Variable current for glow Plug?
 

I am designing the circuits for my new Field Box. I see that most comercial power panels have "variable current" for the glow plug. Has anybody measured the current range that these have? I would assume that these panels don't actually have variable current, but instead have variable voltage (cheaper to make). That being the case, I would make a simple supply that ranged from 1.2 to 2 volts. I have not checked the Ohms value of a standard #8 plug but for ease of calculating lets assume 1 Ohm. If I supply 1.2 Volts to a 1 Ohm load I get 1.2 Amps. If I supply 2 Volts, I get 2 Amps. I checked my Nicad battery in my portable ignitor and it is a 1400ma battery. So my previous calculations seem reasonable. Has anybody made their own supply? If so what range did you use? What are the recommended specifications for the glow plug?

Before I get flamed, I know you can buy a whole power panel for $20.00 but I hate to buy things that I can make.


Mike B.

RE: Variable current for glow Plug?
 

Mike, if you have a 'scope, see if you can borrow someone's panel and see what it's doing.

I'm under the impression that most of the glow drivers are actually providing a switched 12V to the plug. But I'm sure they don't all work that way.

RE: Variable current for glow Plug?
 

Montague,

Yes I have a scope. I just figured somebody has already done this and would save me some time. I hate re-inventing the wheel, If you know what I mean. Well I figured by the $20 dollar price tag that they were just using a simple regulator like an LM317 or equiv. (Or mabey kids build them in Mexico or China.) Well, I'll hold out to see if anybody has any information before I borrow one. Gee, I'm begining to sound like a couch potato.

RE: Variable current for glow Plug?
 

They're normally switched. I can hear mine (Hobbico Accuglow) make a buzzing noise.

Try this:

http://www.uoguelph.ca/~antoon/gadgets/glow.htm

BTW, the resistance of a glow plug gets higher as it gets hot. May have an impact...

The new Hobbico Accuglow II also has a charger you can clip your C Cell glow ignitor on to. Very convienient. Hard to beat the price with a home brew setup.

RE: Variable current for glow Plug?
 

Great, Thats what I was looking for.



Thanks for the help!


Mike B.

RE: Variable current for glow Plug?
 

I can't find the one that has a specific power panel schematic and parts list at the moment...

http://www.uoguelph.ca/~antoon/circ/circuits.htm Has several circuits, some of which could be modified into the glow driver.

If I remember correctly... they are using a pulsed 12 volt to do the glow, as the resistance form of voltage drop is power-hungry and produces a lot of heat.

The simple resistance circuit would be a primay resistor of appx 8 to 8.5 times the resistance of the glow plug... and then an adjustable resistor to adjust the current. The nominal 12 volt gell cell, just as the nominal 1.2 volt NiCd actually reads higher when fully charged. The Gell cell will be close to 13.8 durring most of its useful charge. That's close to 10 times the 1.4 to 1.5 volts seen from a NiCd durring most of its useful charge.

The circuit used in the power panel is simple... and has been published in all kinds of places. I just can't find a link to it at the moment and my favorite RC gadget site, which has it, (linked fron the above...) is down right now.

***********

The better site is up...

The glow driver circuit is listed sepatarely from the power panel... The panel assumes you built that circuit and are sticking it in.

http://www.uoguelph.ca/~antoon/gadgets/gadgets.htm

RE: Variable current for glow Plug?
 

Yes, a power panel switches a full 12 volts to the plug for a short time then off for a long time. Typical values are 1 millisecond on, 9 milliseconds off. All you adjust when you turn the current control knob is to change the duration of this on pulse. Very evident if you monitor the plug voltage with a scope.

RE: Variable current for glow Plug?
 

Thanks, The replies are much appreciated!


Mike B