Rechargeable AA cells and chargers

[ericmark]

I have a whole range of cells bought over many years some NiCad and some NiMH and a couple of odd alkaline ones which unlike the rest are 1.5 volt not 1.2 volt.

I had a really good ΔV charger which could charge up to 12 but unfortunately it died. So I am left with a whole series of chargers some will only charge pairs of cells, some are mains powered, some are USB powered and in the main I have no idea if designed for NiCad or NiMH.

Some have a time out, some have temperature sensors, and in the main instructions have long gone.

Cells at least do say if NiCad or NiMH and have some mAh rating but even the NiMH vary from 800 mAh to 2500 mAh, but since no idea what size the charger is designed for how can one be sure the batteries are charged, but not over charged?

I tend to use the finger test if warm I assume charged if electrical energy is being transferred into chemical energy no heat but once charged the electrical energy is being transferred into heat one charger I have the instructions for does say it will switch off when temperature reaches 65°C or charging time has elapsed but that time varies with capacity of cell from 12½ hours for a 2600 mAh to 6¼ hours for a 1300 mAh as to 800 mAh not even listed.

It was after coming to use the Philips SCB5050NB I decided to ask the question how can one work out what type of charger and what needs to be done to ensure fully charged cells without damaging them by over charging?

The charger is USB and fit one pair of batteries, and red charge lamp comes on. Put in a second set and lights go off, swap the USB lead from one powered USB hub to another powered USB hub or Lap top and lights work with two pairs of batteries. Clearly the one hub can't supply enough power, but raises the question how do you know if charge completed or hub overloaded? Charger says Input DC 5.0V 500 mA which in theroy should allow it to work in any USB powered hub but not it practice.

Main use of cells is to power my photography flash guns, so I want to go out with a couple of sets for each flash gun so need 8 cells 4 in use and 4 spare. The 800 mAh I have found useless around 6 flashes a pair, but the 2500 mAh will last more like a 100 flashes not 20 as one would expect being just 3 times larger. But they have to be fully charged.

I am sure I am not the only one to use AA Cells, unlike lead acid volts don't help. But my camera also uses NiMH and has an indicator to say how much charge is left, as does many items that use NiMH so there must be a way to work out state of charge, but how?

 

[JohnD]

I find the lithium cells are fantastic for heavy loads like flashguns and cameras, and they also last for many years in low-drain things. The voltage is a bit high though, 1.8v IIRC

I have a little battery voltage-test meter which is adequate for detecting cells in low state of charge, though it does not test them under load. I use rechargeables in portable radios, so soon spot the ones nearing end of life, as they soon go flat.

Maplins have a multi-charger which is supposed to be suitable for all popular types. I don't know how (if?) it can decide which charging regime to use.

 

[Jackrae]

I have a Technoline BC700 which is an "intelligent" charger capable of charging, cycle-charging and discharging of AAA and AA cells. It can recondition cells by repeated charging and discharging cells until their optimum capacity is achieved.

 

[endecotp]

Some of the best battery info I have found:

http://www.powerstream.com/tech.html

I suspect that even the smartest of chargers don't know the capacity of the battery they are charging, and make some non-ideal assumptions as a result.

 

[^woody^]

Have a look at the BL-700 or BC-700 chargers. They do delta-v intelligent charging at various rates, and have test, refresh, capacity measurement and cell matching functions.

I've more or less standardised on eneloop type, low discharge units now. Mainly Tronic brand from Lidl, which are 2400 mAh and as good as eneloop pro units. They will tend to be at more or less full capacity if left unused for a few months, so no worries of taking out drained batteries. Then a charge after each use before putting them away.

 

[ericmark]

I am now also using Tronic form Lidi rated 2500 mAh which does point out part of the problem even same make from same shop they have moved from 2400 to 2500 mAh. My Minwa Electronics battery charger picked up at a radio rally was ΔV and had red (on full charge) green (on trickle charge) and yellow (on discharge) (although not required with NiMH only old NiCad needed the discharge option) for each of the 12 bays (10 for AA cells) however it failed and I have not found a replacement at reasonable price.

Charge current of 250 mA for AA seems standard for most good safe battery chargers using ΔV but there are models with 850 mA charge rate. 16 hours time out at 250 mA = 4000 mAh input even with losses this should fully charge a cell but some time out much earlier and at 8 hours or 2000 mAh clearly it can't fully charge a 2500 mAh cell.

I tend to look for pre-charged batteries read for use as in the main these do hold their charge. I avoid distance buying where possible but finding battery chargers which actually say how they control the charge rate seem to be hard. One has to read through the users manual to find out how they work.

But as long as the cell is flat before putting on charge it's not a problem with any charger but return from taking photos and I have not counted how many flashes and have simply no idea how much power is left. The camera can give a battery level reading so there must be a way but how the voltage is rather static from full to empty unless a suppressed zero volt meter is used. So is that the method of testing a NiMH battery/cell?

 

[JohnW2]

The camera can give a battery level reading so there must be a way but how the voltage is rather static from full to empty unless a suppressed zero volt meter is used. So is that the method of testing a NiMH battery/cell?

I presume, but do not know or sure, that all types of battery do show at least some gradual fall in voltage during discharge in the 'plateau' phase of voltage, even if that fall is very small. I would therefore imagine that looking at the voltage can be used as an indicator of the state of charge/discharge (as you say, using the concept of a 'suppressed' zero meter). However, the rate of that fall in voltage (and, indeed, the actual voltage when fully charged) will vary, at least a little, according to the type of battery - so, unless one 'tells it' somehow, I can't see how something like a camera could know what type of battery was in it.

Kind Regards, John

 

[Jackrae]

Some cameras actually have a menu option which requests battery chemistry - presumable for that very purpose. However the slope of some nickel chemistry units is so flat that voltage indication is a poor measure, since individual cells may have slightly differing operating voltages with the same state of charge.

 

[JohnW2]

Some cameras actually have a menu option which requests battery chemistry - presumable for that very purpose. However the slope of some nickel chemistry units is so flat that voltage indication is a poor measure, since individual cells may have slightly differing operating voltages with the same state of charge.

Fair enough - so, as eric has asked, what, if anything, can one use as an index of the state of charge in such batteries? During charging I suppose one can look at battery temperature, but what about during use?

Kind Regards, John

 

[ericmark]

Well with my cameras the batteries have to be NiMH as non made with earlier technology so I suppose it is simply a volt meter with suppressed zero. So I suppose one wants 1.1 to 1.3 volts well to knock off 0.6 volt easy simple silicon diode Zeners seem to start at 2 volt and finish at around 5 volt where they change effect so also name to avalanche diode. Not really looked at Schottky diodes or germanium diodes, but they may work to suppress the zero, but likely it will need an Op-amp to reduce the range of the meter to what is required.

A simple battery tester

goes one decimal place more than my multimeter maybe that is enough? At £3:50 hardly worth making one. I suppose one would have to make ones own chart to show charge remaining by measuring a battery after 1 flash and 10 flashes then 20 flashes and so on until it fails.

I had hoped for a easy way I suspect the fail point will vary as to the mAh rating of the battery?

 

[Iggifer]

Main use of cells is to power my photography flash guns, so I want to go out with a couple of sets for each flash gun so need 8 cells 4 in use and 4 spare. The 800 mAh I have found useless around 6 flashes a pair, but the 2500 mAh will last more like a 100 flashes not 20 as one would expect being just 3 times larger. But they have to be fully charged

Eric, what flashgun are you using to get such awful battery performance? With my Nikon SB-400 I get literally hundreds of flashes from two AA's before I even have to think about changing the batteries.

It's not the best or biggest flashgun in the world, but it's already overpowered for my use but does let you do cool stuff like this

 

[JohnW2]

Well with my cameras the batteries have to be NiMH as non made with earlier technology so I suppose it is simply a volt meter with suppressed zero. So I suppose one wants 1.1 to 1.3 volts well to knock off 0.6 volt easy simple silicon diode Zeners seem to start at 2 volt and finish at around 5 volt where they change effect so also name to avalanche diode. Not really looked at Schottky diodes or germanium diodes, but they may work to suppress the zero, but likely it will need an Op-amp to reduce the range of the meter to what is required.

I'm sure you could do it with a combination of silicon and germanium (or Schottky) diodes, but I don't really see the need to 'suppress the zero' electronically at all. With a standard digital multimeter one could simply subtract whatever figure one wished, either 'mentally/manually' or, if one was designing a custom device, digitally.

It was different in the days of analogue meters because unless one used 'electronic' modification of the 'zero', one would not have been able to get the required degree of precision of measurements over the (small) voltage range of interest.

Kind Regards, John

 

[ericmark]

I will need to buy one of those battery testers as my meter only has one decimal place. As to Flash gun it's a Vivitar Zoom Thyristor 3500 rather old bought around 1985 it was at the time one of the few which could use re-chargeable batteries. I also use a Prinz Jupiter 177 but can't use this on the camera hot shoe as voltage is too high over 100 volts on hot shoe but that 100 volts does mean it will work with a Nissin slave unit so I can use both flash guns together.

The Zoom on the Vivitar means camera set to 800 ISO (still says ASA on flash gun) and f5.6 I can take pictures 50 feet away handy with a 400 mm lens as can't even focus at less than 8 foot. Using both flash guns I have taken pictures of a water fall at night freezing the motion very well.

Today using the Nikon D7000 rather than Pentax D10 which has a more modern sensor I can get away with a lot less light. The old Pentax will only go to 1600 ISO where the Nikon is really something silly I was able with a 18 ~ 270 zoom lens to take photos of my granddaughter at the international eisteddfod from the back seats without any flash gun in fact flash photography is banned.

Today with really high ISO the flash is used in the main to black out the back ground. The add for Nikon SB-400 does say 60 foot but does not give at what f-stop or zoom setting. It is clearly a lot newer technology and in real terms today there is no point in have a weak flash gun as that is already built into the camera.

As with many flash guns mine has a sensor to read the reflected light so used in a confined space it cuts short the flash duration it can be from 1/2000 second to 1/20,000 second clearly at latter the batteries will last 10 times as long.

Odd but slave flash will not work with built in camera flash it would seem even with red eye turned off it gives a short pre-flash which sets off the slave too early. So to use slave I have to use hot shoe flash gun.

But there is nothing as annoying as walking 10 miles to take photos only to find one has discharged batteries. Well there is and that's when you find the spare one is also discharged.

 

[Iggifer]

Today with really high ISO the flash is used in the main to black out the back ground. The add for Nikon SB-400 does say 60 foot but does not give at what f-stop or zoom setting. It is clearly a lot newer technology and in real terms today there is no point in have a weak flash gun as that is already built into the camera

I use mine generally under 60ft, I can't really ever see needing to use it for anything longer than that. In reasonably close quarters it produces decent results at ISO100 and an F stop of something like 12, generally on my 50mm prime, but also 17-70 I have no issues. This is in lighting levels I couldn't shoot in at 1.8/1600 so that gives you some indication of the light. The recharge on the capacitors is pretty quick, and the flash bulb itself is about 10x the size of the one built in to my D200. Time to upgrade I think Eric!