I am trying to power a photon using a solar panel. The panel is 6 volt max output. Photon is 5.5 max inputā¦ I guess I could get away with the 6vdc on the rare occasion fn super sunny dayā¦ But long term might fry something and hey .5 volt is .5v and I need to limit 6volt to 5.5 maxā¦ I canāt use voltage divider here because I will kill efficency. And the input voltage is unpredictableā¦ Only the top limit is knownā¦ I could use a regulator but I canāt find a suitable one that will output 5ish volt with an input of 4~6volt!! See my solar panel can have less light than optimal and output 4ish to 6volt!! So I donāt find a suitable regulator that will do the job the jobā¦
I need a voltage limiterā¦ Or a regulator that I donāt know about ā¦ Any ideas???
Although a Great product it does not solve the problemā¦ the load sharing feature will let 6 volts go thru the output of the chargerā¦ So I still need to limit the voltage some how into the photonā¦
Interesting. Iāll keep that in mind and either avoid that one or use parallel diodes to limit the battery voltage.
With the Adafruit product, a diode would drop the voltage by 0.6 or 0.7 volts depending on current. Thatās a crude method and assumes the output wonāt exceed 6.1V so itās a little sketchy to do that method.
The proper way is an external 3.3V regulator that can do a low dropout and a high dropout, skipping the onboard regulator. A backfeed diode may be necessary if thereās a capacitor on the Photon, although the large capacitor on the Adafruit product may eliminate the need for it.
It looks like the only reason to connect to āload sharingā is to save a little bit of energy by skipping the dropout between the solar panel and the battery. But that would be lost anyways with a linear 3.3V voltage regulator. The only way to gain that energy is a DC-DC converter I think.
Would a 5V zener diode do the trick? I havenāt actually used one as a regulator of any sort, so Iām going on general Google theory. It might be something worth investigating since I donāt think it will affect anything below the 5V threshold.
@frlobo: you should check output voltage of the panel. As I know in many cases you get 6V only when no load (so called Open circuit voltage). Try connecting a load around 50 Ohm to panel and measure panelās voltage. I think itāll be 5.2-5.4V. If so you can use panel to power Photon without any voltage limit. If more than 5.5V then find new solution. May be to buy new panel, 5V for example?
I think that the best solution is a voltaje regulator that can accept 4volt and regulate down to 3.3vā¦ Il search for somethingā¦
Another solution to research is the zener diodeā¦ Although I see too many warnings that I should not use it as a regulator, but I guess in this case itās a voltage limiter, not exactly a regulator?
only thing is 3.3v will be too low for charging the battery if your using it with the battery shield, the fully charged lipo will be about 4.2V, and there is a diode too so say +0.5v for the drop so 4.7 is the minimum you will need to fully charge the battery.
if the photon is powered on and drawing power then you should not reach the 6v mark. if it gets to high you could maybe open a relay using an output from the photon, protecting the photon from the high voltage, then the photon runs on battery reducing it voltage then close the relay to start charging again.
Zener: yes if it doesnāt overheat. It is dropping ~5V. Calculate watts and compare with rating.
Transistor switch might work in response to slow changes of the sun, but if you suddenly walk in front of it creating a shadow and then walk away there could be a voltage spike.
Hereās an advanced charger I found:
A really cheap charger would be to set a variable regulator to 4.0V to avoid overcharging. Add a diode to reg input prevent the panel from depleting the battery at night and protect reg. The solar panel would need to have enough voltage to cover 4.0V + regulator dropout + 0.7V and still generate enough current at that voltage to be useful.
Sure. A 5.1V zener in parallel would prevent the voltage from exceeding the 5.5V limit of the Photonās regulator input, but the solar panel may generate enough current to overheat the zener depending on the wattage rating of the zener and the Voltage-Amps curve of the solar panel. My guess is that your solar panel would fry a small 5.1 zener diode which are often rated for only 0.5 to 1 Watt.
Itās simpler to just wire the battery positive terminal to the Photonās regulator because the battery tops out at 4.2V (connecting grounds also, which is battery negative terminal in this case). The MPPT Sparkfun regulator has the load connecting directly to the battery (I think, the site is down for maintenance). With the Adafruit charger, I think itās the pad that says B+. With a multimeter you can check this before soldering.
In the Photon datasheet, it says VIN can take 3.6 to 5.5V DC. If you search ālithium polymer discharge curveā images, youāll see that it usually stays above 3.6V throughout most of the battery life.
The MPPT Sparkfun regulator will capture the most energy from your solar panel throughout various light conditions. But it may put a limit on max current thatās below the max current of your panel. I donāt know what youāre doing. A 5W panel might be overkill for most projects. The Photon has a sleep mode that reduces power consumption.
If you only want the Photon to work when the sun is shining, the thing you need is an LDO regulator - LDO means ālow drop outā, meaning that it can deliver its output voltage (say 5V) even when the input is only a little more than 5V. Something like an ST L4940V5 looks right (youāll get a better dropout performance if the regulator is rated for a higher current than youāre actually using).
If you want the Photon to keep going when a cloud goes past the sun, youāll need a battery. The Photonās minimum 3.6V is ideal for a single lithium-ion cell - personally Iād use an off-the-shelf 18650 cell in a battery holder and just connect the solar cell straight across it (thatās all most cheap solar power banks or garden lights do).
If itās really sunny and you want to avoid overcharging the Li-ion battery, you might consider a cheap Li-ion charger module. Look for āTP4056ā on Amazon or Aliexpress - various Chinese manufacturers will sell you cheap modules that do the trick. These arenāt as efficient as the Adafruit or Sparkfun āMPPTā regulators, though.
I am using a spark fun battery shieldā¦ And. 1000 mah battery packā¦ I like the idea of the LDOā¦ Il take a look at itā¦ I am more worried about the over chargeā¦ I hope the sparkfun shield takes care of thatā¦ I need to read moreā¦ The diode is more to prevent the cell from depleting the battery. Also I have a voltage divider prior to the diode to measure the voltage of the cellā¦ I calculate the amount of sun by dividing 6 volts in 2 and read the voltage with ADCā¦
I have made something similar using a 5W solar panel, a all-in-one charge/discharge board and a Li-ion battery. Working quite well so far, except the battery capacity is a bit too small so it wonāt last more than 2 rainly/cloudy days. I am also working on an improvement but I see so far is to use a solar array.
Question: what happens of the battery drains? Will it ever get power back in when the sun comes up? Will the low voltage condition cause side effects to the photon?
Yes, the charging broad will ensure the battery got charged when the sun is up again. As for the low voltage, the DC-DC regulator will ensure a 5V supply to the Photon. However, there are occasions that the 5V output will flicker, Iād have to add a 1000uF capacitor to ensure the flicker will not cause problem. On the other hand, the Photon is taking too much power and probably overkilled to use as a weather sensor.
