FAQ

Frequently Asked Questions (FAQ) – Pi-UptimeUPS

  1. Are batteries included? No ‐ batteries are not included. 18650 batteries are readily available and can be purchased from ebay or Amazon or other locations.
  2. Are there recommended battery suppliers? No, we do not recommend battery supplier. However, having said this, please be careful of cheats in the industry. Many battery suppliers rate their batteries at 5000 mAh or more. Typical capacity of a 18650 battery is 3500 mAh or less. The chemistry and the amount of material which can be packed in the battery does not currently allow the batteries to be more than 3500 mAh. So please do not purchase batteries with false capacities being advertised on ebay or Amazon.
  3. What battery do you recommend? A battery following the Toshiba, Samsung or LG technology manufacturing standards are recommended.
  4. Can I use unprotected batteries? Yes ‐ the protection circuit on the batteries are replicated on the board. No need to spend the extra money to purchase protected batteries.
  5. Can I charge my phone or other USB device from Pi-UpTimeUPS batteries?  Yes – the Raspberry Pi has USB ports which provide power and using these USB ports, it is possible to charge a USB device or a phone. Please keep in mind that the run time will be reduced.

Note – not all devices can be charged from the USB ports on the Raspberry Pi. The current (amps) provided by the Raspberry Pi may not be sufficient to charge some devices. For example, some models of the iPad require a high charging current (2.1A). When an iPad is plugged into the USB port, it does not charge.

  1. Will the Raspberry Pi work as the batteries recharge?  The electronics on board simultaneously powers the Raspberry Pi system and charges the batteries on the Pi-UpTimeUPS board. If there are no batteries installed, power to the Raspberry Pi is provided. The Raspberry Pi system has priority over the battery charge current – so your Pi system will always operate as designed.
  2. If the external power fails, will the USB devices connected to the USB ports on the Pi continue to receive power from Pi-UpTimeUPS batteries? Yes – the power is available to the Raspberry Pi board. For example, if you have a cellular modem adapter on the Raspberry Pi, it will continue to operate as long as the battery has the necessary power. When the battery runs low, with no external power, the shutdown sequence is triggered. When the Pi is shutdown, on some Pi models, the UPS continues to provide the power. This could drain the battery down completely and damage the battery. The protection circuit will cut off the battery from the board when it reaches 2.8V.
  3. Will Pi-UpTimeUPS work with other boards? Yes, as long as the other boards follow the Raspberry Pi Foundation standards for connections.
  4. Do you plan to add relays or other things to Pi-UpTimeUPS?If you have thoughts or ideas on how to enhance the boards or make them more useful, please send us an email. We would like to listen to what you have to say.
  5. What is the warranty on the board and what does it cover? Warranty is for 90 days (3 months) and covers all parts and repair labor. If there are any issues, mail the board back to us with the purchase receipt or a copy of the receipt. We will mail you a replacement.
  6. Where can I get additional standoff’s (spacers) for the boards? Many sites sell those. An example of such a site is the Adafruit website and the recommended standoff is the Brass M2.5 Standoffs for Pi available here (11mm).
  7. Can I use the Raspberry Pi power port (micro-USB port) to charge the batteries and to power the Pi? No, you have to use the micro-USB power port on Pi-UpTimeUPS. If the existing Pi power port (micro-USB port on the Raspberry Pi) is used, the Pi will power up, Pi-UpTimeUPS batteries will not re-charge the batteries after a discharge cycle.
  8. Will Pi-UpTimeUPS work with only one battery?Yes, the available operating time will be reduced approximately by half. The electronics on board are flexible enough to charge one or two 18650 batteries.
  9. How is the shutdown sequence triggered? Python code monitors the battery level and triggers the shutdown sequence when the battery power runs low. This code should be run as a “cron” job. Documentation is provided to show how this can be setup to monitor the system automatically. In the code, there are two defined values: (1) lowValert  – the low Voltage alert value. When the Voltage falls below this value, an alert is sent. This should be set to 3.2V. (2) lowVshut –  the Voltage at which the shutdown sequence is triggered. In the Python code provided, when the battery voltage reaches approximately 3.2V (lowValert), the low battery warning is triggered to all logged in users using the “wall” command. When the battery voltage is less than 3V (lowVshut), the automated shutdown process is triggered. The unit shuts down in about two minutes once the alert is seen. Note if the power drawn is higher than 400mA, the voltage levels should be adjusted so as to shutdown the system faster. All of the above parameters can be reprogrammed using the program sources provided.
  10. Is a Real Time Clock (RTC) needed?The Raspberry Pi does not have an on-board clock. It depends on the Internet and time synchronization services available in the OS. The Raspberry Pi uses time services on the Internet to synchronize its clock. If the internet is not available, the time will drift. If the Raspberry Pi is used for applications where time is critical, it is important to have a RTC. Optional RTC boards can be added as needed. The UPS functionality depends on the fake hardware clock implements with the Raspberry Pi and Internet time synchronization once the Internet is available.
  11. Are all RTCs similar?No, cheaper versions of the RTC drift a lot i.e. lose the time accuracy quickly. Low drift RTC chips maintain the clock time very accurately – typically a few seconds drift per month. Depending on your needs for time accuracy, please add the proper RTC oard.
  12. Can I get just a RTC board for the Raspberry Pi?Yes – there are many RTC boards available for the Pi. The cost will vary depending on the accuracy of the clock. An example of such a board is available from Adafruit and other suppliers.
  13. Does a Raspberry Pi need a Power Reset Switch? When the Raspberry Pi is shutdown (using the shutdown command), the only way to reboot the Pi is to unplug and plug the micro USB power connector. With Pi-UpTimeUPS connected, there is power available to the Raspberry Pi from Pi-UpTimeUPS batteries.  Without a Power Reset switch, one way to reboot the Pi is to disconnect the power, remove the batteries and plug them in again. To prevent this tedious sequence, a Reset Switch is provided on Pi-UpTimeUPS. The Reset Switch disconnects the power source (as long as the switch is pressed). The red LED indicates the power reset function.
  14. What batteries are used with Pi-UpTimeUPS?Two 18650 2600 mAh Samsung rechargeable batteries are recommended for use. Batteries are not included.
  15. How long will it take to charge Pi-UpTimeUPS? It depends on how much the battery has been discharged. Fully discharged 18650 batteries (with the discharged cell voltage around 3V or more) should charge to full capacity in 5 to 6 hours (at approximately 1.2 Amps.)
  16. Why is battery protection needed? Some USB devices connected to the Raspberry Pi may continue to drain the power even after the system is shut down. This could drop the voltage of the battery below safe levels. If the battery voltage drops below 2.8V Pi-UpTimeUPS disconnects the batteries from the circuit. Only when the external power is available, will the Raspberry Pi reboot and Pi-UpTimeUPS batteries start charging.
  17. Do you plan to create an enclosure for the Raspberry Pi and Pi-UpTimeUPS stack? No, not currently. You can adapt the Ice chassis for the Pi for this. See the case on MCM Electronics web site.
  18. Can we replace the 18650 batteries with higher capacity units? Yes. We assume that the people doing this are responsible and can do that independently. Also note that higher capacity batteries will take longer to charge. They will also increase the run time.
  19. Can we replace the batteries when the battery life is over? Yes. This was one of the key factors for choosing the 18650 batteries – batteries with high power capacity and batteries which are widely available. We want to make sure you can use Pi-UpTimeUPS for a long, long time.
  20. What method is used for charging the batteries? The electronics use the “Constant Current followed by Constant Voltage” (CCCV) method for charging the 18650 batteries. There is a lot of literature available on the web for the CCCV charging methods and why this method is critical for batteries.
  21. Are there LEDs on Pi-UpTimeUPS board? Yes – there are four LEDs on board. The red LED comes on when the power Reset Switch is pressed and is used to indicate a power reboot sequence. Three other LED’s indicate the operational status of the board. See table below.

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The important thing to note is that when there is no external power, none of the LED’s are lit. If all three LED’s are lit – something is wrong. Most likely there are no batteries installed or the batteries are installed incorrectly.

  1. Do you have battery polarity protection on Pi-UpTimeUPS? No ‐ inserting the batteries incorrectly will damage the board.
  2. Which ADC chip is used?Pi-UpTimeUPS uses the Linear Technology LTC2497 chip. Sixteen ADC channels. The details for the chip are provided in the data sheet from the Linear Technology web site.
  3. How is the current measured? The current sense resistor for the input power measures the current. The ADC chip is used for measuring Input current, current used by the Pi and all its peripherals, input Voltage and battery level.