Reverse polarity protection.

[ericmark]

It is common for a battery charger to have a relay which has to be energised by the battery so if connected wrong way around not damage will be done. Easy to get two clips mixed up.

However I have two battery chargers for my Nikon camera, neither original, one from car cig lighter the other from USB the latter will charge two batteries at the same time. When transferring pictures I did not switch off camera at end of transfer so the battery was run completely out.

On putting the battery on charge, nothing, no green or red LED but putting the other battery in the charger showed charger OK. So put the suspect battery in the car powered battery charger, then transferred back to USB charger and it charged OK.

It seems it the battery was simply too discharged to charge up again. But why, the battery can’t be connected wrong way around, just not physically possible.

 

[Jackrae]

Some "intelligent" chargers will not charge a battery if it is over-discharged. This to protect against a faulty battery. Over-discharging NiMh or similar drastically reduces their life.

 

[securespark]

From memory, CTek intelligent chargers need 2V in the battery to work.

I remember heating my car battery up with a hairdrier to increase the voltage from 1.6 - 2.1V to get the charger to work.

 

[stillp]

Chargers usually need to see some voltage before the output turns on. This means that the terminals of the charger are not live when no battery is present, so there is no risk of shorting the terminals together.

 

[ericmark]

Some "intelligent" chargers will not charge a battery if it is over-discharged. This to protect against a faulty battery. Over-discharging NiMh or similar drastically reduces their life.

I was surprised that the Nikon D7000 DSLR camera which is not cheap would actually over discharge the battery. Poor design for camera, however your point about faulty battery is good, we hear all too often how NiMh batteries have burst into flames, for Dell computers, to BOAC planes, to Samsung mobile phones, it seems it is a very real problem.

For the battery in question you can't touch terminals on battery or charger or fit wrong way around. You drop the battery into one of the charging holes LED goes red, and when charged goes to green. The one used in car was originally mains powered, but the mains bit went faulty, but the mains bit unplugs and there was a cigarette lighter adaptor which still works, which was lucky as I was able to charge the battery enough so it then worked with the USB charger.

The battery is a Nikon EN-EL15 7 volt 1900 mAh 14 Wh but the charger is not a Nikon charger. It suits me to charge from a USB supply rather than the mains. I never got the official Nikon charger. The charger rated input 5 volt 2000 mA DC max and output 8.4 volt DC at 800 mA with one battery and 600 mA each with two batteries. So it will take up to 4 hours to recharge battery. But since a camera the likely use is after being out for day want to recharge over night for next day, and charging both batteries together means no getting up in middle of night to swap them.

I know with Nickel iron batteries they should be stored discharged opposite to lead acid, with the NiCad battery there was a problem with crystal growth if charged the crystal is zapped as it starts to grow, but if discharged the crystal stops you being able to charge the cell, so as new they were supplies discharged, but once used they should be kept with a least some charge in them. I do not know if NiMh batteries have crystal growth problems, but as new many are supplied discharged, which is a problem if the charger needs a small voltage to start them charging.

The CTek intelligent chargers are designed for lead acid so there is no problem expecting the battery to have some voltage, however other than with a battery rather than a cell over discharge causing reverse charging of a cell in a battery which is clearly going to cause damage, I do not think there is any need to limit how low a NiMh battery is discharged. With lead acid it depends on the design of the battery, traction batteries can be discharged much lower than starting batteries as used in cars.

 

[Jackrae]

Not many traction batteries used in cameras

 

[JohnD]

Not many

One should be enough.

 

[ericmark]

As far as I am aware lead acid is not used with cameras, however the thread got expended with the CTek intelligent charger which is designed for lead acid.

The valve regulated lead acid is used in portable equipment and so one could use on to power the lighting used with cameras, they are very like the traction battery in that it has a long use then long charge, they are used in mobility scooters, wheel chairs, and stair lifts.

But as far as a NiMh go although there is a reason not to fully discharge a battery, there is no reason why a cell should not be fully discharged. So why have a charger that will not recharge a cell or battery from fully discharged as long as it can't be inserted wrong way around?