[RE-wrenches] Solar Boost Controller in Senegal
Bob-O Schultze
bob-o at electronconnection.com
Tue Jun 30 07:13:37 PDT 2009
alt,
In addition to those possible replacement controllers you mentioned,
you might add the BZ MPPT 500 to the list. I've had a few issues with
them but that seems to have mostly sorted itself out. Very reasonably
priced for a MPPT controller, 100 Voc input. The catch is you've got a
500W output limit.
Bob-O
On Jun 30, 2009, at 1:26 AM, Walt Ratterman wrote:
Hello all,
Thanks to all of your responses, and particularly Rick’s confirmation
of the appropriate ranges for the SB50, it has become clear that these
panels can not be made to work with the SB50, and that the SB50 was
the wrong choice for these pre-fabricated systems, or perhaps better
phrased, the panels were the wrong choice for the controller.
Actually, it is probably more accurate that the panels were the wrong
choice because their characteristics severely limit the possible
options of what to do next.
I would like your input on what you think should be done here.
Nine systems were purchased from Earthwalk. One has been deployed for
four months. A second unit is being deployed now. This leaves seven
in the warehouse. (And we wont even get into the fact that we have
AGM batteries here instead of the advertised GEL batteries, and the
voltage is so low they might not even work……I will deal with that
separately…..)
While it is clear that the panels do not match up with the controller,
it is not clear why they are still working (other than the heat and
dirt) and if they will continue to work.
One solution would be to just leave everything alone and tell them
what they should do if the system(s) fail. In some cases, this might
be the right action to take. But in this case, I think the folks who
sold the prefabricated unit should be held accountable, and provide a
system that is designed to work properly. The schools paid good money
for this equipment and they should at least have a running start at
success, which is difficult to come by in this part of the world on a
good day.
So – when we tell the schools to insist that the system be fixed,
what do you think we should tell them?
Due to the characteristics of the panel (not being either 12V or 24V
nominal) they need a MPPT controller. I suppose we could tell them to
change to a controller that will accept the output of the panel. This
would be either Outback, Midnite Solar, or possibly the new
Morningstar 15A controller. Any suggestions?
The other route would be to have them change the panels, and keep the
prefabricated system as it is. Rick: what would you recommend the
best voltage / current combination to replicate the need for a 440 to
500 watt peak array output with the SB50?
Given the relative cost of the panels versus the controller, the
manufacturer may likely decide to switch the controllers, but it is
not as easy as it sounds. If either the Outback or Midnite
controllers are used, they will not fit into the small space the
cabinet allowed for the SB50. But I will deal with that another way.
(We will just build an all new cabinet here in Senegal).
So – any ideas or thoughts I have missed are welcome!!
Thanks so much for all of the great feedback. I think, like most of
us, every day is a learning experience, even if we think we have done
this 100 times before.
Take care,
Walt
From: Rick Cullen - Blue Sky Energy, Inc. [mailto:rick at blueskyenergyinc.com
]
Sent: Monday, June 29, 2009 10:14 AM
To: wratterman at sunenergypower.com; 'RE-wrenches'
Subject: RE: [RE-wrenches] Solar Boost Controller in Senegal
Hello Everyone,
The SB50's maximum input voltage spec it 57VDC. This should be
considered an absolute maximum above which the controller will be
damaged in a manner not covered by warranty. Our recommendation is to
not apply a total Voc at STC of more than 57V/1.25= 45.6V. There are
transient voltage protection diodes on both battery and PV inputs on
ALL Solar Boost charge controllers. These are not "tell tail"
indicators but real protection devices designed/selected to protect
down stream electronics from transient voltage damage resulting from
ESD, lightning, etc. On the PV side of the SB50 the protection diodes
will begin to clip at about 58-60V. They can eat a 1 millisecond 3000W
transient without damage, but will burn up if they receive more than
about 10W continuously. These two diodes are located right behind the
PV terminals.
In the application described below I would expect the SB50 to be
damaged. What typically happens with excess over voltage is the diodes
fail short, and then clamp PV voltage low and protect the down stream
electronics. If PV current is sufficiently high the diodes will burn
open and the SB50 may continue to operate since down stream devices
have somewhat higher voltage withstand capability, or it may suffer
catastrophic damage.
Why these systems continue to operate must be due to actual Voc not
getting high enough long enough to cause catastrophic damage. If the
controllers were to not switch to Float (unloading the PV's), the
brief Voc sample as part of MPPT may not have burned up the diodes and
they are successfully eating the excess voltage transients which would
seem to occur during the Voc sample. It may also be that the modules
are so hot that their actual Voc & Vmp are low enough that when PV
voltage is clamped to 60V by the SB50's protection diodes insufficient
power is delivered at 60V to burn up the diodes...
Needless to say, this is a situation that need to be corrected.
Technical Bulletin #100214 available on our web site describes proper
voltage, current and power sizing for all Solar Boost charge
controllers.
Regards,
Richard A. Cullen
Blue Sky Energy, Inc.
760-597-1642 x102
fax 760-597-1731
rick at blueskyenergyinc.com
www.blueskyenergyinc.com
From: re-wrenches-bounces at lists.re-wrenches.org [mailto:re-wrenches-bounces at lists.re-wrenches.org
] On Behalf Of Walt Ratterman
Sent: Friday, June 26, 2009 3:22 PM
To: 'RE-wrenches'
Subject: [RE-wrenches] Solar Boost Controller in Senegal
Hello,
I am in a very remote part of Senegal, (near the Guinea and Mali
borders…) and I have come across some prefabricated “plug and
play” American made systems installed for educational institutions.
The systems use two Sharp panels that are 220Watts, 33.6 Voc, 29.2
Vmp, wired in series, using #10AWG home run wire from the panels back
to the charge controller.
Charge Controller is a Solar Boost 50.
Batteries are Dekka AGM – two strings of 250AH, 12V batteries. (four
batteries total).
My specific question is about the controller. This is a 24V in / 24V
out charge controller with MPPT. I have not used this before, so I am
not familiar with the details of operation.
The data sheet that I downloaded says that the maximum open circuit
voltage is 57 VDC. But, this system is hitting the charge controller
with two panels of 33.6 VDC wired in series for 73.2VDC. So, why is
the controller not fried, or what am I seeing wrong here. I suppose
with the panel temperature being elevated maybe 35 degrees above 25
degrees and a resulting 17.5% loss, coupled with some voltage drop,
the system may actually be seeing less than the 57 volts.
But…..isnt this a dangerous way to design a system? (it will get
cooler here ….)
Or am I missing something?
What would be the appropriate application here….
Sorry, I cant do a lot of internet research from here – limited
download capability on the satellite….
Thanks!!
Walt
Walt Ratterman
SunEnergy Power International
11 Laurel Lane South Washougal, WA 98671
(360)-837-3680 ▪ fax (360)-837-1315 ▪ Skype Walt-Mobile
wratterman at SunEPI.org ▪ www.SunEPI.org
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