Joule Thief

[xee2]

@ jeanna

Hazens1 was able to lower the frequency so much he could see the LEDs flashing on and off by adding a 10 uF capacitor across a 10K base resistor. You may not be able to duplicate this since your circuit is different, but it does seem to support the idea that increasing the base capacitor lowers the frequency.

[TheNOP]

I think it was Gadgetmall who first suggested this and he also noticed that he needed less battery current for a given output voltage when the base capacitor was added.

yes it is Gadgetmall.
he was using the cap to limit the current, by changing the frequency and probably duty cycle too.

and its also work in reverse.
it might not be obvious, but i stated this before.
we can change the cap and/or resistance (RC circuit) values to fit the frequencies we want/need.


@jeanna
thanks for showing that the pickup coil can affect the frequency.
i was expecting something like this, from an impedence point of view, but could not confirm it.

note that things will not be exatly the same with a load on the pickup coil(s).
a cap is only a load while charging(acte like a variable load).
once charged, it is not a load anymore, unless you discharge it.

[WilbyInebriated]

i'm a little confused as to this what this base cap actually is.
is this a cap in parallel with with the base resistor? is that what's meant by 'across'?
or is this cap going from the base resistor to the negative rail??

[hazens1]

is this a cap in parallel with with the base resistor? is that what's meant by 'across'?

Yes

[jeanna]

@ jeanna

When I look at your data it seems like adding the capacitor increased the frequency (opposite of my theory - so maybe theory is bad).

I used the base capacitor to get enough voltage across the collector coil to light a neon (about 100 volts). I do not still have my data, but I think I was not able to get that high a voltage without the base capacitor. Also, I was able to reduce the battery drain needed to get a given output voltage by adding the base capacitor and simultaneously increasing the base resistor value. I think it was Gadgetmall who first suggested this and he also noticed that he needed less battery current for a given output voltage when the base capacitor was added.

Hi xee2,
Thank you for all your comments.
I am returning to this one for a few reasons.

Your theory was not entirely wrong.

The frequency did decrease and it did a lot when I used a higher value cap. It was just some good luck that the length of wire I had cut off gave me just enough to get to the number of turns necessary for the 103 (=10000pF) to come into play in the way to oppose your theory. So, under a certain threshold your theory applies.

I went back and retested the turns/cap value again and that is what I showed in the table last night.

The other part is I never put a cap across the battery. I had not seen any help from it since you suggested it to Gadget, and I eventually removed it.

I would like to try that again. Would you suggest a size and style cap to put here, please? (you don't have to be right, just get me close!)

Also, was the neon which you were able to light because of the base cap placed across the E-C of the transistor? You got 100v across there?

Thanks, xee


@Dog812,
Maybe you have too many turns on your secondary?

I am not sure what made me want to say this today. I don't have a theory to support it.
I just think something is wrong.
5 turns on your secondary is enough to light one light blazing bright. One is the same as 20 if they are in parallel.

I think you are the person who put all the lights in the battery rail, aren't you?
Run the secondary around the toroid 5 times then put the ends into the battery rail that is NOT being used for the battery.

Then put one light into the rail and keep adding them. Keep the polarity of all the lights the same. If they suddenly go dim, put the latest one aside and use another one. Or if you have an extremely bright one and the rest are not so bright do the same.

Please let me know how this works.

@theNOP,
Somehow, many times you seem to be talking about something different from what I am talking about.
So, just to be very clear about my set-up,
There is NOT a cap attached to the ends of the secondary.

@Wilby,
Yes, Hazens is right. The cap has one leg on the base of the transistor and the other leg on the far end of the base resistor.

Thanks everybody,

jeanna