It may still be possible to make that 5Kva toroid work, by placing one of the 20v primary windings in series with the secondary.

So you then have 20v primary, and 120v + 20v = 140v secondary.

If we did that, to reach 120v across the combined secondary, only requires 17.1 volts across the primary. Peak primary voltage would then be 24.2 volts, still a bit higher than ideal but it might just be workable.

Secondary max power would be 31.25 amps x 120v = 3750 watts
Primary max power 31.25 amps x 7 windings x 17.1v = 3740 watts
So nothing is over stressed at the above power levels.

This would also reduce idling power significatly.

Ooh, that sounds like I wouldn't even have to wind my own primary. Did I understand that correctly?

I can get 2 of these for $100.

  Warpspeed said  

This would also reduce idling power significatly.

Why does this work?

R
Edited 2021-05-20 04:23 by flyingfishfinger

  flyingfishfinger said  

Ooh, that sounds like I wouldn't even have to wind my own primary. Did I understand that correctly?

I can get 2 of these for $100.

  Warpspeed said  

This would also reduce idling power significatly.

Why does this work?

R

You are not driving the transformer as hard as it was designed for. Less flux density. Less volts per turn. That equals less idle power.

You won't have to wind your own primary (for a 24v system).

The trade-off is a lower power output of 3740 watts, instead of the rated 5kw. Pretty good trade-off if you ask me.

Yup, Phil has nailed it.

Idling power will be less because you will only be driving the 20v primary to 17v not 20v.  Lower flux density = lower idling current.

I think its at least worth a try, and if you need to, its always possible to rewind the primary.

Cool, sounds good. I'll try and pick them up in the next week or so.

If it works nicely I could just build two full inverters since I need to order more than one Powerboard anyway, ha.

Does anyone have more input on chokes? I could just go ahead and buy those E-cores Peter recommended, but I'm wondering if I can do better.

If salvaging for this, what do I need to be looking for?

Side note: Peter, would you be willing to share the source for your Powerboard? I'd like to make the ground plane tweak before I order a couple.

Cheers,
R
Edited 2021-05-21 09:54 by flyingfishfinger

  flyingfishfinger said  

I'm not QUITE starting from scratch. My little PV system out there runs on a Victron BlueSolar MPPT, which can only charge 12 or 24V batteries and I'd like to keep that.  

I currently have 2 x  105Ah 12V marine deep cycle batteries in parallel which will be enough for the time being, but I can wire them either way.

R

Before you get too far into it have a think about how much battery you will need and how much you have to spend on it.
Most people running a very small house need 600ah @48v at a minimum to live properly.

One thing many overlook is how horrendously expensive the battery bank they need will cost.

It does seem odd building a 5Kw inverter with only 2.5Kwh of battery capacity.
It will have only MINUTES of battery capacity at full load, not half an hour.

Battery capacity is most often rated for ten hour discharge.
A hundred amp hour 24v battery six to eight amps discharge overnight would really be thrashing that battery, and that is only 144 to 192 watts of average load.

Even if you can get 100% battery capacity recovery every single day, its just not going to be enough. Battery life is going to be very short as well.

  Warpspeed said  

It does seem odd building a 5Kw inverter with only 2.5Kwh of battery capacity.

Point well taken. My expectation is 100% that we will upsize the battery sooner than later. I just need something by mid-August that will run inductive powertools for short periods of time.

It's easier (in my head) to add more batteries than rebuild / add an inverter even if its design is simple. We can get batteries in the closest town on short notice but I'm not set up to build electronics anywhere nearby.

(Also, this is not a place where anyone will live permanently. It will be visited a few days at a time every other month or so)

R
Edited 2021-05-22 11:18 by flyingfishfinger

The way that transformer is wired allows you to easily change to a 48v system in future anyway.

  Haxby said  

The way that transformer is wired allows you to easily change to a 48v system in future anyway.

Yup, that might be a good plan.

Time to search for parts! Picking up the transformers next weekend.

- MOSFETS: How do we know the HY4008s from Aliexpress are legit (non-fake)?
- I don't see those big predrilled heatsinks anymore. Any specific search terms that make them appear that people know of?

Cheers,
R

seller "Aoweziic store" has been recommended on this forum before for the MOSFETs.

  Haxby said  

seller "Aoweziic store" has been recommended on this forum before for the MOSFETs.

I can confirm that every mosfet I got from that seller (~100 pieces) was good with low RDSon. I posted a simple schematic a while back how to bench test them.

Its wise for a first time inverter builder to order more than you need for your project.

Yup, I think I'll order the 50-pack. If I don't blow them all up, I can use some for the MPPT (Side note actually - can I? Peter's MPPT uses  FDH055N15A at 150V, but my input voltages will be lower with the appropriate transformer).

Further thoughts (stream of consciousness, please critique if anything sounds wrong):

- Heat sink: After some more searching I DID find the aforementioned pre-drilled ones,  but I'd need x4 of them for $60. I think I can do better if I can drill & cut to size some other ones. x4 of the 130mm  for $40? Or this , needs lots of trimming?

- Caps, good for MPPT as well

R
Edited 2021-05-24 08:11 by flyingfishfinger

Hey R,

the HY4008 will be good if your solar array does not produce more than about 80V.
I have tested the HY4008 for breakdown voltage from Drain to Source and it's
about 84V. So we can not go much more than 80V

I expect the battery is 24V nominal so the mppt will be very efficient when converting from 70-80V down to 24 - 27V. And you can use the HY4008 for both MOSFETs and DIODES in this application. They are really good diodes with very low Vforward

My home has a 48V battery and so I need 3 panels in series, which usually makes about 90-100V. So that is why I use FDHO55N15A and the diodes are the 100V versions of the HY4008, namely HY5110. I got them from lcsc.com
maybe aliexpress can supply now, dunno

As far as trimming heatsinks, I use a 7 inch Makita circular saw, with it's
OEM carbide tipped crap-ola saw blade.
If you go slow, with the fence guide, and maybe a spray of WD40 along the cut
things will work out nice. I secure the work very, very well with screwed down blocks of wood into a wooden workbench. Then wheel it outside. The amount of alum chips this makes is insane.

The caps are ideal for both projects.
I would use one only on the output stage of the mppt, and maybe 2 for the input.
I would use 6 for the power board.

Testing has shown the mppt code works perfectly even with the 10,000uF on the output stage. I suspected it might run totally wrong and be useless with the far longer
time constant implied by the 10,000uf across the output. But a decent battery or a 1 ohm load resistor is good enough to make the output respond fast enough for the mppt search to function correctly.

(the 1 Ohm resistor is 3 x 6 foot lengths of 0.8mm stainless welding MIG wire dunked in a bucket of water. It's good for 3kW+)

the picoverter boards have arrived.



You of course have your name on 2 of them.

In the mean time, obtain a couple of
these 80V ->15V modules since you will need one for the picoverter.
Or use something else you have handy that makes 15V at 1 Amp. It's not important
what you use. just need 15V, ground referenced to the battery -ve.

  flyingfishfinger said  

- Heat sink: After some more searching I DID find the aforementioned pre-drilled ones,  but I'd need x4 of them for $60. I think I can do better if I can drill & cut to size some other ones. x4 of the 130mm  for $40? Or this , needs lots of trimming?

- Caps, good for MPPT as well

R

A tip about those heat sinks: Remember you have to drill & tap them for the mosfets. Now the last thing you want is the drill coming through halfway between fin and gap -  a sure way to break it.
Yes, you can drill & tap blind holes but then the heat sink back needs to be about 1/2" thick for sufficient thread. Its also much easier to break small taps in blind holes.

Here in oz we use mainly re cycled heat sinks which are free from junked inverters. These usually have a 6-8mm gap between the fins, plenty for a 3mm screw to poke through.
I would look out for junked inverters first.

It's always tricky to order components from China.
But I also have good experience with those suggested Hy4008 mosfets, seller and plan to order more of them in the future.

I don't know on what level you can check components but I recommend using quality parts from companies like RS, Farnell, tme, mouser, reichelt, etc
I think it was Peter having some troubles with Chinese capacitors? Some had issues with voltage regulators, mosfet drivers, etc Just be careful with what you buy.

  poida said  

the HY4008 will be good if your solar array does not produce more than about 80V.

The MPPT will be for the F&P hydrogenerator. I should open a separate thread for that, as I'd like to make some modifications to drive a dump load. I just wanted to make sure I don't buy stuff I don't need & can repurpose things :)

  poida said  

You of course have your name on 2 of them.

Oh! I'm happy to make my own - I was actually just waiting for functional confirmation on your latest build, but if you've got extras... thank you!

  poida said  

just need 15V, ground referenced to the battery -ve

If you drop it to 12V using the series diodes (IIRC correctly), can't we just use a 12V module? This part supplies power from the battery to the Picboard yes?

  Murphy's friend said  

Here in oz we use mainly re cycled heat sinks which are free from junked inverters.

You're lucky, California doesn't seem to have a highly active off-grid community, or I haven't found it yet. Point is, I haven't seen (yet) any dead inverters on CL or Ebay, so that may be a dead end, pun intended. EDIT: Just checked - CL has some DEAD SolarEdges being sold for $120 - $220. Lol.

  nickskethisniks said  

It's always tricky to order components from China.
But I also have good experience with those suggested Hy4008 mosfets, seller and plan to order more of them in the future.

I don't know on what level you can check components but I recommend using quality parts from companies like RS, Farnell, tme, mouser, reichelt, etc
I think it was Peter having some troubles with Chinese capacitors? Some had issues with voltage regulators, mosfet drivers, etc Just be careful with what you buy.

Trust me, I know - I do this for a living and I am VERY weary of Chinese-supplied components. We have been having to consider Chinese-branded alternatives for several chips in our product because of the chip shortage, it's never fun.
That's why I asked specifically about recommended vendors for the MOSFETS, as they seem to have a legit datasheet but can't be acquired on the usual "known" sites and "quality" substitutes bought here will break the bank in quantities required.

I'm less worried about the capacitors, as long as I'm operating at half the rated voltage or lower. Peter did say they got warm when overvolted, but that's more or less expected for electrolytics when abused. It's also why they're designed to "pop their tops", minor explosions are the expected failure mode.

I'll get the rest from Digikey.

Regarding trimming heatsinks - we have a machine shop at work (band saw & drill press), so I think I'll be fine there.

Picking up the transformers next Sat, hoping to get the long-LT Aliexpess order in sooner.

Thanks for the advice so far!

R
Edited 2021-05-25 03:19 by flyingfishfinger

  flyingfishfinger said  

The MPPT will be for the F&P hydrogenerator.
R

Hydro output voltage will double under zero load conditions, so make sure you have plenty of safe voltage headroom without relying on any protection.

  Warpspeed said  

  flyingfishfinger said  

The MPPT will be for the F&P hydrogenerator.
R

Hydro output voltage will double under zero load conditions, so make sure you have plenty of safe voltage headroom without relying on any protection.

Good point. If I stick with a 24V system the HY4008 should be fine (set nominal input to 30V & let it double to 60V).

However, that would mean I DO need the higher-voltage MOSFETs for the MPPT if I switch to a 48V system later...

R