Charging my car battery - Page 1
Forum section: electronics / general

author: trophosphere
author_rank: Frequent Contributor
timestamp: December 03, 2016, 09:41:57 pm
content: This is for when you are working 16+ hour shifts during winter and your car battery is having trouble holding a charge when it's freezing. Seems to have worked for the past 3 days. Car battery will be replaced on the next coming day off.

author: RoGeorge
author_rank: Super Contributor
timestamp: December 03, 2016, 10:10:17 pm
content: Nice instruments!Similar setup here, except I am using 2 channels from a Rigol DP832 connected in parallel through a double diode, each channel pushing 3A.A series diode is recommended anyway, even for a single channel power source, just in case (e.g. a mains power outage).Here is some info used to do the setting for the power source:Code:Lead Acid generic specs-----------------------At a comfortable temperature of 20°C (68°F), gassing starts at charge voltage of 2.415V/cell. When going to –20°C (0°F), the gassing threshold rises to 2.97V/cell.Battery status-40°C (-40°F)-20°C (-4°F)0°C (32°F)25°C (77°F)40°C (104°F)Voltage limit on recharge17.116.215.314.714.1Float voltage at full charge15.314.714.113.813.5or loweror loweror loweror loweror lowergasing at 20*C for V >= 14.4Vnominal, no load = 12.6Vfloating charge = 13.5...13.8V

author: trophosphere
author_rank: Frequent Contributor
timestamp: December 03, 2016, 10:16:02 pm
content: @RoGeorge Thanks for the table of information and the suggestion of using a diode. Did not think of what would happen if the power went out as I have been leaving the battery connected overnight while I am asleep.

author: tautech
author_rank: Super Contributor
timestamp: December 03, 2016, 10:59:01 pm
content: If you want to mimic what an auto charging system does set your PSU to 13.8 - 14.2V.Note the current drawn and monitor it as it rolls off down to say ~100mA as the battery gains full charge.Of course most PSU's will go into CC mode initially so be sure to get the "set" voltage right first and just leave it to it.

author: trophosphere
author_rank: Frequent Contributor
timestamp: December 03, 2016, 11:19:04 pm
content: Yup, I noticed that the battery would draw up to the current limit (with the power supply set at 14v) and then by morning the current draw would be only a couple of milli-amps.

author: fubar.gr
author_rank: Unknown
timestamp: December 04, 2016, 12:44:22 am
content: You've connected the banana jacks on the battery terminals with clear tape

author: Macbeth
author_rank: Super Contributor
timestamp: December 04, 2016, 12:58:21 am
content: Quote from: fubar.gr on December 04, 2016, 12:44:22 amI know, right? I usually use rubber bands.

author: trophosphere
author_rank: Frequent Contributor
timestamp: December 04, 2016, 03:05:50 am
content: Quote from: fubar.gr on December 04, 2016, 12:44:22 amOf course. We should all follow the KISS principle. It is an excellent example of simple, fast, cheap, good availability, and lasts as long as its intended application.

author: Delta
author_rank: Super Contributor
timestamp: December 04, 2016, 03:33:28 am
content: That is one very expensive trickle charger!

author: Brumby
author_rank: Unknown
timestamp: December 04, 2016, 04:28:42 am
content: .... not if you already have one.(BTW - I don't have one of that calibre)

author: trophosphere
author_rank: Frequent Contributor
timestamp: December 04, 2016, 05:28:49 am
content: The power supply is really good if the majority of your circuits consume current on a the scale of nanoamps to microamps. The graphing capability is awesome because I can monitor, in real-time, my MCU projects as they switch between different low-power operating modes for given scenarios. Of course you can replicate this feature by using any power supply coupled with a graphing DMM such as a Keysight 34461/5.

author: Fraser
author_rank: Super Contributor
timestamp: December 04, 2016, 12:28:06 pm
content: Just take care when disconnecting the battery. PSU off before touching the terminals. Clear tape fastening is risky.Why ? In my teenage years I had a motorcycle battery that was on charge from my bench PSU. A spark ignited the hydrogen that was in the top of the battery and it exploded. Very messy, much acid damage and costly in terms of replacing acid contaminated materials.Just be careful when Jerry rigging lead acid battery chargers. They can really ruin your day if the battery explodes. Remember, sealed lead acid batteries still vent hydrogen to atmosphere that acts like an ignition fuse to the gas pocket above the plates. The relatively gas tight confinement then creates the explosive gnition event.Fraser

author: VK5RC
author_rank: Unknown
timestamp: December 04, 2016, 12:52:43 pm
content: Do you think its the charging (probably 1A ~= 0.01C ) or keeping it warm inside?

author: System Error Message
author_rank: Frequent Contributor
timestamp: December 04, 2016, 01:01:03 pm
content: you could always try using super capacitors instead. Its possible to have super capacitors to start the car and some lithium batteries to keep everything else (like the clock, alarm) powered when the engine is off.

author: SeanB
author_rank: Super Contributor
timestamp: December 04, 2016, 01:35:40 pm
content: My car battery charger is an old unit, made by GE circa 1950, and it does the job, though i did upgrade it a bit over the years. The boost charger is by using the arc welder, as I added a half wave rectifier diode, a press stud diode I had around on an aluminium plate, a 40A thermal breaker and a charge socket for a wire. Will give enough charge into a flat battery to start in the time it takes the thermal breaker to heat up to trip point, and then a few reset cycles and it will be enough in most cases. Works on 12 and 24V systems, you just have to set the arc current shunt to change the voltage and current by shunting the magnetic field in the secondary. Kills SLA batteries though, current is a little high for them.

author: HighVoltage
author_rank: Super Contributor
timestamp: December 04, 2016, 02:00:09 pm
content: Just today a friend came with his 12V GEL battery for a mobil home and it was sitting at 4V for a few month probably.I have been using this MAAS PSU as a battery charger for many years now and it works really well.Charging up to 32A and regulated really well to 13.80 VBut no tape or rubber bands on the terminals, I have been using real 8 mm screws and huge cables.I also had an experience as a child to have removed the charging cables from a 24V truck battery while the charger was turned on.It was a good explosion and the battery was good for the junk.Well, I am still surprise that I survived it. I jumped in to the shower right away.But all my clothing had holes.

author: rollatorwieltje
author_rank: Unknown
timestamp: December 04, 2016, 02:18:24 pm
content: Be aware some power supplies have a crowbar circuit on the output terminals for overvoltage protection. You really don't want that to trigger when there's a battery connected. My Agilent e3615a has it, in the manual it recommends charging batteries through a diode to prevent nasty things happening.

author: HighVoltage
author_rank: Super Contributor
timestamp: December 04, 2016, 02:20:50 pm
content: Quote from: rollatorwieltje on December 04, 2016, 02:18:24 pmThat is very true.I learned that lesson many years ago with a brand new Agilent PSU and only a small 12V battery.The Crow-Bar trace on the PSU was gone in a few seconds.

author: SeanB
author_rank: Super Contributor
timestamp: December 04, 2016, 04:22:17 pm
content: Bet the SCR survived though.....

author: HighVoltage
author_rank: Super Contributor
timestamp: December 04, 2016, 04:57:44 pm
content: Quote from: SeanB on December 04, 2016, 04:22:17 pmYes, it didLuckily the evaporated trace was on the top layer and other parts of the circuit were not damaged.I think there should be a big warning label one every laboratory PSU that has a crow bar inside.It is so tempting to use a Lab PSU for battery charging.

author: CraigHB
author_rank: Regular Contributor
timestamp: December 04, 2016, 05:51:27 pm
content: I use my lab PSU for battery charging once in a while. Sometimes for a Li-Ion cell I use in bench testing and also for a 12V SLA battery I use as a mobile power source. I just picked up a new PSU, no idea if it has a crowbar circuit or not, hopefully not. Any way to check?

author: helius
author_rank: Super Contributor
timestamp: December 04, 2016, 05:58:18 pm
content: There will be a SCR directly across the output terminals, with a voltage setting potentiometer connected to it.

author: CraigHB
author_rank: Regular Contributor
timestamp: December 04, 2016, 06:06:28 pm
content: Quote from: HighVoltage on December 04, 2016, 02:00:09 pmI guess your friend is not aware that allowing a LA battery to get below 1.75V per cell damages it severely. For the best longevity LA batteries should be stored fully charged with a maintenance charge every few months. An LA battery should not be discharged below 1.75V per cell with 1.85V per cell ideal to minimize wear. Interestingly Li-Ion batteries provide the best longevity when stored under half charge, but they too suffer damage when discharged too deeply.

author: trophosphere
author_rank: Frequent Contributor
timestamp: December 04, 2016, 06:49:53 pm
content: Quote from: VK5RC on December 04, 2016, 12:52:43 pmIt probably is due to the warmth but not 100% sure on that as I have been taking it off the charger in the morning and starting my car with it. My coworker jumps my car when we are about to leave from the parking lot at night. The current consumption drops towards negligible after an overnight's charge where as when I first charge it at night the PSU would be at the current limit of 1A. I don't think that it is my alternator that is bad as the voltage across the battery increases to about 14v with the car running but will find out when I replace the battery on my day off tomorrow.Quote from: System Error Message on December 04, 2016, 01:01:03 pmI saw couple of implementations like that on the internet. Would be a worthwhile project to do later but for now would rather get a new battery and be done with it.The PSU now has a diode in series with its output when charging the battery. Thanks for the heads up.

author: SeanB
author_rank: Super Contributor
timestamp: December 04, 2016, 07:56:51 pm
content: Probably has a dying cell, and this is what is limiting your cranking ability. With the new one get a battery thermal insulator, it will both keep the battery warmer in winter and cooler under the hood, so it does not degrade so fast.

author: HighVoltage
author_rank: Super Contributor
timestamp: December 04, 2016, 08:13:28 pm
content: Quote from: CraigHB on December 04, 2016, 06:06:28 pmWell, once it is charged up completely, I will discharge it with a DC load and graph the voltage.Will see how bad it is and how much capacity is left.