Alt-BEAM Archive

Message #08835



To: beam@sgiblab.sgi.com
From: Brad Guillot mach50@netzero.com
Date: Wed, 05 Jan 2000 17:41:23 -0600
Subject: [alt-beam] Re: Lens Motors


do ya'll have a url for their web pages?(the lens assembly)

Bruce Robinson wrote:
>
> Bob Shannon wrote:
> >
> > I just found the a lens assembly at Herbach, description lists 2
> > gearmotors...!
>
> You've got more patience then I do, Bob. Which heading was it under, do
> you remember?
>
> Bruce
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8836 Wed, 05 Jan 2000 17:44:04 -0600 [alt-beam] Re: ZVD was D1 beam@sgiblab.sgi.com Brad Guillot This circuit looks neat, espicially since i was about to try and built a
d1.
But i don't see where the load is attached to the circuit. Am i missing
something?

brad


Wilf Rigter wrote:
>
> While not a direct answer to your D1 question (later that), here is
> some related information in the first BEAM article of the 21th century
> :
>
> The Zero Volt Diode (ZVD) is a circuit useful in a variety of
> applications including solar chargers of all types. It is a novel
> circuit in which a power mosfet acts like a very low voltage drop
> diode which switches state at 0V! and which is used to conduct
> NEGATIVE! current from drain to source.
>
> In D1 type solar engines, a low loss diode can be used to charge a cap
> to the open circuit voltage of the solar cell and used in solar
> battery chargers, the battery is charged at the maximum rate when the
> source voltage is highest. The diode must be used in series with
> the solar panel or else the cap or battery would discharge through
> the solar panel when the panel voltage drops below the stored voltage.
>
> The diode or equivalent polarity sensitive switch is therefore
> essential to solar chargers.
> Most diodes used in BEAM SEs and solar chargers are Silicon diodes
> like the 1N4001 which have a voltage drop of 0.6V to 1V at currents up
> to 1A. More efficient diodes for currents form >100mA to tens of amps
> applications are the Schottky type rectifiers with a voltage drop of
> from 200mV to 1000mV depending on the current level. For <100mA
> applications a Germanium diode can used with 200mV or less drop.
>
> This voltage drop issue is important in competition solar engines
> since you would like to have the maximum voltage to charge the cap and
> supply the load (low diode drop) and keep the charge stored on the cap
> when the lightlevel drops (leakage current cut off).
> and the SE triggers. Moreover, since the energy in the cap is
> proportional to the square of the voltage even the small voltage drop
> of a diode reduces available energy.
>
> One obvious simple improvement over the original D1 design is to
> substitute a Ge 1N34A diode (Radio Shack) instead of the Si 1N4001
> diode.
>
> An ideal diode would have zero voltage drop. While a straight hookup
> of the solar cell has minimum voltage drop it leaks if the light drops
> and any real diode has a forward voltage drop. What to do?
>
> The solution is to use a mosfet as a rectifier just like the
> synchronous rectifier applications in volatge converters. The mosfet
> should be switched ON when the solar voltage is larger than the
> capacitor or battery voltage and switch OFF when the solar voltage
> is lower than the stored voltage.
>
> Here is a little design for charging capacitors from solar cells with
> zero voltage drop at the end of the charge cycle. It can be easily
> scaled to higher currents by changing the 2N7000 for a larger mosfet.
> If a parallel load is present, the circuit also delivers maximum
> voltage with minimum insertion loss from the solar cell. The mosfet
> turns on when the voltage difference is zero and turns off when the
> solar voltage drops less than 100mV below the cap or battery .
>
> The NPN transistor is normally ON when the cap voltage is more than
> .6V and this clamps the gate of the 2N7000 which is turned OFF. The
> PNP tarnsistors is connected to the negative terminal of the solar
> panel and when the voltage on that terminal drops below 0V the PNP
> turns ON. This in turn turns the NPN OFF and the 2N7000 turns ON.
> MOSFET have an interesting characteristic in that they act like
> bidirectional switches, so the 2N7000 is perfectly happy to have it's
> DRAIN conduct a negative current to the 0V line. When the voltage on
> the negative terminal of the solar panel is more positive than 0V the
> PNP turns OFF and the NPN ON and the 2N7000 turns off with the drain
> voltage positive with respect to the source voltage and 0V line.
> Since the 2N7000 does not turn on until the gate voltage is more than
> 2V (in practice: higher according to the data book) a logic FET with
> a lower gate turn on voltage would be preferred. In any case the
> mosfet has a integral reverse diode from drain to source which will
> carry the current until the voltage on the cap reaches 2V at which
> point the mosfet turns on and the forward voltage drops to a few 10s
> of mV.
>
> Anyway it's a start to revisit some of the more primitive solar
> circuits and get the technological edge on your competitors in the
> WCRG solar races!
>
> enjoy
>
> wilf
>
>
> [Image]
>
>
>
> Bumper314@aol.com wrote:
>
> > I'm looking for a solarengine that works better then the D1. The D1
> > is so
> > twitchy and needs alot of tweeking so I'm looking for something that
> > will
> > just charge up all day and kick off for the night..I have found that
> > there is
> > always plenty of power left in the cap when the D1 turns off (after
> > about 10
> > minutes even with a .47F cap) Does anyone have a solution
> >
> > Steve
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8837 Wed, 05 Jan 2000 19:02:59 -0500 [alt-beam] Re: ZVD was D1 beam@sgiblab.sgi.com Bob Shannon Brad Guillot wrote:

> This circuit looks neat, espicially since i was about to try and built a
> d1.
> But i don't see where the load is attached to the circuit. Am i missing
> something?
>
> brad

Yeah, all this circuit does it to replace the diode between the cap and
solar cell. Its not a D1 replacement by itself.

Maybe Wilf can do something with the NPN phototransistor / PNP switch
'smart-cap' circuit and the ZVD together....?

That could rock.

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