48V relay question [RE-wrenches]

[Jeffery Wolfe, Global Resource Options]

Geez Allan, you're a true wrench. EVERYONE else is listening to history
being made by the Boston Red Sox who just knocked Clemens out of the game!
(4-0, Red Sox).

Not that I'm a big fan or anything, but...



-----Original Message-----
From: Allan Sindelar [mailto:allan at positiveenergysolar.com]
Sent: Thursday, October 16, 2003 8:06 PM
To: New wrenches posting
Subject: 48V relay question [RE-wrenches]



Fellow Wrenches,
Here's a fun one that I could use advice on, please:

We are installing a 48V full Outback PS2DC system for a new offgrid
residence. The client already had an ETApump 48V PV-direct deep well
installation, with an array of 7.9A @48V nom. The well pump is feeding a
storage cistern, with a separate 48V Booster Pump on a DC line from the home
power system for its power.

I would like to use the float switch to actuate a relay that directs the
well pump array through an additional pair of conductors to boost the home
array input. This way, in winter when water use is low, this array adds to
battery charging capability once the cistern is full. I would like this to
be automatic, hence the relay. Switching to battery-based ETApump operation
is not an option.

48V relays are hard to find, because standard coil/contact units have arcing
problems at higher DC voltages. I can use an MDI 48V-coil mercury contactor
(as used in the old APT Powercenters) but it's a single action relay
(normally open is standard), and I need both NO and NC to easily direct
power between two loads.

Is there a way I could use the ETA reverse-action float switch circuit to
control this? Can the float switch also power a relay coil, so that
close-on-rise also activates a 48V relay? Could I bypass the float switch
control in the ETApump controller, and simply let the float switch divert PV
input power away from the pump when the tank is full? Could I use a
dual-action float switch (3 wires, both NC and NO action in the same switch)
to control a NO relay?

Any good ideas would be appreciated. Must be simple, reliable, and
foolproof.

Thank you,
Allan @+E

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