Cooling Secondary Ignition Coils

[WesRagle]

Hi Guys,

I'm wondering if running a blast tube to the secondary ignition coils on VW conversions is worth the trouble. Any experience or thoughts on the matter?

Thanks,

Wes

[pappas]

I have run blast tubes for quite a few purposes over the years including ignitions. I am a fan assuming there is a need.

[gammaxy]

I haven't heard much on the forum of other people having failures, but this has been my experience:

I've actually had 2 pairs fail in about 250 hours. The first pair were red that I understood were supposed to be more reliable than the previous (green?) ones. The first failure happened around 170 hours. As those failed, I bought more from AeroConversions that were also red, but actually have the AeroConversions logo on them (my previous ones had no logo). When those failed (didn't last as many hours as the first pair), I bought similarly spec'd (3 Ohm) Dynatek ones that I'm currently flying behind, but don't have enough time on them to determine their reliability.

There's a recent thread where guys are successfully trying 5 ohm coils for the lower current draw: viewtopic.php?f=7&t=4978 I've bought a pair for when the current ones fail with the thought that they might be less sensitive to external heat since their internal resistive heating will be lower. Dynatek even has a FAQ that addresses this:

The resistance of the coil determines how much current flows through the ignition system. The 3 ohm coils, because of their lower resistance, pass more current and therefore run warmer than the 5 ohm coils. This is most likely to occur under worst case conditions, such as creeping along in traffic on a hot day in Arizona (this isn¹t so great for an air cooled engine either!). Rather than get into the specifics of every application we make the general recommendation - 5 ohm for street, 3 ohm for race.

I've also had both primary ignitions fail once each.

All these failures have been making me think that I should learn something about blast tubes, but I don't have any proof that these failures are due to heat and hate to add complexity if it isn't required. I've got quite a collection of failed coils, though, if anyone has an x-ray machine or otherwise knows how to inspect them :-)

[mike.smith]

I've been flying for 6 years and nearly 500 hrs behind the red secondary coils. They are mounted on the firewall and that's it. No additional air or anything. No issues.
http://www.mykitlog.com/users/display_l ... 25&row=158

[Onex107]

I just had one of the Sonex coils fail at 260 hours. It was corroded in the sockets and had a waxy substance on the outside. Looked like heat was a factor.

[pappas]

I also bought and installed the 5-ohm black coils. Not because my red ones failed but because I thought it would be an inexpensive way to capture a few more amps from the Aerovee charging system. I had a lot of problems, in the beginning, keeping the battery charged while learning how to optimize the electrical system at low rpm and short flight times.

I have since learned how to manage the electrical system. Start-up on both coils, then turn off the secondary until take-off, don't turn on the intercom, IPad charger, Landing lights, strobes, or autopilot until just before throttle advance on the take-off roll.

Now that I have those things on the checklist I have not had any problems maintaining the Lithium battery charge. I don't know if I needed to make the coil change but I'm sure it didn't hurt and it was cheap. $65 bucks for 2 coils and free Amazon shipping. I also have two good Red spare coils now.

[WesRagle]

Hi Guys,

It sounds like one of those "It can't hurt" kinda things. So why not? I did have one of the green coils fail on my AeroVee years ago. I never did know if it was because I forgot to turn the secondary ignition off or if it was just a random failure.

I have 3 Ohm DYNA COILS. I'll do my best to run blast tubes to them. They are somewhat buried with little around them to support the blast tube but I''ll give it a shot. I'll also taxi on primary ignition alone and use secondary for takeoff and flight.



Thanks,

Wes

[WesRagle]

Hi Guys,

I was poking around the web and found this:

http://www.greatplainsas.com/isecign.html

Pertinent to this thread is the note:

"NOTES CONCERNING USE: The coils must be mounted in a position where you can direct cooling air on them. If mounted on the back of the accessory case, the coils must be insulated from the case. They must be grounded to the engine. The maximum operating temperature of the coils is 180°F. degrees. Keep them cool.

YMMV,

Wes