Solar Charging Port

[Higgins]

I will be conducting an EV design/build training seminar for some high school instructors and one of the objectives of their program is to build a solar charging carport.  I know that this is not always the most practical thing to construct, but this is for educational purposes.  I would like to get some advice from anyone who might be able to point me in the direction of some ideas.  I am trying to propose the simplest solution possible; it doesn't need to be as practical as educational (if it takes a few days to charge the car, that is OK).  I am most interested in charging techniques, namely how to deal with the fact that the charger will probably not make a complete charge in a single pass, and how to best deal with this scenario.  I am assuming that the way to go is for the carport to charge some flooded cells, which then run thru an inverter, to a 110v charger... but if the charger only runs a few hours a day, how will that effect a "smart charging" cycle.  I am also considering wind power, so a combined solar/wind scenario might be interesting.

[StarMage187]

If we aren't concerned with practicality, I can think of two ways that it would work. Neither would be real efficient, but they'd work. You could get a DC charger and wire it into the solar panels and/ battery pack. If not that, use the inverter technique, but use a voltmeter and only allow it to discharge the batteries when they are fully charged. That should allow the AC charger to behave normally (I would think).

--- On Thu, 11/13/08, Higgins <[hidden email]> wrote:
From: Higgins <[hidden email]>
Subject: [EVDL]  Solar Charging Port
To: [hidden email]
Date: Thursday, November 13, 2008, 10:44 AM

I will be conducting an EV design/build training seminar for some high school
instructors and one of the objectives of their program is to build a solar
charging carport.  I know that this is not always the most practical thing
to construct, but this is for educational purposes.  I would like to get
some advice from anyone who might be able to point me in the direction of
some ideas.  I am trying to propose the simplest solution possible; it
doesn't need to be as practical as educational (if it takes a few days to
charge the car, that is OK).  I am most interested in charging techniques,
namely how to deal with the fact that the charger will probably not make a
complete charge in a single pass, and how to best deal with this scenario.
I am assuming that the way to go is for the carport to charge some flooded
cells, which then run thru an inverter, to a 110v charger... but if the
charger only runs a few hours a day, how will that effect a "smart
charging"
cycle.  I am also considering wind power, so a combined solar/wind scenario
might be interesting.
--
View this message in context:
http://www.nabble.com/Solar-Charging-Port-tp20482420p20482420.html
Sent from the Electric Vehicle Discussion List mailing list archive at
Nabble.com.

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[Doug Weathers]

Disclaimer: this is from my memory of old EVDL posts.  I've never done
it myself.

Higgins wrote:
> I am assuming that the way to go is for the carport to charge some flooded
> cells, which then run thru an inverter, to a 110v charger...
That would work, but would add some inefficiency from the inverter.  
Also, to get high current charging, you'd need an expensive inverter.

However, you can leave out the inverter.  This is sometimes called "dump
charging" - discharging a large battery pack into a smaller one.

If you pick your voltages carefully, you can just connect 'em up
directly with no charger needed in between.  Make the dump charge
voltage be the same as your EV pack's charge voltage.  Put in a beefy
contactor and/or big DC circuit breaker and go.  The advantage is it
really doesn't take very long to charge the EV to 80% full.  
Disadvantage is that there's a bigger potential for excitement - arcing,
boiling batteries, melting posts at loose connections, etc.

Rich Rudman, John Wayland, and Steve Clunn have all described their dump
charging experiences on the list.  It's been a few years, so you might
need to hit the older archives.

Another way to do this without the drama of high amp dump charging, is
to put a Manzanita Micro PFC charger between the dump pack and the EV
pack.  Again, no need for an inverter.  The PFCs can run on a wide
voltage input range, and don't mind DC.  A PFC-50 can accept 50 amps
from the dump pack, which should also be a pretty fast charge.  
Advantage is you get the full charge routine so you can get to 100% full.

Oh yeah.  You need to replace the PFC's on-off breaker with one that's
rated for breaking the DC volts and amps you'll expect from the dump
pack.  The one that's included is for AC and expects the voltage to hit
zero 120 times a second, which extinguishes any arc in a hurry.  DC
doesn't do that, so the arc might not extinguish until the charger has
burned away.


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[Cor van de Water]

Why make things more complicated if you are not (yet) concerned about it
being practical?

The easiest way to get a solar carport to work is to feed the output
directly into the
charger of the car, preferably the charger is a multi-voltage type that
can handle DC input.

Even simpler is to feed it directly into the pack, but then you need a
means to switch it off
(charge controller) and solar output must be higher than pack voltage.
Example: for a car with a 120V pack (10x 12V battery) you will also need
about 10 panels in series
(170V peak, but about 140-150V in normal operation, so just enough to
push the pack to equalisation).
Typically a solar charge controller consist of a passing diode to send
the solar output to the load
and a shorting FET to short-circuit the solar output before the diode.
When the output (pack) voltage is measured to remain below a certain
threshold or else the panels
are shorted, you get what you want: battery pack is protected and can be
connected to the solar roof
as long as you want and over as many days as you want.

Hope this clarifies,

Cor van de Water
Director HW & Systems Architecture Group
Proxim Wireless Corporation http://www.proxim.com
Email: [hidden email]    Private: http://www.cvandewater.com
Skype: cor_van_de_water     IM: [hidden email]
Tel: [phone]        VoIP: [phone] FWD# 25925
Tel: [phone]x109 XoIP: [phone]

-----Original Message-----
From: [hidden email] [mailto:[hidden email]] On
Behalf Of Higgins
Sent: Thursday, November 13, 2008 10:15 PM
To: [hidden email]
Subject: [EVDL] Solar Charging Port


I will be conducting an EV design/build training seminar for some high
school instructors and one of the objectives of their program is to
build a solar charging carport.  I know that this is not always the most
practical thing to construct, but this is for educational purposes.  I
would like to get some advice from anyone who might be able to point me
in the direction of some ideas.  I am trying to propose the simplest
solution possible; it doesn't need to be as practical as educational (if
it takes a few days to charge the car, that is OK).  I am most
interested in charging techniques, namely how to deal with the fact that
the charger will probably not make a complete charge in a single pass,
and how to best deal with this scenario.
I am assuming that the way to go is for the carport to charge some
flooded cells, which then run thru an inverter, to a 110v charger... but
if the charger only runs a few hours a day, how will that effect a
"smart charging"
cycle.  I am also considering wind power, so a combined solar/wind
scenario might be interesting.
--
View this message in context:
http://www.nabble.com/Solar-Charging-Port-tp20482420p20482420.html
Sent from the Electric Vehicle Discussion List mailing list archive at
Nabble.com.

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http://evdl.org/help/index.html#conv
Archives: http://evdl.org/archive/
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[Higgins]

Direct feed to the batteries sounds simple, but it no longer gives me an
intelligent charging profile. (isn't it kind of like a "bad solar boy"
charger?")

I would like to use a  charger with a direct feed from the  solar panels,
but at that high of a voltage, the available line current is going to be
pretty low.  I don't know of a charger that can easily accept a varying
level of supply voltage/current like that.  Obviously the best answer to an
efficient system seems to sell the solar power back to the grid during the
day, and charge the car off the grid at night but I think that defeats the
purpose of their project.

Also, the ability to have a parallel supply (both solar and wind) at the
same time is an option we wanted to consider.  I am sure that gear to handle
this scenario exists, it's just nothing I have played with before.  

-----Original Message-----
From: [hidden email] [mailto:[hidden email]] On Behalf
Of Cor van de Water
Sent: Thursday, November 13, 2008 3:27 PM
To: Electric Vehicle Discussion List
Subject: Re: [EVDL] Solar Charging Port

Why make things more complicated if you are not (yet) concerned about it
being practical?

The easiest way to get a solar carport to work is to feed the output
directly into the
charger of the car, preferably the charger is a multi-voltage type that
can handle DC input.

Even simpler is to feed it directly into the pack, but then you need a
means to switch it off
(charge controller) and solar output must be higher than pack voltage.
Example: for a car with a 120V pack (10x 12V battery) you will also need
about 10 panels in series
(170V peak, but about 140-150V in normal operation, so just enough to
push the pack to equalisation).
Typically a solar charge controller consist of a passing diode to send
the solar output to the load
and a shorting FET to short-circuit the solar output before the diode.
When the output (pack) voltage is measured to remain below a certain
threshold or else the panels
are shorted, you get what you want: battery pack is protected and can be
connected to the solar roof
as long as you want and over as many days as you want.

Hope this clarifies,

Cor van de Water
Director HW & Systems Architecture Group
Proxim Wireless Corporation http://www.proxim.com
Email: [hidden email]    Private: http://www.cvandewater.com
Skype: cor_van_de_water     IM: [hidden email]
Tel: [phone]        VoIP: [phone] FWD# 25925
Tel: [phone]x109 XoIP: [phone]

-----Original Message-----
From: [hidden email] [mailto:[hidden email]] On
Behalf Of Higgins
Sent: Thursday, November 13, 2008 10:15 PM
To: [hidden email]
Subject: [EVDL] Solar Charging Port


I will be conducting an EV design/build training seminar for some high
school instructors and one of the objectives of their program is to
build a solar charging carport.  I know that this is not always the most
practical thing to construct, but this is for educational purposes.  I
would like to get some advice from anyone who might be able to point me
in the direction of some ideas.  I am trying to propose the simplest
solution possible; it doesn't need to be as practical as educational (if
it takes a few days to charge the car, that is OK).  I am most
interested in charging techniques, namely how to deal with the fact that
the charger will probably not make a complete charge in a single pass,
and how to best deal with this scenario.
I am assuming that the way to go is for the carport to charge some
flooded cells, which then run thru an inverter, to a 110v charger... but
if the charger only runs a few hours a day, how will that effect a
"smart charging"
cycle.  I am also considering wind power, so a combined solar/wind
scenario might be interesting.
--
View this message in context:
http://www.nabble.com/Solar-Charging-Port-tp20482420p20482420.html
Sent from the Electric Vehicle Discussion List mailing list archive at
Nabble.com.

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http://evdl.org/help/index.html#conv
Archives: http://evdl.org/archive/
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[Jon Glauser-2]

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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[Harris, Lawrence]

To make it practical I think charging a battery bank using off the shelf
solar and/or wind technology is probably the easiest solution.  You can
then consider a dump charger that would allow something like an 80%
charge very quickly and then a smaller finishing charger.  If you
monitor and estimate the amount of energy you get from solar and wind
you could take the rest from the grid and have a semi-green charging
system.

Lawrence Harris

-----Original Message-----
From: [hidden email] [mailto:[hidden email]] On
Behalf Of ev
Sent: Thursday, November 13, 2008 1:44 PM
To: 'Electric Vehicle Discussion List'
Subject: Re: [EVDL] Solar Charging Port

Direct feed to the batteries sounds simple, but it no longer gives me an
intelligent charging profile. (isn't it kind of like a "bad solar boy"
charger?")

I would like to use a  charger with a direct feed from the  solar
panels,
but at that high of a voltage, the available line current is going to be
pretty low.  I don't know of a charger that can easily accept a varying
level of supply voltage/current like that.  Obviously the best answer to
an
efficient system seems to sell the solar power back to the grid during
the
day, and charge the car off the grid at night but I think that defeats
the
purpose of their project.

Also, the ability to have a parallel supply (both solar and wind) at the
same time is an option we wanted to consider.  I am sure that gear to
handle
this scenario exists, it's just nothing I have played with before.  

-----Original Message-----
From: [hidden email] [mailto:[hidden email]] On
Behalf
Of Cor van de Water
Sent: Thursday, November 13, 2008 3:27 PM
To: Electric Vehicle Discussion List
Subject: Re: [EVDL] Solar Charging Port

Why make things more complicated if you are not (yet) concerned about it
being practical?

The easiest way to get a solar carport to work is to feed the output
directly into the
charger of the car, preferably the charger is a multi-voltage type that
can handle DC input.

Even simpler is to feed it directly into the pack, but then you need a
means to switch it off
(charge controller) and solar output must be higher than pack voltage.
Example: for a car with a 120V pack (10x 12V battery) you will also need
about 10 panels in series
(170V peak, but about 140-150V in normal operation, so just enough to
push the pack to equalisation).
Typically a solar charge controller consist of a passing diode to send
the solar output to the load
and a shorting FET to short-circuit the solar output before the diode.
When the output (pack) voltage is measured to remain below a certain
threshold or else the panels
are shorted, you get what you want: battery pack is protected and can be
connected to the solar roof
as long as you want and over as many days as you want.

Hope this clarifies,

Cor van de Water
Director HW & Systems Architecture Group
Proxim Wireless Corporation http://www.proxim.com
Email: [hidden email]    Private: http://www.cvandewater.com
Skype: cor_van_de_water     IM: [hidden email]
Tel: [phone]        VoIP: [phone] FWD# 25925
Tel: [phone]x109 XoIP: [phone]

-----Original Message-----
From: [hidden email] [mailto:[hidden email]] On
Behalf Of Higgins
Sent: Thursday, November 13, 2008 10:15 PM
To: [hidden email]
Subject: [EVDL] Solar Charging Port


I will be conducting an EV design/build training seminar for some high
school instructors and one of the objectives of their program is to
build a solar charging carport.  I know that this is not always the most
practical thing to construct, but this is for educational purposes.  I
would like to get some advice from anyone who might be able to point me
in the direction of some ideas.  I am trying to propose the simplest
solution possible; it doesn't need to be as practical as educational (if
it takes a few days to charge the car, that is OK).  I am most
interested in charging techniques, namely how to deal with the fact that
the charger will probably not make a complete charge in a single pass,
and how to best deal with this scenario.
I am assuming that the way to go is for the carport to charge some
flooded cells, which then run thru an inverter, to a 110v charger... but
if the charger only runs a few hours a day, how will that effect a
"smart charging"
cycle.  I am also considering wind power, so a combined solar/wind
scenario might be interesting.
--
View this message in context:
http://www.nabble.com/Solar-Charging-Port-tp20482420p20482420.html
Sent from the Electric Vehicle Discussion List mailing list archive at
Nabble.com.

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http://evdl.org/help/index.html#conv
Archives: http://evdl.org/archive/
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[Cor van de Water]

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: [hidden email]    Private: http://www.cvandewater.com
Skype: cor_van_de_water     IM: [hidden email]
Tel: [phone]        VoIP: [phone] FWD# 25925
Tel: [phone]x109 XoIP: [phone]

-----Original Message-----
From: [hidden email] [mailto:[hidden email]] 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

_______________________________________________
General EVDL support: http://evdl.org/help/ Usage guidelines:
http://evdl.org/help/index.html#conv
Archives: http://evdl.org/archive/
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[Cor van de Water]

For their system design, the first question to ask
is if they require the solar/wind system to deliver
charge (into a battery bank) while the car is not there
or only directly into the car's pack.
In the first case you have effectively split the problem
into two with one easy to solve, as it is a standard
solar/wind situation with adequate market supply.
Only the part how to transfer power from the solar/wind
battery bank into the car's pack is new, but this has
also been done.
If you want to go entirely with off-the-shelf components
then it is as simple as using a (good - preferably sine-wave)
inverter and plugging the car's charger into that as if it
were "the grid".
If you want to make it less costly and more efficient
then you should look for a charger that can accept the
(low) DC input voltage from the solar/wind bank.
If you just need a cheaper/scrounge-solution then you
could use any cheap UPS that often can be had for a
song when its battery is tired, rip out that battery
and hook it up to your solar/wind bank (proper fusing).
That will give you standard grid AC power to plug the
charger into.

The other solution (without bank) can be more efficient
if the car is normally parked there during the day, it
also avoids the extra battery bank (expense, maintenance)
but requires to size the solar and wind solutions to the
car's pack, or (what I was suggesting before) using a
DC/DC converter to adapt the typical and abundantly
available solar and wind component output voltage to
the car's pack voltage.

When you can give more guidance which direction the
system design is going then we can give more guidance.

Success,

Cor van de Water
Director HW & Systems Architecture Group
Proxim Wireless Corporation http://www.proxim.com
Email: [hidden email]    Private: http://www.cvandewater.com
Skype: cor_van_de_water     IM: [hidden email]
Tel: [phone]        VoIP: [phone] FWD# 25925
Tel: [phone]x109 XoIP: [phone]

-----Original Message-----
From: [hidden email] [mailto:[hidden email]] On
Behalf Of ev
Sent: Friday, November 14, 2008 3:14 AM
To: 'Electric Vehicle Discussion List'
Subject: Re: [EVDL] Solar Charging Port

Direct feed to the batteries sounds simple, but it no longer gives me an
intelligent charging profile. (isn't it kind of like a "bad solar boy"
charger?")

I would like to use a  charger with a direct feed from the  solar
panels, but at that high of a voltage, the available line current is
going to be pretty low.  I don't know of a charger that can easily
accept a varying level of supply voltage/current like that.  Obviously
the best answer to an efficient system seems to sell the solar power
back to the grid during the day, and charge the car off the grid at
night but I think that defeats the purpose of their project.

Also, the ability to have a parallel supply (both solar and wind) at the
same time is an option we wanted to consider.  I am sure that gear to
handle this scenario exists, it's just nothing I have played with
before.  

-----Original Message-----
From: [hidden email] [mailto:[hidden email]] On
Behalf Of Cor van de Water
Sent: Thursday, November 13, 2008 3:27 PM
To: Electric Vehicle Discussion List
Subject: Re: [EVDL] Solar Charging Port

Why make things more complicated if you are not (yet) concerned about it
being practical?

The easiest way to get a solar carport to work is to feed the output
directly into the charger of the car, preferably the charger is a
multi-voltage type that can handle DC input.

Even simpler is to feed it directly into the pack, but then you need a
means to switch it off (charge controller) and solar output must be
higher than pack voltage.
Example: for a car with a 120V pack (10x 12V battery) you will also need
about 10 panels in series (170V peak, but about 140-150V in normal
operation, so just enough to push the pack to equalisation).
Typically a solar charge controller consist of a passing diode to send
the solar output to the load and a shorting FET to short-circuit the
solar output before the diode.
When the output (pack) voltage is measured to remain below a certain
threshold or else the panels are shorted, you get what you want: battery
pack is protected and can be connected to the solar roof as long as you
want and over as many days as you want.

Hope this clarifies,

Cor van de Water
Director HW & Systems Architecture Group Proxim Wireless Corporation
http://www.proxim.com
Email: [hidden email]    Private: http://www.cvandewater.com
Skype: cor_van_de_water     IM: [hidden email]
Tel: [phone]        VoIP: [phone] FWD# 25925
Tel: [phone]x109 XoIP: [phone]

-----Original Message-----
From: [hidden email] [mailto:[hidden email]] On
Behalf Of Higgins
Sent: Thursday, November 13, 2008 10:15 PM
To: [hidden email]
Subject: [EVDL] Solar Charging Port


I will be conducting an EV design/build training seminar for some high
school instructors and one of the objectives of their program is to
build a solar charging carport.  I know that this is not always the most
practical thing to construct, but this is for educational purposes.  I
would like to get some advice from anyone who might be able to point me
in the direction of some ideas.  I am trying to propose the simplest
solution possible; it doesn't need to be as practical as educational (if
it takes a few days to charge the car, that is OK).  I am most
interested in charging techniques, namely how to deal with the fact that
the charger will probably not make a complete charge in a single pass,
and how to best deal with this scenario.
I am assuming that the way to go is for the carport to charge some
flooded cells, which then run thru an inverter, to a 110v charger... but
if the charger only runs a few hours a day, how will that effect a
"smart charging"
cycle.  I am also considering wind power, so a combined solar/wind
scenario might be interesting.
--
View this message in context:
http://www.nabble.com/Solar-Charging-Port-tp20482420p20482420.html
Sent from the Electric Vehicle Discussion List mailing list archive at
Nabble.com.

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[Lee Hart]

Cor van de Water wrote:
> Why make things more complicated if you are not (yet) concerned about it
> being practical?

I agree. Get a simple solution working first; then improve on it as the
situation permits.

Since the panels generate DC and the batteries are DC, the easiest
solutions will be ones that directly connect the panels to the
batteries. Either use enough panels in series to produce pack voltage,
or rewire your EV's batteries in parallel groups for charging.

I prefer the latter solution, as it's safer (low voltage on the
connector), and tends to automatically balance the batteries) the
strings charge in parallel, so the least charged ones take the most
current).

For example, suppose your EV has a 108v pack (18 6v batteries). Wire the
emergency disconnect switch or breaker at the 36v tap, and the main
contactor at the 72v tap. When both are opened, the pack is divided into
three 36v strings.

Solar panels always have a blocking diode in series to prevent the
batteries from discharging into the panels when there is insufficient
light. In this example (charging three battery banks in parallel), use a
blocking diode for each one. I would use *two* blocking diodes per
battery bank; one in the positive and one in the negative lead. This
prevents shorts and fuse-blowing if someone forgets to turn off the main
contactor or emergency disconnect switch before plugging in the solar
charger. The diodes should be rated at about double the PV panel's
maximum current, and at least 2x the maximum pack voltage.

Also include fuses, of course. Batteries can deliver enormous fault
currents, and the fuses will prevent a fire. Put a fuse in series with
each diode. The fuse's current rating should be about 2 times the PV
panel's maximum current output. The fuse's voltage rating should be for
DC at the full pack voltage (*not* low-voltage automotive fuses)!

A bad old ASCII schematic shows the overall scheme. View it with a fixed
width font like Courier:

+36v__________|\|___/\  ________+108v to EV motor controller etc.
solar     |   |/|     \/  |
panel     |   D1    F1  __|__+
           |              ___  36v string of batteries
           |   D2    F2    |  -
        __ | __|/|___/\  __|
       |   |   |\|     \/  |
       |   |                /  main contactor
       |   |___|\|___/\  __|
       |   |   |/|     \/  |
       |   |   D3    F3  __|__+
       |   |              ___  36v string of batteries
       |   |   D4    F4    |  -
       |__ | __|/|___/\  __|
       |   |   |\|     \/  |
       |   |                /  emergency disconnect switch
       |   |___|\|___/\  __|
       |       |/|     \/  |
       |       D5    F5  __|__+
       |                  ___  36v string of batteries
       |       D6    F6    |  -
-36v__|_______|/|___/\  __|
solar         |\|     \/
panel

The scheme can be extended to any number of batteries. You just need
more switches or contactors to break the pack up into 24v to 48v size
groups, and 2 diodes and fuses per battery group.

It's unlikely that your solar panels will be large enough to overcharge
a car-sized EV pack, so a charge controller is optional. But if they
can, a charge controller will be needed. Size it for a 36v string (or
whatever voltage group you break your pack into).
--
Ring the bells that still can ring
Forget the perfect offering
There is a crack in everything
That's how the light gets in    --    Leonard Cohen
--
Lee A. Hart, 814 8th Ave N, Sartell MN 56377, leeahart_at_earthlink.net

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[Higgins]

Great idea relocating the breaker and contactor, you found another crack to
let some light in!!  There is nothing better than a simple solution to a
complex problem.  This is for educational purposes, so it leaves the school
open to expanding the technology as the students become more advanced.  I'll
be sure to post the results of the project when we are complete.



-----Original Message-----
From: [hidden email] [mailto:[hidden email]] On Behalf
Of Lee Hart
Sent: Friday, November 14, 2008 11:31 AM
To: Electric Vehicle Discussion List
Subject: Re: [EVDL] Solar Charging Port

Cor van de Water wrote:
> Why make things more complicated if you are not (yet) concerned about it
> being practical?

I agree. Get a simple solution working first; then improve on it as the
situation permits.

Since the panels generate DC and the batteries are DC, the easiest
solutions will be ones that directly connect the panels to the
batteries. Either use enough panels in series to produce pack voltage,
or rewire your EV's batteries in parallel groups for charging.

I prefer the latter solution, as it's safer (low voltage on the
connector), and tends to automatically balance the batteries) the
strings charge in parallel, so the least charged ones take the most
current).

For example, suppose your EV has a 108v pack (18 6v batteries). Wire the
emergency disconnect switch or breaker at the 36v tap, and the main
contactor at the 72v tap. When both are opened, the pack is divided into
three 36v strings.

Solar panels always have a blocking diode in series to prevent the
batteries from discharging into the panels when there is insufficient
light. In this example (charging three battery banks in parallel), use a
blocking diode for each one. I would use *two* blocking diodes per
battery bank; one in the positive and one in the negative lead. This
prevents shorts and fuse-blowing if someone forgets to turn off the main
contactor or emergency disconnect switch before plugging in the solar
charger. The diodes should be rated at about double the PV panel's
maximum current, and at least 2x the maximum pack voltage.

Also include fuses, of course. Batteries can deliver enormous fault
currents, and the fuses will prevent a fire. Put a fuse in series with
each diode. The fuse's current rating should be about 2 times the PV
panel's maximum current output. The fuse's voltage rating should be for
DC at the full pack voltage (*not* low-voltage automotive fuses)!

A bad old ASCII schematic shows the overall scheme. View it with a fixed
width font like Courier:

+36v__________|\|___/\  ________+108v to EV motor controller etc.
solar     |   |/|     \/  |
panel     |   D1    F1  __|__+
           |              ___  36v string of batteries
           |   D2    F2    |  -
        __ | __|/|___/\  __|
       |   |   |\|     \/  |
       |   |                /  main contactor
       |   |___|\|___/\  __|
       |   |   |/|     \/  |
       |   |   D3    F3  __|__+
       |   |              ___  36v string of batteries
       |   |   D4    F4    |  -
       |__ | __|/|___/\  __|
       |   |   |\|     \/  |
       |   |                /  emergency disconnect switch
       |   |___|\|___/\  __|
       |       |/|     \/  |
       |       D5    F5  __|__+
       |                  ___  36v string of batteries
       |       D6    F6    |  -
-36v__|_______|/|___/\  __|
solar         |\|     \/
panel

The scheme can be extended to any number of batteries. You just need
more switches or contactors to break the pack up into 24v to 48v size
groups, and 2 diodes and fuses per battery group.

It's unlikely that your solar panels will be large enough to overcharge
a car-sized EV pack, so a charge controller is optional. But if they
can, a charge controller will be needed. Size it for a 36v string (or
whatever voltage group you break your pack into).
--
Ring the bells that still can ring
Forget the perfect offering
There is a crack in everything
That's how the light gets in    --    Leonard Cohen
--
Lee A. Hart, 814 8th Ave N, Sartell MN 56377, leeahart_at_earthlink.net

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[Tom Bowes]

There are any number of off-the-shelf DC charge controllers available for PV applications. The first thing you need to determine is how large the solar array will be since this determines the amperage capacity of the controller (Imp + 25%, usually). If the array is large enough and can deliver 25 amps or more you can go with a maximum power point tracking (MPPT) charge controller and gain about 20% in efficiency. There is one lower amperage model that I'm aware of but it is designed to work only with 12 or 24 volt packs.

You must keep in mind that unlike other power sources PV modules are not constant in their output characteristics, varying in voltage and current with changes in temperature and irradiance. The Vmp voltage for the array must be a few volts above the battery pack voltage at a minimum. If a MPPT unit is used the modules can be strung together in series to get the voltage up to about 100 to 150 volts and then the controller can modulate it back down to the pack voltage.

Yes, you can go DC to AC to DC, or charge a larger pack and then dump charge the car, but either scenario sacrifices efficiency and adds cost. On a small PV system you could also design it so that the open circuit voltage of the PV array is about 20% above the pack voltage and use a direct connection for charging. Again, overcurrent protection and blocking diodes would be required to keep the batteries from back-feeding the array. Modern PV modules DO NOT have blocking diodes included so you'd have to come up with some that could handle the voltage and current.

Tom Bowes

 

Higgins wrote:

I will be conducting an EV design/build training seminar for some high school instructors and one of the objectives of their program is to build a solar charging carport.  I know that this is not always the most practical thing to construct, but this is for educational purposes.  I would like to get some advice from anyone who might be able to point me in the direction of some ideas.  I am trying to propose the simplest solution possible; it doesn't need to be as practical as educational (if it takes a few days to charge the car, that is OK).  I am most interested in charging techniques, namely how to deal with the fact that the charger will probably not make a complete charge in a single pass, and how to best deal with this scenario.  I am assuming that the way to go is for the carport to charge some flooded cells, which then run thru an inverter, to a 110v charger... but if the charger only runs a few hours a day, how will that effect a "smart charging" cycle.  I am also considering wind power, so a combined solar/wind scenario might be interesting.