solar power for security alarm system

[inetdog]

It can be done. But I have to ask why would you want to convert 12 volt DC to 120 VAC when the system only needs 12 volts? It is not necessary.

True only if you manage to defeat the AC-input failure sensor of the system so that it will still operate at full functional level instead of just low-function backup mode.

And at this point you're probably asking "why not just power the whole thing off 12VDC and forget the 120VAC inversion and the 16.5VAC step-down?" Great question. The answer is that I could, but the alarm system loses a lot of functionality when it loses the 16.5VAC input voltage and essentially the sytem, now operating only on 12VDC input, shuts down every non-essential function and just keeps the system functional until 16.5VAC is restored.

[Sunking]

It can be done. But I have to ask why would you want to convert 12 volt DC to 120 VAC when the system only needs 12 volts? It is not necessary.

OK th efirst thing you need to do is determine how many watt hours the system uses in 24 hours. If the transformer is 45 Va then the system obvisiouly uses less than 45 watts. Let's say for example it actually uses 30 watts. So the system would use 30 watts x 24 hours = 720 watt hours.

Next peace of information is the location so we can determine the winter Sun Hours to determine the panel wattage required. So for example let's say 3 Sun Hours in December and January.

So if it uses 720 watt hours in a day with 3 Sun Hours in winter you would need:

400 watt Solar Panel
40 Amp MPPT Charge Controller
12 volt 300 AH Battery.

So your job now is to give use the daily watt hours and location. Or just do it all yourself and read this post and it will tell you most everything you need to know.

[fraggedout]

I'm new to the solar aspect of powering devices, so be gentle with me. But one of our customers recently asked us to install an alarm system on a mini-storage complex that has been broken into a number of times and has no available grid power. It would be possible to get grid power to the site, but would be exceptionally expensive. I opened my mouth and said, "Why don't we use solar?". Customer said okay, so now I have to figure out how to make it happen.

Situation: A typical alarm panel receives its power through a 16.5VAC transformer (typically a 40VA transformer), which steps down the power from 120VAC to 16.5VAC. The alarm panel then converts the incoming 16.5 VAC to 12VDC for charging the internal backup battery (12V/7Ah SLA) and supplying 12VDC power to hardwired detection devices. I know that I can use an inverter to boost the 12VDC from solar backup batteries up to the 120VAC required by the 16.5VAC transformer and I'm guessing that such a small inversion draw would create a minimal drain on the backup batteries (compared to, say, a blow dryer) even though it's pretty inefficient to convert from 12VDC to 120VAC to 16.5VAC. And at this point you're probably asking "why not just power the whole thing off 12VDC and forget the 120VAC inversion and the 16.5VAC step-down?" Great question. The answer is that I could, but the alarm system loses a lot of functionality when it loses the 16.5VAC input voltage and essentially the sytem, now operating only on 12VDC input, shuts down every non-essential function and just keeps the system functional until 16.5VAC is restored. That's why it looks to me like I'll need to use a 120VAC inverter.

Here's my problem...being a novice and this being an important customer, I don't have the luxury of taking a lot of time and experimenting on his dime. When I quote him a price, I need to be pretty sure I can pull it off for that price. The unknown factor is I'm not sure how to figure the size of panels and storage batteries I'll need for this application. If there is someone is this forum that can help a solar noob get going with this project, I would be forever indebted. Thanks.