# 12V Bench testing battery or transformer



## mullum (Sep 16, 2011)

I need a way to test LED bulbs without constantly fitting them in the car. Ideally something mains connected with a transformer but possibly a battery (perhaps one of those big ones you put in large spotlight torches).
Can anyone suggest anything I could use for this ?


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## spaceplace (Mar 10, 2013)

the obvious would be a car battery but a bit of an effort to charge' you used to be able to get those plugs (house plug) which had all different adaptors on it and had dials on the top where you could change voltage and switch between ac and dc, they were only about 10 quid

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## Hoggy (May 8, 2002)

Hi, Get one of these with 8 AA batteries, that will give you 12 volts to test LEDs.
http://www.maplin.co.uk/p/8-aa-battery-box-rk44x
Hoggy.


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## spaceplace (Mar 10, 2013)

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## SVStu (Dec 11, 2006)

If you have an old desktop pc then you can use the power source as cheapo bench supply. Check ebay for cheap old PC's (about £10) local to you but try to get one with a switch, they tend to be older computers, and saves wiring in a load resistor thingy.

Stu.

http://www.wikihow.com/Convert-a-Computer-ATX-Power-Supply-to-a-Lab-Power-Supply.


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## mstew (Mar 17, 2012)

As spaceplace says, just search for any '12v dc supply' get any old one that plugs in the wall, chop the end off, strip the wiresback and solder on some crocodile clips and use some shrink wrap to tidy it up of course. Also please do all that when it isn't plugged in :roll:


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## Hoggy (May 8, 2002)

Hi Mullum, a Mains powered 12 v source will have to have a very pure DC output for LEDs to work correctly.
Hoggy.


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## mstew (Mar 17, 2012)

Also get one with decent amperage to cover the range of watts your bulbs put out. P = IV, watts = voltage * amps

Don't worry about getting one too large as only current needed is drawn, voltage is the key thing to keep consistent here


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## brittan (May 18, 2007)

A 12v sealed lead acid battery (the sort you find in your house alarm etc), supported by a cheap trickle charger would work and supply a steady voltage.


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## Hoggy (May 8, 2002)

Hi Mullum, If you already have a suitable charger, then one of these. 
Depends how many LEDs you have to test & whether worth the extra expense.
http://www.ebay.co.uk/itm/Fiamm-NP1-2-1 ... 417eb879d3
Hoggy.


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## brian1978 (Jul 10, 2013)

Charged 12v drill battery?


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## davelincs (Jan 1, 2010)

Do you have a battery charger? If so use that


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## mullum (Sep 16, 2011)

Thanks for all the suggestions - pretty much all of which I hadn't considered. A 12v drill battery is a good one ;-) I was about to chuck out a couple that were for some garden tools I don't use any more. They are the old type though (Nicd) and they dont hold their charge well any more.

I do have a battery charger - a ctek - but I'd have to buy another cable for it as the other is permanently attached to the cars battery.
The old PC power supply idea is interesting - but I binned my old pcs ages ago and if I'm going to spend money then I'd rather buy something that wouldn't need modding.

My favourites so far are the battery Hoggy linked to - which I can recharge with my ctek, and the rechargeable power tool batteries which have their own chargers. Although it may be a bit of a faff getting some wires onto the contacts without preventing the batteries from fitting back in their chargers.


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## John-H (Jul 13, 2005)

Neighbour's car :wink:

I seem to remember a brake light is 21W so 21/12 = about two amps. You'll easily do this with a lead acid battery of any reasonable size like a big torch or house alarm - for a short while. 5AH = around two hours at 2A but then it's flat. Your C-~Tech I think may struggle but I'm not sure what the output current is - it may be only 1 Amp or so as a trickle charger and it may sense the lack of voltage it's connected to and go into some funny battery recovery mode and flash your light on and off. Put a 12V lead acid in the circuit too and it will keep it charged of course and the 12V will be stable. A PC power supply is a good idea as a bench supply with lots of oomph.


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## mullum (Sep 16, 2011)

What are those 12v big torch batteries called ? (As in "AA" or "AAA" etc). Only thing is they're not rechargeable, of course.


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## brittan (May 18, 2007)

mullum said:


> What are those 12v big torch batteries called ? (As in "AA" or "AAA" etc). Only thing is they're not rechargeable, of course.


Square ones with 'spring' terminals? 6v lantern battery.

What is the range of operating voltage for the LED bulbs?
A simple 9v battery could be sufficient if simply proving that they work is the object of your test.


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## mullum (Sep 16, 2011)

Yes it's basically just testing they work and how bright they are. Not sure if the voltage range though.
How about one of these ?
http://bit.ly/RoolzG


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## Hoggy (May 8, 2002)

Hi Mullum, The 12v torches that I've seen use the lead acid I've already linked to. 
The batteries I believe you are thinking of with springs on top are 6 volt. 2 of those in series would do the job.
These are 12 volt but expensive & would require a Ni-MH charger.
http://www.ebay.co.uk/itm/1-x-Rechargea ... 4d0ce6f780
Hoggy.


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## Hoggy (May 8, 2002)

mullum said:


> Yes it's basically just testing they work and how bright they are. Not sure if the voltage range though.
> How about one of these ?
> http://bit.ly/RoolzG


Hi, Mullum, that is just a charger & wouldn't give the pure constant volt/current you would require.
Just keep it simple.
Hoggy.


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## Spandex (Feb 20, 2009)

I used to use a Maplin bench PSU for testing car stuff. Looks something like this (can't get on the Maplin site to give a link at the moment for some reason):









Don't use it anymore but it's a bit heavy to ship...


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## spaceplace (Mar 10, 2013)

Or these? The potatoes are cheap as chips 
















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## mullum (Sep 16, 2011)

Spandex said:


> I used to use a Maplin bench PSU for testing car stuff. Looks something like this (can't get on the Maplin site to give a link at the moment for some reason):
> 
> 
> 
> ...


£7-10 tops with myhermes ;-)



spaceplace said:


> Or these? The potatoes are cheap as chips


:lol:


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## Spandex (Feb 20, 2009)

mullum said:


> £7-10 tops with myhermes ;-)


Don't really fancy packing it and waiting in for a courier (especially not my local myHermes chimp, who's incapable of turning up on the right day, let alone at the right time). If you're ever in London, you're welcome to it though.


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## mullum (Sep 16, 2011)

Ok cheers 

I use their parcel shops to drop stuff off instead of waiting in for them. UPS do a really cheap shop to shop service too (via parcel2go) but both parties need to be up for going to one of their drop off shops. Luckily I'm near one, they're good for heavier insured items for example.


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## Spandex (Feb 20, 2009)

Just to add to the discussion about what you could potentially use, remember that with the engine running you're looking at a 13.8v supply, not 12v. If you're just looking to confirm an LED works then it's not really an issue, but if you want to test actual output then you should bear it in mind.


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## mullum (Sep 16, 2011)

Good to know. I was only thinking to check that they're not defective from the factory and to gauge their brightness - but that's a good point.


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