Hello everyone,

I found this simple circuit on the internet, but I need help with it. I am not very good with designing circuits.
I was wondering if someone would help me make the most simple circuit, within the circuit I provided, that turns off charging automatically when the battery reaches full charge. I want to charge a single NiCd 1400 mAh battery with this circuit.

Here is the original post: https://www.eeweb.com/extreme-circuits/low-cost-universal-battery-charger-schematic

Thank you in advance. Best regards.

 

That simple circuit won't charge NiCd batteries properly.

http://batteryuniversity.com/learn/article/charging_nickel_based_batteries

Excerpt from article referenced above:

To achieve a reliable voltage signature, the charge rate must be 0.5C and higher. Slower charging produces a less defined voltage drop, especially if the cells are mismatched in which case each cell reaches full charge at a different time point. To assure reliable full-charge detection, most NDV chargers also use a voltage plateau detector that terminates the charge when the voltage remains in a steady state for a given time. These chargers also include delta temperature, absolute temperature and a time-out timer.

 

That circuit is intended to be used at a charge rate of C/10 (15 hour rate). NiCd batteries can tolerate overcharge at that rate and that circuit will satisfactorily charge NiCd batteries as long as the C/10 current is used.

For faster charging that circuit is not suitable and the NDV method should be used.

 

That simple circuit won't charge NiCd batteries properly.

http://batteryuniversity.com/learn/article/charging_nickel_based_batteries

Excerpt from article referenced above:

That circuit is intended to be used at a charge rate of C/10 (15 hour rate). NiCd batteries can tolerate overcharge at that rate and that circuit will satisfactorily charge NiCd batteries as long as the C/10 current is used.

For faster charging that circuit is not suitable and the NDV method should be used.

So I can charge a single cell with this circuit with 140mA and won't damage it? The author says that I can double the current and will not damage the battery?

 

That simple circuit won't charge NiCd batteries properly.

http://batteryuniversity.com/learn/article/charging_nickel_based_batteries

Excerpt from article referenced above:

Thank you for your answer.

I intend to use 2 cells for let's say a power bank. That is not very demanding circuit. Can I use this charger circuit for charging NiCd batteries, and then use them in power bank. Will I be able to use is a year or so without damaging the batteries?

 

You can charge at 140mA if the cell capacity is 1.4Ah and then the charge time is not critical. If you double the current then you should discharge the cell before charging it and it is important to remove the charging circuit after 7.5 hours. Leaving it too long will damage the cell.

 

You can charge at 140mA if the cell capacity is 1.4Ah and then the charge time is not critical. If you double the current then you should discharge the cell before charging it and it is important to remove the charging circuit after 7.5 hours. Leaving it too long will damage the cell.

Ok, that is clearer to me. But that is the question, can somebody help me build a simple circuit that will auto turn off charging when the battery is full-charged?

 

If you use the 15 hour rate you don't need to worry about auto-turn off and is the simplest way to do it. It is only if you need to charge fast that you need to worry about overcharging.
Is the 15 hour rate too slow for you?

 

If you use the 15 hour rate you don't need to worry about auto-turn off and is the simplest way to do it. It is only if you need to charge fast that you need to worry about overcharging.
Is the 15 hour rate too slow for you?

Yes it is, the perfect charging time for me would be 7-9 (overnight) hours without a need of turning it off by myself. I saw some circuits with the LM317 that can auto turn off the charging?

 

In that case the simplest, and kindest to the cells is to use a dedicated charge controller chip like this one:
http://www.linear.com/product/LTC4060

 

In that case the simplest, and kindest to the cells is to use a dedicated charge controller chip like this one:
http://www.linear.com/product/LTC4060

Yeah, I know about that chip, but it is not available in my store. Thank you a lot for your help.
Maybe someone who knows something else will see this post and help me in a different way.

 

I intend to use 2 cells for let's say a power bank. That is not very demanding circuit. Can I use this charger circuit for charging NiCd batteries, and then use them in power bank. Will I be able to use is a year or so without damaging the batteries?

I wouldn't use the circuit referenced, and I definitely wouldn't charge two batteries in series. Invariably, one of the cells will be weaker than the other. The weak cell will charge first and will spend more time in overcharge (i.e. it wiill be cooked and it's deterioration will accelerate).

Read the article I referenced.

 

I wouldn't use the circuit referenced, and I definitely wouldn't charge two batteries in series. Invariably, one of the cells will be weaker than the other. The weak cell will charge first and will spend more time in overcharge (i.e. it wiill be cooked and it's deterioration will accelerate).

Read the article I referenced.

I read it, and sorry for not mentioning but I plan to charge individual cells, not connected in series.

 

I saw some circuits with the LM317 that can auto turn off the charging?

Reliable end of charge needs to be able to detect a NDV on the order of 5mV. That's not something a simple circuit is going to be able to do.

 

Reliable end of charge needs to be able to detect a NDV on the order of 5mV. That's not something a simple circuit is going to be able to do.

Ok thank you a lot for your help.

 

Yeah, I know about that chip, but it is not available in my store. Thank you a lot for your help.
Maybe someone who knows something else will see this post and help me in a different way.

If you google nicd charging ic you should be able to one that is available to you.

 

If you google nicd charging ic you should be able to one that is available to you.

I will try it thank you.