Inverters (again...)

Status update:-

PowerJack : No reply to enquiries in to what CPU they are using in this years models.

OpenEnergyMonitor forum : No replies so far to my post asking for model numbers of Powerjack inverters that are known to have the ATMega CPU.

The Chrome browser does do a nice job of automatically converting German to English - going the other way I'm guessing is laughable but I'll join the German forum and post there anyway, at the very least I'll make a couple of members laugh at the translation!

I've ordered a dual bench power supply (0 - 60V @ 5A or 0 - 30V @ 10A) which will let me play about with various input voltages for the inverters I've got and see where they "wake up" and what the current consumption waveform is like - I have heard people have discovered their MPPT inverter when connected to a battery source, wildly varies the current drawn between almost nothing and double their rated input current - not at all good for longevity.

(I have various power supplies, 5V - 17V @ 35A, 24V @ 45A, 0V - 14V @ 1A, but nothing that goes upto the 55V these inverter can require, and nothing with current limiting, save a selection of fuses!)


I've traced out the DC voltage sensing circuitry in these 500W inverters and now know what is needed to get that part working from 26V, so when the power supply arrives I'll do that and test one. What the rest of the inverter does when working off a low voltage totally depends upon the design and CPU code.


Other alternatives I've been looking at are large online UPS modules - the problem is that any decent UPS uses a DC battery voltage of 72V, some even more, so they're unusable for my project.


Also looking into just getting an 8WK non grid tie inverter, adding a second fuse board and swapping over all lighting and all the sockets (apart from kitchen, utility room, garage, workshop - anywhere that has a high power load) and a switch over relay to switch back to grid power when the battery goes flat - the switch over does concern me, I suspect if the inverters waveform was 180 degrees out from the grid there could be an instantaneous change from (say) +270V to -270V (rough absolute max voltages) which would, well, I'm not exactly sure what it would do. Generate a short burst of high frequency noise for one. And I imagine any inductors will try to maintain the +270V and generate a lot of back EMF.

Saying that, this is how offline UPSs work, a simple relay without any inverter waveform synchronising.

There is also the problem that may arise if some unsuspecting person plugs a high load into the inverter powered circuit. I can get an 8WK inverter with a 30 sec peak of 16KW which is way more than one device (connected via a 13A slow blow fuse) should use, but instantaneous switch on currents can be very high, 10 times rated power isn't uncommon, so 30KW for a few mS.


Hence I will continue to pursue the GTI solution for now. This new PSU can supply enough voltage to "turn on" any GTI, so I can check my modifications and also connect my scope and see what the voltage and current draw is like. Also the new 1KW GTI should be hear next week, and that should be fine for working from my battery.


I've also read a lot of (valid) concerns from people about these inverters that just plug into a wall socket, and taking their concerns into account in the final system I'll have to modify the GTIs to remove any output sockets and make sure they're hard wired with proper earths and protection in place, enclose all components in a decent ventilated box / case, and also locate the system next to the fuse board and put it on its own spur. All common sense really.