Automatic switching from Battery to Grid on a small system

[davecook89t]

How many days do you want the security system to stay up, in case of blackout or storm damage ? 3 days? 8 days ?

Power outages in the 3 or 8 day range that you are postulating could only occur in the event of a major hurricane. In such a case, I would not expect to have constant access to my security cameras. If I were fortunate enough to have the solar panels remaining in place on the roof after a hurricane, I would hope to get at least a few hours of video per day from solar power, even if the power company could not repair the lines for a few days. Under those circumstances, I would be happy with that.

Just build a big super sized UPS with enough battery. Forget the solar, if you are not there to keep the leaves/debris/palm fronds/lawn chairs off of it

The UPS that died cost maybe $50 and could have kept my system running for perhaps a half hour if the power went out. If I were willing to spend hundreds, I might be able to get a few hours of continuous service in the event of a major power outage, but how is that better that what I would get with solar? Thanks for your honest advice, but I am not going to forget the solar. (I thought this forum existed to help people implement solar solutions, not to discourage them from doing so). My panels are hooked up in parallel, so a few stray leaves will not cut my power. So far after 3 months of admittedly calm weather, there has been little in the way of clearing debris that I've had to do.

I'm still hoping to find someone who has a solution to my switching problem. I can't imagine that no one has ever thought of doing this. I'm pretty sure there are electronics out there that will do what I'm asking. I've seen several possibilities on Amazon and elsewhere, but before I order anything, I'd like to know that they will work.

[inetdog]

I'm still hoping to find someone who has a solution to my switching problem. I can't imagine that no one has ever thought of doing this. I'm pretty sure there are electronics out there that will do what I'm asking. I've seen several possibilities on Amazon and elsewhere, but before I order anything, I'd like to know that they will work.

Your basic problem of instability comes from the fact that when the relay trips on low voltage the removal of load and imposition of charging current, however small, from the panels if the transition is during daylight immediately raises the battery voltage. Which causes the relay to change state, and so on.

The classic solution to this kind of problem is to introduce what is called hysteresis into the switching process. Simply stated you want the difference between the switch-to-grid voltage and the switch-to-batteries voltage to be large enough to cover the jump in battery voltage when you remove the load.
Mechanical relays usually are designed in a way that automatically gives you a pretty wide gap between the drop-out voltage and the pull-in voltage.
If you are using a relay specifically designed for low hysteresis or a solid state relay without enough hysteresis designed in you will have to provide it externally.

One simple way to do it, not necessarily the best way, is to use an auxiliary contact set on the relay to put a diode or two (or a zener diode) in series with the relay coil input as soon as the relay switches on low voltage. That forces the voltage to rise by the additional diode drop plus any built-in hysteresis before the relay switches state back.

[Mike90250]

So, I personally do not sell any solar components. I don't have skin in the game. I call 'em as I see 'em.
Your situation could certainly be done with solar.

It can be done for less then half the price with batteries, inverter/charger with a transfer relay, Without getting into the nasty business of holes in your roof, wondering f the neighbors lawn chair that your cam captured flying past at 80 mph is going to end up on top of your panels. With hurricanes, you are looking a simple power outages for 3-5 days, unless your site got hit hard. If your site got hit hard with 3 weeks outage, your panels are not likely going to be functional anymore anyway, flying debris will remove them.

I want people I consult with, to be happy. If you require a solar solution to be happy, there are many peddlers that will sell you something big and expensive, and then you will find it stops working when the panels get smashed, or the cell sites that relay your video, go down.

I'll keep my eyes open for a relay that will solve the chatter problem.