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36V UPS 18650 Conversion
#1
Thought I'd make a thread about my mini project since it's powerwall related. I'm converting a free Ultra 2000VA UPS that was being thrown out from lead acid to Li-Ion 18650 since the original batteries were toast (0V and not taking a charge). It's a 24V system so not ideal for Li-Ion voltages but after some testing it seems like it will work pretty well. The low voltage cutoff is around 21.5-22.3V depending on load, which lines up nicely for a little over 3V/cell. I've also tested it up to 30V on the input without any issues. The goal for me is to be able to run some 300-500W tools off the UPS which I could trickle charge from a car 12V socket.

Here's the inverter on the bench with a 7s4p pack I put together for testing. I'm currently capacity checking the parallel groups in the pack to see which ones need more capacity, since my discharge test showed the cells pretty out of balance at the discharge state and under load:


The 7s4p pack can run up to 300W loads for 83WH out (measured at the 120V outlet). The battery gets quite hot after this though, up to around 140F in open air. Adding the extra 2p cells should help a bit but I think I'll need some forced air to cool the cells in operation. I also added an XT-60 connector to the front panel so I can charge the battery externally (e.g. from a solar controller) or add more capacity.

Next step is to get the 18650 pack up to the full 7s6p configuration, get it together more securely, maybe with some plexiglass sheets and screws, and modify the charger to charge the battery up to 29.05V instead of the current 27.25V.

Edited thread title for recent changes.
Korishan likes this post
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#2
Actually 24V is much better than 12V systems on UPS. The 24V can almost be working fully Smile Especially if you can set charging voltages.
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#3
Pretty decent setup. I plan on doing something similar to my APC 450 UPS. It's a fairly dumb UPS, but I think it'll work non-the-less. Just change the charging/discharge. The biggest issue is that it uses 12V, not 24V. So not sure what I'm gonna do about that. I may get some LiFePo just for that alone. It's about the same size as the unit you showed in the pic.
Yes, definitely add more in parallel if you can to decrease amp draw. Every little bit helps. I can't tell from the pic, but do you think you might be able to move the transformer closer to the back? This would give you more space in the battery section. You won't need the metal battery holder as it isn't quite the right size for the new batteries, anyways. I took mine out.
And a computer case fan in the front behind the bezel might work to help with extra air flow.
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#4
After around 30-40 minutes of poking around, I still can't quite decode the charging circuit. Here's a snapshot of my layout scratchpad I put together in Photoshop:



The good news is I found that the potentiometer on the top side adjusts the charge voltage, I cranked it to max which is 28.13V. Not quite the 4.1V/cell that I wanted, but it'll have to do. At least it should give me around 75-80% of the "full" capacity instead of only 60%.

On another note, it's brutally slow waiting for the capacity results (charge -> discharge -> charge test) at 1.5A for my ~8AH cell...

I measured the output, it's a modified sine, with +/- 185V pulses with about 3.6ms pulse width.
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#5
If you're going to let the bms charge the battery, you're gonna want to have an intermediate charge regulator to make sure they are charged with the proper CC/CV curves. Otherwise, the UPS will just dump max amps and max voltage until it thinks it's done; shortening the life of the cells in the process.
Proceed with caution. Knowledge is Power! Literally! Cool 
Knowledge is Power; Absolute Knowledge is Absolutely Shocking!
Certified 18650 Cell Reclamation Technician

Please come join in general chit-chat and randomness at https://discord.gg/c7gJ5uA
(this chat is not directly affiliated with SecondLifeStorage)
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#6
(12-09-2017, 12:00 AM)Korishan Wrote: If you're going to let the bms charge the battery, you're gonna want to have an intermediate charge regulator to make sure they are charged with the proper CC/CV curves. Otherwise, the UPS will just dump max amps and max voltage until it thinks it's done; shortening the life of the cells in the process.

It appears to be current limited already, it's more of a trickle charger really, it only charges at around 280mA.
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#7
Thanks for posting about this. I was recently looking at 24V UPS's (for a 7S lithium conversion), and I am trying to find out what devices can be found very affordably as a used unit. Since most UPS's seem to use lead-acid, dead batteries are a common complaint after a few years (or less), meaung that ebay has high quality UPS's for sale cheap when someone upgrades to a bigger unit, and the lead-acid is old or dead.

There are a lot of electronics inside that are well-engineered to perform some of the jobs we need for a small back-up power station, so...this could end up being a popular hack.
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#8
Just an update, I've sorta scraped the original plan, I'm going to use a 36V Tripp Lite SMART1500 instead, I didn't realize this other unit I had was a true sine inverter (Edit: I was wrong, this is a modified sine inverter also), and is significantly lighter to boot. I'll still use the original battery pack as a starting point but I'll be upping the size and changing the configuration to 10s, I now have the full volume of 3x 7AH 12V batteries to work with, and the case is plastic so much easier to add ventilation. I'll have some fun teardown pictures and data to post about the new inverter soon since I had to tear out the annoying beeper Wink

Here's a quick table showing the quiescent draw across voltage and also the cutoff voltage for operation. This confirms the inverter works across the full range of a 10s battery:



The quiescent draw is better than the old inverter (old one was 18-19W) and when you shut it off with the power button it really disconnects the battery, <1mA draw. These are still available, the link is in Jehu's video about the large solar generator (http://j35.us/950w-UPS), cost me $44.33 including shipping.

I had to trim down some plastic tabs on the battery cover to fit an extra row of 18650s, but now I should be able to get 80 cells in the UPS (10s8p) which is much easier/cleaner to build than the funky 10s7p that fit before the mod. I changed the connector to an XT-60 also.

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#9
(12-14-2017, 11:06 PM)rev0 Wrote: Just an update, I've sorta scraped the original plan, I'm going to use a 36V Tripp Lite SMART1500 instead, I didn't realize this other unit I had was a true sine inverter, and is significantly lighter to boot. I'll still use the original battery pack as a starting point but I'll be upping the size and changing the configuration to 10s, I now have the full volume of 3x 7AH 12V batteries to work with, and the case is plastic so much easier to add ventilation. I'll have some fun teardown pictures and data to post about the new inverter soon since I had to tear out the annoying beeper Wink

Here's a quick table showing the quiescent draw across voltage and also the cutoff voltage for operation. This confirms the inverter works across the full range of a 10s battery:



The quiescent draw is better than the old inverter (old one was 18-19W) and when you shut it off with the power button it really disconnects the battery, <1mA draw. These are still available, the link is in Jehu's video about the large solar generator (http://j35.us/950w-UPS), cost me $44.33 including shipping.

I had to trim down some plastic tabs on the battery cover to fit an extra row of 18650s, but now I should be able to get 80 cells in the UPS (10s8p) which is much easier/cleaner to build than the funky 10s7p that fit before the mod. I changed the connector to an XT-60 also.


The link for the ups goes to a paypal payment page. Is this the link from Jehu's video?
I could use some of them wonder if the Sona 36volt hoverboard batteries would fit. Could just install 4  batteries in parallel would be 10s2p4p I think that is right. going with external batteries might work.

 later floyd
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#10
(12-16-2017, 02:37 PM)floydR Wrote:
(12-14-2017, 11:06 PM)rev0 Wrote: Just an update, I've sorta scraped the original plan, I'm going to use a 36V Tripp Lite SMART1500 instead, I didn't realize this other unit I had was a true sine inverter, and is significantly lighter to boot. I'll still use the original battery pack as a starting point but I'll be upping the size and changing the configuration to 10s, I now have the full volume of 3x 7AH 12V batteries to work with, and the case is plastic so much easier to add ventilation. I'll have some fun teardown pictures and data to post about the new inverter soon since I had to tear out the annoying beeper Wink

Here's a quick table showing the quiescent draw across voltage and also the cutoff voltage for operation. This confirms the inverter works across the full range of a 10s battery:



The quiescent draw is better than the old inverter (old one was 18-19W) and when you shut it off with the power button it really disconnects the battery, <1mA draw. These are still available, the link is in Jehu's video about the large solar generator (http://j35.us/950w-UPS), cost me $44.33 including shipping.

I had to trim down some plastic tabs on the battery cover to fit an extra row of 18650s, but now I should be able to get 80 cells in the UPS (10s8p) which is much easier/cleaner to build than the funky 10s7p that fit before the mod. I changed the connector to an XT-60 also.


The link for the ups goes to a paypal payment page. Is this the link from Jehu's video?
I could use some of them wonder if the Sona 36volt hoverboard batteries would fit. Could just install 4  batteries in parallel would be 10s2p4p I think that is right. going with external batteries might work.

 later floyd

Yes the link is from his video, and be suggests exactly that, he just parallels 4 of the hoverboard packs with XT-60 Y adapters and fits them in. I already broke down my packs and am using them for a different project so I'm just going to make a battery pack with 18650 holders.
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