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how to get 24vdc@5a?

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phinsil6

Tue Jan 13 2009, 09:32PM

Registered Member #1914 Joined: Wed Jan 07 2009, 06:50PM
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Posts: 17

Im tryin to build a 450vdc output boost converter, however, I need 24VDC@5A to build this converter. Any quick and easy ways to get this kind of power? Thanks in advance

ConKbot of Doom

Tue Jan 13 2009, 09:41PM

Registered Member #509 Joined: Sat Feb 10 2007, 07:02AM
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Posts: 329

Quick and easy? 2 12v lead acid batteries in series.

You could modify 2 computer power supplies, one with the ground lifted and put the 12v lines in series, as long as you load the 5V line with something as well. But that isn't as quick nor easy as 2 12v lead acid batteries.

phinsil6

Tue Jan 13 2009, 09:46PM

Registered Member #1914 Joined: Wed Jan 07 2009, 06:50PM
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Posts: 17

what kind of batteries to be specific? would that really give out 5A?

uzzors2k

Tue Jan 13 2009, 10:06PM

Registered Member #95 Joined: Thu Feb 09 2006, 04:57PM
Location: Norway
Posts: 1308

I don't think you have a proper understanding of electronics. A common newb misconception is that a circuit needs a set voltage, and a set current. This is not the case. A circuit can operate within a defined voltage range, and within that range it will draw a certain amount of current. When power supplies have a current rating it means the maximum you can draw before the voltage drops below some value, or the supply self-destructs. When a circuit has a current rating beside the input voltage this simply specifies the maximum current the circuit will draw, so you know what kind of power supply is needed. So for the 24V, 5A boost converter you need a voltage source that can supply at least (or more than!) 5A at 24V. Two car batteries in series can supply 24V at incredible amperage, so they will work perfectly.

I suggest you look up Ohm's law to get a more thorough understanding of how this works.

Dr. Dark Current

Tue Jan 13 2009, 10:08PM

Registered Member #152 Joined: Sun Feb 12 2006, 03:36PM
Location: Czech Rep.
Posts: 3384

If you want to charge capacitors and can use 230V mains, I have a better alternative for you:
You need just 2 diodes and 1 capacitor to make a self-limiting voltage doubler.

the second cap is your capacitor bank or whatever youre powering.

Edit: the first capacitor must not be polarized and you use it to set your charging current (C=1/(2*pi*f*U) )

If you're on 120V, a tripler should be sufficient.

But if you're a beginner, I would not suggest to work with mains voltage...

Proud Mary

Wed Jan 14 2009, 12:02AM

Registered Member #543 Joined: Tue Feb 20 2007, 04:26PM
Location: UK
Posts: 4992

Toroidal lighting transformers are a cheap way of producing 24V at a decent current.

You will commonly find units that have 4 x 12V windings which you can connect in series or parallel according to need. A 300VA transformer of this kind can often be found new on ebay for fifteen euros or so, and you get a good metal case thrown in!

So with a bridge rectifier and a fat electrolytic you can make a solid 8A 24V DC supply for not very much money at all - and certainly much less than the cost of two lead-acid car batteries.

Dr. Dark Current

Wed Jan 14 2009, 11:25AM

Registered Member #152 Joined: Sun Feb 12 2006, 03:36PM
Location: Czech Rep.
Posts: 3384

Harry wrote ...

Toroidal lighting transformers are a cheap way of producing 24V at a decent current.

You will commonly find units that have 4 x 12V windings which you can connect in series or parallel according to need. A 300VA transformer of this kind can often be found new on ebay for fifteen euros or so, and you get a good metal case thrown in!

Well I think they are 12VAC in which case there's no way to get 24VDC out of them.

Proud Mary

Wed Jan 14 2009, 11:52AM

Registered Member #543 Joined: Tue Feb 20 2007, 04:26PM
Location: UK
Posts: 4992

Dr. Kilovolt wrote ...

Well I think they are 12VAC in which case there's no way to get 24VDC out of them.

I have bought on ebay only recently three such which have 4 x 12V windings on a single toroid as I have described, or I should not have suggested it!

Connecting two windings in parallel, and connecting these with the other paralleled pair creates 24V at a good current. In practice, with a solid bridge rectifier, and a single 100,000uF capacitor, I have found this transformer will provide 31.5V at 8A of stiff DC all day long without any significant heating.

Unfortunately, this older type of lighting transformer, in a large metal case, is now being replaced by much smaller electronic supplies, which you were thinking of perhaps.

GeordieBoy

Wed Jan 14 2009, 04:59PM

Registered Member #1232 Joined: Wed Jan 16 2008, 10:53PM
Location: Doon tha Toon!
Posts: 881

> Im tryin to build a 450vdc output boost converter, however, I need 24VDC@5A to build this converter.

Rather than build/buy/hack a PSU to convert mains voltage to 24VDC, then build a boost converter to convert from 24VDC back up to 450VDC, it would be much easier to do this:

Design/build a boost converter to give you 450VDC from whatever mains supply flavour is available in your region. The resulting single stage converter will be simpler, more efficient, cheaper and more compact. Do a google search for "Active PFC pre-regulator". These normally generate something between 380VDC and 400VDC but you may be able to mod an existing design to give 450VDC with some component changes.

-Richie,

Proud Mary

Wed Jan 14 2009, 05:30PM

Registered Member #543 Joined: Tue Feb 20 2007, 04:26PM
Location: UK
Posts: 4992

Yes, I would look first to the power requirements of the application for which the 450V is required, and then decide on the most reliable and economic means of providing it.

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