Remote LED Running Indicator For Gas Engines

[OperaHouse]

On another forum I have been discussing a problem that is unique and might be of interest to some here. This poster
operates a rice farm in the Philippines that has 17 gasoline engines from 6 to 10HP which are pull start. These drive
water pumps that operate during the night. These engines/pump are in line of sight 100-400 yards from where they can
be viewed. They thought a LED could somehow be used.  No battery or generator power was available.

Last year I purchased a number of 3W Lights of America 3W 120V GU10 white spolt lights and began experimenting
with them.  Disassembly of these was easy because they were just screwed together. I noticed the rectifier board
had an anti ghosting resistor that in normal operation wasted about a quarter watt in power. This resistor prevents
the LED from ghosting on due to stray capacitance of household wiring. I wanted to make a low power night light for
my dog so she could go out the basement dog door when it was dark.  I was surprised to see that these lamps could
be powered with just a few mocro amps with the ghost resistor removed.

That got me thinking that the voltage across the points could power one of these LEDs. Most gas engines have a
provision to be turned off or protected by low oil by shorting out the points. I tried this experiment on my
lawnmower today and the results were good.  The 3W 120V LED had a 6X6 array with the LED in series.  The normal
power board had been removed because of damage in some experiments last year.  The 6X6 array in series normally
starts conducting at about 90 some volts if I remember. When the engine was running I measured about 100V AC on
the points.  I figure the peak is generally about 300V on any ignition system.  In order to catch as much coil ringing
as possible I decided to use a capacitive input voltage doubler. My power circuit was a .1uF 400V capacitor
from the points connected to the center of two 1N4005 diodes in series.  The minus side of the diode string
connected to ground. The + side of the string connected to another .1uF cap filtering the output and a 300 ohm
resistor going to the + side of the LED string.  These component values have not been optomized. 

The engine was run at a little faster than idle and I estimate this was 0.01W (as shown in picture) of power going
to the lamp.  Not very bright but visable in daylight.  The individual LED elements are clearly visable.  I tried
another 120V LED lamp directly across the points but that didn't work at all. This is likely because this lamp
contained an anti ghosting resistor.  It is likely a commercial 120V  LED lamp would work if just this ghosting
resistor is removed.  Typically the resistor value is between 47,000 and 100,000 ohms. I Think any 120V LED
lamps are a good match if they have somewhere close to 36 LED in series. A red LED string might be more efficient.

The first schematic shows the voltage doubler schematic and the circuit that actually powered the LED.  The second
circuit shows a typical LED rectifier circuit found in a lamp.  The two AC terminals of the bridge rectifier would normally
go to120V AC, often through a low ohm resistor that acts as a fuse.  To modify this lamp for engine use remove the 47K
to 100K anti ghost resistor.  SMD resistors are often best snapped with a wire cutter.  Then just connect one of
the AC inputs to the points through a .1uF 400V capacitor.  The minus of the bridge then goes to the engine case.
These engines are probably running much faster and the lamp will be brighter as the speed increases.  I don't
think the capacitor should be any higher than .22uF.  This lamp has a reflector around the LED die and it would
be best to select a lamp of similar construction.

If this brightness is not sufficient for the application, charge could be stored on a larger filter capacitor
and then strobed using a SCR or FET.  Timing could be through a simple neon lamp RC timer circuit.  In warm
climates a 9 inch fluorescent tube might be used in place of the LED.  This would trigger on at a high voltage
and turn off as the voltage on the capacitor drops.  Speed of flash would be determined by the value of the capacitor.

[DanG]

Having a pilot light lit when the engine has shut itself down might be a tad more helpful?

Not many people can tell at a glance if there are 16 or 17 varying lights glowing in the distance, plus then factor in weather conditions.

Will insects swarm or ignore the light colors chosen?

Can you armor and weatherproof any connection and connected devices to the high-voltage ignition to be fail-proof for 1000's of hours use?

if the engine-out-light-on idea is sound most any bicycle tail-light LED by battery power (annoying winky red lights) would work since it's a very limited on cycle; plus unit can be switched off when engine shut down normally --- the key is a fail proof engine-out-light-on switch when engine shuts off.

[electrondady1]

perhaps the light could be used to lure insects into a trap and as a result there proteins could be harvested and utilized

[OperaHouse]

Some other facts about this project.  It normally takes about 2 1/2 hours to check all the pumps, the path on the dikes is very narrow and there are occasional snakes of the nasty variety.  They claim it is very dark without any artifical light to mask the signa.  And the budget is less than $10 per unit.  Even Indiana Jones hates snakes.  I think I would choose taking a few minutes staring into binoculars over venturing out on the trail charming snakes. The eye is a lot more sensitive than we think. I tried it at night and have no doubt it would be visible.  The poster will have to workout environmental and part selection. 

What I have done is proof of concept and hopefully provide a teaching moment.  Pretty interesting that you can get that much light from just 60 microamps of current. With a 1uF filter cap the LED would ghost for over ten seconds after power was removed. A 3W LED wastes about 10% of the power just in this ghosting resistor. Being able to develop a couple hundred volts from the points ought to have some application in the future.

[ghurd]

Just a thought.
60uA is going to make x amout of light per LED.
Lots of voltage available.
Series a whole slew of water clear extra super duper red LEDs.
Can see that from a LONG ways!

Pretty much the same idea as what I did here.  When ringing at night, it lights up the front of the house 75 yards away.  I can't recall, and don't have the sketches handy, but seems the whole circuit uses 1mA?
http://ghurd.info/amish_flasher.html


Not sure how many amps flow through me, but same LED as above, me as the resistor, left hand to right toe.
Water clear LED.  The red is light.
A dozen of those would be easy to see from a distance.
G-


(edits)

I do not belive the reflector is needed with regular 5mm 20 degree LEDs because the reflector is built in.  20 degrees would be better than a wide angle LED array with a still wide angle reflector.  In this situation candela is more important than lumens.

E-daddy1's comments are valid, I think.  There must be some kind of minnow in the paddies, eating fish make fertilizer.  Fish farms hang bug zappers over the water to feed the fish.

Wow, "With a 1uF filter cap the LED would ghost for over ten seconds after power was removed".

And oops, sorry, I missed "A red LED string might be more efficient".  Agreed.  Water clear red would be best.