J-3

Does anyone know how or if you can step the voltage down on a 24v power supply to power 12 volt chargers?
I have searched through this forum but I did not find anything.

Thanks for your time....Brian

bgosselin

Yes, it's possible, but it would be far easier to simply get an inexpensive 12v power supply.

Goldenduff

I agree with the above post. Something to think about is the bigger the voltage change the less efficient. So going halfing the voltage would waste a fair bit of energy.
Be much better to invest the money you would spend on dropping the voltage on buying a 12v supply (you could go to a scrapmetal place where real cars go when they die and get 3 or 4 12v 6A+ batteries for very little, connect in series and you're done!)

Good luck

HunkaJunk

You could do it by building a voltage regulator circuit using a 7812 voltage regulator or more than one if you need more current. You could also use a DC-DC converter. The problem is either option would likely cost more time and money than a cheap Radio Shack 12V power supply would.

I did see a 5 amp DC-DC converter at an electronics surplus store a couple weeks ago, I think it was $25 (used), these are often used in labs where you need very clean isolated DC power.

There are also numerous tutorials on the internet on how to convert an old computer power supply into a stand alone power supply (+12v, -12v, +5v)

bgosselin

The OP wants to use this 12v supply to use with a charger, so I'm guessing he is going to want at least 10A.

Yes, a 7812 regulator could work, but is only able to deliver 1A of current. You can add some PNP "pass" transistors to the regulator, and that will add cost and complexity. Not to mention the huge waste in power. At 10A current draw @12v, those transistors will need to dissipate 120w of heat! That's going to require a very large heatsink and fan!

Or, you could go with a DC-DC converter, otherwise known as a switching buck regulator. These are much more efficient, but getting/building one that will go from 24 to 12v and handle <10A is not easy for most. And we are getting back to cost. If this is the route you want to go, probably the easiest solution would be to get a Castle Creations [link=http://www.castlecreations.com/products/ccbec.html]CCBEC Pro[/link]. It will take voltages up to 50v input and output from 4.8v up to 12.5v @ 20A (10A continuous). This device is $45 though.

In the end, the easiest/cheapest thing to do would be to get a spare ATX computer power supply, do a couple simple mods, and use that for your 12v supply. These work well up to ~10-15A depending on their rating. If you need more current, it would be cheaper to get a server power supply (which outputs 12v @ ~20-50A) but will need modding as well. Or, just bite the bullet and get a purpose built supply with the current rating needed.

Andrew

EDIT: bgosselin posted while I was composing this, but we are in complete agreement.

Either of the above suggestions are probably the best approach. One of your primary considerations is the current demands of your charger. If you plan to charge high capacity packs, then your charger may approach its maximum current ratings and the supply will need to have a sufficient power rating to carry the charger. You can always check eBay for available supplies, but pay attention to shipping charges - many of the sellers low ball the starting prices, but make their profits on unreasonable shipping charges.

I like Pyramid supplies, but you will have to pay to get a 14A to 16A supply.

A PC powersupply conversion is relatively inexpensive and simple to do. Some computer repair shops may give you a used supply or sell one for a few dollars and the required components will run less than five dollars. Expected output voltages will run in the range of 11.8v to 12.2v with ratings on the 12v1 and 12v2 rails of 16A to 18A. These are regulated and most do not offer a means to easily push the output voltage much higher. I use these conversions for charging, cutting foam, pack substitutes for RX and servo drivers and for digital prototyping.

While you can build a regulator circuit, the 78xx series regulators are linear, fairly inefficient and have low power ratings. Should you choose this route, the switching regulators have higher efficiency ratings, improve in efficiency as the Vin/Vout differential increases and generally have higher power ratings. Even so, most are rated under 5A - marginal for charging higher capacity packs.

http://web2.murraystate.edu/andy.bat...OWERSUPPLY.HTM

andrew

J-3

Thank you very much for all your comments. I will look at getting another power supply for my 12 volt charger. I was thinking about trying to convert one of the PC power supplies, I try that first. Thanks for your time....Brian

blikseme300

My Feedback: (118)

Brian,

Hang on to the 24v power supply. Those make great power supplies for foam cutting bows.

Bliksem

J-3

Good point Bliksem, I did not have any intentions on getting rid of it. Brian

RC-Bearings

My Feedback: (1)

I know it may be too late for you now, but I have their 24v supply for my foam cutter. I am going to get one of these for my battery chargers:

http://www.ebay.com/itm/12V-15A-Swit...item19c1ec3c38

EloyM

My Feedback: (194)

Take a look at the transformer in your power supply. Many commercial supplies have one with dual primary windings - the one that the 110VAC is
applied to. With both windings connected in series, a certain output voltage will appear at the secondary winding, and thus at the DC output of the
supply. The available current (amps) is determined by the transformers design; Read "size".

If the windings are connected in parallel, the output voltage is halved, and the available current is doubled.
No other changes have to be made to the supply when changing the primary winding connections. Luck!

J-3

Hi EloyM,
When I asked the opening question i was thinking about the Mean Well 1000W, 24v power supply I bought. Considering my 2 year warranty I'll refrain from opening it but it sounds like it might be worth checking into down the road. I have purchased a couple of the HP 575W Watt Power Supply DPS-600PB to provide the 12 volts I need for a couple of my chargers. Thanks...Brian