motor pulse circuit for micro-pellet furnance

[helpmonkey]

I made this circuit to run a small dc motor which will turn a small auger device on the feed shoot of a micro-pellet mass heater furnace ... I would like to get it to work with one battery but if the relay coil is hooked to the same battery the last LED gets fried... any HELP would be greatly appreciated.

 

[Fluence]

Take the LED that burns off and measure the voltage on the wires that connect to the LED, that way you can see if the LED is being burned by excess voltage.

If that's the case you can use a resistor.

 

[tcmtech]

That seems like an overly complicated way of doing what a simple 555 timer can do but with less parts.

 

[bryan1]

With that crude circuit how does it measure the amount of pellets going into the furnace ???? I do assume the furnace is for warming your house as the weather over in Canuck land would be close to Brass Monkey weather. A much better way would be use a LM18200 H-bridge chip and pwm the motor for the feed, one could simply use a pic micro and use a temp sensor far enough away to monitor the temp, the best solution would use a thermocouple but the complexity is way beyond the beginner. Sparkfun sell a breakout board for the LM18200 as the pinout is 0.67mm off memory which aint standard. A 12f675 would fit the bill to a tee for something like this and if you need a hand with the circuit thats what this forum is all about (Helping).

Just provide some more details about the furnace and it's job then we can go from there.....

Regards Bryan

 

[helpmonkey]

@Fluence... i think the led is burning out from a reverse current as the Cap is charged by a joule thief as it spikes above Vcc??
@tcmtech...I had to make the circuit from readily available scrap (recycled) parts ... scrap 555 timers are difficult to find.
@bryan1... the pellet furnace dosnt use a heat sensor as the design uses the auger for anti-jamming not pellet feed ... the pellets are gravity fed... as for the circuit I am using mostly computer scrap to find parts ... motor driver chips (stepper) can be found in printers but I am not sure about H-bridge chips?

 

[RMMM]

You can build an h-bridge out of scrap transistors.

I would look for a 555 in the scrap.. They are still used.

As for the drive:
Does the auger ever stop turning? Does it just continually deliver pellets?

Or is there a "FULL" signal that stops or slows the auger?

 

[helpmonkey]

the circuit pulses the motor about once every few minutes... Im going to try putting a resistor in to protect the last LED as suggested by Fluence ... I will post the results

 

[tcmtech]

You can buy 555 timer IC's from DigiKey for around 54 cents each or radio shack for around $1.

Your circuit has me stumped as to how it creates a pulse every few minutes. Care to elaborate on the design?

 

[helpmonkey]

the toroid winding, pot and transistor on the left side of the schematic make a basic joule thief circuit ... this charges the cap via a diode... once the cap charges enough to turn on (forward bias) the LED string a voltage occurs across the center LED, which has its anode connected to the 2nd transistors base and cathode connected to its emitter, this forward biases the base emitter p/n junction switching on bat1 and energzing the relay which disconnects bat2 from the joule thief. the relay will remain energized as the cap discharges slowly when its charge drops below the LED strings forward bias voltage the LEDs turn off switching off the 2nd transistor, relaxing the relay which connects bat2 to the joule thief which quickly charges the cap again.. the motor is in parallel on the bat2 side of the circuit and is powered until the relay energizes again. the circuit seems to be very very efficient... although it would appear that bat1 would drain via the relay I think what happens is the joule thief spikes bat1 each cycle which causes a charging effect to occure in the lead /acid chemistry? on the bat2 side of the circuit a joule thief is of course an efficient circuit to start with, the cap charge is used efficiently by both the leds and the relay coil and the quick pulse to the motor draws very little current as the motors coils would present a high impedance during most of the pulse. There are also claims that the spark at the contact points provide a high energy spike also???