Is there a solar controller to switch to AC power if DC goes to low

About a year ago now I got a 100 watt solar panel. Now I have 3 big marine type battery's for it to charge. They are out in the garage with a 50 foot power going back to my room for the ARM server. I had it run a ARM server with 2 hard drives. 12 volts right in for the hard drive. Use a USB 12 volt to 5 volt to power the ARM server. It worked good on 1 battery for about a mouth till power went under 12 volts on about a week of cloudy days. So for a long time I gave up on it. I have to run a fix disk on the hard drives then.

Now I have it powering my arm server again. But I got a Low Voltage Disconnect on it now From Rogue Engineering Inc. Only had it like this about 2 weeks now and its working good. Have not got the power turn off yet. It is set for 11.5 volts to cut off and says will do power back at 12.5 volts.

I like it to not turn off. If the 12 volts goes to 11.5 then have a 12 volt power supply that gets it's power from the wall plug AC power. To switch to that till the battery's get back up to 12.5 volts. Or just have a AC plug on the solar controller with a 12 volt power supply built in.

Looked and I can not find any solar controller like that. At lest that don't cost $1000's and as big as a closet.

Seems like others would have this set up too but I guess not, because so hard to find a solar controller to switch to AC power if the 12 volts gets to low and switch back when the 12 volts get back up in power.

So any one know if there is a solar controller like this? Or know any one that all ready has a set up like this?

Guess people would like to see how I got the battery's I will put a photo in here of them.
Attachment not found.


-Raymond Day

Comments

  • BrluxBrlux Posts: 73Solar Expert ✭✭✭
    I have a less elegant simple solution , get an adjustable 12V power supply and a power diode. Put the diode in the positive lead form the power supply and then tie it to the battery bank. Stripe on the diode to the battery positive, other side of the diode to the positive power supply, negative of power supply to negative of the battery.

    You can then set the voltage of the power supply for where you want to power supply to start taking over. There will be about a .5V transition period (assuming a power Schotkey) where the lower it goes below the power supply set point the higher percentage of power will come from the power supply. about 0.5V below the power supply nearly all the power will be from the power supply. When the battery voltage is higher than the power supply the diode will be reverse biased and no power will come from the power supply. You did not say how many amps you server draws but just make sure your power supply can handle 100% of it if needed. Here are some examples of the type of power supplies I am referring to.

    http://www.amazon.com/Universal-Regu...v+power+supply

    http://www.amazon.com/Universal-Regu...v+power+supply

  • john pjohn p Posts: 814Solar Expert ✭✭
    A simple low voltage switch will easily do the job it just needs to be connected to the batteries. it will auto switch back to battery when adequately charged,,and the off voltage can be set over a wide range same for reconnect. use it to operate a double pole double throw relay to switch between inverter and grid output..
  • RaymondRaymond Posts: 4Registered Users
    Thank you I did not think of a diode that makes power only go one way. My server is taking 0.7 amps. That is what the solar controller shows mostly. It can go to 0.3 some times. I guess that can go up to about 2 amps when the hard drive spins up and as it's spinning a little lower then that. I thought of this power supply. would work or something like that.

    Any thing like a wiring diagram to show how to hook it up? I would have to know what type diode to get. I have a 100 watt solar panel on this.

    To bad they don't all ready make a solar controller like this.

    -Raymond Day
  • BB.BB. Posts: 27,686Super Moderators admin
    Probably would be better to simply have a 12 volt AC charger "turn on" to recharge the battery bank if the voltage fall below ~12.0 to 11.5 volts minimum (under light loads).

    Now you have a solar based UPS (uninterruptable power supply) system. Best of both worlds.

    Use a voltage controlled switch that turns "on" at 12.0 volts and turns off at 14.2 volts or so. Use the output to turn on a 120 VAC relay on the charge controller's AC input.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • BrluxBrlux Posts: 73Solar Expert ✭✭✭
    You really want an adjustable power supply. This 2A one sounds like it should be enough for your needs. It has a small pot for changing the voltage. You can change the voltage depending on the level of discharge protection vs harvesting of solar power you want to do.
    http://www.amazon.com/Universal-Regu...v+power+supply

    This diode should work.
    http://www.amazon.com/Signal-Gleichr...Schottky+diode

    Here is a quick image search that yielded a similar idea. Your power supply will be in the place of the solar cells in this image. Your existing solar/charge controller will stay attached to the battery as it is now. The image shows a 2 series 2 parallel 6V battery configuration, like golf cart batteries but you know what you have with all parallel 12V batteries.

    ser_par3.gif

    The advantage of this setup besides cost and simplicity is it will allow to actually use the majority of your solar power while protecting your battery from over discharge.

  • RaymondRaymond Posts: 4Registered Users
    Still looking if they have something that would work. I found this web page. But I don't think any of them would work for how I want to use them.
  • RaymondRaymond Posts: 4Registered Users
    Been looking at the Mini-Box.com link I posted here. On there "PicoUPS-100 12V DC micro UPS system /battery backup system" It says this:

    "The picoUPS-100 will automatically switch in between V(In) and Batt depending on who has a higher voltage. The switching hysteresis is as low as 10mv. As a result, when AC/DC power is lost, the picoUPS will automatically switch to Battery output. The switching speed is about 100nS." So all I have to do is hook up some 12 volt power supply to it from the AC wall power and if the battery is over 12 volts it will stay powered by the battery/solar power. I guess I could put like a resistor on the wall 12 volts to get it just under 12 volts so it stay on the battery/solar as long as it can.

    It all so says "NOTE: Unit will work as low as 6V, but battery will not be charged if V(in) is lower than 15V! " so if I just have a 12 volt power supply on it it should not charge the battery's just the solar will.
  • BB.BB. Posts: 27,686Super Moderators admin
    Raymond wrote: »
    Been looking at the Mini-Box.com link I posted here. On there "PicoUPS-100 12V DC micro UPS system /battery backup system" It says this:

    "The picoUPS-100 will automatically switch in between V(In) and Batt depending on who has a higher voltage. The switching hysteresis is as low as 10mv. As a result, when AC/DC power is lost, the picoUPS will automatically switch to Battery output. The switching speed is about 100nS." So all I have to do is hook up some 12 volt power supply to it from the AC wall power and if the battery is over 12 volts it will stay powered by the battery/solar power. I guess I could put like a resistor on the wall 12 volts to get it just under 12 volts so it stay on the battery/solar as long as it can.

    Just to be clear, as I understand the picoUPS is a DC to DC type ups system. The logic to switch a DC power system is pretty simple. If DC power is below 12.6 volts on the "primary" DC power input (say from AC power), then switch over to battery power.

    For an AC UPS system, it is much more difficult. One of the problems is that the 120 VAC sine wave goes through zero voltages 120x per second (60 Hz AC cycle). So, the UPS hardware/software has to figure out when the AC power is no longer a "sine wave" but a failing sine wave. That is why it typically takes a ~1/2 cycle to figure out the AC power has failed, and switch over to AC inverter output and disconnect the AC mains.

    For critical systems, nominally they are just wired to the battery bank directly. Either the AC charger "floats" the battery bank at ~13.6 volts or if the AC mains fail, the battery voltage falls to ~12.7 volts or less, and the battery now supplies the current needed to run the loads.

    I can see soem advantages to the picoUPS (you can replace the battery bank without turning off your DC loads, possibly longer battery life as battery does not see "ripple current" from loads, more accurate charging voltage to battery, if it has a "nice battery charger"--that would be one less component to worry about, etc.)... I am not sure it is really needed for most people.

    Generally, you should not use a resistor for dropping voltage to charge a battery bank... Generally the DC loads are variable, so the current through the resistor is variable too, and the voltage drop is therefore variable and not very useful.
    It all so says "NOTE: Unit will work as low as 6V, but battery will not be charged if V(in) is lower than 15V! " so if I just have a 12 volt power supply on it it should not charge the battery's just the solar will.

    Many "12 volt" power bricks are "unregulated" -- they just output a roughly filtered DC voltage between 12 and 19 volts or so (some AC ripple from the AC to DC conversion circuitry).

    You can get a simple/cheap AC to DC converter and use the picoUPS own battery charger to keep the battery happy.

    Turns out that charging a lead acid battery is more complex than just putting 13.6 or 14.2 volts on the battery. There is time, temperature, depth of discharge issues, type of battery (flooded cell, AGM, GEL) that all affect the design & operation of a battery charger. If the picoUPS charger is relatively "smart", it can extend the life of your battery significantly. A typical "cheap" UPS system batteries really only last 1-2 years before they are significantly damaged by the UPS hardware/method of charging.

    In theory, you use just need a DC power source that is >15 volts for the system to charge the battery bank and run the DC loads. It will let the battery power the DC loads down to ~6 volts. But in reality, the Lead Acid Battery chemistry does not have any "useful power" below ~10.5 volts (dead and damaged battery bank).

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • JoshKJoshK Posts: 232Solar Expert ✭✭
    Bill, not sure if the forum notifies you or not, but I sent a message to you with the PM if you want to take a crack at it. If not it's fine, I'll watch for a reply either way.
  • BB.BB. Posts: 27,686Super Moderators admin
    Yes, I got your message but real life is taking a lot of time right now. ... At emergency vet with our pet rabbit waiting. Think he will be/is ok.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • JoshKJoshK Posts: 232Solar Expert ✭✭
    I hope the rabbit's ok. There is no urgency or anything. In fact you don't need to tackle it if you don't want. I didn't think vBulletin notified recipients. I recently discovered I had 10 'messages' I didn't know about two days ago. They weren't really messages, but none the less...
  • BB.BB. Posts: 27,686Super Moderators admin
    With Doctor right now.

    The current software does not email notify other than the little red counter in the top right of screen.

    A new update may add the email notification back.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • BB.BB. Posts: 27,686Super Moderators admin
    We are back home and the bunny does appear to be healthy. ...

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
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