Long-term battery charging

[OuBallieParticipant @ouballie]

John,

Take a breather or let your fingers have a rest please.

I'm breathless and my fingers are aching in sympathy

Very informative post, but would you comment please on Harry's post about connecting an LED to create a slow discharge?

Geoff – Head spinning from all that info covering batteries

[John FieldingParticipant @johnfielding34086]

Hi OuBallie,

Sorry my post was long but it is a deep subject and without all the facts people jump to incorrect conclusions.

The old LED on the battery (used to be torch bulbs in olden days) does absolutely nothing, zip, nada, to prolong a battery life. In fact it is about the worst thing you can do.

As I tried to explain, ALL rechargeable batteries no matter what the technology, NiCad, NiMH or SLA suffer from a slow and steady inherent discharge mechanism. The old wives tales that you should only ever store batteries in a fully charged state is total rubbish. A typical NiCad, or similar type, will discharge at about 2 to 3% per day at ambient temperatures of around +20C. One thing we did for the military users here to prolong man-pack radio battery life was to buy old supermarket freezers and store the batteries in them. In the Free State at the main store the warehouse temperature gets to +45C in summer. High temperatures make batteries discharge faster, lowering the battery to about -10C slows down the discharge by a couple of % per day. But it doesn't stop the discharge altogether.

Also this boll*cks about never stand a car battery on a concrete floor is also BS. There is no scientific proof it does anything at all to a battery capacity. I have been around batteries my whole working life and worked on many battery designs and charging systems, so I think I know a little bit about the topic. In 2006 I published a textbook on this topic which is sold worldwide and nobody to date has pointed out any errors in my statements. They are all based on well documented facts.

Sorry for the rant – time to cool down.

[EmgeeParticipant @emgee]

For those with acces to old ME mags can check the index pages to find an article detailing a battery stand by unit that I think was aimed at caravan owners who wanted to keep the battery conditioned during winter months.

From memory the unit would trickle charge a 12v wet cell battery to a terminal voltage of 14.2v and then change over to discharge mode through a car headlamp bulb until the terminal voltage dropped to 12v. The unit then switched to trickle charge again and the cycle continued until disconnected from the unit.

It was a pretty simple circuit with a relay and some electronic components but did provide for adjustments to max voltage, charge rate and changeover points. For sealed lead acid batteries terminal voltage limit recommended was 13.8v.

Emgee

[OuBallieParticipant @ouballie]

Thanks John.

Absolutely so need to apologise, as receiving the correct information is vital!

I will continue charging my stored car batteries, 12v & 6v, using my Accumate charges.

Regards,

Geoff – Time to oil my main door lock mechanism.

[EmgeeParticipant @emgee]

John, having used Nicad batteries for a number of years I have to disagree with your comment re the discharge rate of 2-3 % per day, it may be true for the other types mentioned but certainly not Nicads.

Emgee

[Neil WyattModerator @neilwyatt]

Anyone who remembers NiFe cells may be aware that they are best stored in the discharged state- in fact with the two terminals wired together!

Neil

[Anonymous]

Posted by Nicholas Wheeler 1 on 12/03/2016 11:43:09:

the basic CTek charger **LINK** is what you want. Buy hard-wire kits for each vehicle, charge occasionally and you're done. This is the same charger that Bentley, Ferrari Porsche etc sell with their own badge for people whose toys don't get used enough

I can second the CTek chargers. We have one at the gliding club for keeping a spare tug battery on condition in case of problems.

I've had a tour of the CTek factory in Vikmanshyttan, and had dinner with the owner. We were out there to install a new type of battery in a hybrid car for testing purposes. The factory is located on an old, but small, steel works so there is plenty of old heavy engineering stuff about. Quite what the legality of driving a UK registered car, on a UK driving licence, on Swedish roads at night with a totally new battery pack and BMS is we didn't ask!

Andrew

[Ady1Participant @ady1]

I've only observed from a distance kinda thing and some brands seem to do very well and last a very long time

Varta car batteries are very good IMO

[Cornish JackParticipant @cornishjack]

Geoff

"Time to oil my main door lock mechanism."

Each to his/her own, of course, but an old mate of mine, some years back, advised NEVER to use oil on locks. His method was powdered graphite, sold in little 'puff' packs'. Graphite maintains its lubrication qualities whereas oil becomes 'sticky'. This is, of course, second-hand info, so no supporting expertise!!

rgds

Bill

Edited By Cornish Jack on 13/03/2016 11:53:43

[Russell EberhardtParticipant @russelleberhardt48058]

Posted by Emgee on 13/03/2016 10:53:18:

John, having used Nicad batteries for a number of years I have to disagree with your comment re the discharge rate of 2-3 % per day, it may be true for the other types mentioned but certainly not Nicads.

Emgee

Well, John's statement certainly holds true for the NiCads in my drills. A month without use and they are all flat! Must buy a drill with a Li-ion battery.

Tim, if you only bought the battery last August take it back to the supplier. I had the same problem with a six month old battery in my camper-van. Left unused over the winter but connected to a float charger. In the spring it wouldn't turn the engine. It was guarantee for three years so I took it back and they changed it for a new one with a new four year guarantee so I'm hoping that one will die in three years

Russell.

[EmgeeParticipant @emgee]

Russel, manufacturer's haven't been fitting Nicads in hand drills for years because of environmental concerns over disposing spent cells. If you have nicad cells and not NiMh then they are old and passed their best, so don't take a full charge and retain it.

Emgee

[Steven VineParticipant @stevenvine79904]

Posted by John Fielding on 13/03/2016 10:31:14:

The old wives tales that you should only ever store batteries in a fully charged state is total rubbish.

Hi John

What do you advise as the minimum voltage a car battery can drop to, before requiring a top up?

Thanks

Steve

[Neil WyattModerator @neilwyatt]

I've been taking advice from this website for years:

**LINK**

One good thing is he keeps up to date with recent research and posts links to it.

Neil

[John FieldingParticipant @johnfielding34086]

Hi Steve Vine,

That is a bit like how long is a piece of string, but I will try and give some pointers.

The minimum voltage is highly dependent on the plate technology in use. Modern batteries use silver and other exotic materials to alloy the basic lead and these are claimed to be able to drop to lower minimum cell voltage. For a standard lead-acid cell the figure of 1.75V is considered to be fully discharged, but that is the open circuit voltage. As soon as a load is applied it will drop because of the ESR. The generally accepted min and max voltages for 12V automotive batteries is 10.5 to 15.6V in use. The problem is that if a batteries is unused for a long period the plates start to sulfate and the ESR goes up even more. So a simple answer is – if in doubt put it on charge!

[John FieldingParticipant @johnfielding34086]

Emgee,

Have you actually performed capacity tests on NiCads?

I have done many charge/discharge tests on hundreds of different types to ascertain the actual capacity in various stages of a battery life and it is very clear that 2% per day at elevated temperatures is quite normal for some cells. NiMH are slightly better but not by much. The change to NiMH was more to do with environmental aspects than battery life or capacity.

I developed automatic charge/discharge equipment to do extended life testing for NiCads and other types to assess the best choice for our applications and there is a huge difference between different manufacturers cells and batteries. Some batteries which claim 40Ah for example struggle to make half of the when tested under standard conditions. This is the Peukert Factor coming into the equation!

[Mike PooleParticipant @mikepoole82104]

Makita seem to still be making Nicad drills.

Mike

[Tim StevensParticipant @timstevens64731]

Thank you to everyone who has contributed to this strand. I am coming to the conclusion that my stand-by charger is not man enough. It says '4Ah to 75Ah' and so it should cope with my 75Ah battery, but clearly does not. The max current it can supply is 1.2A (it says on the tin) and reading John Fielding's stuff that is just not enough. So, the battery is now connected to my old fashioned transformer cum rectifier set up and we will see if it can hold a charge after a day or two. And I will be looking closely at the C-tek charger.

Watch this space …

Regards, Tim

[Neil WyattModerator @neilwyatt]

If you have a battery hand drill with a clockwise-off-anticlockwise switch, always leave it in the off position – I suspect the crude resistor and FET speed controllers let a little current through even when the trigger is released as my drill goes flat much faster if I forget to do this (days rather than months).

In the past I have revived nicad packs by charging, repeatedly shorting and raising a spark.

Of late I have started using a 12V leisure battery wired + to – when doing this (ONLY for the duration of a series of brief sparks across the terminals). This has revived two out of three packs I have done it to (one success and one failure being Makita packs costing ~£40). Only do this to Nicads – these are prone to the growth of internal metallic filaments that can short out one or more cells. – and the brief overcurrent literally vapourises them.

Don't bother doing this with NiMH as they don't have this problem and not with Li-ion as they will catch fire…

Neil

[mike TParticipant @miket56243]

I think Tim's battery problems have been discussed at some considerable length. It should be safe to widen the discussion without hijacking his topic

All the Nicad battery packs for my cordless drill have failed over the years. I decide to try a brand new three cell Lipo battery ( from my quad drone). The voltages were about the same. The drill worked better than ever and I finished the job with seemingly power to spare. When I checked the Lipo's battery state I discovered to my horror that the voltage was below the critical "do not discharge below" voltage. The drill was still running well but the battery never recovered. Some very expensive holes were drilled that day.

If I ever repeat the exercise, I will be sure to fit one of those audible low voltage alarms.

I must give Neil's method of reviving old nicad packs a try, I have plenty of those

 

Edited By mike T on 13/03/2016 19:16:09

[I.M. OUTAHEREParticipant @i-m-outahere]

+ 1 for c-tek chargers .

There are some really crap trickle / float chargers out there that kill batteries , i had one of those so called float chargers that are meant to keep your battery topped up but after it killed the second battery in my boat it was binned and a c-tek purchased .

One extra bonus for those in colder climates is the temperature sensing abillity of the c-tek unit so it won't punch in full power into a cold battery.

Best thing i ever bought for my boat – along with the Ultimate brand battery , now 5 yrs old and still going strong !

Ian

[Clive HartlandParticipant @clivehartland94829]

Dendrites , Neil.

[Neil WyattModerator @neilwyatt]

There are chips out there that will revive over-discharged Li-ions by applying a very small trickle charge until they get above the critical voltage.

[John FieldingParticipant @johnfielding34086]

As the thread seems to have wandered off course into NiCads and other rechargeables I can tell you some interesting facts about these.

Over the years in my professional career I was involved in several deep studies into rechargeable battery packs for the military equipment my company manufactured. The original range of products all used a 15V dry-cell battery made by Eveready. Since this was the "standard" battery pack all man-pack radios were designed around this battery. Two of our competitors also standardised on this battery and it became "the battery of choice". The original radios were "build to print" ones we obtained a licence to manufacture from a European company and they used the same battery. So it made sense to use the same shape and format when a new radio was on the drawing board. The radio could be extended in length very easily but the same bottom die-casting and battery box was used throughout the series.

Later Ni Cads became available and naturally we looked at changing the battery to this type, but still keeping the same battery box mechanics. The box could be made a bit deeper if need be to accommodate various cell configurations.

In selecting the cells we had a limited choice as the sanctions had a severe impact on our source of supply. We had two choices, Tadiran in Israel and Eveready in this country. Of the two Tadiran was streets ahead in the technology.

To decide on the cell which best suited our various products we ran extensive tests over about a 2 year period. From this mass of accumulated data we learnt all the was to know about NiCads, warts and all. One serious problem is that when a NiCad battery pack is discharged below its recommended capacity the battery can suddenly develop a drop in output voltage. This is caused by poor capacity matching between the individual cells. If all the cells had the same capacity then they would all sink in voltage as the battery is discharged. But if one or two cells had a lower capacity they would run out of energy before the others and then they flip in polarity as the discharge current through them continues. So when the pack is recharged the flipped cells stsy flipped and now subtract from the total voltage. Charging a cell with the wrong polarity normally damages the cell beyond repair.

A flipped polarity cell can only be reversed to the correct polarity if you have access to the two terminals on the cell. Simply recharging the whole battery pack does nothing to reverse the cell polarity. I devised a method of reversing the polarity which in 80% or more cases was viable. I called this technique "cell zapping". Basically it uses a huge pulse of current applied for a very short time to blow away the crystaline growth which develops when the NiCad is left in a dischaged state and which also occurs when it is reverse polarised. But for this to work you must be able to connect to the individual cell terminals and preferably with the other cells disconnected. Hence, you have to dismantle the battery pack. In the military radios we didn't have a moulded plastic casing at first. The individual C-size cells fitted into a carrier like a torch or other appliance. So swapping out a dud cells was simple and quick.

I hope this post isn't too long!

[Russell EberhardtParticipant @russelleberhardt48058]

I think there is a bit of confusion over the use of NiCd batteries. They should preferably be stored in the discharged state. Most manufacturers recommend discharging (only to about 40% capacity to prevent cell reversal) before long term storage. Indeed they are supplied by the manufacturers in the discharged state.

Storing them discharged does not encourage dendritic growth. Dendrites form by a similar process to electroplating and current must flow for it to occur. The usual cause is overcharging. The cheap unregulated trickle chargers supplied with some consumer equipment are a common culprit.

As John said, "zapping" should only be applied to individual cells.

Russell.

[John FieldingParticipant @johnfielding34086]

Hi Russell,

Actually it doesn't really make any difference what state of charge the NiCads have before being put into storage. Over a long time period they will self discharge down to zero. Lower temperatures slow down the inherent discharge but don't completely stop it.

I went over to Germany and spent a very informative few days talking to the scientists and engineers at Varta. They were the original inventors of the NiCad technology under the original German company name, which I now forget, but they gave me dozens of research papers written over the years. The subject of cell matching was my particular topic but we covered the whole gammut. It seems that cell matching is really a waste of time and effort and my experiments also seemed to point to that particular area, so that is why I convinced the company to send me overseas!

The top scientist, who was one of the original patentee's, was well into his 80s and he told me the original work was done during WW2 for the Nazi war effort for the V2 missile battery pack. He also told me cell matching suffers from aging. If you take say three or four identical cells and they are matched to within 0.001%, which they somehow managed to find by selection from thousands of cells, then over a charge-discharge cycle of ten they tended to drift apart by as much as 10%. Over twenty cycles it was like 20% and so on. After 50 or more cycles they can be as much as 70% variation and that was what he was currently working on to find the reason and a solution. That was in the mid 1980s so things have improved a bit but not by a huge amount. He is obviously now designing batteries in heaven!

NiCads were killed by the environmental lobby and NiMH became the chosen flavour for a while, now it is LIPO and the other variants.

The scientist was also intrigued by my information about zapping cells to bring them back to some sort of life.  After a while he leaned over during our discussion as said "Jah, that is absolutely correct. But you should have asked us, we could have told you that!"

 

Edited By John Fielding on 14/03/2016 10:53:24

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