I want a desulfator...

Discussion in 'General Electronics Chat' started by Lectraplayer, Jan 2, 2015.

  1. Lectraplayer

    Thread Starter Member

    Jan 2, 2015
    77
    5
    It's been years since I have messsed with building electronics, so since I am getting a LOT of batteries of various types, I may as well start on some chargers. One of which (this project) comes because I'm getting these regularly:

    http://www.batteriesplus.com/produc...ed-Lead-Acid-Batteries/102645-Werker/12V.aspx

    It's a 12 volt 7 amp hour SLA if you can't see it.

    Since many have been in use for years and may have seen their better days, I've been looking at desulfators to compliment my normal charger. For what I'm seeing them for, I think I can build one for pennies on the dollar.

    It sounds like I can use a RC charging circuit that charges to around 167 volts from 120 volt Alabama Power. Once the RC circuit is full, it discharges into the battery (and hopefully will be destructive to the sulfate crystals). As the RC circuit charges again, I intend to check the voltage of the battery. If it's 12.6 volts or so, I won't fire the capacitor. Total charging power in RMS should be less than 5 watts, all short high current bursts. That's the theory I'm going for...

    My first question is along these lines: I keep looking for guidelines on how much current and voltage I need, and can get away with using to desulfate, so I can size my capacitor. I know I will have to be careful not to go too much or I will be gassing my own dumb self with this one.

    I hear there's also a resonant frequency of the battery itself I need to get my pulse width longer than. Again, no info on that to be found.
     
  2. Lectraplayer

    Thread Starter Member

    Jan 2, 2015
    77
    5
    You think pulses won't even break up hardened sulfate crystals? I gathered that pulse charging is controvercial, but that's not what I'm working on here. I'm finding some science on desulfation, though no guidelines on how to apply it yet.
     
  3. MikeML

    AAC Fanatic!

    Oct 2, 2009
    5,450
    1,066
    First things first. Simply try charging them.

    1. If with ~14.4V applied, they draw > 1/2A, just leave the charger on for several hours. If the current tapers to a few 10s of mA after a couple of hours, the battery has some residual life.

    2. If with 14.4V applied, the battery draws less than 10 mA, the battery is very far gone. Try connecting a 25V power supply which has an adjustable electronic current limit set to ~250mA to the battery for a few hours. If the battery wakes up, and begins accepting charge, then go back to step 1. If after several hours the charging current is still essentially zero, then send it to the recycler; no amount of pulsing will help it.

    Everything that the so called pulsing circuits do has already been done in steps 1 and 2, above.
     
    KJ6EAD likes this.
  4. Lectraplayer

    Thread Starter Member

    Jan 2, 2015
    77
    5
    Sounds like no amount of science can change tradition... There's a lot I've seen, just on the Wikipedia article for lead acid batteries, and that's just the starting point.

    I've had batteries wake up after being on charge (14.4V @ 1.5A bulk, 13.6V trickle) for weeks, but I am going for soething a bit more battery friendly than just hooking a high DC voltage to it and having a gas well. I can't just add water to these like you can a car battery. There's enough science to (at least to me) warrant a build.
     
  5. MikeML

    AAC Fanatic!

    Oct 2, 2009
    5,450
    1,066
    If the battery is not accepting charge and essentially no current is flowing, then initially how do you suppose that the battery is outgassing? Once the battery begins accepting charge, the supply goes into current limit, dropping the output voltage to whatever the battery clamps it at, so again, all the current is going into charging and none is contributing to gassing.

    Guess what. All the pulsing circuits do is to force a momentary high voltage across the battery terminals from a pulse source that has a relatively high source impedance. If the battery is in the mode of accepting charge, then the pulse does nothing, because the battery clamps the voltage, just as in the current-limited supply above. If the battery is so badly discharged that it is not accepting any charge, then the instantaneous voltage across the battery goes much higher than the 25V I talked about in the previous post. The only difference is that a 25Vdc supply does it in a couple of hours while the stupid pulser takes days to get the battery to accept charge.

    I have built, analysed, and studied the pulsers, and I conclude that I can do anything a pulser can do using a simple lab supply in one tenth of time.
     
  6. Lectraplayer

    Thread Starter Member

    Jan 2, 2015
    77
    5
    It's a wonder MikeML hasn't wound up with pyrotechnic acid bombs. Time for some research.

    https://www.google.com/url?sa=t&sou...JAGh7XPLjjwZxLHcw&sig2=W-3PXNW3jM4nr3uOaDpiQQ
     
  7. bwilliams60

    Active Member

    Nov 18, 2012
    722
    88
    KJ6EAD likes this.
  8. ian field

    Distinguished Member

    Oct 27, 2012
    4,413
    782
    The absolute simplest way to pulse the battery as you suggest, is a capacitance discharge type with a DB3 diac as the breakdown device, the DB3 is rated 2A peak, but you can use it to fire a SCR. You need a supply somewhat more than 32V which is the typical breakover voltage of the DB3, the capacitor has to charge through a higher resistance than can maintain the diac holding current.

    There was a blog somewhere about living off grid that had an article about desulphating batteries - something about 2 or 3MHz pulses, but I never got around to trying it out.
     
  9. bertus

    Administrator

    Apr 5, 2008
    15,647
    2,346
  10. Lectraplayer

    Thread Starter Member

    Jan 2, 2015
    77
    5
    That's sorta along the lines of what I was planning Ian-Field, and 168 volts peak woulh certainly fit the bill, and then some. ...though I was thinking more of a comparator-based trigger circuit at this point. I just wish I could find specs on how much energy is really needed to bust up those sulfate crystals. That's what this circuit is for, NOT for charging (though it may accomplish charging). The 12.6 volt detection is a safety disable. Research is telling me that strong pulses (and they specify pulses) do the job, but pulses that are too long, or constant DC will cause gassing, even on a low battery. I guess since this is a new development in charging, info isn't on datasheets.

    I saw one of your posts (#2 in fact) was deleted.
     
  11. ian field

    Distinguished Member

    Oct 27, 2012
    4,413
    782
    The way I normally attack sulphated batteries wouldn't be allowed on this forum because it involves feeding mains to a bridge rectifier via a dropper capacitor.

    Frankly; If it takes that to get the battery going - its just barely good enough to get to the shop and buy a new battery.
     
  12. tcmtech

    Well-Known Member

    Nov 4, 2013
    2,034
    1,639
    I built a capacitive coupled battery charger/desulfator years ago. I gave it two settings. One is a ~2 amp trickle and the other was a ~10 amp high charge.

    It sort of worked a few times but to be honest very few batteries die from just sulfation issues. Most have lost so much plate material to physical breakdown, and there is no way to get it back, or they have physically shorted plating or physically separated connections between cells and plates that they are junk.

    From personal experience with trying to rejuvenate dead batteries I got for free I would say you have at best a 1 in 10 chance of getting one that will recover long enough to pass for functional under light loading.

    If you're looking to turn old junk batteries into good used ones you would be far ahead to simply take all your junk one to the local salvage dealer and trade them off towards any used ones you can find that can pass a basic voltage and amp load test. The salvage places tend to gets lots of batteries that come from sets where one or two out a many failed and the business that had them does not swap out bad ones for good ones individually but rather swaps the whole set out.

    Thats what the company I work for does with our fleet equipment. One battery in a truck that has four goes bad and all four get switched out for new so whom ever goes to the recycler where our batteries go would have a great source for really cheap good used heavy batteries! Personally I have a few big old tractor batteries that are junk and one of these days they are going to find their way into work and get traded out with some good used ones that came off one of pieces of equipment.

    Thats the best way to turn desulfated batteries into good reliable used ones. ;)
     
    strantor likes this.
  13. ronv

    AAC Fanatic!

    Nov 12, 2008
    3,282
    1,236
    Sounds like you want to build one. :)
    I would keep the voltage under 48 volts (safer).
    How do you plan on monitoring the voltage in between pulses?
    I wouldn't worry about the resonant frequency stuff. It's really the inductance in the leads those people are measuring.
    So maybe just a 24 volt transformer that would charge a cap to 34 volts, then discharge it into the battery.
     
  14. ian field

    Distinguished Member

    Oct 27, 2012
    4,413
    782
    My method puts very nearly the mains voltage across a badly sulphated battery - there is often a bit of internal arcing, so its just as well charging (gassing) is a long way off starting.

    It really is a desperate bodge to get as far as the shop to buy a new battery.
     
  15. tom_s

    Member

    Jun 27, 2014
    285
    333
    12v 7.2ah batteries here $18 to $40AUD depending on where they bought.

    taking time and parts into consideration, new battery is cheaper
     
  16. CptBriGuy

    New Member

    Jun 24, 2014
    2
    0
    I have some homebrew high power lead acid battery desulfators I will send you one for the cost of shipping
     
  17. Lectraplayer

    Thread Starter Member

    Jan 2, 2015
    77
    5
    I appreciate the offer CptBriGuy, but what's the fun in that? ;)
     
  18. ozarkshermit

    New Member

    Feb 7, 2009
    7
    1
  19. Dodgydave

    Distinguished Member

    Jun 22, 2012
    4,978
    744
  20. Ancel UnfetteredOne

    Member

    Jul 3, 2015
    36
    14
    That statement doesn't tell the whole story.
    While it is true that pulsers are just slow equalizers in MOST cases there are certain pulsers that do MORE than a lab supply can.

    One task that a low impedance pulser can execute that a lab supply cannot is: dedendriting AND stress testing of the battery interconnects & grid for conductive integrity.
     
Loading...