Bookmark and Share

Voltmeters and Ammeters

Accurate and sensitive meters enable the best use and understanding of a system. 

Analogue (moving needle type) meters are cheapest and for some applications with fluctuating current, eg. wind turbine output, preferred. 

Digital voltmeters allow much greater resolution and so provide more information about state of charge etc.. 

Voltmeters are connected between positive and negative. If connected directly to a battery a small (eg. 100mA) fuse should be fitted in the wire to positive. 

Ammeters are usually connected in a break in the positive wire of the circuit being measured. For currents above 25A ammeters making use of an external shunt are used. The shunt is usually placed in the negative wire to the load or charge source being measured, and the meter mounted remotely using smaller signal wires.

Ammeter DiagramNote - To accurately measure modified sine wave inverter AC outputs, meters which record true RMS values are required. POA To measure energy generated or consumed kilowatt hour (kWh) meters are needed. OFGEM approved kWh meters are available to enable credits to be obtained for renewable generation -

See Grid Connect Accessories.

Amp-hour metersVictron BMV-600S Battery Monitor Round Front

These digital meters measure Ampere hours (Ah) or energy used or generated in a system, so giving an accurate indication of the battery state of charge at any given time. Useful for assessing stored battery power, spare capacity, performance or fault detection. 

Starting at zero for a fully charged battery Ah consumed are shown as a negative display, charging Ah are added until the reading is back to zero. 

Measurement is via an external current shunt which is usually sited in the main negative feed to/from the battery. Signal cables are then taken to the remotely mounted display. 

They act like a battery ' fuel gauge '! 

Using one of these meters increases awareness of battery state of charge and electrical usage, translating into longer battery life and smarter use of your power resource, - every battery system should have one! For optimum use:

  • Locate where easily seen eg. in a living area rather than the battery room.
  • Educate yourself about how much each appliance uses by observing amps reading with appliance off and then on.
  • Check Amp-hours reading daily to see that you are keeping within your energy budget.
See: Battery Monitors

Battery charge indicators

These are included in many charge controllers and give an easy to understand indication of how full batteries are, whether they need to be charged, and whether to turn off your charging source. While in no way as useful or accurate as proper metering they give a simple measure of system performance.