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analog8484 Senior Member Joined: 11/11/2021 Location: United StatesPosts: 111
Posted: 04:30pm 31 Aug 2023
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It appears that static transformer resonance is no longer so important. So, it looks like the cap size can just be selected as part of a typical LC filter design and maybe with some consideration for inverter idle power consumption.
KeepIS Guru Joined: 13/10/2014 Location: AustraliaPosts: 1685
Posted: 10:58pm 31 Aug 2023
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Yes, that's what it's looking like, and why it was there in the first place.
It's also appears that with respect to Idle current, the Cap value influence is dependent on the value and type of choke material, two chokes with the same inductance but different core material, will behave differently in the inverter as each will present a different value of inductance to the Inverter under varying load conditions. So in my case the cap makes almost no difference in idle current.
I spent a lot of time testing almost every previous choke design in an effort to come up with a choke that gave the best results under very high peak DC input currents up to 500A and above in some cases, I found that I only had to sacrifice a small amount of idle current and SPWM filtering to accomplish this.
I do notice that using Wiseguys Power Board design and Controller, the Idle current hardly increase even with half the choke inductance. I put that down to his design having very fast FET switching and his SPWM Symmetry drive, both reduce FET heating/current and it appears this inverter is less dependent on high choke inductance for low idle power.
Under some high current startup loads, the higher value of secondary cap appears to reduces harmonic distortion and is reflected in the inverter DC Input current sensor waveforms, at least that's what it looks like to me. There may be another explanation?It's all too hard. Mike.
wiseguy Guru Joined: 21/06/2018 Location: AustraliaPosts: 1156
Posted: 11:00pm 31 Aug 2023
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There is a downside of making the capacitor too large and that is circulating current which is not the same as idle current. The capacitor should be selected to be the minimum size required for an acceptable level of distortion. For instance if the street power is usually 4% distortion ( and we are happy to connect to it (except for cost and maybe reliability)) why try to make the inverter achieve 0.1% distortion as there is a downside to pay for this.
The circulating current is easily seen on the 50Hz mains power side, if you put an AC clamp meter on one lead of a 10uF AC filter capacitor, you will see 1 - 1.5A of AC current which is the circulating current. Considering it is at ~ 240V and that is well over 200W of power, but hang on the DC input idling power is only ~ 20W, what gives ?
During the rise to the peaks of the 50Hz waveform current flows into the AC capacitor but after the peaks at 90 & 270 degrees the energy we just filled the AC capacitor with is "pulled out" of the AC capacitor & returned to the inverter input DC filter capacitors resulting in the low idling input power - thanks to FET switching magic. If we see 1.5A of 240VAC circulating current this energy had to come from somewhere and it came from the input DC power initially and due to say a 1:8 turns ratio the primary current will be 8 times the secondary side or 12A for the example just given (at 50Hz).
So the FETs are already switching an RMS AC current of 12A @ 48V (note the HF switching current is greater then this) with only 20W of input power which is equivalent stress on the FETs of running a 600W load but with no load connected as yet. This is why we should be happy to accept a distortion figure that is maybe equivalent to or marginally better than the mains to be kind to our FETs.
I know Mike (KeepIS) will be saying that my FETs run cold no matter what size cap I have used and that is also a fair comment but 4 x HY5608 are not what a lot of others are using so I thought a comment on capacitor size was timely, bigger is not always better.
Lastly I am fairly confident very few on the Forum here have access to a mains analyser that can show the distortion and harmonic content of the AC waveform so maybe Mike (if he has the time and inclination) can fill in a few gaps on examples of say 1uF 2uF 4u7 & 10uF caps on the inverters output with and without other filtering, and log the resulting real measured distortion for the record. Edited 2023-09-01 09:15 by wiseguyIf at first you dont succeed, I suggest you avoid sky diving.... Cheers Mike
KeepIS Guru Joined: 13/10/2014 Location: AustraliaPosts: 1685
Posted: 11:14pm 31 Aug 2023
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Thanks Mike, just replied and then saw your post.
Yes, I was happy when the Inverter THD was no more than the Mains THD for the same good and bad loads. Just some extra spikes under bad loads between the 15th and 25th order harmonics from the inverter, I guess due to the nature of the AC generation scheme and the sink capacity of the Mains.
I was wary about going to 12uF across the transformer but I wanted to be sure that the low resonance values produced by caps between 5uf and 12uf, each running for a few hours in the inverter, would caused no resonance problems - they did not.It's all too hard. Mike.
wiseguy Guru Joined: 21/06/2018 Location: AustraliaPosts: 1156
Posted: 11:16pm 31 Aug 2023
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I just edited my previous post with a final paragraph..... please don't yell at me....If at first you dont succeed, I suggest you avoid sky diving.... Cheers Mike
KeepIS Guru Joined: 13/10/2014 Location: AustraliaPosts: 1685
Posted: 11:45pm 31 Aug 2023
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No worries, I'll try and remember do that, surprisingly the THD did not show any real improvements with various filter configurations or values of inductance, capacitance and core material used. I really was not expecting that, sure there were slight AC waveform differences but THD - Only changed with Loads just like the Mains?
Inverter THD with 100W of resistive load is around 0.9% to 1.2% and the Capacitor value I selected is 4.5uF as it gave a slight visual improvement AC waveform over 3.3uf, and the inverter gives a better waveform on DC input current on some loads.
BTW I had the inverter running at 4.5kW for over an hour yesterday, once again the FETs and heat sink are just room temperature, and there is no fan cooling of the heatsink. The heatsink thermostats [on the heat transfer bars) are redundant, although still good for measuring room temperature It's all too hard. Mike.
wiseguy Guru Joined: 21/06/2018 Location: AustraliaPosts: 1156
Posted: 12:11pm 23 Jan 2024
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Mike, Hope you are well and having fun. I have had a few queries about my inverter power board and its actual power rating/capability. As you have challenged my power PCB a lot and run it now with constant significant loads, I have a few questions.
What constant power rating would you give the power FET board ? You are welcome to give 2 ratings if it helps, 1 conservative 2 intuitive & not actually measured.
What peak power rating for say 5 seconds would you be comfortable with rating it ?
Have you run an IR viewer scope or temperature probed the PCB to see what gets hottest under a good continuous load ?
Can you confirm the kw rating (each) of the 3 toroids you are using ? Can you also confirm the MOSFET types (are they HY5608s) ?
Thanks in advance & sorry for not reading 26 previous pages for the answer Edited 2024-01-23 22:13 by wiseguyIf at first you dont succeed, I suggest you avoid sky diving.... Cheers Mike
KeepIS Guru Joined: 13/10/2014 Location: AustraliaPosts: 1685
Posted: 11:12pm 23 Jan 2024
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Hi Mike, looks like we both had a busy period.
I am a few day away from finalizing the complete rebuild of the batteries, cabling and solar charging side of system
I would love to get back to that simplified control board design when/if you get it finished.
I ran the board at 7kW output for about 30 minutes, the FETS in mine are sandwiched directly between the PCB Power planes and four heavy individual intermediate heat transfer bars. There is a temperature sensor on two of the heat bars, right next to the FETS.
The heat bars got to 42 deg, basically warm to touch, all four were the same. I think for continuous use I would want a second set of Terminals for both the DC and Toriod Cables. I was planning to tap the intermediate heat bars, but as I will never run at that level there is really no need.
Slightly hotter part of the PCB was the Terminal connectors, obviously very hard to verify the PCB planes, but they felt slightly warmer than the Heat bars at 7kW, that could have just been the FETS?
To refresh you mind, the four heat transfer bars are connected to a massive heatsink via a sheet of insulating heat transfer mat, amazing heat transfer when you do it this way.
NOTE: There is NO FAN cooling of the board or Heatsink.
I have run it at 13kw output for 3.5 seconds and the peak DC input has been as high as 32kW, both of these events have been repeated over and over on numerous occasions.
The Toriods are rated at 1.150 kW each, however that is the 230V AC rating when mounted in a sealed small box.
These Toriods have a 93 volt heavy duty single layer winding on the Core, the 230v volt winding was wound over this. The 93v winding is so thick that it would be impossible for me to wind even one turn on a single core by hand. From memory it was between 2.6mm 2.8mm, I would have to check though.
As you know, I removed the outer 230V windings of each toriod, simply stacked the three, wired the 93V windings in series, and wound a 35mm2 single 14 turn primary.
The MOSFET are HY5608s.
Hope this is of some help.
BTW. Still running the Inverter 24/7, even during the battery rebuild, today will be the first day off when I shut everything down to rewire the DC bus in the system. . Edited 2024-01-24 10:04 by KeepISIt's all too hard. Mike.
wiseguy Guru Joined: 21/06/2018 Location: AustraliaPosts: 1156
Posted: 01:07pm 24 Jan 2024
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Thanks for the information and your time taken to reply. I had work today so a belated response.
I never realised the toroids were only 1.15kW each I thought they were like 2.5kW+. It is amazing the high throughput levels you can get briefly from ~ 3.5kW total nominal power of the cores.
2 other questions, are your gate resistors 1.2 or 2.2 or something else? What is your idling power with no load connected ? What is the uF of the mains filter cap ?
I am thinking that a conservative power rating of the PCB is probably around 5-6kW continuous, with a 5 second peak capability of 10 - 12KW and short peaks of 20+kW ?
It is relatively easy to add more terminals for Bat + & - and the A&B outputs, plenty of room around them, but a bit costly. 10 of those boards delivered in 2oz are ~ $150, 5 delivered are ~ $130. Edited 2024-01-24 23:08 by wiseguyIf at first you dont succeed, I suggest you avoid sky diving.... Cheers Mike
KeepIS Guru Joined: 13/10/2014 Location: AustraliaPosts: 1685
Posted: 04:00am 25 Jan 2024
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A single toriod of similar size can easily start the Bandsaw etc. I might be wrong, but I think if a core is wound correctly so that it doesn't saturate, then the only limitation to output power might be the gauge of the windings, and controlling the heat in the core to a manageable level?
I think the nominal power of these Cores are underrated because of the 235vac winding and the heat generated inside the sealed pressure cooker design of a very compact case, these units were usually outdoor mounted in the blazing QLD sun.
Running 5kW continuous for an hour or two bought the triple Toriod core to 39c, just warm to touch, same as the Chokes, however that was with forced air cooling through the toriods kicking in when they hit 37c. Two Sensors, one sandwiched either side of the center toriod.
I don't recall the gate resistor value, I vaguely recall you deciding on a value and I went with that. I will have to get into the inverter power board to confirm.
The idling power with no accessories @ 235vac was around 17 watts.
Toriod cap is 3uF. I will have to get to the Mains filter to check my final value.
Yes, your rating sounds about right for the current build state.
I think it's likely conservative when I see how hot commercial gear runs
I'm a heat sook , if I can't hold my fingers on any part for a few minutes then I think it's running hot.
I'm happy with the price, it's just shame we can't get more people interested. . Edited 2024-01-25 14:03 by KeepISIt's all too hard. Mike.
rogerdw Guru Joined: 22/10/2019 Location: AustraliaPosts: 853
Posted: 01:59pm 25 Jan 2024
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Mike and Mike, I was shocked to hear that the transformers were only rated at 1.15kW too. I assumed they were 2 or 3kW each ... especially reading the power levels you've been pulling from it.
If you had access to the ideal transformer ... what would be the specs? Is that a theoretical calculation ... or a heap of trial and error required?Cheers, Roger
wiseguy Guru Joined: 21/06/2018 Location: AustraliaPosts: 1156
Posted: 02:25pm 25 Jan 2024
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Not a heap of trial and error, if its got some iron and some copper and a few wires hanging out it'll probably work...
I think Mike has shown that with a bit of lateral (or is that vertical) thinking there are some options that are worth a try without a complete rewind, that will work surprisingly well.If at first you dont succeed, I suggest you avoid sky diving.... Cheers Mike
KeepIS Guru Joined: 13/10/2014 Location: AustraliaPosts: 1685
Posted: 03:45am 26 Jan 2024
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The ideal transformer for my current usage would be the one I have, but with a single wound primary.
The tradeoff with 3 primaries in series is that it uses about 20% more cable then a single winding through three cores, and it likely produces a bit more heat due to slightly higher secondary R-Loss.
But I doubt I would notice any difference in my real world operation.
Interestingly, each core has almost the same cross sectional dimensions as the 6kW - 28kW peak single toriods designs used in the past, and I have three cores stacked. The Peak power available from this transformer and Mikes Power Board is insane.
I would need a chain lift if I wanted to lift the inverter up onto a bench, the Toriods are that heavy. That's why I designed a large Inverter Cabinet, I made sure that any part could be removed, serviced or modified with the cabinet on the floor.
Big HD wheels, removable back, huge full opening front door, and three very big compartments, and designed with natural and forced air flow in mind.
Top compartment has all the AC/DC interface, inverter meters and controls and isolated DC-DC supplies. Middle compartment has the Power board and driver board, and bottom compartment has the Toriod, chokes and AC filter.
When I think about it, that question is almost like "How long is a piece of string", and like the string, the ideal changes with the constant power level you think the inverter will be running at, and the size and weight you can accommodate.
BTW I spent a lot of time testing a couple of single toriod designs for the turn ratio required to keep the core well away from saturation. I allowed for the wide DC input range that I wanted to have for the selected AC output voltage.
That's why I didn't unwind any of the three 93V windings, these produced 281Vac, and that is higher then most wind the secondary for. I was happy to leave that after testing the final primary winding and the ratios were keeping the core away from the apparent saturation knee for any input voltage down to the lowest SOC cutoff.
I could have reduced the Idle power even more but I chose to trade that off a bit. I did look at the formulas, but I was still guessing numbers with the triple core design, so I was more interested in the real world bench testing and abuse to back it up.
So true - It's all too hard. Mike.
Murphy's friend Guru Joined: 04/10/2019 Location: AustraliaPosts: 651
Posted: 07:54am 26 Jan 2024
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With regard to gate resistors for the HY5608's, the data sheet mentions 6R (under rise time specs). I used 5R6 in my small caravan inverter that uses just 8 HY5608's. That seems to work well for me..
Notice. New forum software under development. It's going to miss a few functions and look a bit ugly for a while, but I'm working on it full time now as the old forum was too unstable. Couple days, all good. If you notice any issues, please contact me.
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, if I can't hold my fingers on any part for a few minutes then I think it's running hot. 
