I'm working on powering my arduino via a 12V SLA that will be charged with a solar panel. I've got the solar and battery bit worked out, and I'll be putting a regulator between the battery and the arduino just to be sure since a 12V can go to 13.X and that's a no-no for an arduino.
Anyway, here's my thought. If it's cloudy outside, the panel itself maybe providing say 12.X volts or even 11.X and probably still a fair amount of current, most likely plenty to run the arduino, but that won't charge the battery. I was thinking that to save the battery on a cloudy day, I could provide the arduino with two sources of power, the battery (via a regulator) and straight from the panel through a regulator. So I'd have two parallel regulators, one for the panel and one for the battery and combine them just before going into the arduino. Can anyone tell me if that will in fact help reduce battery comsumption. Will it just pull equal amounts of current from each providing it is available? What if the board needs 300ma and the panel is only giving me 100. Will it use 200 from the battery, will it use all 300 from the battery? That's really my question, if I hook it up to two regulators from different sources how does that react? Thanks everyone.
That's really my question, if I hook it up to two regulators from different sources how does that react? Thanks everyone.
The simplist method to do this is to use two diodes to form a 'or gate' for current steering. The output of each regulator would wire to the anode lead of a diode. The two cathod leads of the diodes would wire together and then wire to the Arduino external power connection. Whichever voltage source is higher would supply 100% of the current being drawn by the Arduino.
That wouldn't really work would it, because the regulators are going to put it at 5V regardless, so neither would (or should) really be higher than the other. Also, this setup wouldn't result in battery saving, because on a cloudy day, the battery voltage would be higher. My thought is that on a cloudy day, the solar panel is still good enough to drive the arduino, but not good enough to charge the battery (from what it has used up the previous night). So instead of letting the arduino run off the battery more and have the solar panel energy do nothing, let the battery do nothing (being saved for over night) and have the panel run the arduino. I should mention that the battery will be big enough to run everything for many days even w/o solar charging, I'm just trying to maximize any and all sun.
Well the regulators will provide their rated regulated voltage as long as the input voltage is above the drop-out voltage rating of the regulator.
Another method might be to measure the raw voltage of the solar panel's output (via voltage divider to keep it below the 5vdc measurement limit of an Arduino) and let some program logic you write determine when you should switch voltage sources using relay or semiconductor power switching.
That's certainly an option. I might be a little short of pins though, so I'll have to think that one over.
I wonder though if we just thought of the solar panel and the battery as power supplies. If I have two power supplies and one can deliver 100mA and the other can provide 1000mA and I hook those both to a circuit that needs 500mA, what will each supply provide? There's gotta be math for that
If I have two power supplies and one can deliver 100mA and the other can provide 1000mA and I hook those both to a circuit that needs 500mA, what will each supply provide? There's gotta be math for that
Can't think of a simple way to do that without a lot of external feedback electronics to control the regulators.
basically the two power supplies will not have the same amount of voltage output, so the one with the biggest output supplies all the power plus puts current into the other supply. This is normally a bad thing.
In practice there is usually a voltage / current droop and so the one drawing the largest current will drop furthest and so will drop below the lower one. Then the lower one supplies the current. Eventually the reach an equilibrium position where they share power but not equally.
You need to know the output impedance and the voltage / current curve for each before you can do the maths. In practice resistors are used to increase the output impedance and get them to share better. However, a series diode will prevent back charging in the event of one supply collapsing.
If I were doing this and didn't want to pop for an expensive solar controller I'd connect the solar panel through a diode to the battery to prevent discharge during low light conditions. Then I'd take a 9 V low drop out regulator and drive the Arduino from that. If the solar panel doesn't have enough energy to charge a 12 V source, it probably doesn't have enough current to run the Arduino. Rather than mess around trying to get the last ounce from the panel, I'd opt for a larger battery and/or more solar panels.
If getting the most efficiency from a solar panel is your goal, get a good charge controller.
basically the two power supplies will not have the same amount of voltage output, so the one with the biggest output supplies all the power plus puts current into the other supply. This is normally a bad thing.
This seems like a good thing to know - if you saw my FAQ post a few weeks back, I purchased a couple of ECI digital power supplies; I was wondering if I could parallel the voltage outputs to gain more current output, but it seems like that may be a bad thing...?
I know I have seen web pages detailing paralleling PC power supplies for more current output, generally in the position of using a PC power supply as a bench supply. Is this just as "bad"...?
Something tells me that it could be. Is there any way of using two power supplies at once on a single project to increase current, or is the only option to use them for separate voltage sources (if needed) in the same project?
Something tells me that it could be. Is there any way of using two power supplies at once on a single project to increase current, or is the only option to use them for separate voltage sources (if needed) in the same project?
Generally if you use wired diode isolation, multiple supplies will work together to be able to supply more current then any one supply can supply.
What happens is that as the PS supplying the bulk of the current sees an increased load it's output voltage will begin to sag due to it's internal impedance limit, and as it's voltage droops another supply will then have a higher output voltage then the first and it's diode will start to conduct and supply current to the load. Eventually the multiple supplies will come to a balance where the load gets it's total current demand but each supply is handling only up to it's own current limit.
We had such a design used in a large process control rack that used dozens of +5vdc, +/- 15vdc supplies and diode isolated from each other and then wired to a common DC power buss that all the loads wired to. There was probably 200amps of +5vdc flowing but each individual +5vdc supply was only rated for 20amps or so. It was a Foxboro Spec-200 control system.
AverageGuy....I'm going to need a charge controller anyway simply because the solar panel can get quite a lot higher in voltage than the battery and it's got enough amperage to damage the battery without.
So retrolefty, are you saying that you believe that having the battery on its own regulator then a diode joined up with a regulator straight off the panel with its own diode will some to balance itself.
If this is correct, as the panel can provide more and more power (voltage is higher and more current can be provided) the battery side should draw less and less until it's not doing anything?
Generally if you use wired diode isolation, multiple supplies will work together to be able to supply more current then any one supply can supply.
So I take it you just put a diode in series on each positive terminal, wire all the ground terminals together, and wire the ends of the diodes together, and each diode has to have a current rating equal or greater than the output of the individual power supply it is connected to...?
If this is correct, as the panel can provide more and more power (voltage is higher and more current can be provided) the battery side should draw less and less until it's not doing anything?
That's how it works. Getting multi paralleled supplies set-up initially takes a little time to adjust each power supplies output voltage so that it about equal to all the other supplies output voltage. How we did it to balance the load was to keep a volt meter on the common positive buss output (after all the diodes) and carefully adjust each supply so it it just started to raise the common voltage output and then back off a little. The idea is to start off with each trying to output some of the current. This all changes with temperature and the length of each supply to the common buss, but keeps the whole system in close enough balance so that the common buss sees little change in output voltage over time. Every couple of years during scheduled downtime we would recheck the balance and readjust as needed. Worked well for several decades before the system was replaced with a Honeywell system.
The advantge of this type of set-up in the process control system was that there was more power supply capacity in total then the load ever required, and the failure of any one supply would not effect the commom load voltage. There would then be voltage alarm detectors on each supply to show if any one supply was off so that it would be repaired on the run.
The advantge of this type of set-up in the process control system ...
This was an excellent explanation on how to wire multiple supplies together.
Fort this particular application however there's a battery in the system and I see no reason why you should separate the two supplies. Rather I would wire the output from the solar charge controller to the battery and the output from the battery to the Arduino regulator (e.g. a pre step-down regulator as suggested above). The battery itself will act as a regulator and you get away with a simpler circuit.
The solar regulator will see the combined load of the battery and the Arduino at all times and supply current as follows:
When the battery needs charging, the solar panel will supply current to both the battery and the Arduino up to its capacity.
When the battery is fully charged, current will flow from the solar panel to the Arduino only.
When the solar panel regulator shuts down, current will be supplied from the battery to the Arduino.
If using a SLA battery, a fixed voltage set point at 13.7V should do the trick. If the output from the solar panel regulator drops below this point, it should disconnect itself from the battery.
That's how it works. Getting multi paralleled supplies set-up initially takes a little time to adjust each power supplies output voltage so that it about equal to all the other supplies output voltage. How we did it to balance the load was to keep a volt meter on the common positive buss output (after all the diodes) and carefully adjust each supply so it it just started to raise the common voltage output and then back off a little. The idea is to start off with each trying to output some of the current.
That sounds easy enough; the supplies I have have a built in digital readout (7-seg LED display) to monitor voltage and current (and current setpoint), if the current goes over the setpoint it trips automatically, shutting off the output and flashing an LED. Adding a voltmeter after the diodes would be no problem. I just wanted to be able to use both supplies at once, if needed - they can output about 1.3 amps each on the variable supply, and I think 2 amps on the fixed 5V supply (which can be somewhat adjusted with an "internal" adjustment pot). I don't think I will ever need to use them together, but you never know.
Before I can do any of this, though, I have to calibrate the supplies; fortunately I was able to get the service manual, so all I need now is a few simple parts (mainly a couple different value power resistors).
