stunthanger.com
Engine basics => Engine set up tips => Topic started by: Tim Wescott on May 18, 2018, 01:56:56 PM
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I'm sure this has been asked before, possibly by me -- what's the normal current range for a glow plug? How about a flooded glow plug with 1.5V on it (i.e., no one's turning up the power to burn off the excess fuel)?
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Increasing current only burns out fuel touching the glo plug. Increasing current only shortens glo plug life, and can burn it out. Best solution for flooded engine is to turn the cylinder upright and crank it in reverse, or wait a few seconds for fuel to fall away.
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I'm sure this has been asked before, possibly by me -- what's the normal current range for a glow plug? How about a flooded glow plug with 1.5V on it (i.e., no one's turning up the power to burn off the excess fuel)?
It makes a big difference which plug you have, but figure around 3 amps dry and maybe 4.5 flooded. Talk to Howard about his voltage regulator system.
Brett
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Increasing current only burns out fuel touching the glo plug. Increasing current only shortens glo plug life, and can burn it out. Best solution for flooded engine is to turn the cylinder upright and crank it in reverse, or wait a few seconds for fuel to fall away.
I'm more interested because people are asking me about current meters that the can mount on their forearm-mounted racing kits. Knowing the meter current lets me keep my eye open for something better than disassembling a metered glow starter (which, so far and in the absence of any real experience, seems to me to be the best bet).
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0-5 amps is a good range for an ammeter. I've tried various power supply schemes. I settled on one that maintains 1.0 volt at the plug (a little more for Cox plugs). Use an analog system: pulses start fires.
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An ammeter is a handy device used on a flight box/battery. You can instantly see the health of the glo plug and battery. When the engine doesn't want to start, a meter helps in isolating the problem.
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I've been asked to help a local racer with a dead plug detector that he can build into his arm-mounted kit. He'd be happy with just a light that indicates current above some threshold -- I'd be happy with an existing product that I could point him to.
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Any passive device for measuring current necessarily causes a voltage drop in the circuit. An ammeter causes a voltage drop. A sensing resistor (producing a voltage which can be measured in many ways) also drops the voltage.
An active current sensor would require a magnetic field detector for the weak magnetic field surrounding a straight wire carrying current. This would require an amplifying circuit because the resulting signal would be too weak to indicate directly.
Any meter using a D'Arsenval movement is a delicate instrument, easily damaged unless protected. Iron Vane type meters are more rugged.
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Any passive device for measuring current necessarily causes a voltage drop in the circuit. An ammeter causes a voltage drop. A sensing resistor (producing a voltage which can be measured in many ways) also drops the voltage.
I think I'd be happy with a 0.01 ohm sense resistor. That works out to a 50mV drop, which is considerably smaller than the drop in the battery, and probably less than in the wiring in a typical glow plug setup. I checked on what's available on the market today -- I think it would be doable, maybe even easy, to make a meter with an LED bar graph that wouldn't light up until there was glow plug current, and that would take a couple of years to suck the charge out of a single D cell, much less a few in parallel.
But, I'd need time...
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I think I'd be happy with a 0.01 ohm sense resistor. That works out to a 50mV drop, which is considerably smaller than the drop in the battery, and probably less than in the wiring in a typical glow plug setup. I checked on what's available on the market today -- I think it would be doable, maybe even easy, to make a meter with an LED bar graph that wouldn't light up until there was glow plug current, and that would take a couple of years to suck the charge out of a single D cell, much less a few in parallel.
This one seems small enough and you can change the shunts to get it in the right range:
https://www.ebay.com/itm/Dual-LED-Digital-Voltmeter-Ammeter-Panel-Tester-0-28-DC-100V-10A-Red-Blue-Shunt/183188976926?hash=item2aa6e9f51e:m:mG1OmsQ3VVYTF0nQaufeHyQ
This will be much more durable than an electromechanical meter.
Brett
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This one seems small enough and you can change the shunts to get it in the right range:
https://www.ebay.com/itm/Dual-LED-Digital-Voltmeter-Ammeter-Panel-Tester-0-28-DC-100V-10A-Red-Blue-Shunt/183188976926?hash=item2aa6e9f51e:m:mG1OmsQ3VVYTF0nQaufeHyQ
This will be much more durable than an electromechanical meter.
Brett
Hello Brett
Neat little meter and a so cheap.
Could it not be hooked up with out the shunt using as shown in the first diagram of the auction images?
Regards Gerald