/diy/ - Do It Yourself

[Anonymous No.465577]

First time here

I'm not too good with electronics and would like some help.

I have a small 24v generator, and I only need 12v of its output.

How would one go about "limiting" the output of that source ?

[Anonymous No.465579]

You want to use a chip called an LM317T. It's an adjustable voltage regulator. They're cheap and can be found at The Shack. 24v goes in the IN pin, and 12v goes out the OUT pin (+- 1.5v), depending on the resisters you set up between the ADJ pin, the OUT pin, and the ground. Google for it, there will be mountains of info.

MAKE SURE YOU USE A HEAT SINK FOR THE CHIP! THE UNWANTED VOLTAGE IS BLEED OFF AT HEAT ENERGY

[Anonymous No.465582]

>>465579
Alrighty, I'll look into resistors now.

Thanks

[Anonymous No.465587]

>>465582
Right. The two required resistors, referred to as R1 and R2, determine the percentage of the input voltage that is present at the output. There is a formula for this that you can find online by searching for "lm317t calculator".

[Anonymous No.465600]

There's also the buck part of a buck/boost converter. They can be very efficient.

[Anonymous No.465620]

anybody know what is shown in OP's pic?

[Anonymous No.465623]

>>465620
it's a failed IED detonator ; note the palm trees in the background, the one failed missed call and the military dress of the obsured figure, also the FRICKING FILENAME goddam, why didn't I see that in the first place...

[Anonymous No.465625]

>>465623
herp derp you must be a genius.

but really, anybody know what that device is? the phone alone could act as a detonator. what's on it?

[Anonymous No.465628]

>>465625
derp, it's a relay..

that chip is [pdf] http://www.datasheetcatalog.org/datasheet/motorola/4N35.pdf

It's not that hard to google part names if you don't know...

[Anonymous No.465629]

>>465628
impossible to read on this device; no PC available. but thanks.

[Anonymous No.465637]

>>465587
>>465579

Huge issue these posts aren't addressing:

How much power do you need off that 12V input? Linear voltage regulators aren't generally used to dissipate a dozen watts of heat or so, save for special applications.

If you're asking for a hundred watts or two, you're going to need a really fat regulator and a similarly fat heatsink (think like the average stock CPU cooler) with active cooling.

Or, what would probably cheaper is to use a switching regulator (DC/DC converter), which is much more efficient and can handle much higher power levels for an equivalently-sized package.

[Anonymous No.465860]

>>465637
>If you're asking for a hundred watts or two

100W at 12V would be over 8A of power. At 12V. What do you think he's doing, precisely? I mean it's *possible* but it seems unlikely (and inefficient)

[Anonymous No.465863]

I never understood why they don't install cell jammers in all their vehicles.

[Anonymous No.465878]

>>465863
Because IEDs don't all use cellphones as the detonator.

I used to work for a division of a defense contractor, and we were building (among other things) an IED-specific jammer. IEDs are built with every sort of radio control imaginable, from cellphones to FRS radios to garage door controls to toy car remote controls, you name it they've used it to build an IED. I remember we had a box of all the above and more that we were using for testing to decide how the hardware and software needed to be designed for the jammer. See, it's not just a matter of transmitting a strong carrier wave in the vicinity of the device you want to jam against receiving, you need to do things like distort the signal being sent to detonate the IED so the receiver doesn't have a chance at pulling signal out of the noise. The devices we were building would actually receive the transmitted signal, process specific distortions into it as close to realtime as possible, then re-transmit the corrupted signal. Very effective.

[Anonymous No.466231]

> I never understood why they don't install cell jammers in all their vehicles.

coz then the home team will make IEDs that trigger on those jamming signals. those would be very effective coz you just set them and forget them: no need to tie up an insurgent waiting for hours or days.

[Anonymous No.466243]

>>465582
You going to waste a lot of power using resistors.

Another way is make your regulator by using high current diodes. The forward voltage drop of diodes is about 0.7 volts. 17 of them in series would give an approximate 12 volts voltage drop. Connect this string of diodes in parallel with the output of the generator and you don't have to worry about voltage going above 12 volts.

[Anonymous No.466245]

>>465577

no offense, but you need to understand the relationship of power, voltage and current.

POWER is the unit of measure for electrical energy. voltage by itself is no indication of how much POWER you have.

water analogies work here: a squirt gun can lift water 6 feet in the air (analogy: high pressure == high voltage) but the total amount of water is small. a garden hose (no nozzle) will only squirt up 12" (low voltage) but the quantity of water is larger.

quantity delivered per unit time is CURRENT
pressure is VOLTAGE

power is the product of the two.

a car battery is "only" 12V, but it can deliver 700 - 1000 amperes for a minute or more. lots of power!

1/2

[Anonymous No.466246]

2/2

your generator makes some amount of power, but comes out at 24V? dropping the voltage with resistors (bad, unregulated) or an LM317 or equiv (bad, regulated, but wastes half the power) is the wrong approach.

you want whats called a "buck converter". that will use fairly complex electronics to actually transform the higher voltage power to lower fixed voltage (12, whatever) and wastes only 5 - 20% instead of over half. which is critical for low-power systems.

there are also boost converters, that'll take the "wild" output of say solar cells and output fixed 5V.

you can buy both types on eBay. usually cheap and small. $5 - $20. yes buyfag, as they are definitely not a simple hobbiest thing to make.

[Anonymous No.466247]

>>465577

WOAH! NICE PIC!!!

missed call indeed!

[Anonymous No.466248]

>>465860
>What do you think he's doing, precisely?

I would have no idea. That was kind of the point.

Even a few 12V incandescent lights would be more than your average linear regulator could handle off a 24V source. Something like a 12V air pump would be a bit much, too. Just about anything that isn't low-power stuff, like digital logic, would call for a switching power supply here, actually.

>>466243

He's going to waste a lot of power with diodes, instead, if he does that.

[Anonymous No.466336]

AC or DC? If it's all AC, why not just use a 2:1 transformer?

[Anonymous No.466367]

>>466245

>POWER is the unit of measure for electrical energy.

[Anonymous No.466376]

>>466367
Didnt real entire thread, but what is the unit of electric energy? there seems to be a bunch, amps, omes, watts, volts, joules, ect

wtf man, why they do that?

[Anonymous No.466397]

>>466376
those all measure different things

[Anonymous No.466400]

OK there seems to be alloy of confusion and ignorance here so let me enlighted you all...
R*C=V
resistance(ohms) * Current(amperage) = voltage.
Voltage can be expressed as power, energy or w/e the hell you want it all means the same fucking product.

>>Tl;Dr ohms law.

[Anonymous No.466401]

>>466400
>resistance times capacitance is voltage
nigga get your letters straight

[Anonymous No.466439]

>>466400
RI=V

[Anonymous No.466440]

>>466376
Amps = current (I)= flow (so many electrons per second) (similar to Gallons per minute)
Ohms = Resistance (R)= opposition to current (similar to a small hose)
Volts = Electrical pressure (V or sometimes E)(similar to water pressure)
Watts = Power (P)= Work done (similar to spinning a turbine)

Joule = a specific number of electrons (very large number)

OHMS LAW:
R * I = V
V * I = P

>>466400
> let me enlighted you all...
>Voltage can be expressed as power, energy or w/e the hell you want it all means the same fucking product
wut?

[Anonymous No.466444]

>>466440
Power means power, or work done per second.
Joules measure energy or work. A number of electrons is a charge, measured in coulombs or more commonly ampere hours (Ah mAh).
If a battery or a capacitor has a charge of 1 C (or ampere second, which means the same thing), it can put out one ampere for one second, two amperes for half a second, and so on.

These things are easy to look up from wikipedia.

[Anonymous No.466453]

I designed 1600V to 820V input to 800VDC output linear regulator for an ion chamber

[Anonymous No.466465]

>>466336
I'm guessing op's 24v generator is powered by wind or some other physical means. In that case, the frequency won't be consistent enough for the output to be converted with a transformer.

[Anonymous No.467572]

Apologies for bumping old thread, but I really have to address the misinformation being posted.

>>466245
>>466400
>>466440

>POWER is the unit of measure for electrical energy.
>R*C=V
>Voltage can be expressed as power, energy or w/e the hell you want it all means the same fucking product. [WHAT?!]
>Joule = a specific number of electrons (very large number)
>Power (P)= Work done (similar to spinning a turbine)
>OHMS LAW: V * I = P

These statements are all incorrect in some way or another. These people have no idea what they're talking about.

Listen to this guy instead:

>>466444

If you don't even understand what voltage, current, power, energy and charge are, you should not be posting in electronics threads.

I recommend Sadiku's Fundamentals of Electric Circuits if you want a book to read. There are torrents for the pdf floating around.