I have an inverter, then a UPS, as the inverter does not always keep the PC on. The inverter does not power the UPS so it cuts out after a few mins, I then have to take the UPS out of the system until the power comes back on?

Hello,

As I understand your statement, Your inverter (Powerline 200watt) has the UPS plugged into it, but it is not able to keep the UPS powered on. You didn't mention the size of the load (PC), nor the wattage rating of the UPS, or the batter bank size that supplies the inverter.

It sounds like you are trying to create an electrical system with double redundancy. If this is the case, you are going about it wrong. Most inexpensive inverters will have a Modified Sine Wave output, that the UPS will detect as a poor AC signal, and revert to backup mode, rather than pass the inverter power to the load.

200 watts isn't going to be very much for anything. 200watts / 120 volts (assuming 120vac system) is only 1.6amps or so. The charger on the UPS will likely use this much just to keep the internal battery topped off. As the PC is turned on, and the battery charger is doing its thing, there now exists an overload at the inverter. The inverter will respond by trying to increase its output by lengthening the pulses in the MSW waveform. The UPS then sees this, interprets it as bad power, and kicks into backup mode.

Since the powerline inverter is obviously a 12volt unit (cig. lighter plug), then check the battery configuration of the UPS itself. If it is 12volts as well, then you may be able to connect the UPS directly to the batteries that were powering the inverter. Note that some modification to the UPS will be needed if there external battery connections are not already present. Even then, there is no guarantee that the charger in the UPS will be able to charge the internal plus an external battery bank.

Since the battery that powers the inverter is likely larger than that of the UPS, why not run the PC directly off the inverter itself and forgo the use of the UPS altogether?