Car battery charging with desktop power supply  - Page 1
Forum section: electronics / beginners

author: dav
author_rank: Regular Contributor
timestamp: June 06, 2016, 11:02:29 am
content: I should charge a 12V 35Ah car battery (unused for some months).Battery manual suggests to charge at 3.5A for 5-6 hours .Initial battery voltage is about 9V.Then I connected my korad power supply to the battery, with a diode (to avoid damages to the power supply).2 meters show the voltage on the battery and the current.I set the voltage on the power supply so to have 14V on the battery, but I can read just 0.5A flows in the battery!So the question is how to pump 3.5A in the battery?Thanks

author: SteveyG
author_rank: Unknown
timestamp: June 06, 2016, 11:17:04 am
content: Quote from: dav on June 06, 2016, 11:02:29 amIf you want more current into the battery you need to increase the voltage, however I'm not sure this is what you really want.You probably just want to float charge the battery so make sure you measure the voltage after the diode to see if you're reading around 13.8V. If it's been flat for a while the battery might be dead though.

author: Maxlor
author_rank: Frequent Contributor
timestamp: June 06, 2016, 11:18:50 am
content: As for charging: you can go a bit higher with the voltage, since you also need to to account for the diode drop; stay below 14.5V at the battery terminals though (you could charge it at higher voltages, but it'll start gassing - not great in an appartment.)However: assuming your setup is ok (Diode not broken and suitably big, no current limit on the Korad) it might just be that the battery's dead and unrecoverable; 9V is way too low for even an empty automotive battery. I guess I'd try letting it sit at 0.5A for an hour or two to see whether it comes back or not.

author: dav
author_rank: Regular Contributor
timestamp: June 06, 2016, 11:26:27 am
content: Thanks to all.I know, battery could be dead.Diode supports up to 8A.14V are exactly on the battery (not the output of my Korad).I set the power supply as 15.21V and 3.5A (current limit).Now, after 1 hour, current is at 0.585A.Should I increase the voltage on the battery?I readit's not safe to put 20-30V on the battery.

author: Simon
author_rank: Unknown
timestamp: June 06, 2016, 11:41:09 am
content: The plates have gone hard and won't allow a faster charge, it may pick up after a while it may be a dead battery.

author: dav
author_rank: Regular Contributor
timestamp: June 06, 2016, 12:12:24 pm
content: Maybe do I need to add water?

author: dav
author_rank: Regular Contributor
timestamp: June 06, 2016, 03:54:36 pm
content: Now current is 0.993A (same voltage on battery: 14.30V)Maybe is it resurrecting??

author: jitter
author_rank: Frequent Contributor
timestamp: June 06, 2016, 04:29:28 pm
content: The low initial charge current sounds like sulfation. You may be able to recover it if you take some time.Watch this:Basically this guy says to forget pulse chargers, they don't desulfate a battery. Instead lots of time and slight overcharging may improve the battery to a usable state, but it will never be as new.From the description:Quote

author: Simon
author_rank: Unknown
timestamp: June 06, 2016, 04:30:51 pm
content: Quote from: dav on June 06, 2016, 12:12:24 pmDo check

author: Red Squirrel
author_rank: Super Contributor
timestamp: June 06, 2016, 04:49:10 pm
content: Wait, is it at 9 volts? It may be dead beyond repair but worth a shot, there are tricks that may help, like what jitter posted. But that said, to properly charge a battery you want to give it 13.5v, or 2.25v per cell (12v has 6 cells). You can leave it like that indefinitely if you wanted to - a lot of systems are like that. Well, there's other factors like temperature. This is assuming below 25C. There's some rules of thumb on what float voltage should be based on temp. I would start at a lower voltage for this one though so 12v ATX psu may indeed work. You'll eventually want to find a way to bring it up to 13.5 though.I'd also check if you need to add water. Make sure to use distilled.

author: dieseltech82
author_rank: Contributor
timestamp: June 08, 2016, 11:49:20 am
content: With a battery that's dead, I like to overcharge with high voltage (15.5) and high amps to boil the plates. You don't want to boil for extended time but this helps clean the sulfate me plates. Your charger isn't going to do this on its own. You could try a good car battery in parallel to help push more current to the battery.Sent from my iPhone using Tapatalk

author: tautech
author_rank: Super Contributor
timestamp: June 08, 2016, 12:40:28 pm
content: To answer the OP's thread title question; yes no problem.Modern battery chemistries allow higher charge voltages than in the past when it was generally accepted 13.8-14.2V was the charging range but up to 14.5V is considered safe these days.As you've seen a fall then a slight rise in the current drawn IMO this indicates the battery is taking a charge and will likely give more service. However 6 months idle for a LA auto battery is downright abuse and some steps can be taken to reverse some of the plate sulphation that has taken place.When the current draw has fallen to a couple of hundred mA remove any cell caps and proceed with an Equalisation charge as dieseltech82 has described, checking electrolyte levels are maintained with distilled or rain water or better still some new electrolyte.Cycling the battery with a gentile discharge and recharge a couple of times can help recover tired batteries and you'll get a feel for when it's charged from the charge current falling off.(CV)Good luck as you don't get them all back.

author: Circlotron
author_rank: Super Contributor
timestamp: June 08, 2016, 12:41:32 pm
content: Quote from: Red Squirrel on June 06, 2016, 04:49:10 pmFor a sealed lead acid battery that may be so, but for a modern low maintenance car battery that has a certain amount of calcium mixed in with the lead the proper charging voltage is about 14.2 volts. Old skool car batteries from the 60's and earlier that had to be topped up with water every fortnight or so I think we're about 13.5 volts.Edit -> was typing at the same time as tautech.

author: dav
author_rank: Regular Contributor
timestamp: June 08, 2016, 07:26:22 pm
content: After a few hours the battery started to drain more current, up to 3.5A at 14.20V (for about 5 hours).Then the current went down.Now it's 1.035A at 14.20V.I'm charging for about 3-4hours a day, only when I'm at home (I want to check periodically the battery, to avoid damages...)

author: jitter
author_rank: Frequent Contributor
timestamp: June 08, 2016, 08:13:17 pm
content: At that voltage, the drop probably means that the battery is reaching full charge. With "full" I mean as much as it will take given that there may be sulfation damage.When current drops further, you should drain the battery on a load (e.g. a couple car halogen headlamps) until it reaches 11 V and measure how long it takes. If this is short, then it has lost most of its capacity.From what I understand from the video I linked to is that a high discharge current will make the plates inside the battery swell and that would break the hard sulfation layer. If repeating this charge/discharge process leads to ever longer discharge times, it may mean that the battery is salvageable. If not, it's irreversibly damaged.

author: tautech
author_rank: Super Contributor
timestamp: June 08, 2016, 09:12:29 pm
content: Quote from: dav on June 08, 2016, 07:26:22 pmGreat, it's coming back.You can start pushing more current now with a charging voltage of up to 14.5V.When the current falls to ~300mA (charged or very close to) do the Equalisation charge....3-4 hrs should be long enough.Discharge/charge cycle it if you wish......it will give you a good idea if the charging currents are repeatable and the fully charged voltages are consistent.If you have the time little exercises like this can teach you a lot about battery behaviour, I'm no expert it's just decades of managing my own equipment that has taught me what works best. (for me)

author: dav
author_rank: Regular Contributor
timestamp: June 09, 2016, 01:15:44 pm
content: Now current is at 700mA, which is 2% of battery capacitance (35Ah), so let's start equalization....Ah, I also found this interesting article:http://www.evdl.org/pages/hartcharge.html

author: dav
author_rank: Regular Contributor
timestamp: June 10, 2016, 11:38:16 am
content: After equalization, battery rested for about 16 hours; now voltage is 12.80V.Now I'm draining power from it (unfortunately I haven't got an electronic load, so I connected some ceramic resistors).Current is at 0.630A

author: jitter
author_rank: Frequent Contributor
timestamp: June 10, 2016, 09:05:58 pm
content: Get some cheap 55 W car bulbs (headlamps).

author: johansen
author_rank: Super Contributor
timestamp: June 10, 2016, 09:37:19 pm
content: Quote from: dav on June 10, 2016, 11:38:16 amA 1 amp load will discharge that battery to 80% discharge when the voltage drops to 12 volts under load. when it gets below 12 volts, charge it again. repeat this process a few times and the amp hours should increase.it might be better to terminate the discharge at 12.3 volts though.at higher discharge currents the terminal volts drop much faster. a 3.5 amp discharge, when the terminal volts drop to 12, its at 50% discharge.

author: Rick Law
author_rank: Super Contributor
timestamp: June 13, 2016, 01:52:47 am
content: Quote from: dav on June 06, 2016, 11:02:29 am(Bold added to quote)You said you have a diode but didn't say what kind. Are you measuring the voltage before or after the diode? Depending on the type of diode, you may be dropping 1V to 1.5V after the diode! A rectifier diode dropping 1.5V would mean you are at 12.5V, barely enough to get charge going. If it is dropping over 0.5V, switch to schottky diodes - it would typically drop less than 0.5V.At 3.5A, don't forget the power dissipation of the diode. you need a fairly good size diode to take that much.

author: jitter
author_rank: Frequent Contributor
timestamp: June 13, 2016, 06:58:48 am
content: Quote from: Rick Law on June 13, 2016, 01:52:47 amI had interpreted the red text as after the diode.

author: Rick Law
author_rank: Super Contributor
timestamp: June 13, 2016, 07:05:43 am
content: Quote from: jitter on June 13, 2016, 06:58:48 amI must have been reading it carelessly first time. Re-reading it, I have to agree with your interpretation.

author: Brutte
author_rank: Frequent Contributor
timestamp: June 13, 2016, 07:20:36 am
content: A 35Ah 12V automotive battery has to crank the engine. At ~300A at rated load, at any conditions.If the battery was drained to 9V then the maintenance failed somehow, it should have never happened. Put your effort to avoid that abuse and not to resurrect the abused FLA.It may be that after some recharging/recharging it would crank one or two times occasionally but the effort put into it and additional cost related with time lost while playing with it (or when it won't crank and you won't get to work) is not worth it.The FLA automotive battery easily lasts for a decade, 99.99% reliableif not abused, costs <$50 . Do not try to invent or follow any wonderful means of prolonging its life after abuse - the subject has been beaten to death over the last 200 years and there is nothing new in the subject.My FLA topic.

author: hushaoxin
author_rank: Contributor
timestamp: June 13, 2016, 08:53:14 am
content: if the initial battery voltage is about 9V, sure, the battery is dead

author: dav
author_rank: Regular Contributor
timestamp: June 19, 2016, 08:55:00 pm
content: Quote from: jitter on June 10, 2016, 09:05:58 pmThat's exactly what I didQuote from: tautech on June 08, 2016, 12:40:28 pmI cycled 2 times.Now the battery retains the charge and works fine