Car battery maintenance charger - Page 1
Forum section: electronics / projects

author: jrmymllr
author_rank: Regular Contributor
timestamp: December 26, 2020, 11:27:42 pm
content: Being as how we're driving our cars much less often, I'm running into dead batteries more than I ever have. What is the correct way to maintain a lead-acid car battery if I want it connected for long periods of time to avoid the dead battery syndrome?Constant voltage supply? What voltage? Seems like either 12.6 or 13.5V is what I want, but I can't find any sort of reputable info on this.I could buy one of these cheap 'trickle chargers' but I have a lot of extra parts around I could use.

author: NiHaoMike
author_rank: Super Contributor
timestamp: December 27, 2020, 01:12:42 am
content: 15V regulated wall wart through a diode to give about 14.4V, then plug the wall wart into a timer set to turn on for 30 minutes or so every day.

author: floobydust
author_rank: Super Contributor
timestamp: December 27, 2020, 01:32:05 am
content: I bought a chinese "12V 2A" SMPS charger $12 and it works fine but the two electrolytic capacitors get really hot. It's cheap and such a hassle - no NTC so huge mains inrush spark plugging it in, cheap PVC wire gets stiff when cold and it's not earth-grounded so the car floats up due to Y-cap. It has a two-states: bulk charge up to 14.6V then floats at 13.8V using oddball YX008A "pulse controlled coin timing charge control IC". This has equalized the battery's cells. I want something more reliable and safety certs would be nice.Other times I use a wall-wart and LM317 with added temperature compensation because it can get cold here. Or a bench power supply. But this doesn't do an equalization charge without running in and out of the garage.After a day the float charge current drops to about 200mA on a 70Ah battery and no water loss.Note that a car's ECU does things when parked - evap canister purge/test, some cycle the fuel pump, keyless entry/TPMS RX is always running etc. so there are loads that come and go. Subaru's have issues killing the battery 150mA quiescent (70mA is a typical max.) and a newclass action suitstarted over that.I was going to make an ESP8266 car battery charger and started the project, I want the WiFi remote display. But it's on the list of projects to finish.For the power supply, thinking of a laptop 19V 3A power brick with an MCU controlled buck-converter, or ripping the brick apart and hacking the regulation loop.There are also low cost 15V 2-3A power supplies.edit: added schematic of my junkbox LM317 car battery float charger with temperature compensation, I got about -27mV/°C, close to my target of -30mV/°C.

author: T3sl4co1l
author_rank: Super Contributor
timestamp: December 27, 2020, 01:37:39 am
content: CC/CV + cutoff works just fine. This is more or less true of lead acid, as well as lithium ion, polymer etc. Just different settings for them all.CC: limit charging current to some fraction of Ah rating (divided by hr). Unlikely to be a problem for a car battery (~50Ah), so anything under say 10A, not a problem.CV, fast: 14.3V until current under 1A or so, or timed with a low duty cycle. This voltage will cause some water electrolysis; monitor bubbling at the filler caps, keep ignition sources well away, etc. Inspect electrolyte level from time to time, and top up with distilled water as needed.CV, float: 13.8V, no timer needed (unlimited duty cycle). Shouldn't cause much electrolysis.Note the voltage has a tempco, -20mV/C relative to STP, more or less. So, if it's 0C outdoors and STP ~ 25C, set it ~500mV higher. Purpose-made chargers should adjust for this already (and yeah, you can get those modules for cheap, no problem).Personally, I reuse a few things I have handy. A 12V 10Ah* gel cell powers a 18V 20A converter I made, output set to 14.3V. This is a bit aggressive (both in terms of discharging the gel cell, and available charge current), but it also has UVLO and temp throttling, so I think if it does start out at a high current, it won't stay there for long, and the rest of the time it'll do a nice slow soak.Once a week or two seems to be often enough to keep things happy, with infrequent use (moving for parking, grocery store etc.). We'll see if the suddenly cold weather takes any more*Which through some age and abuse, one cell has failed. Fortunately, it's manged to fail shorted, so it works just fine as a 10V battery.Tim

author: trobbins
author_rank: Frequent Contributor
timestamp: December 27, 2020, 04:37:49 am
content: Quote from: jrmymllr on December 26, 2020, 11:27:42 pmPretty simple - keep it on charge with a commercial charger designed for automotive battery applications.It sounds like you aren't able to define the nominal method(s) to charge such a battery, or have checked what specific battery you have (as it may be a more premium AGM VRLA), so competently designing your own charger to suit your battery is likely a step too far.Can you keep the battery above about 15C, and below 30C ?Do you have a voltmeter?Do you want to periodically check the battery (voltage and terminal corrosion and temperature and ability to crank start the engine), or just leave it unattended for many months? I guess the same question can be asked about the car.

author: Rerouter
author_rank: Super Contributor
timestamp: December 27, 2020, 04:54:24 am
content: For me, a low wattage 12V panel, into one of those dirt cheap buck converter modules, diode on the output of the buck converterand then adjusting the output until it puts out 12.5V after the diode.The panel is a current source, so when there is light it has enough voltage to drive the buck converter, if there is not enough light, the diode doesn't let it discharge the battery or hurt the output of the buck converter,Been using in my car for the past year without any issues, the goal for me was just to maintain, not to float charge and cook off all the water, The panel is small enough to live in my glove box when not in use, and I just stuck an OBD plug on the other end for a battery connection.

author: jrmymllr
author_rank: Regular Contributor
timestamp: December 27, 2020, 04:05:53 pm
content: Quote from: floobydust on December 27, 2020, 01:32:05 amYep, it's a few year old Subaru. Not an Outback though but I'd assume the electronics is similar.

author: jrmymllr
author_rank: Regular Contributor
timestamp: December 27, 2020, 04:12:07 pm
content: Quote from: trobbins on December 27, 2020, 04:37:49 amIt's a generic lead-acid car battery, nothing fancy. I can't keep the battery at any specific temperature. The car is garaged, but not temperature controlled.I have a DMM, sure, and the ability to design any sort of regulation circuitry. I just wasn't sure what the correct method was to maintain a car battery when the vehicle isn't driven for long periods. The longest period of inactivity is about a month, no more. I suppose I could check the voltage periodically but I'm not sure if that'll tell me SOC (thinking about some 1.5V cells that measure a good voltage but can't sustain any load).

author: bdunham7
author_rank: Super Contributor
timestamp: December 27, 2020, 05:33:24 pm
content: You just need a readily-available commercial float charger, but if you want to build your own the most effective ones are the simplest. Just give the battery a small continuous current and it will be happy. A regulated 14.2 volt supply in series with a 1 ohm resistor and current-limited to 1 amp will keep your battery topped up, but will only charge it very, very slowly if it is low. You can easily just use a Class 2 wall wart that puts out 15 volts and 1 amp or so.You mentioned the car gets out at least once a month, but unless you drive it several hours, the battery isn't getting fully recharged. It is best to use a separate higher-current charger overnight if the battery is significantly discharged. The same 14.2 volt supply without the 1 ohm resistor and current limited to 5-10 amps would work for this. Obviously you can make one device to do both if you want a project.

author: jrmymllr
author_rank: Regular Contributor
timestamp: December 27, 2020, 05:55:35 pm
content: Quote from: bdunham7 on December 27, 2020, 05:33:24 pmI realize that given a car battery is 60Ah or so it takes a lot of amps and/or a lot of hours to fully charge it. This is just to fight self discharge and parasitic current draw.I'm not sure about the several hours figure though. I always preach that car engines need to get to operating temperature during most drips to burn off condensation in the exhaust and oil, and that's maybe 15-20 minutes. It's very rare for either of us to drive several hours in one trip and haven't had this dead battery problem until COVID-19 meant much less driving.I did find some numbers after I posted this that "float" charging, apparently that was the keyword I should have been looking for, is 2.25-2.27V per cell. So looks like 13.5-13.6V constant voltage is what I should be aiming for, with maybe a few comparators and LEDs showing some status indication.

author: bdunham7
author_rank: Super Contributor
timestamp: December 27, 2020, 06:41:45 pm
content: Quote from: jrmymllr on December 27, 2020, 05:55:35 pmThe several hours refers to the situation where the car has been sitting and either barely starts or needs a jump. If you only run the car for 20 minutes, you will have only charged it up a fraction of its capacity. If you drive it just often enough, it can live in a state of perpetual partial charge for quite some time. If you drive it 20 minutes every day, it will eventually migrate to a higher level of charge and you won't notice any problems.I have a fair amount of experience with this and my recommendations were based on that. The lower-voltage float charge recommendations you found are based on a couple of flawed assumptions.1) The 2.25 V per cell would only apply to a specific cell chemistry at a specific temperature, perhaps a standard lead-antimony cell at 23C or something like that.2) Float charge assumptions are based on a fully charged and balanced battery, discharged or unbalanced batteries require a lot more. Float charging at those levels will not charge a battery.3) Those numbers also assume you want to minimize gassing and water loss4) There is another separate regimen of regular charging and balancing.5) There is a temperature compensation system in place to increase the voltage at colder temperatures.In your case you have:1) A slightly different type of cell, likely with calcium added to the alloy to assist in gas recombination and allow higher maximum charging rates. This common chemistry requires slightly higher voltages.2) A battery that may not be fully charged when you connect the charger to it so that it is desirable that the 'float' charger will also eventually charge the battery (but not balance or equalize it).3) A battery that has the recombination capability to tolerate a significant continuous charge current without water loss. 1 amp or less won't tax that capability at all.4) There may not be any other charging regimen if you don't drive the car--so you want a system that will maintain the battery completely on its own, indefinitely.5) You don't have a temperature control so you need a compromise solution.Using a 13.5 volt float charge on a partially-charged battery in a colder environment may keep it charged enough to start your car, but will result in shortened battery life. Even 14.2 volts is a compromise based on not knowing the temperature your battery is stored at. 14.4 would be better at 0C. Keep in mind that with the 1R series resistor, the battery never gets all the way to that voltage. In fact, if your battery has been damaged by being discharged, the voltage may struggle to even get above the 13.5 volt level and you may need to charge it at the higher current I suggested.

author: jrmymllr
author_rank: Regular Contributor
timestamp: December 27, 2020, 11:25:54 pm
content: Quote from: bdunham7 on December 27, 2020, 06:41:45 pmAhh, yes that makes sense if the battery isn't fully charged. I misunderstood. Even if the alternator was cranking out 50A to charge the battery that's roughly more than an hour. I know most alternators can do 100A or more but I'm not sure how aggressively batteries are charged (and I used to test the charge control algorithm for a certain OEM at a previous job, too long ago though to remember specifics).Quote from: bdunham7 on December 27, 2020, 06:41:45 pmHmmm, would it be worthwhile to change the charge voltage based on ambient temperature? Or if I'm lazy I could use a selector switch for two different temperature ranges (or something like that). What would be a good regulator voltage at say two different temperature ranges, or would you recommend 3 or more? What higher current are you referring to if it can't get above 13.5V? Above 1 amp?I can design a circuit to do this, but I'm not good at the battery chemistry part and what they like given different conditions!

author: ttx450
author_rank: Regular Contributor
timestamp: December 27, 2020, 11:58:47 pm
content: the none scientific method.pull battery, put on wood surface or something.. do not directly set on cement. Will discharge. there's a debate.. better to sit on something. many new items drain batteries over time, let along it's own discharge..every month or two charge. lithm is different.. just pull from foul weather and store inside

author: bdunham7
author_rank: Super Contributor
timestamp: December 28, 2020, 12:26:46 am
content: Quote from: jrmymllr on December 27, 2020, 11:25:54 pmIn a car, unless it is a special case with an AGM battery or the like, the battery is typically just presented with a more or less consistent voltage and how much current goes through the battery is primarily a function of its internal resistance. Newer models may reduce this voltage at times, but that is an energy conservation thing not battery management. More importantly, how much of that current translates to charge and how much to heat (and gassing if things don't go right) is dependent on its temperature, state of charge, condition, etc.QuoteIts always a compromise and batteries are all slightly different. As long as you aren't trying to recharge a discharged battery, at low currents it probably doesn't matter much unless your temps are below freezing or above 100F. If you like, you can compensate it 3mV/C from 20C (higher when colder) If you can't get above 13.5V with the circuit I described, then your battery is damaged or discharged or is exceptionally hungry. In that case you could cut the series resistor in half, or you could not worry about it too much as your car will likely still start a month later.

author: ttx450
author_rank: Regular Contributor
timestamp: December 28, 2020, 12:32:25 am
content: just get a battery maintenance charger like from HF if to lazy to remove.. not that important

author: jrmymllr
author_rank: Regular Contributor
timestamp: December 28, 2020, 01:07:13 am
content: Quote from: ttx450 on December 28, 2020, 12:32:25 amPulling the battery is just too much of a hassle, yes. It may need to be driven at short notice and having to lug the battery in and out is inconvenient.I know maintenance chargers are commercially available, the one from HF is $7 I think. I don't know how much I trust something like that. I'm good a building this kind of stuff so I'm considering that.

author: jrmymllr
author_rank: Regular Contributor
timestamp: December 28, 2020, 01:23:37 am
content: Quote from: bdunham7 on December 28, 2020, 12:26:46 amThat sounds familiar now. I think they applied as much as 15.something volts in the coldest weather, although if the headlights were on that was a factor too. The battery guys and lighting guys were always fighting over this as each group needed something opposite to decrease their warranty claims LOL.Quote from: bdunham7 on December 28, 2020, 12:26:46 amPlenty of below freezing weather here as I live in a state that borders Canada, so the 3mV/C compensation might be important in my case.So, you said 14.4V (at 0C), then subtract (3mV * 20C) to get to 20C = 14.34V. Let's say 14.3V through a 1R resistor, then increase by 3mV/C below 20C? Maybe a few output voltage indicator LEDs as a quick assessment of things, i.e. if battery voltage is above 13.5V.

author: ttx450
author_rank: Regular Contributor
timestamp: December 28, 2020, 08:31:45 pm
content: Quote from: jrmymllr on December 28, 2020, 01:07:13 amas long as it a maintenance type charger, should be good to go.you might be handy, but I bet shipping will eat you up before parts.. at least here in us, shipping is expensive.

author: georges80
author_rank: Frequent Contributor
timestamp: December 28, 2020, 08:45:48 pm
content: I have 2 vehicles that don't get used much at all when I'm not in oz (could be a year or more). Mate drives them once every few weeks to keep fluids etc moving.I have both vehicles connected 24/7 to their own Ctek charger and it takes care of maintenance. One of the vehicles has dual batteries (4wd) and I just flip a switch to keep them in parallel so they both get maintained. Batteries last years and don't get damaged.The Ctek's work well and do the 'right' stuff to maintain versus cook. Some things aren't worth buildingcheers,george.

author: ttx450
author_rank: Regular Contributor
timestamp: December 28, 2020, 09:18:40 pm
content: this is how I do it.. I am cheap.. should add if I had a fleet, would get maintenance chargers..vehicles I run once a month like George stated. I let them warm up and run them up down the drive way a few times for the ones I dont drive. Its good for much more then the battery.The ones that sit, I live in MI we get very cold weather.. my mower and dirt bike batteries are right here next to my elc work bench. I charge them 1 once a month. My dirt bike ktm450sfx has a lithium.. so dont need maintenance, just keep inside.

author: floobydust
author_rank: Super Contributor
timestamp: December 28, 2020, 09:37:21 pm
content: Ctek looks very sophisticated and the product lineup is just overboard - I've never seen so many offerings that are really similar with a few different LED's lol. It's just overpriced.Cheapest is the US 0.8A 6-step for CAD $85, and cold weather MUS 4.3 is $136 although reviews say the (comfort) wiring is brittle and breaks when cold.I like the way it shows the 8-step charger graph that no consumer can make sense of

author: StuartA
author_rank: Regular Contributor
timestamp: December 28, 2020, 09:46:00 pm
content: I don't see that anyone has mentioned the problem of damage caused when a battery goes flat,As the voltage falls to somewhere around 10 volts, different chemical reactions kick in which are not reversible. So, every time battery gets really flattened, some of it "dies", and if this happens a few times, you end up with a battery that is increasingly useless, and won't accept much charge.I'm not doing much driving either, and I constructed two small, cheap modules which sit connected to the batteries and let out a screeching sound when V falls <~11V, and then I'm out with my old fashioned transformer-based homebrew charger which may well put in 20-30 amp-hours and cuts off at ~14.8V.

author: ttx450
author_rank: Regular Contributor
timestamp: December 28, 2020, 09:56:05 pm
content: Quote from: StuartA on December 28, 2020, 09:46:00 pmyou are talking sulfated battery? if you keep it charged, it should not go there..edit- actually a slow charge can sometimes bring back sulfated batteries..I do this on reg slow charger.. not maintenance

author: StuartA
author_rank: Regular Contributor
timestamp: December 29, 2020, 12:48:51 am
content: The OP is talking about dead batteries, so I assume he's referring to batteries that have slowly drained (most central locking and security systems will do that) and slowly but surely they will head toward zero volts, but even at ~10V the damage starts. If it's already a battery that's been in use for some years, it can be the "straw on the camel's back".RE sulfation, have you ever tried one of the pulsation units which put 16V spikes (microsecond duration) on the battery; I do believe that they work, at least to some degree, as sulfation is just one of the failure modes of batteries..Re any kind of charger, I wouldn't touch any charger that doesn't tell you what the volts and amps it's providing are, and a has atransformer, which is to say that I want none the stuff that'scurrentlyon the market for domestic use.Bigmeters, or LED digital displays... must have them

author: SilverSolder
author_rank: Super Contributor
timestamp: December 29, 2020, 07:22:31 pm
content: Quote from: jrmymllr on December 28, 2020, 01:07:13 amI have a couple of the cheapy HF float chargers - they work well. You couldn't even buy the parts to make one for what they sell for... If you build one, it would have to be for hobby reasons, which is of course a perfectly valid reason to do it!

author: ttx450
author_rank: Regular Contributor
timestamp: December 30, 2020, 12:28:26 am
content: Quote from: StuartA on December 29, 2020, 12:48:51 amdone a ton of work on fleet & non-commercial batteries.. Last ditch effort includes much more then 16v and a few amps...again if I am cheap..when batteries are that far off, I would only screw around with it, if I was board, curious, or no $ I have a 600 amp carbon pile resistor to check... not much resurrection after that.

author: jrmymllr
author_rank: Regular Contributor
timestamp: December 30, 2020, 03:07:00 am
content: Quote from: SilverSolder on December 29, 2020, 07:22:31 pmI've seen a few people complain the HF charger went bad and discharged their battery. Not here, but some other forum I believe.Anyway, I found that a reputable company, Schumacher, has these maintenance chargers that seem to be really good...and they are closing them out for $15 directly on the Schumacher website. And so I started thinking about it....I like designing electronics but right now I'm feeling lazy (or too much other stuff to do) and buying a couple of these instead sounds really good right now.

author: SilverSolder
author_rank: Super Contributor
timestamp: December 30, 2020, 03:44:24 am
content: Quote from: jrmymllr on December 30, 2020, 03:07:00 amThere are only so many hours in a day... and so many days in a week. Better to build stuff that can't easily be bought!

author: floobydust
author_rank: Super Contributor
timestamp: December 30, 2020, 05:54:28 am
content: Aside from HF which I can't buy in Canada, it's just scams in the store bought chargers.Schumacher Electric look terrible, misleading specs and price gouging:SC1339$98.99 "Steel Case 10A" look in the manual and "12VDC, 2A Continuous, 10A Intermittent. 55 Seconds Maximum On, 120 Seconds Minimum Off". So it's basically a ripoff 2A charger."This Charger/Engine Starter meets the highest industry standards."Oh wow I can start my car with it? "Engine Starter" ?These are some reasons I'll mod an old charger or build a new one with quality parts from the junkbox. Overhyped chinese products being sold by an American since 1947 company, with such a bad product lineup and fake marketing, yuck why bother.edit: teardown/repair vids are hilariousCapXon, SAMXON forever lolCTEK MXS5.0 Battery Charger Dead - Detailed Fault Diagnosis and Component Level RepairHe says "what a cheap and nasty design" lol. I agree. Interesting troubleshooting the SMPS, worth the watch.

author: jrmymllr
author_rank: Regular Contributor
timestamp: December 30, 2020, 01:53:04 pm
content: Quote from: floobydust on December 30, 2020, 05:54:28 amSchumacher is the best bang for the buck I can get and makes some attempt at quality vs. the HF unit. I think every company misleads with their specifications, but probably all of us on this forum can read the fine print and understand the limitations.As for the crappy caps, yeah, what has Nichicon or Panasonic caps anymore? Sure some high end stuff I suppose. Caps are easy to replace.

author: SilverSolder
author_rank: Super Contributor
timestamp: December 30, 2020, 06:41:33 pm
content: The HF unit is actually not bad for the money, you probably can't even buy the battery clamps for what the unit costs. I paid less than $5 each for my two units on sale with coupons etc., but it was maybe 8 years ago (remember, when you look at today's price, there is no inflation, they tell us!) and they still work fine.Here's someone that took the trouble to trace the circuit diagram:The circuitry is linear and simple. (I don't know what's inside the wall wart...)\[Edit:] The wall warts are heavy, so likely regular transformers (not switch mode).The output voltage of both my chargers measured at 13.07V which pretty much corresponds to a 100% charged lead acid battery. Source:https://batteryuniversity.com/learn/article/how_to_measure_state_of_chargeI think pushing the voltage to 13.6 like the guy in the video is doing, is a mistake... he is looking at a different page on Battery University that shows 13.6V is the theoretical absolute max for a brand new battery in perfect condition. As the battery ages, it means some cells will get pushed too hard, since the cells are all in series and there is no way to balance them (they always age unevenly). The risk of damaging the battery is not worth the extra charge by pushing the voltage... just get a bigger battery!Bottom line, these float chargers are surprisingly well made for the $6 they currently cost:https://www.harborfreight.com/automatic-battery-float-charger-64284.htmland have worked well for me (storing "summer" cars over winter).

author: ttx450
author_rank: Regular Contributor
timestamp: December 31, 2020, 12:38:11 am
content: Quote from: SilverSolder on December 29, 2020, 07:22:31 pmI never looked close , but looked to be good working maintenance units for hf.. HF, you never know.. some times good, sometimes junk. no coin toss emio

author: ttx450
author_rank: Regular Contributor
timestamp: December 31, 2020, 01:40:36 am
content: did not listen through.. board.everything was 13.8v for a billions yrs.. have not been up to date, but dont thk were going bk on voltage?

author: deadlylover
author_rank: Frequent Contributor
timestamp: December 31, 2020, 01:53:09 am
content: I use a Victron blue smart IP67 charger, I can't tear it down because it's all potted and stuff but from the teardowns from their other (albeit more expensive) products it shouldn't be total junk inside.It was only very slightly more expensive than a Ctek here in Australia which is what nearly everyone uses, but I wanted the control of the Victron instead.Bluetooth is a godsend, no more having to whip out your clamp meter to check the charge rates. You can also control the charge voltage of the absorption, float and storage modes (even the temperature coefficient as well). The power supply mode is handy for testing/troubleshooting all the various little motors in a car. (my wimpy bench supplies max out at a couple of amps tops, the charger is good for 17A which is more than enough for window actuators and most fuel pumps)

author: bdunham7
author_rank: Super Contributor
timestamp: December 31, 2020, 02:11:51 am
content: Quote from: SilverSolder on December 30, 2020, 06:41:33 pmHow are you measuring that? You need to consider the peak voltage, not the average or even rectified RMS, because as long as there is a rectifier so that the battery cannot discharge into the charger, the battery will be receive some charge as long as its voltage is below the peak of the charger.QuoteThere is a way to balance them, it is called equalization. Also known as 'a good boil'. As I explained above, the calcium chemistry of a modern car (starting) battery can withstand a substantial continuous charge current. The voltage measurement to determine the state of charge is entirely different than the optimum or maximum charging voltage. If you test a fully charged battery of this type properly, by putting a small load on it for a few minutes and letting it rest for a few more before measuring, you will almost always get less than 13.6 volts. However, if you use 13.6 volts DC as your charging voltage, you will never, ever fully charge it.

author: SilverSolder
author_rank: Super Contributor
timestamp: December 31, 2020, 04:14:38 am
content: Quote from: bdunham7 on December 31, 2020, 02:11:51 amA float charger is just supposed to provide a constant voltage to keep the battery full, it isn't meant to be a complete battery charger.The circuit of the HF float charger has a linear voltage regulator IC so its output voltage is constant and smooth - there are no "peaks" or "valleys" and there aren't supposed to be any on a float charger.

author: lucatz
author_rank: Contributor
timestamp: December 31, 2020, 01:38:50 pm
content: Amazon.comSchumacher SC1279 8A 12V Rapid ChargerOn Special its 39CAD not sure in USLuca

author: Renate
author_rank: Super Contributor
timestamp: December 31, 2020, 03:17:13 pm
content: I haven't seen anyone mention this yet...Wait for garbage day and snag an ATX power supply off the street (or maybe you have an old one already?)They need a jumper to run.They usually resistor mix the 12 V and the 5 V as feedback to the voltage controller.Pull the 5 V resistor, then you'll probably need to cut the 12 V resistor somewhat in half and have some trimmer range.You should be able to adjust for 13.6 V.I used to have a Peltier style camping cooler that I used as my main fridge that ran off this.

author: IDEngineer
author_rank: Super Contributor
timestamp: December 31, 2020, 04:38:22 pm
content: FYI, Costco has been carrying the larger sized Battery Tender brand units lately for $40.Speaking of automotive quiescent current, my Lotus came with a Lotus logoed Battery Tender unit for that exact reason. Without it the battery will drain in about 3-4 weeks to the point that it won't start the engine.

author: SilverSolder
author_rank: Super Contributor
timestamp: December 31, 2020, 06:01:12 pm
content: I have no less than 4 different batteries that need a float charger. Hence my appreciation for low cost devices!

author: floobydust
author_rank: Super Contributor
timestamp: December 31, 2020, 07:52:29 pm
content: Car battery chargers have become a walk into the "Too Cheap Casino". Contract made in china to a very low price point I guess. They are all marketing, totally overboard - fake specs, they don't put out advertised current, firmware bugs, 4 step no 6 step no 8 step! "Repairs, reconditions"Jay Leno gets some free and then promotes the CTEK maintainers OEM use by McLaren, Corvette, Mercedes Benz, BMW, Acura - it should be king of the hill, but inside it's a crappy cheap build, Amazon CAD $121 for the MXS 5.0 good for 4A with cheap capacitors and no ventilation holes. But it's Swedish design right?If I'm paying $100 or more I expect it to last more than a couple years and work in cold weather, and have firmware that works - people are having to reboot their chargers, the Schumacher XCS15 on youtube is scary. I wonder if that (unknown yellow charger) crashed and caused thebattery explosionThe Harbour Freight/Centech battery maintainer/float charger $5.99 with wall wart wow (you could get any one of four versions) has a good idea using a BJT for reverse-polarity protection, much better than an output diode. But a 7805 jacked up to 13.6V? BAD. Lots of reported under/overcharging issues.Battery Tender/Deltran - capacitors are failing so they aren't any better.

author: lucatz
author_rank: Contributor
timestamp: December 31, 2020, 08:29:23 pm
content: Maybe we design one with LTC1325...I'm still poking at it for NIMH but it can also do Lead Acid

author: SilverSolder
author_rank: Super Contributor
timestamp: January 01, 2021, 12:48:58 am
content: Quote from: floobydust on December 31, 2020, 07:52:29 pmAccording to Battery University, a lead acid float charge is simply a constant voltage - the Harbour Freight/Centech battery maintainer is all you need. Looking at the circuit, it seems hard to improve significantly without adding unnecessary complexity.The only way the HF circuit can over- or undercharge is if the voltage is wrong... too high, or too low. I measured my two units, they were both 13.07V.I am buying two more in the weekend, since there is a 25% off coupon for Harbor Freight for 3 days. That means they will only cost $4.50 which is really, really hard to argue with!Modifying them to give 13.6V is definitely a terrible idea. Especially if you live in a warm part of the world! The absolute max is 13.2V - any more than that, and the voltage should be reduced, not increased!

author: floobydust
author_rank: Super Contributor
timestamp: January 01, 2021, 02:49:30 am
content: Float voltage at 25°C typically is given as 13.5-13.8V (2.25-2.35V/cell). Your float voltage spec could be wrong. Battery University also has several numbers incorrect.There are many different types of lead-acid batteries under mainstream use in cars - lead calcium, lead antimony, AGM, gel. Carbon, selenium are also newer tech.PbCa is given as 13.02V-13.80V (2.17-2.30V/cell). Then there is a temperature correction factor, usually –3.3mV/°C for gel, AGM and -5 to -6.3mV/°C (Exide) for flooded types. Voltage on the lower end is better for really long-term float charging for less water loss. I would always check the manufacturer's specs though.The Harbour Freight float charger needs precise voltage and an LM317+heatsink and power transformer is likely what the original design started with. Now, the 15V SMPS wall-wart isn't enough with losses in a linear regulator. I wonder if they have any output current at 13.02V ?

author: SilverSolder
author_rank: Super Contributor
timestamp: January 01, 2021, 03:24:46 am
content: My understanding is pretty much all batteries are PbCa these days?I haven't looked sufficiently deeply into the Harbor Freight circuit, but there has to be means to limit the current to what the wall wart is capable of (400mA) otherwise things could become problematic! Perhaps the current output of the wall wart itself is limited. I'll try a couple of measurements tomorrow, head permitting!

author: SilverSolder
author_rank: Super Contributor
timestamp: January 01, 2021, 08:37:55 pm
content: A few minutes of quality time with an ammeter this afternoon showed that the HF charger is a 500mA constant current charger below 13.07V (including short circuit), and becomes a constant voltage source at 13.07V - which is pretty much as it should be!I note that HF has now increased the price to $10. Maybe they are reading this blog?

author: cdev
author_rank: Super Contributor
timestamp: January 01, 2021, 08:57:53 pm
content: Quote from: SilverSolder on January 01, 2021, 08:37:55 pmI have one and I found that it produces enough RFI to warrant two huge ferrite beads and lots of turns through them to be suitable for use here.

author: IDEngineer
author_rank: Super Contributor
timestamp: January 01, 2021, 09:05:12 pm
content: I once found myself on a business trip needing to do some unexpected development work in my hotel room. I had all the tools except a 12VDC power supply. So I found the local Harbor Freight, bought one of their battery chargers, and modified it to run as a steady state supply. Worked fine, though as already noted it was really trashy power. Our products tolerate automotive electrical systems so no problem! Got the work done, presented it to the customer the next morning, and closed the deal.Since then I've boxed up one of those little switchers that have an LCD and can configure voltage, current, etc. I run it off a leftover 19V 4A laptop supply. It's my "power supply in a ziploc bag", weighs little, and consumes very little space. But I'll always be thankful to HF for saving that business trip!

author: SilverSolder
author_rank: Super Contributor
timestamp: January 01, 2021, 09:27:26 pm
content: Quote from: cdev on January 01, 2021, 08:57:53 pmDo you have the newer model? The old one is not switch mode. I don't know about the new one, but I noticed the new wall wart outputs DC, whereas the old one was AC....

author: MIS42N
author_rank: Frequent Contributor
timestamp: January 01, 2021, 09:59:42 pm
content: I have many 12V batteries on a float charge of 13.8V, some for years. As long as they are given a quick hit with 14.4V a couple of times a year they are good. As far as I am aware, at 13.8V modern batteries recombine the outgassing because none of them say they have lost electrolyte (they are sealed so I'm not opening them up to find out). I'm relying on the little plastic window that shows green and green if the battery is charged and has electrolyte.I found a 'float' voltage of 13.2V is too low and the battery will deteriorate more quickly.I test them before hitting them with the 14.4V using a simple battery tester that draws about 50A and note the voltage drop. This gives a good indication of how the battery is going. Another test of a battery is to take it off charge and leave it for 48 hours. A good battery will show above 12.6V and then survive the 50A test.Temperature where the batteries are kept is very variable, sometimes up to 40°C at times. This doesn't seem to have caused any problems.I read all the literature and there is so much conflicting advice I just stick with what works for me.

author: SilverSolder
author_rank: Super Contributor
timestamp: January 01, 2021, 11:46:44 pm
content: Quote from: MIS42N on January 01, 2021, 09:59:42 pmThere is a Wikipedia article on float voltage:https://en.wikipedia.org/wiki/Float_voltageLooks like temperature compensation may be important, which the simple Harbor Freight item does not do. It seems to be set up to not damage batteries in hot environments, which may be sub-optimal in cold climates.Either way, having a float charger is still much better than not having one - cars constantly drain their batteries these days, with various computers, alarms, etc., all leeching power constantly...

author: ttx450
author_rank: Regular Contributor
timestamp: January 02, 2021, 03:10:07 am
content: dead batteries.. good luck with that. if a individual "cell" goes below 1.2v u have more problems. . after that you get questionable cells and maybe

author: SilverSolder
author_rank: Super Contributor
timestamp: January 02, 2021, 03:48:52 pm
content: Yep, no float charger will help if the battery is already dead, or has one or more weak cells!A float charger is preventative maintenance: it stops a good battery from going bad due to becoming discharged from lack of use (and "phantom power drains" in a car, such as alarms etc.), basically.

author: ttx450
author_rank: Regular Contributor
timestamp: January 05, 2021, 12:22:45 am
content: Quote from: StuartA on December 29, 2020, 12:48:51 amif truly dead.. you might want to freshin up the bath of acid, if open cell.. u can test.. I just refresh.. will burn hole through u. be careful.if- was reversed (around <1.2v).. best hope to very slow charge afterwards.. if that dos not work.. sell for lead

author: gold oxide
author_rank: Newbie
timestamp: June 13, 2022, 10:42:15 pm
content: Quote from: deadlylover on December 31, 2020, 01:53:09 amThey do sell an IP65 version in Europe that is not potted (it's not cheap either). Just got the 12V/15A unit and it works fine so far. The bluetooth logging is a handy feature.Says "Made in India" on the bottom and screws open without trouble (Ctek 5A are glued these days, 10A aren't yet). No big surprises inside. Build quality looks ok. Their Silastic guy could work on his aim a bit but no big deal.However I have to give it a rebuke for running one of the AC input wires over the edge of an aluminium heatsink. If that ever rubbed through the isolation, interesting things were bound to happen (as a quick fix I just moved the cable tie so it's sitting againt the edge now). That's something QA should catch in my opinion.Caps are Sancon, from what i could find that's one of the better chinese brands. The BT module is visible near the DC output. I did not take the board out. The µC should be on the back of the PCB.

author: floobydust
author_rank: Super Contributor
timestamp: June 14, 2022, 10:29:48 pm
content: That construction looks pretty good, but a big problem is the heat can't get out? 93% at 12V/15A is 13W. I see the output filter caps 3 of 2,200uF 25V have a PC board option to use larger parts, so it has been "cost improved". I'll bet they're really hot at 15A.I have not repaired the crappy Ctek units, they use really cheap capacitors. Have to ask Jay Leno how many have croaked at his garage.

author: Monkeh
author_rank: Super Contributor
timestamp: June 14, 2022, 10:33:33 pm
content: Quote from: gold oxide on June 13, 2022, 10:42:15 pmBut they did add reinforced insulation to them! Not terribly afraid of that.

author: gold oxide
author_rank: Newbie
timestamp: June 15, 2022, 12:51:05 am
content: The trapped heat comes with the IP65 certification (resistant against dust and low pressure water ingress). The caps are 105°C rated. Victron says these chargers run at 95% efficiency producing far less heat than the competition.I've only charged one half empty car battery with it so far and it does get warm at full current. Maybe somewhat less than the 10A Ctek but much less than the 5A Ctek which gets really hot even on the outside at full load.There's an inside view of the 10A Ctek on Youtube as well. Didn't find anything on the Victron on the net so I had to take a look into mine as soon as it arrived.