john melia 1 Posted April 28, 2014 Share Posted April 28, 2014 How can I find out what a glowplug is drawing from a 2200mah 1.2v battery , I would like to know how long this battery would heat the element , if it were connected continously. Quote Link to comment Share on other sites More sharing options...
Bob Cotsford Posted April 28, 2014 Share Posted April 28, 2014 probably around 40 minutes to an hour John. Most plugs draw around 2 amps, but the only way to tell for sure would be by using an ammeter in series with the plug. Quote Link to comment Share on other sites More sharing options...
Steve Hargreaves - Moderator Posted April 28, 2014 Share Posted April 28, 2014 You'd need to connect an ammeter in line John but it's probably pulling around 2 to 2.5A or so (assuming its a "medium" plug) so if you allow about 45mins continuous use you won't be far off..... Quote Link to comment Share on other sites More sharing options...
Steve Hargreaves - Moderator Posted April 28, 2014 Share Posted April 28, 2014 Snap Bob..... Quote Link to comment Share on other sites More sharing options...
Richard v.K. Posted April 28, 2014 Share Posted April 28, 2014 I am curious about the measurement with the Amps meter. Cannot explain why, but I was told a glowplug needs less Amps when the engine is running. Is that correct? Quote Link to comment Share on other sites More sharing options...
Bob Cotsford Posted April 28, 2014 Share Posted April 28, 2014 great minds - or birds of a feather? Quote Link to comment Share on other sites More sharing options...
cymaz Posted April 29, 2014 Share Posted April 29, 2014 Richard , hot wire equals less resistance ??- some mad scientist will put you right here Quote Link to comment Share on other sites More sharing options...
crispin church Posted April 29, 2014 Share Posted April 29, 2014 all correct above the battery heats the wire in the glow plug after engine started the engine heats the plug there for the plug dont need the battery so much but will still be taking a little if the glow plug burns out the the engine stops as there no heat to back fuel burn you can put a micro switch on the throttle so battery only connected at low revs which would make battery last longer Quote Link to comment Share on other sites More sharing options...
Peter Beeney Posted April 29, 2014 Share Posted April 29, 2014 With the greatest respect, but I think the glowplug wire element has a positive temperature coefficient of resistivity, or in other words the resistance actually gets higher as it gets hotter. Going from normal (cold) temp to red/orange hot is quite a jump, several hundreds of degrees, which does limit the current, but the rise in resistance per single degree is probably quite small. When the glow driver is connected to a running engine, at least when I’ve tried it, the current flow remains the same; this is because the glow element temperature under normal running conditions might be less than when the battery is connected. If it were to glow brighter when running, and thus indeed get hotter, this would then reduce the current, but I think this would have to be considerable to be noticeable. Someone at the patch once asked the same sort of question about current consumption, so I did a few checks. I used my 2 volt, 8 ampere hour lead acid, to ensure a steady 2 volts supply. Five random plugs, one required a lowly 1.2 amps to fire up, one was at the other extreme, 5 amps, and as I remember the others clocked in at between 2 and 3 amps. So as has been suggested, an ammeter might give a rather more definitive answer. However, there is a tiny proviso, if you use an inline meter you might need to consider the result. This is a relatively low resistance circuit, and depending on the resistance of the meter, how much difference does it make? For example, if the circuit resistance was 0.5 ohm then using a 1.2 volt battery supply 2.4 amps would flow; but if the meter resistance is also 0.5 ohm when it’s placed in series in the circuit the resistance becomes a total of 1 ohm, thus reducing the current to 1.2 amps. The difference, perhaps, between glowing and not glowing… I’m not at all saying that this is what the meter residence is, I don’t really know now, it’s many years since I’ve used a series meter. A quality item will have a low resistance when measuring current, the lower, the better, but this is surely related to it’s cost. One check might be - short the meter leads together when it’s in circuit and see if the plug glows any brighter, if it does then the the meter resistance is significant. Hope this is of some interest. PB Quote Link to comment Share on other sites More sharing options...
John Mccullagh Posted April 29, 2014 Share Posted April 29, 2014 Hello John, why would you want to run your glow plug continually ?the norm is to start your engine then the fuel keeps the glow plug alight for the whole flight,there are devices to light your glow plug in flight but i have never needed one and have flown in all weathers ( Not rain ) or have i missed something john. Quote Link to comment Share on other sites More sharing options...
john melia 1 Posted April 29, 2014 Author Share Posted April 29, 2014 Posted by John Mccullagh on 29/04/2014 15:30:37: Hello John, why would you want to run your glow plug continually ?the norm is to start your engine then the fuel keeps the glow plug alight for the whole flight,there are devices to light your glow plug in flight but i have never needed one and have flown in all weathers ( Not rain ) or have i missed something john. John i dont want to run the plug continously i just wanted to find out what the plug draws from the battery so i can figure out how long the battery would last Quote Link to comment Share on other sites More sharing options...
Bob Cotsford Posted April 29, 2014 Share Posted April 29, 2014 weeks unless you spend more time in starting the engine than flying Quote Link to comment Share on other sites More sharing options...
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