I have a few remote sensors that needs 'embedding' in inaccessible positions but which have to last for years (ideally 10 years). The problem is that the mains supply will be cut off for 8 to 14 hours every day and completely for 3 days or so every 4 to 6 weeks. I thus need a battery that will spasmodically (4-6 weekly) be discharged down to (say) 30% of capacity (or whatever is prudent) and daily be discharged a few percent and subsequently recharged.
What battery chemistry am I looking at here and how must it be electronically handled.
you will need: AGM (absorbed glass mat) sealed lead acid gel cells a 4 stage automatic charger (bulk, boost, top, and float stages) a load controller a voltage stabilizer with low voltage cut-off.
given the current draw for your equipment, you need a battery bank that will delivery (draw * 200) amp/hours of capacity... that is approx 72 hours * 3 so you never take the batteries below 1/3 discharge except in extreme contitions
the voltage stabilizer is a 13.8 volt boost converter that will run on 10-14 volts in... as your batteries discharge, their output voltage will drop.. the stabilizer will make sure you have a precise output voltage no matter the condition of the batteries for equipment that is sensitive to input voltage fluctuations. The stabilizer you choose should have a low voltage cut off so that if the battery voltage drops to 10v, everything gets cut off -- this protects the battery from over-discharge which will cause damage and shorten the life of the battery. Stabilizers are readily available for up to 40 amps load.
Lastly you will need a load controller to make sure that when mains power is up, the battery system is isolated from the load.. this should cut over when the voltage from the mains power supply drops below 11 volts. Depending on how criticaly your supply voltage must be regulated, you may want to put the stabilizer after the load controller.
that might be a good idea for carrying some of the load during those planned 3 day outages -- but I wouldnt count on it as part of the load handling capacity, and it just adds complexity to a system that already has a "reliable" means of recharging the batteries.
I forgot to ask ?? is your equipment line powered or does it run off of 12V ?? if its line powered -- there is an easier solution
The Xantrex Freedom series of charger/inverters handle up to 3000 watts load of AC load, include the 4 stage smart charger for your batteries, and will automatically cut over from charger mode to inverter mode when the AC mains are lost. Then all you need is enough batteries to meet your total load requirement for 9-10 days.
The batteries I use for reserve power for my ham radio systems come from cell phone tower reserve power systems and are rated for 10 years life -- the cell companies regulary replace them after 4 years, and they show up on the surplus market with plenty of life left in them.
PowerSafe SBS C11
with your slow discharge rates, and if you dont deep discharge them regularly, they would probably last a bit longer than that !!
Solar cells are usually rated for 10% degradation over 20 years life, but you still need a battery system to hold the power, and a charge controller to perform the 3 or 4 stage charging process required by SLA batteries
ok -- since you didnt give a voltage, I cant compute power... so I'll assume
12 volts at 400mw (1/2 amp close enough) * 200 hours reserve capacity is 100 amp hours required, and you can get that from a single SLA... a 10 amp SLA smart-charger will restore full charge on a fully drained drained battery in
10 hours or so... which should have no problem recharging the system in 3-4 hours after your planned 3 day outages.
There are some 3 panel 150 watt solar panel systems that include a charge controller on ebay reasonably priced (
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Many thanks,
Don Lancaster voice phone: (928)428-4073
Synergetics 3860 West First Street Box 809 Thatcher, AZ 85552
rss: http://www.tinaja.com/whtnu.xml email: don@tinaja.com
Please visit my GURU\'s LAIR web site at http://www.tinaja.com
your right -- my bad -- I saw it as milliamp :) Can the attitude -- everyone makes mistakes now again :)
ok -- 400mw or 1/2 w and 200 hours = 100 watt hours -- at 12 volts you could cover that with 10 amp hours with some spare.. at 3v (lithium) need 33 amp hours (at about 2 amp hours per cell from googling various batteries -- call it 16 cells with some headroom)
so a small gel cell or a triple handful of lithium AA size batteries
The gel cell is still cheaper -- the battery charger is about equivalent in cost considering there are off the shelf charge controller chips for both types of cells
Many "emote" alarm sensors use a Lithium battery and there is no provision for charging; most claim a lifetime of 5 years or more. There are re-cheargeable Lithium batteries that might be worthwhile for comparison purposed during component evaluation and survey. You give no idea as to how much power drain there will be durint useage, you give no idea of the device will have "sleep" and/or "power down" modes, etc & etc.
Now where in the heck did you manufacture the voltage he needs as well as the power/current he needs? Maybe he needs 3V at a microamp (max); a Lithiumcoin cell will do for at least 5 years. Maybe he needs 440VAC three phase at 10,000 amps continuous load. There is no clue.
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