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#### Audioguru

Sep 24, 2016
3,656
Stage 1. Constant current until the upper voltage is reached.
Stage 2. Switch to constant voltage until the charging current becomes low.
Stage 3. Switch to reduced voltage (as shown on the graph) for low current trickle charging.
Battery university says that, "Over-saturation by not switching to float charge (trickle charge) causes grid corrosion on the positive plate. This also leads to gassing and water-loss."

#### Karthik rajagopal

May 9, 2016
257
Stage 1. Constant current until the upper voltage is reached.
Stage 2. Switch to constant voltage until the charging current becomes low.
Stage 3. Switch to reduced voltage (as shown on the graph) for low current trickle charging.
Battery university says that, "Over-saturation by not switching to float charge (trickle charge) causes grid corrosion on the positive plate. This also leads to gassing and water-loss."
Yes sir I read that . But I was trying to make things simple because designing a circuit with these stages is a difficult task . So I reduced it to constant current mode where I detect the upper voltage limit then switch to constant voltage. I don't know how to switch to float mode. I read in a website where they stated that float voltage must be around 2.3v/cell which is actually my charging voltage and the current must be 3-5 percent of the battery's rated current . So the problem again is ,how will I reduce my current from 0.5A(charging current )to 0.2A during float charge?

#### Audioguru

Sep 24, 2016
3,656
I guess your charging voltage is too low. Your charging current is only 0.5A? The battery must be tiny.
When the charging voltage reaches the voltage limit then you must detect it and regulate the voltage to the constant voltage amount. Then the current will gradually reduce and when it is low enough you must reduce the charging voltage even lower so that the trickle charge (float) current is what you want.

#### Karthik rajagopal

May 9, 2016
257
I guess your charging voltage is too low. Your charging current is only 0.5A? The battery must be tiny.
When the charging voltage reaches the voltage limit then you must detect it and regulate the voltage to the constant voltage amount. Then the current will gradually reduce and when it is low enough you must reduce the charging voltage even lower so that the trickle charge (float) current is what you want.
Yup, thanks for the great explanation !
As per my battery specification , it must charged with 6.75-6.9v with an initial current of 0.15c(0.6A) if it is going to be used in stand by mode (I am using it in my emergency lamp ).So I decided to use 6.8v and limit the current to 0.5A. Am I right ?

#### Audioguru

Sep 24, 2016
3,656
As per my battery specification , it must charged with 6.75-6.9v with an initial current of 0.15c(0.6A) if it is going to be used in stand by mode (I am using it in my emergency lamp ).So I decided to use 6.8v and limit the current to 0.5A. Am I right ?
Then without having a reduced voltage and reduced current for a float charge the battery will not last long because it will have "grid corrosion on the positive plate. This also leads to gassing and water-loss." If the battery is sealed then it will be doomed to fail soon.

#### Karthik rajagopal

May 9, 2016
257
Then without having a reduced voltage and reduced current for a float charge the battery will not last long because it will have "grid corrosion on the positive plate. This also leads to gassing and water-loss." If the battery is sealed then it will be doomed to fail soon.
As far as I have searched in google, it was given that the float voltage for a lead acid battery is 2.3v/cell. Here it is 2.3*3=6.9v which is my charge voltage. If I must reduce both current and voltage ,then what should me by float voltage ?

#### Karthik rajagopal

May 9, 2016
257
Then without having a reduced voltage and reduced current for a float charge the battery will not last long because it will have "grid corrosion on the positive plate. This also leads to gassing and water-loss." If the battery is sealed then it will be doomed to fail soon.
According to the circuit that I have designed inside my emergency lamp , I have connected an operational amplifier as a comparator so as to switch my lamp off when my battery voltage reduces to 6.1v in order to avoid deep discharge of the battery . Therefore I will be charging my battery when it's charge is going to be around 5.9v-6.1v. So can I use a constant voltage source to charge it till its current drops to a lower value? Will that affect my battery life ?

#### Audioguru

Sep 24, 2016
3,656
I think a Lead-acid battery in Google is a huge and heavy car battery that is charged with 10A or more. Your tiny battery is completely different.

You should not begin charging a discharged battery with unlimited voltage (something might explode) which is why they say to begin charging with a constant current until the battery voltage rises. Then you must regulate the voltage so that it does not rise too high.

Your battery manufacturer should say the recommended beginning charge current, the regulated and limited charge voltage and the limited float voltage.

#### Karthik rajagopal

May 9, 2016
257
I think a Lead-acid battery in Google is a huge and heavy car battery that is charged with 10A or more. Your tiny battery is completely different.

You should not begin charging a discharged battery with unlimited voltage (something might explode) which is why they say to begin charging with a constant current until the battery voltage rises. Then you must regulate the voltage so that it does not rise too high.

Your battery manufacturer should say the recommended beginning charge current, the regulated and limited charge voltage and the limited float voltage.
What will be the expected life for my battery if I charge it with a constant current till the full charge and stop it without float charging ?
And
What will be the expected battery life if I charge with a constant limited voltage source of 6.8v and stop till the current drops to a set low value?
I am not able to get a solution to my problem . Neither can I construct that complex smart charger circuit nor charge the battery incorrectly. So, my last resort will be to construct a charger (either based on CC or CV which ever is better based on your view) with a compromise in the battery life .

#### bushtech

Sep 13, 2016
1,025
Is buying a 6V battery charger out of the question?

#### Audioguru

Sep 24, 2016
3,656
I use modern Ni-MH and Li-PO batteries and I am too young (73) for this thread about antique lead-acid batteries.
Does anybody make an antique 6V charger for an antique 6V lead-acid battery anymore? I think cars used a 6V lead-acid battery a long time ago.

#### bushtech

Sep 13, 2016
1,025
I see some on ebay. lol 5oomA wall warts

#### Karthik rajagopal

May 9, 2016
257
Is buying a 6V battery charger out of the question?
First of all we don't get a smart charger for a 6v lead acid battery here. Even if I get it online ,as already stated it must fit into my lamp i.e it must not be bulky.

#### Karthik rajagopal

May 9, 2016
257
I use modern Ni-MH and Li-PO batteries and I am too young (73) for this thread about antique lead-acid batteries.
Does anybody make an antique 6V charger for an antique 6V lead-acid battery anymore? I think cars used a 6V lead-acid battery a long time ago.
Yes you are right . We don't generally use a 6v lead acid battery . But for my application ,6v one was the best option . But we still get it here in all market .
Sadly ,when I asked for a charger in the market , they provided me with a battery eliminator .
Even though you are not an expert in lead acid batteries, can you help me find whether CC or CV is better for my application (prev message )

#### Karthik rajagopal

May 9, 2016
257
I use modern Ni-MH and Li-PO batteries and I am too young (73) for this thread about antique lead-acid batteries.
Does anybody make an antique 6V charger for an antique 6V lead-acid battery anymore? I think cars used a 6V lead-acid battery a long time ago.
I think I have an another question for you. This about my Ni-Mh battery which I got it from an old JVC camera. It is a 6v 4000mAh battery. I bought a new camera so this one was not in use for about 10years. I took them out yesterday to see whether they can help me with my circuit . I had 2.5v in one of my batteries and 200mv in the other one. I tried charging them with a constant current source of 6.5v 400mA(i don't know the exact charging parameters , just tried it with a rough setting ). I just removed it to see whether it was fully charged and it had 5v in it which began to drop slowly to 3v.
I don't know how to charge them. I might need your help.

#### Bluejets

Oct 5, 2014
6,916
Does anybody make an antique 6V charger for an antique 6V lead-acid battery anymore? I think cars used a 6V lead-acid battery a long time ago.

Many motorcycles still use 6v.
The old world famous VW beetle was 6V as were many more.
Plenty of 6/12v smart chargers available, Ebay or where ever.

You can get some ideas from Talkingelectronics site.
http://www.talkingelectronics.com/te_interactive_index.html

Another here ( for 12v but could be changed to suit)
This site has many charger circuits
https://electronicsforu.com/electronics-projects/hardware-diy/12v-battery-charger-absorb-float

Oct 5, 2014
6,916

#### Karthik rajagopal

May 9, 2016
257
Many motorcycles still use 6v.
The old world famous VW beetle was 6V as were many more.
Plenty of 6/12v smart chargers available, Ebay or where ever.

You can get some ideas from Talkingelectronics site.
http://www.talkingelectronics.com/te_interactive_index.html

Another here ( for 12v but could be changed to suit)
This site has many charger circuits
https://electronicsforu.com/electronics-projects/hardware-diy/12v-battery-charger-absorb-float
Thanks for the help.
The one in the talking electronics , aren't they inaccurate ? It would have a better accuracy only when the resistor values in the circuit have the exact value . I have tried many circuits like these but due to their inaccuracy I was forced to use an op amp

#### Bluejets

Oct 5, 2014
6,916
Thanks for the help.
The one in the talking electronics , aren't they inaccurate ? It would have a better accuracy only when the resistor values in the circuit have the exact value . I have tried many circuits like these but due to their inaccuracy I was forced to use an op amp
Now you're being argumentative. Up to you.

#### Karthik rajagopal

May 9, 2016
257
Now you're being argumentative. Up to you.
I am not argumentative. My earlier charger had a circuit similar to the one in the link you gave me . It didn't charge my battery properly and it became completely dead within a month. I took it to a service centre where he told me that the inaccuracy in the values of the resistor caused the battery to overcharge each time I connected it to charge as it switch the circuit off only after it got to a few volts above the full charge voltage . So I decided to get help and got satisfying and confident replies from many here. But I was unable to design a circuit for that for which I again resorted to get help from few proffessionals here as I can't take a chance and damage my battery again. I am sorry if my repeated messages have been frustrating you.

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