[RE-wrenches] Third Radian

Fri Apr 21 16:20:10 PDT 2017

Greetings William,

I worked through this issue a little while back while designing and
installing a five Radian GS8048A system.  I designed a custom DC Bus
System which included two 1,500A, 150mV shunts.  One for metering DC
to and from the Radian inverter/chargers, and one for metering
combined charge controller production to the battery system.

Below I have copied and pasted a couple of sections of text from
OutBack Application Notes which you may find helpful.  I do not know
if using a mix of differently rated shunts is an issue or not; such as
one 1,000A, 100mV shunt and two 500A, 50mV shunts.  It is best for you
to speak directly with Applications Engineering at OutBack to inquire
and confirm details for your project.

Also; I suggest trying to find out from OutBack when the next
generation MATE System Display & Controller will be available.  The
MATE3 has a number of limitations and issues which will hopefully be
resolved with the release of the new MATE product.  It would be great
if you could get the new next generation product and not have to work
with the MATE3...  Assuming the new MATE will be better than the MATE3
and you would be upgrading to the new MATE eventually.

Also to note with multi Radian systems, or I believe any battery based
grid interactive inverter system with multiple inverters which have
H-bridge electronics architecture; the AC energy may flow to and from
the inverters sharing a common AC "Grid" combiner and AC "Out"
combiner.  The Radian's AC "Grid" and AC "Out" terminals/connections
are common with each other when the inverter is "selling" in Grid-Tie
Mode.  This allows energy to basically circulate to and from the
multiple inverters in the system before/as it is exported to its grid
connection.  This affects the MATE3 metering and graphing.  The more
inverters and power capacity in the system the more this is noticed
and the more the kWh values may be effected.  I believe this may also
effect system energy production efficiency as well.  This issue is
recognized in whole house back up systems and may not be noticed or as
evident in systems with dedicated loads continually served from the AC
"Out" connections.

I have attached 3 pictures of my custom DC Bus System with the two
shunts for reference.

This (below) from an OutBack FLEXnet DC (FN-DC) Application Note
(FA‐RP‐12/14/15):
"A Note on Current Shunts
Although OutBack products come equipped with 100A and 500A current
shunts, the FD-NC has the ability to work with shunts as high as
1000A. The only requirement is that the voltage and current ratio
(resistance) of the shunt remain the same. For example, the 500A
shunts have a ratio of 0.0001 at 500A and 50mV. A 1000A shunt should
have a voltage of 1000A at 100mV."

This (below) from an OutBack Application Note entitled "Wiring and
Combining Methods for Multi-Inverter Systems" (R1-RL-8/14/15):
"Shunts and battery monitoring
As with smaller systems, a separate shunt is needed for charge
controllers and inverters in order to monitor loads and charging
sources on separate battery monitor channels. When selecting a shunt,
keep the following design considerations in mind:
1) A/V Ratio The ratio of amps to volts for a shunt must be 10,000:1
for systems using the OutBack Power FlexnetDC (FNDC). An example of a
suitable shunt is one rated at 1,000A and 100mV.
2) Amps rating Shunt manufacturers recommend that a shunt not be
loaded to more than 66% of its rated capacity. This derating, combined
with the maximum 100mV limit on the FNDC, dictate that the largest
recommended shunt be rated at 1500A, 150mV.
3) mV rating The voltage drop across the shunt when passing the
maximum current for which the shunt is rated. For the FNDC, the
maximum voltage drop across the shunt should not exceed 100mV. That
does not mean the maximum shunt size is 1000A at 100mV. Taking into
account #1 and #2 above, the limit is 1500A at 150mV with a usable
current limit of 1000A. This ensures the maximum voltage drop across
the shunt is 100mV (when passing 1000A).
4) Dimensions Ensure that the dimensions of the shunt are compatible
with the bus bars specified and that the assembly (bus bars + shunts)
fit on the backplane of the enclosure.
The shunt design considerations above, combined with the FNDC’s
maximum current monitoring limit of 1000A per channel essentially
limit the system size if FNDC battery monitoring is to be included.
Practically speaking, this limits systems that are to include FNDC
battery monitoring to:
a) At most five GS8048/GS8048A inverters or ten 3.0kW FXR inverters
b) The same limits on FNDC battery monitoring limit the system to at
most twelve FM80
charge controllers. Due to the 1000A current monitoring limit of the
FNDC, large systems will have to be split up into smaller sub-systems.
For example a system with 10 Radians and 20 charge controllers could
be split into two sub-systems. Each would have five Radians, ten
charge controllers and an FNDC. This would keep the current seen by
each FNDC channel to below 1000A."

I hope some of this information may be helpful.  OutBack may have
removed some of the Application Notes regarding larger multi Radian
systems from their website.  Give a shout if you can't find what you
need, I may be able to help out and send you what I have on file.

Best regards,

----MATT

Matthew Sirum
P.O. Box 1227
Greenfield, MA 01302-1227  USA
phone: +1.413.773.0611
email: MatthewSirum at gmail.com

--------  Original Message Below  --------

[RE-wrenches] Third Radian

William Miller william at millersolar.com
Thu Apr 20 20:16:12 PDT 2017

Friends:

I am designing our first three 8K Radian stack.  I think I have a good
handle on the plumbing and wiring but I was wondering about one thing:
With three Radians and a PV recombiner, we are out of shunt ports on the
Flexnet DC.  Have any of you dealt with this?

My proposal is to gang the negatives for two or three Radians and run them
through a 1000A/100mV shunt.  The ratio is the same as the 500/50 offered.
Will the FNDC accept that analog input?

Any other considerations that might not be realized at first?

Thanks in advance,

William Miller

[image: Gradient Cap_mini]
Lic 773985
millersolar.com <http://www.millersolar.com/>
805-438-5600
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