Re: 12 volt power source?

On Fri, 21 Dec 2007 10:54:18 +1300, I said, "Pick a card, any card"
and Greg Procter <procter@xxxxxxxxxx> instead replied:

Carter Braxton wrote:

I don't know if this is a dumb question or if it just SOUNDS like a dumb
question, but is 12 volts really 12 volts?

No.
12 volts was the figure set because car batteries were nominally 12
volts. They are actually 13.8 volts in their fully charged state.

Nonsense.

12 volts is the maximum voltage set by such organisations as the NMRA
and MOROP.
MOROP further defines that model locomotives should run at scale maximum
speed x 1.3 at 12 volts DC.

I'm asking because I'm
installing tortoise machines and in checking some of my old 12v DC power
sources, I see that they actually measure about 16 v DC... even though they
are labled as 12 volts.

Transformer voltage output will vary with load. One would expect a
non-stablized trafo labelled 12 volts to show perhaps 16 volts at
no-load and 10 volts at 1.5-2 times maximum rated load.

This is more correct. The load is the issue, not the 13.8 charge
voltage. Unloaded power supplies will in fact go to the rail, the
term used for the upper limit of the regulator. Loaded power
supplies will be stable at 12 volts if they are not faulty.
--
Ray
.

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