Can we charge Li-Ion battery with lead acid charger - Page 1
Forum section: electronics / beginners

author: Vindhyachal.takniki
author_rank: Frequent Contributor
timestamp: October 20, 2017, 05:28:30 am
content: 1. I have a lead acid charger of 48V/20A , I can set its voltage to 54.6V to charge a li-ion battery of 13 cells in series with slightly less currnt than 20A.2. Can we charge the li -ion battery with the lead acid charger?What could be downfall of this?

author: Signal32
author_rank: Frequent Contributor
timestamp: October 20, 2017, 07:24:18 am
content: I don't see any issues with this.The only thing you have to consider is balanced charging for the cells to make sure that the 54.6v actually gets distributed evenly among cells - though this is not related to using a lead acid charger. Do your cells already have balanced charging circuitry ?But, you probably only need 2-3A to charge the LI-ION batteries in series, you won't use the full 20A of current.EDIT: Forgot about current limiting. Don't use it. Was thinking this was like a bench supply and you would have current limiting.

author: adras
author_rank: Regular Contributor
timestamp: October 20, 2017, 10:14:11 am
content: Well, all battery types I know of are charged in the same way. Constant current, then constant voltage. But the point where you switch from CC to CV is different for all battery types. A lead acid charger switches at 2.3V per cell to constant current. Whereas the voltage for LiPo batteries will be 4.2V per cell.You shouldn't use that charger, unless you want to cause a fire.While writing the next paragraph I noticed how dangerous it will be to use that charger. There are too many things to consider. The underlined numbers are just rough guesswork!!If you really, really have to use it, one time only. And you can set the voltage of your charger in a range of 40V-60V. You could hook up a multimeter in series to measure the charging current. Then set the charging voltage to1/2 or 1/4of the final 54.6 voltage. Immediately measure the current which has to be at most 2-3A. If it's higher, the voltage is too high. This must be verified in a couple of seconds,10at most! Then every5-10minutes check the battery temperature (cool enough to touch), and check that the current is below2-3A. You should also disconnect the charger every 5-10 minutes, and measure the voltage of the battery pack to ensure that it's below 54.6V. The voltage of the pack discharged is 3.4V * 13 = 44.2V. You can't check the voltage of the pack while the charger is connected (will give you the wrong reading). The range, 44.2V -> 54.6V gives you an indication how far the pack is charged. When the charging current reaches let's say1A-1.5A, you can increase the voltage in small steps to increase the current. When you reach50Vyou should start to decrease the charging current to0.5AIt's very, very important, that you regularly check the packs voltage, check the current, check the temperature (50°C max).So many underlined numbers, this is not good. I'd take the risk, outside, with a huge bag of sand to extinguish any fire (water only makes it worse!!). On an inflammable ground, with safety goggles, heat resistant gloves, gas mask ....If you want to learn more about the topic google for "charging lipo" that just gave me some nice results!

author: samnmax
author_rank: Regular Contributor
timestamp: October 20, 2017, 10:23:00 am
content: Quote from: Vindhyachal.takniki on October 20, 2017, 05:28:30 am20A? Woa! What capacity are your Li-Ion cells? No moderately sized cell can charge at 20A without nasty consequences. For Lithium ion, you need to charge with constant current until reaching 4.1-4.2V, and then constant voltage. The constant current depends on the cell specifications, but is usually between 3% and 10% of the rated capacity (a 2000mAh cell can be usually charged safely at 200mA).Also, 13 cells in series is prone to becoming unbalanced. I think you need a proper charger/balancer circuit designed for Li-Ion.Quote from: adras on October 20, 2017, 10:14:11 amThis ^

author: IanMacdonald
author_rank: Frequent Contributor
timestamp: October 20, 2017, 05:23:31 pm
content: Agree.Don't. The issue is that if one cell goes faulty/short the charger will continue to dump 20A into the whole string indefinitely, because the overall voltage will never reach the cutoff level. The result is likely to be cells bursting and/or flames.You need a balancing board for the requisite number of cells, and unless they are massive cells you also need a lower current limit.

author: james_s
author_rank: Super Contributor
timestamp: October 20, 2017, 06:02:15 pm
content: I will echo the concerns. Unless the battery contains an internal BMS that is intended to be charged by a lead acid charger then don't even think about it. Lithium ion based battery chemistries must be charged by a charger specifically designed to do so. The gap between fully charged and burst into flames is very narrow, a fraction of a volt. Unlike most other battery types, Li-ion is not self limiting, you can keep charging it until the voltage goes so high that it fails catastrophically.