C40's and SW's [RE-wrenches]

Tue Feb 4 17:32:51 PST 2003

I agree on the VRLA batteries, but most of our grid-tie is still vented
cell.

We design all our wiring pretty conservatively, 2% voltage drop max, even
considering module interconnects, etc. We do sometimes squeeze into a wire
size, but typically are generous. We think it's pretty cheap $ to upsized
the wire and get all the power you can during those 38 minutes of great
winter sun on a typical December day...

So when using a C40, we've typically got plenty of voltage available.

Interesting thought about the total kWh generated. But both your numbers and
mine put the system into the 55-58 VDC range for the vast majority of the
time. Only during grid disconnected bulk charge would we be at 59 to 60 VDC.

I consider a grid connected backup system to be the toughest to set up and
design properly. With off-grid, you've got the gen problems, but with
on-grid, there's a lot more fine tuning that should be done, and a big
uncontrollable utility to match to. That, coupled with generally much less
awareness on the part of the typical on-grid owner.

Jeff

-----Original Message-----
From: Bill Brooks [mailto:billb at endecon.com]
Sent: Tuesday, February 04, 2003 6:42 PM
To: RE-wrenches at topica.com
Subject: RE: C40's and SW's [RE-wrenches]

Jeff,

I think if we are talking about AGM VRLA batteries, 53.6Volts is the right
number. That's what the manufacturer says in their literature. I believe
that this is the right battery for grid-tied systems and is designed to
operate at the voltage (temp compensated) year round. I don't think
sulfating is an issue at that voltage. Plus the fact that we have a healthy
(or unhealthy) ripple current of 15 to 30 amps on the batteries during the
day time.

55.2 will dry out a VRLA battery quite nicely so I think you should
reconsider that value. I still contend that even in Vermont, the number of
kWh generated when the array max power voltage is in the 55-58 Volt range is
more than the number of kWh generated in the 60-64 volt range. (Also
remember that that old thief voltage drop usually works us on these low
voltage systems)

I also agree that any set point on any charge controller has to be manually
tested rather than using any numbers printed on a circuit board. Good
discussion--lots of plain lack of knowledge out their on these systems.

Bill.

-----Original Message-----
From: Jeffery Wolfe, Global Resource Options
[mailto:jeff at globalresourceoptions.com]
Sent: Tuesday, February 04, 2003 11:29 AM
To: RE-wrenches at topica.com
Subject: RE: C40's and SW's [RE-wrenches]

Bill,

Although you're right that the C40 should never control, the point of the
higher voltage settings is to make more power. We all know that the PV's
will put out more power at higher voltages, so setting the inverter higher,
for float, is better. We also need to balance this with battery high limits,
and the fact that you need a pretty significant "dead band" in the control
setpoints between the C40 and the Trace, due to inaccuracies in the voltage
meters in both units. (Trace told me 1.5 V, I'm typically using about 1.0
V).

The 53.6VDC default on the inverters is also on the very low side of where
we're floating batteries, even on-grid, today. We're moving hotter, more
like 54.8 to 55.2. Batteries that float all year long tend to have sulfation
problems, and it seems that the hotter setpoints help reduce this. (Along
with the little black boxes.) Couple this with the fact that on-grid higher
float voltages are going to produce more power, the case is made for setting
the floats about as high as the manufacturer's will let you. We do use bulk
mode, as it's good (IMHO) to bulk the batteries occasionally. So we set the
bulk up at about 58 VDC. This then pushes the bulks on the C40's up to 59 to
59.5, in order to provide as much dead band as possible.

We've got three years on our double C40 / SW system, as well as several
others around the area. The low set points "work", but are not the best for
power production (remember, we all complain about power production on PV
systems), and are not necessarily the best for battery life.

I do agree that the C40 float and bulk can be set the same, but it's more
like setting the float to the same as a more typical bulk, rather than the
other way around.

I also always use a Fluke to set up the C40 (and any other controller). I
never trust the little dials or displays. They can be wrong (on any
controller).

Jeff

-----Original Message-----
From: Bill Brooks [mailto:billb at endecon.com]
Sent: Tuesday, February 04, 2003 1:10 PM
To: RE-wrenches at topica.com
Subject: RE: C40's and SW's [RE-wrenches]

Graham,

I believe that bulk charging is meaningless in a grid-connected application.
Since the system is floated all the time, except during a power outage, the
focus is on the float settings. I would set the bulk timer on the inverter
to 0:00 so it automatically goes to float. The default for the inverter is
53.6 Volts for float and I think that is fine for most lead-acid batteries.
The key is making sure the C-40 is set at least one volt higher. It is also
critical that all controllers and inverters have temperature compensation
probes installed and sensing basically the same temperature.

Finally, check the C-40 while operating to make sure it is not controlling.
By testing the voltage drop across the C-40 positive battery and PV array
inputs, you can tell whether it is controlling. The voltage should always be
below 0.75 Volts, otherwise it is controlling. It should only control in an
outage. Set the C-40 bulk at the same as the float, since the array should
not be bulk charging the battery anyway. Bulk charging doesn't help a
battery that stays at float all the time. It can actually hurt a VRLA
battery by overcharging it if you allow it to bulk for more than a half-hour
or so. Hope that helps. Others may see it differently but I have over four
years of grid-connected experience with my C-40s and SW.

Bill.

-----Original Message-----
From: Graham Owen [mailto:graham at solarexpert.com]
Sent: Monday, February 03, 2003 9:01 PM
To: RE-wrenches at topica.com
Subject: C40's and SW's [RE-wrenches]

Dear Colleagues,

I need some Wrench assistance with a PV service call, for the Xantrex
Power Module system (or power panel for that matter), you have to set
the C40 charge controllers and the SW inverter so that the inverter can
sell PV power to the grid without the controllers restricting current
into the inverter in the first place. I am trying to determine which set
of values works the best.

Are these good figures?

C40  bulk   56.0
     float   55.0

inverter bulk  54.0
       float   53.2

Thanks in advance!

Graham

P.S. Joel, I am working on finding your CPUC answers, I was working out
of town today.

- - - -
To send a message: RE-wrenches at topica.com

Archive of previous messages: http://www.topica.com/lists/RE-wrenches/

List rules & etiquette: http://www.mrsharkey.com/wrenches/etiquete.htm

Check out participant bios: www.mrsharkey.com/wrenches/index.html

Hosted by Home Power magazine

Moderator: michael.welch at homepower.com

- - - -
To send a message: RE-wrenches at topica.com

Archive of previous messages: http://www.topica.com/lists/RE-wrenches/

List rules & etiquette: http://www.mrsharkey.com/wrenches/etiquete.htm

Check out participant bios: www.mrsharkey.com/wrenches/index.html

Hosted by Home Power magazine

Moderator: michael.welch at homepower.com

- - - -
To send a message: RE-wrenches at topica.com

Archive of previous messages: http://www.topica.com/lists/RE-wrenches/

List rules & etiquette: http://www.mrsharkey.com/wrenches/etiquete.htm

Check out participant bios: www.mrsharkey.com/wrenches/index.html

Hosted by Home Power magazine

Moderator: michael.welch at homepower.com

- - - -
To send a message: RE-wrenches at topica.com

Archive of previous messages: http://www.topica.com/lists/RE-wrenches/

List rules & etiquette: http://www.mrsharkey.com/wrenches/etiquete.htm

Check out participant bios: www.mrsharkey.com/wrenches/index.html

Hosted by Home Power magazine

Moderator: michael.welch at homepower.com

- - - -
To send a message: RE-wrenches at topica.com

Archive of previous messages: http://www.topica.com/lists/RE-wrenches/

List rules & etiquette: http://www.mrsharkey.com/wrenches/etiquete.htm

Check out participant bios: www.mrsharkey.com/wrenches/index.html

Hosted by Home Power magazine

Moderator: michael.welch at homepower.com

==^================================================================
This email was sent to: michael_welch at sbcglobal.net

EASY UNSUBSCRIBE click here: http://topica.com/u/?bz8Qcs.bz9JC9.bWljaGFl
Or send an email to: RE-wrenches-unsubscribe at topica.com

TOPICA - Start your own email discussion group. FREE!
http://www.topica.com/partner/tag02/create/index2.html
==^================================================================