Re: Solar Charging Port

Correct, these typically work well in very cold environment
(winter time) where every watt counts, so if the panel is
truly putting out 17V (higher in cold, lower in heat) then by
stepping it down, a few more Amps go into the batteries.
For a solar car roof, you can do the same, stepping it up or
down from the solar panel voltage to the car's pack voltage
by using a DC/DC converter that can deliver the max solar panel
power or slightly less if it has buit-in limiting.

For example say you have only 4 panels on the solar roof,
delivering nominally 48V but in practice around 68V DC and
you pack is 120V then you need a DC/DC that will accept
a voltage over 60V and transforms it to the pack voltage,
which will go up from around 120V to 150V for equalization
but at least 140V to be able to fully charge it.

NOTE that now you will need to make a shut-off for the DC/DC
when voltage is below 60V and attach the solar panels to a
capacitor bank feeding into the DC/DC so that it is allowed
for low power operation (when not full sun) to slowly charge
the capacitors, have the DC/DC come on briefly to transfer a
burst of energy to the car, then the DC/DC shuts down again
from undervoltage until the caps re-charge.
Keeping the solar panel voltage around 15V per panel will
ensure max power delivery.
NOTE: this voltage should be temp-compensated.
If panels are very hot, their output voltage can drop and
their optimal power point may be below 15V. If they are
cold, then their optimal power point is higher.
Also, this point varies with the panel type and nr of cells
that are put inn series in the panel.
Typical silicon (mono or multi-crystal) 34-cell panels are
what are most used for 12V battery charging and that are
the voltages I quote above, check your panel's datasheet
to find the optimum for your installation.

Regards,

Cor van de Water
Director HW & Systems Architecture Group
Proxim Wireless Corporation http://www.proxim.com
Email: CWater@...    Private: http://www.cvandewater.com
Skype: cor_van_de_water     IM: cor_van_de_water@...
Tel: +1 408 383 7626        VoIP: +31 20 3987567 FWD# 25925
Tel: +91 (040) 23117400x109 XoIP: +31877841130

-----Original Message-----
From: ev-bounces@... [mailto:ev-bounces@...] On
Behalf Of Jon Glauser
Sent: Friday, November 14, 2008 4:30 AM
To: Electric Vehicle Discussion List
Subject: Re: [EVDL] Solar Charging Port

I remember seeing a schematic for a peak power tracker battery charger
for solar. It measured the POWER from the PV and the POWER going into
the battery and adjusted the current/voltage to keep the most efficient
transfer going.

Something like this might be what you're looking for? The one I was
looking at was microprocessor based, so a charge profile could be put in
easily.

-Jon Glauser
http://jonglauser.blogspot.com
http://www.evalbum.com/555

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