Long-term battery charging

[Trev67Participant @trev67]

Hi

It never ceases to amaze me the wealth of knowledge on this forum, thank you to all those contributing it's is very interesting.

I don't wish to hijack the thread, but it does seem to have evolved from the original lead acid battery question.

I have a number of NiMH drill battery packs, they where fine when being used regularly, but since being stored unused for some months, a number of them whilst appearing to charge ok, have little or no power. Is there a way to revive these?

Trevor

[John FieldingParticipant @johnfielding34086]

Hi Trev67,

In a word NO. But I did have some success using a method devised by Westinghouse in the USA. This method they claim can reclaim most troublesome cells. Note I used the word cells and not battery. This method I have tried and it does to some extent work but there is no guarantee.

What it consists of is a huge power supply that can bang a huge current into the cell for 1s and then it immediately discharges it at the same rate. They call it "Pulse Charging" or "Pulse Reconditioning". Repetitive pulses over a period of a few minutes can make a cell recover to about 70% or more of its original capacity. Note the original capacity is what the cell had before it died. If the cell was a 2Ah cell and when it went belly up it was down to an actual capacity of, say, 1Ah then you might get 700mAh after pulse charging, but it is a moot point.

I messed around with this method for a few months and then lost interest. The Westinghouse papers describing this technique said that the repetitive pulsing and discharging appears to "shake up the chemicals" and bring them back to life. It can work but I didn't think it worth the effort to productionise and market the product. However, some folks do sell such rejuvinators and make some pretty fantastic claims to its efficacy. Somehow I am bit sceptical from my experiments, but I haven't tried one of these modern types.

[Trev67Participant @trev67]

Thanks John,

I thought that might be the answer!

What is the best way to store NiMH batteries when not in use, they do seem to self discharge quicker than Nicads.

Thanks

Trevor

[roy entwistleParticipant @royentwistle24699]

Further to this thread Can anyone tell me why my cordless phone needs charging more frequently than it used to ?It has ni-mh batteries and I,ve changed them several times It still needs charging every day even if not used

Thanks all Roy

[Gordon WParticipant @gordonw]

Roy- I know next to nothing about mobile phones, we have the same problems now, I have been told that the phone is seeking connections all the time. Weaker signals take more finding. Also it seems ours is constantly trying to down -load "apps". Best, maybe only, way to stop and save battery life is to switch off.

[roy entwistleParticipant @royentwistle24699]

Gordon Thanks but it is not a mobile it is a cordless landline

[Gordon WParticipant @gordonw]

Sorry roy- Just got rid of our landline as wast of money, I'm fixated with mobile now. We had same prob with the batteries in our cordless, even charging them outside the setup. I think they are just rubbish cells.

[John FieldingParticipant @johnfielding34086]

Hi Roy Entwistle,

I can try to explain the life mechanism of typical rechargeable cells.

Each manufacturer normally gives an indication of how many charge/discharge cycles the cell should be capable of achieving. But this is something hard to replicate in actual use as they are very sensitive to charging methods and discharge currents. Almost without exception all rechargeable cells (and batteries when 2 or more cells are connected in series) are specified at a discharge rate of C/20. C is the capacity of the cells in ampere-hours (Ah) and if you discharge at a different rate than this then the apparent or effective capacity differs, sometimes by a large amount. This explained by the Peukert Factor, named after the scientist who discovered the effect.

If you take a 40Ah battery and discharge at the C/20 rate then it should be able to supply 2A for 20-hours before the battery hits 10.5V (for a nominal 12V type). However, if you try and discharge at 10A and expect to get 40/10 = 4-hours, you will be rudely surprised. You will get more like 3-hours, because at higher discharge rates the Peukert Factor rises. At 40A discharge instead of getting 1-hour, you will be lucky to get more than a little over 30-minutes. The apparent capacity is now only about 20Ah for the same reason.

Now as the apparent capacity can differ due to the discharge rate it can also differ by using improper charging methods. Some chargers destroy cells/batteries because they are not correctly designed for the application. In all rechargeable cells, no matter what the type, the amount of energy you can extract from them is always less than what you put in when charging. Numbers like 40% deficit are common. So in order to get out 100% of the cells actual capacity you need to put in about 140%.

Now the chemical bit. In any cell or battery there is a finite volume of electrolyte, in a AA cell it is about 2.5cc, so not a lot. Think of it as the petrol in your car. When it is used up the cell stops working. The amount the cell degrades for each charge/discharge cycle with a perfect charger and a discharge rate of C/20 is very small, but 500 or 1,000 to perhaps 2,000 cycles is the maximum in practice you will likely achieve under the ideal conditions. Better quality cells (the most expensive usually!) can out perform an el cheapo cell by as much as 5 to 1. Fast charge cells favored by RC car racers have particularly poor life cycles because to be able to withstand the abuse the user expects then to tolerate have to be made in a slightly different way. Emergency lighting cells etc have to be ultra reliable so they are also made in a slightly different way. But don't try and use one for a RC car because they will die very quickly. It is a very deep subject and not helped by the secrecy of some manufacturers!

If the conditions the cell is operated under are not ideal then the degradation rate goes up and you get less charge discharge cycles. Operating temperature and depth of discharge can all degrade the life. So the manufacturers can only give a guideline under very specific operating conditions, which may be very different to how your appliance or charger operates them. The manufacturers are not telling fibs, its just that it is impossible to say with any certainty that ABC cell will give X number of cycles before the capacity is considered below tolerable allowance. Which most manufacturers peg at about 80% of the original capacity, so it isn't totally finished. It is just not as good as it was.

I know this sounds a bit nebulous but unfortunately that is the way cells work.

[frank brownParticipant @frankbrown22225]

A bit more info on cells:- i was asked to look into the short life of sealed lead acid batteries that were used as processor PSU back up batteries in a major bit of capital kit. I got the battery companies rep. in to explain! His first point was he lifted a cell and said that it was short of water so we weighed it an it was several hundred grammes lighter then supplied. He then said it looked like a case of "micro charging". This is when the charging current comes from a switch mode power supply with insufficient smoothing. The fast pulses of current do not distribute them selves evenly over the plates (to reform them). Instead they over charge the plate nearest to the terminal, that then dies so the charging current moves further away and gradually kills the battery.

As the batteries were relatively cheap the decision was made just to changes them annually (all seven of them).

Frank

[frank brownParticipant @frankbrown22225]

A bit more info on cells:- i was asked to look into the short life of sealed lead acid batteries that were used as processor PSU back up batteries in a major bit of capital kit. I got the battery companies rep. in to explain! His first point was he lifted a cell and said that it was short of water so we weighed it an it was several hundred grammes lighter then supplied. He then said it looked like a case of "micro charging". This is when the charging current comes from a switch mode power supply with insufficient smoothing. The fast pulses of current do not distribute them selves evenly over the plates (to reform them). Instead they over charge the plate nearest to the terminal, that then dies so the charging current moves further away and gradually kills the battery.

As the batteries were relatively cheap the decision was made just to changes them annually (all seven of them).

Frank

[John FieldingParticipant @johnfielding34086]

Hi Frank,

Yes he was absolutely correct and I have seen that problem.

No matter what fancy modern chargers appear on the market the old transformer – rectifier system running off 50 or 60 Hertz still takes a lot of beating. The pulsing current does seem to be a better way of charging than a bench regulated supply which is pure dc. Many people have tried to find the reason but it eludes them. One theory, which I think seems the most logical explanation, is that the charging and discharging is a very SLOW process and the chemicals get sort of lazy and sluggish. But if they get hit by a rapidly changing current they seem to wake up. Westinghouse in the USA patented such a system and it does seem to work better. But changing out critical batteries every year is a wise plan, as long as the cost isn't too high.

[MuzzerParticipant @muzzer]

That's funny. For almost 5 years (until mid 2014), I was engineering director of a company in N America that designed and manufactured advanced battery chargers for industrial and leisure applications. Have a look for yourself. I was responsible for the design and development of the actual chargers (hardware, software, mechanical, production etc), including the power conversion topology selection and the development and application of the charging algorithms. Not just some supplier to Halfords etc – turnover of $50M in 2015, 80% of the world golf kart market and significant industrial applications (Karcher, Aichi, Raymond etc etc).

The battery packs in these vehicles have manufacturers warranties between 3 and 5 years and the potential warranty costs are very significant. If the battery life could be boosted mysteriously by the application of an alternating current you could be pretty certain that's what would be happening. It isn't. Personally I wouldn't trust a word a battery salesman told me. Most of the manufacturers have little idea beyond how to manufacture them and the salesmen know even less – apart fro how to close a sale.

Believe me, the world is full of self-confessed battery experts and snake oil salesmen who claim the next breakthrough in charging technology. In my previous role (automotive power electronics focussed on electric and hybrid vehicles), I saw even more of the charlatans. Last time we looked, none of them had delivered on their promises, oddly enough. It's really not the black art it is often made out to be but you do need a lot of good, evidence-based expertise.

So no, absolutely nothing wrong with good old DC. As an aside, it's almost impossible to measure the returned charge accurately when you have a complex waveform. That's why effective battery management systems for hybrid vehicles and proper EVs (with regen) are so hard to develop. If you look at the waveforms that they have to work with, a lot of this fine talk becomes irrelevant, as you have no control over it.

Murray

[OuBallieParticipant @ouballie]

Posted by Cornish Jack on 13/03/2016 11:52:44:

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

Bil,

I should have qualified the post by saying the 'door' bolt mechanism.

Locks I do do with graphite using them puffers.

Geoff – My Nom-de-plume is used for a reason

[Peter G. ShawParticipant @peterg-shaw75338]

Zapping of NiCads.

There was an article by K C Johnson in Wireless World, Feb 1977 re this very subject. His recommendation was to first test them to see if there was any voltage, or if they were short circuit. Then to try gentle charging, but if nothing happened, to try a large current for a short period to see if the cell could be persuaded to make volts, followed by normal charging if the cell produced volts. He suggested a car battery in series with a headlight bulb, or possibly two known good cells. The idea was to melt the short circuit. I have tried these ideas and had some short-lived success. I'm now not sure that it's worthwhile.

Concrete floors and Gordon Reads Battery Conditioner (from Wireless World circa 1980-1990)

I built this device, and still use it but only to prevent my transformer/rectifier home made battery charger from overcharging the battery. My problem was that in the winter of 1995, when the temperature around here became very low indeed (*) the relay in Read's circuit seized – froze – in the discharge position and thus fully discharged the battery. Unfortunately, it was sat on a concrete floor next to the door and one of the end cells must have frozen solid. It did not recover! Whether this was because of a draught under the door, or the cold of the concrete floor, or a combination of both, I do not know, but it wrote off a 2 year old Exide 75Ah leisure battery. Now obviously extreme cold doesn't often happen, but it's worth remembering that a discharged battery will freeze more readily than a charged battery – and a garage floor in winter is darned cold.

* At this time, many £10K's worth of damage was done to one of the local lifeboats in West Cumbria when the crew attempted to start it. Apparently, the hydraulic fluid had turned semi-solid due to the cold and thus caused damage to the pumps. I can't remember what the temperature was stated to be, but it was well below zero.

Telephone Exchange batteries.

Many years ago, exchanges in the UK did indeed have a 24 hour battery reserve, however, the cost of providing batteries of sufficient capacity became so high that the battery capacity was drastically reduced and standby diesel generators provided. I don't know what current policy is. Also, battery life in exchanges was measured in decades, not the few years for car batteries. Which suggests to me that the charge/discharge and maintenance practices followed were reasonably good at prolonging battery life.

Control equipment for these batteries varied over the years, with more modern plants being electronically controlled float systems, whilst earlier plants used Ampere-Hour meters and counter-emf cells and ran on a partial charge-discharge system.

Peter G. Shaw

 

 

 

Edited By Peter G. Shaw on 17/03/2016 20:31:45

Edited By Peter G. Shaw on 17/03/2016 20:32:23

[John FieldingParticipant @johnfielding34086]

Hi Peter Shaw,

 

I began my career as a battery technician in the BPO back in the late 1960s. In those days a battery had to last a minimum of 8-hours in case of mains failure and the minimum life of a battery had to be not less than 15 years. If it croaked in say 12 years there was a huge spanish inquisition. A great deal of my time was doing recovery work on the exchange batteries the LTOs had neglected, because they would rather do other things than mess with stinky batteries!

Remedial work was a series of charge-discharge cycles to bring the battery back to near full capacity. Some were so badly neglected it took 2 or more weeks of work to get them back up into reasonable service.  A telephone exchange battery is nominally 50V dc and often positive ground.  It consisted of 24 cells connected in series with link straps.  The battery was normally doubled up so there were two identical rows of cells, one was in use and the other trickle charged as a back up.  Once a week the battery switch was swapped over so the other battery was the main battery and the one just out of service became the back up.  All the batteries had at least two spare cells awaiting fitting in case a cell went AWOL and it was common to find we had to swap out a dud cells with one of the spare ones whilst in standby or back up mode.  One old exchange I was involved in decommissioning was built in the early 1940s and it was a very small manual exchange and the battery was still perfect after all those years, because the maintenance was done correctly by a traveling technician who called once a week.

In bigger exchanges it was normal practice to also install standby generators, but the smaller exchanges didn't warrant the expense. The biggest battery system I worked on was the one in the Edinburgh trans-atlantic job. IIRC it is at Murrayfield or it could have been Muirhouse, it was a long time ago!

Forgot to add a bit about telephone exchange battery systems.

All the types in common use in my days at BPO were "float charge" systems. They may have had different types later but I was gone by then.  In a float charge system the main charger supplies the current requirement of the exchange and also kept the battery topped up.  In effect the charger and battery were simply connected in parallel, so if the mains failed the battery stepped in to take over the load, with no break in service.  The 8-hour parameter was a reasonable time period, in the UK the mains supply was pretty reliable and if an exchange was off-line for more than a few hours then we also had a number of vehicle mounted large diesel generators which could be sent to an exchange to provide backup if the battery was in stress with the load.  Not sure what the policy was prior to that but 24-hours does seem rather a long time and I never heard it mentioned?

Car alternator system work in exactly the same way, the alternator provides the current required and the battery steps in to offer assistance if the alternator output falls too low.  If it wasn't for the starter motor the battery could be a lot smaller.

Edited By John Fielding on 18/03/2016 09:13:41

Edited By John Fielding on 18/03/2016 09:24:40

Edited By John Fielding on 18/03/2016 09:33:55

[John FieldingParticipant @johnfielding34086]

Hi Muzzer,

Yep you are quite right!

The thing that gives me the giggles the most is the "Gas Gauge" trend. Almost all portable appliance which uses rechargeable batteries today seems to have one sort or another. But none of them work accurately and are easily fooled. I have tried a few of these ICs and although they do give some sort of guide they are at best a gimmick to sell the expensive toy.

To be able to predict with any degree of certainty how much capacity a cell or battery actually has takes a bit more than measuring the joules put in by charging and the assumptions made thereof. You would need to know the precise capacity of the cell during discharge and the environment and even then you could be out by 20% or more. You would also need to know the capacity degradation per charge-discharge cycle for that particular cell or battery, which you don't have as it is a new cell. Using data from another cell of the same type is no guarantee either, cells differ even from the same batch over quite a broad spread.

The basic problem with batteries is the user, most people know absolutely zip about them and salesmen take advantage of this fact and then its your money they are after and nothing more!

[Peter G. ShawParticipant @peterg-shaw75338]

John.

The basic problem with batteries is the user, most people know absolutely zip about them and salesmen take advantage of this fact and then its your money they are after and nothing more!

Very true. Just try ringing round a few caravan dealers, especially the smaller ones, asking for a leisure battery and how much it costs. Or even better, go and see them. Then ask what the capacity is and note how many say "75Amp"! Which as you and I know is a nonsense. Then start talking about Ah, and look at the blank incomprehension on the salesman's face. Having suffered from this phenomenon, I now have a rule of thumb – if the salesman, when asked what the capacity is, mentions Ah, eg 75 Ah or 80Ah etc, then he gets the sale. If not, I go elsewhere.

I actually bought one of these so-called 75Amp leisure batteries and did a test charge and then discharge. It lasted less than 10 hours at the 4amp rate (terminology might be a bit awry here). I took it back for a refund and went and found an Exide 75A battery – and nearly dropped it due to the weight! Under the exact same test conditions, it ran for something in excess of 20 hours. Ok, it cost 50% extra, but it was worth it.

I've also had cheap odd-named car batteries with a 3 year warranty. They lasted a month or two over the three years. I then bought a Bosch 4 year warranty battery. At six years old, it was still working albeit with not too much reserve. All on the same car.

Nowadays, I only buy well known recognised brands – Bosch, Exide, Lucas, Varta. Names like "Jolly Green Giant" or whatever it is, don't get a look in.

Peter G. Shaw

[AjohnwParticipant @ajohnw51620]

I spent a number of years designing and developing batteries primarily lead acid. Initially for car use and later trying to use the same technology for traction where watt hrs kg really does matter. The rules on plates follow JF's early comments culminating in an entirely different internal construction for very long life deep cycling but even those can be played with in terms of the surface area exposed and depth of oxide which also matters.

SLI doesn't really deserve the name and hasn't since the wide spread use of alternators rather than dynamos. All the car manufacturers really care about is cranking performance for starting. That has been specified in a number of ways but boils down to so many amps for some period down to 10.2 volts under load at -40C. The 10,2v is interesting because although lower figures may be quoted for specific applications in real terms there isn't much power left and going lower is far more likely to cause problems. Higher is even better really.

Charging potentials have changed over the years. One way of doing that is playing with the antimony levels in the lead that makes up the grid that supports the oxides that actually store the energy. They may even be using calcium instead now and probably are. This is done to prevent gassing – electrolyte water loss – but from work I have actually done if the charging voltages aren't changed the batteries have less total capacity. On cars this needn't make much difference and maintenance free batteries are highly desirable. This is one of the ways it can be done. Others may also be used on gel batteries. It didn't work out well on traction. I did dream up a charging regime that solved the problem but at the expense of some water loss – made me a bit unpopular at the time but I believe it was adopted eventually. Part of the "problem" was that I also found that one single over discharge changed the charging characteristics for ever. No one wanted to hear that.

Lead acid is wonderful for what is effectively load levelling applications such as starting a car. For anything else they have problems as do other forms of battery for exactly the same reasons. When they are discharged there will be minor differences in the capacity of each cell so some will be more deeply discharged than others. If the level they are discharged to is reasonable this wont be noticed immediately. The problem comes when they are recharged especially if cell voltage is used to determine full charge. There is not much else available really. The higher capacity cells will boost the apparent cell voltage of a number in series so the lower capacity ones never get fully charged again. Then they are discharged again and the same thing happens again making things even worse. Eventually whoops and cell gets seriously damaged.

So if you want to float your batteries for extended periods make sure that all cells are fully charged first and top them up if needed. If you have already "abused" it tough as you may still have problems that will need higher float voltages which may mean periodic topping up or do boost charges now and again. Just add – constant current charging will be better for floating batteries rather than voltage.

All sorts of things can happen inside them as they are used. :Lead sulphate forming for one, denditic growths through the material that separates the plates for another. Things get really interesting if a cell goes down to levels where they have no power at all and other cells in series continue providing power.

The cell voltage is more like 2.2v really so 12 is actually 13.2 and a well designed battery in good order will provide over 12v under load for a while at least.

John

–

Edited By Ajohnw on 18/03/2016 17:15:08

[Ian S CParticipant @iansc]

The method I have used for restoring NiCd batterys I got from the "Hints and Kinks for the Radio Amateur" ARRL publication (late 1970s, early 80s). Their method is to charge a reasonably large (34000uf or more)electrolytic capacitor on a 12v supply, and discharge it across each cell a couple of times.

Ian S C

[john fletcher 1Participant @johnfletcher1]

Years ago there was an excellent electronics magazine called Electronics Today International ETI and there was an article called zapping Ni-cads, which is much like ARRL idea. In the text it described burning off the cell internal whiskers. I have been doing this on my 20 year power tool batteries on a sort of annual basis. Occasionally I taken the battery box apart and replaced a cell, from my spare collection.John

[peak4Participant @peak4]

Posted by john fletcher 1 on 19/03/2016 10:35:17:

Occasionally I taken the battery box apart and replaced a cell, from my spare collection.John

I did that once, well several times really on different batteries, both power tools and portable 2 way radios.

On one memorable occasion, I replaced a cell in a Skil drill pack with a new cell from somewhere and all worked fine for a while.

One day I put it on rapid, rather than trickle charge, still with the standard charger; it had two settings.

Some time later, there was a serious bang; the new cell hadn't liked the rapid charge, even though I'd checked the spec before purchase. I assume the vent was blocked.

The cell exploded, with the spiral wound interior expanding a bit like Zeberdee's spring. This blew the next cell in the stack clean through the plastic battery case, finally leaving a dent in the bedroom ceiling.

Edited By peak4 on 19/03/2016 13:53:42

[John FieldingParticipant @johnfielding34086]

Hi Ajohnw,

You are correct about terminal voltage and car alternators. GM some years ago were persuaded to change from standard SLI types to lead-calcium and found they had a flood of complaints from owners because they didn't hold the charge. So they had to redesign the IC regulator in the alternator to raise the terminal voltage from about 14.0V to 14.4V to suit the new battery technology. Now the danger is that if the battery supply shop – who are almost clueless about things technical in many cases – sell you an old style battery, it will boil with the higher cut-off voltage.

Same thing if you have an older vehicle with a 14.0V alternator, and a new technology battery is fitted. It will never get the battery into a fully charged state. Most owners who use their cars every day will probably not detect a problem, but go away for a couple of weeks and then try to start your car and it will be pretty flat.

[frank brownParticipant @frankbrown22225]

I have a "Site" battery powered drill, its about 15 years old (bought from B&Q). My problem is that they seem to have vanished , I can't find any reference to the name site, only, the word site as a description. So I have to fiddle with dead cells every 6 months or so so am getting fed up with having to do that. I was wondering if I measured the internal resistance of each cell when they are mean't to be charged would be an indication of how much further life they might have?. Sort of electronically switch between a charging current of .2A to a discharge of 5A 100 times a second. The drop in voltage (ripple) would be proportional to the cells internal resistance. But would it actually mean anything?

Frank

[John FieldingParticipant @johnfielding34086]

Hi Frank Brown,

There is a simpler method!

The voltage drop between no load and some current if you can accurately measure it is a good indication of the ESR. You just need to be able to measure the two voltages and the current accurately and then apply Ohms Law.

[Tim StevensParticipant @timstevens64731]

Interesting comments from John Fielding about Lead Calcium needing a rather higher voltage. This should not apply in my case (yes, I started this thread) because I seek out batteries with filler plugs, having a pre-war voltage 'regulator' system (which is neither system nor a regulator), so I know I need to top up when the car is in use. It ought to be the case that such an old-fashioned spec battery has old fashioned lead plates – plates that would work with a modest charger-conditioner.

But, what if the battery supplier took a short-cut, and used Lead Calcium plates (off the shelf, no messing) to put in an old-style screw-filler case? Wouldn't that mean I had a ~ 14.0 volt charger and a ~ 14.4 volt battery? And so, no real charge over a long period …?

Regards, Tim

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