Working with Inverter/UPS Lead Acid Batteries

[rsaeon]

That’s why I say it’s strange, they have a step-up converter for charging the batteries and a step-down converter for the inverter circuit

There’s only four wires (of significance) to/from the transformer, two for 0-230v and two for 0-25.4v, it’s not a 25-0-25 winding.

The 13.85v winding appears to be feedback, it’s not powering anything, I couldn’t measure any current flow.

I measured the voltages, and you can see in the photo, there’s no other connections, they just designed the inverter in this weird way. As if they just modified a 24v model.

What’s even stranger is that this inverter will power on with just two batteries! It doesn’t need the full 48V.

[yugaaa]

Which DSP is used ? May be we can look up the data sheets . Which model inverter is this ? May be I can look up the circuit .

An inverter operating at 24v cannot operate at double the voltage at 48v . I possibly cannot imagine the catastrophe .

[rsaeon]

It’s a luminous cruze 3.5kVA, this place has a few of their main boards for sale:

You searched for cruze » ELCMART

@yugaaa

An inverter operating at 24v cannot operate at double the voltage at 48v

It appears to be designed that way, their 96V 9kVA inverter has a 52V transformer:

They must have some kind of voltage doubler for the inverter and a boost converter for the charger.

@yugaaa

Which DSP is used ?

I’ll reply back with a photo later today

..

Consolidating some information:

@rsaeon

I never faced transfer time issues with my Luminous Cruze because it’s likely the only model that uses mosfets instead of relays, giving it a near zero transfer time (another thing to add to the list of things that I was not aware of when I originally purchased it).

From u/Snoo_24051 on reddit:

Luminous iCruze models are basic, transformer based, no nonsense machines. Think of it like an old Nokia Symbian phone simple but rock solid.

Optimus is like a modern smartphone software driven, less transformer dependency, more digital features like smart load sensing and multi stage charging , they also provide a cleaner output.

But here’s the problem: that software logic adds transfer time. The Optimus series has around 20ms transfer time, while the older iCruze models are under 10ms. For PC users, this is the critical issue. Anything beyond 16ms(in ideal world) IRL its 10ms and your PC reboots during a power cut. AS icruse models are no longer available as of now and they are discontinued by luminus its out of the list

https://www.reddit.com/r/IndianGaming/comments/1m47b60/my_experience_with_luminous_vs_microtek_inverters/

That mirrors my experiences with the Luminous Optimus that i got as a temporary replacement since I had two good batteries and didn’t want to buy anymore lead acid batteries.

What I had originally is the Luminous Cruze, the predecessor to the now-discontinued iCruze, which I believe was a facelift of the regular cruze model to match the styling of their single battery inverters.

Around that time Luminous got into the UPS market, so I believe they discontinued the fast-switchover Cruze/iCruze models in favour of their UPS line and “downgraded” their inverters to the Optimus line.

[rsaeon]

@yugaaa

Which DSP is used ?

dsPIC30F2010

It’s impressive that they used a microcontroller released in 2011 for a product that was manufactured/released in 2012:

What’s less impressive is that I was sold a 2012 manufactured product in 2021.

[Heisen]

@rsaeon

dsPIC30F2010

Still in production.

Kinda expensive.

[yugaaa]

@rsaeon

dsPIC30F2010

Seems the DSP is capable of various voltages . Interesting processor . May be this processor is used for EV vehicles as well .

DSPIC30f2010 PURE SINE INVERTER CIRCUIT WITH CHARGER

@Heisen

Kinda expensive.

It should be around 200 rupees in the local market .

[rsaeon]

let’s hope I don’t end up making my own inverter now

…

I’ll probably do it

[yugaaa]

@rsaeon

let’s hope I don’t end up making my own inverter now

For me the problem is programming the IC . Rest all I am capable .

but , I see a lot of potential with the DSP IC and li-on cells . They could be a perfect match especially given the digital display output . May be even have a selector switch for various types of battery or a digital card interface for different batteries .

[rsaeon]

If I can find a universal design using SCRs instead of relays, I’ll probably find a way to build it, or maybe I can hack a way into using SCRs

There are universal pcbs with this DSP but they’re all using relays, there’s even a basic development pcb on Amazon India

But then again, considering the fully populated board for this inverter is under 4500, maybe I should focus on making a copper transformer instead

Apart from efficiency, I want to make it wall mountable with a toroidal transformer so that it’ll take up less space

[rsaeon]

@yugaaa

https://manycircuits.blogspot.com/2018/04/dspic30f2010-inverter-with-charger.html

So I figured it out, why the winding is half of the battery voltage.

For the first half of the duty cycle the winding is 0-25 and the for second half it is 25-0, the polarity of the wires is reversed every half cycle

Effectively making the transformer see 50V peak to peak on the 0-25.4 winding

I’m sure there’s a technical term for this @Heisen

So it is 3500VA but it’s rated for 3500/50 = 70A and not 140A.

I assume the batteries are charged in the same way, except with filtering caps.

And the tiny 13.85V winding is for feedback, so the inverter can correct the output when the batteries go from 48V to 44V.

[Heisen]

@rsaeon

For the first half of the duty cycle the winding is 0-25 and the for second half it is 25-0, the polarity of the wires is reversed every half cycle

Effectively making the transformer see 50V peak to peak on the 0-25.4 winding

I’m sure there’s a technical term for this @Heisen

In the image in your link. H-Bridge drive.

---

So two windings in parallel is just for high current capability, has nothing to do with voltage doubling or anything like that? So confusing, head hurts thinking about this.

[Heisen]

Is AI correct?

In inverter mode (DC → AC)

• The H-bridge switches connect the 48 V battery alternately to each half of the 25–0–25 winding.
• The transformer therefore sees about ±25 V (≈ 50 V p-p) on its low-voltage side.
• The high-voltage side steps that up to ~220 V AC RMS.

---

In charger mode (AC → DC)

• The 220 V winding is energized from the mains.
• It steps down the voltage to about 25 V AC on each half, or 50 V AC total across both halves.
• After rectification and filtering, that becomes ≈ 56 V DC, which is perfect for charging a 48 V battery bank.

[yugaaa]

@Heisen

So two windings in parallel is just for high current capability, has nothing to do with voltage doubling or anything like that? So confusing, head hurts thinking about this.

It is a H class amplifier circuit bridged . The transformer is the speaker here . Since circuit is bridged . In a bridge circuit half the voltage is needed on each side to make it work .

Now the circuit makes sense .

[Heisen]

This is confusing, to me all makes sense if transformer had center tapped (+25.4v 0v -25.4v), but this is only (0v 25.4v)

[rsaeon]

yeah, I’m pretty sure I lost a few brain cells in figuring it out

at any point of the ac cycle, you’re not putting more than 25v

for the first half of the wave form, it’s positive

then for the second half it’s reversed, negative

so instead of a sine wave from 0 to +25v and back to 0 (like how you’d see a square wave for clock signals)

you have 0 to +25v to 0 to -25v and back to 0, or 50v from peak to peak

ac works in strange and mysterious ways ha

[Asterisk]

All the cheap 600-650VA ups of less than Rs. 2000/- uses 6.5 volt transformer with 12V 7AH battery.

[rsaeon]

@rsaeon

@rsaeon

I’ve sunk in 10k with used batteries so far (bought the second one after my last update here) so it’s more likely that I’ll change the inverter. Maybe do some kind of exchange with a reseller on OLX. Or buy a new inverter on EMI that does have a charge setting/profile for SMF.

Quick update: After a few months of saving and budgeting, that is what I ended up doing. The Luminous Optimus and iCruze inverter models have a SMF battery setting that float charges at 13.45V which is acceptable for the Amaron Quanta batteries.

I sold two of the dead 100ah Quanta batteries for scrap at Rs 3000 each and purchased a physically damaged but perfectly operational 24V Luminous Optimus/iCruze inverter (the lowest tier 2000VA one). It’s hooked up to the remaining two used batteries that I purchased about six months ago.

So in retrospect, this wasn’t the best decision.

I shouldn’t have purchased the Optimus and should’ve just bought two more used batteries at another 10k instead.

Those two used batteries that I got for 10k, I sold them for scrap yesterday for 6k, bringing the cost of ownership for two years down to just 4k, or Rs 170 per month.

I had bought the Optimus for 13k, and sold it yesterday for 4k, a loss of 9k, or Rs 500 a month. In the grand scheme of things, it did offset far more than that so it wasn’t a bad purchase, just not the best purchase.

The Optimus is a good home inverter, but not a very good solution for my needs. A 1kW load would often cause it to overload and cut off power completely. That’s what you want in a home inverter, but not for a homelab.

So I’m happy to have it gone and also to own two less lead acid batteries. The battery/inverter dealer did try to tempt me with a few used 200Ah Quanta batteries at 8500 each.

But I’m done with lead acid batteries, it’s time to move forward with putting everything on LiFePO4. It’s been a memorable twenty-five years or so with lead acid but no more. The future is now.

[msvsme]

I can only get ₹1000 for selling a 150ah dead lead acid battery. It’s pretty low. Wonder what is the price for scraping lifepo4 packs for recycling.

[rsaeon]

That’s really low, I sell mine to a second-hand dealer. I remember getting 5500 for my 150Ah and it was seven years old at that point.

@msvsme

Wonder what is the price for scraping lifepo4 packs for recycling.

Ha, you’d probably have to pay for scrapping.

Lead acid batteries are 90% recyclable and require almost no skills at all:

[yugaaa]

@rsaeon

Those two used batteries that I got for 10k, I sold them for scrap yesterday for 6k, bringing the cost of ownership for two years down to just 4k, or Rs 170 per month.

This is the reason why I said Lead acid batteries are cheap in the long run and total cost of ownership . Lead acid batteries you get more than half of the amount as scrap which needs to be considered in the TCO .