Glossary

Glossary of Electrical Terms

MPPT

Maximum Power Point Tracking is algorithm that is included in charge controllers used for extracting maximum available power from a Photovoltaic panel. The voltage at which PV module can produce maximum power is called maximum power point (or peak power voltage).

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Split Charge Relay

An old method for connecting the Leisure battery pack to the vehicles battery & alternator when the ignition is turned on, thus charging the leisure batteries from the alternator. Although this is a cheap option it has many associated pitfalls :

- The leisure batteries would never be fully charged due to the alternator output voltage being reduced by the relays resistance in the circuit.
- This system simply does not work with modern smart alternators
- Tapping into a live ignition feed on vehicles is not always easy.
- No intelligent charging pattern, so charging much slower.

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Voltage Sensitive/Sensing Relay (VSR)

Voltage sensing relays sense the voltage of the vehicles battery and trigger a relay at a pre-set voltages (On 13.3v off 12.8v) thus allowing the leisure batteries to be charged from the alternator. Over the last 15 years this is the type of system fitted to most camper van with 100 to 200ah leisure battery banks. Its relatively inexpensive and simple to install (no need to modify vehicles electrical system). However like split relays there are pitfalls :

- The leisure batteries would never be fully charged due to the alternator output voltage being reduced by the relays resistance in the circuit.
- When fitted to a vehicle with a smart alternator, it will trigger many more times and will be prone to premature failure.
- No intelligent charging pattern, so charging much slower.
- Not suitable for a larger leisure battery bank >300ah.

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Leisure battery bank

This is where 2 or more leisure batteries are connected in Parallel to maintain the voltage (12v) but increase the overall amperage, ie 2 100ah batteries connected in parallel will make a battery banks of 200ah at 12v.

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Parallel battery connections

Connecting the positive terminal to the positive terminal and the negative terminal to the negative terminal on leisure batteries, maintains the voltage at 12V but doubles the current.

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Residual Current Device

A life-saving device which is designed to prevent you from getting a fatal electric shock if you touch something live, such as a bare wire. It can also provide some protection against electrical fires.

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Volts, Watts and Amps

Volts - Electrical force of pressure behind the electrons in a circuit. Analogous to water pressure or PSI, it tells us the system voltage (12, 24).

Amps - The number of electrons flowing past in a second. Like litres per second in a pipe, it defines the electrical current in a wire.

Watts - Total amount of electrical energy, per second.

The conversion formulas are:

Watts = Volts times Amps
Volts = Watts divided by Amps
Amps = Watts divided by Volts

Amp hours (Ahr) - A measure of power, E.g. .one amp consumed for 5 hours has used a total of 5 Ahr of power.