Recently I was asked how to ensure that electronic equipment is fed clean power when using a generator.
The quality of generators varies, and while most devices are happy to run from cheap generators, delicate electronic equipment wants a clean, pure sine wave, not the "modified sine wave" often found coming from generators.
There are two ways to fix this:
- get a generator that gives "pure sine wave" output
- clean the generator output.
Buying a higher quality generator sounds like the obvious solution, but the difference in price between a "modified sine wave" and "pure sine wave" generator of the same capacity can be significant.
Coming at the problem from a tangent, I would recommend the use of an "on-line" UPS between the generator and the sensitive load. On-line UPSs are designed such that the input power never gets to the UPS load - all the power goes through the battery conditioning circuitry, with the input power being converted to DC, then back to AC again for the load. This allows the UPS to be connected to "dirty" generator output, but the load to only see the "clean" power from the UPS. The use of the on-line UPS also means that there is zero fail-over time if the generator goes off line (who forgot to fill the petrol tank? Come on, own up!), and that the load can continue to work while the generator is moved, mains cable re-routed etc., giving a two-for-one benefit.
You have to be careful to choose an on-line UPS, not a line-interactive model. Line-interactive means that the UPS will "top-up" the power to the load if the incoming power drops off a bit, but it does not mean that the power is cleaned before supplying to the load. Line-interactive is good if you don't have to worry about the quality of the incoming power feed, but not in the scenario we are looking at here.