[CAUTION: This article is in response to a reader’s mail. It’s a guideline – there many ways to skin a cat. We do not have nine lives – take caution. We will not be held responsible for incorrect wiring, circuitry and/or modifications that our readers carry out themselves. Always consult an electrician. It is highly illegal to tamper with wiring connected to your supplier. Electrical code is there for a purpose- read it, understand it, be responsible].
As a result of a previous article “Power Inverters – The Real Thing” we had a reader drop us a mail on how he managed to reduce spikes and line transients from the genset by using a UPS and line regulator connected to the UPS output. This should never be done. The surge protection device, if it is a movistor, will damage the UPS. Connect the surge protection before the UPS. Not all UPS have very sophisticated input protection circuitry – focus on the source and not the output.
Never connect an inverter or UPS back on to the mains supply – read up on back feed or islanding. A UPS is not designed to be looped – i.e. output to input and remember non-grid tied systems do require a transfer switch.
For generators, use an online UPS. Line interactive UPS don’t always like generator power. (neither that from inverters). Often very small gensets do not have a very good AVR and output voltages swing wildly through the recommended safe operating voltage of an electronic load. In some cases it is desirable to use a step down transformer, rectifier and smoothing circuit feeding a SMPSU e.g. 9~15 with a DC 12V 20A output. (look at the SD range from Meanwell with 19 to 36V DC input). It is far easier to control a low voltage than an output voltage possibly exceeding 300V. (this is for low power equipment used for camping possibly). There are many permutations to this trick but like all roads lead to Rome – always check your output voltage before connecting a load. Large diesel gensets are usually rock steady and most UPS types can be used comfortably. A very useful piece of equipment is a self made genset using a 4HP lawnmower engine driving an automobile alternator for 12V battery charging.
DIYers the world over are learning to adapt technology to suit their needs using solar and wind power. To live entirely off the grid is the goal of all.