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Need 6V & 12v Battery Charger

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I have looked and searched on the net as well as on the forums here and it seems that lead acid batteries and sealed/gell batteries have different charging requirements.
I have a few automotive batteries as well as a few small 6 & 12v gel batteries that i would like to charge. Charge time is not important. Is there a simple circuit that can charge both types. IF not can anyone recommend a really simple circuit for each, i have seen some where i think its more complicated than it really needs to be.

Thanks
pete
 

Gayan Soyza

Active Member
If you are going to charge your batteries with 0.1C rate then look at the data sheet of LM317T by national semiconductor for the charger circuit. It has both methods constant current or constant voltage/current limited types.
 
Thanks i downloaded the spec sheet for the lm317 and it shows two simple circuit diagrams for 6 and 12 volt battery chargers. Two questions if may ...How does one know when the battery charging is complete ? Also it doesn't specify if this is for lead acid types (i guess a car battery is lead acid type) or gel cells ?


THanks again
pete
 

Gayan Soyza

Active Member
Two questions if may ...How does one know when the battery charging is complete ?
That’s a common question asking in many forums. After a battery full charged condition if you measure the charging current it will be nearly to ZERO in some charges. Most of these are constant voltage/current limited type. When the battery voltage comes to the adjusted value it will limit the charging current & maintaining the battery voltage. There is a diagram in your datasheet also.

Some chargers called constant current type ones. With this type charges the battery will charge with the calculated charging current but it will not maintain the batteries terminal voltage. It will exceed the terminal voltage to overcharge condition.So all the time you have to check whether its overcharging.

If you want to stop the charging after battery is full charged condition then a COMPARATOR can do the job. When the battery voltage EXCEEDS the comparators ADJUSTED voltage, the comparator output will stop the charging by making output low or high.

But good charger manufactures they won’t suddenly TERMINATE the charging when it’s reached to maximum calculated value, they will look over & over again & switching to very low charging rate & finally terminate the charging.

These are the basic charging termination methods. Also there is TEMPERATURE sensing, internal PRESSURE sensing charges as well. They are too complicated.

Also MAXIM has introduced some charge control IC’s as well but it will well supported to NIMH batteries.

Also it doesn't specify if this is for lead acid types (i guess a car battery is lead acid type) or gel cells ?
Most car batteries (but not all) are lead acid batteries.
The term SEALED LEAD ACID commonly used to refer to either Gel Cell or AGM batteries.

The LM317T version works well for me. If you need a high current version then LM350 can do the job.

Also I have seen some CAR CHARGER circuits they used just the Transformer + Diodes + Capacitor + Ammeter
When the battery is not charged, the ammeter reading shows some amps.
When the battery is fully charged the ammeter reads Zero or nearly zero, after which the battery should be removed from the charger.
 

mcs51mc

Member
amdkicksass said:
...i have seen some where i think its more complicated than it really needs to be. Thanks pete
Why do you think that?
Is it because you're smarter than the engineers who design those chips?
Is it bacause you know all the chemistry that is involved in batteries?

amdkicksass said:
How does one know when the battery charging is complete ?
Some basic "intelligence" in you charger will tell you that but that isn't done with a
amdkicksass said:
really simple circuit

Some years ago I read a app note from Cypress using a PSoC for charging different types of batteries (NiCd, NiMh, LiIon, SLA, ....) All of them had
different charging cycle, and end of charge detection.

There's only one choice when it comes to charging SLA: UC3906 from TI.
It has internal temperture compensation, end of charge indication, ... all you need in just one chip, just add some resisitors according to your battery specs.
Please take some time to read the datasheet, app note, theory of charging, ...
Your battery will thank you for that :)
 
mcs no i am not smarter than an engineer and i am sure i know nothing of what i need to know about battery charging chemistry. My point was that there are many circuits out there that do this process in a smart fashion and can do this day after day. I have 2 batteries and am not worried about time or watching them.

After reading some more info it seems that this is what i got... Lead acid batteries need to be a constant voltage charged while gel cell batteries need a constant current. Is that right ?

Whats the difference between the lm317 and l200 chips ?

pete
 

Nigel Goodwin

Super Moderator
Most Helpful Member
amdkicksass said:
After reading some more info it seems that this is what i got... Lead acid batteries need to be a constant voltage charged while gel cell batteries need a constant current. Is that right ?
No you're not! :D

BOTH are lead acid, so need charging in similar ways, it's just that gel ones need MUCH more care, normal lead acid will take considerable abuse, and do so in cars, a VERY harsh environment as well.
 
Whats that supposed to mean ?....lol.. I am a student engineer and i try to do as much as i can with what i have and the little knowledge i have.

Anyways Nigel are you sure with the battery charging theory ? Most articles i have read have said that a lead acid charger with constant voltage will put out to much current and hurt a gel battery ?

???
pete
 
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Nigel Goodwin

Super Moderator
Most Helpful Member
amdkicksass said:
Whats that supposed to mean ?....lol.. I am a student engineer and i try to do as much as i can with what i have and the little knowledge i have.

Anyways Nigel are you sure with the battery charging theory ? Most articles i have read have said that a lead acid charger with constant voltage will put out to much current and hurt a gel battery ?
I didn't say you could use a lead acid charger, I said they are the same technology, and gel ones need MUCH more care.
 
Thanks guys for your suggestions on using the lm317 chip.

While looking online i found this neat circuit which incorporates a LED for status. I built it and while i can tune the circuit to give me 13.4V using the pot , no matter what i do or connect the LED wont come on ? The explanation states the LED should be on when the current is at max, which i believe happens when one connects a dead battery ?


http://www.electro-tech-online.com/custompdfs/2007/06/gcellchg.pdf


Any ideas suggestions ?

THanks
pete
 

mcs51mc

Member
amdkicksass said:
Any ideas suggestions ?
Yes, use a UC3906 for your gel batteries

After reading attached app notes you may reconsider the use of the UC3906... ... at least do it for your batteries :)

I can't upload the datasheet (??), but go to the TI site, download it, read it but most important don't forget to order your free samples :)
 

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StrikeR.DbZ

New Member
Yes, use a UC3906 for your gel batteries

After reading attached app notes you may reconsider the use of the UC3906... ... at least do it for your batteries :)

I can't upload the datasheet (??), but go to the TI site, download it, read it but most important don't forget to order your free samples :)
Can you please post a schematic, complete circuit diagram for 6v 4ah battery charger using uc3906.

Please keep it as simple as possible.

Thanks in advance:)
 

MikeMl

Well-Known Member
Most Helpful Member
Thanks guys for your suggestions on using the lm317 chip.

While looking online i found this neat circuit which incorporates a LED for status. I built it and while i can tune the circuit to give me 13.4V using the pot , no matter what i do or connect the LED wont come on ? The explanation states the LED should be on when the current is at max, which i believe happens when one connects a dead battery ?


http://www.electro-tech-online.com/custompdfs/2009/07/gcellchg.pdf


Any ideas suggestions ?

THanks
pete
The LED monitor circuit doesn't work as drawn because the current through the LED is too low to light it. Look at this sim., particularly the current through the LED I(D7).

V2 and R6 simulate a transformer, full-wave rectifier, and filter capacitor. R2/C2 (yes, that is 4 Farads) simulate a battery, where R2 is leakage, and C2 simulates the electrochemistry jiggered so the battery "charges" in seconds instead of hours.

In the Plots, I(R4) is the charging current. V(bat+) is the battery voltage. I(D7) is the current through the LED.

ps: I just noticed that I was posting to a year old question. Oh well, maybe someone will get something out of it.
 

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StrikeR.DbZ

New Member
Hi mcs51mc,

I am sorry, but i couldn't link those circuits to my requirements. I am quite a noob:D in this matter but it would be great if you would please post a schematic for my requirements(6v 4ah) so that i can get the parts solder on the board, i already have a uc3906 but i couldn't figure out how to make my circuit out of it.

Thanks in advance...:)
 

bountyhunter

Well-Known Member
mcs no i am not smarter than an engineer and i am sure i know nothing of what i need to know about battery charging chemistry. My point was that there are many circuits out there that do this process in a smart fashion and can do this day after day. I have 2 batteries and am not worried about time or watching them.
Then use the float charge voltage. The battery makers list the recommended set voltage for the charger. In a car, the charging system is set to 14V because it restores charge back to the battery faster. Most slow charger "battery tender" types are set around 13.2 - 13.4V for constant charge. In lead acid batteries, they tolerate a slight overcharge continuously as long as the electrolyte is maintained.

If you want a simple charger just build an LM317 circuit and set the fixed voltage to about 13 - 13.2V (for a "12V" battery) and it will work well. Use about 6.5 - 6.6V for a "6V" lead acid battery for float charge.
 
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bountyhunter

Well-Known Member
After reading some more info it seems that this is what i got... Lead acid batteries need to be a constant voltage charged while gel cell batteries need a constant current. Is that right ?
No. If the gel cells are lead-acid (and all the ones I have seen are) you use what is called a current-limited constant voltage charger for both types. A linear regulator like an LM317 will work for that. It is constant current until the voltage reaches the set point, then goes constant voltage with the current tapering off over time.
 
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