Continue to Site

Welcome to our site!

Electro Tech is an online community (with over 170,000 members) who enjoy talking about and building electronic circuits, projects and gadgets. To participate you need to register. Registration is free. Click here to register now.

  • Welcome to our site! Electro Tech is an online community (with over 170,000 members) who enjoy talking about and building electronic circuits, projects and gadgets. To participate you need to register. Registration is free. Click here to register now.

Charger requirements?

Status
Not open for further replies.

Mishael

Member
i have an airsoft battery thats 8.4V 1600 mA. i fried my last battery putting 1.66 amps and 12 volts through it. this time i used a 12 volt charger with 700 mA. it seems i fried this brand new battery too...i need some help. voltages, times, currents, anything. i dont want to keep replacing batteries
 
Im relatively certain NiCd. should have specefied that earlier. i am wrong. they are NiMH
 
A good rule of thumb would be 1.47 Volts * 7 cells = 10.29 Volts.

Charge them with a constant current source at ≈500mA and have whatever regulator you're using shut down when this voltage is reached.

Newer cells can handle a bit higher voltages but that doesn't generally result in more energy being stored in the batteries.

Continuing to charge the cells past about 10.5 Volts is pretty much guaranteed to shorten their life to a few dozen charge cycles.
 
NiMH and NiCd have similar charging requirements.

If you charge quickly, you should keep the current constant, and switch off when the voltage starts to come down after the peak, or when the cell temperature rises by more than about 5 deg C. The voltage should hit about 10.5 V and then start to come down. The cells will start to get hot and be damaged very soon after the peak.

If you charge slowly, you can probably do so without damage if you overcharge, but you should keep the current below 80 mA and it will take up to 20 hours.
 
really? because the charger for the original battery was 12 volts...if it helps, each cell is 1.2 volts
seeing the post above this after saying my line above this,
crap i fried this battery too. fantastic.
 
Last edited:
In addition to Diver300's post you should see a sticker on your battery telling you the type.

Supposedly your battery is an NiMH battery which was killed by heavy overcharging.

An 8.4V NiMH battery should be charged to a maximum of 9.8V (some manufacturers require lower charging voltage)

Using a wallwart for charging you must discharge the battery to minimum voltage and then charge timed not to exceed the maximum allowable charging current over time.

E.g. battery capacity 8.4V/1.600mAh means charging the fully discharged battery at C/10 (160mA) at a maximum charging voltage of 9.8V for 12 hours (pumping 1.920mAh into the battery because of losses)

A more elegant way would be using a MAX712/713 which monitors charging voltage and terminates charging according to the numbers of cells (1 to 16) programmed by jumpers and monitoring charge voltage slope (terminating charging at max voltage using NiCads and using the descending slope for NiMH batteries.)

But first let's see what type of battery you have.


Boncuk
 
NiMH 1600 mAh, 7 cell, 1.2 VDC each cell, 8.4 total, 10C discharge rate, 2/3 A size. the battery was as dead as i could get it using my gun when i stuck it on the charger. the battery seems to still work but it is most likely damaged. if i had a 9 VDC 500 mA makeshift charger which is literally a wall transformer with just leads on the end, (all i have) how long should i leave the battery on the charger for?
 
What chemistry are the batteries?
AirSoft means nothing to me.

Determine what kind of batteries they are, and read the relevant parts of this site:
 
If you charge quickly, you should keep the current constant, and switch off when the voltage starts to come down after the peak, or when the cell temperature rises by more than about 5 deg C.

This is the preferred method that most of the so-called smart chargers use. It is a bit tougher to implement than simply terminating the charge at a specific voltage though. You can do that with a dual op-amp and a pass transistor. A smart charger needs to accurately detect changes of a millivolt or so in the cell voltage over a period of minutes to properly terminate.

1.47 Volts per cell is merely where my Maha C9000 charger/analyzer typically stops charging my Accupower AA's. The 10 year old, practially worn out NiMh cells I had terminated quicker, at about 1.44 Volts per cell. They are why I bought the Maha in the first place. 3 out of the 14 old cells tested bad after ≈200 charge cycles in spite of using a semi-smart charger. The rest were down to just 1100mAh. It charged cells in pairs until they peaked at ≈2.9 volts. The weaker of the two cells ends up getting overcharged in that arrangement.

Same thing happens in all battery packs. The weakest cell or two repeatedly get overcharged until they fail. Once the first cell starts failing to charge, the remaining ones get overcharged until they start falling like dominoes.

really? because the charger for the original battery was 12 volts...if it helps, each cell is 1.2 volts.

Not unusual. It works for a while. If it's 12V and about 100mA, it could work for quite a while if you pay close attention and remove the battery pack after ≈16 hours before it has a chance of being seriously overcharged. On the charger in the morning, off the charger in the evening, no leaving it on the charger for days at a time,....

if i had a 9 VDC 500 mA makeshift charger which is literally a wall transformer with just leads on the end, (all i have) how long should i leave the battery on the charger for?

I'd say about 4 hours. 9V isn't likely to damage the battery. It will just end up half charged.
 
Well now this is different than what I've been instructed to do in the past. is it any different for NiCd?
4 hours at 9VDC and 500 mA, a cooling break (?), and another 4 hours should charge it fully? Given that's its fully discharged
 
Halfway charged was just a shot from the hip. Can't say exactly without examining the wall wart in detail.

9 Volts / 7 cells = 1.28 Volts per cell, not quite enough to put a full charge on a NiMh cell.

It will probably get them up into the 1.10-1.15 Volt range without ruining them though.

If the open circuit output is up close to 10 Volts, it might get a solid 90% charge on them.

Like a mentioned before, I can't say for sure.
 
Status
Not open for further replies.

Latest threads

New Articles From Microcontroller Tips

Back
Top