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Forum Index : Electronics : Another three-stack toroidal transformer
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| FET cemetery Newbie  Joined: 17/04/2024 Location: AustraliaPosts: 25 |
The (nearly) finished product:  A bit of background, I've been off-grid for 20 years. Bought a powerjack inverter about a decade ago to run the kind of loads I didn't want to risk on the house inverter, eg welders, cutoff wheel, and the big one a 3.6kW pottery kiln. It lasted 5 or 6 years, when it finally blew up I put together an egs002 driver board and did the Oztules mods to the Fet board. Got another identical blown inverter from a neighbour and basically ran 2 sets of powerjack transformers in parallel as one set was never really up to 3.6kW continuous. EV charging has recently been added to its duties. Efficiency and output voltage stability was never great, but it was only ever switched on during the day for big loads. It would run fine for months or even more than a year sometimes, and then seemingly at random half the Fets would blow (see my username!). This is basically the setup that is driving the new transformer until I build the Wiseguy boards.  Note the green rings that were the chokes on the powerjack inverters. Totally inadequate now, the new transformer is a completely different animal. Waveform with the green rings and 4.7uF across the transformer output, 500W resistive load:  No stone unturned, no FET unburned. |
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KeepIS Guru  Joined: 13/10/2014 Location: AustraliaPosts: 1731 |
A bit late to post this, but I found using a heat-gun on low quickly warmed up the plastic convening on the cable where it needed to bend/form, one turn at a time, that allowed the cable to smoothly wrap around the toriod and also stay flat on the inner and outer surfaces of the toroid, holding it's new shape as the covering quickly cooled. I noted you wound 12 turns, do you remember what AC voltage was requited across the 8 turns to produce 240Vac from the 3 series windings? Yes, will needs better chokes  The Idle current will likely be higher as well at the moment.. Edited 2025-02-13 14:46 by KeepIS NANO Controller: Full download or Hex files Mike |
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| FET cemetery Newbie Joined: 17/04/2024 Location: AustraliaPosts: 25 |
Hi Mike, a 12 turn primary gives about 28 - 28.5V in for 240V out. I used low heat , a rubber mallet and brute force on the windings, I think I could do a better job now. Try not to laugh, this is the choke setup at the moment:  One leg has a single loop running through the remains of an old microwave transformer. The other is running through 2 smallish ferrite rings. (Any comments are welcome, I don't really know what I'm doing with chokes!) The "microwave choke" runs warm enough to need a small fan running slowly at 4.3kW continuous. I'm well aware its not ideal, for starters its welded together so the laminations are shorted. Interestingly, an old 1.5kW induction motor aircon makes the choke run even hotter, must be an ugly load for an inverter. The ferrite rings run cold unless the inverter is running at less than say 200W, then they'll run up to 20C above ambient. I have 9.4uF across the transformer output now, haven't checked the resonance it's just what gave a cleaner waveform under load. Since late December this setup has pushed over 600kWh into the car. You can still see the zero crossing on the scope but it's much tidier now. Voltage stability is excellent, efficiency is about 90% and standby power is about 55W. Good enough that I don't have to rush assembling the Wiseguy boards. No stone unturned, no FET unburned. |
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| FET cemetery Newbie Joined: 17/04/2024 Location: AustraliaPosts: 25 |
The PWM Fets run at the same temperature as the 50Hz ones with this choke setup, in the past they've run much hotter so something is working. One loop through the microwave transformer was 33uH. No stone unturned, no FET unburned. |
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| KeepIS Guru Joined: 13/10/2014 Location: AustraliaPosts: 1731 |
If you can keep startup surge loads down then the Inverter will survive, especially with mostly resistive loads with those chokes, although it's a bit hard on the FETS at idle. The Iron core choke heating at Idle is expected as they are not suitable for high frequency work, that's why the Idle current will be high with them, along with excess heating as you have found, incorrect ferrite chokes will also heat. The 9.4uf capacitor is a bit much, around 4uf is all you should need, much higher will start to cause other loss issues. Don't worry about resonance, it's not relevant. I think if you can get some correct sendust rings, 4 to 6 stacked, with 4 or 5 turns you will notice a big improvement, even in that old inverter board. Looks like everything is going in the right direction though  Interestingly, I needed 14 turns to produce 240vac with 28.4v input, which is around 40v DC, my Inverter is fully regulating at 240vac (with little headroom of course) at 44V DC into the Inverter . Edited 2025-02-13 16:00 by KeepIS NANO Controller: Full download or Hex files Mike |
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| FET cemetery Newbie Joined: 17/04/2024 Location: AustraliaPosts: 25 |
Yep I had a fair idea the chokes weren't right, just using what was in the shed to get something going. Will look into the sendust rings, I want the choke sorted before I use the Wiseguy boards, thanks. This setup holds 240V under load down to 47.5V at the battery, haven't gone lower. No stone unturned, no FET unburned. |
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| KeepIS Guru Joined: 13/10/2014 Location: AustraliaPosts: 1731 |
When you get the Nano Inverter running with the LCD, with the %PWM display you can see the headroom reduce as you lower the Inverter input voltage, it will be around 74% @ Idle @ 54V (due to my winding ratio) to above 95% where SPWM regulation starts to fall off . NANO Controller: Full download or Hex files Mike |
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Revlac Guru Joined: 31/12/2016 Location: AustraliaPosts: 1088 |
@FET cemetery, The steel box your inverter is sitting in, looks like an Ericsson Rectifier, 48v battery charger? they had a good transformer in them, I used it in one of my inverter builds,  thanks for sharing a few build pictures. Cheers Aaron Off The Grid |
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| FET cemetery Newbie Joined: 17/04/2024 Location: AustraliaPosts: 25 |
Well spotted Aaron! I felt guilty dismantling it, but it had a failure on the '80s pcb that I couldn't work out and probably wouldn't have been able to find parts for anyway. I used it for years to charge batteries with a generator. I use the original power switch and the old analogue Amp and Voltmeter. Just because I can! No stone unturned, no FET unburned. |
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wiseguy Guru Joined: 21/06/2018 Location: AustraliaPosts: 1172 |
@FET cemetery, I had 3 of those rectifier units, they had the C transformer from hell, I could hardly lift them. I cant remember but I think they were ~3KW. I reckon I still have the analog Volt and AMP meters if anyone wants them, the units I had used a 3 Phase plug but only wired for and using one Phase. I also still have the grey steel L and the U shape brackets they stood on. Unfortunately when I sold my business I had a couple of days to clear the building so they ended at the dump with big Toroids & so much other good electronic stuff it still hurts. If at first you dont succeed, I suggest you avoid sky diving.... Cheers Mike |
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| Revlac Guru Joined: 31/12/2016 Location: AustraliaPosts: 1088 |
I still have 2 of them, 1 working and a complete handbook for it, parts list etc (old and a bit difficult to read), yes they are very heavy units. Cheers Aaron Off The Grid |
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| FET cemetery Newbie Joined: 17/04/2024 Location: AustraliaPosts: 25 |
Found the manual, and yep it was heavy  I bought mine from an ex-Telecom guy through a classified ad in the local paper. We kind of tipped and slid it into the back of my station wagon, when I got it home we slid it out and leaned it back a bit so we could "walk" it in to position. No picking it up. Had to repair a couple of signal wires that a mouse had taken a fancy to. The manual says 48V 50A, it used to charge my batteries to 60V so I'd call that 3kW. My 5kVA generator was pretty much flat out powering it. No stone unturned, no FET unburned. |
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| FET cemetery Newbie Joined: 17/04/2024 Location: AustraliaPosts: 25 |
Looking at sendust rings, is this the sort of thing I'm after? https://www.aliexpress.com/item/1005003179581137.html#nav-description The 57.1 x 26.4 x 15.2 mm ones? Not exactly cheap, don't want to get the wrong ones. No stone unturned, no FET unburned. |
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| Solar Mike Guru Joined: 08/02/2015 Location: New ZealandPosts: 1147 |
Beware that seller, I have ordered several sets of those exact same cores and had to raise a dispute; the seller shipped me the other 57 x 35 x 14 cores instead, not as wide with the larger hole size, so less material. They change the item listing every so often as this erases any bad reviews. These are second hand cores and don't always have them in stock, but advertise them being available anyway. If they dont have any, they will send you the other sort. Cheers Mike Edited 2025-02-14 13:42 by Solar Mike |
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| FET cemetery Newbie Joined: 17/04/2024 Location: AustraliaPosts: 25 |
Thanks Solar Mike, duly noted. Wow, second hand and still pricey. No stone unturned, no FET unburned. |
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| KeepIS Guru Joined: 13/10/2014 Location: AustraliaPosts: 1731 |
I agree with Solar Mike, they either cancel the order after a week or two, or wait until you cancel it after the delivery time timeout. I ended up using AS225-125A Black N7R6 @ $37 for 4, when I made the last two chokes. Quick search finds them available in link below, but likely other places. Toroids Due to the lager hole you will need 8 toroids per choke, gets a bit expensive, but if you limit surge current you could get away with 4 and an extra two or three turns to bring the inductance up. NANO Controller: Full download or Hex files Mike |
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| FET cemetery Newbie Joined: 17/04/2024 Location: AustraliaPosts: 25 |
Thanks KeepIS, will get 8. Limiting surge current is not really in keeping with my username... These are listed as ferrite, not sendust, does that make a difference? No stone unturned, no FET unburned. |
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| KeepIS Guru Joined: 13/10/2014 Location: AustraliaPosts: 1731 |
A lot are listed as Ferrite but they are a typical Sendust Core mix, 85% Fe, 9%Si and 6%Al, depending on who makes them they are also know as KS225-125A among others. . Edited 2025-02-14 15:02 by KeepIS NANO Controller: Full download or Hex files Mike |
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