Expert: Mike Fulcher - 6/8/2010

Question
I am trying to run an RC glow plug off of the smallest battery possible. For more info on RC glow plugs go here: http://www.rc-truckncar-tuning.com/rc-glow-plug.html
I am NOT using the glo plug for an engine, I just need it to come on for a moment then off again. I am using a AA battery attached to a momentary switch to do this. To start a glo plug, a direct current (around 3 amps and 1.25 to 2 volts, often provided by a single, high current capacity rechargeable NiCd, NiMH or lead-acid battery cell, or a purpose-built "power panel" running on a 12VDC source) is applied to the glow plug, initially heating the filament. (The name 'glow plug' comes from the fact that the plug's filament glows red hot.)The filament is made of platinum.
The regular AA battery works great, but I need a small battery (watch battery) to run this for just a second, even if it depletes the battery. Is this even possible with a watch battery? If not how do I find out how many mah I need to get a filament of platinum to glow? Filaments of platinum range from 54 gauge and larger. I have been hitting my head against the wall trying to figure a solution, but I just do not fully understand mah to amps, the relation to volts, and the amount it takes to "glow" a platinum wire, etc... Any suggestions will help. I appreciate you taking you time.

-Matt

Answer
The issue with heating the wire has everything to do with the rate the battery can discharge and its voltage, and not much to do with anything else.  So, if you can get a higher volatge battery it won't need to put out as much current.  Problem is watch batteries and the like are design for low continuous rate discharge, and won't be bable to do much more than warm the wire.  About the smallest I think you can do would be a AAA Ni-Cd or Ni-MH. Those chemistries have the best high current performance.  Alternatively, if you can caluclate the power you need you could size a capacitor and then slowly charge it with a watch battery until it's ready to go.  You may want to seek an electrical engineer to help you understand the size of what you're looking for.