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Using a 240-12v brick as a full time battery charger

Discussion in 'Electronics & Electrics' started by Ratzz, May 12, 2021.

  1. Ratzz

    Ratzz Member

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    I want to run a few small devices from a small 12v SLA or LiPo battery. Battery will be at minimum 12v 6Ah (deep cycle of course), probably more like 10Ah if I go with my usual overkill MO. Doubling the capacity is nothing like doubling the cost, so the larger capacity is the most likely, even though I doubt this would be necessary unless I choose to use it as a full system UPS.

    I'll be using THIS 3A buck converter to provide 2 devices with 5v, totalling less than 1A max. This battery will be essentially a poor mans UPS. I may choose to use it on some other things too, including perhaps a USB fast (charge only) hub. I may buy a second buck converter specifically for the hub, should I even choose to run a hub, given the 3A limit of this one. Unlikely though, the only thing I would ever be likely to want the charge hub for is a couple of phones.

    I did consider just buying a 6v battery, but prices are similar to 12v and I've already ordered the buck converter so I figure why not? I may wish to also use a small 12v device occasionally, I can't even say what device that may be, let alone what it's power draw may be, I'm simply trying to leave myself the option.

    This may perhaps be the ability to use it as an actual UPS and providing 12v to the PC for a very short period, to allow proper shut down or avoid brown outs, I really haven't thought that through much as yet.

    This will be an internal component within my custom case, and will be mostly tasked to running battery backup to a couple of small displays and an LED clock, and potentially a RaspPI, Arduino, etc.

    So here's the question.

    There will exist within said case multiple household 240v switched sockets, from which I could run a 'proper' automotive style 240v-12v charger . I'm not sure as to the suitability of running such a charger in this way full time though.

    Although the mains power will occasionally be off, I'd guess that at least 95% or more of the time the power will be on and hence the battery charger constantly providing power to the battery (and hence any attached devices), and capable of providing much more than the actual current being used by devices.
    Although - the time the battery backup is needed may increase when I stop whining to my resident power Nazi that she has killed my 'always on' devices by turning stuff off at the wall at bedtime :lol:.

    To this end, I assume the trickle function of an automotive charger would be a good idea? Better than full power from say the PSU whenever it's on? Or am I incorrect? My assumption is that given batteries and devices only pull as much power as required, it shouldn't 'overfill' the battery at all or create any hazards?

    I also have already lying around a 240v-12v3A power brick from an old laptop. Since this will easily cope with any devices I am currently planning on using, and I have 240v available within the case, this would be perfect (and free !!) if I can simply connect the output wires directly to the battery, along with the device supply wires.

    Or would it be totally safe to maintain charge on said 12v6Ah battery via a 12v output from my HX1000 PSU, complete with any devices attached to the battery? Is there an intermediary circuit I should include for safety if this is a viable option?
     
    Last edited: May 13, 2021
  2. HSV_Enigma

    HSV_Enigma Member

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    As long as you get a good quality charger I cannot see the issue with it, depending on the battery chemistry you may want to cycle the battery occasionaly or get a 'smart' charger that automatically conditions it for a better lifespan. I do something very similar with a solar setup powering 24v worth of batteries which is stepped down to 5/12/etc. volts using the same style buck converters you linked, these power Rpis, arduinos, routers etc. Just make sure you stay well under 3 amps, I found they are better with around 1amp draw at any output voltage and don't forget to fuse things individually.

    A computer power supply will only ever supply 12v, this will not charge a battery and will just get flatter and flatter until it eventually dies under load. A proper battery charger will cycle up to around 14v, this should be noted when powering any devices directly (even 12v ones).
     
    Ratzz likes this.
  3. OP
    OP
    Ratzz

    Ratzz Member

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    Cool, so I can rule out the PSU. I hadn't even thought of that. The accuracy of a good PSU is going to guarantee no more (or less) than 12v, give or take a few mv. I hadn't thought of the additional voltage a battery should hold, I should have as I have a volt meter on each of the dual batteries in my car, and they are always at 14.4v with engine running and about 13.6v with the engine off. That's a step forward, thanks.

    I might consider an extra buck converter for other devices, the 2 devices I am currently most interested in total well under 1A, so they'll be OK with the one.
    I'm big on fuses, I tend to fuse all da fings if I can, so that was a given. Thanks for the reinforcement though.

    I also want to include a dedicated USB charge hub. I have a 4 port x 2.1A on hanging around which runs on a 5v5A wall wart to provide a total of 5A to divide among the ports. I can't see me needing all 4 ports at full strength at any time, so a 5A buck converter, or probably even 3A such as the one I already have coming, should suffice for that - replacing the 240v supply for the 12v battery supply.

    To be more specific, the main device is a simple USB powered LED clock. It has facility for battery backup, but only for timekeeping. I want the display to run as well, I like having the easily seen and read clock at night, and don't want it to lose the display in a power outage or a power Nazi strike.

    I'm currently using a pass-through power bank, which works fine for maybe 12hrs or so, but I also want to run a graphics thingy on my 7" LCD backlit display, which will probably be too much for the pass through power bank, and as it happens I have a use for that power bank so it will save me buying another.

    The 7" display normally will show PC stats like temps, OC stats, etc, but when the system is off I want to have it revert to running an animation/video, like maybe a rat on a spinning wheel :lol:. Hardly an important thing as such, but all part of personalisation which is the whole point of building my own case. Just before anyone jumps in, I'm aware that I'm planning on spending money on useless shit, but most of anything that personalises possessions is basically useless shit... :D. I'm happy to hear other solutions for the same 'problems' though :lol:.

    To run that animation with the power off, at the wall or even when the computer is still simply turned off, I will need some kind of RaspPi, Arduino etc and some brushing up on my limited coding skills. PHP, C++ or Perl is all I have any real (and very limited) understanding off, so I'll have to decide on something using one of those, with a small video stored on the OS microSD card, unless I can find a tailor made script somewhere, which seems a little unlikely.

    The battery is most likely going to be a 12v10Ah Deep Cycle battery, it seems to be the sweet spot in terms of capacity, physical size, and cost. I could save 30 bucks or more by going with SLA but this 10Ah LiPo is appealing at @ $80 shipped.

    So now the options are:
    • A traditional car battery charger (presumably one with a trickle charge function)
    • My 12v 3A Laptop charger
    • Or other suggestions?
     
    Last edited: May 12, 2021
  4. OP
    OP
    Ratzz

    Ratzz Member

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    I settled on THIS BATTERY for now. If it isn't suitable or my plans change, as they often do, at least I won't have invested much, a mere 31 bucks. The dimensions suit the case well too.
     
  5. paulvk

    paulvk Member

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    Get one of these and a bridge rectifier ( cheap and will isolate battery from power supply)
    https://www.ebay.com.au/itm/273214232626?hash=item3f9cd65832:g:imQAAOSwwcda-T5T&frcectupt=true
    Put the output of the supply on the AC pins and you put the battery on the plus and minus out
    adjust the supply voltage so you get 13.8 volts on the output of the bridge
    in series with the out from the bridge to the battery put 20 watt car globe to limit the current if the battery gets discharge deeply.
     
  6. OP
    OP
    Ratzz

    Ratzz Member

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    I have one of those PSU's, but a 24v version, sitting in the shed. I was going to use it to run my case speaker amp, but the consensus seemed to be that it would at best not be very good, and at worst downright dangerous.
     
    Last edited: May 19, 2021
  7. xc351

    xc351 Member

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    That battery is pretty small id be looking at the noco genius chargers as they can do lithium also ctek also worth looking into but not much lithium wise. Size wise id go prolly 2A you can then use it on a car battery (would take a long time) Ive used my ctek .8A to keep my n70 Landcruiser battery healthy & toped up as it only rarely used for a clay target thrower.

    Some bigger chargers 5A+ will have a repair function does it do much no ive used them many times to try to recover battery's from work vehicles ( a work truck generally has 4 x 12v n70 batterys) and its not uncommon for some muppet to leave something on and drain a new set of batts. But i have zero luck generally.

    What are you actually trying to power? you may just be better of buying a 30000mA USB battery bank or a jump start back if you really need 12v
     
  8. OP
    OP
    Ratzz

    Ratzz Member

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    Powering anything that normally runs off 5v or 12v, with the exception of the actual PC and monitor. It's all pretty much overkill, and only doing it because Eva is a power Nazi and loves to turn shit off at the wall.

    I have already been using a 40000 mAh passthrough power bank for the clock, this is just an expansion of that concept. The new battery is 12v 12Ah SLA, and the charger is 8A with repair function etc.
     
  9. xc351

    xc351 Member

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    That charger looks pretty adverage so just keep an eye on it. Also look at max charge currents that 8A may be pushing it.

    I generally go for 10% charge rates eg 1.2A in your case. You are pushing 66% equilvlent of putting 80A through a cruiser sized N70 deep cycle.

    But having said that seems like this is a more for fun thing rather than keeping your life support system on.
     
  10. OP
    OP
    Ratzz

    Ratzz Member

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    Yeah, I am installing a voltage/amp LED display on the front of the case so I can see if it goes berserk, can't do much more than that. A more expensive charger would have taken too much space in the case apart from the additional cost. None of it is really necessary, I have been using a passthrough 40000mAh power bank for backup power to the LED display for the clock for ages with no probs, its really just boredom and the desire to do something different that makes me do this shit. I want to run more than just the clock on backup power, hardly necessary, just something to do I guess.

    Once I get it all hooked up I'll see what it does, but I'd be stunned if it actually pushes out 8A as claimed anyway. Since it is supposed to be a 'smart' charger it shouldn't really ever be running much more than a trickle anyway, so if it jumps straight into 8A to begin with and doesn't slow down as it should, at least I'll know I guess.

    The reason for getting the 8A version in the first place was for the 'smart' functions which should (allegedly) prevent overcurrent and overcharging etc.

    Not fussed about a fire hazard or anything, everything I'm sticking into it has ADR stickers so if it all goes pear shaped insurance will take care of it. I'd actually come out well in front if the place was to burn down :lol:.

    The car has an N70 sized deep cycle in it, dual batteries in a Kia :lol: with a 120A alternator, but that literally does run my life support when travelling...

    The charger actually arrived today, I will probably do a dry run with a few devices attached for a week or so, it will be some time until the case is ready to populate anyway.
     
    Last edited: May 19, 2021
  11. juzz86

    juzz86 Member

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    I did this on a charger mate (3 x 8AH batteries in parallel in a fireproof bag) and had issues - definitely the charger, which was a NoCo coincidentally. My no-name thing from eBay charged them as expected but was too noisy.

    I switched to a 30W solar panel and 10A charge controller like this kit - cheap stuff, but working well so far for 12 months - great for camping lights and both the solar panel and charge controller have two USB ports each for phones and low-current stuff. The camp lights will go all night on the batteries for the kids, and despite being worth about ten bucks the little controller stops the load on the batteries at 12V and tops the battery out at 14.2V, as it should. Even works in Tassie :p

    For higher-current stuff, I have a 90AH battery on a 100W panel with a more expensive 20A controller. Heavy, but works well - it's serving as UPS for my security cameras and DVR at the moment. The battery was an old pull from my ute - the no-name charger restored it from buggered with a maintenance cycle and it's been good for at least an overnight run of about 4A ever since. I wouldn't be putting it back in the car, but it does what I need it to.

    If you can be bothered with a panel somewhere and a pair of leads, well worth the time and money to set up. Next step is an inverter for 240V, but I'll step the battery and panels up before that :thumbup:
     
  12. xc351

    xc351 Member

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    In your kia that 120A would go into running the vehicle then excess would go into battery. Over 2 battery's as well.

    I don't think it's a fire hazard, I think battery may swell and leak acid put a container under it and she will be good.

    I presume at low volts it would pump out 8A then ramp down. It prolly has a range in the manual.

    Even my 5A ctek I gotta put it on motorcycle mode.
     
  13. OP
    OP
    Ratzz

    Ratzz Member

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    A solar panel doesn't fit the whole 'self contained' ethos of an 'AIO' though mate.
    I haven't fired up the charger yet, it does have a fan, I'm hoping it's not painfully loud.
     
  14. OP
    OP
    Ratzz

    Ratzz Member

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    That's actually something I've wondered about, having not even opened the box yet. I know it has a motorcycle mode, I'm guessing that's the one I'll be using on the little 12Ah battery. I'll give the manual a thorough read later.

    EDIT: I just opened the box out of curiosity. It says that on Motorcycle mode, it maxes out at 1.5A, so that's encouraging.
     
    Last edited: May 19, 2021
  15. OP
    OP
    Ratzz

    Ratzz Member

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    A quick look... ironically the phone battery ran low and stopped recording at the end of the video, chopping me off mid sentence :lol:. The fan is audible but not terrible, and obviously the charger isn't going to be doing much work so in what will be a very well ventilated case in a temperature controlled room, I can't see that being a problem.



    and after a couple hours (no discharge happening though) it was still off. I did realise before I walked away that I had it on AGM/GEL and moved it to the next option, motorcycle, so for the couple hours I waited it was on motorcycle, not AGM/GEL as it appeared when the video shut off.

    Switching the power off, the display and choice of charging mode remain set, obviously getting power from the battery.

    Disconnecting it from the battery as well as the wall, it reset to the default car charger setting when I hooked it all up again, but I can't see the battery ever going flat so I doubt that is likely to be an issue. I'll only be operating pretty low powered devices on it, and most likely all 5v via the buck converters.

    Even when I did remove both battery cables and turn the power off, when it restarted it displayed the voltage for a second, ran the fan for a second, displayed 1A for a second, and then switched off.

    Before I install it in a case though, I'll hook the battery up to the car stereo, which should be able to run it dead flat in about half an hour, and then try and see how it behaves with it set on the fast (car) charge default setting on a battery that actually needs charging. The (12v 12Ah SLA) battery is supposed to be deep cycle too so it will be interesting to see if a total discharge causes any issues.

    So far, looks promising I think.

    Of course I'll be removing the battery clamps and replacing them with blade connectors to suit the blade tabs on the battery once I'm satisfied all is good, and I'll be running it through the fuse box as well. If it doesn't immediately kick into 8 amps when I fire it up again with a dead flat battery hooked up to it, then a 5A fuse will do nicely, otherwise I guess I'll have to go with a 7.5A or 10A fuse (on the output side).

    Given that the whole back of the PC will fold down on hinges, secured at the top with a mere pair of thumbscrews, it won't be any great problem if I need to change fuses occasionally of course, so if a 7.5A fuse is borderline I'll go with that, especially given the very rare occasions that I might happen to flatten the battery. For that matter, I could just as easily just always use a 5A fuse and just bridge the fuse box when powering up just for long enough to set the charge cycle to motorcycle before it blew the fuse I guess.

    That would only ever be possible if I went on holidays or something for a couple of weeks though I think, the only thing pulling any charge in that situation would be the displays, on the LED clock and the 7" LCD. At most the power is only likely to be off overnight on any other occasion, when Eva does the power Nazi thing and shuts the whole desk off at the wall.
     
    Last edited: May 20, 2021
    juzz86 likes this.
  16. OP
    OP
    Ratzz

    Ratzz Member

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    I left a PSU fan hooked up to the battery overnight with the charger connected but not turned on. About 18hrs, the battery had lost virtually no volts, and when I switched the charger on it went to the default car charging mode but only fed it a couple of amps. I then switched it to motorcycle mode and it instantly dropped down to 1.5A. About 2 hours later, it switched off completely, with the battery on full charge, but the PSU fan still running.

    Pleased with that, it looks like it will look after itself and the battery pretty well. Not bad for a $26 charger and a $36 sealed battery :thumbup:.

    I also remembered I have a decent quality and healthy battery sitting in the carport. A Century MF68, 660 CCA. It's been there for several months, not doing anything. It's lost a small amount of charge while it sat, it read 12.6v on my Fluke 101 multimeter.

    I connected the charger, turned it on, and it started at 4A, not 8A. I assume it starts at 4A and then adjusts the current to whatever level it deems appropriate after that.
    I watched it lower the charging load in .1A increments down to 2A, where it held steady. It does actually appear to sense battery needs accurately and behave normally. An hour later it is still feeding the battery, but it's down to 1.2A, so it's slowly going into trickle mode I assume.

    EDIT: five minutes after I typed that, it shut off. Now its switching on and off at 1.2A. The fan is audible but not terribly obtrusive, I can hear the charger cutting in and out. This behavior went on for about half an hour, then it switched itself off and stayed off. Voltage was now at 12.9.

    I'm pleased with that. All seems to work exactly as one would expect.

     
    Last edited: May 20, 2021
  17. MakerZone

    MakerZone New Member

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    I've been considering doing something similar to this as a DIY UPS for a bunch of raspberry pis and other single board computers.

    AGM or SLA are definitely the best choice AFAIK because they prefer to be kept (mostly) fully charged. Lithium batteries prefer to be kept at their nominal voltage (about half charged).

    I would think that the 2 biggest issues to avoid with something like this would be overcharging and overdischarging.
    AGM and SLA prefer (or even require) not to be discharge below 50% of their capacity (and in an ideal world not even below 70% if you want to make the battery last as long as possible). Fully discharging them is the fastest and probably the most common way to kill a battery.

    Even with a quality charger I would add voltage sensor controlled relay modules. One to cut off power below 50% capacity and maybe another to cut off power from the charger if the voltage ever gets too high (although this may not be necessary if you're using a good charger).

    Don't use a car or truck battery for a project like this. They're design to rapidly discharge power then immediately be recharged by the car/truck. Slow discharge and then not being recharged for a while AFAIK will shorten its lifespan.

    Cheers,
    John
     

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