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  1. #1
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    Default Restoring Nicad Batteries

    Hi all, I have an 18v cordless drill and both batteries are losing charge. I looked at buying new batteries but they cost more than a new drill kit. I have heard there is a way to restore your Nicad batteries with a voltmeter but cant find any info on this. Can anyone help me.

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  3. #2
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    There are two methods I am aware of:

    1. Freeze the batteries then charge them. I have done this with some DeWalt batteries and there was a significant improvement (lasted a month or more).

    2. 'Zapping' the battery with a 30v or so DC power supply. If I recall it requires eight 'touches' over about ten seconds to work. Suggest you google the technique rather than follow my memory. There is also a video on youtube of a guy demonstrating it.

    Note there are also battery places that can rebuild your batteries for a reasonable price.

  4. #3
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    Dan, For an 18V nicad pack, you have 15 nominally 1.2V cells arranged in series. The output of the pack is limited by the weakest cell in the pack. There are a number of things that kill Nicads.
    1. Loss of electrolyte (pasty fluid between the plates), caused by old, age, or with tools by overheating cells when charging or discharging.
    2. Dentrite formation, where the electrolyte crystalises in places, forming something like a miniture stalagmite that bridges between the battery plates, and shorts out the battery.
    3. Cell imbalance. Individual cells will have a range of performance levels. Manufacturers could buy premium cells, test them individually through 5 charge/discharge cycles, and then assemble packs so that all cells match to 5%, 1%, or 0.5%, but the pack would be extremely expensive and would not sell. Instead, they tend to buy cheap to moderately priced cells and assemble battery packs on a production line environment. On this basis, individual cells in any new pack could have a performance spread of at least 20%, and the weaker cells will die first.
    4. Individual cells being reverse polarised by extended use beyond the point where they have dropped below their minimum output voltage.
    Loss of electrolyte is generally terminal, as there is no way to replace it. It occurs as the cells have a relief valve built in to vent if the cell overheats and evaporates the electrolyte. Without the vent, cells would explode catastrophicly whenever they got hot, like left in a car on a hot day.
    Traditionally, nicads are charged at a current of 1/10th of the AH capacity for 14 hours, so they are overcharged by 40% of their rated capacity. The overcharge provides for the energy conversion losses associated with charging. With the slow, low current charge the cells don't heat significantly so they don't vent. If they are supplying moderate currents over extended periods, or significant currents for brief periods, they also don't overheat.
    Overheating is fairly common in tool use however for a number of reasons. The tool manufacturers pack cells in cardboard sleeves for electrical insulation, but this also traps heat into the pack. Cells are close packed, and maybe half are near the outside of the pack, with the others surrounded by cells that are heating up. Very few people want tools with a 14 hr charge, so the charge times get pushed to 1 to 3 hours by increasing the charge current, but unless the charger is fairly expensive, there is no monitoring or protection for the cells, they get left on and cook. Tools tend to get used fairly hard, with users stalling the motor to open/lock chucks, when a bit grabs etc. These all combine to cook the cells and cause them to vent and permanently degrade. There is no repair for cells that have lost too much, they just deteriorate at an accelerating rate.

    Dendrites form over time and can short out individual cells in a pack. If the pack can be opened safely and conveniently, you can measure the individual cell voltages. Working cells should measure 1.1 to 1.4V at rest on the bench. Cells that measure 0V have dendrite formation which has shorted the plates and the cells.
    Dendrites can be literally burnt out by zapping the individual faulty cells a number of times with a relatively high current. I have used a 12V motorbike battery for this, zapping for a max 0.5 sec followed by a 15 second rest to allow the cell to cool. Cooling time is essential or the cells will cook off.
    There is no point in zapping the whole pack as a unit, or working cells as the process will only remove dendrites that are shorting the cell. When a dendrite has been zapped, there will be a small drop in cell performance, but overall the cell should be limited by other factors such as plate area and electrolyte levels. Once a pack has some cells zapped, it is common to have to go through the pack checking and zapping on a regular basis, as all cells will be carrying immature dendrites which will continue to develop.

    There is no real cure for cell imbalance other than to match cells in the first place. However a slow charge on a regular basis will help to keep each individual cell at peak performance, without degrading the rest of the cells in the pack by cooking them. However most chargers don't have a slow charge or 'normalising' facility.

    Reverse polarisation is a result of cell imbalance and user error. The loaded output voltage of your 18V pack has dropped to about 16 Volts, but you still have a few things to do, and the spare pack hasn't finished charging yet. You press on with the job, but the drill is getting weaker and weaker. What is happening inside the pack is that the weakest cell has flattened before the rest. But because you push on, the power produced by 14 cells has to flow through the weak one to get to the motor. In doing so, it force discharges the weak cell, driving it toward 0V, or worse still, forcing it to a negative polarity. If you keep going, the second weakest cell then suffers the same fate, then the third.
    The cells can be forced back to the correct polarity by charging, but they take an overall performance hit of maybe 5% each time it happens. This keeps reinforcing the imbalance problem. The only solution is to load test the individual cells and replace the weaker ones. The method of avoiding the problem is to use the best batteries you can get, regularly give them a slow 'normalising' charge, and give them a charge as soon as the pack performance starts to drop off.

  5. #4
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    I had put aside a dewalt drill for many years due to the cost of replacing the dead batteries. Bought a Makita but was never that happy with it. Last year I found an Aussie seller on Epay who sells aftermarket/ generic batteries (about$70 incl shipping from memory). I think it was http://stores.ebay.com.au/OZ-DEAL-INC. I have had no problems and the Dewalt is just as good as i remember

    regards,

    James

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    I cant find any after market batteries for hitachi.

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    malb,

    It is good to see a sensible response to the NiCd question.

    As one who worked in battery research, holds patents in battery technology and fast charging techniques and has work as a consultant developing very fast chargers costing $M's, I think melb's post sums it up very nicely.

    It is worthwhile adding that the dentrite formation is a battery problem, rather than an user issue, and as such is likely to keep reoccurring. In my view, zapping them is just a stopgap measure and not worth the risk or effort. The cure is battery replacement.

    The best advice for battery life is not to over discharge the pack and recharge soon as the performance goes off (don't rest and reuse!). Using a good charger helps battery life enormously and can provide an equalisation charge if the pack is left in long enough. Just because a (good) charger indicates a battery is charged doesn't mean it is fully charged or equalised - leaving the battery pack in a good charger until it re-equalises will help battery life.

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    Maybe one of you guys could explain why freezing has such an effect? When I first heard of it I was dubious, but gave it a go about two years later. That battery initially could hardly spin the chuck but after freezing the battery charged up like new - why is that?

  9. #8
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    Well............. what about charging the battery in the fridge.

    Has any one tried it?
    Last edited by Buzzer; 28th Feb 2008 at 09:49 PM. Reason: missed a word
    Cheers,
    Buzzer

  10. #9
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    This is one of the cheapest replacement battery suppliers I have found.

    http://www.battery-charger.com.au/
    Regards Bazza

    Skype Username: bazzabushy

    "Experience is a hard teacher because she gives the test first, the lesson afterwards."
    -Vernon Sanders Law

    The views expressed by the poster are general in nature and any advice should be taken in this vein. The poster accepts no responsibility if this advice is used. When undertaking any work personal professional advice should be sought from suitably qualified persons in the field of work being undertaken.


  11. #10
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    This place has batteries for Hitachi power tools:

    http://www.batterydoctor.net.au
    Geoff
    My place

  12. #11
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    Quote Originally Posted by Groggy View Post
    Maybe one of you guys could explain why freezing has such an effect? When I first heard of it I was dubious, but gave it a go about two years later. That battery initially could hardly spin the chuck but after freezing the battery charged up like new - why is that?
    Groggy,

    The short answer is that I don't truly know.

    However, speculating, you maybe aware that the charging reaction within the cells causes crystals to form. Slow charging tends to lead to a small number of large crystals forming, whereas fast charging results in a large number of small crystals. Smaller crystals are more beneficial due to the larger surface area (more reaction surface, lower resistance). This is why fast chargers are preferable and give better battery life. It could be that the "freezing" (I'm not sure if the electrolyte will solidify at temperatures reached in a domestic refrigerator?) may help breakup some of the crystals and improve the performance. However, I expect this would just result in a slight improvement to the battery performance rather than a complete recovery.

    Considering the remarkable improvement you noticed, it is more likely that the pack had a high resistance contact somewhere within the pack - possibly in one of the internal connections within one of the cells. A high resistance contact will prevent the battery pack being charged and discharged properly. Maybe the freezing resulted in something mechanically moving within the the pack or cells somehow restoring the connection?

    The freezing trick seems harmless enough so I suppose it can't hurt to give it a try - if it works, it works!

  13. #12
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    Quote Originally Posted by snowyskiesau View Post
    This place has batteries for Hitachi power tools:

    http://www.batterydoctor.net.au
    I just did a comparison check on a Hitachi Tool Battery EB9H and the BatteryDoctor was $69.00 compared to $63.99 at http://www.battery-charger.com.au/

    As I said I haven't found any one cheaper than http://www.battery-charger.com.au/
    Regards Bazza

    Skype Username: bazzabushy

    "Experience is a hard teacher because she gives the test first, the lesson afterwards."
    -Vernon Sanders Law

    The views expressed by the poster are general in nature and any advice should be taken in this vein. The poster accepts no responsibility if this advice is used. When undertaking any work personal professional advice should be sought from suitably qualified persons in the field of work being undertaken.


  14. #13
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    Quote Originally Posted by Groggy View Post
    Maybe one of you guys could explain why freezing has such an effect? When I first heard of it I was dubious, but gave it a go about two years later. That battery initially could hardly spin the chuck but after freezing the battery charged up like new - why is that?


    Gudday Groggy, all the freezing does is reduce the cells internal resistance hence the apperance of more charge.

  15. #14
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    Thanks for the battery links guys but they dont seem to have mine. I need a EB1814SL (18v) for my Hitachi DS18DVF3.
    The drill has been really good which is why I didnt want to replace it but being the genuine Hitachi batteries are going to cost me $150 each and the drill + 2 batteries and a tourch pack is around $250 I may need to look at a new drill.
    I wonder if any hobby shops can rebuild my batteries with new cells?

  16. #15
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    Quote Originally Posted by dan76n View Post
    Thanks for the battery links guys but they dont seem to have mine. I need a EB1814SL (18v) for my Hitachi DS18DVF3.
    The drill has been really good which is why I didnt want to replace it but being the genuine Hitachi batteries are going to cost me $150 each and the drill + 2 batteries and a tourch pack is around $250 I may need to look at a new drill.
    I wonder if any hobby shops can rebuild my batteries with new cells?
    Dan

    Try Battery World. I saved $80 on a laptop battery that the rebuilt for me. The original was $280 and they rebuilt it for me for $199 with a better battery with a better amphr.
    Regards Bazza

    Skype Username: bazzabushy

    "Experience is a hard teacher because she gives the test first, the lesson afterwards."
    -Vernon Sanders Law

    The views expressed by the poster are general in nature and any advice should be taken in this vein. The poster accepts no responsibility if this advice is used. When undertaking any work personal professional advice should be sought from suitably qualified persons in the field of work being undertaken.


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