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Official Q&A: VEXU 2020-2021: Change Up
625: Question on VUR6
VUR6 c. ii. states that you may power sensors and additional electronics from "an additional lithium ion, lithium iron or nickel metal hydride battery pack (only one (1) additional battery can be used for sensor/processing power). Battery pack must operate at a maximum of 12 volts nominal."
Would it be possible to expand this to allow for a 4s lithium iron battery (the same as the V5 battery) which has a nominal voltage of 12.8 volts?
The word "nominal" was intentionally chosen, to account for the fact that the "operating" voltage of power sources tend to vary depending on the source and the load. That is to say, a 12V nominal battery will usually likely operate at some other voltage than 12V.
4x 3.2V Li-iron battery cells wired in series will read 12.8V on a multimeter, but is still often described as a "12V nominal" battery. A lead-acid car battery will read 13.7-14.7V while the car is running, but is typically labeled as 12.6V nominal.
One additional intent of this rule is to provide a guardrail for what third-party sensors and processors are permitted in VEX U and the VEX AI Challenge. Sensors that operate on a far different nominal voltage than the V5 system, such as 24V automotive sensors, are prohibited by this rule. It is much easier for an inspector to review a battery label than to request sensor documentation (or for us to provide a comprehensive list of legal and illegal sensors).
Would it be possible to expand this to allow for a 4s lithium iron battery (the same as the V5 battery) which has a nominal voltage of 12.8 volts?
Knowing nothing other than what is stated in the question (i.e. that this is a 4-cell lithium iron battery with a nominal voltage of 12.8 volts), this does not seem to violate the intent of VUR6-c-ii, provided that no other rules are violated by its use. However, it is impossible to issue a blanket ruling on all hypothetical batteries beyond what is already stated in the manual. If you have questions about the legality of a specific battery example, please re-post with a link to the battery's product specifications and we would be happy to provide a clarifying ruling.