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The XL4005 and XL4015 modules have a 5A current limit which was appropriate for the Pi3 B+ but not quite enough for the Pi 5 etc. I have an un-named module that is capable of supporting 10A with up to 60V input, which may be more appropriate. The specs are below:
I'm also interested in testing the following, but both have a maximum input voltage (14V or 15V) that is lower than the max from USB-C power (20V+), which could be a problem if configured incorrectly. https://thepihut.com/products/dc-dc-buck-converter-6-14v-to-5v-8a https://thepihut.com/products/60w-adjustable-dc-dc-buck-converter-module I'm going to test a few options on the cody build. |
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I noticed some issues with the Pi behaving erratically when battery voltage is low or a 9v power supply is used. It seems that 12V+ is more appropriate for this project. This could be because my wiring is not the correct guage, or could be because the DC-DC converters are, in practice, at the limits of their current rating during brief spikes.
Nevertheless, there are benefits to improving how we manage batteries (and the batteries used) in future versions.
18650s
It would be easy enough to swap the 3x 18650 holder with a 4x holder, either in the same format (1x4) or 2x2. However both would require a redesign of the body.
https://www.switchelectronics.co.uk/products/18650-x-4-battery-holder-150mm-leads
https://www.digikey.co.uk/en/products/detail/mpd-memory-protection-devices-/BH22CL/3775
Alternate Batteries
Alternatively, we could utilise existing batteries that are commonly already owned, such as batteries and chargers from power tools.
A good example of this is the Bosch battery packs:
https://www.screwfix.com/p/bosch-18v-5-0ah-li-ion-coolpack-battery/5296f#product_additional_details_container
This could be mounted to the robot using an adapter like this:
https://www.aliexpress.com/item/1005006785931479.html
This way larger batteries could be easily used, or swapping batteries more simply. It is also less risk when transporting the robot or clearing airport security checks etc.
Charging and Mains Switching
If we were looking to create an 'always on' solution for the robot, we could include a Backup Battery Switching Module that would detect and switch to external power when connected, and reconnect the battery when disconnected.
This wouldn't allow charging in the robot (something I'm planning to avoid for safety reasons) but would allow the battery to be removed and charged, and only used when the robot was mobile.
https://www.amazon.co.uk/Switching-Charging-Automatic-Emergency-Controller/dp/B07B4CPVLB/ref=asc_df_B07B4CPVLB
** Weight **
The only other consideration here is weight, where 4x 18650 (2.5Ah) = 200g, whereas the Bosch 18V 2.5Ah battery is 360g. So the 18650s will be lighter for the same power (16.8V vs 18V = 160g lighter with 18650s).
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