120V lead acid battery charger - Page 1
Forum section: electronics / projects

author: MartinFO
author_rank: Contributor
timestamp: April 30, 2025, 08:09:51 pm
content: HiI need to charge at lead acid battery pack of 10x 12V batteries serial connected. The nominal voltages of the pack is 120v and has a 8Ah capacity. I need a charger for this, but common chargers seem to be 12,24,36 or 48V. So I was wondering if I could just serial connect multiple chargers? Is it possible? Is it safe? Is there a better way.I cannot disassemble the pack or charge each battery individually.🙏Br. Martin

author: thm_w
author_rank: Super Contributor
timestamp: April 30, 2025, 09:45:20 pm
content: If you can't access the inner points of the battery then multiple chargers might not work. Some require sensing the battery voltage before they will begin to charge.Is this repeated charging or just a one time thing? If its a one time thing you can use a 150-200V adjustable power supply and a diode.

author: NiHaoMike
author_rank: Super Contributor
timestamp: May 01, 2025, 03:54:44 am
content: I assume it's a UPS battery, so the logical answer is to find a compatible UPS. If it's at least somewhat common, you should be able to find one for really cheap that just needs a new battery but otherwise is in good working order.Other than that, mains through a motor run capacitor into a bridge rectifier to make a high voltage current source, with a zero cross SSR to modulate the charging current. Use a sensing circuit that turns on the SSR when the voltage is below the setpoint, otherwise turn it off.

author: PCB.Wiz
author_rank: Super Contributor
timestamp: May 01, 2025, 05:02:19 am
content: Quote from: MartinFO on April 30, 2025, 08:09:51 pmLead acid chargers usually make state decisions, so series wiring would not work.There are some 120V chargers, but not cheap...https://www.aliexpress.com/item/1005001954107923.htmlhttps://www.aliexpress.com/item/1005008491771283.html?https://www.aliexpress.com/item/1005008894473634.htmlthis one claims 3 state charging for lead-acid ?https://www.aliexpress.com/item/1005005334795009.html

author: richard.cs
author_rank: Super Contributor
timestamp: May 01, 2025, 01:28:40 pm
content: How sophisticated do you need it to be? Full multi-state charging? Simple CV with current limit? Just throw some charge in and manually monitor it? Are they flooded cells, AGM, gell cells?

author: MartinFO
author_rank: Contributor
timestamp: May 01, 2025, 06:55:11 pm
content: Thanks for all your inputs.It is actually for a UPS (great guess). I have attached a picture of the battery. The charger is intended as a maintenance/storage charger for new battery packs in storage. It needs to be rather professional, as I will produce multiple of these. I was hoped to just buy multiple chargers (or have a simple circuit made) wire them in a cabinet.

author: thm_w
author_rank: Super Contributor
timestamp: May 01, 2025, 09:54:31 pm
content: If its just a maintenance charger then maybe a simple trickle charger of ~130V current limited at 0.5A or 1A is good enough.Test and charge the batteries first when they come in loose at a higher rate.

author: MartinFO
author_rank: Contributor
timestamp: May 06, 2025, 05:37:21 am
content: Sound like a good solution, but I cannot charge them individually. Will this pose a problem?The max charge current is 2.4A, so 1A is with a look margin. Could I just use a 130V power supply, with a current limit of 1A and a timer for 8hrs?

author: trobbins
author_rank: Frequent Contributor
timestamp: May 06, 2025, 09:03:15 am
content: Perhaps elaborate on why you can only charge the pack in total? Is this for charging whilst the battery could be powering the UPS (ie. battery typically on float, but could be instantaneously used for backup if the mains fails)? Or is this for a maintenance event, where the pack is completely disconnected - in which case individual 12V charging is far far better. Have you confirmed the 12V monoblocs are all healthy, and what their float current is at rated float voltage, and that each monobloc discharges to same EODV for nominally the same discharge capacity, at the nominal discharge rate of the UPS?

author: thm_w
author_rank: Super Contributor
timestamp: May 06, 2025, 11:06:12 pm
content: Quote from: MartinFO on May 06, 2025, 05:37:21 amYou showed a photo of loose batteries above, so I assumed you were building the packs.QuoteYou'd need a bit more time or current if you want to guarantee a full charge (charge efficiency might be 80%). And voltage closer to ~144V. But I would expect that to work.https://electronics.stackexchange.com/questions/14174/charging-lead-acid-batteries-in-series