Electric stand by varies somewhat in design and function.
The larger diesel stand alone systems such as Thermo king/Carrier /Zanotti to name a few ,all have a main Refrigeration compressor.This compressor is powered by a small say 4 or 3 cylinder diesel engine for example via belt drives or gear drives ..This same compressor is, when connected,driven by a large usually 3 phase electric motor .So 1 compressor driven by 2 separate power sources when required ..These high end Refrigeration units come with multiple sensors to detect if the electric power drive has failed and will start the diesel engine to keep things cooling in the back .A very handy thing to have ..These high end refrigeration units have many other sensors that monitor many functions ,,but we are discussing Electric stand by in this post .
Important note that when you have your unit above running on electric stand by unattended,say overnight ,that as noted the electric power fails for any reason ,then the diesel engine drive will start ,so don’t have your vehicle sitting anywhere that is exposed to exhaust fumes .So these units are as i said high end and made of some of the best available engines.parts etc available on the market and of course they come with the price tag to match ,,,but if your hauling expensive product you cant go any other way/Keep in mind these units are big and heavy and only suitable for say 6 to 26 pallet type applications .
Now we come to the smaller off engine drive with an independent Electric stand by unit .These Refrigeration units are driven by the vehicles engine.And the Electric stand by is mostly independent from the vehicle ..
Normally a separate compressor is used ..You will find that these days a compressor called a danfos type is used these are a highly reliable enclosed rotary compressors and are wired in to 240 volt /10amp that can be run off your normal household plug .These are a commercial brand and high quality .When purchasing these ,they should be completely independent and not have any affect on your vehicles systems .
There is another type of electric stand by available that incorporates another engine driven type compressor and also has a small electric motor that drives this compressor ,they do work very well up to a point ,,,as the compressor cycles the gas builds up pressure this causes the compressor to lock making it harder for the smaller electric motor to drive the compressor .The electric motor starts to overheat causing fuses to burn out and circuit breakers to trip out .
Many operators will be found running the engine on there truck whilst the vehicle is sitting stationary to keep things cool rather than plugging in to an electric power source ,understandable if you don’t have electric power .But keep in mind that most of these types are not designed to operate this way for extended periods .,You will flatten your battery and given the lack of air flow over the evaporator .the unit will heat up and cause damage as they are not designed wholly for this .(Check with the supplier)
Do your homework when purchasing electric stand by with your refrigeration units ,,It pays in the long run and re sale value will be higher