DIY Pure Sine Wave Inverter

OffGridInTheCity

OffGridInTheCity

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I recently had a couple of 12,000w inverter fails and in the AIMS case, a control board is not available and there is no ETA in sight. In the case of WWIII we may not be able to get any parts at all. All of this makes me wonder...

For example, I have a useless AIMS but it has big coils and good mosfets and a box and... seems such a waste not to try do something with it. The inside of my AIMS and SUNGOLDPOWER look soooo complicated but I don't care about charging or MPPT or UPS or anything other than straight inverting to create a clean sine wave for US home appliances.

Can one (reasonably) build 8,000w (continuous or better) 48vdc -> 240vac/120vac inverter themselves? A little googling turned up - https://www.instructables.com/DIY-Pure-Sine-Wave-Inverter/ , but of course the devil is in the details such as how to change it for 48vdc input for example and what are the issues for 8,000w+ power levels. More googling shows various (different) approaches for lower power inverters.

Is there any ongoing project like Stuart Pittaway's DIY BMS where one with no low level electronics education or experience could learn how to do this?
 
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I'm trying to remember who it was that built a DIY Inverter. Not sure if it was @Wolf or someone else. I believe they did an oil submersion with the coils. But I think they used the same, or similar, to what is linked in the instructables you provided.
 
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Ahhhh, it's @completelycharged who did the work and writeup.

When it's been years since a thread was created, kinda hard to remember what to search for to bring it back :p
 
If I'm understanding correctly, I can build an inverter with 4 parts
1) Pure Sine Inverter - https://www.aliexpress.com/i/2251832723456167.html?gatewayAdapt=4itemAdapt
1677665004972.png
1677665112481.png


2) Inductor - https://www.aliexpress.us/item/2251832722422361.html?spm=a2g0o.productlist.main.3.63e3232bYiVD22&algo_pvid=d1b52809-b233-438c-a439-6953a8f0a881&algo_exp_id=d1b52809-b233-438c-a439-6953a8f0a881-1&pdp_ext_f={"sku_id":"65859583483"}&pdp_npi=3@dis!USD!110.0!99.0!!!!!@211bf55216776640060773942d06c7!65859583483!sea!US!0&curPageLogUid=aF9hsXYqkDUa

3) 5uF 275V AC 400V DC MKP-X2 Capacitor - https://www.tomsonelectronics.com/products/5uf-275v-ac-400v-dc-mkp-x2-capacitor

4) TRANSFORMER.... 28v -> 220v, 60hz, 8kva like this - https://www.alibaba.com/product-detail/Single-Phase-230v-220V-110V-240V_1600477772968.html
The concept being that Toroidal is a 'good'/'cheap' form of high power transformer. For US, it sounds like I would prefer 28v -> 240v or perhaps 240v with center tap for 120v legs that can handle 8000va levels of power instead of 28v -> 220v. I presume the 120v taps would be single phase. So realistically I can't do 240v/120v split-phase compatible with US panels but I could do 240v to my AC compressor and cooktop and water heater kind of thing with 'single phase' 240v and/or specific 120v single-phase circuits.

**Will these components provide a useable pure sine wave inverter, with a little voltage tweaking of pots on the control board verified by a scope and voltmeter, that's safe to operate? (Yes it needs a box, cooling, safety precautions).

I read about the noise filters near the end of @completelycharged thread but don't understand if they are needed.
 
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After digesting @completelycharged 's thread a bit more and looking at the Alibaba parts / wiring diagram above for the base Alibaba inverter I think I understand better.

Isn't this "16000W Low Frequency Split Phase Pure Sine Wave Power Inverter DC48V/AC 110V,220" - https://www.ebay.com/itm/125394217937 - essentially a raw, low cost inverter (already in a box), a ready-to-go implementation of the basic parts above in the range of (realistically) 6000w of continuous power.
1677701085126.png

Is there anything fundamentally risky in terms of sine wave quality or power steadiness (or whatever) if hooked up to my Lennox whole house heat pump or kitchen refrigerators etc?
 
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OffGridInTheCity said:
I recently had a couple of 12,000w inverter fails and in the AIMS case, a control board is not available and there is no ETA in sight. In the case of WWIII we may not be able to get any parts at all. All of this makes me wonder...

For example, I have a useless AIMS but it has big coils and good mosfets and a box and... seems such a waste not to try do something with it. The inside of my AIMS and SUNGOLDPOWER look soooo complicated but I don't care about charging or MPPT or UPS or anything other than straight inverting to create a clean sine wave for US home appliances.

Can one (reasonably) build 8,000w (continuous or better) 48vdc -> 240vac/120vac inverter themselves? A little googling turned up - https://www.instructables.com/DIY-Pure-Sine-Wave-Inverter/ , but of course the devil is in the details such as how to change it for 48vdc input for example and what are the issues for 8,000w+ power levels. More googling shows various (different) approaches for lower power inverters.

Is there any ongoing project like Stuart Pittaway's DIY BMS where one with no low level electronics education or experience could learn how to do this?
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This is an interesting project! And something that I've considered. So I build out a sweet system and it runs great but what if... What if something happens to supply chains and I have a failure on the ac side? Now what? Do I stock up on extra inverters? Electrolytic capacitors have a timeframe where they start to fail due to time and not use. This is the case in the new generation of inverter welders. 7-10 years and they often need new caps. And usually a cap failure leads to a board failure somewhere.

I'm curious to see how much you can DIY! Super cool.
 
I am very interested in this topic and have thought about trying out something like this or a DIY MPPT myself but figured I should start with something a little smaller to get my feet wet. I did do a lot of research and it seems there are good resources out there from folk who have done small 1kw inverters that one could scale that system. My biggest challenge was getting my head around how to figure out the right specs for the inductor and then also how to build it since the big inductors don't seem to be easily purchased(hadn't thought to use aliexpress although I don't know how much I trust them) The science of inductors is crazy heady and many of the referenced calculator tools don't seem to be online anymore :O The real challenge seems to be that things become very unforgiving once you are dealing with high currents(I would likely be working in the 100A range). Of course I was aiming for a full DIY version like the DIY BMS if you are going the route of buying the various major components that seems much more doability but doesn't address the fixability a whole lot. For me building everything from the PCB up means I know it all and can easily replace or repair failure parts and more importantly that things are open source. One could DIY repair many failures like the ones you have been having with sufficient schematics and design specs but folks generally don't share those and if the main controller chip fails like it looked like it did in one of your cases and in the case of my kweld then you are out of luck since the software on it is very not available. It is one reason why I am hoping to find an alternative to the Kweld. I love the Kweld but I would really rather support a platform that is fully open source so that I and anyone can repair things properly themselves and as I have learned through my failure the Kweld system is not open source so now it is about finding a similarly heavy duty open source project or revamping the existing DIY spot welders that seem way underpowered for my needs.

Well all that rambling to say I would love to collaborate with folks if there is an interest in putting all our minds together to figuring out a DIY house sized inverter. I think there would be much interest in it if we created a platform to take away some of the crazy hurdles of things like the inductor sciences.
 
cak said:
My biggest challenge was getting my head around how to figure out the right specs for the inductor and then also how to build it since the big inductors don't seem to be easily purchased(hadn't thought to use aliexpress although I don't know how much I trust them)
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You could see about salvaging inductors from old inverters. I think there isn't much to cheap out on on an inductor, so not much to fake, unless they replace the copper wire with copper clad aluminum (CCA)
There are some name brands that use AliExpress. Same with AliBabba. So you could use that as a guide.

cak said:
figuring out a DIY house sized inverter
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Personally, in this kind of situation, I wouldn't mind building a fully modular inverter, where all the major components are just tight contacts and slip into a control board of sorts. That way if there is a failure, just replace a whole module. Or easier to repair the module due to ease access.

When dealing with "home" sized inverters, there's usually plenty of space available. Not to mention the larger footprint would allow greater air flow.
 
OGITC: I admire the work you have done, and are doing on an on-going basis. With all the craziness and insecurity, I might suggest a different approach. Personally, I'm focusing on buying spare parts upfront with purchases. Looking into the use of automotive parts that can be adapted. Breaking power delivery systems down into smaller, more discreet sub-systems with serious serious protection for electronic devices.

I shy away from any system that requires the use of electronics to utilize it in a simple manner. Numerous small inverters rather than one big one. I'm a diehard DIYer, but I have to draw the line at troubleshooting electronics. My take on it is if you have to ask how to go about doing something like that, you are probably not a good candidate to do it. I love to learn, but there are so many things that one cannot prepare for. Like sub-standard components that come on brand new equipment. My approach is to buy the highest quality every time, scour for clean used stuff, adapt military equipment, stockpile components, etc.

I'm very concerned that the same problems plaguing you about getting parts will lead our inability to maintain critical infrastructure, food supplies, etc. Oh, and banks are failing? When the 2020 derecho hit the Midwest, we were without power for up to a month, no internet for 6-8 weeks, most stores where closed, no gasoline, etc. It taught a lot of people some valuable lessons. Then Covid hit, and now all the shortages. I'm rethinking everything, including the need to have 48 volt systems.
 
prepared1 said:
OGITC: I admire the work you have done, and are doing on an on-going basis. With all the craziness and insecurity, I might suggest a different approach. Personally, I'm focusing on buying spare parts upfront with purchases. Looking into the use of automotive parts that can be adapted. Breaking power delivery systems down into smaller, more discreet sub-systems with serious serious protection for electronic devices.

I shy away from any system that requires the use of electronics to utilize it in a simple manner. Numerous small inverters rather than one big one. I'm a diehard DIYer, but I have to draw the line at troubleshooting electronics. My take on it is if you have to ask how to go about doing something like that, you are probably not a good candidate to do it. I love to learn, but there are so many things that one cannot prepare for. Like sub-standard components that come on brand new equipment. My approach is to buy the highest quality every time, scour for clean used stuff, adapt military equipment, stockpile components, etc.

I'm very concerned that the same problems plaguing you about getting parts will lead our inability to maintain critical infrastructure, food supplies, etc. Oh, and banks are failing? When the 2020 derecho hit the Midwest, we were without power for up to a month, no internet for 6-8 weeks, most stores where closed, no gasoline, etc. It taught a lot of people some valuable lessons. Then Covid hit, and now all the shortages. I'm rethinking everything, including the need to have 48 volt systems.
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Agree 100%. I'll be interested to follow what you do!

In my case I have a couple of 240v circuits at 5,000w and a couple more at <1000w. For example, the whole house heat-pump I need 20a@240v = 4,800w. The cooktop and dryer is similar. Plus I have the rainharvest 240v pump and hot-water heat-pump that need 240v but lower watts.

Thus, I need 240v/120v split phase. And I need at least 1 x 8000w level of inverter. So I went with 2 x 12,000w inverters to run the whole house and I'm in the mindset of a couple of 8000w or higher 240v/120v split-phase inverters. An array of smaller or 120v only won't work.

Currently, I have 2 x working 12,000w inverters and 2 x broken 12,000w inverters. I'm hoping to fix both so I will have 2 x backups if I succeed in repairing them. If I wind up with 1 (or both) that can't be repaired I'm going to try to re-use the metal-case + Toroid transformers in the broken ones paired with one of these -
28CMOS - https://www.aliexpress.us/item/2255800069646480.html
32CMOS - https://www.aliexpress.us/item/3256803185275498.html

This process has spurred me to purchase
- A scissor lift table - https://www.amazon.com/dp/B08BCNBTCL?psc=1&ref=ppx_yo2ov_dt_b_product_details - so I can manhandle the inverter unit on it from the floor and lift it up to work on it comfortably + move it around.
1679930498245.png

- An oscilloscope - need to learn how to use one :)

And to setup
- A 48v power take-off from the battery bank so I can power the unit for test
- A plug at the generator distribution panel so I can direct Inverter output (instead of generator output) to apply test loads without risking the home appliances.

It's the sheer weight and ungainliness of 175lb units that was daunting at first, but with equipment + reading @completelycharged's Inverter thread I'm now understanding the basic ingredients better. For example, I now recognize that both the AIMs and SGP have dual toroid's (in parallel I think) to reach 12,000w as apposed to the 1 big one that you see in a PowerJack.

Even if I fix both inverters, I might just order an inverter board (link above) + 48UH 100a Inductance + 400v 5UF Capacitor + a lessor toroid and experiment anyway. :)
 
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ogitc: Sounds like you have a pretty good plan. I've been thinking of buying one of those lift tables myself. I have a complete BMW battery I have to tear down, and don't really want to do it on the floor. Might try to use an engine hoist to get it lifted, and blocked up to a better working height.

Have you considered getting a couple of smaller inverters that can be stacked for more total output? It typically costs more, but you can still power loads if you lose one unit. Also, by any chance is your jurisdiction on NEC 2020?

Those are some pretty big loads you have...I can see why you would be in the market for a big inverter.
 
prepared1 said:
ogitc: Sounds like you have a pretty good plan. I've been thinking of buying one of those lift tables myself. I have a complete BMW battery I have to tear down, and don't really want to do it on the floor. Might try to use an engine hoist to get it lifted, and blocked up to a better working height.
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Agree - the right tools are worth getting.

prepared1 said:
Have you considered getting a couple of smaller inverters that can be stacked for more total output? It typically costs more, but you can still power loads if you lose one unit.
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~5 years ago I went the 'dumb' inverter route. Paralleling wasn't as popular and I didn't understand it at all back then. Plus, I don't have vertical wall space to mount multiple units and my dumb inverters can sit horizontally. So I'm sticking with large, dumb, inverters.

prepared1 said:
Also, by any chance is your jurisdiction on NEC 2020?
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Have no idea. The initial install/inspection by the city was ~5 years ago. Since then, I use the 'homeowner may extend circuits' rule and religiously copy what the original electrician did.

prepared1 said:
Those are some pretty big loads you have...I can see why you would be in the market for a big inverter.
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I could get buy (only run 1 thing at a time) with 8,000w but with 12,000w we can run several things. For example - background + full-scale-heat/cool + cooktop + microwave all at once will near 12,000w BUT add the the k-cup or toaster oven and it can tip over. 12,000w is perfectly livable but 24,000w covers it all. And, with 2 inverters I have a spare if one goes down.... as in my recent AIMS failure.

If one of the 120v MPP Solar or EG4 or Victron or xxx paired units for 240v split-phase goes down, you loose the 240v capability. Would need at least 4 of them for redundancy + at 6000w, I'd need at least 6 for 18,000w.

Also. ETL/UL certifications is also a major consideration for me as I've been told that home insurance will more likely pay off for a fire if all equipment is ETL/UL listed. This narrows the available units. The AIMS and SGPs only make certain models that are ETL - and this is what I purchased. Not sure about MPP Solar, Growatt, EG4, etc.

I really liked the idea (and efficiency) of parallel'ed Magnum MS4448PAE 4000w units as each one is 240v/120v split-phase but the controller can bring the 2nd, 3rd, 4th, ... up (or down) as needed as the loads vary - at least that's my understanding. However, this brand seem to be dying out and they mount vertically.
 
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OffGridInTheCity said:
A 48v power take-off from the battery bank so I can power the unit for test
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Use a cheap 1200W DC boost converter with the current limit set at say 10A. This saved me a few times when testing....

lol on the scissor lift table... I only avoided that route as I could not get a table out the shed to the house, lol. The inverter stays on the floor until I'm feeling I have a hero complex and lifting it onto the shelf soon brings reality back into focus.
prepared1 said:
if you have to ask how to go about doing something like that, you are probably not a good candidate to do it
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I'd say rather if your curous enough and determined enough, you are the right person. I did not know how the inverters worked, posted questions and researched on the backshed forum and here. Don't create your own limitations.
Korishan said:
it's been years since a thread was created
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And, it's still working, charging the car and powering the house when needed (typically, just before the power is reconnected). About 2MWh through it so far. The baby oil is still sat on the shelf waiting for something, lol.
OffGridInTheCity said:
ETL/UL certifications is also a major consideration for me as I've been told that home insurance will more likely pay off for a fire if all equipment is ETL/UL listed.
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That's why my setup is in the shed.... don't care about the shed, rather it's more the element of a fire when your asleep in the house...
OffGridInTheCity said:
Is there anything fundamentally risky in terms of sine wave quality
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The board I use gives out a good sinewave but the capacitor is the critical part as this is what bridges/smooths the otherwise HF oscillations. The only issue I would say is that the startup surge for some appliances is what is typically an inverter killer. The inductor is a partial defense to this until it is saturated at the peak of the waveform, so only a real help in smoothing out a current spike, hopefully enough for a circuit breaker to trip before the FET's blow out. For some items I plug them in before switching the inverter on... like a 5kVA 110V site transformer, the soft start slow voltage buildup abvids any sudden surge. The 5kVA transformer frequently trips a 32A breaker in the house when plugged in. Any none sinewave output inverters should be avoided for anything other than resistive loads (e.g. heating elements) because the sharp voltage steps create large current surges that will say burnout the brushes on a drill more quickly.
 
OffGridInTheCity said:
If I'm understanding correctly, I can build an inverter with 4 parts
1) Pure Sine Inverter - https://www.aliexpress.com/i/2251832723456167.html?gatewayAdapt=4itemAdapt
View attachment 29196View attachment 29197
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As an EE, I can tell you that is a piece of junk.

I have several times contemplated building my own inverter after making acquaintance with the engineer-designed brick (both shape-wise and ruggedness) of a inverter from unknown Taiwanese company BA Power. I don't know if it was a design requirement or if the engineers just had a field day and free reign over implementation since it would not only ramp up voltage at startup to facilitate starting motor loads with massive inertia, it would also not trip but rather employ cycle-by-cycle current limitation and distort the sine wave accordingly when for example a refrigerator compressor would kick in. At 300 W rated power, it would operate such motor loads most 3 kW units will fail to. A true marvel.

It wouldn't be difficult to make such an inverter compared to a crapy one, just takes that know-how on how they are used and the mindset to help the end customer as opposed to just meet minimum requirements and sell it.

If anyone is looking for just the inverter part without transformer, a class D amplifier + a 50/60 Hz signal source will be a better option but with the caveat that 48 V is an unusually high input voltage.
 
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