battery life

Discussion in 'General Electronics Chat' started by bladerunner, Oct 21, 2012.

  1. bladerunner

    Thread Starter Member

    Apr 15, 2012
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    Have 12V D cell size NiCd/NiMH battery pack with a 8.5 Ah rating.

    How long will this battery pack be able to run/charge a 5V 1A system?

    I have tried all the calculations, some look good and some don't.

    Thanks for any help you may heave this way!
     
  2. bountyhunter

    Well-Known Member

    Sep 7, 2009
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    depends whether you use a linear regulator to get the 5V or switcher. If a linear, about 8.5 hours. A good switcher, maybe double that.
     
  3. bladerunner

    Thread Starter Member

    Apr 15, 2012
    83
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    thanks a bunch for the info.


    will have to study up on that.
     
  4. Audioguru

    New Member

    Dec 20, 2007
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    Who makes a Ni-Cad or Ni-MH D cell rated for a whopping 8.5Ah?

    Energizer sells a lightweight Ni-MH D cell with a little 2.5Ah AA cell inside.
    Duracell also sells a lightweight Ni-MH D cell with a little 2.2Ah AA cell inside.
     
  5. bladerunner

    Thread Starter Member

    Apr 15, 2012
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    http://www.powerstream.com/NiMHP.htm

    In theory, could you recharge another battery (3.0 to 4.5V, 900-1000 mAh) with this type setup? If so, it would not take 8 hours and you should have a reserve left for recharging later before they have to be recharged themselves.
     
    Last edited: Oct 21, 2012
  6. THE_RB

    AAC Fanatic!

    Feb 11, 2008
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    The Ah is likely specced at a lower discharge rate (often 10 or 20 hours), so 8.5Ah cell running at 1A might give you half that capacity, or only 5Ah or so.

    Also factor in that NiCd and especially NiMH lose capacity after a few uses and might be down to half capacity within a few uses, so you might only get a couple hours (if that!) at 1A from a "8.5Ah" cell once the device is in use.
     
  7. Audioguru

    New Member

    Dec 20, 2007
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    You can charge another battery very quickly if the charging battery is allowed to be charged with a high current very quickly. The mAh does not change much when the discharge current is increased. 0.85A for 10 hours, 8.5A for 1 hour or maybe 30A for 15 minutes.
     
  8. Audioguru

    New Member

    Dec 20, 2007
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    Energizer Ni-MH cells have their capacity spec'd at a 5 hour discharge rate. At a 1 hour rate it is the same. At a half hour rate the capacity is reduced to 83%.

    No.
    An Energizer Ni-MH cell gets better after 5 cycles and lasts for hundreds of cycles.
     
  9. bountyhunter

    Well-Known Member

    Sep 7, 2009
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    Radio Shack used to sell the full capacity C and D cell Ni-Cads. The C cells were 2.2 A-Hr and the D were around 5 AHr ballpark. A NI-MH version of the full D cell should be about 9 A-hr. Don't know who makes them?

    Here's a 10 A-hr D cell in NI-MH:

    http://www.amazon.com/Tenergy-Premium-4-10000mAh-Rechargeable-Batteries/dp/B00408IF1Y

    PRICEY!
     
  10. THE_RB

    AAC Fanatic!

    Feb 11, 2008
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    Thanks for the info.

    Apparently you don't have a house full of failed NiMH batteries like I do? They are garabge, and their capacity is usually way less than advertised and gets worse every time they get used. It's probably the suppliers fault as much as anything, selling batteries that have sat around for 6 or 12 months (or worse) in the "new" packets and the high self-discharge rates of NiMH.

    I have a very strong dislike of NiMH, the only reason the consumers got burdened with that garbage NiMH technology was because of that silly "let's get rid of Cadmium" mentality. Fortunately before people really worked out how bad NiMH is we've moved on to Lithium batteries.
     
  11. Bob T.

    Member

    Oct 22, 2012
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    Capacity=(mA)/(Hour)
    You have current and a apecified capacity of the batt, so you can calculate..
    Thanks
     
  12. kubeek

    AAC Fanatic!

    Sep 20, 2005
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    Definitely not. Capacity=(A)*(Hour)
    You know, the unit is Amp-hours, not amps per hour.
     
  13. Audioguru

    New Member

    Dec 20, 2007
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    None of my many Energizer Ni-MH AA battery cells and 9V batteries have failed. Some are old.
    I don't buy RadioShack crap because they are gone from Canada and I don't buy Duracell batteries because their management closed their engineering office in Canada.

    Energizer AA Ni-MH cells are made for them in Japan, maybe by Sanyo.
    Their 9V Ni-MH batteries are made for them in Germany.
    Energizer makes their own alkaline cells in USA.
     
  14. bountyhunter

    Well-Known Member

    Sep 7, 2009
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    I have not heard any gripes about their NIMH. However, if they are charged in NI-CD chargers or any charger that supplies continuous trickle current above about C/30 ballpark, they will die pretty rapidly.

    The cadmium thing was a small component: I was collaborating with Gates energy back around 1990 when they were ramping up the first major NI-MH products for consumer usage: being "cad free" was one plus, but they also had about 30% (or more) better capacity than NI-CD. They had visions of segmenting the market into two camps and NI-MH would be the "premium" camp and command very high prices..... did not work out.

    Li-Ion was brought out by Sony very shortly and basically gutted the market for Gates because Li had so much more energy and lighter weight they quickly owned the "premium" slot for all major consumer products (phones, camcorders, laptops, etc). Sony also did a brilliant move when they took the technology to sanyo and set them up in business as a direct competitor. Companies won't adopt a single source technology and Sony knew it. They wanted to own 70% of a billion dollar market, not 100% of a ten million dollar market.

    Gates and NI-MH just got run over by Sony. Ni-Mh is still a good technology and holds the niche of being a little better than NI-CD. The consumer benefitted because NI-CD makers quickly increased capacity WAYYYY beyond what it had been for years and NI-MH had to increase theirs. The result is battery capacity is way up, prices are low and consumers really benefitted. Gates lost a bundle of money but that's life.
     
  15. JMW

    Member

    Nov 21, 2011
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    NiMH takes a special charger. They don't like to be overcharged. NiCd doesn't either, but are bit more tolerant. Back when I was doing 2 way radios, NiCd was usually good for 700 cycles or so, NiMh only 400 max. The only valid way of determining full charge is by temperature change. Good battery packs have these built in, as do the better chargers.
     
  16. Audioguru

    New Member

    Dec 20, 2007
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    My Energizer Ni-MH charger is simply a timer. If It charges cells that are already charged then it is stupid and over-charges them for 6 hours. Then they are HOT!

    My Li-Po charger does not over-charge my Li-Po batteries because it is smart.
     
  17. THE_RB

    AAC Fanatic!

    Feb 11, 2008
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    Thanks for the "inside info" Bountyhunter that was great.

    I'm still dirty on NiMH, and have NEVER seen one with better capacity than NiCd. I used to test the capacity of batteries when doing repairs and had a couple of setups of constant current loads. The new NiMH never measured anywhere close to the marked Ah rating, the NiCds often did. Also once NiMH had been in use for a while they go really bad and go to a fraction of the new capacity.

    Maybe the Australian heat factors in a bit with the poor NiMH results I've seen, but I would rate them in real life use as MUCH less capacity than NiCd in the same size cell.

    I dare anyone here with a NiMH battery or cell to charge it full, then discharge at about a current of 5 hour rate (based on labelled Ah) and you see it dead in about an hour or maybe 2 if your lucky and have a good one.

    You can make a constant current discharger from a LM317 and a resistor to set the current, then stack the battery on top of a DC power supply like a 5v supply. I got good at testing the batteries this way on the bench while I was working in the shop on repairs etc, and just check the battery with an analogue voltmeter left attached to it.
     
  18. MrChips

    Moderator

    Oct 2, 2009
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    Could you elaborate what you mean by that last part?
     
  19. bountyhunter

    Well-Known Member

    Sep 7, 2009
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    Around here, we have AA NIMH cells with capacity in the 2000 - 2500 mA-hr range. Never seen a AA NiCD that could do that. Best AA Ni-Cds are about half that. I was using the AA NiMh in my dig camera and they really did last twice as long as my Ni-Cds (I was swapping between sets as they recharged).

    http://www.batteryjunction.com/sanyo-eneloop-xx-4hr-3uwx.html

    http://www.batteryjunction.com/nc-aa-1200.html
     
  20. THE_RB

    AAC Fanatic!

    Feb 11, 2008
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    "Stacking" means to put a power source PSU or battery etc in series with another power source.

    You put the 1.2v cell in series with a 5v PSU, giving 6.2v, then connect a LM317 set to X mA as a constant current source. Then measure the cell voltage as it discharges at a constant current. It's not a typical test just the kind of thing you do in an appliance workshop situation when a customer wants you to test a battery capacity and you have to "wing it" with a capacity test.

    Well I probably would have put that down to "Chinese honesty" as they tend to increase the labeled capacity on batteries by X percent just like their labelled wattage on audio gear.

    However I respect you and am not calling you a liar, if you have found better capacity with NiMH than I believe you. My opinion of NiMH comes more from when I was working in electronic goods repair and saw the problems with NiMH from real world issues like people forgetting to charge or bad shelf life (which we had problems with as a fact, from more than one battery supplier). Sometimes I would test new NiMH straight out of the packet and charged on a proper charger and the capacity would be less than half the labeled capacity, maybe 1/3 of label value if they were charged then tested a week later. It was a huge problem especially with cameras where people might not charge/use them with weeks inbetween.
     
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