Alarm System - Off-Grid Power

I'm not qualified to comment on how you're building your system, but I've done a little disaster planning and failure analysis in my life.

Generally speaking, saying that a system "absolutely must not fail" is the wrong way to think about the problem. All systems have some probability of failure, and as you try to push that probability closer to zero, the costs go up exponentially.

The questions you should be asking yourself are: 1) What probability of failure are you willing to accept? 2) How much are you willing to spend to get there? 3) If something does go wrong, how quickly can someone be there to fix it?

If this is truly a critical system which has to have a minimum probability of system failure, usually the cheapest way to get there is through redundancy. Put in extra of everything, and design it so that any one component can break and you still can be functional. So extra panels, extra batteries, extra inverters, etc.

I'm guessing, though, that your real design goal is not "must not fail" but something closer to "as reliable as possible without spending any extra money." That's perfectly reasonable, just make sure your expectations are realistic.

Then fire the installer because he is incompetent. There is no justification for AC power or an inverter.

Impossible, all off grid systems fail no matter how much money you throw at it. Just 4 or 5 cloudy days and your system is down period unless you have an emergency generator.

Thanks for your input!

Correct, there are no absolutes. But I can't say "I'll be satisfied with 99% fail proof"... I'll do what I can to make it 100% fail proof, and deal with the failures when they present themselves... and learn from the failures/causes.

The redundancy I will build into the system is a circuit that bypasses the inverter and transformer in case one of them fail.
As far as the PV Panel, CC or Batteries is concerned, I can have that replaced the same day as the failure.
The Alarm sends a notification if the back-up battery voltage gets low... which gives me time to respond.

Thanks for your input.

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I built these Solar Lights for the Property Owner...
That is how we got to talking about an Alarm System Power Supply...
Unfortunately, He already has an "Alarm Guy"...

Well take it from a EE who designs critical electrical systems for telecom, data centers, banks, and military what you want is not possible regardless of how much money you dump into it. Switching from commercial power to solar even makes it more difficult and expensive because solar is so much more unreliable and unpredictable.

The more I work with Off-Grid PV Power, the more I am learning that, Sunking.

The best I can do is continue the quest of finding combinations of the most reliable components.

Your batteries will always be the weak point. Telcoms swap them out on a regular basis. Any battery over 2 years old would be suspect in a critical application. I'd also use AGM batteries. (2, 6v golf cart in series for 12V)

The voltage in a PV system will swing from 12v - 15V, and perhaps the alarm tech is concerned that the high recharge voltage will BBQ the alarm gear. That's the only thing I can see. So instead of an inverter (of which I would use the Suresine 300 which is quite robust) you may use a DC-DC supply, and let it make the alarm circuit happy. There are some good Telcom 48-12V adapters, but that means 4, 12V batteries, larger PV & controller. Other 12v-12v adapters are not as robust, methinks.

Also a lot of 24 to 12 volt.

Thanks!

Don't do that, just one one single battery. Odyssey makes a 120 AH @ 20 hour rate in a 12 volt battery. At your discharge rate more like 160 AH. PC2250

No golf courses on that island ? But there are some nearby? The batteries will be the thing you don't want to skimp on, (well, if it's mission critical, skimp on nothing)
Just be sure the ones you get are indeed AGM, not GEL, they are different beasts.

Wiring the alarm without the inverter could void the warrantee on it. I'd say the installer is just covering his ass should anything go wrong.

WWW

I knew I'd get backlash for the 2xparallel set-up...
but really the only way with local suppliers I can obtain the needed 140ish AH with AGM.

No PC2250 available locally... the only other Ody sold locally is the 100AH PC2150... but out of stock.

The Interstate Batteries Distributor has a PC2150 equivalent for $500+++
When asked what the AH rating is, he told me they don't sell batteries by AH... they sell them by CCA.
I refuse to deal with them.

I have more confidence in parallel than I do Interstate.

Seriously, All the 6volt batteries I have found locally are Flooded.
The cost to freight anything of that weight here is absurd.
Another important factor is replacement availability.

*Limited Selection of Deep Cycle Batteries is a price we pay to live in the middle of the Pacific.... and it sucks.