analog8484 said  

Looking forward to seeing the build.  It's a bit surprising to see a 40uH inductor given the 40kHz switching frequency.  Based on the ~47uH inductor sizing for the 20kHz switching frequency used in the more recent nanoverter builds, it seems a significantly smaller inductor could be used for 40kHz.  Increasing the switching frequency is one thing I've wondered about for the nanoverter as a way to reduce the quite large inductor size used in the recent builds.

Edit: I consulted an AI, ChatGPT, it recommends using 2 x 10uH inductors

Mike
Edited 2026-08-24 09:08 by Solar Mike

Footnote added 2026-08-24 10:04 by Solar Mike
ChatGPT recommends if paralleling two H-Bridge power modules, then it is more efficient to have one running 180 out of phase in the 40 Khz SPWM inputs. This is easy to do with the PICO2 RP2350.

Hi Mike, just wondering , as you said you have plenty of batteries and are going to make up a 110 volt bank or so. Whether a GTI inverter running off that bank of batteries would have enough grunt to help start the pump.
You would need to have some sort of method of getting the GTI to start up before you tried to start the pump, but it may just give enough kick to get you over the line.
Pete

Will a GTI work off a 110v bank??, can think of other Hybrid inverters that would work here to sync with the generator AC and boost output current, but quite expensive.

Mike

HI Mike, some GTI inverters work off reasonably low input voltages.
I am using Zeversolar GTI inverters on my system, they are supposed to work from 100 to 500 volts input.

I was thinking that you could use the batteries as pretend solar inputs. So plugging the batteries into the MPPT controllers on the GTI inverters. Then AC coupling the inverters to your current inverter.
You would need to make sure that the GTI is backfeeding to be sure that it will come on in time to assist the battery inverter.

Of course that depends on whether you have one laying about or can pick a second hand one up that will run on around 100 volts from the panels or in your case battery bank pretending to be panels

Pete

  Quote  

Looking at various options, have decided to build a LF inverter, I have an old toroidal core stripped out of a variac, the core needs demagnetization, so will have a go doing that.

If the Toroid isn't salvageable a C Core transformer will do the job if you can find one, they were sometimes used on 1980"s Telecom rectifier battery charger's and a few other things, they will be plenty good enough for motor starts.

GTI is an interesting idea but the backfeed issue could be tricky.  Also, depending on the GTI model, it may stop producing power immediately if the AC voltage is distorted too much by the load startup surge.

Ideally, a parallelable voltage source inverter that has generator/grid power assist/shaving functionality would be more suited for the task.  AFAIK, only commercial inverters (e.g. Victron) are available with such functionality.

I do have a couple of GTI's here, ENASolar 2kw, have been sitting in the shed for many years wrapped in original packaging, unused. I looked at the manual and they require min 185v and have a limitation on input power; connecting them to a battery would do some serious damage I think. Easier just to build something, least if it blows up I can repair it.

I need some small MPP type cores for the inverter output inductors type Micrometals MP300060-2, have emailed MicroMetals in USA see if I can purchase a few. Looked on AliExpress, nothing really suitable there unless you stack about 8 together, whereas the MP300060-2 just need 1 on each output lead to the transformer primary.

Mike

Just throwing a thought in about adding some sort of spinning mass inertia into your system. The spinning mass could be turned on some seconds before you need it so that it gets up to speed, then locks on to your inverter frequency. When the pump is commanded to turn on, the spinning mass can act as a very high current supply, just for a second or two.

The question would then be what sort of spinning mass you might have available...... a generator head with a heavy flywheel? A 3-phase motor?... Just some thoughts....

Hi Mike, just wondering after reading Haxby's respone
You said your batteries are Lead Carbon, I don't know about their specs but you also say you have a collection of Lithium batteries too.
Would it work to make a 48 volt bank of lithium batteries and a relay that allows them to be paralleled with the lead carbon bank to supply the starting current your pump needs.