Glow current draw

Measure the resistance and apply ohm's law? V=IR

V = voltage
I = current in amps
R= resistance

Voltage would be 1.5 V for most glow plugs

I=R/1.5 in amps. Multiply by time desired in hours for Amp Hours.

Yes, the measurements would help.

Phil


I measured .3 ohm and .5 ohm on the two (well 3, one blown) heads I had on my desk. So

.5/1.5 = 1/3 amp (.333 repeating)
.3/1.5 = .2 amp

So if you want to drive for 1 hour 400 miliamp hours should hold you, but not much safety factor. If you are using rechargeable batteries you probably want to double the desired time

Phil

Phil, you divided R/E, not E/R

I=E/R
I=1.5v/.3ohms=4amps

2-4 amps is the generally accepted value. So figure amps/hours to decide what you need. That's going to be a fat battery pack.

screwed up the algebra


Thanks Rusty.

Phil

pkrankow wrote:
screwed up the algebra


Thanks Rusty.

Phil

No problem Phil, that's why y'all have an electronics guy on the forum.

Most glow plugs are about 0.3 ohms cold and 0.5 ohms hot, so the actual current drawn by a glowing plug is about 2.5 A.

Cheers

Thanks boys.
So my thought of a 800 mah triple aaa cell
Should suffice for a couple flights?

20 minutes-ish

But we already know my math is suspect

Phil

Thanks Phil
I'll explain my latest crackpot idea in a few hours
Time once the first gallon of coffee has
Time to circulate.

Hi all,

Normally around 2-3 ampere. Depends on type of glow head.

I used low nitro fuel a lot, my glow plug need to be real hot for easy start. Short and thick wires will be much lower impedance and glow brighter.

Some AA size battery can't give enough current because of higher internal resistance. Tripple A type batteries always have much higher internal resistance and might not suitable for glow plug, you might have. Lower heat and hard to start.


-ew-

Good Afternoon Ew . I kinda thought that too.
It'll only have to work for 5 mins though
And it's only a 'supplementary' glow that
I'll need for duration of a flight 4 mins max.
If you look at my utube channel (the button
At the bottom of my avatar now works) you'll
See why I think I need it on the FF5/Extreme.
Still haven't got a tach on it yet but I will
This afternoon/after midnight where you are.

Hi John, good day!



For glow plug power, i used 4 pieces of AA rechargeable battery in parellel.


And thanks for your fuel, I flew diesel yesterday, plenty of power and flight time.


Regards,
Ew

John Goddard wrote:Good Afternoon Ew

Hi John,


Nice plane you have there. Have you tried hotter glow head?

Ew

Sorry Ew re read my last post, I was having
Trouble getting past Good Afternoon for some reason.....

Great to hear you got to use the Diesel, I'm going to
Pick up some from a guy who makes it in a few weeks
So if you'd like some more let me know.
As you can see from the vid and Glens comment about
Trimming I do chuck my aircraft around a bit.
Obviously in a lot of manoeuvres the throttle
Is closed but because of the needle position needed
To fuel an engine that fast and no low speed running
Jet I think the influx of lots of fuel at low(er) revs is
Extinguishing the glow particularly in the air where of
Course it runs cooler.
That's why I'm thinking 'on board' glow which of course
Means 1 battery not 4.
I'm going to pop into Maplins later and buy some Aaa's
And some AA's and play around to see if 1
Of either may provide a little assistance to a glow for
The required 5 mins.

tru168 wrote:Hi John,


Nice plane you have there. Have you tried hotter glow head?

Ew

No hot plug no good Ew, it's running 30% at
The mo+ it's brrrrrrrrrr very cold over here
At the moment

I almost forgot that your country are freezing cold now. :-)

Keen to know the RPM reading .

pkrankow wrote:Measure the resistance and apply ohm's law? V=IR

V = voltage
I = current in amps
R= resistance

This is not correct, the filament's resistance is much lower when it is cold. You would have to measure the resistance once the plug is glowing, and that might not be easy.
The correct way to do this, is to apply the nominal voltage and measure the current directly.

I remember measuring vacuum tube's filament resistance to tell one type of the tube from another (the markings on some of them would easily come off). That works, as long as you remember to multiply the resistance by a factor of 3 to 5.

We recently had a huge discussion about glow drivers on another forum.

The thing to remember with re-chargables is that they are only 1.2V so the length of leads between the battery and the glow plug comes into play. This is why those NiCD glow drivers have no leads. 1 meter of wire will add about 0.1 to 0.2 ohms in series which will drop the voltage down below 1.2V at the plug and therefore the current will go down and the plug may not glow well enough to start the engine.

The Cox 2 x D cell starter packs were designed to be used with 1.5V carbon or alkaline batteries and had short thick leads to ensure you got a good supply to the plug.

Food for thought.

Yep
Got it guys
Starting to wish I'd paid attention in Physics
Don't worry about leads too much Lads they'll be 4ins long at the very most.
I'm going to Maplins later to get an armfull of gear for some olde fashioned trial and error.
Might even get my old man (family electronics expert who did pay attention in school) to knock up
some sort of regulator and use a 4.8v 220 mah....
Only prob then is we're getting v close to an extra oz on the airframe.
As you can see in the vid it's quite lively, taking off in 3 yards with vertical climbability. I wanna keep it that way.

Although there is that nagging feeling at the back of my mind that I may be asking just too much
of a 50 year old design.

Yes, heater filaments are non-linear device.

Quite surprise to know someone in this forum have experience with vacuum tube ;-)

I build vacuum tube amplifier too!

ew

dirk gently wrote:

pkrankow wrote:Measure the resistance and apply ohm's law? V=IR

V = voltage
I = current in amps
R= resistance

This is not correct, the filament's resistance is much lower when it is cold. You would have to measure the resistance once the plug is glowing, and that might not be easy.
The correct way to do this, is to apply the nominal voltage and measure the current directly.

I remember measuring vacuum tube's filament resistance to tell one type of the tube from another (the markings on some of them would easily come off). That works, as long as you remember to multiply the resistance by a factor of 3 to 5.

Try rechargables - Robert Dyas have them on special at the moment. I hour charger and four batteries - can't remember how much. I use these to light a plug for starting.

Some of them are also lighter than the alkalines and have no restriction on current draw.

I once dropped one in my tool box and .......................

P.S.
Just so we're clear guys this isn't to start the thing.
I'll do that with the flight panel and M/C battery.
This is just to give the glow a little help once in
The air and the needle valve is swamping the glow
With fuel at lower revs during 3d type manoeuvres.

You can also try lightly insulating the head for winter flying. I wrapped yarn deep in the cooling fin gaps of a head so it would not go out as readily in the cold.

Phil

Hi John,

Just a few suggestions

1. Try a "proper" head that will take a plug with an idle bar.
2. Show your age and revert to spark ignition.
3. Be British and run diesel.