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I want to make a voltage doubler to run a 24vdc, 13 amp motor from a regular 12v car battery. I plan on using 2 caps and 2 diodes like I saw on you tube. Can you tell me what caps and diodes to buy. I'm going to Micro Center today to buy them, but I don't know one from the other; I don't have electronics training. Thanks! .

A standard voltage doubler circuit requires a clock like signal as input ("rectangular" input signal), not a DC input.

There are DC to DC 12V to 24V converter for less than 3.00 US, transport included, on eBay, and probably at your micro center too if they are selling electronic pre-assembled kits.

Thank you for your informed reply. I apologize for being such a novice on electronics. It sounds like it must be an AC input so the cap can discharge, and the diode(s) keep it from being an off-on, or even forward- reverse, output. I guess I should have known better even with my limited knowledge. To tell you the truth, I want to replace the two small 12v 18Ah batteries on my elec. lawn mower(24V,12A) with just one full size car battery for more mowing time.

I don't see a 24V 300W converter for less than $30; this one: https://www.walmart.com/ip/1200W-High-Power-DC-DC-Converter-Boost-Step-up-Power-Supply-Module-20A-IN-8-60V-OUT-12-80V-Adjustable/494679745? Will this take a 12vdc input? Are the 2 blue things pots; one for V and another for amps?

That seems to be a possible booster, indeed. I don't see the detailled instructions for this particular ones, but generally you have two plugs V in ( one for + and one -, if the intended input is DC ) and two V out. The description says that V in (the difference between the + and the -) should be of at least 8 volt. No problem for that. Since it allows a high power, so is the ... high... price (well relatively high, some can go past the 300 US, but low power ones can be one hundred times less.

As for the two adjustments, one is to limit the output voltage in the constant voltage mode. Indeed, your output voltage is often "selectable", and that is how they acheive it. This particular one seems to also have the option to have a constant amperage mode, instead of a constant voltage mode. You cannot have bot active but you "probably" ( I extrapolate, but that features exsist on "some" booster) can have constant selectable voltage WITHOUT exceeding a given selectable amperage. (If not, someone can use a standard fuse, as protection for the device/motor AND also for the wiring itself, to not catch fire.) Oh, important, if you plan to use it outside, better to double check if the booster is certified (ULx, CSA, ... ) for outdoor uses.

(If you wonder about why someone would use a constant amperage mode, a possible case is to charge super capacitors, just as one possible example).

And indeed, you can also have "booster" with DC output working with AC inputs. That is still in use in many places, such as in Desktop PC of some age, because it can produce a very stable output. They are heavier, by much, since their tranfo required much more copper. And more expensive. But potentially, they deliver a more "stable, clean" output.