24V/48V UPS as an inverter for mini power-wall

[spinningmagnets]

edit: I'm probably going to go for the 48V UPS, but...here is the link to the 7S / 24V UPS lithium swap. One of the nice things about 24V is that you can find a 24V alternator, and also alter a 12V car alternator to output 24V, then run it with a lawn mower engine...

https://youtu.be/OtBI_Dr2cII?t=244

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There are some 48V Un-interruptble Power Supplies (UPS's) that work fine with a 14S lithium pack, meaning that...in a temporary power outage, your 48V / 52V ebike battery pack can be used to power your TV.

UPS's are designed to make sure sensitive electrical components will continue to run during a short temporary power outage, like computers that control vital components. They use 12V / 24V / 48V packs of SLA, and apparently...when the lead-acid batteries die...it is sometimes cheaper to simply buy a new UPS instead of having a service tech come out and swap-in new SLA batteries. Of course, its not hard to swap-in new SLA batteries, but many businesses simply don't want to mess with anything that they already have a business expense budget for, and they want the UPS's to remain under warranty so the tech-support is carried by someone else.

I was delighted to recently find out that most 24V UPS's with two 12V SLA batteries will run quite well on 7S lithium. Perhaps there are some models that will not, so do your homework before spending any money. However, the higher the voltage, the wider the input range needs to be, so...charging a 14S pack to 4.0V per cell will result in 56.0V at full charge, and it appears that almost all 48V UPS's will work at 14S (52V nominal ebike packs).

The good news for us is that UPS's can often be found on ebay or a local used-electronics recycler for a very cheap price. I've known for a long time that 48V UPS's existed, but I already have three large 52V ebike packs (I feared they wouldn't work, and would fry the $300 UPS experiment). I considered building a DIY power-wall from used laptop cells, but I am very happy to see that my existing ebike packs can now be used. Here's a 15 minute video (episode 45 + 47, "AveRage Joe" on youtube...100-P modules shown, X 14S = 1,400 cells):

https://www.youtube.com/watch?v=WpuBFlpfRkY
https://youtu.be/Dr5tI7hLRa0?t=393

Here is a 2700W unit for consideration, input is 48V/52V...output is 120V AC. In episode 49, he compares the standard SUA3000RM2U to the "XL" version of 48V UPS, the SUA3000RMXL3U. Possible to occasionally find these with a dead SLA battery pack for $300-ish...

https://youtu.be/_UTUZx1DX54?t=104

The cell-end holders were glued-together rings cut from 3/4-inch schedule-80 PVC pipe. Episode 37

https://www.youtube.com/watch?v=wz-uDd-mM1c

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Sizing the system:

edit: keeping the cell phones charged up and the laptop computers too would be very easy, along with running a couple LED bulbs and 18650-cell flashlight (for a temporary power outage of just a few days). Roughly 100W-200W if you were doing everything at the same time? Here are the next milestones:

1,000W________________microwave oven, common size
150W__________________TV, depending on type and size, could draw more
1,400 Watt-hours a day___Fridge, large 20-cu ft
1,200-3,800W___________Central air-conditioning, only when running, 10K-24K BTU sizes. A small window unit in the bedroom would draw less?

https://www.wholesalesolar.com/solar-information/how-to-save-energy/power-table

It looks like this 2700W UPS would run everything except the A/C, but perhaps I could run a small window A/C after everything else is off and we are going to sleep?...(assuming power is out in the summer). Tornado season is the spring and fall, so it's most likely that for my family, running the A/C is something we could likely live without for a few days.

If 2700W at 120V AC is 22A (the UPS output) then the 52V battery input needs to be at least 52A (2700/52=52), when running at full rated capacity...

 

[Harold in CR]

I have 2 of the older 24v 1400 Kva SMART APC UPS's. They put out a true sine wave. I believe I can parallel them to get twice the amp capacity and add computer fans and use them as my inverter for my partial off grid system with Chevy Volt modules.

You tube has some really smart people that show how to do these things for electronic dummies like me.

Jehu Garcia has many videos about the powerwall build that guys have copied.

 

[spinningmagnets]

Thanks for the input, Harold.

kVA is a new term for me, similar to watts, but adjusted for the power factor? 3000-VA (3kilo-Volt/Amp) is an actual 2700W of load?

http://searchdatacenter.techtarget.com/feature/How-do-I-figure-size-requirements-for-new-UPS-unit

From what little I have gathered so far...I want an MPPT solar controller, because they can accept a wider range of input voltages from the solar panels. I also want a pure sine-wave inverter, because they can run anything, compared to the less-expensive "simulated" sine wave inverters, which make some devices (such as tool motors) run with a lot of noise (or so I'm told, I have no experience yet).

The smallest system I would get can power just my laptop charger, smart-phone charger, and 18650-cell flashlights, however...I want to be able to expand the number of solar panels, and also expand the size of the battery pack over time. The next big item to run would be the TV, and then the big one on my list is the refrigerator. I don't know if this model would run the fridge (or if it did, for how long), but...it will definitely run all the smaller stuff, including the TV.

My interest isn't in spec-ing a comprehensive off-grid system to run the air-conditioner or charge an electric car, it's only for a temporary disaster relief if the grid goes down.

Part of the reason I'm now excited about this is that...I can get a significant and large inverter (the 48V UPS), that will allow me to use my existing ebike batteries, and I will quickly have a back-up system for short power bumps.

Of course I will add an MPPT charge controller someday, and solar panels. Their performance and prices are improving every day, and I am holding off on the panels for a little while because I may retire and move in a year or so...why mount them twice? especially since I don't really need them right now...

 

[fechter]

Being able to use my bike battery worked out really well the last time I had a power failure. In the "old days" I had a 12v inverter that ran off a big lead-acid battery. Short run time, very heavy, and the tendency to leak acid made it pretty unattractive. Now I can grab any one of my several 52v bike batteries and have about a kW-hr worth of power. With the true sine wave output, no need to worry about damaging the load.

The only thing I was missing on the setup was some kind of A-hr meter to keep track of how much I was consuming. I would recommend adding one of those cheap chinese power meters on the inverter to at least give you some idea of where the battery is at.

 

[billvon]

24V/48V UPS as an inverter for mini power-wall

A few warnings here:

1) Powerwalls can feed back to the grid. UPS inverters will go up in smoke if you try that; they are really only good for backup.

2) Inverters for UPSes are designed almost exclusively for computer power supplies - which are either capacitive (and terrible power factor) or use modern switchers, which are very high power factor. They often do not do well on inductive loads like motors or compressors.

3) They are designed for a fairly narrow range of input voltages. They may well work outside that, but at that point they may see thermal or current stresses they were not designed to handle.

 

[Hillhater]

I have 2 of the older 24v 1400 Kva SMART APC UPS's. They put out a true sine wave. I believe I can parallel them to get twice the amp capacity .......

Dont you have to synchronise the sine waves ? ...is that automatic?, Or doesnt it matter ?

 

[Punx0r]

kVA is a new term for me, similar to watts, but adjusted for the power factor? 3000-VA (3k-VA) is an actual 2700W of load?

Yes, watts in the AC world is dependent on the power factor - which is the degree to which the current and voltage are in phase. Quoting the output as VA (volt-amps) rather than W removes the influence of power factor.

3kVA inverter will output 12.5A @ 240V (=3000)

Power a load with a power factor of 1 (normally a purely resistive load, although a power-factor corrected load can be 0.95+) you will get 3000VA x 1 = 3000W of useful power to the load.

If you had a PF of 0.5 (small induction motor or transformer, say), you will only have 3000VA x 0.5 = 1500W

 

[spinningmagnets]

Thanks everyone, for reminding me of those important concerns. One of the videos I watched (there were dozens, I don't remember exactly which one) mentioned that some UPS's synch-up the output, some don't. He pointed out a chip, that the UPS on his bench had, providing that function (if I understood correctly).

As far as back-feeding the grid, that is very important to mention, and I am embarrassed I didn't already do that. If the power lines go down in a storm, and my UPS battery starts feeding the appliances in my home, it is also sending electricity into the grid near my home. This means that a lineman working on a downed power cable will think the grid is de-energized because he is the one who flipped the large switch at the electrical station. Then...when he is touching the lines (with gloves that are likely wet) he can be electrocuted.

My current plan is to keep the UPS in a closet, and only drag it out during a power outage. Plug in the ebike battery, and plug the TV (laptop, cell-phone, 18650-flashlights) into the battery+UPS until the battery is dead. For charging, I would swap-out the ebike batteries and drag the dead ebike battery out to the yard when it is sunny and plug it into a charge controller and solar panel set-up, with solar panels simply laid out in the grass, hidden by my backyard fence...

At no time would the UPS be able to back-feed current into my local grid, and I realize I should have been more clear on this.

 

[Harold in CR]

At hillhater Yes you have to sync the 2 inverter sine waves.
https://www.youtube.com/watch?v=THh_2ssHWL0

We might have to start a thread. Don't want to hijack this one anymore. Sorry Spinningmagnets

 

[spinningmagnets]

Not a hijack, synch-ing sine waves is an issue concerning using a UPS for power, so...I say it's perfect for this thread. Keep the tips and links coming!

 

[Harold in CR]

Ok then. In the link I provided, the guy took 2 SMART APC UPS's, which are true sine wave not modified square wave, and they were not equal output. One was 950 W and the other 1500W if I remember correctly. Been watching videos quite a bit lately, because wife and I are both under the weather. He used the 950W as the master and the 1500W as the slave. He soldered in a jumper wire to make the slave think the voltage to a component was already too high so it would not try to jack the voltage to the master and fry the stuff.

I'm kind of learning a little from these videos so I might be able to start troubleshooting things eventually. This stuff is fascinating. All I have to do is remember what I watch.

 

[Papa]

I have a PowerCom ULT-1000 that originally used 36v SLAs. I tried 10s packs and it charged them to exactly 42v. Not overly efficient however, at slightly over 70% on battery power. I'm hoping to eventually find an efficient, SW inverter rated for 24Vdc below 300W, or so. Primarily to power a varity of cordless tool chargers.

 

[spinningmagnets]

Whether I choose 24V or 48V, a lot depends on what components I find at an affordable price, but...I already have three 52V ebike batteries (58V max SOC), so its unlikely I will go the 24V route.

That being said, a quick google shows 24V car alternators are available to use as a back-up generator. It uses common automobile parts and the windings have been chosen to output 24V, along with the voltage regulator. Here is a model using common GM parts, and the internal VR is case-grounded so it only has a single wire exiting the case to connect to the positive. It is advertised as being a 50A "universal" model for tractors, sailboats, and anyone who wants 24V in a simple package. $99

https://www.amazon.com/Exciting-Alternator-Universal-Tractor-Applications/dp/B004KMTRXK

Here's an "80A" John Deere for $103.

https://www.amazon.com/dp/B01N0NZNAX/ref=sspa_dk_detail_0?psc=1