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Time Calculation for Different Charger

02/04/2011 5:31 PM

I have Battery charger with

Input 120V - 60Hz 80 mA and out put 5.6V 240 mA Time for full charging 14-16 hours

If I change the charger with

Input 100-240V AC 200mA and output 5 V DC 1300 mA

HOW MANY HOURS FOR FULL CHARGE?

What formula I can use?

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Anonymous Poster
#1

Re: Time calculation for different charger

02/04/2011 5:34 PM

How much amperage can the battery withstand before it explodes?

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#3

Re: Time calculation for different charger

02/04/2011 5:51 PM

How can I find it? I will have to open the battery compartment. I presume they are 3 AA Nicad batteries.

I am talking about "Portable Power Source" (Welch allen model # 75200

Thanks for consideration.

Govinda

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#5

Re: Time calculation for different charger

02/04/2011 6:35 PM

I cannot find any specs, anywhere. They do sell plug-in AC adaptors though.

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#6

Re: Time calculation for different charger

02/04/2011 7:04 PM

I talked to Tech. He says it is 3.6 volts DC (also he gave me - max. 6.6 v DC 240 mA. - I do not understand this.)

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#7

Re: Time calculation for different charger

02/04/2011 7:14 PM

That may be what he believes the maximum power input should be. If that's true, you may damage the cells with 1300 mA input. That's 1.3 amps, which is 5 times the current of 240mA.

If you try it, cover the battery with something in case it does explode.

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Anonymous Poster
#12

Re: Time calculation for different charger

02/05/2011 2:13 PM

Batteries are in a case.

I had charged the package, for 6-8 hours; and was working fine. I wanted to learn how to calcualte exact time (IF there is formula) Do you know if there is a formula, to calculate current, Voltage, Ampere and time?.

Hearing your suggestion, shoud I be charging perhaps for 3-4 hours?

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#13

Re: Time calculation for different charger

02/05/2011 2:43 PM

I honestly don't know. Without know a lot more, there's no way to advise you.

You will just have to experiment. One thing for sure, Ni-cad and Nickel metal hydride batteries must be fully discharged and fully recharged each cycle for maximum life.

Good luck.

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#28

Re: Time calculation for different charger

02/07/2011 3:39 PM

Thanks

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Anonymous Poster
#36

Re: Time calculation for different charger

02/08/2011 4:03 PM

In the manual, I found Battery type NiCad voltage capacity 3.6VDC/1.8Ahr.

I also noticed 3 cells, length 1.5" & total width 2.5". Presumably C type!)

Can I charge till it feels little warm; to see CLOSE TO fully charged? After 8 hours it was at room temperature.

Some good learning for me.

Any remarks ...

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#38

Re: Time calculation for different charger

02/09/2011 12:27 AM

So 1/10C would be 180 ma. Probably your existing charger is best.

You could also make up a pack of NiMH, which do fine a 1C charge rate -- i.e., one hour charge. For that you would need a 1800 ma charger.

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#41

Re: Time calculation for different charger

02/09/2011 2:32 PM

I want to know what will happen with

charger with

Input 100-240V AC 200mA and

output 5 V DC 1300 mA

HOW MANY HOURS FOR FULL CHARGE?

What formula I can use?

Can I charge till it feels warm to touch?

3 cells 1.5"X2.5" should be C type?

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#42

Re: Time calculation for different charger

02/09/2011 4:21 PM

What formula I can use?

The rough formula was already explained I think, but in general, the time (T) required to charge a battery is equal to the batteries AH rating (C) divided by the charge current (A).

T= C/A

So, a 10 AH battery takes 10 hours to charge at 1 Amp, 5 hours to charge at 2 amps, etc.

Can I charge till it feels warm to touch?

Generally. But its better to use the correct charger, for many reasons. What happens if you decided to walk away at just the point where the battery is beginning to heat substantially, and it blows up? Near the end of the charge, the voltage must be regulated.

3 cells 1.5"X2.5" should be C type?

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#44

Re: Time calculation for different charger

02/09/2011 6:37 PM

So with battery pack of 1800 mA, and my new charger of 1300 mA out put; it should fully charged in

T=C/A

i.e. 1800 mA (battery)/1.3 (Charger 1300 mA)= 1.3846 hours

It should have been fully charged around 1 h 25 m.

I charged for 3+2+3 = 8 hours feeling for the heat, but batteries were at room temperature (case was open)! Battery has been used may be 8-10 times. It has charge, I tested the head light.

Thanks for the help.

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#43

Re: Time calculation for different charger

02/09/2011 5:56 PM

The charger

Input 100-240V AC 200mA and output 5 V DC 1300 mA

Also there are 3 batteries and measure 1.5" x2.5". Does it mean they are type C?

I charged for 8 hours and did not feel that batteries were warm.

Can I decide to charge more till the batteries are warm to touch?

HOW MANY HOURS FOR FULL CHARGE (If can be calculated)?

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#39

Re: Time calculation for different charger

02/09/2011 5:24 AM

Dear Guest,

If your battery is 3.6V NiCd, use of a 5.0 V 1200 mA charger would apply 1.666 Volts per cell [compared to a maximum of about 1.45V/cell allowable], and with 1200 mA available would exceed the C/10 = 1800/10 = 180 mA allowable with high cell voltage. Use of this charger will overcharge, causing high pressure, blowing of safety vent and overheating. I do not advise use. If you have to use this charger, to limit the current, I would use a 4.7 ohm 10 watt wire-wound resistor in series with its 5V DC output.

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#2

Re: Time calculation for different charger

02/04/2011 5:42 PM

What is the nominal terminal voltage of the battery?

All that can be said without knowing what it is, is that it will take longer.

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#4

Re: Time calculation for different charger

02/04/2011 5:55 PM

How do I calculate it?

It is Portable Power Source (Welch Allyn Model # 75200)

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#11

Re: Time calculation for different charger

02/05/2011 1:48 AM

Calculate the voltage? Er, why not look at what is on the outer packaging of the battery, and read it?

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#8

Re: Time calculation for different charger

02/04/2011 7:22 PM

I talked to Tech. He says it is 3.6 volts DC (also he gave me when I asked at "How much amperage can the battery withstand before it explodes?" - max. 6.6 v DC 240 mA - I do not understand. It seems he was also reading from the notes. He did not answer, If the pack was 3 AA Ni-Cad batteries)

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#10

Re: Time calculation for different charger

02/04/2011 7:46 PM

Which part of 6.6vdc and 240ma was hard to understand?

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#9

Re: Time Calculation for Different Charger

02/04/2011 7:42 PM

Chemistry? We know nothing about your stinking chemistry. You will make my battery fully charged, now!

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#14

Re: Time Calculation for Different Charger

02/05/2011 11:07 PM

You are heading into dangerous territory. If you are charging NiCd as it seems, you need to know that these cannot be charged too quickly - in fact compared to LiPo and other batteries, they are charged quite slowly. NiCd also to be charged more slowly at the end so that they do not get too hot. The charge process is one that needs current control because the battery voltage does not increase with increased charge.

It seems that your original charger is part of the "el cheapo clan" - this approach uses C/10 for 16 hrs to achieve a charge. What is C/10 you say?

C is the basic unit for battery charge rate and it is current that will charge the battery to its capacity in 1 hr, if things were perfect. So if a 2000 mAh battery was charged at 1C the charging current would be 2000mA or 2 amps. At C/10 it would be charged at 200 mA.

In practice charging at C/10 for 16 hrs is an easy way to charge a NiCd.

The temperature of a NiCd battery should not exceed about 45 C - that's about hot to touch/hold, and a bit short of burning. If you have a thermistor and temperature controlled charger you can probably charge at 1C till this temperature is reached and then the rate has to be decreased. Sophisticated (read expensive) battery chargers do all this automatically, but this is not the league you seem to be in.

First problem with your question is that if your proposed replacement battery charger is not designed for charging NiCd batteries it may charge too quickly, and specially near the end of the charge.

You will probably be OK if the battery pack does not exceed 45-50 deg in temperature, but that is the temperature on the battery, not on the outside of some box around the battery that is insulted by air or something else.

You can charge for 16 hours at C/10, and from your advice a low risk guess is that this is 250 mA. If you charge at higher than at that rate, the beware of the battery getting too hot as the charge nears completion. If you charge at a rate lower than that, then multiply the time of 16 hrs up by the inverse of how much less the charge rate you are using is - i.e. if you are charging at 190 mA or ¾ of the 250mA rate, then charge for 16 hrs x 4/3.

To be able to use the above you will need to be able to measure current. You could do this by measuring it directly with a meter, or if you only have a voltmeter, you might be able to cheat by inserting a very low resistance in the charge lead - say 1 ohm - and measuring the voltage across this - and even if you only do this initially to get a feel for what the currents are. Remember that Voltage (volts) = Current(amps) x Resistance(ohms)

Bottom line - all is OK as long as things don't get too hot.

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#15

Re: Time Calculation for Different Charger

02/05/2011 11:15 PM

Gee, so the chemistry does matter. Who'd a thought that.

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#29

Re: Time Calculation for Different Charger

02/07/2011 3:41 PM

Thanks

Off Topic (Score 5)
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#16

Re: Time Calculation for Different Charger

02/06/2011 7:05 AM

http://www.angelfire.com/electronic/hayles/charge1.html

http://www.atmel.com/dyn/resources/prod_documents/doc1659.pdf

http://www.qsl.net/eb4eqa/batt_charger/batt_charger.htm

http://cache.freescale.com/files/microcontrollers/doc/app_note/AN3392.pdf

http://www.datasheetcatalog.org/datasheet/SGSThomsonMicroelectronics/mXyzxtz.pdf

http://www.st.com/stonline/books/pdf/docs/2074.pdf

I will like to tell you that Ni-Cd battery have serious problem of over discharge and these should never be completely discharged else they enter into a non-reversal phase where they stop charging and all energy is spent as heat and then they may blow off very easily. Make sure these are not stored for long without charging and they are not old stock and have manufacturing date < 1 year.

I think LM317 based variable current source is a good idea.

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#17

Re: Time Calculation for Different Charger

02/06/2011 7:40 AM

From above reference http://www.st.com/stonline/books/pdf/docs/2074.pdf temperature goes up sharply near full charge and charging rate is also rapid and then it saturates. One should not over charge else serious heating can explode the battery.

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#26

Re: Time Calculation for Different Charger

02/07/2011 3:32 PM

Govinda

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#27

Re: Time Calculation for Different Charger

02/07/2011 3:38 PM

Welcome.

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#45

Re: Time Calculation for Different Charger

03/10/2011 6:45 PM

Harih Om Syàmajï:

Can I charge, till the battery is warm to touch? I charged the battery pack for 6-8 hours, and did not feel warmer than the surrounding air.

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#46

Re: Time Calculation for Different Charger

03/10/2011 9:16 PM

If battery is not warm then either the charging scheme has failed to inject current into the batteries or charging current is too low to be destructive. Low current charging mechanism is employed for energy harvesting where energy source is very weak and requires charging for almost entire day, perhaps from small solar cell in day light. By limiting maximum voltage and current sure makes it much safer. Just current alone does not make it safe. Often higher voltage if applied then cut off circuit after full charging is a must. faster charge injection heats the battery and requires charge injection control on the bases of temperature and voltage on battery under load sensing both.

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Anonymous Poster
#18

Re: Time Calculation for Different Charger

02/06/2011 7:43 AM

Use Ohm's Law for calculation. Do not use amps higher than the rating for your battery.

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#30

Re: Time Calculation for Different Charger

02/07/2011 5:42 PM

Theoretical aspects as in Ohms law are used as a guide or reference - which are all based on ideal conditions. The actual time to expect when the battery will be fully charged will be an approximation, hopefully within a short span of time only.

I don't think anybody can be certain for sure on the exact time when a battery will be fully charged! I believe the fully charged condition of any battery will be dependent upon and determined by the actual physical and chemical conditions existing for that particular battery!

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#32

Re: Time Calculation for Different Charger

02/08/2011 3:46 AM

This is a matter of engineering, not black magic. I suggest you look at

http://en.wikipedia.org/wiki/Battery_charger

for an explanation of how a charger may be designed to charge a battery rapidly and safely.

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#37

Re: Time Calculation for Different Charger

02/08/2011 4:22 PM

Mr. phph001 -- Theres no conflict on the different theories as related to the different applications in electrical /electronics engineering. On the same token, an engineer should be aware and always must consider theory applications and limitations in the real world. Ohms Law as an example, is limited and no longer holds true when certain conditions as in temperature is reached - super conductivity application is a good example of this! Relative to my comment, just reiterated that physical and chemical type and conditions of the battery must also need to be considered, since they will affect charging time. Unless the OP is dealing with battery forming rectifiers as used in pre-charging newly manufactured batteries, existing chemical condition in it as they do deteriorate over time should be taken into account in approximating when it can be expected to be fully charged! Kind of been there 40 years ago - done those things, and learned from others as well as from my own mistakes!

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#40

Re: Time Calculation for Different Charger

02/09/2011 5:55 AM

That is what I am saying. Engineers have been there and done that already. We all know that batteries deteriorate over time. We also know the engineering solution, namely a charger which can detect a state of charge. This appears to be a solution of which the OP was originally unaware.

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#33

Re: Time Calculation for Different Charger

02/08/2011 3:55 AM

The saturated ion current limits the charging capacity of the battery and there after all energy is wasted in heat and degrading electrodes and electrolyte.

Most of the manufacture do this research thoroughly and their data is often made available for best charging and discharging cycle as well as for misuse and likely to be damaging conditions.

Look at the web site of the manufacturer for the data sheet and one should not try to rediscover the wheel as it is going to be expensive and perhaps not very productive than just the already available information.

Battery charger designers have to look into details to optimize the design and any short cut will also be a short cut to the life of the battery.

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#35

Re: Time Calculation for Different Charger

02/08/2011 10:15 AM

Mr. phph001 and prof Shyam -- Theres no conflict on the different theories as related to the different applications in electrical /electronics engineering. On the same token, an engineer should be aware and always must consider theory applications and limitations in the real world. Ohms Law as an example, is limited and no longer holds true when certain conditions as in temperature is reached - super conductivity application is a good example of this!

Relative to my comment, just reiterated that physical and chemical type and conditions of the battery must also need to be considered, since they will affect charging time. Unless the OP is dealing with battery forming rectifiers as used in pre-charging newly manufactured batteries, existing chemical condition in it as they do deteriorate over time should be taken into account in approximating when it can be expected to be fully charged! Kind of been there 40 years ago - done those things, and learned from others as well as from my own mistakes!

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#19

Re: Time Calculation for Different Charger

02/06/2011 7:48 AM

A NiCad cell has a nominal voltage of 1.2V and a variable capacity in mAh, which we will call C. In theory if the C is 600 mAh we could charge it at 200 mA and it would be charged in 3 hours or we could charge it at 600 mA and it would be charged in 1 hour. The first question is how fast it it can be charged, because charging too fast will cause it to heat up and destroy itself. In general terms it is always safe to charge a NiCad cell at C/10, or 60mA for a 600 mAh cell. At that rate the cell will never overheat, but it will take longer than the nominal 10 hours, partly because of self-discharge. That is the basis of the 14-16 hr recommendation. Indeed, it does not matter if the cell is left on charge beyond that time. Things are rather different if one wishes to charge more rapidly than C/10. It is safe to do this only with a charger which detects the point of full charge and switches to a trickle current and which also has a temperature sensor. Such chargers do exist, but cost more. Under no circumstances should you use a simple charger with a higher current supply than the one originally specified to charge your NiCads.

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#20

Re: Time Calculation for Different Charger

02/06/2011 8:03 AM

Re: "A NiCad cell has a nominal voltage of 1.2V"

Isn't it an NiMH cell that has a nominal voltage of 1.2 V, while a NiCad cell has a nominal voltage of 1.6-1.7 V?

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#21

Re: Time Calculation for Different Charger

02/06/2011 8:11 AM

1.6-1.7V ??

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#22

Re: Time Calculation for Different Charger

02/06/2011 8:48 AM

Oops, sorry, I'm totally wrong--not sure what I was thinking of, a NiCd's nominal voltage is about 1.2 volts.

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#23

Re: Time Calculation for Different Charger

02/06/2011 8:51 AM

Both NiCad and NiMH cells have a nominal voltage of 1.2 V. An alkaline or zinc-carbon cell (non-rechargeable) has a nominal voltage around 1.5 V

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#24

Re: Time Calculation for Different Charger

02/06/2011 8:56 AM

The assumptions were all based on the theoretical aspects of things! The reality will prevail which will be the determining factor. I don't think anybody can be certain for sure on the actual time when the battery will be fully charged! The full charged condition of any battery will be dependent / determined by the actual condition of the battery itself, be it physical or chemical in nature!

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#25

Re: Time Calculation for Different Charger

02/07/2011 1:31 PM

If you have a 5.6 V charger, it is probably for 4 cells at 1.4 V each. 3 cells would make 1.87 volts/cell - which will destroy them. 5 volts will give only 1.25 volts/cell - only open circuit on nickel-cadmium - this will give a very limited % charge. Time is not enough, there must be enough voltage to achieve a high % of full charge. If Nickel cadmium are charged at C/10 [e.g. 100 mA for 1000 mA/hour cell] the rule is that you need 160% of Amp-hour i.e. 16 hours.

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#31

Re: Time Calculation for Different Charger

02/07/2011 9:38 PM

Charging rate(s) are recommended as under:

at 1/10-C for 14~16 hrs

1/5C for 7~8 hrs

So you need quick charge so have a charger having these 2 rates.

It is for safety & life of batteries.

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#34

Re: Time Calculation for Different Charger

02/08/2011 8:29 AM

Normally all good chargers now a day incorporate to shift to Trickle-Charge or float charge rate which may be as low as C/50~100 or even low.

Batteries are not damaged in such cases and may be kept connected for long period.

Example: UPS Battery /Battery Bank remains connected unless a failure occurs.

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