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Inducktion

Sun Jan 23 2011, 08:26PM

Registered Member #3637 Joined: Fri Jan 21 2011, 11:07PM
Location: Buffalo, NY
Posts: 1068

What is the best way to get power to your projects that you build?
Simple Microwave Oven transformer?
A Switch Mode Power Supply?
Lead Acid or Lithium Batteries?

I need to figure out which one is the best in terms of overall price and performance...I'd like a balance between the two. The microwave oven, however, i can't do because 1. I can't seem to find one to take apart, and 2. It's heavy as hell.

Comments...Opinions...Whatever. :D

Sulaiman

Sun Jan 23 2011, 09:00PM

Registered Member #162 Joined: Mon Feb 13 2006, 10:25AM
Location: United Kingdom
Posts: 3140

I suggest 12 Vdc as your 'standard' voltage,
you can get Lead-Acid batteries in various capacities and prices,
(or LiPo, NiMH,... packs >= to 12V)
12V systems can work on vehicle electrics easily,
a mains-to-12 Vdc power supply is common and cheap,
or easy to make, same for battery chargers.
Try to design for 12 V +/- 2 V to allow for low-battery voltage (10V)
and battery-on-charge (c14V).

3.3V, 5.0V, 12V and 15V are the most common circuit voltages used for analogue/digital circuits.

It appears that Laptop PCs are standardizing on 18/19 Vdc

Industrial equipment commonly uses 24 Vdc

Telephone systems use 50 Vdc nominal

Mycologist

Sun Jan 23 2011, 09:13PM

Registered Member #2413 Joined: Sat Oct 03 2009, 08:27PM
Location: Essex, UK
Posts: 22

I think Sulaiman pretty much summed it up, but in my opinion (as the thread title says ^^), it really is a case of particular solutions for particular problems.
If you've got a high power level with no real regulation, an MOT is usually fine, but if you want precise regulation and variability, some sort of inverter would serve you better.
If you want something low power, use a wall wart transformer or something like that, then stick a regulator on the output; useful for inverter drivers.
I only ever use batteries on something that needs to be portable, because in value for money terms, compared to a transformer or smps, they're fairly awful.

Adam Munich

Sun Jan 23 2011, 09:52PM

Registered Member #2893 Joined: Tue Jun 01 2010, 09:25PM
Location: Cali-forn. i. a.
Posts: 2242

I know inducktion irl, he plans on using this for zvs's, induction heaters, etc.

Personally I prefer my 100Ah 12V AGM batteries. They are nearly impossible to kill and they can provide huge currents. $200 a piece may be out of your price range though. (I got them for free

)

If weight is a concern then I'd go with lipos, a 5000mAh 20C lipo can provide 100 amps, though not for very long.

A rewound MOT is by far the cheapest plug in the wall option, but keep in mind you'll need to get a high current bridge rectifier and a big smoothing cap, as well as some c-clamps to hold down the core you dremeled open.

Junkyards often have big transformers in their "assorted copper" bin. They hate transformers so they'll let them go cheaply. If you can find an old DC welder then you have both your big x-former and your bridge rectifier.

Mattski

Mon Jan 24 2011, 04:01AM

Registered Member #1792 Joined: Fri Oct 31 2008, 08:12PM
Location: University of California
Posts: 527

You can often pick up ATX supplies for free out of computers that are headed to recycling, most of my home prototyping projects will be powered by one of these. Note that you will often want to load down the rails a certain minimum amount, I use something like a 10watt 10ohm on the +5V rail, and 10watt 50ohm on +12V. If you ever see a wall wart being thrown out or recycled pick it up too, unless you already have a good collection. Printer power and laptop wall warts usually good (higher current, good regulation).

Pretty much all of my home projects are powered either by ATX, 9V battery, or random wall warts.

Steve Conner

Mon Jan 24 2011, 09:57AM

Registered Member #30 Joined: Fri Feb 03 2006, 10:52AM
Location: Glasgow, Scotland
Posts: 6706

There is no single best way that suits all projects. Some of them run off batteries, others plug straight into the wall, etc.

If you want lots of low-voltage DC power, a couple of sealed lead-acid batteries, or even car batteries, is a reasonable option. The only problem is that they have no current limiting and will happily melt your wires and ruin your circuit.

Sometimes you can find old batteries for free that are a bit worn out. Positive grid corrosion makes the internal resistance of SLAs increase with age. After a few years they won't supply enough current for golf carts and UPSs any more, which is why you get them for free, but they might power your circuit just fine.

Lipo batteries are too expensive and electrically fragile. You need to buy an expensive charger to treat them right and get a long service life. I wouldn't use them unless you were building a RC model that needs the high energy density.

ATX power supplies are quite good, there is a lot of information on the forum about how to use them for your projects. If you want more power, you can often find large 12, 24 or 48V SMPS cheaply in surplus stores, on Ebay and the like. Just watch out for the really big ones that need a 208V 3 phase supply to run.

Eventually the urge for "moar power" will lead you to circuits that run directly off rectified wall voltage. They are more efficient than 12 or 24V ones, because the high voltage allows efficient switching with 600V IGBTs, so you can get the most sparks/plasma/whatever per dollar.

Dr. Slack

Mon Jan 24 2011, 01:46PM

Registered Member #72 Joined: Thu Feb 09 2006, 08:29AM
Location: UK St. Albans
Posts: 1659

There is no "one size fits all", so how about you split your projects into "low power" and "high power" varieties.

For low power, I'd say Sauliaman +1. The co-incidence of ATX PSUs and vehicle electrics with commonly available gel-cells makes 12v a very attractive common voltage. There are a lot of one-chip SMPS which run quite efficiently off 12v to give you other rails, and it's low enough that a linear regulator for logic rails or a resistor for LEDs is often OK.

For medium power, big car batteries will get you there, when you are away from your ATX supply.

For high power, you plug into the wall and do what you have to do each time.

Inducktion

Thu Jan 27 2011, 12:49AM

Registered Member #3637 Joined: Fri Jan 21 2011, 11:07PM
Location: Buffalo, NY
Posts: 1068

Well, I'm not really going to be moving around anything i build too much, and if i do move it it'll be somewhere with a power source. So batteries or something to that effect sound like the best thing I Guess.

Dr. ISOTOP

Thu Jan 27 2011, 04:49AM

Registered Member #2919 Joined: Fri Jun 11 2010, 06:30PM
Location: Cambridge, MA
Posts: 652

For anything using reasonable power, I use an ATX supply.
For big power, I use a good ol' variac + step-down transformer + rectifier + filter setup.

big5824

Thu Jan 27 2011, 02:41PM

Registered Member #1687 Joined: Tue Sept 09 2008, 08:47PM
Location: UK, Darlington
Posts: 240

atx psu's are awesome, my small one can provide 12v at 15A, bigger 600W+ ones can often source 30A

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