NIMH issues

HELP from over in rec.photo.digital

The new digital cameras are power hogs ! Industrys solution is the nimh battery. PROBLEM; Camera user manuals "promise" 150 > 200 pics per fully-charged battery set. ( 2 X AA cells )

Many of us are seeing 40 > 50 pics before the camera shuts down saying "battery discharged"

A trypical ( Energizer ) charger says; "Let batterys charge 8 hours"

QUESTION; a. How do we know the batterys are "fully charged" ?

b. When the camera says "not enough power", How can we verify this ?

I've put my trusty SIMPSON meter on a fully charged nimh battery. It reads 1.3 volts, and about 2.1a using the 10 amps setting.

??

Reply to
Anonymous
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Manufacturers lie. You might be using the camera is such a way as to minimize the battery life (like keeping the backlit LCD screen on)

You should be using at least 1800 Milli Ampere Hour NMH batteries, or

2200 if you can find them. The mah is the capacity rating of the battery. They aren't designed to put out two amps for an hour, but a few hundred milliamps at any one time over the course of a longer time. (1800 mah might put out 100 milliamps for 18 hours, and 200 milliamps for 6 hours . . . higher current discharge means less total capacity, as a rule)

Bigger (larger mah) cells take longer to charge. I leave mine on 24 hrs with a cheap charger. I have a Rayovac charger that costs a little more that gives an indication when each battery reaches full charge and shuts down. Unfortunately I don't see any model number on it. Does 1-4 AA or AAA batteries and does NMH NiCAD or rechargeable alkaline's. It will take about 8+ hours to charge a set of AA 1800's.

Most of the cameras do use some power when shut off, so it may help to remove the batteries (if that's practical) when not in use.]

Don't measure the amps the battery can deliver into your meter. It isn't good for the meter, it is very bad for the battery, and it doesn't prove anything.

Batteries discharge even if you don't use them. In a week they lose a significant amount of charge if stored at room temperature. Colder is better to prevent self-discharge.

You can't expect to get hundreds of shots over the course of a month on a fully charged battery of any size. You might be able to do it if the battery has just been charged and you use it without using the LCD screen, or flash.

If the camera is one of the super inexpensive ones - - they sometimes use a type of memory that eats power as long as pictures are being stored. Flash memory cards don't require power, dynamic memory does. The dynamic memory is usually wired in and not on a card that can be removed.

Most or Many cameras do a little initialization routine every time you power them up - that power up cycle costs some energy, so you might get more pictures in one go, than you would if turning the camera on and off a lot. Same thing with removing batteries - the owners manual should tell you if you should remove them and over what time period it makes better sense to remove them.

Batteries do die - their capacity slowly drops over time. When they say up to 1,000 cycles, they generally don't mean you might actually get 1,000 cycles or that you will get a full 1800 mah after a twenty or thirty cycles . . . battery quality does matter.

Carry a few extra batteries with you . . . its cheap insurance.

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Reply to
default

Based on a fully charged, at least close to new NiMh, of a specified minimum capacity when new..that are given ample time to recover between cycles and are used at the recommended temperature. One certainly should get, in normal use,. close to what the manual says.

Then the cells are not charged correctly, old or were not used for awhile so need to be exercised or "broken in" with a few full cycles..

That seems to be a timed charger so it is designed for a specific cell capacity. Higher capacity cells may not be charged correctly.

For individual cells out of a collection,-- by discharging them into a known load -- there is no other simple way. Experience, knowing the cell age and type etc., , and simple measurements as you gave can give ballpark ideas only of the charge end points i.e., discharged-no capacity. or seems close to a full charge right now (but capacity is still unknown)..

There is nothing to verify except possibly a weak cell in a pair. A camera draws what it draws and each has different requirements so those same cells could well work in another camera and very likely will still give many hours of power in a radio etc. with the lower current needs..

Only assuming it's fully charged?

Several hours after fully charging and cooling, an unloaded good NiMh will settle around there but that voltage does not mean too much. A weak low capacity (aged) cell or one with high self discharge will measure about the same initially.

A 10A range usually has about a 0.1 ohm shunt resistance. A good

2500mAh AA has about 30-40 milliohms internal reistance when fully charged so that 2A reading indicates an old cell (the internal resistance goes way up)., Even an undercharged good cell should do better than 2As momentarily.. Don't forget it could still be quite useful for low current draw devices. A camera needs a couple amps pulsed at the beginning of each cycle. The very detailed battery and charger links below may be useful but the variation between branded cells of a given nominal capacity, and good chargers isn't going to be all that wide.

The importanr thing is use brand cells and chargers designed for that capacity. And, try to use 2-6 hour smart chargers as their lower cell heating will give longer cell life and generally more accurate full charges . batteries:

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chargers:
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As posted already, NiMh have self discharge but current branded cells these days are very good. One month after charging should still give a lot of capacity if kept cool to room temp.

Cycle life varies by manufacturer but 60 to 80 % of original nominal capacity is the range used to determine that. More than

300 cycles for 80 % is a conservative figure and I would expect at least 500 cycles nowadays with branded cells. After that the internal resistance starts to increase so some cameras could be problematic but the cells can still be used elsewhere.
Reply to
H. Dziardziel

Or it may depend on the batteries itself. Some electronic devices may have been measured with super high capacity battery or even their propierty battery.

One example, I have Cybershot P100 that uses propierty battery. Fully charged it claims 200 minutes of power on time and I've already taken nearly 500 pictures with about 80% flash use rate and the battery still shows about 125 minutes left. That's off only one full charge and has never been recharged yet.

Mileage does vary depending on the type and brand of batteries used, quality of 3rd party batteries, and the claimed rating on the batteries.

Another factor: some cheap batteries will rarely measure up if at all to decent ones because the cheap one may actually be smaller batteries inside large case. I have seen size D cells that only offers 1500 mA and if I were to take that apart, I bet I'll find a standard AA cell inside D shell.

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Reply to
Impmon

yeah, I've seen those too, with nicad C size in them. A good nmh D will have 5+ amp hours of capacity, and cost a small fortune.

My best batteries are Sanyo and Yusa brand and I've never been able to squeak by the 40 shots my old HP camera was supposed to get. Considering I had to pay twice what walmart gets for their Energizers for slightly better quality - spare batteries are the better bargain in my opinion.

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Reply to
default

I'm using 2400mAH Vapextech NIMHs I bought on eBay for cheap and have had great results. I have to charge them up before using them because they can sit around for as much as 2 or 3 months between holidays. I've also seen tourists in Hawaii using large shoulder carried battery packs to run their cameras. Richard

Reply to
spudnuty

Depends on the design of the charger. NiMH cells exhibit a characteristic "bump" in the voltage when they are full after which the voltage actually goes down slightly. Many chargers look for this bump or the negative slope or the change in the slope. See diagram at..

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Logic devices (including those used in cameras) need a minimium votlate to work. The camera manufacturer will know what that is and design in a citcuit to detect when the battery voltage falls below this level. It's not quite that simple in practice but that's the idea. You can't just measure the voltage of the battery because batteries "recover" when the load is removed. You have to measure them on load. A NiMH cell is generally considered empty when the voltage on-load falls below about 0.9V per cell but remember the camera might need 1V per cell.

Cell voltage is NOT a good indication of charge state because the curve is very flat. See this article...

App Note 121: Inaccuracies of Estimating Remaining Cell Capacity with Voltage Measurements Alone

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Quote.. Data is provided that demonstrates the high degree of error introduced when implementing voltage measurement as a fuel gauge method when the battery is subjected to real world conditions of varying temperatures and discharge rates. End Quote.

This is one reason why some battery meters are very inaccurate or next to usless particularly as cells age.

Reply to
CWatters

200 pics was probably done in low resolution mode without using the flash

Solution carry spare batteries in the camera case.

Get a better charger. ideally one that you can run in your car and that charges in fewer hours, tyhe one here claims to be able to charge

1800ma NIMH cells in 3 hours.

my charger has a red light that goes green.

ask it again. :)

load the cell with say a 3.3 ohm 1/2 watt resistor and measure the voltage. or yse one of those testing strips energiser was giving away with their batteries a few years back (last time I bought energisers)

prolly not real good for the battery doing that.

Bye. Jasen

Reply to
Jasen Betts

You can get 2300, 2500 and 2700mAH AA cells now.

Reply to
CWatters

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