# Multiplexing battery voltages with high precision

I would like to multiplex battery voltages used for impedance measurements. The battery cells are not connected. My idea is to have one multiplexer chip for the positive poles, and one chip for the negative poles. Then the outputs are compared to get the battery voltages.

Is it OK to multiplex floating voltages like this, and then compare them afterwards? What factors might affect the measurements? Are there better alternatives?

I am planning on using the mux MUX506IDWR. The outputs of the muxes will go to a measuring device (Gamry Reference 3000) which I assume has high impedance and will not draw current in the voltage measurement. I don't really know what goes on inside of the Gamry device. All I want is to deliver the battery voltages without distorsion, as if a battery is directly connected to the Gamry.

4-point measurement is used, with a relay multiplexer used for the current cables. Relays are used for the current wires, since 3 A will be used in the measurement. Using mux ICs for the voltage measurements are used in order to save money and space.

• You should draw a circuit to show what you intend to do. The mux you selected has a typical series resistance of 125 ohms that will need to be accounted for if you want your measurements to be accurate. You might think you can just subtract 125 ohms but it's not that simple, the 125 ohms is a typical value, it can be much less or a bit more. In a properly designed circuit you would not let any current flow through the mux used to measure the voltages. Then the current is low and the series resistance can be neglected. Use a 2nd mux to switch the currents. Read up on 4-point measurements. Jun 26, 2018 at 13:56
• It is very important that you tell us how you intend to "compare" the outputs of the multiplexers. Please provide a schematic and links to the components you plan to use. Jun 26, 2018 at 14:01
• No links for the multiplexer or Gamry? How is the relay multiplexer connected and why don't you just use another one of those? You are really making it hard to help you. Jun 26, 2018 at 14:29