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I haven't noticed the spark being that weak during cranking but haven't made any specific measurements of it either. The spark will be weaker due to the voltage drop of the battery if nothing else, even if there is no drop in the wiring.

Dwell on the EC2/3 during cranking (below 400 rpm) depends on the version/engine type but on the 20B it should be well beyond the minimum saturation time of the coils. My concerns have been that it is too long during cranking rather than too short. Dwell time longer than required for coil saturation adds nothing to spark strength but does heat up the electronics in the igniter.

IIRC, Steve is using the RX-7 type igniters which is a different situation. They control their own dwell internally (after the first cycle) and the EC2 only controls ignition time with the negative edge of the control pulse.

Tracy

On Wed, Nov 25, 2009 at 8:30 PM, Al Gietzen <ALVentures@cox.net> wrote:

I did a measurement today for the resistance from the starter flange at the re-drive plate to the copper tube, which is my ground bus going from engine compartment back to the batteries that are in the nose of the Velocity. The ground strap from the engine is from the bottom right corner of the front cover. So this is the measurement through the engine (20B), back to front, and after the two connections – cover to strap, strap to bus.

The resistance measurement was really too small the get a good reading on the Fluke; say less than a milliohm. Then measured the voltage drop while engine cranking – about 10 milivolts. Clamp-on ammeter suggests about 50-60 amps draw to the starter after first surge. The math says resistance is about 0.2 miliohms. So as least in my case; grounding in this manner is not an issue.

So weak spark during cranking is some other reason; I’m wondering if it could be due to very short dwell time from EC2 at low rpm that Steve Boese reported here some time back. Don’t know if 3-rotor would have same effect, but likely would. Tracy; maybe you could comment on whether that could be a factor. Never had starting problem, just noted spark during cranking significantly weaker than test mode – hard to get it to jump ¼”.

Al G.

-----Original Message-----
From: Rotary motors in aircraft [mailto:flyrotary@lancaironline.net] On Behalf Of Steve Brooks
Sent: Sunday, November 22, 2009 7:44 AM
To: Rotary motors in aircraft
Subject: [FlyRotary] Ground isn't ground

The mystery of my intermittent spark is solved. Thank you to all of

those who made suggestions, as it helped get to the bottom of the issue.

This morning I decided to repeat the test I made yesterday hooking the

starter to a separate spare battery that I had.

This time I removed both the large cables going to the starter and

engine block ground. That way, I didn't have to mess with a jumper

cable. I hooked up the battery, turned the master on and engaged the

starter. To my utter amazement the spark was intermittent again. I

thought thgat certainly I hadn't made a mistake yesterday an imagined

that the spark was good on a separate starting battery. After some

swearing, I thought about yesterdays test, and the only thing different

was the ground cable. So, I removed the ground cable from the

battery,and hooked up a jumper cable from the negative terminal of the

battery, and hooked it up to the reduction drive plate, as I had done

yesterday. Cranked the starter and had good spark. Did it twice, just

to make sure.

What the **** !

So, I decided to connect the jumper cable to the ground cable end,

instead of clamping it the the reduction drive plate. Cranked the

starter, and had intermittent spark again. Somewhat amazed, but onto

something here.

I measured the cable (0 gauge multi-strand silicone) with the Fluke

meter, and it showed pretty much zero ohms. I measured from the spot on

the front engine housing where I had the ground bolted on to the

reduction plate, and measured about 3 tenths of an ohm.

Since my original installation, I always had the ground cabled bolted to

the front housing, with a bolt into one of the tapped holes where the

air conditioner mount was. It is a pretty large bolt, and I never

suspected that, considering all of the bolts that hold the engine

together, and the many bolts that hold the reduction drive plate, that

there would be any issue. Boy was I wrong.

I reconnected the cables to the main battery, instead of the spare

battery, and instead of bolting the negative cable back on, I used the

jumper cable to connect to the reduction plate again. Perfect spark

!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!

My current ground cable isn't long enough to reach from the battery to

the mounting plate. I found the cable that I had left, and I have

plenty of spare cable, but I don't have any more of the lugs for the

ends, so I will have to order some. I am going to attach to ground

inder one of the mounting bolts for the starter.

Regards and thanks for the help,

Steve Brooks

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