Series & Parallel and Meter Testing Flashcards
When two or more PV modules are wired in series, voltage is _______ and current is _______ in all parts of the circuit.
additive; equal
When multiple modules of the same make and model are wired in series to form a PV source circuit, the circuit voltage equals the sum of all the module’s voltage specifications, or the number of modules in series times the voltage of one module. The current equals that of a single module, at all points in the circuit.
When testing the Voc of a module, what is the correct setting for a digital multimeter?
VDC
In order to test the open circuit voltage (Voc) of a module, the meter will need to be set to read direct current (DC) volts
A clamp-on meter is used to test circuit _________________ .
current
Clamp-on meters, whether integrated into a digital multimeter (DMM) or as a separate meter that plugs into a DMM, offer a much safer way to test current then using meter probes. This is the only method to use when testing a high current circuit. Clamp-on meters sense the magnetic field generated by current in order to measure it, and do not require circuits to be opened or wires to be disconnected
Testing for polarity ensures__________________
the positive and negative conductors are correctly wired and identified
PV circuits are DC and must be wired with the correct polarity. This can be confirmed by using a meter to test voltage and to ensure that the polarity is correct before turning the system on for the first time.
Checking for continuity will reveal if:
a fuse is still operable or if it has blown.
If a fuse has blown, then there will be no path for current to flow across it, and thus no continuity. This is a great way to test if a fuse is good or needs to be replaced.
When measuring for correct maximum power current (Imp) of an operating PV array, which two of the following should be used?
pyrometer; clamp-on meter
To accurately estimate current output, a pyranometer is used to measure the sun’s irradiance. After learning the irradiance, expected operating current can be calculated and tested with a clamp-on amp meter to confirm the correct amount of current is present on the circuit
A crystalline silicon PV module with a maximum power point voltage (Vmp) around 36 volts is likely made up of how many individual PV cells?
72
Crystalline silicon PV cells typically have an operating voltage around 0.5 volts. Seventy-two of them wired in series would result in a Vmp of approximately 36 volts
Are typical household loads and appliances that are all on a single circuit wired together in series or in parallel?
parallel
Because most loads in a house require the same voltage (i.e. 120 VAC for lighting and standard plug loads), the voltage must be the same throughout the circuit. If wired in series, the loads would not operate or could even be damaged since the voltage provided would be incorrect. It would also cause the “x-mas” light effect that when one light bulb burns out (fails) all others in the series circuit would also turn off.
In a series connection, the positive lead of one module connects to the ____________ lead of the next module.
negative
Series connections occur between the positive lead of one module and the negative lead of the next, or vice versa. This is easily accomplished during installation since the majority of modules have “quick connects” that only allow the positive to be connected to the negative
All source circuits connected to a single MPPT must have the same number of modules wired in ___________ so that all source circuits have the same voltage characteristics.
series
When connecting multiple source circuits to a single MPPT, it is important that each source circuit has an equal number of modules wired in series to ensure that the voltage characteristics are the same for each source circuit
To increase the current of a PV output circuit, PV source circuits are connected in _________.
parallel
A parallel connection means the current of the series string of modules will be added together, increasing the total current of the PV output circuit. Parallel connections are made by connecting the positive output of one series string to the positive output of another series string and the negative of one series string to the negative of another series string
True or False: When a parallel connection is made, the current remains the same.
false
Current is equal through all parts of a series circuit; current is additive in parallel circuits. Parallel connections are established by connecting the positive output of one module to the positive output of another module and connecting the negative from one to the negative of another. This parallel wiring typically occurs in a combiner box.
Two arrays with the same tilt angle, orientation, and amount of shading are wired to separate Maximum Power Point Trackers. Each array consists of ten of the same make/model modules. The first array is wired in a single series string of ten modules. The other is wired in two series strings of five modules each (two circuits in parallel).
True or False: The total available power at STC conditions of these two arrays is the same.
True
Regardless of the configuration, the total power of the array will be the same, the sum of the power of the individual modules. The circuit voltage and current characteristics will be different, but their product, in watts, will be equal if there are the same number of modules in each array.
Individual circuits of PV modules in series are known as ___________.
PV source circuits
PV Sources circuits consist of PV modules in series and are commonly called series strings
When measuring for correct maximum power voltage (Vmp) of an operating array with electrically insulating gloves, _________________ and _________________ should be used. (choose two)
temperature sensor; probe tips of a digital multimeter
To accurately estimate voltage, a temperature sensor is used to measure cell temperature. After learning the cell temperature, expected operating voltage can be calculated and tested using the probe tips of a digital multimeter to confirm the correct voltage is present
