power supply help - Page 1
Forum section: electronics / general

author: Dr.Morgus
author_rank: Newbie
timestamp: April 08, 2013, 12:07:15 am
content: Hi allcan't seem to get it to work I need 7.4 volt with about 2.5 amp load i am a newbiethanks Dr.Morgus

author: Deckert
author_rank: Regular Contributor
timestamp: April 08, 2013, 12:40:29 am
content: Hi,Quote from: Dr.Morgus on April 08, 2013, 12:07:15 amWhat did you try?Also, what are your other constraints (enclosure size, heat restrictions, etc)?--deckert

author: Dr.Morgus
author_rank: Newbie
timestamp: April 08, 2013, 02:24:00 am
content: could you suggest the right size i am using a 6"x4"x2" plastic box how much heat will there be

author: c4757p
author_rank: Super Contributor
timestamp: April 08, 2013, 02:33:09 am
content: Huh? That depends entirely on the power supply design. The less heat you can accept, the trickier it will be to design. Personally, I'd probably go for a transformer putting out ~12V followed by a buck converter, but I think that's a bit out of your league right now. Just a transformer followed by a rectifier would be the easiest, but you're not going to find a transformer that puts out 7.4V, and I promise you can't afford to have one custom-wound. Can you please give a bit more of a description of your requirements? What's the input? (Mains, I assume? But it could be an automotive 12V supply as well) How well does the output need to be regulated?What youcanafford is to separate your posts into sentences so we can read them. Seriously, the forum doesn't charge per punctuation mark.

author: Dr.Morgus
author_rank: Newbie
timestamp: April 08, 2013, 03:39:06 am
content: My transformer is a center tap type.It is 12.6 fromouter wires to center tap wire and 25.2 betweenthe two outer wires.The transformer is rated at 2 amps.I'm trying to replace a battery because it drains it to fast.the motor is rated at 7.4 volts 2.5 amps. Proberly couldrun it between 1.5 to 2.0 amps. Sorry for the punctuationhope this is a little better.

author: c4757p
author_rank: Super Contributor
timestamp: April 08, 2013, 04:22:19 am
content: Ah. If you want to go from 15-17V (12V rectified) down to 7.4 with that much current, you're going to want a buck converter. I think designing one yourself is a bit much now, butthisseems suitable.Is the transformer truly center-tapped, or is it one of the ones with two separate secondary windings? If it has two secondaries, put them in parallel, run through a bridge rectifier rated for this much current, filter with a few thousand uF of capacitance, then into something like that converter module. If it's just center-tapped, do the same with the full (25.2 VAC) output voltage. Keep in mind that 25.2 VAC rectifies to 36 VDC, so pay attention to capacitor voltage ratings, and you probably shouldn't go touching it.

author: mariush
author_rank: Super Contributor
timestamp: April 08, 2013, 05:00:06 am
content: Have a look at this guide and pick whatever's most convenient to you. Make sure to pick properly sized diodes (or bridge rectifier) as the instructions and the estimated current your choice results to.

author: orbiter
author_rank: Frequent Contributor
timestamp: April 09, 2013, 11:24:52 am
content: Where is that page from please mariush?

author: mariush
author_rank: Super Contributor
timestamp: April 09, 2013, 11:48:12 am
content: It's from Hammond Manufacturing's catalog. The complete pdf in on their site:http://www.hammondmfg.com/pdf/5C08.pdf(page 11 is the one I posted)Quite a nice document, besides the listings for their transformers there's plenty of chunks of good info and tips.

author: orbiter
author_rank: Frequent Contributor
timestamp: April 09, 2013, 12:25:03 pm
content: Thanks buddy