OT: 12V DC-DC 2A regulator?

[Seri]

I know this is completely off topic, but over the years I've discovered this news group can provide some of the most unexpected and helpful information so I thought I would chance a strange question here on the off chance...

I'm trying to find/source/build/pull-out-my-xxx a 12v DC-DC 2A regulator, basically I want to use a 12V battery to power something that's supposed to be 12V mains powered so I wanted to introduce a regulator into the equation to stop me ending up with an expensive pile of trash at the end of it.

Does anyone know of a supplier of such things, or even does anyone know where I could find a diagram for such a thing? I know there's only about 3 components involved, but my electronics knowledge is sadly lacking.

Thanks for any replies

Seri

[Mark]

Have you not tried Google there are literally thousands of PSU designs using for instance a L200

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[Andy Dee]

Wouldn't a 3A fuse do?

A

[Seri]

I had tried googling under various terms, I'd also searched Instructables, HackADay and the news groups, but the one thing I didn't look for was PSU, thanks for the link, it has some good info that I'm reading through.

[Seri]

Unfortunately not for my needs, I actually need to provide as smooth as possible 12V feed. I'm trying to power a 10" HD LCD screen for use as field monitor for my video work.

Seri

[Mark]

ok here a few more which may help

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[Bob Mannix]

You can't get anything smoother than a battery. Adding a converter would make it less smooth (if anything).

[Pete C]

Try a google 'amperor voltage stabiliser'

cheers, Pete.

[Seri]

My worry was about under supplying the current when the battery might reach the 40% charge and below mark. I would hate to damage the LCD or controller board by supplying something that was too far below the operating voltage. So I guess the use of the word "smooth" was inaccurate, I should have said stable.

Seri

[Bob Mannix]

The current (and voltage) still has to come out of the battery at the end of the day. Any regulator will assume the battery is OK, once it isn't all bets are off and so will the regulator output be!

[Seri]

I guess I'm showing the truth of my initial comment that "my electronics knowledge is sadly lacking".

I think this all being the case, that I should just go with my initial view of running two 12V 6A batteries in parallel and keep the output unregulated which scares me a little but am sure it should be fine... (a deliberately open ended statement in the hopes that someone will tell me I'm worrying over nothing and that yes everything will in fact be fine, fine, fine).

[Adrian]

It'll be fine....fine....

Seriously - why not have a couple of 12v 6A batteries (Sealed Lead-Acid ones, for choice) - but, rather than run them in parallel, which might cause problems, have them switchable so that you either get battery 1 or battery 2. Stick a little volt-meter with a 'push-to-test' switch in the same box and you can decide when it's time to switch from one battery to the other....

If you're nervous, why not beg, steal or borrow a variable power supply, and wind the volts back down from the nominal 12v and see at what point the monitor has problems. The manufacturer may give specs for the operating voltage - which may give you some reassurance....

I'd imagine that the likely 'failure mode' will be 'below a certain voltage = picture all gone' - rather than anything more serious and long-term happening to the electronics....

As others have said - a 'keep the volts up whatever happens to the battery' device will only work as long as there is sufficient voltage / capacity in the battery - beyond that point it'll give up in the same way as a flat battery does....

Hope this helps Adrian

[Mike Dodd]

Exercise care connecting high-capacity batteries in parallel - for one thing, a failing cell in one can cause the other to discharge through it. If you do need to connect two in parallel, fuse each battery separately to the load

e.g. (monospaced font)

Fuse1 Bat1 + -------------O\O-----------+--- Load + | Bat2 + -------------O\O-----------+ Fuse2

Bat1 - ---------------------------+ | Bat2 - ---------------------------+---- Load -

...and yes, I'd agree with all advice given to date - forget the regulator, stick with the batteries.

Mike

[Harry Bloomfield]

The simple series regulator circuit, needs a voltage difference between input and output of around a minimum of 3v to be able to work. With such a small voltage difirence a parallel regulator might be one way, or even a small DC to DC switch mode power supply. Maplin used to offer a switch mode IC capable of delivering 3amp and also offered a ready built switch mode rated 5amp with selectable voltage output intended for running laptops.

[JohnW]

You -may- be correct to worry :-)

Don't forget that a 12v battery is actually some 12.8v when fully charged, and down to 11.6v discharged, (12.2v for 50%, which you shouldn't go below, if you want a reasonable battery life). Check your device being powered can accept this range. Some are designed to run using a switched-mode, mains PSU so are designed for a regulated 12.0v input.

If you are going to run the load when trickle-charging, then the input volts will be over 13v, or even some 14.5v. if charged by an intelligent charger.

I'd look for a car-type power supply that can give a clean 12v out for a battery input, preferably switched-mode, to save wasting power.

[Seri]

now with hind-sight, and taking into account that for field based filming, it's highly unlikely that there will ever be a need to keep the screen powered on continuously over the space of hours, I think I'm going to rig a single 12v 6Ah battery at a time for roughly 3 hours continuous filming and that way I only have to lug one battery at a time from the car or wherever the location is.

I have to say a big thank you to the newsgroup, as ever once the problem was reduced down to the basics it ceased to be a problem. Now I just need to construct an enclosure for this screen and get shooting.

Thanks all

Seri

[Peter Parry]

Those are good broadband jammers!

[Dave Plowman (News)]

A basic 12 volt regulator won't work from a 12 volt battery - you need several volts higher from the supply. You could make a SMPS that delivered

12 volts from a wide voltage range - but that's a much more complicated beast.

[The Natural Philosopher]

guys are actually GOOD and responsive to e-mails.

That partcular prodiuct is not on the market yet tho.

[mick]

I would suggest that the OP look for a DC/DC converter. You can get them from suppliers such as RS or Farnell. Typically input volts would be 9 to

18V with a solid 12v output.

Typical (but probably a bit bigger than you need):

's more than 3 components if you do it right... :-) Note that you will probably also need screening of some kind for it.