Re: [EVDL] Solar Emergency Charging

[Lee Hart via EV]

Robert Bruninga via EV wrote:

I want to develop a way to charge an EV from a Solar array when the
grid is down cheaply.

My thiking is that typical modified sine 12v/120VAC inverters do their
inversion first from 12VDC to high voltage DC first, and then they chop
it to make it modified sine.

There are several different topologies used for 12vdc-to-120vac 
inverters. Some have two stages; they boost 12vdc to 180vdc, and follow 
that with an inverter. Others have a single stage that chops the 12vdc 
into AC, and steps that up to 120vac with a transformer. There are 
several other less-common topologies as well.


The big issue is finding a schematic for any of them. Without one, it's 
going to be a challenge to reverse-engineer it sufficiently to make it 
work for your purpose.


Another option: If this is for emergency use, how about a 
motor-generator? I have one from the 1980's for my Elec-Trak. 36vdc in, 
120vac at 600w out. Not the most efficient (around 80%) but reliable, 
and simple as dirt. They also produce a perfect sinewave, and can handle 
very high peak loads (for starting motors, etc.) Many sizes have been 
made, and can be found in surplus outlets pretty cheap.


You can also hack one together out of stuff you have. Any 120vac 
induction motor can be used as an induction generator; just hang 
capacitors on the AC bus to provide its leading PF excitation current.


--
In computing, the mean time to failure keeps getting shorter. (Alan Perlis)
--
Lee Hart, 814 8th Ave N, Sartell MN 56377, www.sunrise-ev.com

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Re: [EVDL] Solar Emergency Charging

[Robert Bruninga via EV]

A GT inverter is not a voltage source able to supply power to a load.  It is
a CURRENT source that pushes an MPPT derived amount  of power in phase with
an existing waveform that is connected to a near ZERO IMPEDANCE load (the
grid).  Withtout the grid, even if you fool it with a  waveform, the voltage
would soar to extremely high voltages when the load is not there.

And until the EVSE has concluded its dance with the car, the load is not
there.  Adding kludge onto kludge to make this work is not viable.

So it needs to be a common power inverter, that is fed HV DC to match its
output xwitching circuit to deliver 60 Hz AC at 1500W for a standard EVSE.

Actuaslly, I guess it is worth going to the full 16 amps allowed for 120v so
probably starting with a 2 kW inverter would be worth doing.

The goal is something that fits in a box, about the size of a standard 120
VAC inverter than can be on hand to "clip" onto a solar array in an outage
to provide EV charging.

Bob


-Original Message-
From: EV [mailto:ev-boun...@lists.evdl.org] On Behalf Of Matt Lacey via EV
Sent: Friday, October 06, 2017 4:33 PM
To: Cor van de Water via EV
Cc: Matt Lacey
Subject: Re: [EVDL] Solar Emergency Charging

You could get a 120vac grid tie inverter. Those typically have a mppt front
end that boosts or bucks to a nominal 180vdc before inverting to 120vac.

Connect the two 180v dc buses and you're good to go.

Having a bit of storage capacity on that dc bus would be ideal for starting
loads

⁣Sent from BlueMail

On 6 Oct 2017 21:39, at 21:39, Robert Bruninga via EV 
wrote:
>I want to develop a way to charge an EV from a Solar array when the
>grid is down cheaply.
>
>My thiking is that typical modified sine 12v/120VAC inverters do their
>inversion first from 12VDC to high voltage DC first, and then they chop
>it to make it modified sine.
>
>If that is the case, it should be possible to inject high votage DC
>from the solar panels at that same point and produce the same 120VAC.
>This then can drive any standard 120v EVSE.
>
>We can tap into solar panels in increments of 30 VDC and should find
>one close.  The problem will be the starting process to bring the VOC
>down to the Vmax that matches the HV in the inverter..  That can be
>done with a trivial big resistive load a few caps and then transfer
>relay maybe.
>
>Thoughts?
>Bob
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Re: [EVDL] Solar Emergency Charging

[Matt Lacey via EV]

You could get a 120vac grid tie inverter. Those typically have a mppt front end 
that boosts or bucks to a nominal 180vdc before inverting to 120vac. 

Connect the two 180v dc buses and you're good to go.

Having a bit of storage capacity on that dc bus would be ideal for starting 
loads 

⁣Sent from BlueMail ​

On 6 Oct 2017 21:39, at 21:39, Robert Bruninga via EV  wrote:
>I want to develop a way to charge an EV from a Solar array when the
>grid
>is down cheaply.
>
>My thiking is that typical modified sine 12v/120VAC inverters do their
>inversion first from 12VDC to high voltage DC first, and then they chop
>it
>to make it modified sine.
>
>If that is the case, it should be possible to inject high votage DC
>from
>the solar panels at that same point and produce the same 120VAC.  This
>then can drive any standard 120v EVSE.
>
>We can tap into solar panels in increments of 30 VDC and should find
>one
>close.  The problem will be the starting process to bring the VOC down
>to
>the Vmax that matches the HV in the inverter..  That can be done with a
>trivial big resistive load a few caps and then transfer relay maybe.
>
>Thoughts?
>Bob
>___
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>http://lists.evdl.org/listinfo.cgi/ev-evdl.org
>Please discuss EV drag racing at NEDRA
>(http://groups.yahoo.com/group/NEDRA)
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Re: [EVDL] Solar Emergency Charging

[Cor van de Water via EV]

Bob is right in that it is often in the inverter that the voltage gets
boosted first, then chopped into a sine wave.
In fact, I have an inverter laying around that I want to do this, not
for solar charging (I will explain why in a minute)
but for running it off my Nissan Leaf pack, which consists of 2 banks of
180V series cells with a disconnect in between
(which poses its own challenge, as you do not want to defeat the
disconnect with your connected inverter.

Since the full pack of a Leaf is typically between 350 - 395V the
emergency solar charging that I eventually going to plan for
is to properly and legally install a grid-interactive inverter with the
solar panels wired to provide a MPP of just under 400V
(the inverter is pretty efficient at that voltage, so that is a plus)
and let the Open Voltage go as high as needed, but under the
600V that the inverter is rated for (note that this is legally required
to be calculated at freezing temperatures, so it is always
a lot higher than the Voc spec of the solar panels at 25 deg C!)

Now in an emergency, when the grid is down and I *need* to charge my EV
as backup bank for my home or for travel, I can
open the DC disconnect switch next to the inverter (it does not have a
built-in switch), safely jerry rig the panels to the plug that
I have connected to my EV battery bank (for this purpose) and turn on
the DC disconnect switch to DC-charge my battery bank
while keeping an eye on the charging voltage.

Why am I charging my EV battery instead of directly using solar panel
power in my home?
Simple - solar panels are current limited devices. This means that there
output voltage varies strongly with the load.
So, if you plug in your panels directly into your home inverter and
there is little load, the panels will deliver their Voc which will
typically be much too high for the inverter, it can be almost 50% higher
than the max power point voltage.
Then, when the inverter tries to draw a large start-up current because
the fridge or furnace blower motor comes on, the 
solar panel will deliver its max current limit and the voltage on the
inverter will crater, causing the inverter to turn off due to
undervoltage and you never get that load started, even if it just takes
a peak of one second long. So, you need a buffer and a constant load
to capture the energy from the panels and effectively use it when
needed. That is why I want to connect the panels to my
(EV) battery bank (essentially a mobile PowerWall) and run the inverter
from the battery bank.

The inverter that I have laying around is actually a UPS without its
120VDC battery bank. I used it on my 120V Ford Ranger conversion
but removed it before selling the truck.
I noticed that (like all inverters in USA) it converts the voltage up to
almost 200V to chop a 120V AC waveform, but unlike other inverters
where the cap with the 200VDC and the chopper gets switched back and
forth between Phase and Neutral outputs to create the + and the - half
waves
from the same floating 200VDC, this inverter seems to have 2 caps and
choppers, each taking care of one half wave on the Phase output (which
is the usual H-bridge),
so the neutral is always connected to the center connection between the
two caps.
That opens possibilities to feed the inverter from the 2x 180V banks of
a Leaf pack, but first I have to make sure that what I traced in this
inverter
is actually the way it works.

The other option is the use of one of the two SURT inverters that I
have, one takes a single 192V battery bank, the other (the SURT-8000)
actually has two battery banks in series, which is pretty much what the
Leaf pack also has, so it seems a natural fit to use. They need an
output transformer due to the weird choice in how they use their input
AC, causing a weird offset AC voltage on their outputs and that is one
of the reasons that you need an output transformer to isolate and
convert it back to 2x 120VAC output. I happen to have 3 of those
transformers, if anyone is interested in a SURT and/or the 5kVA output
transformer (rack mount)
then let me know. I plan on creating a vertical rack: mounting two
L-shape brackets to the garage wall so the 19" rack mount provided by
the two brackets is not
vertical as usual, but horizontal, so I can hang the UPS and the
transformer in between the two brackets, hanging down along the wall for
minimal intrusion into
my garage space. Then I can run the 2x 120VAC output into a subpanel to
feed critical circuits in my home.

Enough plans to keep me busy for a while...
Cor.

-Original Message-
From: EV [mailto:ev-boun...@lists.evdl.org] On Behalf Of Jay Summet via
EV
Sent: Friday, October 06, 2017 10:40 AM
To: ev@lists.evdl.org
Cc: Jay Summet
Subject: Re: [EVDL] Solar Emergency Charging

The device you are describing is called a "micro-inverter". Typically
they are designed with "anti-islanding" proteciton, so they require a
system (the grid) already making 240v sine waves before the

Re: [EVDL] Solar Emergency Charging

[Jay Summet via EV]

The device you are describing is called a "micro-inverter". Typically 
they are designed with "anti-islanding" proteciton, so they require a 
system (the grid) already making 240v sine waves before they add 240 VAC 
back to the grid. You can purchase microinverters without this 
protection, but it may be easier to "simulate" your own grid with a 
small battery and a true sine wave inverter.



I think your easiest solution is to have a "traditional" solar system 
set up with it's own (small?) battery bank and inverter, and just use 
each component in the "normal" way. (e.g. Solar cells feeding a charger 
that charges the battery bank, and an inverter that produces 120 (or 
240?) VAC to use to charge your car.


Perhaps you could find/use a specialty inverter/charger combo box 
specifically made for the solar industry, but depending upon size of 
your system, it may be cheaper to use a separate 12v inverter and one 
(or more) 12 volt solar charge controllers.


A single 12 volt battery may be enough if you are primarily going to be 
charging your car while the sun is shining and have more solar PV panel 
wattage than the car charger draws. The battery will give you a little 
buffer to provide for brief clouds, etc


If you had a slightly larger battery bank on your solar system, you 
could also use it to run a fridge overnight, etc...


Jay


On 10/06/2017 09:39 AM, Robert Bruninga via EV wrote:

I want to develop a way to charge an EV from a Solar array when the grid
is down cheaply.

My thiking is that typical modified sine 12v/120VAC inverters do their
inversion first from 12VDC to high voltage DC first, and then they chop it
to make it modified sine.

If that is the case, it should be possible to inject high votage DC from
the solar panels at that same point and produce the same 120VAC.  This
then can drive any standard 120v EVSE.

We can tap into solar panels in increments of 30 VDC and should find one
close.  The problem will be the starting process to bring the VOC down to
the Vmax that matches the HV in the inverter..  That can be done with a
trivial big resistive load a few caps and then transfer relay maybe.

Thoughts?
Bob
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