Inverter with periodic enable (power-up)

[Riley5781]

Hi Folks -

I have an unusual requirement as I design an "off-season" add-on to my off-grid cabin power system. The basic idea is to enable power/inverter periodically (from a second set of less expensive batteries). This would allow for periodic network communications with the on-site network, cameras ect.

The goal is to avoid cycling my expensive battery bank in the winter time when there is no sun. I would likely exercise my generator once every 2 weeks or so to charge things back up again. If I allowed this inverter to run 24/7, it would be too big a drain on my small back-up battery bank. So to reduce that, I was thinking to only enable the inverter for a couple of hours a day. That would all I need to keep an eye things.

Of course I could also make use of the stand-by feature on most inverter but that would require that I somehow disconnect the load of my communications systems. That's not that simple unless I use a mechanical timer(?) on the output of the inverter (will think about that).

Anyway - does anybody know if there is a smaller inverter that has a feature where it would turn on periodically based on a real-time clock ?

[organic farmer]

What you are asking for, is really difficult.

I have a friend who volunteers for a state Fish & Game group, they maintain a 'youth camp'. That camp has a solar-power system AND it eats batteries. They keep looking for some magic to make their system perfect. But it eats batteries.

The best that I know to advise you is this. Set it up as if you were going to be there every day. But only turn on one 40-watt light bulb. If your system is viable, it should be able to power one 40-watt lightbulb 24/7. Then walk away and stop messing with it.

[Riley5781]

What you are asking for, is really difficult.

I have a friend who volunteers for a state Fish & Game group, they maintain a 'youth camp'. That camp has a solar-power system AND it eats batteries. They keep looking for some magic to make their system perfect. But it eats batteries.

The best that I know to advise you is this. Set it up as if you were going to be there every day. But only turn on one 40-watt light bulb. If your system is viable, it should be able to power one 40-watt lightbulb 24/7. Then walk away and stop messing with it.

Actually what I am doing is preventing eating the batteries in my main system and instead run a low power system just for my communications network. Not that it matters but my main battery bank is now 5 years old and working perfectly and I want to keep it that way (design goal is 7 year lifespan). What I do is in the off-season, I totally shutdown my main solar power system (disconnect batteries) and shut the entire system down. This avoids cycling the batteries and also leaving them in a discharged state and sulfating them.

But I want to have periodic access to my network and sensors in the off-season so I am designing a completely separate system with a different (low cost) battery bank. I will leave my main system off. I only need periodic communications. in the 'off-season', This secondary system that doesn't need much power (approx 20W to 30W) to power my wireless WAN link and security cameras (USB powered).

What I am now leaning towards is avoiding the conversion losses of going to 120VAC and instead source some DC/DC converters to feed my PoE link to the Wireless WAN radio and a couple of DC/DC USB chargers. My onsite generator can run once a week or so to charge up my secondary battery bank.

Trust me, this is all very do-able. It's just matter of the power budget of my communications gear, cameras and sourcing the right equipment.

[organic farmer]

Almost sounds like you would be better off with a small generator.

[Riley5781]

I will use my on-site generator to charge the small battery bank. I need to run it periodically run it anyway on it's own timer. I likely won't bother to connect any solar panels to this secondary system since in the winter time, they won't help much. The genny runs once a week for an hour or so... and it can charge the small battery bank then. I need to do some math on this but none of this is rocket science.

My main goal is to just to keep an eye on my cabin given it's remote location without fear of damaging my main 48volt battery bank. Some folks do something similar with their main battery bank but it's risky. If the generator fails to start, it's costing them $3500 in batteries. Worst case with my secondary system is $150 for a deep cycle 12V battery.

[organic farmer]

I will use my on-site generator to charge the small battery bank....

Should be more than enough, ... for periodic network communications with the on-site network, cameras ect.