Tired Old Man

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While swapping ignitions from a twin CH that lost a side to an RC Exl today I came upon an interesting observation. The hall sensor bracket used with RC Exl ignitions is rather thick and can cause the sensor to be located too high above the hub magnet to sense the magnetic pulse, rendering the ignition inoperative. This might explain why I've been reading so many posts about new engines with "defective" ignitions.

The solution was to shave the underside of the sensor bracket enough to permit the sensor to lie closer to the magnet. I sanded away until the pulse was sensed as indicated by the presence of a spark at the plug caps. If someone buys a new engine and it will not spark, try removing the hall sensor and bracket. of Marking their positions relative to the hub magnet, and remove the spark plug caps from the plugs, and try getting the bottom of the sensor closer to the magnet. Rotate the magnet back and forth, holding the sensor over the magnet, with the ignition on to see what happens. The ignition may be fine, but the sensor could be too far from the magnet to be effective. An engine with a tapered front hub might be more prone to this situation than square cut hubs.

Another tidbit. The energy of the spark is directly proportional to the proximity of the sensor to the magnet. Closer makes for a stronger spark.

pe reivers

One reason to use only rare earth magnets I suppose?

gkamysz

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Why would this be? The distance does not change the signal sent to the ignition.

Antique

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Hey Pat, I think you've gone round the bend...No offense...

Ed Vollmer

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quote: Another tidbit. The energy of the spark is directly proportional to the proximity of the sensor to the magnet. Closer makes for a stronger spark.

That may be the case with DA and 3W ignitions that use coils in the sensor. In my experience, the only difference sensor gap makes on a Hall Effect Switch is increased or decreased dwell. The switch is either on or it is not on.

I always used a business card to set the gap.

Ed V.

Tired Old Man

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I can only relate what I experienced. Doubt there may be but magnetic fields do weaken with distance, and the sensitivity of RC Exl hall sensors is unknown to me. I know what did not work, and I know what it required to make it work. As for equipment used, it was all basic audio and visual. The visible, and audible, strength of the delivered spark increased with closer proximity to the magnet. The why is unknown to me.

What I saw and experienced did not lie. I don't give a rat's behind for any complicated engineering theory intended to dispute physical evidence that's bound to be presented soon.

Ed,

The air gap between the bracket and magnet was ~3/32" with the unmodified provided parts. I tried three different brackets an all were roughly the same for air gap spacing.

Pe,

The hub magnet was on the hub of one of the original BME 115 engines.

w8ye

My Feedback: (16)

As long as the Hall Effect switch makes and breaks is all that counts. The closeness effects reliability but does not change the strength of the spark.

BadAzzMaxx

Just use the sensor on the engine, It probably has a small deans connecter that will plug into the RCexl connecter, Just match the colors, Have did it a lot of times.

Tired Old Man

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The only reason for changing the sensor was to avod changing a plug. Another CH was replacing the old one but the replacement CH had a different lead connector. I had changed it to a JR type some years back. What started out to be a straight swap got a little more involved to avoid doing any soldering or crimping today. Two screws appeared to be a lot less work, but, ya know....

gkamysz

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I'm fairly certain RCEXL is using Allegro A1104 sensors. They have a very wide spec range for triggering, so in addition to the distance, the sensor itself comes into play. I've had RCEXL sensors that triggered and ran with a 5mm gap.

captinjohn

TOM, I think you got a good idea....make sure the pick-up clearance is fairly close. I noticed when I removed the sensor pick-up on my engine, that gap looked pretty big. I was thinking then it seemed like the distance could have been cut in half and still have good gap. Maybe the strength of the magnet on low side,with too big a gap and a little lower than normal voltage from the ignition pack could cause some starting & running problems. I will check into this more. Capt,n

Darn spell check anyway!

skip1320

My Evo 58 w/rcxell, stock magnets and hose clamp has to be at least a 4mm gap,never an issue,done the same w/rare earth from radio shack on the weedy,s

Tired Old Man

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It's possible themagnet itself is weak. Who knows what K.B. was skimping on in the last days he owned the company. One thing is certain, the sensor that came with the engine would trigger with much greater spacing. The RC Exl had to be about 1mm to trigger. For the few that will question, the alignment of the sensor with the magnet was checked quite carefully. Until the mounting bracket was modified the ignition would not function with the two sensors I had in hand.

Aussie Maddog

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I always machine my magnet hub 1 mm (40 thou) bigger in diameter than the Sensor securing hub and this gives me a nice close fit.

The ST G2300 below has the securing ring 1 mm under the standard prop hub diameter.

pe reivers

When adjusting gaps, I use 0.2 - 0.5mm between sensor housing and magnet

airega1

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Hey! who's Clarence?

Tired Old Man

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Don't know how that got there! It's clearance, Clarence

BTW, I'm aware that a stronger spark with closer spacing makes no sense, but it was what it was. I don't know why either.

w8ye

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Maybe it was dwell time that differed the spark intensity? Spaced farther apart, the sensor would have to be dead center of the magnet to come on and the minutest movement would make it open and trigger the spark upon collapse of the magnetic field?

Rocketman_

I agree with the dwell time idea. A longer dwell allows more time to build up a strong magnetic field which produces a more powerful spark.

gkamysz

My Feedback: (19)

But the charge for the spark is built up during the time the magnet is not under the sensor. As soon as the ignition fires it's charging for the next cycle and probably charged before the expansion stroke is over in most engines. It doesn't have anything to do with how a magneto works. The sensor just tells the ignition when to dump the charge.

Antique

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Question for all you prefessional experts..You want dwell time ? .How much dwell time is there at 18,000 rpm ? Bill's (C&H) greatest will do a 3/4" spark with a 1/8" samarium cobalt magnet...Using 4.8 to 6.6 volts....I HAVE ONE, it does it....
Ed Vollmer's Syncro Fire, no longer available, will do it too...Anyone wants a REAL ignition can maybe talk Bill into making one...Don't expect Chinese prices, just good old MADE IN RIVERTON, WYOMING, USA QUALITY...Don't get me wrong, RC EXL is very good, but it's NOT a C&H.....

Rocketman_

Thanks for clarifying that.

Tired Old Man

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I already have a bunch of super hot ignitions but I more of a need to send my good old CH SS twin back for some repairs.

Antique

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I know YOU knew that I knew that YOU knew etc.......................

Tired Old Man

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Luv ya baby