simplest_battery_ charger

[shegzzyy]

Have you tried the "Add an Image" option located at the bottom right of the Quick Reply Box, next to Post Quick Reply and Go Advanced?

I find it much more convenient, I usually leave the "Add an Image" tab/window open as it can be used for all posts.



Just copy and paste the generated BBCode window into your current post.


BigDog

i have tried it once.i thought it would only add the image to my avatar?

 

[shegzzyy]

Here's the charger

 

[kam1787]

can you tell for what type of batteries? details on T1 and B1,2?

 

[betwixt]

Looks like instant death to the LEDs to me....

Brian.

 

[shegzzyy]

T1 depends on the battery you want to charge.for me t1 is a 3v xformer.i use it to charge two 3v rechargable battery thus the led is not at risk.for higher voltage you can add a resistor in series with the led

 

[betwixt]

Still looks like instant death to me...

If the battery is fully discharged, both LEDs will pass excessive current, they are essentially wired staight across the transformer secondary. If the batteries are fully charged (say 3.25V) the voltage across the LED on non-conducting cycles will peak at 3.25 + (sqrt(2) * 3) = 7.5V across them which for most LEDS is beyond their PIV rating.

Brian.

 

[shegzzyy]

No.i've used it for years without any problem.when the battery is fully charged the led will be off bcos the potential at the battery terminal is at logic1 thus current 'wont' flow through the led thus led is off.when the battery voltage falls to a certain level {logic0},curent will flow through the led during charging thus the led will be ON

 

[betwixt]

I agree with that but when the battery is charged the LED still has AC on one side of it. The voltage across the LED is the battery at one end and peak transformer voltage at the other which almost certainly exceeds the LEDs PIV rating. It would make far more sense to put the LED where the 1N4007 is on both sides of the circuit. That would limit the PIV and LED current to safe levels but reduce the battery charging current.

Brian.

 

[kam1787]

It is unfortunate there are so few details. Even for your experience you do not state the T1 secondary voltage nor current, nor the battery type, nor the AH of the battery, nor the LED details (Vd, max current).

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.............when the battery voltage falls to a certain level {logic0},curent will flow through the led during charging thus the led will be ON

Is that not a possible problem? That the current flow will exceed the max current of the LED? And that, even if the LED is 'protected' by a resistor (which is not in your diagram) that the charging current is limited and hence the charging current is low and so the charging time can be very long.

 

[shegzzyy]

@kam1787 For me i use a 220v/3v, 100ma xformer.the battery is 3v/800mah rechargable battery.i use a red led.the charging current will depend on the xformer,battery and the resistor.you can adjust the value to suit ur current need.when the charger is pluged and the bat is removed the led will be off thus no current flows through the led because there's no path to ground for current flow since only the positive half cycle is used in charging the battery.if the bat is restored and the battery is low the led will light since a path to ground is created.majority of the curent will flow through the resistor&diode.when the batery is full the led will be off since 'little' curent flows through the battery when fully charged.i agree that a resistor can be placed in series with the led for better protection

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@betwixt.most led has piv of around 5v.for me,the bat is fully charged at around 3.8v.only the bat voltage can breakdown the led and not the xformer voltage.if led is placed in series with the diode,charging curent would be xtremely low <=15ma.it's better placing a resistor and in4007/in4148 in series with the led thus eliminating any posible led breakdown and still maintaining better charging current

 

[betwixt]

So a fully charged battery is 3.8V, the transformer peak voltage must be at least 3.8 + Vf of the LED or you would never be able to reach that charged voltage, so the transformer has to peak at no less than 3.8+1.6=5.4V. Physics says you cannot charge the battery if it is less than that so if your circuit is working, your transformer secondary must be producing ~3.82V RMS or more.

When the battery is charged the LED has 3.8V on it's cathode and negative peaks of -5.4V on it's anode so the reverse voltage across it is 9.2V, almost twice what you correctly quote as PIV of most LEDs.
Can you see why I consider it bad design?

Brian.

 

[shegzzyy]

I know it's not the best of design.i built it about 8years ago .i just needed some basic charger to charge my four 1.5v rechargable battery for my workman radio.i wanted it to show some basic indication of the battery level.the circuit works when i built it.i just came across the schematic when searching for some books(although i didnt see the schematic clearly because it's very rough and old) and decided uploading it.

 

[tpetar]

What exactly rechargable battery type you use (NiMh) ?



Best regards,
Peter

 

[shegzzyy]

What exactly rechargable battery type you use (NiMh) ?



Best regards,
Peter

yeah nimh battery.it is actually 1.2v battery not 1.5v.the xformer is 1.5v xformer not 3v xformer as earlier stated

 

[tpetar]

yeah nimh battery.it is actually 1.2v battery not 1.5v.the xformer is 1.5v xformer not 3v xformer as earlier stated

For NiMh its better to make constant current charger not float charger.

NiMh have nominal voltage of 1,2V and cell is charged to 1,45V-1,5V.


Simplest charger for mains voltage BUT NOT RECOMMENDED have only three parts one capacitor, one resistor and one diode. All depends what we trying to do. When working with batteries always is better to have decent charger.



Best regards,
Peter

 

[shegzzyy]

Here's one with xformer&battery details