Installing LEDs in my WorkVan, Electronics help...

[FvnnyL3tt3r1ng]

For the inside ceiling of my workvan:

So the LED light fixtures I bought from harbor freight use 3 AAA batteries in series or ~4.5V. There are two separate circuits of these on the fixture so all 6 lights be powered.

I'm not sure on the power draw (yet) but I need to step down my battery/alternator input (12.5-14v) to the 9v needed for the lights rigged up in series.

Alternatively, I could step up to 18v and wire all 4 circuits in series as well.

After a little research it seems that they sell "Buck converters" specifically for this purpose. I'd rather just solder a few components together from my home supply if I can do it a simpler way.

I know the linear conversion method is said to be inefficient and generates heat but I don't see that being a big problem considering I am only using these lights typically less than 10 minutes at a time.

Could anyone reference me a circuit or give me some pointers on this? Could I just solder enough diodes to induce a big enough voltage drop? I'm thinking 6 of them??? Would I also need to size a resistor?

[Brother Michigan]

My knowledge of circuits is entirely theoretical, but couldn't you just measure the current draw of each using a multimeter then simply use Ohm's Law to calculate the proper resistance needed to produce the desired voltage drop?

[FvnnyL3tt3r1ng]

Originally Posted by Brother Michigan

My knowledge of circuits is entirely theoretical, but couldn't you just measure the current draw of each using a multimeter then simply use Ohm's Law to calculate the proper resistance needed to produce the desired voltage drop?

You may be on to something.... I'll have to put some batteries in them tomorrow. Good thinking

[FvnnyL3tt3r1ng]

Well I did what I should've done in the first place and posted my question on an electronics forum. The response I got brought up a good point.

A small change in the input of the regulator brings about an even bigger one in the output. That means I could easily blow my LEDs if the voltage jumps which I was told is very common in automotive.

The voltage could easily be well above the max input rating and even negative which would also short the LEDs.

The buck switching regulator with a diode and varister in the input was the solution given.

I think the resistor idea would generate too much heat (14v-9v=5v...5v*current of LEDs=Wattage of heat across resistor(s)) in the end.

[verboten1]

http://www.lightingever.com/12v-led-...C9kaAr3C8P8HAQ

more light than you will ever need, and it will take 2 wires.

[dcj13]

3 fixtures in series will probably work ok with what the alternator puts out.

[Brother Michigan]

That is a good point.

I guess it's moot anyhow, but as for the heat generated by the resistors, I don't think it would be that bad; if each LED draws 20mA, the total heat to be dissipated by any resistors would only be 1.2W. If you needed to bring down the power per resistor, you could just wire up a few in series.

[verboten1]

http://www.ebay.com/itm/2x-Super-Bri...9831e2&vxp=mtr


http://www.ebay.com/itm/Waterproof-4...item5b0d65d690


I have something like this in my trunk

http://www.ebay.com/itm/0-5M-50CM-12...item35e2a617e2


there is a reason they give those lighst away. they are junk.

Mine has maybe 5 minutes of use and has 2 dead diodes already.

[FvnnyL3tt3r1ng]

Originally Posted by dcj13

3 fixtures in series will probably work ok with what the alternator puts out.

Only problem is they put two circuits per fixture....

If I were to wire them straight to the battery with an inline fuse I think I may have the problem of having to change the fuse too often....

[FvnnyL3tt3r1ng]

Since I already have the light fixtures total cost of the buck regulator is less than $5 including the additional varistor and diode....

The fixtures were about $15 total for a total of about $20 for the setup.

I think the light output on these is adequate, but if I were to start over from scratch it seems like there would be a better light output from another manufacturer, and possibly cheaper.

[verboten1]

understood. all of the things I posted are 12V, and a 5 pack of 50 CM lights is $20 with free shipping. 250 CM of lights (8+ feet)

these things are great for freebies. my last one lasted about 5 minutes.

just letting you know, don't be upset when you have to redo the work because the LEDs failed.