Transformer Sourcing

1) Score Toroidal Transformers From Old LF Grid Tie Inverters.

Old Aerosharp grid tie inverters are obviously an excellent candidate for donor toroids with so much already known about them … with many 1.5kW, 2kW and 3kW versions already having failed or simply upgraded to higher power systems.

Apparently Aerosharp made a 5kW version as well, though I have never seen one.

Many early SMA models also had toroidal transformers. Their main drawback being that they were potted in some sort of resin … and usually quite a lot of damage was done, at least to the outer windings … in trying to get them apart.

There are many 1.5kW, 2kW and 3kW SMA’s with transformers as well … and even some 6 and 7kW versions.

An SMA model SMC-6000A Sunny Mini Central has a 6kW toroid and an SMC-7000A has a 7kW toroid … again encapsulated … but still with very healthy cores suitable for decent power in a homebuilt inverter.

If you have an opportunity to check out any old SMA’s … bear in mind that a model number ending in “TL” means quite literally “Transformer Less” … so obviously they are not going to be suitable.

LF inverters with toroidal transformers are usually very heavy, especially compared to their later HF cousins … so check any ones you can find that are particularly weighty. And while old Aerosharps were the main source here in Australia … it’s quite possible there are other suitable brands in other geographic locations.

Many people struggle to find donor GTIs … but I never had any trouble. I checked for local “Inverter Repairers” online and started calling.

First one I called said they have a heap of old inverters down the back and after checking said there were some Aerosharps amongst them. They said they normally wait till there’s a decent heap then send them off for scrap but if I wanted any they were $25 each. I couldn’t get there quick enough and picked some up every time I went to the city.

I occasionally picked up inverters other than Aerosharp just so I could have the fun of stripping them down and see how they were built and rob any decent parts from them. Where else can you get fun like that for just $25? I often wish I’d have bought more.

I had come to the conclusion that many of the inverters were not even actually faulty … they were simply replaced during an upgrade and still worked perfectly well!!!

At one stage I needed another one and my original supplier didn’t have any … so I started calling other repairers. Once again, the very first business I called said they had one but they wanted $50 each. Still a bargain, so I picked it up.

Of course I eventually had enough toroid cores for my Warpverter, so I don’t have any excuses to buy more.

One big advantage of the Aerosharp inverters was the number of high voltage electrolytic capacitors in each one … 470uF and 560uF 450V. I built four 150V 60A MPPT charge controllers and each needed 13 capacitors … so I saved heaps by being able to use up some of the secondhand ones.

I needed some sheet metal work done at a local engineering place … and while talking to the owner was offered a faulty inverter free of charge. It turned out to be an SMA SMC-6000A with a massive toroid. And I wasn’t even looking. So they are out there, you just need to keep your eyes peeled and keep asking questions.

2) Purchase Bare Cores From Your Local Transformer Suppliers

I live in regional South Australia and our capital city Adelaide is an hour away. It turns out that AEMCores in Adelaide is the only company in the whole south west Pacific region manufacturing toroidal cores.

From their website ...

"The maximum single strip width for a Toroidal core is 105mm, anything greater than this can be manufactured using multiple strip widths and stacked together. This would then be annealed, tested and packed as 1 core. For example a required strip width of 140mm would be manufactured from 2 x 70mm strip widths."

Interestingly, the large toroid in my 15kW Warpinverter was built with two 71mm cores stacked to be 250mm OD x 120mm ID x 142mm High and while I did get a quote from AEMCores, because I had already collected the used ones, I went ahead with them.

While the price would have increased since then, I recall thinking at the time that it was a quite reasonable amount ... especially seeing the amount of time and $ saved from chasing down scrap inverters ... and with the added advantage that they would be professionally wound and annealed afterwards.

There are likely a lot more core suppliers in the US and Europe ... and if you come across any, please let us know and we can list them here.

3) Locate Someone Willing To Wind What We Need

I also wonder if it may be possible to find someone to wind transformers as one off jobs.

There are suppliers on aliexpress who sell high power toroidal transformers in various winding configurations … mostly for Power Jack style inverters … but it would not surprise me that they would agree to wind transformers to our requirements.

Of course, freight remains the biggest problem.

And You Tube has many videos of people in SE Asia winding toroid cores by hand … and then laying on the windings also by hand. Most of them are for huge audio amp supplies … but again, if they could be convinced to wind to our ratios, they appear to have the skills to do so.

If we weren't faced with massive freight costs because of the weight ... I'm pretty sure I could be convinced to wind another one if the price was right. :)

Click image below to see aliexpress prices and options. Of course there's no getting away from the shipping being the majority of the price. Where the shipping is free, the toroid price is high and vice versa.

Some Random Photos

Click on photos to open enlarged versions

Scruffy, scrapped 1.5kW Aerosharp inverter. A whole $25 from my friendly solar repairer.

Ended up with about a dozen different Aerosharps by the time I was finished.

Lid off showing the workings of the Aerosharp inverter with lots of useful bits.

The large electrolytic capacitors ended up in one of my MPPT solar charge controllers.

And the mother lode ... another toroid to unwind and repurpose.

This one became the "Small" #3 Tx in my Warpverter.

And the choke on the RHS are also useful for MPPT solar charge controllers.

Another 3kW toroid

And some more

A 1.5kW Aerosharp toroid

1.5kW, 2kW and 3kW Aerosharps were pretty common in Australia and even 5kW ones though rare were also available.

An SMA Sunny Boy and an Aerosharp Toroid.

Being encapsulated makes it difficult to strip and be able to re-use the wire ... so I aimed for more Aerosharp ones.

There were two different sized toroids used in 3kW Aerosharp inverters ... see middle two cores.

Top one is 185mm OD while bottom one is 205mm OD. Both 70mm high and 100mm ID

Starting to unwind the Mylar insulation tape.

Expensive and difficult to buy new, so well worthwhile saving to re-use.

The Mylar tape comes off all wrinkly and distorted ... but a careful wave of a hot air gun and it miraculously straightens out like new.

The centre of the toroid becomes raised because the turns are closer together where they exit the hole.

A surprising amount of large toroids available on aliexpress, though prohibitively expensive due to freight.