Re: DC-> AC Power Switching

["Tesla list" <tesla@xxxxxxxxxx>]

Original poster: "S&JY" <youngsters@xxxxxxxxxxxxxxx>


Dave,


----- Original Message -----
From: "Tesla list" <tesla@xxxxxxxxxx>
To: <tesla@xxxxxxxxxx>
Sent: Tuesday, March 29, 2005 8:06 PM
Subject: DC-> AC Power Switching


> Original poster: Davetracer@xxxxxxx
>
> Hi,
><SNIP>
> >
>      Inverters are expensive and the transformers and sheer iron are
> terribly expensive. Again, "cheap tech". He came up with the idea of
> patterning a sine wave, from 0 to 120 volts and on down to 0, by
connecting
> an increasing number of batteries in series with medium speed, computer
> driven, semiconductor switches (probably transistors). I mean, at 60 times
> per sec, I don't think relays are going to keep up, but probably someone
> will mention how wrong I am (grin).
>
>      Thus at (+)0, nothing is connected; at the first point in the sine
> wave, as it approaches +12, the first battery connects, as it approaches
> +24, the second battery connects, and so forth, up to 120V, then back
> down.  Yes, I know a true AC sine wave goes up past 120V, but this is more
> of a "does this approach stand a chance" versus "nailing it on the dot"
> question. We'll definitely be outputting sinewave data much faster than
Mr.
> Nyquist requires; 60 Hz is not a big challenge to even a slow 8 bit
> microprocessor.
<SNIP>

That can work, BUT think about the amp-hour drain for each battery.  The
first battery will be discharging almost continuously, and the last one will
discharge for just a brief moment near the top of the stepped sinewave.
Thus the first battery will "poop out" much sooner than the others, and you
will not get nearly the total amp-hours out that the batteries are capable
of producing.

I think you should use a converter instead.  I would think you can scrounge
some DC-AC converters, such as Uninterruptable Power Supplies that were
junked because the batteries went bad.

You can get a rough idea of how efficient a lead-acid battery is by
measuring it's temperature rise as you charge or discharge it.  Then use a
small direct contact heater to cause the same temperature rise in the
battery and measure the energy consumed by the heater.

Sounds like a winning project!

--Steve Y.