Need help with glow plug driver

audioguru said:

your battery is 12.6V or more.
the glow plug needs only 1.5V.
Then you are wasting 11.1V at 3A (33.3W) making heat. Then the circuit uses 7.4 times the power of the glow plug. What a waste of power!

You should use a switched-mode buck power supply to efficiently convert 12.6V to 1.5V at 3A.

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But it doesnt matter, a car battery has a huge capacity.
I certainly never flattened mine even with loads of use.

(Good circuit removed because people prefer to use a bad circuit. )

audioguru said:

your battery is 12.6V or more.
the glow plug needs only 1.5V.
Then you are wasting 11.1V at 3A (33.3W) making heat. Then the circuit uses 7.4 times the power of the glow plug. What a waste of power!

You should use a switched-mode buck power supply to efficiently convert 12.6V to 1.5V at 3A.

Click to expand...

i believe this is wrong.
Every time the fet goes on it ill deliver 12v to the glow plug. this is why they use pwm.
the circuit will deliver 8 times the load's power for 1/8 the total time.
There is no power waste.

i liked the ideia of the switch mode power supply.
Also there is an on going thread of a PIC controlled Buck converter.

Mr RB said:

Ok, I've stripped it down to the minimal stuff you need to do the job.

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I dont know about this.
this is the kind of circuit i´m not confortable about.
i´m afraid of never getting it to oscilate and then afraid of not being able to tune it.
I like it without the caps on it.

audioguru said:

Why use a switch to change the current?
Aren't all glow plugs for model engines 1.5V? My glow plugs also worked fine when my 1.5V battery dropped to 1.2V. When the battery was only 1.0V when loaded then the engines were difficult to start.

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Well, i wrote i would have to search some info on that.
I just decided to speak ahead.

I was just refering to the diferent types of glow plugs.
there are A type, R type and others. some for RC cars, some for planes and special ones for helicopters. some depending on the fuel used.

i only use R type ones. Mainly because i only use one type of fuel.
I´ll try to search some info on the glow plugs.

best regards

option circuit

in my search i find **broken link removed**.

he actually made it to be an onboard igniter, using one radio channel.
his circuit mentions jumpers for battery selection, but instead he just soldered (hard-wired), once he is just using one type of battery.

one thing this circuit has going for it self, is the use of lower battery voltage, since it uses the receiver's battery.

01Sporty, it seems to me that all you are after is an indication that current is flowing? If you are not set on a LED than maybe a voltmeter across Rm would do the job? You need something with a range of 0-1V. This would display a current up to 5A. If you can pick up an old VUmeter out of an old cassette player or something that might do the job.

Well, you all have come up with some interesting ideas, BUT-----------

The PWM circuit I started with is a proven concept. All the commercial units use something similar. I also already have all the stuff for this circuit.

Unfortunately, the led indicator is the least of my problems. I've put the circuit together twice now and have had very little success. And, of course, I have no idea of how or what to change or check.

The first time I put it together, I did have it working briefly, sort of. I found that IC1 was outputting voltage on pin 3 that varied with the pot. This voltage wasn't triggering Q1 however. In trying to trace the voltage, I inadvertently shorted across R1 and it worked but was entirely too hot. While trying to figure out if the problem was R1 or C5, I lost it again and never got it back. Not surprising since I have no idea what I did to get it working in the first place.

As things stand right now the voltage on the pins for IC1 are: 1) 13.04 (battery voltage), 2) 11.69, 3) 12.59, 4 & 8) 13.02, 5) 13.03, 6 & 7) 12.96.
None of the voltages vary with the pot.

Any troubleshooting suggestions?

Cheers,
Walt

Pin 1 on the 555 IC in the schematic is shown at 0V, not at 13V. That is why it doesn't work and why all the other pins have voltages too high.

ameal said:

You can use a Current Regulator....

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It will be a smoke generator. Calculate how much power it will dissipate.

the smoke generator

audioguru said:

It will be a smoke generator. Calculate how much power it will dissipate.

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I understand what you're trying to say. maybe it wont burn.

1.5v for the glow plug + 1.25 for the sense resistor = 2,75v
12 volt suplly - 2.75v = 9.25v
9.25v * 3 Amp ~= 30Watt
Its not that much. But my other sugestion as the receiver battery, so not 12v. so half the value.

Any power supply, going from 1,2 to 30 (usually), in its worst cenario, being output 1,2v (lowest voltage) and 3Amp (highest current),
will have to dissipate an excess of 90Watt.
Besides the LM350 datasheet mentions the output power being Internally Limited.

just for everybody to know:
my setup is a female panel RCA (audio type) in the car side. and a male one the 1.5v Ni-Mh battery side.
So i plug it, start the engine, with both hands free, warm it up a bit and unplug. the battery comes out and stays in my pocket.
I dont use the usual igniter.

i´m really interested in this topic. but i really dont like the first schematic presented here.
i've been using the 555 since i can remember.
since 12v is almost 10 times the load average voltage, the max on time will be 1/10th the pulse size.
if something goes wrong thats no saint that will help you.
I understand that sporty said its a proven circuit, but i struggle in using such a high voltage.
sporty, i really hope you can make it work soon.
also i have no use for a 12v field box, since my plane is electric.

maybe i just need something diferent from the topic discussed here.

audioguru said:

Pin 1 on the 555 IC in the schematic is shown at 0V, not at 13V. That is why it doesn't work and why all the other pins have voltages too high.

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Pin 1 is connected directly to the negative terminal of the battery so maybe I made the measurements incorrectly. I had the positive lead of my vom hooked up to the positive lead of the battery and used the negative lead to make the measurements.

When I connect the negative lead of the vom to the negative lead of the battery and use the positive lead to make measurements, all of the pins measure 0V with the exception of pins 2 and 3. They measure .005V and .006V respectively.

Did I get the measurement right this time?

Thanks,
Walt

More info.

Between R3 and D3 I get 13.04V but on the other side of D3 I get 0V. I'm reasonably certain that D3 is good, could C1 be shorted?

The latest voltage measurements of your 555 IC are completely wrong.
The power supply pin8 and the reset pin4 should be +12V. Most other pins should have voltages.
Maybe your 555 is plugged in backwards.

the only measurements you will be able to take are in pin 4 and 8. pin 1 will be 0v.
Trying to read the other pins with a regular voltmeter will probably jam or alter the behaviour of the circuit, since you have values there of about 750k.

The only other pin readable is pin 3, the output.
do you have an analog volmeter?
connecting one to the output will give you the PWM average value, near the 1,5v range. either 0v or 12v is circuit dead.
care to try?

audioguru, agree?

have you checked the IC orientation?

DVMs today have inputs that are 10M ohms. This circuit won't notice any loading.

audioguru said:

DVMs today have inputs that are 10M ohms. This circuit won't notice any loading.

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By that, I assume you mean I can go ahead and use my digital volt meter.

I may still have an analog meter somewhere but it's been a long time since I've seen it. I'm really hooked on that auto ranging you get with the digital.

I'm embarrassed to say that I did get the IC in there backwards once the first time I put the circuit together. I check it pretty carefully now.

I pulled D3 and C1 and they both check out Ok.

Sounds like I may have killed the IC. I'll put a new one in. I found a circuit for a 555 checker. Maybe I should build it first.

Any suggestions on preserving the IC? I'm doing all my assembly on a grounded aluminum plate.

You can preserve a 555 IC if you don't plug it in backwards.

i wasn´t aware that digital volmeters' input impedance had those values. my bad.
sincerely because i use the scope for this kind of measures, and mine is 1 MOhm. so i need to choose my measure points wisely.
Maybe i could start thinking about seaching for a new one.

you can use any such volmeter but it wont give any usable reading.
Maybe a unit with True RMS reading above 10KHz. If that exists.
the values are always either 0v or 12v. you need the average.

the analog meter or even a LED and 1K resistor could help to some point.

best regards