Help with 24 led light powered by 12 Volt car battery

[KJ6EAD]

These converters should already be running about 70kHz.

The only chance of measuring the frequency digitally is at pin 3…

Lmin = ( (Vin(min) - Vsat(sw) -Vout) / Ipk(sw) ) * ton(max)

What current and voltage are you trying to achieve now for the converter?

The converter as purchased was running ≈20kHz. It's now ≈75kHz.

The MC34063A as configured produces less than 300mV on pin 3. My Fluke meter can measure it but Sabrina's meter needs at least 500mV to measure Hz.

The design goal is 3.4V @500mA. We've got the voltage and are trying to increase the current.

I've been using the On Semiconductor MC33063/MC34063 design worksheet but some component specifications are unknown. Semiconductor and Integrated Circuit Devices

Using the formula for Lmin, the design value could be as low as 32µH and as much as 63µH depending on other (partially known) variables. This is a minimum value and it's likely that the Chinese designer went to the low side of this range or less and assumed a 500mA ripple current (100% inductor saturation) to save cost. By changing the inductor to 220µH, we should be able to run as low as 29% saturation and still get our required current out. I'm intentionally building in some margin so that if we have to change anything later, it will be something cheap, like a chip capacitor or resistor.

 

[campus189]

Ok, the 1st one would be huge, bigger than the whole pcb itself,lol
the second one looks like the same size inductor as the 1st.
20PCS 220 UH/1.5A Radial Leaded Power inductors 9*12MM | eBay

Thanks for the reply.

 

[campus189]

**broken link removed**

Think this will work ??

 

[KJ6EAD]

Yes, but it will be a little tricky to mount.

 

[campus189]

Yes, but it will be a little tricky to mount.

Closest I can find on ebay..
I dont want to wait for 30 days for it to come from china,lol

 

[DeepOne]

possible this is useful

if required connect to converter several led chains, possible use "current mirror".

 

[KJ6EAD]

We would have done something like that if we were building from scratch instead of modifying existing circuits. I may decide to redesign mine into a boost converter putting out around 30V to feed three strings of 8 LEDs but that will require a lot of trace cuts and jumpers.

 

[campus189]

Yea, this is been an interesting project,lol

**broken link removed**
States that they are inductors, but look like resistors..

I might have to get them from china ..
Darn things are expensive.. :evil:
It will be nice getting this worked out, as I have a bunch of PCB's all the same size with led's ready to go on them

 

[KJ6EAD]

Those little inductors are not rated for enough current, probably only 200mA or so. You need something that can handle at least 1.5A. Jameco Electronics has some inductors on closeout that might work, part numbers 208283, 371653, 371661 & 371670, but they charge $7 for shipping and another $5 for handling if your order is less than $10.

What's the distance in mm between the two points marked in this photo?

 

[adammonsen]

Thank you for your thread. It is useful for me.

**broken link removed**


Hopefully someone can help me here..
I want to run this 24 led light on a 12 volt car battery. This will be for when the power goes out.
I want to run about 4 of these if I can in my house with the battery being charged by a 4 watt solar battery charger in the day.
It takes 3 AAA Batteries & draws about 480mA , a little less than ½ an amp. And has a voltage reading of 4.7 Volts
I tried using LM317 & 7805 on a bread board, they both heat up a lot.
Without the led light hooked up, I used a potentiometer and got the voltage to a perfect 4.5 volts DC
When I connect the **broken link removed** light it dims big time and the heat sink heats up big time.
I got a feeling that the resistor values may be wrong.
I tried to use the LM317 resistor calculator, but am still having problems..
Any idea what I am doing wrong? I don’t want to spend tons of money trying to figure this out.
If someone could give me some idea as to what to use for resistors or something else, it would be greatly appreciated..

Thank You

 

[campus189]

Yes, I had to put this on hold due to family problems, so. i'm still working on this..
But now I will be posting once again..

 

[campus189]

About a 1/4 of an inch

 

[campus189]

To be more precise , it is .445 Inches or 11.32 mm exactly.
Thanks

 

[khankll]

what are the updates ?


i eagerly red first 3 pages but .... got bored jumped to last page..

u mentioned u will be using it during loadsheding .. for general/daily usage purposes.. and ur powering source will be 12 volts car battery ..
AND u also want to use the led lamp at hand ..

well if u dont want to use the led lamp at hand and want some other alternative way then i may suggest one .. do u need it ?

 

[lordu]

Thank you for this thread. It has helped me immensely.
I registered just to say on this post in this thread.

I would have never thought to have used a USB adapter for a cigarette lighter to get a DC to DC converter to bring down the voltage and especially the current of the said used LEDs.

Recently found out that over current kills the lifespan of LEDs when connected directly to the car battery.
Im a novice myself when it comes to electronics. So at first, I thought easy, connect a string of leds in series to match near 12v, connect leds to battery, connect battery to panel, then done. And yet, that was a wrong way to do it. It does however work for a short period of time.


- U

 

[KerimF]

Hi Lordu and welcome to your forum. You are right. A car battery (being big) has a rather very low internal resistance to limit the LEDs current if an external resistor is not added in series. Also the car battery voltage may vary from about 10V (when empty) to about 14.5V (at full charge). On the other hand, increasing the voltage on an LED by 0.25V only, its current may increase about 10 fold (I mean it follows an exponential function).