Li-ion UPS battery substitution in UPS

I've seen the charging methods indicated as being similar, constant current, constant voltage, then a topping charge. But lithium ion batteries do not tolerate a float charge. Even if this wasn't an issue, the details of current and voltage will not be the same. I would not expect the lithium batteries to live very long being charged as lead acid.

I added some Li cells to my dying LA battery. Yes, there is LA in EV. However, i have to be careful not to over-charge it for extended period of time. I disconnect it during extended usage, when the LA can handle the load. Unlike LA, Li does not like to be fully charged.

tirsdag den 18. oktober 2022 kl. 17.43.44 UTC+2 skrev Bert Hickman:

might look at LiFe4 instead, afaik you can get LiFe4 car batteries so they must be reasonably compatible

LiFe4 should also be bit safer the Li-ion

Yes, i use 4S (3.2V x 4) LiFePO4 and 3S (3.7V x 3) LiPo.

BTW, i am using some old 12V module based on the TI BQ20Z95 and some new one based on BQ20Z65. Half of the BQ20Z95 doesn't work or cut-off at low 11V. BQ20Z65 works better, but still cut-off at around 11.5V or sometimes lower, even with all new cells.

For emergency, i put 32 to 34 of them in series to run at 400V.

Yes, you need good BMS and manual disconnect.

Tell him to put it on ebay and give me a link here. I might get them if the price is right.

Mine is essentially Li UPS. LA is too heavy.

BTW, my 12V to 400V DC/DC converter is 100% efficient.

Why would you want to? There are several parameters to consider.

Li batteries age quite fast if kept at full charge. Lead-Acid batteries last the longest when kept at full charge.

LA's biggest disadvantages, compared to Li, is that they are heavy and large. For a UPS, those disadvantages are normally not important.

LA is simply the best choice for standby applications such as UPS, emergency ligting and similar.

But those gel batteries ARE lead acid! They just have the gel to hold the acid in place along with catalysts to aid recombination of evolved gas. Some car batteries are gel or glass mat types. However, LiFePO4 batteries do seem to avoid most of the problems of original Li ion batteries. Tesla are now using them in most of their cars. Ford and VW are planning to do the same. John

Good BMSs stop over-charging and under-discharging. Good EVs don't have pillows.

Go for LiFePO4 (lithium iron), but only if the firmware is updated to allow for proper charge termination and voltage settings.

A capacitive balancing circuit is a good idea.

RL

Not in mine. It uses lithium cells, is easy to hold in one hand and has started a variety of large engines including diesel vans and a Ferrari FF. One of the nice things about Li cells is that the starter pack can sit on the shelf for a year without any attention and then "just work". (I do leave it slightly discharged to help preserve battery life.) It was very reasonably priced about 3 years ago, mostly because I bought it on an Amazon "flash" sale. I had been browsing for such things but considered all the good ones to be too expensive. Then an offer of a 40% discount, valid for 1 hour, popped up and I took it.

John

I think it varied according to which vehicle. A couple of weeks ago I used it every time I started the engine (1.8l petrol) of my car because the car battery had developed a very high internal resistance and probably also had a shorted cell. The voltage dropped to 6V on trying (and failing) to crank the engine. The charging voltage was only about 12.5V. With the Li starter pack the engine would start immediately. I have now replaced the battery. In the case of the Ferrari FF (not mine, sadly) the battery was completely dead and it took many attempts to get it started with the Li starter pack, so the Li battery really was doing all the work. However, this was a 6.3 litre, 650HP V12 engine. It did start in the end. Its battery accepted no charge whatsoever - it would not even run its lights after a 20 minute drive. In the case of the diesel van, it may well have added just enough charge to make a difference in the 20 seconds or so between connecting it and starting the engine. My unit has very short, very thick (6AWG) cables:

no.co/gb70

Usefully, it also has a regulated 12Vdc output.

John

My Leaf won't wakeup after 2 or 3 days sleeping. It's mostly because of the 100W power relay. I could just jumper short the relay output, when i open up the battery next time. For now, i just added a 200Wh (3S9P) Li power brick (around 5 pounds) to the LA battery. The Li BMS cutoff at 11.5V when charging. It's fine in this case. The Li battery mostly keep the LA battery from dropping too low.

Yes it does. But better to keep the LA when close to fully charge, and less cycling on the Li.

Charge rate is no big deal. A small 18650 can take up to 3A to 5A charging. Voltage is more important. My eTank #2 is 34x 3S batteries without BMS. Typical EV equivalence is 32x, which run the cells between 3.5V to 4.2V. I run mine at 34x with cells between 3V and 4V. I check and balance them manually. No pillows and/or firecrackers yet.

My eTank #3 will have EMS.

No, 100W when the car is on. After a few days, the 12V battery is too weak to pull the 100W power relay (switching 400V on).

Yes, i also did an emergency jump charging from 400V to 12V with 5S5P 200K resistor. Not very efficient, but works and i happened to have the resistors in the car, and 400V tap in the backseat. The traction/propulsion battery is 24kWh 96S Li.

Just old age. The battery is 10 years old. The solar charger is probably dead also, or not enough sun in SF.

Yes, the Li power brick is essentially a built-in automatic jump starter. It's around $28 including shipping, but with more capacity than the $2899 UPS.