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48V 5000W Oil cooled inverter build
#71
hi user completelycharged
Why I did not find this forum before I did almost same research as you Big Grin 

I don't have one bigger transformer so I tried use two combinations: first is parallel connected two transformers (~28/230V 2500VA) and second combination serial connected bigger transformers ( ~14/230V 3700VA).
I'm using almost same board as you.. with 28 fets and I don't want to go above 7kW of load with air cooling. 
0,65A at 48,1V so nice 31W iddle consuption
I recommend to use two inductors at both poles..
And I want to use same filtration at output (I bought 40A version)
You did great research and work Smile
completelycharged likes this post
[Image: pv.png] FS-272 ~ 4600Wp, Poly 230 ~ 3300Wp, MakeSkyBlue 60A, [Image: battery.png] Pb Traction ~ 48V 1000Ah, 18650 14s80p 143Ah, AC ~ PIP-4048GE, DC ~ still consuption 250W, Own monitoring ~ Domoticz
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#72
Like it, the position of the chokes does not seem to matter (one or two with one on each output leg). 31W idle with two transformers is quite good.

Using two transformers (3 at most) in parallel seems to be the ideal route to get the rating sustained above 5kW without having chokes that are getting the same size as the transformer. My next build will be using 2-3kVA toroidal transformers, possibly 3 x 2.5kVA but the idle losses start to add up with each toroidal transformer potentially using about 18W. Don't want to go auto switching route as it's just more parts to go wrong.

Using multiple transformers in series is only useful if you have them spare as you can't use the aggregate rated capacity due to the primary windings ending up being twice the voltage and only supplying them at half thier rated... unless it's primary in parallel and secondary in series then they really need to be identical.


The existing 6kVA unit works fine at the moment temporarily sitting in a metal box, the only ongoing issue is the 2100TL SolarRiver inverter creating some harmonics on the sine wave which makes the wind grid-tie unit get a bit confused as to where the peak is and just trips off refusing to stay synced to the local off-grid grid. Plus the E chokes need sealing / glue applied as they hum quite loudly with the harmonics from the solar inverter and it seems to be the center of the E creating the majority of the noise.

Separately the wind grid tie does not seem to like the stormy gusty west coast winds as it seems to loose track somewhere above about 600W and just refuses to play and resets (disconnect overvoltage). That's even with the settings V and A so that the unit should work up to 1kW. Maybe a design coincidence as the blades start to really complain above 850W, although it is a 700W turbine.. lol. Don't think it has anything to do with back feeding voltage spikes through the inverter at the moment as it happens on both 6kVA and 1kVA inverters with other loads attached (e.g. while 1.8KW kettle is on the 6kVA unit).

Temporary harmoinc solution is to use the smaller 1kVA unit for the wind grid tie and the 6kVA for the solar, along with the kettle, oven and microwave. This eliminates (hides) the harmonics issue for the moment and will only be able to resolve it when I get back home (>500 miles south) and have a look at the sinewave in deatil with different parts in the circuit. Might just be due to the large output capacitance the solar inverter appears to present.
Johnny.sk likes this post
If you can't quantify how much they cost, it's a deal, I'll buy 5 of them for 3 lumps of rocking horse ......
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#73
(01-30-2020, 08:03 PM)completelycharged Wrote: Like it, the position of the chokes does not seem to matter (one or two with one on each output leg). 31W idle with two transformers is quite good.
Of cource it does matter.. But not for down the idle consumption but for TDA noise.. When you will connected oscilloscope, you will see the difference.
I read some tries by Australian builders and their use combinations of two different chokes with different cores and impedance. Results was amazing. Pretty harmonic 50Hz sine wave.
(01-30-2020, 08:03 PM)completelycharged Wrote: Using two transformers (3 at most) in parallel seems to be the ideal route to get the rating sustained above 5kW without having chokes that are getting the same size as the transformer. My next build will be using 2-3kVA toroidal transformers, possibly 3 x 2.5kVA but the idle losses start to add up with each toroidal transformer potentially using about 18W. Don't want to go auto switching route as it's just more parts to go wrong.
Did you try parallel toroids? Because I tried.. And mosfets burned in 3kW load (2x2500VA toroid on 12kW board) I think, toroids are not identical.. And one filed core of second one and that pushed some voltage back to the invertor.
My first concept was based on adding 2.5kVA toroids, 2pcs at start and add 1-2pcs when i will have money but inverter dies with 2pcs.
I have nove serial connected primary on toroids and parallel connection of 230V secondary side of toroids.
Result.. Nice stable voltage with any load.. But you have right. This is my second toroid combination. First combination had different cores and core fill was 0.12A and 0.35A so at load voltage was ok but one core was warm and second was cold. So I asked factory to measure cores, choose more similar and then make windings.
Now it works perfect.
[Image: pv.png] FS-272 ~ 4600Wp, Poly 230 ~ 3300Wp, MakeSkyBlue 60A, [Image: battery.png] Pb Traction ~ 48V 1000Ah, 18650 14s80p 143Ah, AC ~ PIP-4048GE, DC ~ still consuption 250W, Own monitoring ~ Domoticz
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#74
I registered just to comment on this post.. i have the same 7 per leg mosfet board, with a custom wound 5kw (VERY conservative rating) oil cooled toroidal transformer... VERY VERY happy camper so far, months and many kwh under its belt, with every imaginable load ... no faults so far...

Few minor " fixes " i had to do, replace all the electro caps as they were all 16v (25v board rated) , increased primary capacitance to over 100k uf, and drilled and tapped new stonger bolt holes for heavy cabling..
Johnny.sk and completelycharged like this post
I think it works !!!!
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#75
noneyabussiness, that is great to hear.
Good point with that primary capacity..
You can share more details (images) with us. Everyone will be happy for share any experiences..
Maybe, why did you make decision to increase capacity.. Do you recommend that for everyone? Or it's required for 24V version only?

I yesterday repaired died board. I unsolder FETs, measure them and replace dead pcs. And today board work again Smile
[Image: pv.png] FS-272 ~ 4600Wp, Poly 230 ~ 3300Wp, MakeSkyBlue 60A, [Image: battery.png] Pb Traction ~ 48V 1000Ah, 18650 14s80p 143Ah, AC ~ PIP-4048GE, DC ~ still consuption 250W, Own monitoring ~ Domoticz
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