Insufficent Power Supply for the XBee 3G (750ma @ 3.3V)

Q&A forumCategory: QuestionsInsufficent Power Supply for the XBee 3G (750ma @ 3.3V)
sidmyr asked 3 months ago

Dear Ardusimple,
you rate the 3.3V current available for the XBee to be a maximum of 750ma – however for the 3G Module XBee states a necessary minumum of 1.5A.
http://cms.digi.com/resources/documentation/digidocs/90001541/#reference/r_cell_power_supply.htm%3FTocPath%3DDesign%2520recommendations%7C_____1
Operating voltage may be below that (around 700 ma) but the extra power is required in certain cellular connection stages and especially when having a poor overall cellular reception.
 
My Question:
Is the DC DC converter of the simpleRTK2B capable of delivering the necessary current in order to power a 3G Module in all connection stages?
If not – are you planning on changing that for the revised Version of the Board? Or is there any other solution to power the xbee externally?
 
Thank you and best regards,
Martin
 
PS.: A nice addition would be a possibility to disconnect the XBee from UART2 TX (e.g. via a Jumper) – otherwise you always have to reconfigure the F9’s UART 2 Output when using the XBee USB Port.

Ardusimple Staff replied 3 months ago

Hi Martin,
Good questions.
We can confirm that simpleRTK2B board can only output up to 750mA, peak current a bit higher, but depends on the length of this peak. But for sure not 1.5A. Doing so was increasing the cost of the board and we decided to focus on cost for the first generation. But continue reading as there are solutions.

With the 3g xbee module, there’s some tweaks you can do to have it working:
– Disable the 2g part of the module. The 1.5A are only needed in bad signal conditions using 2g technology.
– Use supercapacitor. We left C30 capacitor for this purpose.
– Limit the output power. Many modems have this feature.
– Use good external antennas. The better the antenna the less power the module needs to transmit the same.
– Don’t squeeze the data connection. Only send corrections.

Your inputs are very welcome because we started now working on simpleRTK2B v2, which should be available towards second half of the year. The power supply increase it’s a candidate for v2, but is not included in v1.1 that we are shipping now.

1 Answers
sidmyr answered 3 months ago

Thank you for that swift reply and your recommendations, really appreciate it.
-2G Mode is already disabled by factory default as even XBee’s own devkit is not designed to provide the necessary power (3.0 A @ 3.8 V). So unfortunately, the 1.5A peak is a necessity to ensure smooth 3G connectivity :(.
-I have not found an option to limit the output power of the modem and we already struggle with reception so limiting it further would likely make that problem worse.
-I’ll definitely give the capacitor a shot, this seems to be a nice option in order to stabilize power. What size capacitor would you suggest for that application?

Ardusimple Staff replied 2 months ago

Hi sidmyr,
Excuse our delay. The capacitor minimum 220uF which is available in 0805 format.