SunAirPlus 2 - Next Gen Solar Controller / Data Collector

From our instrudtable, MichaeW616 writes:

I have both your sunairplus and sunair solar charge circuits, and am currently building out an esp8266 weather station and have a few questions:

1) Have you considered making a variant of your board that supports lifepo4 batteries? As they can be used (charged) in sub-zero temperatures, they would be a LOT more useful for semi-permanent, 24x7x365 deployments. The charging logic ics are fairly common and are getting cheaper, and you would be one of the first pcb lifepo4 charging solar 6V solutions out there.

2) Is there a way to attach a thermistor to the board to monitor battery temperature (I believe this is a supported feature of the base charging chip)? If not., a solar charger (outdoors) in almost any American climate is dangerous if it can charge the lipo battery below or above its operating temperature, effectively making the charger useful only for small temporary projects.

3) I know the board is really useful for education / temp projects, and I really really value the built in current measurement, is there any way to get a version where the output is the ~3-3.5V such that no power up conversion is required.

In short, I would love, and believe you could profit by building a lifepo4 6v solar charge board with current measurements, outputting 3.3v and (if jumpered) 5v/usb power. Considering the cost (both power and $) of the adc and other components associated with pointing the solar cell, It might be better to sell a separate higher power add-on board.

If you are not really interested in this, please let me know and either I will build it or will find someone else interested.

Again, thanks for the simple hackable solar charge boards you supply.

Oh – one other suggestion – on the sunairplus, consider letting us put the 4700uF capacitor on the board right over the sun logo… it wont hide anything except the spiral, and could be safely (both from a temperature as well as being physically strong and stable).

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charles.elms@yahoo.com'
CharlieE
FEBRUARY 27, 2017 AT 10:17 #19815
See comment above.

With all the bad press about lipo battery issues lately, I’m a bit concerned running my 24x7x365 weather station outside in Maryland. Temperature extremes can be expected to be from about zero to 105 F here.

If this new board will better support temperature extremes I would buy one (and new battery if required) just for peace of mind.

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SwitchDoc Labs
MARCH 2, 2017 AT 08:01 #19904
CharlieE,

Thank you for your suggestion. While we haven’t settled on the CN3065 for the charger control yet for the new board (this is the charger for the current SunAIrPlus board), we are looking to to provide an optional input for the temperature control to the charger. Basically, this “TEMP” input will shut down charging if it gets too cold or too hot.

This function could be pretty easily implemented off board by setting up a relay (or a solid state relay) controlled by temperature to shut off the solar panel input to the board if the temperature is too hot or too cold.

The controller itself limits charging if the die gets too hot, but that is not battery temperature as you asked.

What is too hot and too cold?

Typically, the specs talk about 0 – 50 degrees C. That means your hot temperature is really not an issue.

The 0 degrees F is more of a problem, but you can charge most LiPo batteries below zero, but you need to charge at very small rates.

By the way, if your system is operating, then the battery temperature is probably not much of a problem. However, if the system is shutdown and then starts charging, you have more reason to look at this.

With the new board, we will have a section on temperature control.

Best,
SDL

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lutz@bendlin.us'
lbendlin
MARCH 21, 2017 AT 13:53 #20963
On the existing SunAir and SunAirPlus boards the servo connector is sharing the Vcc with the rest of the circuitry. I found that this is not a satisfactory solution when the servo current pulls everything else down. It would be good to have the option to provide a separate Vcc to the servo.

Using the current measurements on the SunAirPlus I deduct that the board itself consumes about 80 mA. That is a lot, especially given that my load only consumes 120 mA on average. It would be nice if the board’s consumption could be dialed down a lot.

Thank you for considering to include the power control circuit. If you can include two of them then one could be used for the load and one for the servo circuit. This would allow to power the servo only for the periods when motion is needed (I am currently turning my solar panels to the sun every 30 minutes, for example)

Can you please make the output voltage configurable, or at least elevate it a bit above 5V? That way wiring and other circuit losses can be better compensated. It would also be nice to be able to measure the output voltage and current AFTER the power control circuit (if you choose to include it)

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lutz@bendlin.us'
lbendlin
MARCH 21, 2017 AT 14:00 #20969
uh, one more thing. The INA3221 is currently sitting at address 0x40 which conflicts with a lot of other devices, namely the SHT21 temperature/humidity sensor. Would be nice if the address would be configurable.

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SwitchDoc Labs
MARCH 23, 2017 AT 08:58 #21027
Lbendin,

Excellent suggestions.

1) Current consumption. We are measuring 5mA tops. We will put a board up and check it again.

2) We aren’t going to continue the Servo support. The power supply issues and cost of doing it right was too high for the new board. But, we looked at it.

3) We have added a method for temperature detection and control.

4) the voltage has been moved up to 5.2V Still within USB spec and then we have some leeway for wiring and other losses.

5) The comment about address 0x40 is well taken. We have the same problem with our HDC1080 temperature/humidity sensor. We are adding a pad that you can pull up to change the address. This just made it into the final design. Final layout is starting tomorrow.

We are not including support for the LiPoFe. Requires a different charging chip and so we will have to make a new board. Won’t be an entirely new design, but enough of a change that we need to make another board.

Best,
SDL

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SwitchDoc Labs
APRIL 19, 2017 AT 11:33 #22226
Folks,

First of all, thank you for all the comments and suggestions to this topic and via other channels. The information was very helpful.

We have now finalized the board and have completed the layout. The Kickstarter is set to go live in about two weeks.

Attached is the new block diagram of “SunControl”. And yes, we caught the typo! Dara instead of Data.

John C. Shovic, PhD
CTO
SwitchDoc Labs

This reply was modified 4 weeks by SwitchDoc Labs.
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bonnette_l@yahoo.com'
bonnette
APRIL 20, 2017 AT 05:53 #22268
I like your Ideas for the new solar board.
I would also suggest that you re-examine the brand of power switch you put on it.
I have been using the current solar board for about 4 months now and the switch on it is all corroded to the point that it is now frozen into the “on” position.
See if you can source a switch that is less prone to corrosion or, maybe just leave the switch off of the board all together.

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SwitchDoc Labs
APRIL 24, 2017 AT 15:03 #22421
Bonnet,

We replaced the switch and redesigned the power system so it is not carrying any current. You must have a very humid or salty environment.

Thank you for the comment. We really appreciate it.

Here is the preview link. The kickstarter goes live tomorrow.




BP