[RE-wrenches] Using same PV array for water pump, battery charging

[Matthew Sirum]

Greetings Larry,

I can think of a number of ways this may be done.  Not knowing the
details of the existing system configuration, if the switching needs
to be manual or automatic, what (if any) cycle of the NEC is in effect
at the project location, and if the PV array is ground mounted or
mounted on a building I do not know what design thoughts/suggestions
may be most appropriate and helpful.

If I understand the general goal and manual operation is acceptable
this could be as simple as installing an appropriately rated
double-throw switch (on-off-on switch) or transfer switch into the PV
output circuit between the array and the charge controller.  The PV
output circuit would be the feed to the switch and the charge
controller and pump would be the selectable loads.  Some details to
consider for this would include; if the double-throw switch or
transfer switch is load break rated or not, where the array over
current protection device(s) (OCPDs) and disconnect(s) are located,
where the charge controller input disconnect is located, and if and
how this configuration impacts any GFDI (Ground-Fault Detector
Interrupter) and AFCI (Arc-Fault Circuit Interrupter) protection
provided by the charge controller or other components in the system.
Proper labeling and signage for sequence, operation, safety, and
applicable NEC requirements will need to be considered as well.

I installed some double-throw switches manufactured by Eaton not too
long ago.  I believe they were 250VDC rated.  If you are interested in
looking into double-throw switches you may want to call the folks at
the Eaton Flex Center (1-888-329-9272) to get assistance with
specifying an appropriate double-throw switch.  Circuit breaker type
bypass assemblies and transfer switches are available and may be less
expensive than a double-throw switch, but these may not be readily
available with the DC rating this project requires and most I have
seen are only rated for indoor installation.  I am not sure if you
will be looking for a solution which will be installed indoors or
outdoors, but this is a detail to consider.

If you are looking for an automatic or semiautomatic solution I
believe the Magnum PT-100 charge controller does have an auxiliary
relay which can be triggered based on battery system voltage.  I have
not worked with the PT-100, but it is my understanding it needs to be
networked with a Magnum remote control to use the auxiliary relay
based on battery voltage.  This auxiliary relay could signal an
automatic transfer switch system or contactors to perform the needed
switching.

Also; I believe Morningstar has a DC transfer switch for use with
their 600VDC TriStar charge controller...  I do not know if they may
offer this as a separate item, but you may want to reach out for them
to inquire as well.  Learning the details about the switch they use in
their product and sourcing it as a separate item could provide you
with a solution you custom build to suit the project.

I hope you may find some of these thoughts helpful.  Please let us
know how you proceed and how it all works out.

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] Using same PV array for water pump, battery charging

Starlight Solar Power Systems larry at starlightsolar.com
Thu Feb 16 14:24:44 PST 2017

Hello Wrenches,

A customer has 3250 Watt PV array @ 139Voc. The PV controller is
Magnum PT100. He wants to install a Grundfos SQFlex pump and be able
to switch the DC from the PV controller to run the pump directly. He
would like to switch midday after the battery (48V) is at a high SoC.

I’m looking for a switching arrangement to do this without arcing
since it will be used a few times each week. Any have a
recommendation?

Thank you,

Larry Crutcher
Starlight Solar Power Systems