Switching Power Supplies For A MIcrocontroller

[Ozwurld]

Hello all,

I am currently busy with a project that involves powering a micro controller from a 7V solar panel. I would like for the Micro controller to be able to switch to a back up battery pack whenever the Solar Panel doesn't provide enough output voltage to power the micro controller i.e at night preferably.

Can anyone please suggest how i can go about doing this.

Thanks.

 

[Reloadron]

You make no mention of voltages or required currents. However, for the basics of a simple circuit give this a read.

Ron

 

[NorthGuy]

With solar, you usually use a rechargeable battery, which is charged when there's a light, or discharged at night. The microcontroller would be connected to the battery wether it's charging or discharging, so you do not need a switch, just straight connection.

You do need some sort of controller to prevent battery from overcharging.

 

[Nigel Goodwin]

You do need some sort of controller to prevent battery from overcharging.

It depends on the size of battery and size of panel, you only need a controller if the panel is capable of overcharging the battery, which depends entirely on the systems design use (if it's just for powering a micro then a controller isn't likely to be required, and may not be required anyway).

 

[Ozwurld]

You make no mention of voltages or required currents. However, for the basics of a simple circuit give this a read.

Ron

my bad, i have a super cap boosted to 5V as a backup.. and thanks for the link: its just what the doctor ordered!

 

[NorthGuy]

It depends on the size of battery and size of panel, you only need a controller if the panel is capable of overcharging the battery, which depends entirely on the systems design use (if it's just for powering a micro then a controller isn't likely to be required, and may not be required anyway).

That's true. I had to go with lead-acid batteries because of wide temperature range. Lead-acid batteries get sulphated if left uncharged for long. Therefore, I had to use the panel big enough to keep them charged most of the time, including dark winter. When so sized, the panel can easily overcharge the battery without a controller.

With li-ion, you probably can oversize the battery so that it'll be sitting half-charged most of the time, but a comparator along with few resistors is a much cheaper solution than oversized batteries.

 

[Mosaic]

Wide temperature range = wide variation in Lead acid end of charge voltage => temperature smart controller is required.

@ Northguy , this might interest u...http://www.clubjameco.com/index.php/projects/project_brief/24/21263/auto_battery_capacity_logger

I also posted it as a DIY article here in ETO.

 

[Ozwurld]

You make no mention of voltages or required currents. However, for the basics of a simple circuit give this a read.

Ron

My solar pannel open circuit voltage is 7.5V and i am using a 2.3V rated super capacitor of which im taking through a boost converter to provide 5v for the micro. The charging voltage of this capacitor i think is 2.3V so with the schematic in the picture that i've attached.. wont the solar pannel harm the super cap whilst charging... i'm confused about this.... should i buck it maybe???

please advice

 

[NorthGuy]

You only need one diode (the one on the top). From the bottom two diodes, remove (open) the left one and short the right one.

A panel with Vmp of 7.5 should be able to charge the capacitor up to about 8V (7.3V after diode drop). This is not good for 2.5V capacitor.

If you want to stay with these voltages, you'll need some sort of controller. You can use a voltage limiting controller, but it'll waste (7.5-2.5)/7.5 = 67% of the available energy. Or, you can build a buck controller to downconvert the panel voltage.

Or you can use 3 capacitors in series. The voltage will go to 7.3 while charged, but it'll be dropping to lower levels during the night.

Batteries are more suitable for storing energy because they provide a steady voltage while capacitor's voltage decreases as it discharges.

 

[Nigel Goodwin]

My solar pannel open circuit voltage is 7.5V and i am using a 2.3V rated super capacitor of which im taking through a boost converter to provide 5v for the micro. The charging voltage of this capacitor i think is 2.3V so with the schematic in the picture that i've attached.. wont the solar pannel harm the super cap whilst charging... i'm confused about this.... should i buck it maybe???

please advice

Dump the super capacitor, they are pretty useless devices, and replace with a proper battery - 4 x AA NiMh should be fine?.

Then simply connect the battery to your micro-controller circuit (no boost converters or regulators needed), to add solar power simply connect the panel via a diode directly across the battery.

That's all you require, one single diode - based on the little you've told us.

 

[Mosaic]

Have a look at tip#2 and #3 here for powering the micro.
https://www.microchip.com/stellent/groups/techpub_sg/documents/devicedoc/en026368.pdf