AA charger questions...

ReP0 · 29th February 2008, 8:00 PM

I'm looking at picking up a charger from dealextreme but want to double check something. The charger in question can be found @ http://www.dealextreme.com/details.dx/sku.6194

Charger has 4 independent channels which is what I want. It also states output is 4V and 2000mA (click on the picture showing the back of the unit). Now my question is if I buy batteries which are rated for 2500mAh will this charger be able to charge these batteries to full capacity?

I guess what the thing I don't understand is what determines in a charger whether a battery is fully charged. I mean I can go from 1800mAh to 2500mAh batteries so what's the crucial bit to look at to know whether a charger will fully charge a NimH battery of a certain capacity?

Finally anyone know what currency Dealextreme are quoting. I assume it's US but if you've bought from them before and can confirm it would be great.

Edit:
Which would you prefer (and why?)
1) http://www.dealextreme.com/details.dx/sku.6152 or
2) http://www.dealextreme.com/details.dx/sku.6194

TIA

MagyaR · 29th February 2008, 8:04 PM

It's USD, I'd get a Maha 800, get a decent charger. Servaas.

ReP0 · 29th February 2008, 8:19 PM

Quote:

Originally Posted by MagyaR

It's USD, I'd get a Maha 800, get a decent charger. Servaas.

It looks impressive but I'm not sure I want to pay that much for a charger though. I'm not convinced that it's worth 4-8x the price of the units I'm looking at.

ReP0 · 1st March 2008, 1:58 PM

So no one has any hints wrt the question posed?

Stinger · 2nd March 2008, 5:17 PM

It should be able to charge your batteries. 2000mA is a charge rate (current) and 2500mAh is the capacity, just means it needs to take longer. Usually end of charge detection is done by voltage dip detection or rate of change of temperature (dT/dt) (or both).

2xCPU · 2nd March 2008, 11:55 PM

Quote:

Originally Posted by ReP0

So no one has any hints wrt the question posed?

To charge a cell, the input voltage must be higher than the cell voltage.
A very crass charger would put (say) 1.6V on your 1.2V cell and tell you to disconnect it after (say) 8 hours.

A more elegant charger could put 4V (current limited) onto the cell. A chip in the charger will monitor the actual terminal voltage and will detect the delta V point indicating the fully charged state has been reached.

2.

dohzer · 3rd March 2008, 12:07 AM

Quote:

Originally Posted by 2xCPU

A more elegant charger could put 4V (current limited) onto the cell. A chip in the charger will monitor the actual terminal voltage and will detect the delta V point indicating the fully charged state has been reached.

How do they monitor the voltage? Do they turn off the source briefly and measure the battery's voltage, or do they measure the current through a known resistance?

newSpeak · 3rd March 2008, 12:36 AM

The battery is charged from a current source. Battery voltage is measured at the terminal under charge. Terminal voltage will gradually ramp up and peak for healthy NiMH/NiCd.

If 4V is the max output it means that the charger will not charge if the terminal voltage rises above 4V.

2xCPU · 3rd March 2008, 12:51 AM

Quote:

Originally Posted by dohzer

Do they turn off the source briefly and measure the battery's voltage,

Yes!
Have a look at the cct diag. on page 7 of this Maxim data sheet.
You can see the voltage sensing taps (VP1-4).
Now have a look at the timing diag on page 11, you can see the charge current is pulsed into each cell providing a "charge" time and a "relax" time to each cell. The description on page 10 puts it better than I can.

2.
Edit:

Quote:

Originally Posted by newSpeak

If 4V is the max output it means that the charger will not charge if the terminal voltage rises above 4V.

If the terminal voltage got to 4V, the charger would detect it as an error condition and shut down that channel.

li21 · 22nd March 2009, 12:05 PM

Any one heard of these?

http://cgi.ebay.com.au/ws/eBayISAPI....m=310129825440

and

http://cgi.ebay.com.au/ws/eBayISAPI....m=280324823502

Like the OP.. I dont want to be paying too much for a charge if the cheaper ones will do the job?

Thoughs?

2xCPU · 22nd March 2009, 1:00 PM

The first only has two LEDs, the second has a [2 - 4] switch.
So it's reasonable that they both charge the cells in pairs.

Your better off looking for a better charger.

2.

li21 · 23rd March 2009, 12:29 AM

Quote:

Originally Posted by 2xCPU

The first only has two LEDs, the second has a [2 - 4] switch.
So it's reasonable that they both charge the cells in pairs.

Your better off looking for a better charger.

2.

Do all chargers have features such as trickly charge, conditioning, discharge etc?

Or only these Maha ones?

2xCPU · 23rd March 2009, 9:00 AM

Quote:

Originally Posted by li21

Do all chargers have features such as trickly charge, conditioning, discharge etc?

Absolutely not.
Some only trickle charge.
Very few discharge or condition.

2.

29th February 2008, 8:00 PM	#1
ReP0 Awaiting Email Confirmation Join Date: Sep 2002 Location: Sydney Posts: 4,259	AA charger questions... I'm looking at picking up a charger from dealextreme but want to double check something. The charger in question can be found @ http://www.dealextreme.com/details.dx/sku.6194 Charger has 4 independent channels which is what I want. It also states output is 4V and 2000mA (click on the picture showing the back of the unit). Now my question is if I buy batteries which are rated for 2500mAh will this charger be able to charge these batteries to full capacity? I guess what the thing I don't understand is what determines in a charger whether a battery is fully charged. I mean I can go from 1800mAh to 2500mAh batteries so what's the crucial bit to look at to know whether a charger will fully charge a NimH battery of a certain capacity? Finally anyone know what currency Dealextreme are quoting. I assume it's US but if you've bought from them before and can confirm it would be great. Edit: Which would you prefer (and why?) 1) http://www.dealextreme.com/details.dx/sku.6152 or 2) http://www.dealextreme.com/details.dx/sku.6194 TIA Last edited by ReP0; 29th February 2008 at 8:11 PM.

2nd March 2008, 5:17 PM	#5
Stinger Member Join Date: Feb 2002 Posts: 265	It should be able to charge your batteries. 2000mA is a charge rate (current) and 2500mAh is the capacity, just means it needs to take longer. Usually end of charge detection is done by voltage dip detection or rate of change of temperature (dT/dt) (or both). Last edited by Stinger; 2nd March 2008 at 5:20 PM.

22nd March 2009, 12:05 PM	#10
li21 Member Join Date: Dec 2001 Location: Sydney Posts: 2,392	Any one heard of these? http://cgi.ebay.com.au/ws/eBayISAPI....m=310129825440 and http://cgi.ebay.com.au/ws/eBayISAPI....m=280324823502 Like the OP.. I dont want to be paying too much for a charge if the cheaper ones will do the job? Thoughs? __________________ Successful Trades: WAY too many to list. Please help save abandoned animals. Adopt a Pet today for life! http://www.saynotoanimalsinpetshops.com http://www.catrescue.com.au/

22nd March 2009, 1:00 PM	#11
2xCPU Member Join Date: Jan 2005 Location: melb Posts: 2,395	The first only has two LEDs, the second has a [2 - 4] switch. So it's reasonable that they both charge the cells in pairs. Your better off looking for a better charger. 2. __________________ If "building a computer" doesn't involve powertools, you're just assembling spare parts. ---- The universe is made up of atoms and empty space, the rest is mere opinion. Democritus, 400 BC.

29th February 2008, 8:04 PM	#2
MagyaR Member Join Date: Jan 2004 Location: Melb Posts: 4,764	It's USD, I'd get a Maha 800, get a decent charger. Servaas.

1st March 2008, 1:58 PM	#4
ReP0 Awaiting Email Confirmation Join Date: Sep 2002 Location: Sydney Posts: 4,259	So no one has any hints wrt the question posed?

3rd March 2008, 12:36 AM	#8
newSpeak Member Join Date: Jun 2005 Posts: 183	The battery is charged from a current source. Battery voltage is measured at the terminal under charge. Terminal voltage will gradually ramp up and peak for healthy NiMH/NiCd. If 4V is the max output it means that the charger will not charge if the terminal voltage rises above 4V.