[Suggestion] Acid lead batteries charge methods - Page 1
Forum section: electronics / general

author: migsantiago
author_rank: Frequent Contributor
timestamp: August 17, 2010, 01:59:16 am
content: HelloI would like to know more about acid lead batteries if it's possible.I want to build a small battery recharger but I don't know what kind of protections I should use, how much current the battery should demand when it's discharged, how the Ampere-hour ratio is calculated, what recharge methods are available and so on.I'd really appreciate this.Thanks!

author: RayJones
author_rank: Frequent Contributor
timestamp: August 17, 2010, 09:59:22 am
content: Panasonic have some good info on their website for the treatment of VRLA batteries.Here's a starter:http://www.panasonic.com/industrial/includes/pdf/Panasonic_VRLA_Overview.pdfGenerally you want to limit current to 1/4C until you reach the absorption voltage (Bulk mode), then hold at the absorption voltage until the current drops to 0.1C (Absorption mode), then switch to the float voltage (Float mode).As an example, a 17AH 12V battery should typically be charged at 4.25A until the battery voltage reaches 14.4V.The charger should then hold at 14.4V until the current drops to 1.7A.Finally the charger holds at 13.8V, at which it can be held indefinitely.Ideally temperature should also be taken into account for the battery you are using and the endpoint voltages adjusted accordingly. These derating specs are published by the reputable manufacturers.

author: migsantiago
author_rank: Frequent Contributor
timestamp: August 17, 2010, 07:17:26 pm
content: Thanks RayJones, I'll study that document.By the way, what do you mean by saying 1/4C? One fourth Coulombs or Capacitance?Quote from: RayJones on August 17, 2010, 09:59:22 am

author: RayJones
author_rank: Frequent Contributor
timestamp: August 17, 2010, 07:49:02 pm
content: One quarter the nominalAmpsper Hour rating, ie 4.25 for the 17AH example. So in this case the C means Capacity.I noted in the actual charging document Panasonic have that they quote <= 0.4C. ( look amongst the OEM industrial batteries portion of their website)I suppose 0.25C could be regarded as a conservative value.The important thing is to only ever use the el cheapo transformer / rectifier for emergency charging, and never leave this sort of charger connected for lengthy periods of time (a day could cook a small LA battery).

author: migsantiago
author_rank: Frequent Contributor
timestamp: August 17, 2010, 08:35:04 pm
content: Quote from: RayJones on August 17, 2010, 07:49:02 pmThat's what I fear, to damage a battery. Someone told me that a floating charge could be left unattended for any period, but now I see that it's not ok to do it.

author: Unknown
author_rank: Unknown
timestamp: August 17, 2010, 08:37:33 pm
content: Quote from: shafri on August 17, 2010, 11:36:11 amYou can charge NiCd in (most) NiMH chargers. NiMH have a smaller -dV/dT, so a NiCd charger would have trouble detecting this, but the reverse should not be an issue. If the NiCd is lower capacity, you obviously need a lower charging current. I believe lead acid is completely different (from memory it's constant voltage instead of constant current, but I'm sure the link and description from RayJones is more accurate). So you'd need a completely different charging mode for lead acid.

author: RayJones
author_rank: Frequent Contributor
timestamp: August 18, 2010, 07:49:56 am
content: Quote from: migsantiago on August 17, 2010, 08:35:04 pmIt is OK leave on float charge provided it is nominally maintained at 13.8V.What is damaging is leaving the battery connected to an unregulated supply, ala tranny and rectifier, for a long period of time.

author: migsantiago
author_rank: Frequent Contributor
timestamp: August 18, 2010, 01:30:06 pm
content: So, I can leave 13.8V applied to the battery.. forever?If so, what would be the maximum current the battery would drain when it's being recharged with 13.8V? I don't want to implement the other voltage stages (bulk and absorption), just start with the floating one.

author: RayJones
author_rank: Frequent Contributor
timestamp: August 18, 2010, 08:17:41 pm
content: Once at float stage, the battery will draw insignificant current.It will however draw current, which should be limited, during the bulk stage, even if you only have an end point of 13.8V.Like it or not, you have to implement a bulk stage current if you want to re-charge a battery.And yes, you can leave the battery at 13.8V forever, or until its useful life is over, which is also a published spec.The basic form is simply a LM317 set to 13.8V - gives you about 1.5A max current, so OK for anything larger than around 4AH.If you don't do the absorption phase, you won't get a fully charged battery anywhere near as quickly as you could.

author: migsantiago
author_rank: Frequent Contributor
timestamp: August 18, 2010, 11:50:56 pm
content: Got it. Thanks Ray.I found another link from Panasonic describing the recharge methods.http://www.panasonic.com/industrial/includes/pdf/Panasonic_VRLA_ChargingMethods.pdfhttp://www.panasonic.com/industrial/batteries-oem/oem/lead-acid-vrla.aspxI will match the info you gave me with the one included in the document and see if I can design my own battery recharger.