Go Back   Steve's Digicams Forums > Digicam Help > Batteries or Power Packs

Reply
 
Thread Tools Search this Thread
Old Aug 3, 2002, 12:41 PM   #1
Junior Member
 
Join Date: Aug 2002
Posts: 5
Default NIMH rechargeables current measuring?

Can we measure the current in NIMH rechargeables batteries?

If they are not fully discharged, should I discharge them first before charging?

I have a Conrad Charge Manager 2000 charger with a little display. With some rechargeables my digital camera displays 'battery low' warning sooner than predicted and I must recharge them. But I don't know how much are they discharged, and therefore I don't know how much should I charge them. For example, after one 1800 mAh cell is charged, the charger displays "Charge Capacity" value of about 500 mA, but is it fully charged? Maybe the battery had a remaining capacity of about 1000 mAh, and the the charger charged it only to 1500 mAh.

I must specify that the charger doesn't display the remaining current in the battery, only the current that itself charged or discharged.
Ilea Cristian is offline   Reply With Quote
Sponsored Links
Old Aug 3, 2002, 12:56 PM   #2
Senior Member
 
Join Date: Jun 2002
Posts: 668
Default

this should answer most of your battery questiones.
Gary

http://thomas-distributing.com/maha-...-batteries.htm
Gary Senkus is offline   Reply With Quote
Old Aug 3, 2002, 11:52 PM   #3
NHL
Senior Member
 
NHL's Avatar
 
Join Date: Jun 2002
Location: 39.18776, -77.311353333333
Posts: 11,547
Default

Ilea Cristian

NiMh charger are usually constant current charge, they detect end of charge usually by a rate of change in temperature of the battery under charge as well as a slight voltage drop at the end...

http://www.stevesforums.com/forum/vi...d=6215#pid6215

The amount of current it put out depends on either it's a slow or fast charger!
NHL is offline   Reply With Quote
Old Aug 4, 2002, 5:05 AM   #4
Junior Member
 
Join Date: Aug 2002
Posts: 5
Default

Ok! Thank you very much, but now I'm a bit more confused about rechargeables and chargers.

I think the time will tell.
Ilea Cristian is offline   Reply With Quote
Old Aug 4, 2002, 9:17 AM   #5
NHL
Senior Member
 
NHL's Avatar
 
Join Date: Jun 2002
Location: 39.18776, -77.311353333333
Posts: 11,547
Default

It sounds like your charger is quite sophisticated. Do you feel the heat from the NiMh cells under charge?

That's how the charger detects when a cell is charged. It put out a high constant current initially until the rate of change in the temperature is too fast, or a slight drop in battery voltage and switch over to the trickle charge (slow, ie much smaller constant current) mode, where you can leave the cells in there for over a year! If you want to be sure, unplug the charger to reset it, and try another charge cycle, but heat detection is the key in all fast chargers! Slow charger doesn't care, just leave them in there overnight or forever...

[Edited on 8-4-2002 by NHL]
NHL is offline   Reply With Quote
Old Aug 7, 2002, 4:33 PM   #6
MK
Member
 
Join Date: Jun 2002
Posts: 57
Default

Do you have the manual to the charger? If not, does the label on the charger say anything about being a 'peak detection' charger?

Almost 100% of the smart chargers out there for rechargeables depend on peak detection method of knowing when the cells are charged. They detect a tiny drop in voltage to stop their charge.

Although temperature plays a role, most chargers rarely have a temp. probe to detect temp. changes.
MK is offline   Reply With Quote
Old Aug 7, 2002, 5:35 PM   #7
NHL
Senior Member
 
NHL's Avatar
 
Join Date: Jun 2002
Location: 39.18776, -77.311353333333
Posts: 11,547
Default

Not all ???

This one: 0deltaV and 0deltaT

... this one: and Delta Temperature

... or this one: Temperature Sensor

... may be this one too: 0deltaV and 0deltaT based detect circuitry

and especially the Quest-2 that come standard with some D7 (ie if you close the lid, the charging time is significantly shorter than when open !!!)

... May be 95%? or may be all the good ones have dT/dt... (BTW they all need temperarture detection may be only just for over temperature protection to prevent a home from catching on fire) or almost every FAST chargers posted over the 1st link: Thomas_Distributing have temperature sensing:

http://thomas-distributing.com/nimh_...y_chargers.htm

[Edited on 8-7-2002 by NHL]

MK

May be what you meant was all the slow chargers, ie several hours or overnighters do not have temperature probe by design, since the amount of current they put out are not large enough to cause the batteries to heat up !!!

[Edited on 8-8-2002 by NHL]
NHL is offline   Reply With Quote
Old Aug 8, 2002, 10:09 AM   #8
MK
Member
 
Join Date: Jun 2002
Posts: 57
Default

Nope, that's not what I meant. The chargers that you mentioned I can count on both hands. Now take a look at the total number of chargers our there and don't restrict yourself to Thomas. Do the math and you'll find that most don't have temp. sensors.

Heat detection is NOT the key in fast chargers as you said. It is the small drop in voltage as the cells peak in charge. It is much more accurate and reliable to measure voltage than heat. Heat detection may be a secondary backup to voltage peak detection but certainly not 'key' as you said.

As for 'all the good ones have dT/dt', not true at all. Take a look at the really really good chargers used for R/C applications. Chargers made by Schulze, Graupner, FMA, Astroflight and a whole bunch of others do not have temperature sensors.

These chargers typically charge nicads at 3C-5C rates, certainly much higher than you would charge digicam batterys. As such, they better know when to stop or there'll be some serious fireworks. They all rely on delta peak sensing.

The chargers that you referred to all mentioned a dT sensor but I dobut that comes into play 99% of the time you are charging unless you have a run away. The only temp. sensors that are effective in battery charging are the ones where you strap the probe directly to the battery. If the sensor is inside the case, there are just too many variables to determine correctly the real temp. of the batteries.

[Edited on 8-8-2002 by MK]
MK is offline   Reply With Quote
Old Aug 8, 2002, 10:32 AM   #9
NHL
Senior Member
 
NHL's Avatar
 
Join Date: Jun 2002
Location: 39.18776, -77.311353333333
Posts: 11,547
Default

MK

Most if not all R/C batteries are NiCad, and they are charged differently than the NiMh used in digicams which are charged with a constant current since the voltage of NiMh drops as the cell warm up so if you rely on peak alone it will falsely undercharge an NiMh (works fine for NiCad)

http://www.gpbatteries.com.hk/catalo..._technical.pdf

Temperature does make a difference:

http://www.stevesforums.com/forum/vi...d.php?tid=1387

[Edited on 8-8-2002 by NHL]
NHL is offline   Reply With Quote
Old Aug 8, 2002, 11:15 AM   #10
MK
Member
 
Join Date: Jun 2002
Posts: 57
Default

Nicads and NiMHs are not charged differently. Both are charged using a constant current. The major differences are that NiMHs have a higher internal resistance than nicads, have no memory (for all practical purposes), have a higher self discharge rate and have a greater power to weight ratio.

The situation has changed in R/C. I would dare to say NiMH has more than 50% of the market now. Take a look at the electric car segment of the market. The race packs that they use are typically 3000 mAh NiMHs. A lot of the e-flight guys use NiMHs to power their planes because you almost get twice as much power with the same weight cost. Same for the radios they use. Tx'es now run twice as long.

As for the heating up thing, nicads also heat up too but not as much since their internal resistance is lower. Voltage does not drop for either types when their temp. goes up. Take a look at the GP link you referred me to. The graph of "Charge Voltage & Temperature of NiMH" does not show this at all. It does not show any voltage drop until the end of the charge cycle where it peaks. As a matter of fact, it shows that at a higher temp. you get higher voltage cells thereby resulting in more power in the cells.

Relying solely on deltaV does not result in false peaking. If that's the case, a lot of chargers will have to be returned to the manufacturers, including the popular Maha C204F, which does not have deltaV sensing. False peaking occurs when the cells are new and haven't been formed yet or the charge rate is not properly set (too low).

BTW, I never said temp. did not make a difference.
MK is offline   Reply With Quote
 
Reply


Thread Tools Search this Thread
Search this Thread:

Advanced Search

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are Off
Refbacks are Off



All times are GMT -5. The time now is 11:18 AM.