Own auto battery charger, 3 cell A123 battery pack

[e-bumby]

I'd like to make my own charger.
I got a 3 cell A123 battery pack thats 9.9v and can be charged at 5 amps.

So I'd like to be able to hook it up to a 12v power source and it shut off when it reaches 12v and it not go over 5 amps...

How could I do this and what would I need ?

Thanks.

 

[Audioguru]

Auto battery charger

You must limit the charge on each cell to whatever is the max shown on its datasheet to prevent a fire. When the voltage of each cell reaches the max allowed voltage then the charging should continue until the current drops below what is said on its datasheet. Then the charger must turn off.

Usually a battery charger IC is used. It can prevent over-charging a battery that is already charged or is partially charged. It prevents a fire.

Your idea of charging 3 cells to 12V will be bad for them since their recommended max voltage is 3.6V per cell (10.8V for all 3). Their voltage is lower than a normal lithium cell.

 

[e-bumby]

Re: Auto battery charger - help needed

The charger will put out more volts than the batteries are rated at, until they reach a charged state then it cuts out.... thats how all battery chargers work..

I've been reading allot about ZIP charging the A123 batteries, some people are hitting them with up to 30amps from a 12v car battery, after 15 min it drops down to 2 amps and less then you stop.

https://www.rcgroups.com/forums/showthread.php?t=795122#post8844692

 

[Audioguru]

Auto battery charger - help needed

The charger circuit is just a unlimited current voltage regulator. When the battery voltage reaches the set voltage then the voltage does not increase. But the battery is not fully charged yet and the simple circuit never shuts off overcharging when it occurs.

 

[e-bumby]

Re: Auto battery charger - help needed

The charger and method in the link is proven and works..... it shuts off all power to the batteries unless they go below the set voltage...

I would build it but have NEVER don anything like this and really not sure about the turn out if I did, but some people with no electronic back grounds have had great luck building and using it....

Are you say'n that it wont work ?

 

[Audioguru]

Auto battery charger - help needed

Without anything limiting the charging current then the battery might explode or be damaged.
The circuit does not shut off like battery manufacturers recommend.

 

[e-bumby]

Re: Auto battery charger - help needed

This is a DIY adjustable charge cut out device intended to be used with A123 battery packs. It's range is from about 9 volts to about 25 volts, so it can be used with A123 packs from 3 cells to 6 cells. It has been tested to 20 amps. A heat sink will be needed for the FET for high charge currents (over about 5 amps). The device will turn on as soon as a battery pack is connected as long as the pack voltage is under the cut out voltage. When the pack voltage reaches the set cut out voltage, the pack is disconnected from the charger. If the pack voltage drops far enough, the device will turn back on. The LED is on when the device is turned on, so the battery is being charged.

 

[Audioguru]

Re: Auto battery charger - help needed

When the pack voltage reaches the set cut out voltage, the pack is disconnected from the charger.

No.
The circuit does not have a disconnect function because it is too simple.
The article should say that it is you who must disconnect the battery from the charger.
The article should also say that it is dangerous to overcharge a lithium battery.
Even a small trickle-charge current (like this circuit produces) is not allowed.

 

[e-bumby]

Re: Auto battery charger - help needed

A123's are NOT LiPO.............. they will not have the heat or over voltage probs as a LiPO anymore so than a NiMH.

I need to read up more on that thread about the cut out deal, I took it that it cut out the circuit it self.... did you read the thread ?

 

[Audioguru]

Re: Auto battery charger - help needed

A123's are NOT LiPO

Yes they are but they are a little different.

I took it that it cut out the circuit it self.... did you read the thread ?

It is designed by somebody who knows nothing about electronics.
The simple circuit has nothing to switch it off. It is just a simple voltage regulator.

 

[e-bumby]

Re: Auto battery charger - help needed

It cuts off cleanly at the set cut off voltage with no current flow, and no current flows until it cuts back in again. The only thing I can think of that would make it work the way yours does is if you have the battery and charger connections reversed. When it cuts out, current would still flow through the body diode, but at a lower current because of the voltage drop of that diode. It would also tend to stabilize at one diode drop below the source voltage. Make sure that the center lead of the fet goes to the battery.


This is quoted from the thread..... it states that "IT" cuts power....

Am I in the wrong web site here ? I cant read the schematic but I thought for sure someone here could...

 

[Audioguru]

Auto battery charger - help needed

Nothing in the schematic shuts it off. When the battery is fully charged its current is less but it is still overcharging which is not recommended.

 

[e-bumby]

Re: Auto battery charger - help needed

OK I just joined that forum to ask about this... I want to see what he has to say about it....

What would be needed to make it cut OFF at a pre set voltage ?

Can you look it over and know whats needed to make one like what I'm talking about ?

This is why I came here, I need to learn more about these things from the people who would know electronics...

Thanks for your patients with me..

 

[Tahmid]

Auto battery charger - help needed

Hi,
It seems there is cut off. The TL431 is used to set a specific voltage, which when reached, turns the PNP transistor on, which turns the P-channel MOSFET off. That is, if this is the circuit being talked about: https://www.rcgroups.com/forums/att...ae3a17fffc36de06553ee95a&attachmentid=1676598
Tahmid.

 

[e-bumby]

Re: Auto battery charger - help needed

This is the reply I got from them...

It does cut off by itself. If it is not clear to you, it goes between the power supply output and the battery and opens the charging circuit when the set voltage is reached.

Maybe they meant that it does not disconnect itself from the battery after it has cutoff the charging voltage? If so, that is correct. The terminator remains connected to the battery and draws a very small amount of current itself.

Added after 4 minutes:

Hi,
It seems there is cut off. The TL431 is used to set a specific voltage, which when reached, turns the PNP transistor on, which turns the P-channel MOSFET off. That is, if this is the circuit being talked about: https://www.rcgroups.com/forums/att...ae3a17fffc36de06553ee95a&attachmentid=1676598
Tahmid.

Yes thats it..... it hooks to a power supply "ZIP CHARGER" that is only a 12v car battery and a length of wire to govern the current flow, this cutoff helps keep it from over charging..... maybe it will over charge if left for a long time I dont know but not in the time we are wanting....

And A123 batteries a ALOT diff than LiPO batteries.... read up on them...

 

[Tahmid]

Auto battery charger - help needed

Hi,
I don't know about A123 batteries, but looking at the circuit, if the P-channel MOSFET is turned off, there's no way that the battery will be charged, until the P-channel MOSFET breaks down or becomes defective or flawed or something.
Tahmid.

 

[Audioguru]

Auto battery charger - help needed

The circuit balances turned on a little but not turned off. It needs hysteresis in a comparator circuit to completely turn off.