36V UPS 18650 Conversion

Thought I'd make a thread about my mini project since it's powerwall related. I'm converting a free Ultra2000VA 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 ittogether more securely, maybe with some plexiglass sheets and screws, and modifythe charger to charge the battery up to 29.05V instead of the current 27.25V.

Edited thread title for recent changes.

Actually 24V is much better than 12V systems on UPS. The 24V can almost be working fully Especially if you can set charging voltages.

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.

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.

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.

Korishan said:

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.

Click to expand...

It appears to be current limited already, it's more of a trickle charger really, it only charges at around 280mA.

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.

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

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.

rev0 said:

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

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.

Click to expand...

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

floydR said:

rev0 said:

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

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.

Click to expand...

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

Click to expand...

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 fitsthem in. I already broke down my packs and am using them for a different project soI'm just going to make a battery pack with 18650 holders.

rev0 said:

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 fitsthem in. I already broke down my packs and am using them for a different project soI'm just going to make a battery pack with 18650 holders.

Click to expand...

Ordered some today. Thanks. for others that might be sceptical of buying from a company that you don't find out where they are located/ if they are trustworthy the company. Here is the companies web site. http://electronicrecyclingcenter.net/

later floyd

Finished half of the 36V pack today (10s4p):




I'm trying a new construction method using copper tape with solid core wire soldered on top. I've got 2 balancing leads, both 8s (one for the top 8 cells, the other for the bottom 8 cells with some overlap) on the pack since my monitor/balancer only does up to 8s.

Here's a close-up of the cell connections:




This pack's capacity is around 300WH. I did plug it in and verify the inverter can turn on and run a light load. One concern is I found the built in charger puts out up to 43.5V when plugged into the wall. There might be an adjustment on the board for this though.

Interesting design. Curious as to how well the tape will hold up under full load. Get out the laser therm gun

I may have missed it earlier, but what model ups are you using? If APC, you should be able to change the voltages, at least on newer models; and especially with server/smart grade.

Korishan said:

Interesting design. Curious as to how well the tape will hold up under full load. Get out the laser therm gun

I may have missed it earlier, but what model ups are you using? If APC, you should be able to change the voltages, at least on newer models; and especially with server/smart grade.

Click to expand...

It's a Tripp Lite SMART1500.

Ok, I mis-read the product info, this is also not a true sine inverter but a modified sine. I guess I'm going to shelve this effort and just go straight for the 14s pack to power my 1500W true sine inverter in the other thread

rev0 said:

Ok, I mis-read the product info, this is also not a true sine inverter but a modified sine. I guess I'm going to shelve this effort and just go straight for the 14s pack to power my 1500W true sine inverter in the other thread

Click to expand...

Since you already have half the 36 volt 10s battery made I would go ahead and complete it. Use the UPS on non critical items. From what I have read a pmw sine wave is relatively clean, suitable for many of the common electronic in the home.
My server, cable modem/router/, monitor is on a cheap ups been on this for much of the last seven years besides the monitor everything works great. Monitors tend to break when stepped on with steel toe boots. But it still works.

>just realized that the ups hasn't been powering the equipment for 7 years only short periods of time when needed<

Later floyd

I have the 36 volt tripp lite and using 4 of the hov batt packs. it works good ran my old refrigerator for 2.5 hours and now running my tv that pulls 200ish watts. Ill post how long that runs later.

the trouble is the red light and alarm sounds at 34.3 volts so unless you want to hear the alarm until cut off you have to disable it. I don't know how to do that. Still it ran my tv for 4.5 hours. I'm Charging the batteries with the tripp lite and it is very slow, batteries are cold so I don't see how they can get damaged.

Just finishing up this thread, here are the pictures I took of the 36V inverter for anyone interested in the future:
Here is the correct link from Tripp Lite for the datasheet:https://www.tripplite.com/support/smart1500

Brent said:

the trouble is the red light and alarm sounds at 34.3 volts so unless you want to hear the alarm until cut off you have to disable it. I don't know how to do that. Still it ran my tv for 4.5 hours. I'm Charging the batteries with the tripp lite and it is very slow, batteries are cold so I don't see how they can get damaged.

Click to expand...

To Silence (or Mute) UPS Alarms: briefly press and release the
MUTE/TEST button.* Note: continuous alarms (warning you to
immediately shut down connected equipment) cannot be silenced.

Looks to be no way to disable the low voltage alarm, other than removing the alarm.
But worth a shot might be a low voltage alarm then shutdown equipment alarm.
once silenced, alarm will re-sound to indicate lowbattery
status
Later floyd