# Simple Ni-cad Battery Charger With Led Indicator

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## Introduction: Simple Ni-cad Battery Charger With Led Indicator

This is a simple Ni-Cad battery charger circuit with Led indicator. it's not a automatic charger but when the battery is fully charged the led glows and you have to turn off it manually. use a 3mm red led and for power supply use a 9v transformer. I have build this circuit and it's working great without any problem.

parts you need :

Led 3mm ( Red) you can use any color you like but red is better because it grabs Attraction
20r
150r

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We have a be nice policy.
Please be positive and constructive.

## Questions

This circuit indicates status of charging, not charged status. Ohm's
law... Victordas said it's for 6V NiCd pack. Nominal voltage of a single
NiCd/NiMh cell is 1.2V, thus a 6V battery consits of 5 cells. The
following explanation is based on 5 cell battery, but in reality the
battery may consist of 4 cells (like common rechargable NiCd/NiMh 9V
replacement battery consists of 7 cells, which gives 8.4V nominal, thus 4
cell battery is 5.8V full and 4.8V nominal), in which case results of
the calculations will be different. At full charge a NiCd/NiMh cell
voltage peaks 1.45. At normal discahrged state it gives1V per cell.
Point of unrecoverable discharge of a NiCd cell is 0.8V under load. Without
load cell should slowly recover to 1V, otherwise it's dead. Typical slow
safe charge current for NiCd/NiMh cells is 10% of their capacity and it
takes typically 14Hrs to charge them with constant current rate. With less than 0.1C
current rate the full charge of the cells is not guaranteed and is hard to dettect
(obviosly, detection is an off-toppic for this circuit). So, how it
works: victordas said he uses 9V supply, which means (9V-5V)/20Ohm=0.2A
initial charge rate; (9V-7.25V)/20Ohm=0.0875A current rate at full charge of the battery. This is
true in case power supply used is stabilized and can provide 200mA
current at 9V (most probably not the case). Let's talk about the LED.
Mentioned LEDs are most probably old school low power LEDs. Very old and
not so old but special very low power LEDs glow with 2mA cuurent and
burn out at 5mA. Most typical low power LEDs run at around 10mA (very
dim light around 2.5~4.5mA and burn out at about 14~25mA). Under these
current rates typical voltage drop on red and green (just a bit higher
than on red) LEDs is 1.9~2.3V. Thus the LED is run under
(9V-5V-2V)/150Ohm~=13mA initially. PLease, mention that since
charge limiting resistor and LED branch are in paralel charging current
increases with the current of the LED. By this point, you should also have
mentioned, that voltage differential between fully charged 5 cell NiÇd
battery and 9V power supply is less than assumed 2V required to glow the LED.
So having the LED off will mean the battery is charged to some level -
also a type of indication. Let's see what this level of charging is:
first, let's assume the minimal current of 3mA to glow the LED and its
voltage drop under this current is 2V. So: 0.003A*150Ohm=0.45V drop on
LED's current limiting resistor plus 2V on the LED itself gives 2.45V. The voltage at which the LED
will stop glowing is 9-2.45= 6.55V, which in therms for 5 cell battery is about 1% of the charge and for
a 4 cell battery is damaging overcharge. Thus even the darkening of the
LED cannot be used as a state of charge indicator. For propper
indication of charging status I would suggest playing with another post of victordas "9v
battery status indicator circuit" or simply a zenner+LED+limiting
resistor connected in paralel to the batery.

I don know what are
you saying and why you are saying, as far I know you are NOT my competitor and
also you are not a “Politician”so I
have a simple question for you Why are you arguing with me or we can say
debiting with me ???????Boss as I “Already”
said “ALL MY Designs and Creations” are “ONLY” basic Idea “NOT” for commercial
Use and as these are 1st stage basic “idea” (Circuits/Projects)
little much miss-calculation is acceptable. If you “can” make it better than me,
brother you are “Most Welcome” . And I like to remind you 1 more thing
“INSTRUCTABLES” is For sharing what you make or create. Innovation/ Creation so
please don make this a messy political place with foolish arguments and
formulas as we all know in reality formulas don work, you may be right at this
point but remember there are no rules or formulas for a Creator in real life. I
am in reality and I will request you to come and see the reality.
And also 1 more thing ,if you Don like me or my projects than Please Ignore all of these , as all my circuits are personally tested by me and also designed by me.
So I know exactly what I am doing or sharing. Bdw 10x for your long description. In future try
to make it very short ,if you make any unwanted comments. take it as my request
as I don wanna read and waste my time in reading such long story. 10q very
much

Please, do not take it personal, at all. It was jast a try to help you and anyone interested to undestand the driving principles. I've helped several friends to restore smiles after having ruined cheap chinese accu-drills after first use, that used the same circuit for charger. Chinese are smart enough to split current and voltage limmiting between this circuit and parameters of the transformer (the transformer having the more important role of these both). Additionally, they mounted these "chargers" in sexy small boxess (plastic adds to the cost) which leave no space to assemble simple charger circuit in them. So I've described the principles of acheaving some simle indication of charged state. Feel free to delete my comments or ban me (whatever this platform suggests) if you feel offended. Have fun :)

How does it work?

Im sorry I dont get it, why 20 & 150?

DerDok please clearfy what u r trying to say.......

The resistors, what formula did you use to derive that? The reasonI ask is that im making to simple little chargers, 1 is a solar one that puts out about about 4v (low amps) to trickle charge 2 Ni-cads that run a little fan for a solar food dehydrator. Number 2 is a picky 3.0V Rechargeable Li-Ion Battery that needs to charge to 4.2v before being regulated, that will attach to just about anything USB, I got a 1/2 a dozen chargers and also wanna attach it to my PC's USB port.

If you need anything specific...I'll try to supply it.

No my friend as you can see (9V) this charger is only ment for 6v battery

How would the resistors change for a 6 volt charger? or a 3 volt or 1.5 volt?

Thanks,
Tom