Variable Input Voltage, Constant 12V 5a Supply

transformer, duh

DC?

Not in this case.

First, a transformer only works for AC signals.

Second, transformers wrk as a ratio (either step up, 1:1, or step down. The output will track the input voltage according to that ratio. So a transformer with a ratio of 2:1 will only provide an output of 12 VAC when the input is 24 VAC. If the input falls to 18 VAC the output would be only 9 VAC.

Here is another circuit that may be better (lower part count).

The two diodes are for protection of the regulator.

The lower limit of 16 VDC input may be pushing things a little at 5A out.

You say:Input 8-40V

Note that the input voltage must always be (about 5V) HIGHER than the required output.

I.e. with 8 V input you won't get 12V output....

Kim

Hi, Say how to go about inductor 22uH, construct one or get to buy these. Also at wat wattage the zener placed. Thanks.

You can get the inductor HERE.

The Zener can also be had at the same place HERE.

5 amp @ 12VDC?

Sounds like a lot. Don't you want us to help size the cable?

Just plug it in and go.

It'll be fine. It's a heater, not a precision instrument.

I would be hesitant plugging in a heater designed for 12 VDC and expecting good results from 24 VDC, let alone the probability of causing the heating element to open.

Come on. Where's your sense of adventure? Besides it's 24-16V.

Well, it's just the engineer in me that says if the upper limit of the specification is 24 VDC, then it needs to operate at that voltage. :)

You suggestion sounds very Klingon. "It's a good day to die! I say hit the switch!!!"

It is always a good day to die.

Thanks for the advice!

Ah, you wanted a new one anyway.

Voltage regulator.

Google 24 to 12 VDC power supply. They are used extensively in 24 volt trucks to power radios etc.

If it is for a single unit and you value your time at more than $10/h (probably $5 in fact), you should follow JW advice and look for a Truck rated unit with overvoltage and surge protection. Note that the charging voltage for a 24V battery should be 27.6V, so you need at least 28 and preferably min 30V input rating.

You might try a 7812 in a T)-3 can(package). It will take up to 24 v input and provide a regulated 12 v output. It is available in several amp ratings, including 5 amps.

Wat abt the heat sink, how should I design that, also I wouldlike to know how I get heat sinkless design. I know 5A is too much without heat sink.

You can buy heat sinks or pull one from a piece of junk equipment.

I would like to suggest using a heat sink with greater capacity for a TO-3 case, such as a Mouser part #507-423-K. The heat sink you have referred to is for a TO-220, a much smaller case and heat dissipation capabilities.

(Not a comment on your posting, just an idea) Also if the current required for the heater is close to the capacity of the LM338, one or more pass transistors such as a 2N3055 can be incorporated in the circuit. They add an addition of near 5 amps per transistor to the capacity of the unit. Also a smaller heat sink for the voltage regulator could be used if a smaller voltage regular (TO-220 case) such as the LM-317 is used in conjunction with the 2N3055 pass transistors. (not a criticism, just a suggestion)

Good Luck, Old Salt

If you can use two of these hotbag things, wire them in series.

And put a fuse in the input line, for safety!

Cannibalize the golf cart for dc voltage converter or get new.