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electrical:nominal

What does nominal mean?

Nominal refers to a thing's name, rather than its actual status in the present moment. The point of the term is to keep new folk from thinking that 12v literally means the system or device is running at 12.0 volts. It's usually not.

The most common uses of nominal for 'dwellers are:

nominal battery bank voltage

The most common battery bank voltage for 'dwellers is 12v, although some run 24v or specialized, exotic voltages like 48v.1)

Nominal 12v banks are rarely actually 12.0v. Examples:

  • lead-acid banks can range from ~12.1v (full discharged) to something like 14.8v (absorption voltage). When full/rested they are something like ~12.7v.
  • LiFePO42) lithium banks3) range from ~12v discharged to ~14.6v when full.4)
  • Non-LiFePO4 li-po5) range from 9v discharged to 11.3v when rested. Just after charging you may see ~12.3v.6)

nominal solar panel voltage

Similarly, “12v” solar panels are called that because they are used to charge/power 12v systems. The voltages on these vary even more widely:

  • As low as battery voltage in the morning, ~12.1v7)
  • they make max power (Pmax) at a particular voltage (Vmp) which is usually way above battery voltage, like ~18v.
  • when unconnected (i.e. “open circuit”/Voc))8) voltages are very high, like 22v.
1)
the latter most often found when using automotive hybrid battery packs for house power
2)
aka LFP
3)
typically 4S
4)
this is why LFP is so well suited for drop-in lead acid replacement
5)
actually Li-Ion, typically 3S
6)
not a good match for 12v systems, which is why this chemistry is relatively rare
7)
pwm
8)
or in late Absorption with MPPT controllers
electrical/nominal.txt · Last modified: 2020/10/11 19:48 (external edit)