New Project: Sub $150 1.5kW Pure Sine Inverter

[Stingy49]

Hey Everyone,

I recently learned about converting pure sine (and modified sine) APC ups's into budget pure sine wave inverters. I decided to make a video series on it to share my findings and progress. The end goal is to mount my 2U UPS into a rolling music case with a much larger battery bank to make a budget pure sine solar generator!

I always love feedback and suggestions. Thanks for taking a look!

-Derek

 

[SolarRat]

Nice vid, sound like you know what you're doing so I'm watching how this turns out!

Knurlgnar is a trip. He also knows what he's doing, but always starts out projects like "I'm gonna show you the RIGHT way to do this, not how those other bums do it!" Then, after multiple fails and tons of $$ wasted he ends up doing it just like "those other bums", possibly worse. So be careful how closely you follow his lead.

I've messed with the inverters on small ~500w UPSs but not the bigger ones yet. Obviously the main problem is these things are meant to run for a very short time, not 24/7. Cooling will go a long way but not totally solve it. Larger or more transistors is a smart first step but then there will be another weak link. I think your and Knurl's idea of boosting the output is not a very wise one in the long run. It will work for a while but... I think if you you want a 2kw inverter, start with a 4kw UPS, not a 1kw UPS. Everything is made so much beefier and can probably handle continuous duty at 50% it's rated load. Even those huge UPSs can be found dirt cheap or free...

 

[Rider]

I'd be curious what the idle current usage would be. My AIMS inverter shows 0A (on a 300 MA scale) when on but no load.

 

[gnubie]

Overall efficiency would be interesting too. Maybe if you have the time to do it, plot a graph showing efficiency vs a resistive load.

 

[Stingy49]

@Rider I'm really surprised by that. Almost every inverter uses a decent amount of power (20-50Watts) to maintain the 120v output due to core losses (I think). I've seen them where they have a power save mode that applies some smaller voltage to the line to look for draw and that will use about 5W or so. This unit isn't gonna be friendly coming in at 50-60watts idle usage. Not sure what it is with the output off.

@gnubie I can definitely try and do some measurements with my heat gun as a 750w and 1500w load. I'm planning to pick up a current clamp meter soon so that would let me do it.

 

[Rider]

@Rider I'm really surprised by that.

Actually, I was too. Some other post in here triggered my need to measure it. The website says .4A (4.8W@12VDC), but I got no reading when on and idle, other than a momentary surge to charge the caps. As soon as I added a load, it ramped up.

 

[New Member]

@Rider I'm really surprised by that. Almost every inverter uses a decent amount of power (20-50Watts) to maintain the 120v output due to core losses (I think). I've seen them where they have a power save mode that applies some smaller voltage to the line to look for draw and that will use about 5W or so. This unit isn't gonna be friendly coming in at 50-60watts idle usage. Not sure what it is with the output off.

@gnubie I can definitely try and do some measurements with my heat gun as a 750w and 1500w load. I'm planning to pick up a current clamp meter soon so that would let me do it.

Mine uses like 3w measured. About 1/3 of an amp.

 

[Stingy49]

Posted part 2 (max charge voltage, inverter cutout voltage, etf) and part 3 (quickie about adjusting the cutoff voltage). Thinking of turning this into a mini power-wall to run my office. Thoughts? I got the cells already, just need bms, solar charge cont, solar panels.

Also gonna move to a shorter video format I think. Less work for me editing.

I also already upgraded the PCB with the caps and fets. I'll post that video sometime also. Maybe tonight.

-Derek

 

[Stingy49]

Aaaaaand Part 4 ft. Physical Upgrades

EDIT: Definitely gonna try and stick with shortish videos. So much easier to edit!

 

[Stingy49]

Does anyone have recommendations on good DC breakers? I see the $13 amazon cheapies but I'm concerned about flammability.

 

[gnubie]

Try searching for DC MCB. They usually have arc traps built in so if something does go wrong at least the arc should be extinguished on opening the contacts.

 

[Stingy49]

Hrmm. All the ones of those I'm finding are 40-60 amp max. I need 80 and 100. I think I'm just gonna go with the ones Will lists on his site. They're UL listed.

Thanks for the suggestion though. I'll definitely remember those for my solar install.

 

[erik.calco]

@Stingy49 That is really super cool! What I loved isn't just cost savings, but look at all the features on the LED display and with the SM! And the potential!

- Looking forward to see how you add MPPT charging.
- And, what's the potential for remote monitoring?

I'd like to integrate something like a PI or Arduino into my solar equipment one day. One thing I'd like to do is have it self-learning and optimizing for the goals I give it, such as maximizing PV utilization while also maximizing UPS reserve, two opposing goals.

The APC UPS's I saved despite becoming faulty for their original purpose aren't nearly as robust as that rack mount you salvaged. But, I held onto them because I knew they had the ability to at least charge batteries, and wanted to one day figure out how to use and re-purpose them. But, now I want one of those rack mounts you have!

TIP: have a video where you do the soldering. Every level of experience will watch your video and want to do it, including someone who never soldered before, has never bought thermal paste, or someone who has done both but knows they suck at it because they never had a good teacher (e.g., me).

When I started posting YT videos, I was surprised that the one that got the most views was the one I simply documented so I could review to see how to put my Evinrude gear case back together after I took it apart. I put it online so my friend could see it. I realized when I got over 500 views there is a very high demand for how-to's.

If you really don't want to do soldering videos, you can link to other people's videos in your description.

 

[Stingy49]

@erik.calco Thanks for the advice! Yeah I don't have the footage for soldering so that opportunity has passed . Maybe I'll make a short video explaining some of the techniques.

I'm planning on using an epever mppt or something similar. As for remote monitoring, I bet you could use the APC software to at least monitor load and battery voltage. You'd have to know your percent difference from the reported numbers vs the actual (based on your scalers you set).

I'm gonna run a diyBMSv4 also, so that has its own web interface.

Always happy to be entertaining another person with my projects

-Derek