BU-407: Charging Nickel-cadmium

NOTE: For NiMH batteries, please read our Charging Nickel-metal-hydride article.

Battery manufacturers recommend that new batteries be slow-charged for 16 to 24 hours before use. A slow charge brings all cells in a battery pack to an equal charge level. This is important because each cell within the nickel-cadmium battery may have self-discharged at its own rate. Furthermore, during long storage the electrolyte tends to gravitate to the bottom of the cell and the initial trickle charge helps redistribute the electrolyte to eliminate dry spots on the separator.

Battery manufacturers do not fully format the batteries before shipment. The cells reach optimal performance after priming that involves several charge/discharge cycles. This is part of normal use and can also be done with a battery analyzer. Early readings are often inconsistent and a battery may require 50–100 charge/discharge cycles to reach the best formation. Quality cells are known to perform to full specifications after only 5–7 cycles. Peak capacity occurs between 100–300 cycles, after which the performance starts to drop gradually.

Most rechargeable cells include a safety vent that releases excess pressure if incorrectly charged. The vent on a NiCd cell opens at 1,000–1,400kPa (150–200psi). Pressure release through a re-sealable vent causes no damage; however, with each venting, some electrolyte escapes and the seal may begin leaking. The formation of a white powder at the vent opening makes this visible, and multiple venting will eventually result in a dry-out condition. A battery should never be stressed to the point of venting.

Full-charge Detection by Temperature

Full-charge detection of sealed nickel-based batteries is more complex than that of lead acid and lithium-ion. Low-cost chargers often use temperature sensing to end the fast-charge, but this can be inaccurate. The core of a cell is several degrees warmer than the skin where the temperature is measured, and the delay that occurs causes over-charge. Charger manufacturers use 50°C (122°F) as temperature cut-off. Although any prolonged temperature above 45°C (113°F) is harmful to the battery, a brief overshoot is acceptable as long as the battery temperature will drop quickly when the “ready” light appears.

With microprocessors, advanced chargers no longer rely on a fixed temperature threshold, but sense the rate of temperature increase over time, also known as delta Temperature over delta time, or dT/dt. Rather than waiting for an absolute temperature to occur, this method uses the rapid temperature increase towards the end of charge to trigger the “ready” light. The delta Temperature method keeps the battery cooler than a fixed temperature cut-off, but the cells need to charge reasonably fast to trigger the temperature rise. Charge termination occurs when the temperature rises 1°C (1.8°F) per minute. If the battery cannot achieve the pace of temperature rise, an absolute temperature cut-off set to 60°C (140°F) terminates the charge.

Chargers relying on temperature inflict harmful overcharges when a fully charged battery is removed and reinserted. This is the case with chargers in vehicles and desktop stations where a two-way radio is being removed with each use. Every reconnection initiates a fast-charge cycle that raises the battery temperature to the triggering point again. Li‑ion systems have an advantage in that state-of-charge is being detected by voltage. Reinserting a fully charged Li-ion battery pushes the voltage to the full-charge threshold, and the charger turns off shortly without needing to create a temperature signature.

Full-charge Detection by Voltage Signature

Advanced chargers terminate charge when a defined voltage signature occurs. This provides more precise full-charge detection of nickel-based batteries than temperature-based methods. Monitoring time and voltage, a microcontroller in the charger looks for a voltage drop that occurs when the battery has reached full charge. This method is called negative delta V (NDV).

NDV is the recommended full-charge detection for “open-lead” nickel-based chargers. “Open-lead” refers to batteries that have no thermistor. NDV offers a quick response time and works well with a partially or fully charged battery. When inserting a fully charged battery, the terminal voltage rises quickly, and then drops sharply to trigger the ready state. The charge in this case lasts only a few minutes and the cells remain cool. NiCd chargers based on the NDV full-charge detection typically respond to a voltage drop of 10mV per cell.

To obtain voltage drop of 10mV per cell, the charge rate must be 0.5C and higher. Slower charging produces a less defined voltage drop and this becomes difficult to measure, especially if the cells are mismatched. In this case, each cell in a mismatched pack reaches the full charge at a different time and the voltage curve flattens out.

Failing to achieve a sufficient negative slope would allow the fast charge to continue. To prevent this, most chargers combine NDV with a voltage plateau detector that terminates the charge when the voltage remains in a steady state for a given time. For additional safety, most advanced chargers also include delta temperature, absolute temperature and a time-out timer.

NDV works best with fast charging. A fast charge also improves charge efficiency. At a 1C charge rate, the charge efficiency of a standard NiCd is 91 percent, and the charge time is about an hour (66 minutes at an assumed charge efficiency of 91 percent). A battery that is partially charged or has reduced capacity due to age will have a shorter charge time because there is less to fill. In comparison, the efficiency on a slow charger drops to 71 percent. At a charge rate of 0.1C, the charge time is about 14 hours.

During the first 70 percent of charge, the efficiency of a NiCd is close to 100 percent; the battery absorbs almost all energy and the pack remains cool. NiCd batteries designed for fast charging can be charged with currents that are several times the C-rating without much heat buildup. Ultra-fast chargers use this quality and charge to 70 percent in minutes. Read more about Ultra-fast Chargers. The full charge must be done with a reduced current.

Figure 1 illustrates the relationship of cell voltage, pressure and temperature of a charging NiCd. We observe an almost perfect charge behavior up to about 70 percent, after which the battery loses the ability to accept charge. The cells begin to generate gases, the pressure rises and the temperature increases rapidly. One can appreciate the importance of accurate full-charge detection to terminate the fast charge before damaging overcharge occurs. In an attempt to gain a few extra capacity points, however, some chargers allow a limited amount of overcharge.

Charge characteristics of a NiCd cell

 

 

Figure 1: Charge characteristics of a NiCd cell

NiMH batteries exhibits similar characteristics to NiCd.

 

Courtesy of Cadex

Ultra-high-capacity NiCd batteries tend to heat up more than standard NiCds when charging at 1C and higher, and this is partly due to the higher internal resistance. Applying a high current at the initial charge and then tapering to a lower rate as the charge acceptance decreases achieves good results with all nickel-based batteries. This moderates excess temperature rise while assuring fully charged batteries.

Interspersing discharge pulses between charge pulses is known to improve charge acceptance of nickel-based batteries. Commonly referred to as a “burp” or “reverseload” charge, this method assists in the recombination of gases generated during charge. The result is a cooler and more effective charge than with conventional DC chargers. There is also the believed benefit of reduced “memory” effect, as the battery is being exercised while charging with pulses. Read about Memory: Myth or Fact? While pulse charging may be valuable for NiCd and NiMH batteries, this type of charge does not apply to lead- and lithium-based systems. These batteries work best with a pure DC charge voltage.

After full charge, the NiCd battery receives a trickle charge of between 0.05C and 0.1C to compensate for the self-discharge. To reduce possible overcharge, charger designers aim for the lowest possible trickle charge current. Even though the trickle charge is carefully measured, it is best not to leave nickel-based batteries in a charger for more than a few days. Remove them and recharge before use.

Charging Flooded Nickel-cadmium Batteries

The flooded NiCd is charged with a constant voltage to about 1.55V/cell. The current is then reduced to 0.1C-rate and the charge continues until 1.55V/cell is reached again. At this point, a trickle charge is applied and the voltage is allowed to float freely. Higher charge voltages are possible but this generates excess gas and causes rapid water depletion.

Comments

On November 22, 2010 at 6:46am
General manager wrote:

Looking for best charger for aa and aaa rechargeble batteries for electronoc locks , Tv remote etc for commercial use and green enegy concepts

On December 6, 2010 at 1:04pm
Harry Spaeth wrote:

For use in a Roland FR-3x electronic accordion, I will need 10 AA type Ni-MH 2000mAh recargeable batteries and a charger for them since they provide only 3 - 5 hours of use per charge.  What is the best of each recommended.  Thanks.

On January 9, 2011 at 8:19pm
Pamela A. Davis wrote:

I need a battery charger for a 7.4V; 2150mAh Ni-MH battery module (used in the Kodak DSC 520 digital camera).

On January 28, 2011 at 8:26pm
H Cohen wrote:

I need either a charger or an adapter for a 18volt NI CAD power tool battery.. I don’t know the brand..I have a set of tools labeled “power to go” with 2 batteries..I do have a Dewalt charger ,so if I can get an adapter to work,that would do it also…The closest battery I’ve seen is one Northern tool sells,that they say is for model # 150785 and # 143396..also no brand given…can you help..

On February 6, 2011 at 6:37pm
Jpette wrote:

About charging Ni-Mh

About this:
“It is difficult, if not impossible, to slow-charge a nickel-metal-hydride. At a C?rate of 0.1-0.3C, the voltage and temperature profiles fail to exhibit defined characteristics to measure the full charge state accurately and the charger must rely on a timer. Harmful overcharge can occur if a partially or fully charged battery is charged with a fixed timer.”

It’s true and false.
I explain.
The result is with the quality of D/A and noise etc…of electronics quality of thes converter
and his algorithms detections.
One good example:
With one Maha C9000 (detect A/N) poor, absolutly ok with you, never use charging less to 0.3C if you want make this, (< 0.3C), this charger “not see” the delta Peak. 

Now you get one BC 700 (Named also RS 700 or Ipc 1L etc), the concerter is fantastic,
here you can catging in less to 0.1C, and the detect of delta Peak is very good.
example: possible without problems charge of 2700mA/H with current of 200mA, and delta peak detection is Good.

and many many examples about this case.
All us in 2 objets: One The quality of converter A/D, and the algorithms for detects the good D Peak.

Best regards

On March 1, 2011 at 12:50pm
Big Kev wrote:

I have a battery charger with a ‘discharge’ button , the instructions though are a bit sketchy! The model no is ‘BC!HU’ and it was sold by 7dayshop here in the UK for about £15 and was advertised as a ‘Smart charger’
What is considered the best practice with regard to ‘discharging’? , pro’s and cons , how often etc , etc.
I’m particularly interested in using Nickel-metal-Hydride batteries with this unit since my wireless keyboard/mouse combo use them!
Many thanks for any advice.

On March 1, 2011 at 1:33pm
Jpette wrote:

@Big Kev
Yes you found this model (BC-700 or RS-700) without problems in UK.
The discharge mode is ine real dischage mode (The processor check in real time slot by slot the state od tension (V) of Ni-Cd or Ni-Mh every 2 sec (average)
In discharge mode, if the Volt is minus of 0.90v, this charger stop the dischange and go
i, mode “charging”....and wait found (emply accus) delta peak.
There are so one security timer (after total cussent sent is more 3700 mA/h, it stop chargin mode), but never fault found (and i have 2 x 100 AA & AAA), old years (some sanyo NI-CD 600mA Yellow), or young (eneloop)

The only default of this charger is:
No respect with new accus (FAD) of trickle current (Many others so..)
For example in charging mode (and current set to 200mA), if you charging one with capacity of 1000mA/h, the tricke current is really average 15mA, it’s many.
The good current “tricke” is average C/300, example for one 1000mA/h it’s 3.3mA
I see this after long time, and it’s verify by this here:
http://www1.duracell.com/oem/rechargeable/Nickel/methods.asp
and this “Apply a maintenance charge of indefinite duration at C/300 rate”

Many chargers no respect this….and all people think’s with Ni-Mh a&fter; C/10 non charging element, it’s false…i think if < to C/100 you continue charging (and create memory effect)

After same with GOOD converter AN/DA, charging in C/10 is no problem with detect Delta peak…But ONLY with GOOD detect, if you use charger with one “AN/DA” edge, nerver charging one ni-mh with c/10, the Delta peak is no see, and you can “kill” the charger or the accus (ex never charging ni-mh with one C-9000 with charging current < a t C/3)

The secret of state of your accus (ni-mh & ni-cd), the quality of charger.

Best regards and excuse my very bad english,
and many thank’s so at this wonderfull website.
Jpette

On March 8, 2011 at 11:49am
Brandon wrote:

This article has been updated as of March 8, 2011 with new information.

On March 14, 2011 at 2:05am
Manjunath Varadaraj wrote:

3 batteries in a set of 20 batteries has failed. They are all are in parallel connection connected to a online UPS. the 3 defective batteries shows low voltage (also it is blotted/buldged on sides). My battery supplier is saying all the 20 batteries have to be replaced instead of replaceing only 3 defective batteries. kindly advise.
All the batteries are more then 2 year old and is presently giving a backup of
approximately 3hrs on full load (5kva). (I haven’t checked exactly since the power failure happens only for 1hr during working hours)

On May 7, 2011 at 8:57pm
Robert Hsu wrote:

Will appreciate receiving info how to maintain Ryobi 9.6V NiCd battery to deliver 800 to 1000 charge/discharge cycles using Ryobi charger.  Are there any more sophisticate charger that will prevent Ryobi 9.6V NiCd battery from over-charging?

On July 14, 2011 at 7:00pm
James L. McCann wrote:

Can you charge the ni-cd batteries with a ni-mh charger?

On July 20, 2011 at 1:02pm
pauline tesnow wrote:

I NEED A CHARGER FOR A HUMMER@H2 IT USES A 9.6V RECHARGEABLENICD BATTERY

On July 20, 2011 at 3:19pm
Jpette wrote:

“James L. McCann wrote:

Can you charge the ni-cd batteries with a ni-mh charger?”
Yes, no problem, you can charging ni-CD Battery With ni-MH Charger.
The Delta Peak of ni-CD is Up to 16mV (easy for detect)

The reverse is not TRUE (FALSE)
The Delta Peak of ni-MH is AVERAGE (Less or More) 5mV, so, charging ni-MH WITH
one ni-CD charger, the ni-CD Charger “not see” the delkta peak because the converter
analog to digital is too “edge”

Excuse my very bad english, but i think you’re understand me
Best regards

On September 9, 2011 at 1:30am
pratik joshi wrote:

can you tell me about similarity between ni-cd and ni-mh charger

On September 9, 2011 at 7:08am
jpette wrote:

I’m not sure understand your question.
With one ni-MH charger, you can charging without problems one battery type Ni-CD.
The reverse is not possible (You cannot charging one Ni-Mh with one charger type ni-CD)

One battery type ni-MH (detect) is some millivolts, and never UP 1,50v for charging by battery.
If you go more (ex: 1.70v) you break the battery (Create Internal Resistance, etc…)

The ni-Cd (After one long storage for example) for 100% FULL, in some case charging with 1,85v (max) for good 100% full, and the delta peak is strong 16mV and it’s easy for charger to detect the delta peak of this battery.

Now you can understand “about similarity between ni-cd and ni-mh charger”

It’s good for explain ?
Excuse my very bad english
Regards,

On October 29, 2011 at 1:35am
srswan85 wrote:

g’day,
      ive just purchesed a nicd 1700ma 7.2v battery and charger backage for my r/c car and i was just wondering if anyone knows how long i should charge hte battery for?
                                      muchly appreciated
                                                          cheers

On November 19, 2011 at 11:17am
mohamed wrote:

how can i calculate the battery efficiency???

On December 25, 2011 at 9:46am
Salmon randa wrote:

I’ve super brain 989 charger
I want to cycle 8 cell of aa nicd battery
What rate recomend for charge (mAh)
What ampere recomend for charge (A)
What rate recomend for discharge (mAh)
What ampere recomend for discharge (A)

 

On June 12, 2012 at 2:38am
Loh Win Hoo wrote:

Dear Sir,

Can i use Nickel Metal Hydride battery charger to charge Nickel Cadmium rechargeable battery?

Thanks & Regards
LOH

On December 9, 2012 at 1:20pm
james edmonds wrote:

i have bought a nickel cadmium maintenance free battery from halfords, if it should need charging in the future bad winters to come.  can i charge it with my existing charger.

On January 17, 2013 at 2:23pm
Mike Cain wrote:

I have a new18V NiCd battery pack, it has 15 1300mAh NiCd batteries wired in a series.  I wanted to trickle charge it to get all the cells to the same charge level.  When I checked the voltage of the wall charger that it came with, it was outputting around 36V.  That seems really high and I can’t find any information on what would the appropriate voltage to be supplied or even if supplying 36V would be bad.  What voltage should I use to charge that battery pack at .1C?  Thanks

On March 1, 2013 at 4:35pm
Leon Follmer wrote:

Good question. I have 3 18 v chargers and their output ranges from 22 to 24 volts.  36 volts seems marginally high, but would work if you disconnect before it gets too hot.  I am trying to find a better answer.  At the moment I am taking 18 v packs apart and finding a few dead cells and many good ones.  I want to find the optimum v for charging the cells. I have found the zapping a cells with 12 v brings them back to life for a while.

On March 1, 2013 at 9:28pm
jpt wrote:

@Leon Follmer:
If i good anwers your question;, you asking how many voltage (v) you must use for best charging, it’s really easy.
If you use the Ni-Cd ou the Ni-Mh v is not equal.
The full charge (v) of Ni-CD is average 1,415v per cell..
The full charge (v) of Ni-MH is average 1,445v per cell (30 mV more)

For example with 10 Cell, if you want fully 10 cell you must have (in Ni-CD).
1,415 x 10 = 14,15 v exactly.
But…. when the cell is 90% Fully there are not current, why ?
I (A) is too edge, exemple two: When the 10 cells are empty the v is 12 V
14,15v - 12v = 2,15v, here the current of charging is high beceause v is many.
When 14,15v = 14,15v = No current.
For fully chargin, just add edge minor v. exemple: 14,15v + 0,3v = v charge is 14,45v
After is delta peak detection technology, use edge more v again 15v
If ONLY linear charge WITHOUT detection D peak use 14,45v average, it’s better

Sorry for my bad english

On March 2, 2013 at 1:36pm
Leon Follmer wrote:

You almost touch on the point, but I’m confused. I want to find the basics.  It takes more than 18 v to charge an 18 volt battery. My chargers put out 22-24 volts.  I assume that is near optimum.  Does this ratio hold for all battery sizes?

I just landed on this site and have not read all the comments yet.  I plan to go through all the info on this site and I figure that my answers are there somewhere.  If you can give me some pointers I would appreciate it.

On March 5, 2013 at 6:43pm
jerry wrote:

Leon,  In order to charge NiMH and NiCD batteries effectively, you need a constant current source, not a voltage source.  When you say your chargers are supplying 22 to 24v, that would be the voltage swing I would expect across a sample of batteries as the charger is supplying constant current at differing voltage rates to account for the variability in batteries.

Once you have a constant current source, you can charge at differing rates from .1C to 1.5C against time for fully discharged batteries without much worry.  The problems start when you attempt to charge by time at constant current batteries with remaining charge.

The only safe and effective way to charge batteries is either 1) by .1C for 15 hours;  or 2) by .5C or higher using a combination of NDV, dTdt, max temp, max voltage, time, etc.  These features are provided by smart IC or microcontroller based chargers attached to a constant current source.

I’ve recently been designing a charger (with the help of those on this board) that is what I consider the ultimate for single cell NiMH or NiCD batteries as I found most of the smart chargers to be lacking.  I am using a combination of microprocessor and computer control to track voltage & temperature curves.  I am amazed how after plotting about 50 such curves how closely the profiles match for good cells.

Feel free to contact me at clist@hanler.com.  The moderator on this forum is very, very, knowledgeable on all these subjects.

Jerry

On March 5, 2013 at 6:49pm
jerry wrote:

To answer your question precisely, the voltage ratio you are seeing of 22/18 to 24/18 is 1.22 to 1.33 which is close but I don’t think you can rely on this for maximum efficiency as my single cells are closer to 1.2 for good, newer cells.  Also batteries with thermistors will charge at higher rates and if you are using leads to connect the batteries they will have a voltage drop as well at high current.

Jerry

On March 7, 2013 at 2:12pm
Leon Follmer wrote:

We are not in phase, no pun intended.  All transformers have an input and output voltage and amperage.  If you measure the voltage at the output clips you get the open circuit emf. On my 18 v chargers I get from 22 to 24 volts. 

I must assume that my charger is a constant voltage output.  So what can I do with it? How can I determine which it is? The discussion above does help me at the stage of a beginner because the discussion has many variables and “code” words which seem ambiguous to me.  Example: how do I achieve 0.1 C?  The concept of C must contain some value for voltage. I assume it is based on the battery.  The discussion above needs examples that show values and calculations, etc.

I did find in a reference that Ni-Cd batteries should be charged at “1.4x the ampere-hours of discharge”.  What does this mean? How do I deconvolute this expression?

On August 13, 2013 at 2:56am
Abdulla wrote:

A 125v transportation ultracap module. Assuming a 2000 kg car deccellerates at a constant rate from 60kph to a stop in 2 seconds. Calculate how much energy could be recovered into this module by the regenerative braking system. Assume the motor/generator is 90% efficient.
hi guys
can u give a hand to solve the problem

On September 21, 2013 at 9:47am
Robert wrote:

I just bought a blow-up bed that has a Ni-Cad battery. The charger they sent plugs into the wall and charges the battery on the pump for the bed. On the charger supplied it reads on it AC/DC adaptor. Class 2 power supply. Input 120v 60 Hz 4.1w Output 7.5V DC 250mA. What I would like is a charger that I could plug into my 12 volt car cigarette lighter and charge the battery’s on the pump. Would you be able to sell me this and if so what is the model #.

On October 11, 2013 at 6:47am
Gizmo wrote:

Hello,
I have a 20-cell 36Ah battery with a problem.
After performing a main charge @ 0,5A for 2 hours, I continue with a final charge of 0,1A for 4 hours. The voltage gradually increases during the main charge, until it reaches 31V (roughly 1,55V/cell) after which I switch to the final charge.
The final charge starts at roughly 30V (the voltage naturally drops a bit when lowering the Amperage), but instead of slowly increasing over the following 4 hours, the voltage actually decreases in those 4 hours, ending at 29V (roughly 1,45V/cell).
I have now done three cycles and it keeps happening. Water level is sufficient, as I have checked during each cycle. I also discovered that it is not just one or a few, but ALL cells that drop in voltage during final charge.
Does anyone have an idea as to why this happens, and what I could possibly do to remedy the situation?

On February 13, 2014 at 1:00pm
Tim Rujera wrote:

I have an Energizer charger that states in its manual to use only Nickel Metal Hydride (NiMH) rechargeable batteries.
Is it possible for me to use the charger for Nickel Cadmium rechargeable batteries?

On May 27, 2014 at 6:18am
paramu wrote:

How much electrolyte liters we need to fill the SBLE 185 Nickel cadmium battery.
I want to know in liters. please advice and let me know.

On June 21, 2014 at 3:47am
Hari Narayan wrote:
On September 12, 2014 at 4:38pm
Donna Davis wrote:

I have several AAA Nic Cad batteries.  Can these be recharged if they do not say rechargeable on them.