So I bought an airplane recently. It came to me with a 2100 2s lipo on the ignition. I was having trouble getting the engine to start, and while it was sparking, I looked at the ignition module and saw that it was only rated for 4.8-6 volts. I disconnected the lipo and installed a 4 cell 2000 nimh pack. The pack was fully charged, and was in good shape. Now I have no spark. I've checked to ensure I did connect the pack properley, the polarity is good, and there is a light in the switch which comes on when you turn the switch on. Has anyone ever heard of an ignition module getting "dependent" on higher voltages? I havent had the chance to switch back to the original battery and recheck, hopefully this morning I can sneak out to the garage for a few hours of fun.

Thanks!

Dependent? No

Fried? Yes

Unfortunately, I think it is fried. Most of those CDI units really meant that 6.0v is the max that can be applied to them. Any higher voltage and they die, usually quietly sometimes with lots of smoke.  You have to ensure that the peak charged voltage of a battery pack does not exceed 6.0v too. Some CDi's are sensitive to the high voltage spike that could come out of a voltage regulator when power is turned on too. So one needs to be careful using the regulators to lower the voltage to 5v.  A 4.8v battery pack is more than enough to operate these CDi's. higher voltages merely increase the current draw but do pretty much nothing to improve performance.

Electronics are built with a limited amount of smoke in them ,when you let it out you're done .
Too many volts will let the smoke out....

Get yourself an RCXcell ignition and use a 4.8 pack and your troubles will be gone.

Running an ignition on a drop down diode is perfectly safe. WrongWayRC carries them configured for A123 or LiPo voltages. We have hundreds of flights with this configuration.

Well, color me stupid, but.....

Got a miniute between other projects, so I pulled the cowl again. I did replace the Champion plug with an NGK, just normal troubleshooting and such. I had pulled the engine, and thought I had spark after I reinstalled it, but, just to be sure, went back and checked the connections. The ignition sensor wire from the engine is pretty standard white/red/black stuff, the sire from the CDI is funky, red, yellow, brown, and I figured that brown to black would befine. Apparently not, I switched the lead around and now it sparks. And runs, as well. But that's another post... Thanks to everybody for yoru inputs... operator error strikes again!

I've never seen red/yellow/brown on a CDI. Is it an extension from the CDI wire?It could be reversed on the other end which would explain your results.

Nope, that's the way it comes out of the cdi unit. New one on me also.