Large Scale Central

A cheap powerpack

Electronics Power and Sound
#21

Greg Elmassian said:
I’ll bet the 24v output is not 15 amps… test it…

HOW? i got a meter, i did plug it up for 10 A and connected it in series between a piece of track and the pack. i tied a toytrain loco to the track, that it could spin its wheels, but could not run away. depending on the direction, i turned the rheostat, at full speed it showed either 0.76 or -0.76 and now i’m stuck. does that mean 0. 76 from 10 Amps?? (i don’t beleive, that this little motor would be that strong) so i suppose, it means 0.76 Amps. about what i would expect for this loco. but how do i test the avayable Amps, without a variable load to connect to the pack?

Quote:
The picture shown earlier has the -12v at 0.8 amps… with the +12v at 15 amps.

yes. i don’t know enough about electrics, but milkmaiden logics tells me, that the higher the voltage used, the lower the amps. as i mentioned above, maximum that the pack took, without shutting down, was seven Stainzmotors at moderate speed. (about a third of full speed) from what i heard, these motors draw at fullspeed nearly 1 Amp each. so, at my chosen speed, each should draw less than 0.5 Amp. - that would mean, that the pack delivered about 3 to 3.5 Amps at about 8 to 10 Volts. the strongest regulator-powerpack i owned up till now had 1.5 Amps under the hood. (0 - 18 V) that was not enough to have 4 motors on a power section at the same time. so, yes, you are right, there is not 15 Amps avayable at 24 volts. but who cares? i found a way to do, what i intended, without importing some costly powerpacks at high freight cost. as a dedicated packrat i still got more than half a dozen powerpacks from my former PCs stowed away. i just have to find adequate rheostats, to come near to Rooster’s animation. edit: i forgot the pic.

#22

hmmm…
i reread the whole thread.

Greg, when i wrote 24 volts and 15 amps, i just wrote, what the young man told me, who helped me.
i will have him test it again.

#23

You have the ampmeter hooked up right.

If the negative 12 volt supply is rated at max of 0.8 amps and you just measures 0.76, uhh… hello? make sense? That will limit the maximum current at a 24 volt output.

You should be good for 24 volts at .8 amps, or 12 volts over that, since you will have maxed out “one side” of your power supply.

Basically what you did is an electrical no no, and should operate as I mentioned above, but it might act even weirder. So you do not have a 15 amp 24 volt supply, what you have is a 12 volt supply that will run over that voltage at under an amp.

Not trying to give you a hard time, but all the people jumping in on “what a neat idea”, well, it’s not a 24 volt power supply. In addition you could get some weird results under varying loads, where the supply will effectively “switch” from 24 volts output to 12 volts output.

This is something I would not recommend to anyone. Get a second meter, and hook it across the rails, set to DC volts.

Now put a load of 2 or more amps on the track and see what happens to the voltage.

My recommendation would be to just use the 12 volt output alone. There even more funny stuff aboard, where the current limiting of one power section could “trip” prematurely and shut it all off, but PC power supplies work differently, they have output signals, input signals, power good, etc.

Get two power supplies, hook the two 15 amp 12v outputs in series and now you have a 24 volt supply. Still cheap.

Regards, Greg

#24

hmmm…
i would be lying, if i pretended to have understood everything, you wrote.
i’ll take your word for it.

Greg Elmassian said:
My recommendation would be to just use the 12 volt output alone.

Get two power supplies, hook the two 15 amp 12v outputs in series and now you have a 24 volt supply. Still cheap.


let us specify, what i almost understood.

  1. so you recommend, to use +12 and 0 for a 12 V output?

  2. if i hook two packs in series, do i have, besides the double voltage, double Amperage as well? (or do i just have double amperage in an indirect way, because i don’t have to open the throttle so far?)

  3. in series, does that mean: 0 from pack A to the rheostat, +12 from A to 0 from pack B and +12 from pack B to the rheostat?

  4. does it matter, if the two powerpacks are slightly different in Amperage and Wattage?

thanks, korm

#25

adding:
i just tried out my testgroup of seven engines upwards on the 6% grade, using the PC pack, that has no rheostat (last pic, first post).
they went at a satisfying speed, from the +12 and 0 connections. (the pack is rated 15Amps too for +12)

#26

Korm, I think what Greg is trying to tell you is that you have an accident, looking for a place to happen!!! What you tink??? LOL Regal

#27

When you put power supplies in series, the voltage adds, the current stays the same (assuming same current from each)…

two 12v 15 amp supplies in series = 24v 15 amp.

when you put power supplies in parallel (assuming they are compatible), the voltage stays the same the current adds

two 12v 15 amp supplies in parallel = 12v, 30 amps.

When you put 2 supplies in series, and one is 15 amps and the other is 0.8 amps, the most you can expect at 24v is 0.8 amps.

Ohms law and so on are your friends.

My recommendation was to get two supplies, and put the +12v outputs in series and get a true 24v 15 amp supply.

Regards, Greg

#28

i think, now i got it.

thank you.

(Ohms law? the only law i fully understand, and that i rely upon is Murphy’s law)

#29

You may not be able to just tie 2 computer supplies in series to get 24 volts from the 2 12 volt outputs. The supplies may have the DC ground tied to the AC ground, so now one supply will be shorted. Also, if the supplies are mounted on the same metal frame they will short out one supply.

A big no no is to float one supply, but this leaves a possible shock hazard.

So, get a supply made for your trains and keep your house and people/pets in it safe, especially if you know only enough to be dangerous.

#30

Dan,
life is always dangerous, and ends normally with death.
but thanks for the warning about two packs in series.
my pets may be safe anyhow. some tests with the changed packs (now +12 and 0 for 12V, 15 Amp) showed, that i will not need the full 12 volts for the wanted slow speed. (i tested with 10 small locos at the same time)
so now i got two 12 volt packs plus some (weaker) original 1 to 18 volt packs.

#31

Yes, Korm it does as you say, you just don’t want to help it along in any way, shape or form, or speed up the process any faster than should be!! What you tink??? LOL Regal

#32

what i think? - the last one, who escaped death was about two thousand years ago.
the rest of us meets the bony guy with his scyte - no matter what we do or don’t.
so i’m still planting trees and building models, playing and even working a little bit. but i wouldn’t abstain from any bad habits, just for the hope to gain some additional days.

#33

well, apart from my different ideas…
these cheap “powerpacks” have worked (using +12 an 0) for ten years now.
and no pet was electrocuted.

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