Adjustable glow Driver

[Jem]

Hello all, I started working on an adjustable voltage glow driver last night. I should preface this by saying I know absolutely nothing about electronics. I'm using a schematic I found that seemed simple enough. I'll try to upload it and a picture of what I've done and maybe someone can say "move this wire over there..." As it stands, the switch works and I get voltage to the banana plugs, and to the actual glow plug clip, but if I insert the glow plug, voltage ceases and the plug won't glow. And yes, I've tested the plug on a regular driver. I'm using a 2 cell 7.2V lithium I had kicking around. I've also tried it on a 12V gel cel. I'll remove the heat shrink so you can get a good look at the disaster I've made :o
Any Ideas would be appreciated. Here's the link to the plug driver I'm attempting in case the pictures aren't clear.
www.auroramodelaircraft.com/lib/Glow_driver2.doc

[Jem]

Pics

[Jem]

One more

[ebill3]

Disconnect everything from the pot (variable resistor).

Connect a jumper wire between the center pot terminal and one of the outer terminals. Connect the black wire from the battery and the black banana jack to those jumpered terminals.

Connect the wire from the LM350 adjust terminal and the fixed resistor to the open outer terminal of the pot.

The LM350 is a 3 Amp device, but it might need a heat sink in order to drive a glow plug.

Bill

[Jem]

Hey eBill3,
Great advice! I did as you said. It works, but the LM350 got very hot and the voltage to the plug dropped over time and the unit got very hot. i added a half inch thick by 1 1/4" aluminum sink, but it it still got way too hot to touch. Do I just need a voltage regulator that can handle the amperage?
Thanks again,
Jeff

[ebill3]

The LM350 must be securely attached to the heat sink. According to the data sheet, it should handle a glow plug current requirement. Limit the voltage to =<1.5 volts.

Bill

[jeffs555]

You need to look at this thread. http://www.rcgroups.com/forums/showthread.php?t=805197
A linear regulator like that is a terrible idea for a glow plug driver. The purpose of a glow plug is to get hot. It does this with 1.5 volts. If you power it with a linear regulator from a 7.2 volt battery, the regulator will have to drop 5.7 volts(7.2-1.5=5.7). This is nearly 4 times as much as the glow plug. Therefore, the linear regulator will have to dissipate 4 times as much heat as the glow plug itself. On a 12 volt battery it would be even worse. The regulator will either shut down or kill itself if it gets hotter than 150 deg C inside, so you would need a huge heatsink to keep it cool enough. Also, the heat conduction from the actual chip to the heatsink is not perfect, and depends on the package. With that TO-220 package, I don't think it is possible to keep it cool enough at 3 amps with 7.2 volts input and 1.5 volts output.

PS Just picture the little chip inside that plastic package getting 4 times hotter than the glow plug.

Also, it is very wasteful of battery power. With a 7.2 volt battery, only 1/5 of the battery power is getting to the glow plug, and 4/5 is being wasted as heat in the regulator.

[Rodney]

You will have better luck, and not waste power, if you use a pulse width modulation technique like most power panels do. Use an LM555 to turn on an FET for 1 millisecond that puts the full voltage accross the glow plug momentarily every 7 to 8 milliseconds (give an average of about 1.5 volts for the period). You can find several schematics for this with Google. That is the way power panels work, they put a full 12 volts across the plug for 1 millisecond then off for 11 to 12 milliseconds to give a proper power average yet not burn out the plug.

[tungym]

Why bother for the efficiency?
I steal the 4.1V through the balancer tap of 2s BEC lipo, step down to 1.5V through 3 pieces of N5401 (rate 3A) serially. The glow plug pulls 3.5A and the 5401 is warm , not hot.

Who cares efficiency for the 10 seconds engine starting? The 2s 2200mAh lipo is gonna to be recharged using balancer charger after 8-9 flights anyway.

[Acetronics]

Who cares efficiency for the 10 seconds engine starting? The 2s 2200mAh lipo is gonna to be recharged using balancer charger after 8-9 flights anyway.

???

is it a Glow/Electric new generation engine ??? :D :D :D

Alain

PS: Electric starter, I presume ...

[gwong]

I was thinking for using a step down dc to dc converter, this item from Dimension Engineering will take large input voltage up to 30 volts and can adjust it to 1.5 volt output at 1amp...anyone thought of using this for a lipo glow plug driver...the price is only $15.00

http://www.dimensionengineering.com/DE-SWADJ.htm

Cheers,

Gord.

[lazy-b]

here is my Cheap Glow Plug Igniter:

http://www.rcgroups.com/forums/showthread.php?t=303050&highlight=cheap+glow+plug+igniter