# 24vdc 2a ======> 12vdc 2a

Discussion in 'FAQs' started by Sempak, Jun 19, 2002.

1. ### SempakMember

I have found a 24VDC 2A powerpack on eBay for AU\$10. Do any of you guys have a suggestion to get it down to a useable volatge (eg. 12V)? A resistor matrix? What resistors? A 2:1 transformer? where in Aus can I get one?

--Chris (Sempak)
2. ### VicActive Member

Stepping Down

Hi Chris, I don't know what might be available in AU but a 24V train power pack is rather unusual.

Yes you could use a rather large resistor to lower the voltage but the heat that's going to be generated will be substanial.

Your best bets for something like that is going to be: 1. Use a variable resistor (rehostat) on the output side (DC) and detent it so that it does not exceed 12 volts or 2. Use a variac (an adjustable AC transformer) on the line side to lower the line voltage to the point that the power pack does not put out more than 12 Volts DC.

Both of these solutions may be a bit "pricey" so you may want to take that into consideration.

By the way...resistance values are computed using a formula called Ohm's Law. I won't go into the details here but look it up...its only simple math and takes about 10 minutes to learn it and you'll never have to worry about what values you need again.

Hope this helped you out

3. ### sumpter250multiscale modelbuilder

Chris,
If there's an electronics parts place nearby, you might see if there is an inexpensive voltage regulator you could use to set the output voltage/current. This could be as simple as one IC chip, or a circuit with a power transistor as the regulator.
BTW, Welcome to the gauge, you found the right place for answers.
Pete
4. ### 60103Pooh Bah

Chris:
You might try a travel supply or electric supply to see if they have a 240:120V transformer (not a plug adapter).

Only problem is you're really spending money for your \$10 bargain.
5. ### billkActive Member

How about coming up with a zippy description and selling it on EBay for \$20??
6. ### SempakMember

Vic- It isn't a train transformer but just a noraml plug pack, it has no control options or anything other than inputs and outputs. You're right about the resistors generating a lot of heat 48w at my count. the only way can see to get this working is with a huge series matrix ! I know how to calculate Ohms law but I wanted a seccond opinion to make sure I was accurate and on the right track!

Sumpter250- I have looked at these regualtors and will be asking at my local electronics shop but most of the cheap (to make my buy worthwhile) ones only go up to 1A current flow.

60103- Again, that probably costs more than the transformer and defeats the bargain!

Billk- Lol, I once bought a Commodore 128 for \$15 at a school fete and sold it for \$152.50 on eBay. That following weekend was an enjoyable trip to the train shop!

Thanks,
--Chris (Sempak)