How can I charge a single 4V battery?

Sun Dog
Sun Dog Solar Expert Posts: 115 ✭✭
in Off Grid Solar & Battery Systems #1
After a warranty replacement I now have an extra 1280Ah 4V battery. One cell isn't great (difficult to get it's SG above 1245) but the other cell is just fine. Anyone know of a 4V battery charger that is capable of 60A or greater............or another solution that would allow me to charge this battery?
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  • Blackcherry04
    Blackcherry04 Solar Expert Posts: 2,490 ✭✭✭
    #2
    Re: How can I charge a single 4V battery?
    Sun Dog wrote: »
    After a warranty replacement I now have an extra 1280Ah 4V battery. One cell isn't great (difficult to get it's SG above 1245) but the other cell is just fine. Anyone know of a 4V battery charger that is capable of 60A or greater............or another solution that would allow me to charge this battery?
    Piggy back it parallel with a set of jumper cables on to you bank for some short term charging. A variable output power supply would do it. I doubt you need 60 Amps though, probably get by with less.
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  • Sun Dog
    Sun Dog Solar Expert Posts: 115 ✭✭
    #3
    Re: How can I charge a single 4V battery?

    Unfortunately my inverter will not go above 32V and I need 29.8V for the bank. I also don't want to leave it permanently connected as the bad cell will drag down the whole system. I could disconnect one of the good batteries and wire in this one from time to time to keep it as a charged backup but that would be a PITA. Really hoping to use it as a standalone power source in my garage.

    I based the 60A on a 5% charge rate. Would the variable output power supply essentially act like an automotive battery charger?
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  • Blackcherry04
    Blackcherry04 Solar Expert Posts: 2,490 ✭✭✭
    #4
    Re: How can I charge a single 4V battery?
    Sun Dog wrote: »
    Unfortunately my inverter will not go above 32V and I need 29.8V for the bank. I also don't want to leave it permanently connected as the bad cell will drag down the whole system. I could disconnect one of the good batteries and wire in this one from time to time to keep it as a charged backup but that would be a PITA. Really hoping to use it as a standalone power source in my garage.

    I based the 60A on a 5% charge rate. Would the variable output power supply essentially act like an automotive battery charger?
    Dragging your bank is not a good Idea, That was just to give you something to get you by short term and not let it go dead. A power supply would not have the control of a battery charger for anything long term.

    You might be able to find a 12 v charge controller you could turn down low enough to charge it. I don't know if something like a Xantrex c-35 will go that low. The idea there is to power the controller with a power supply, 60 amps is the problem.
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  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    #5
    Re: How can I charge a single 4V battery?

    6 Volt automotive charger and keep a close eye on it.
    The higher Voltage potential will cause the output current to exceed the rated amount, and there should be a thermal cut-out which will protect things (you'd hear it click off/on as the current heats things up). If needs be, putting a resistor in series to lessen the current will help (make sure it's beefy enough to take the Amps - try automotive light bulb).

    Not perfect, but then nothing would be without spending a whole lot of money.
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  • Sun Dog
    Sun Dog Solar Expert Posts: 115 ✭✭
    #6
    Re: How can I charge a single 4V battery?

    Marc, I had thought about buying a 2V cell and then using a 6V automotive charger but as you say that all increases costs. What about using a single output switching power supply? I found a 5V @ 60A for $50. It's voltage output can be adjusted from 4.5V to 5.6V but I don't know how it would function as a charger. Would it be a really bad idea or just sort of bad? :roll:
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  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    #7
    Re: How can I charge a single 4V battery?

    I'd say only sort of bad. The problem is the same all around; lack of accurate (or any) regulation of the charging for the specific Voltage. No matter what you rig up you're going to have to watch it or put in some additional Voltage controlled switch to shut it down, et cetera (which is Latin for "this is going to cost more money").
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  • BB.
    BB. Super Moderators, Administrators Posts: 33,613 admin
    #8
    Re: How can I charge a single 4V battery?

    Oh boy--There are so many options for power supplies out there... The really old fashion type of charge controllers (used rectifier tubes) were current limited chargers and you could put something like 1-10 or more 6 volt batteries in series (one I read even had a probe that you put in the electrolyte so monitor SOC/voltage).

    Current mode power supplies are not difficult to do in modern electronic power supplies--But the "safety" systems they use can be dangerous to use with battery bank charging. A common protection system is a "crowbar" where the power supply output is shorted if the voltage goes too high. Very nice to save your computer electronics--Not so good when the load is a big battery bank (crowbar on battery--nothing good will happen here).

    I can think of various ways of making a current limited battery charger--But nothing off the self that would be safe to use or very energy efficient off hand for "non-standard" cells.

    I wonder if your battery dealer is close enough and can try charging your cell for you...

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
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  • Sun Dog
    Sun Dog Solar Expert Posts: 115 ✭✭
    #9
    Re: How can I charge a single 4V battery?

    So far from perfect but workable. Once charged, how would I get the power back out of it? Is there such a thing a as a 4VDC to 120VAC inverter or would I first need to somehow boost the voltage up to 12VDC or ???
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  • BB.
    BB. Super Moderators, Administrators Posts: 33,613 admin
    #10
    Re: How can I charge a single 4V battery?

    More or less--It it will be useless unless you can find a specific usage for it. It would be your "hot spare" in case something else happens.

    Yes, you can get a boost converter and get 12 volts or some other voltage--But then you are back to needing a 4 volt battery charger. Vicious cycle.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
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  • Sun Dog
    Sun Dog Solar Expert Posts: 115 ✭✭
    #11
    Re: How can I charge a single 4V battery?

    Bill, help from the battery dealer unfortunately isn't an option. At first Surrette was just going to send me a replacement cell but fortunately they changed their minds and sent me a whole new battery. Changing the cells would have been tough! Basically I'm just trying to find a way (a safe way) to use this "free" battery as just sending it off to be recycled seems like such a waste as it is only 2 years old and has one perfectly good cell and one marginal cell.
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  • Sun Dog
    Sun Dog Solar Expert Posts: 115 ✭✭
    #12
    Re: How can I charge a single 4V battery?

    Any chance you have a link to one of those boost converters? I have looked but couldn't find something appropriate.
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  • BB.
    BB. Super Moderators, Administrators Posts: 33,613 admin
    #13
    Re: How can I charge a single 4V battery?

    I just cannot think of a way... Think of the good cell as being a 100 AH 12 volt battery... It is not that much energy storage and of questionable value to store for a number of years (and keep charged) just in case something goes wrong. Add the costs to keep it charged for an off grid system. Nope, cannot think of anything useful.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
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  • BB.
    BB. Super Moderators, Administrators Posts: 33,613 admin
    #14
    Re: How can I charge a single 4V battery?

    You would have to design a boost converter--And it would still be a low current device unless you design large FETs and Heat Sinks to deal with the large currents. Low input voltage and high current... There is nothing off the shelf I can think of.

    If you can find somebody in the region that would give you core charge type money and haul it away to replace a bad cell in their bank would be the best use I can think of.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
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  • Sun Dog
    Sun Dog Solar Expert Posts: 115 ✭✭
    #15
    Re: How can I charge a single 4V battery?
    BB. wrote: »
    I just cannot think of a way... Think of the good cell as being a 100 AH 12 volt battery... It is not that much energy storage and of questionable value to store for a number of years (and keep charged) just in case something goes wrong. Add the costs to keep it charged for an off grid system. Nope, cannot think of anything useful.

    -Bill

    Agreed. It would be great to have it if that day ever came but in the mean time it would be a lot of work. Shame it can't more easily be utilized.
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  • Vic
    Vic Solar Expert Posts: 3,208 ✭✭✭✭
    #16
    Re: How can I charge a single 4V battery?

    Sun Dog,

    There are a couple of ways of looking at this. Personally, I'd look at it as you have a good 2 V cell that you are trying to keep in good health as a possible future replacement. Of course, charging a 2 V battery is a bit more difficult than charging a 4 V one.

    There have been converstations here about usind N-1 2 V cells as an intirim solution while waiting for a replacment cell/battery. Attempting to use N+1 cells in perpetuity, especially in a COLD climate (especially on a 24 V system) is probably not a good approach -- forget the high voltage max for XWs.

    Have a Home-Brewed 0-15 V charger here that uses a transformer/rectifier/capacitor bank which runs on the AC output of a Variac (a vairable autotransformer). It is quite good at what it does, but it is manually regulated for voltage or current.

    But for trying to maintain this cell in good health, it should really be cycled in the same fashion as the rest of the bank. Short of manually substituting this cell into the bank in place of others seems a bit tedious. The good cell has a value of about $US 700, plus freight, although having a spare cell that closely matches the others in the bank is interesting.

    It is possible that someone might be able to hack a PWM CC, like the MS TS-60 to make it believe that it was charging a 12 V battery, when really charging a 2 or 4 V one. Believe that this CC has remote Battery Sense terminals, although quite often these things are not just a simple hack. It would be niec if it would have its output section powered from a 4 or 5 V DC power supply ... and so on.

    I would like to have a CC that could charge 2 - 4 or 6 V batts, with high current capability, Temp Comp EQ etc, but have too little time (really too lazy) right now. Good Luck. Vic
    Off Grid - Two systems -- 4 SW+ 5548 Inverters, Surrette 4KS25 1280 AH X2@48V, 11.1 KW STC PV, 4X MidNite Classic 150 w/ WBjrs, Beta KID on S-530s, MX-60s, MN Bkrs/Boxes.  25 KVA Polyphase Kubota diesel,  Honda Eu6500isa,  Eu3000is-es, Eu2000,  Eu1000 gensets.  Thanks Wind-Sun for this great Forum.
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  • Sun Dog
    Sun Dog Solar Expert Posts: 115 ✭✭
    #17
    Re: How can I charge a single 4V battery?

    Vic,

    C'mon why don't you build a couple of those low voltage fully featured CC and sell me one. I did find this DC/DC converter to get the power out of the battery http://www.powerstream.com/dc6-12.htm While it is close, it doesn't sound like exactly what I need. Here is what the manufacturer said about it:

    I don't have a solution to your DC converter problem. At 250 watts you would be drawing over 65 amps, it means low efficiency and a lot of hot power transistors. Our unit will turn on if the battery is fully charged, and will run below 4 volts, but the output voltage will not be fully regulated. Of course many 12 volt applications don't require regulated voltage. But I wouldn't run it over 200 watts below 4.5 volts, it could overheat.

    While I was hoping for a pre-packaged solution, is either a 4VDC to 12VDC or even better a 4VDC to 120VAC transformer likely impossible to find?
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