AC to DC converter  - Page 1
Forum section: electronics / projects

author: richcj10
author_rank: Unknown
timestamp: October 02, 2012, 11:22:14 pm
content: I need 24v 24A power supply.I was looking at this toroid:http://www.digikey.com/scripts/DKSearch/dksus.dll?Detail&itemSeq=120392450&uq=634847987122539538and this rectifier:http://www.digikey.com/product-detail/en/GBPC3510-E4%2F51/GBPC3510-E4%2F51GI-ND/754838and a cap to do some filtering.Is there a cheaper better way?Thanks,Rick

author: FenderBender
author_rank: Super Contributor
timestamp: October 03, 2012, 12:00:38 am
content: Well the link to your transformer is bad.That is probably the simplest way to do it..However, using a PWM controller like a TL494 would allow you to use a much smaller high frequency transformer, perhaps lowering your cost. I don't know how much a 24A/24V toroid is, but I'd have to expect $50-75. I think you could get away with a much more compact design and cheaper if you learned how to put together a PWM based supply.

author: Psi
author_rank: Super Contributor
timestamp: October 03, 2012, 12:24:06 am
content: yeah, good old TL494Assuming you want mains input you could probably source the high frequency transformers from a junked modern ATX psu.Modern ones have dual 12V rails, so repurposing the transformer with the windings in series for 24V should be possible.I don't really recommend using the ATX psu, or modding it, but rather recycling some of its parts.Transformers, fets, mains input section etc. and building a new powersupply.(A midrange ATX supply isn't really designed for 24A at 12V continuously and the noise maybe too much depending on your intended application)But in terms of effort/time yeah, as you have posted, a 50hz transformer + bridge rectifier for 24V unregulated DC would be much easier to build.

author: mariush
author_rank: Super Contributor
timestamp: October 03, 2012, 02:42:42 am
content: It would be a bit cheaper (and also safer) to buy an industrial power supply that outputs 24v by default:http://www.meanwelldirect.co.uk/product/648W-24V-27A-and-5Vsb-Enclosed-Switching-Power-Supply-with-PFC-Function/HRPG-600-24/default.htmI see it at various stores at around $155-175 :http://www.powergatellc.com/mean-well-hrpg-600-24-power-supply.htmlhttp://www.jameco.com/webapp/wcs/stores/servlet/Product_10001_10001_2101930_-1http://www.trcelectronics.com/Meanwell/hrpg-600-24.shtmlIt's probably cheaper on eBay or from some Chinese store.With a linear power supply...You'd need a toroidal that outputs 26-27 VAC - you have to keep in mind that at any moment two diodes in the bridge rectifier are conducting, so there's gonna be a voltage drop.According to that bridge rectifier's datasheet, it has a maximum 1.1v voltage drop per diode, so your transformer needs to be 24v + 2.2v at least.With a big toroidal you'd also need a few beefy capacitors to filter the output and keep it as close as possible to 24v at so many amps. Probably 40000-60000 uF would be the smallest value that would sustain 24 A load.A 33000uF / 50v capacitor is about 14$ but I'm not sure this is good enough:http://www.digikey.com/product-detail/en/ECE-T1HP333FA/P10022-ND/258688Even with some capacitance, the voltage will fluctuate at that high load between about 22.5-23v and 24v, so you might actually want to get a toroidal that's even bigger than 24v + 2.2v, maybe 28v. If the output voltage is too high, you can always add a high power diode or a couple in series to lower the voltage.Here's an online circuit showing the voltage on a 1 ohm load with a bridge rectifier having that maximum 1.1v voltage drop on the diodes:http://www.falstad.com/circuit/#%24+1+5.0E-6+12.562902691361415+50+5.0+48%0Av+144+368+144+80+0+1+50.0+24.0+0.0+0.0+0.5%0Aw+144+80+272+80+0%0Aw+272+80+272+144+0%0Ad+272+144+336+208+1+1.1%0Ad+272+272+336+208+1+1.1%0Ad+208+208+272+144+1+1.1%0Ad+208+208+272+272+1+1.1%0Aw+272+272+272+368+0%0Aw+272+368+144+368+0%0Aw+208+208+208+304+0%0Aw+336+208+384+208+0%0Aw+208+304+384+304+0%0Ac+384+208+384+304+0+0.06+20.962546594475015%0Aw+384+208+464+208+0%0Aw+384+304+464+304+0%0Ar+464+208+464+304+0+1.0%0Ax+499+264+529+268+0+16+load%0Ao+0+32+0+34+40.0+204.8+0+-1%0Ao+15+32+0+35+40.0+25.6+1+-1%0ASame url in case the above link gets broken (it's very long) :http://preview.tinyurl.com/9qppq4zIt needs Java to run. Once it runs, move the mouse over the graphs below and you'll get more information.. slow down the circuit from the right side if it's hard to follow it.You can see even with 60000 uF, the voltage on the load will vary a bit.

author: Paul Moir
author_rank: Frequent Contributor
timestamp: October 03, 2012, 03:30:45 am
content: I know someone who was using a pair of ATX power supplies in series to run some big peltier devices for some experiments. Seemed to work just fine.A lot of the answer will be in what you need the power supply for. If you're running a big inductive load like a motor then a SMPS might not be the best idea because it may trip out on you. Something industrialish or something you're going to sell, get an industrial power supply. Hacking around, a couple ATXs might do. Or even a pair of 12v batteries.

author: richcj10
author_rank: Unknown
timestamp: October 03, 2012, 03:47:05 am
content: I am building a passive "POE" injector panel for a client. He wants ten.I was going to use this:http://www.digikey.com/scripts/DKSearch/dksus.dll?Detail&itemSeq=120283393&uq=634848141235183268But he wanted to lose some of the cost.This will be injected with the cat5 cable to a light duty computer. The computer has its own filtering.The computer is not a true PoE device. (as it doesn't work at 48v)

author: mariush
author_rank: Super Contributor
timestamp: October 03, 2012, 04:26:09 am
content: Those kind of links you paste aren't working. You need to go on the product page and then copy the URL above... or just tell us the name of the toroid or whatever you use.I'm not sure how much current you can push through Cat5/Cat5e cable - on a brief search on the web I see numbers like 48vdc , max 30 watts. At 24v, I guess you can probably do up to 2-3 Amps safely.If that's the case, it might be cheaper to simply get an ATX power supply and use an independent boost dc-dc converter for each cable.A good 600w ATX power supply is about 60$, that will give you up to about 500-550 watts or 40-45 amps on 12v ... dc-dc converters for 12v to 24v @ 2-3A are about 0.3-2$ each depending on how efficient you want them to be... with all the associated components you're looking at about 3-5$ per dc-dc converter... so you'd probably be able to pull it for just under 100$.For example, this should easily do 24 v @ 1A and more with 12v input, the datasheet even has a 12v to 28v @ 0.6A inside, you just have to adjust the auxiliary component values:http://www.digikey.com/product-detail/en/MC34163PG/MC34163PGOS-ND/919090

author: richcj10
author_rank: Unknown
timestamp: October 03, 2012, 05:13:24 am
content: QuoteThat is what the URL is. From the responses above it shows people have been able to use the link.I need it to fit in a one unit rack.I like the step up idea.

author: Psi
author_rank: Super Contributor
timestamp: October 03, 2012, 07:02:16 am
content: It's only an issue when you try and copy/paste digikey search result items. As they're unique for you and don't exist except for your search session.If you want to copy/paste a product click on it from the search results and then copy/paste the product page URL instead. You can tell its a product page by the fact the digikey part number is in the url instead of your random session number.

author: fastfourier
author_rank: Newbie
timestamp: October 03, 2012, 03:27:03 pm
content: How about a couple of these? Seems like it would fit in 1Uhttp://www.ebay.ca/itm/24V-14-6A-350W-AC-DC-Universal-Regulated-Switching-Power-Supply-Brand-New-/350586831279?pt=LH_DefaultDomain_0&hash=item51a09a81af#ht_5746wt_964Whoops, no it won't. This one will thoughhttp://www.ebay.ca/itm/24V-10A-DC-Universal-Regulated-Switching-Power-Supply-/390089267739?pt=LH_DefaultDomain_0&hash=item5ad321da1b