Glowing LEDs and 12v motor

[blckscab]

The circuit works fine after i turned the transistor round!
Glad that is fixed and i understand the cause (dont understand the transistor acting the way it did, but what i know is good enough, hehe)

I have tried the circuit with 1-3 pairs of 2 LEDs in series and all give a desirable fading effect. Should i still replace the 100ohm resister with a 330 one?

None of the components i recieved came with a datasheet... so i guess that didnt help much, lol. Dead again, i havnt scanned the website for one either. Ill have a look in a second to see if they are on there. That pic of the transister was indeed different to the one i used earlier, but now i know some transistors are opposit and can look out for that

Next step would be the rectification circuit and put the 2 together... (dramatic scary music starts now)

 

[blckscab]

Hmmmm, ok good news n bad news

Ive put the whole circuit together, the motor, the rectification and filtering part of the circuit and the fading circuit. (mind you the resistor infront of the LEDs is still 100Ohms and im only using 2 lEDs parellel)

Good news is that it works, LEDs light up, and motor turns

Bad news is that the fade seems to be working oddly. it will fade a little and then turn off and then turn on and restart. After this result i put the 2 LEDs in series just to see the difference, and now the LEDs seem to switch between half on and on with no 'fade' inbetween....

what does that mean?

I also notice that the circuit will carry on for a bit after turning it off. im guessing that is because of the large capasitor used in the filtering circuit?

Edit:
Also when i take the plug out, when it is still goin for a bit it does seem to fade properly.
Is it that the rectification and filtering part of the circuit is messing the fading circuit up?

 

[Torben]

Hey hey! Good stuff.

OK, your LEDs have a Vfwd range of 1.8 to 2.5 V volts. We can calculate the needed resistor to get a desired current through an LED with Rled = (Vsupply - Vfwd) / Iled

. . .which means we can calculate the current through the LED when using a given resistor: Iled = (Vsupply - Vfwd) / R.

I did up a little table in Calc which shows the current through the LEDs using one and two LEDs, at the top and bottom of the Vfwd range, and using 100Ω and 330 resistors:

Vsupply	Vled	R	Iled	Notes
12	1.8	100	.102 A	One bottom-of-range LED at 12V exactly.
12	2.5	100	.095 A	One top-of-range LED at 12V exactly.
12	3.6	100	.084 A	Two bottom-of-range LEDs at 12V exactly.
12	5	100	.07 A	Two top-of-range LEDs at 12V exactly.
12	1.8	330	.031 A	One bottom-of-range LED at 12V exactly.
12	2.5	330	.029 A	One top-of-range LED at 12V exactly.
12	3.6	330	.025 A	Two bottom-of-range LEDs at 12V exactly.
12	5	330	.021 A	Two top-of-range LEDs at 12V exactly.
14	1.8	330	.037 A	One bottom-of-range LED at 14V exactly.
14	2.5	330	.035 A	One top-of-range LED at 14V exactly.
14	3.6	330	.032 A	Two bottom-of-range LEDs at 14V exactly.
14	5	330	.027 A	Two top-of-range LEDs at 14V exactly.

According to that, even the 330Ω resistor is pushing it given that your supply voltage is going to be a bit above 12V after rectification and filtering. I'd suggest trying a 470Ω resistor just to be safe.


Torben

 

[blckscab]

well thats good because im getting a few 470Ω with my assorted resistor pack hehe

 

[Torben]

well thats good because im getting a few 470Ω with my assorted resistor pack hehe

Good. The LEDs might appear a little less bright but they'll last longer.

What does the fading circuit do if you simply disconnect one wire from the motor?


Torben

 

[blckscab]

from what i can tell the same as before.
dim - light - dim - light - etc

i was brave and had it on for a second without the big capasitor in the circuit and the LEDs stayed on while 'blinking' really fast

Edit:
Dc current through the rectification and filtering circuit also has awquard fading...

 

[Torben]

from what i can tell the same as before.
dim - light - dim - light - etc

"Before"? Do you mean that the LEDs do the same thing whether or not the motor is connected, or that they operate as expected when the motor is disconnected but not when it's connected?

i was brave and had it on for a second without the big capasitor in the circuit and the LEDs stayed on while 'blinking' really fast

Yeah. You want that cap in there. When the incoming sine wave is rectified it doesn't make it a nice, even DC voltage; it just takes the sine wave and inverts half of it so it's all on the positive side of 0V. It's still "bouncing" very quickly from 0V up to 12V. The cap smooths that out to a steadier voltage.


Torben

 

[blckscab]

I ment it is still doing the same jeky on/off if the motor is connected or not connected

 

[Torben]

I ment it is still doing the same jeky on/off if the motor is connected or not connected

Hm. Try putting a bypass capacitor in there. Maybe 10uF (I'd try anything between 1uF and 100uF) near the op amp, with the positive leg close to the op amp's +Vcc pin and its negative leg to ground.

Does that help settle things down?


Torben

 

[audioguru]

Hi Torben,
The output of the transistor that drives the LEDs does not go anywhere near 12V when the supply is 12V. My number crunching schematic lists the peak voltage at 7.6V. So a single 1.8V LED will have a current of 58mA, not 102mA.
The schematic is designed for two LEDs in series and a 9V supply. So then the current is only 17mA.

 

[Torben]

Hi Torben,
The output of the transistor that drives the LEDs does not go anywhere near 12V when the supply is 12V. My number crunching schematic lists the peak voltage at 7.6V. So a single 1.8V LED will have a current of 58mA, not 102mA.
The schematic is designed for two LEDs in series and a 9V supply. So then the current is only 17mA.

Argh. That's what I get for overlooking the very obvious, I suppose. Thanks for pointing that out.


Torben

 

[blckscab]

Im not 100% sure what your saying audioguru, but the LEDs are working at a preferable brightness atm, and adding another pair of LEDs in series, in parellel with the other pair doesnt seem to make the LEDs fade at all... Not sure how it all works, hehe....

Putting a 472 capacitor between pin 8 and ground seems to of done something
Its working now! LEDs are fading on and off, and the motor is moving just fine.
at first the LEDs were still fading oddly, but after awhile they corrected themselves. Now i have taken the transistor out of the circuit and it is still fading correctly.

But what i think will happen is that after turning the power off and leaving it for awhile will result in the awquard fading again... Or maybe the circuit just needs to 'warm up' before working properly because of the AC -> DC stuff?

Ill turn it off, wait a hour and look at it then

i have noticed something else now ( sorry to be a pain! lol)
But the motor is getting pretty darn hot. It was originaly taken from a optic fibre light and would of been set up in series with a lamp. Its specs again are12 AC 11/12 rpm 1/1.5w

 

[Torben]

Im not 100% sure what your saying audioguru, but the LEDs are working at a preferable brightness atm, and adding another pair of LEDs in series, in parellel with the other pair doesnt seem to make the LEDs fade at all... Not sure how it all works, hehe....

He's saying that I buggered up the LED voltage calculations. Your resistor should be fine as is.

Putting a 472 capacitor between pin 8 and ground seems to of done something
Its working now! LEDs are fading on and off, and the motor is moving just fine.
at first the LEDs were still fading oddly, but after awhile they corrected themselves. Now i have taken the transistor out of the circuit and it is still fading correctly.

I'm betting you meant that you took the capacitor out, not the transistor.

But what i think will happen is that after turning the power off and leaving it for awhile will result in the awquard fading again... Or maybe the circuit just needs to 'warm up' before working properly because of the AC -> DC stuff?

Ill turn it off, wait a hour and look at it then

Just try it after the LEDs have stopped fading once you've turned it off. Turn it back on without the bypass cap and with the bypass cap.

i have noticed something else now ( sorry to be a pain! lol)
But the motor is getting pretty darn hot. It was originaly taken from a optic fibre light and would of been set up in series with a lamp. Its specs again are12 AC 11/12 rpm 1/1.5w

I'm afraid motors are still a bit outside my field of experience. It could be normal, or it could be about to die a horrible smokey death. I think it's possible that the resistor and cap I put across the motor terminals in the original rectification/filtering schematic are adversely affecting the motor.

What happens if you run the motor straight from the 12VAC adaptor, with the sculpture load attached, but not the rest of the circuit? Does it still get hot?


Torben

 

[audioguru]

You said that the motor is a 12VAC one and you are trying to run it on 12VDC?
A 472 supply bypass capacitor is way too small, it is only 0.0047uF. It should be 47uf which is 10,000 times bigger.

 

[Torben]

You said that the motor is a 12VAC one and you are trying to run it on 12VDC?
A 472 supply bypass capacitor is way too small, it is only 0.0047uF. It should be 47uf which is 10,000 times bigger.

In my original schematic the 12VAC for the motor is drawn from the lines before they go into the bridge. If it's hooked up like I drew it, the motor should be getting 12VAC (assuming that the circuit and motor aren't loading the adaptor enough to drag it below 12VAC).

I forgot to mention exactly what you just said about the bypass cap. I said to try something between 1uF and 100uF, certainly not as low as a 472.


Torben

 

[blckscab]

... yes i ment capacitor.... lol

and the motor is getting 12AC and is a 12AC motor, so that shouldnt be the problem

Ok, i see what is happening now! It starts off pretty odd with the whole, bright -> dim -> bright -> etc with no 'fading' between the 2 states. But gradualy more 'fading' accours and eventualy it does the desired smooth fading.

If i turn it off and back on after awhile, it also fades propely right away. But the longer i leave it off the longer the delay is for it to fade properly, that is probably why i assumed it just wasnt working.

The other 472 capacitor seemed to act as a 'jump start' and disconnecting it from the circuit early on causes the LEDs to fade properly right away.
(cant be sure of that though as the LEDs are working now, lol)


The motor still gets very hot if its directly attached to the adapter with the load on or not.... Thats why i started thinking it could be becuase its not paired with the lamp it was intended to be with as well as the adapter i am using now.

Ive just got the lamp (i kept that too) set up with the motor atm and im going ot leave it on for a bit, see what happens its a 12V 5w lamp

 

[blckscab]

Ok i think that was problem.
Without the lamp there i swear i could of cooked a egg on it. I couldnt touch it without it hurting.
With the lamp there it is now hot, but not half as hot as before! Problem is that i dont want that lamp there and i would say it is still a little too hot.... Hehe.

 

[Torben]

What is the current rating on the adaptor?

Do you have a multimeter which can measure AC voltages? If so, it would be good to know what the actual voltage going to the motor is when it's in circuit.

What was the original power supply for the motor? If you dug the motor and lamp out of an existing unit, can you perhaps also dig out the power supply and use that, if it has a higher current rating than the adaptor you're using.

Have you tried a proper bypass cap?


Torben

 

[audioguru]

Is the timing capacitor for the fading a non-polarized one or two polarized caps connected in series back-to-back?

 

[blckscab]

I cant check the adapter yet because im at work again, but ill look when i get home. Im faily sure it said output: 12v 500hz(?) or something like that
No i dont have a voltmeter to my knowlage....

The lamp, motor and adapter all came from a disco ball toy thing. So im guessing the motor would normaly get that hot.... Its just that originaly the motor was suspended in a plastic box and not between two pieces of wood, and id rather not have it damage all my hard work or be a fire hazzard in my bedroom!

Im still using the original capacitor stated in the fading circuit adobe file. I dont have any non-polarized that match the same value or two polarized capacitors to replace it with at the moment.