Alt-BEAM Archive

Message #05405



To: BEAM beam@sgiblab.sgi.com
From: Sean Rigter rigter@cafe.net
Date: Sat, 24 Jul 1999 18:47:13 -0700
Subject: [alt-beam] Re: Solar cell v. doubler



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Hi Bob,

Thank you for the info on solar cell max power operating point.

Using a 74AC04 and 1N5817 Shottky diodes, the CMOSPUMP (attached)
converter losses are even lower and I get 77% efficiency with 3.1V/103ma
input and 5V/50ma output and a whopping 85% efficiency with 2.9V/50ma
input and 5.0V/25ma output. I don't know what the maximum power point
voltage for those Solarbotic's solar cells but if they use 6 sections
then 2.9V is in the neighbourhood.

When charging a SE super cap the output rises to over 6V if the SE if
not fired. If the typical end of charge SE firing voltage is 3.6V, 4.5V
or 5V (?) it occurs on a more linear part of the charging curve which if
the solar cell efficiency operating point is optimized is faster for
sure (grin) and more efficient that just using the solarcell by itself.
( no free lunch eh? ) With a benchtop supply set to 3.6V and a 100 ohm
series resistor, a 0.047F cap charges through the converter to 3.1V in
about 10 seconds which is the same as without the converter but look
what happens with the converter in the circuit at higher 0.047F output
voltages :

3.6V - 12 sec
4.1V - 14 sec
4.5V - 16 sec
4.8V - 18 sec
5.0V - 20 sec

Which can translate into a significant improvement in the power
efficiency for a number of reasons ie if a higher voltage lower current
motor is used! And it is compatable with the chloroplast SE.

You can scale these results for lower input voltages, typical of low
light levels, and get similar improvements.

I don't have a solar cell and need someone else to test some real
performance figures. One can quickly try out the circuit by using a
typical Beam chip (74HC240) and some 1N4148 Si diodes but best
perfomance and highest output require the specified components. I am
working on a synchronous rectifier and the Bicore INVERTER (attached)
is an early example that works "ok" but needs improvement for low
voltage/startup performance. If all goes well, the final version of the
converter will have synchronous rectifiers and use feedback to regulate
the input voltage to the maximum power point of the solar cell (weird!)
and be embedded in a SE.

enjoy

Wilf Rigter mailto:wilf.rigter@powertech.bc.ca


> From: Bob Shannon [SMTP:bshannon@tiac.net]
> Sent: Friday, July 23, 1999 8:45 PM
> To: beam@sgiblab.sgi.com
> Subject: Re: Solar cell v. doubler
>

---8<---
>
The trick here is to start and stop your charge pump based on the
voltage from the solar cell. If you keep the load on the cell (a small
cap) at the peak efficiency point of the cells V/I curve, you can
easily overcome converter losses.

For polysilicon cells, you want to keep the solar cells output at .484
volts per solar cell junction. By placing a small cap (220 uf) across
the cell, and starting and stopping the converter when the cell / cap
voltage rises above / drops below .484 volts per junction you will
always get peak performance from the cell regardless of light level and
load.
>




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5406 Sat, 24 Jul 1999 20:54:01 -0500 [alt-beam] out of step walker beam@sgiblab.sgi.com matthew landry hey all
well i figured out that the only thing i haven't tried to straighten out
my servos is to use centering springs,
i tried them and it worked great. just one question, how will this
affect my servo's life time?
(well maybe two ?'s) is it bad to run power through a motor that can't
move it's load?

thanks again

matthew

*************************************************************************
matthew landry stratguitar911@juno.com
http://www2.crosswinds.net/~stratguitar911/index.html
*************************************************************************

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5407 Sat, 24 Jul 1999 21:22:26 -0400 [alt-beam] Re: h-bridge problems beam@sgiblab.sgi.com SG 10K ? wow! i was told just 1K at the highest, 500ohm at the lowest.
-Sparky

At 10:26 PM 7/23/99 +1000, you wrote:
>done that, 10k, nothings caught on fire yet.
>
>
>-----Original Message-----
>From: SG
>To: beam@sgiblab.sgi.com
>Date: Saturday, 24 July 1999 12:48
>Subject: Re: h-bridge problems
>
>
>>>Please help, you wouldn't want all the
>>>prizes to go to Darrel :-) David Perry
>>
>>be sure to put resistors on yur LEDs!!!
>>heh heh
>>-Sparky
>>
>
>

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