldn't you need 16,000 sparks/min?

How does the resistor help if the spark never makes it down the HT lead?

 

[Lakc]

The resistor cuts down on the amperage of the spark, and its radio frequency output, but not the voltage.

 

[jpeter]

32k, what was I thinking. Hits every other revolution, dah. You're right, 16k.

 

[jpeter]

I'm probably talking out of my hat here but I think the wires and circuit board traces act like little antennas and pick up the radio frequencies generated at the spark plug. Those voltages can be higher than lots of semiconductors can stand and will pop them. Suppressing those RFs help a lot to extend the life of the FETs. Right? I know for a fact that without the supression resistor I'm gonna have trouble keeping fets alive.

 

[Lakc]

Fets are static sensitive devices, while the induced voltages are usually low unless you create an unintentional coil by winding wires together or running parallel for long lengths. Fets do use extremely low voltages to conduct and unintended conduction can be a problem. The resistor might help in that case, but the primary focus is less radio frequency interference (very important in rc models) and you get a little less spark plug erosion.

 

[mu38&Bg#]

The only way for spark to kill the hall sensor is if it can't arc down the HT lead. If it can't, it goes to the next closest gap. It will jump on the board somewhere and since the gap to ground within the hall sensor is small that's as good as anything. Obviously component layout on a board must be planned to avoid killing the components on the potted board, instead of the hall sensor which can be replaced. The grounded shield is pretty good at protecting the hall sensor because it will spark in the cap if there is no plug connected. But, it still can kill the sensor if conditions are right.