12 volt differential controller [RE-wrenches]

[Tom Lane, Energy Conservation Services]

35 to 40 watt PV modules with the EL SID 20 PV by IvanLabs or a March 12
volt 809 with PV modules rated at 25 watts minimum to 30 watts maximum
should work with this system. The Laing D.C pumps are NOT RATED for
stagnation temperatures possible with solar DHW systems and should never be
used with solar thermal systems.

Gator Tom
----- Original Message ----- 
From: "Mark Downing, Hurshtown Alt. Power" <solarman4 at yahoo.com>
To: <RE-wrenches at topica.com>
Sent: Saturday, October 18, 2003 5:54 PM
Subject: Re: 12 volt differential controller [RE-wrenches]


> Darryl,
>
> This particular job only, I am using a Laing pump which has actually been
> discontinued.  Don't know the model number, but I bought a couple of them
> from Bob-O maybe 6 years ago.  It draws less than 0.3A.
> The collector is a 30 tube Thermomax.  The glycol passes through the
internal
> heat exchanger in a 80 gallon tank and then through a 66 gallon exchange
> tank.  Kind of a science project . . .
> The water to be heated is delivered to the tanks via a 12V RV pump.  A
> pressure tank is included so the pump doesn't spaz-out cycling off and on.
> The power requirements for this system was very minimal before they
> discovered showers.  This family of 10 was adequately supplied with power
by
> a single 40W module.  (This is an Amish household.)  Now that they use the
> heated water for showers and the washing of clothes their PV needs have
> grown.  I replaced the 40W module with a 100W last weekend.
>
> Mark
> --- Darryl Thayer <daryl_solar at yahoo.com> wrote:
> > Hi Mark
> > What is the pump and what size and type pump do you
> > use?  How big is the SDHW, and what type.  I ask just
> > for myself and other wrenches that normally do just
> > 110 volt AC DHW.  I have a customer that wants both
> > DHW and PV installed, so I am thinking of doing 2kW PV
> > and to steal some DC for the SDHW.
> > Daryl
> >
> > --- "Mark Downing, Hurshtown Alt. Power"
> > <solarman4 at yahoo.com> wrote:
> > > Yes I've thought of building my own, but not
> > > designing it.
> > > I was given a tip that Ivan Labs makes the
> > > controller I need, and I am for
> > > the time being going to see about getting one of
> > > these.
> > >
> > > --- Darryl Thayer <daryl_solar at yahoo.com> wrote:
> > > > Is not a differencial controller a comparator with
> > > > hysterisis?  A Schmitt trigger?  That is a simple
> > > > circuit to build, have you thought of building
> > > your
> > > > own?
> > > > Daryl
> > > >
> > > > --- "Carl Emerson, Free Power Ltd."
> > > > <freepower at freepower.co.nz> wrote:
> > > > > Kurt,
> > > > >
> > > > > I would like to swap to this approach but I
> > > suspect
> > > > > that it would take
> > > > > some time to optimize the threshold or
> > > insolation
> > > > > level that the pump
> > > > > comes on at.... or do you not bother.
> > > > >
> > > > > Also the pump will continue to run when the
> > > water is
> > > > > fully up to
> > > > > temperature unless there is a thermostat control
> > > as
> > > > > well.
> > > > >
> > > > > Maybe a combination of the two is needed and
> > > would
> > > > > be more efficient.
> > > > >
> > > > > Carl Emerson
> > > > > Free Power Ltd.
> > > > > Auckland. NZ
> > > > >
> > > > > sunwise wrote:
> > > > >
> > > > > >Greetings Mark,
> > > > > >
> > > > > >I'm not going to be much help regarding the 12
> > > volt
> > > > > controller but I
> > > > > >will mention a trend I see in the industry that
> > > > > does away with
> > > > > >differential controllers completely.  Instead
> > > of
> > > > > using such a
> > > > > >controller, a small (20 watt) solar panel is
> > > wired
> > > > > directly to a 12 volt
> > > > > >circulating pump (typically a Hartel HEH10).
> > > When
> > > > > the sun is shinning
> > > > > >on the flat-plate collectors it is also on the
> > > pump
> > > > > panel, etc.  These
> > > > > >systems work great, especially in off-grid
> > > homes.
> > > > > >
> > > > > >Kurt Nelson
>
>
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