[RE-wrenches] Photosensor for 12VDC System with load controller

[Mick Abraham]

All one could do would be to test the car style relay. One brand may
tolerate an overvoltage on the coil better than another. First connect the
relay to your truck battery (engine running) and leave it energized a bit.
Feel the case to get a "baseline" temperature. Then hook it up per our
discussions and feel for heat. The PV voltage will be highest when the sun
first comes up but before the C12 controller hooks on. That should be a
brief duration.

I fear that you will find too much heat dissipation for good long term
reliability with this solution. If cost is the main problem with that
Grainger relay you mentioned yesterday, try eBay. If physical size is too
tight for a bigger relay to fit...but the coil runs too hot...you could try
adding a resistor in series with the DC relay coil. The downside here is
that the coil won't "pull in" until it sees a higher DC voltage.

Jolliness,

Mick Abraham, Proprietor
www.abrahamsolar.com

Voice: 970-731-4675


On Tue, Feb 1, 2011 at 6:47 AM, Jason Szumlanski <Jason at fafcosolar.com>wrote:

> Does anyone know if an automotive style 12V relay coil can handle the solar
> panel voltages common in a 12V nominal panel? This would be a low cost and
> small size solution that might work best in my case. A $6 relay can switch
> 40A – well over what I need to do.
>
>
>
> Jason Szumlanski
>
> Fafco Solar
>
>
>
> *From:* re-wrenches-bounces at lists.re-wrenches.org [mailto:
> re-wrenches-bounces at lists.re-wrenches.org] *On Behalf Of *Mick Abraham
> *Sent:* Monday, January 31, 2011 9:43 AM
> *To:* RE-wrenches
> *Subject:* Re: [RE-wrenches] Photosensor for 12VDC System with load
> controller
>
>
>
> Maverick's suggestion would give the opposite action to what the original
> poster needs. The C12 "night light" function turns the load on after dark
> but Jason needs the opposite.
>
> The solar array can serve as your "photocell", Jason. The PV +/- terminals
> in the C12 controller have no power on them at nighttime (check me on that
> with your voltmeter), but they are energized when there is sunshine. A relay
> coil connected parallel to the the PV +/- terminals on the C12 should fire
> when the sun is up and that coil would then release at sundown. Use a
> "single pole single throw normally open" relay with a DC coil, and connect
> the positive leg of your DC load across the normally open connection screws.
>
> Make sure the relay coil can accept a wide range of DC input, since it may
> encounter 20 volts across a 36 cell PV module when the sun first comes up.
>
> Jolliness,
>
> Mick Abraham, Proprietor
> www.abrahamsolar.com
>
> Voice: 970-731-4675
>
> On Mon, Jan 31, 2011 at 6:52 AM, Jason Szumlanski <Jason at fafcosolar.com>
> wrote:
>
> I have a customer with a Xantrex C12 charge controller with LVD controlling
> a 5A load. Their battery and PV are not large enough to run the load 24/7,
> and they don’t need it to run at night. I am thinking about recommending a
> photocell to disconnect the load at dusk and turn it back on at dawn. They
> are not interested in upgrading the PV and battery (too costly).
>
>
>
> Can anyone recommend a photosensor source, and maybe a model number?
>
>
>
> Other ideas welcomed…
>
>
>
> Jason Szumlanski
>
> Fafco Solar
>
>
>
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