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12v sla battery charger

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artois

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i build the charger and just some questions, must the led flash from start or only when fully charged. i did drain a battery and tried it but still led flashes from start. how do u adjust the 1k pot and when? also im using a 1 amp ac transformer not 500 ma as mentioned as i see the current is regulated by the 1E8 res. the push switch i take is a latching one. heres the circuit. --- http://talkingelectronics.com/projects/BatteryCharger-12vSLA/BatteryCharger-12vSLA.html
 
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Hi,

It looks like the LED should turn on when the battery is charging because the current through that LED turns on the SCR.
You would adjust the 1k pot to limit the max charge voltage of the battery, turning it so that the LED goes off after the battery reaches the determined voltage level.
A 1 amp wall wart may work ok too, as long as it is AC and not DC.

There are much simpler circuits than this one. This one is way too complicated for what it has to do.
 
thanks to all for helping, if u read the header bit it says led will flash once battery reaches charge voltage. ive checked again over a over i dont see a error in my work. how can i test this circuit if it sends half cycles and where can i check , which points on the circuit.
 
sorry guys my mistake the charger circuit was like this firs ----thttp://skemarangkaian.com/12v-battery-charger-for-sealed-lead-acid/ emit the switch or make it a push to make, as i see in the first circuit the symbol actually shows that.
 
Hi artois,

just in case your SLA charger turns out too weak here is a better circuit using a TI (Texas Instruments) UC3906. It features charge and overcharge indication.

My circuit design disconnects the battery from the load while the battery is being charged to avoid misinterpretation of charge status.

There are two different charging currents (500mA and 2A) selectable via an SPDT switch.

While the battery is being charged the load might be supplied by the 12V regulator, being limited to the absolute value of 1A of supply current.

Using an 78S12 regulator the supply current will be 2A.

Here is the circuit and a PCB design. I used an obsolete PentiumIV heatsink with fan for space considerations. Using any other heatsink the thermal resistance must not be higher than 0.7K/W

Boncuk
 

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Hi,
There are much simpler circuits than this one. This one is way too complicated for what it has to do.

Very true!

I've seen SLA batteries taking off like rockets being charged with a simple (and cheap) charger. :)
 
thanks to all for helping, if u read the header bit it says led will flash once battery reaches charge voltage. ive checked again over a over i dont see a error in my work. how can i test this circuit if it sends half cycles and where can i check , which points on the circuit.

Hi,


You can look across the 1.8 ohm resistors or you can look across the battery. You should see a rise in voltage with each half cycle. If you have a scope this is easier to measure.
 
The charger works well, I set the 1k pot to let the led start flashing at 13.75v and once there it seems to float charge. I am now charging the 2nd battery. And ill see if it floats , just one thing can I change the 1R8 resister to another value so as to charge a little faster? The 1st battery took approx 9hrs to go from 9v to 13.75v or is that time ok for a sla battery.:)
 
Hi artois,

you didn't state the capacity of you SLA battery.

9 hours of charging is a decent time with no risk of damaging the battery.

The MCR100-6 can stand a maximum current of 800mA. It derates considerably with increasing temperature.

Depending on your power supply you might replace the MCR100 with a TIC106, which is good for 5A. It is manufactured in a TO220 package, allowing to mount a heat sink.

It's gate trigger current is the same as that of the MCR100-6.

To increase charging current change the value of both 1.8Ω to be the same for power dissipation considerations.

Boncuk
 
Hi there,


How fast you can charge a LA battery depends on the battery itself, the part number. It's often closely related to the capacity of the battery so bigger batteries can be charged with a higher current, but there is always a limit as to the max. You'll have to tell us what size your battery is or sizes of the two batteries if you have two, and any others that you plan to get. Generally it's not super fast for LA's, but to give you an example i have one that is 7.5Ahr and i can charge that at a maximum of 2.25 amps according to the manufacturer. I would not go above that limit. If i did charge at 2.25 amps, taking into account the charge acceptance of a lead acid battery i would have to charge it for about 5 hours, so that gives you some idea what to expect. It will probably take longer than that too as the voltage has to be limited also. I charge mine at 1 amp max though.
So long story short, i doubt you'll charge in less than 5 hours. That's the nature of sealed Lead Acid batteries.
 
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I have since 1 dec boxed the charger drained a 2ah 12v batt and busy charging it after 24 hrs its gone from 10v -13v is this a normal time period for a sla batt or should I change the 1R8 resister and to what value can someone work out the current charging rate. Looking forward to awnsers
 
I have since 1 dec boxed the charger drained a 2ah 12v batt and busy charging it after 24 hrs its gone from 10v -13v is this a normal time period for a sla batt or should I change the 1R8 resister and to what value can someone work out the current charging rate. Looking forward to awnsers

Hello again,


What you really should do is measure the charging current. Do you know how to do this?
We can start there.
 
hi again i have measured the charge current. its 160ma, in the circuit diagram / write up it says the circuit is designed to deliver 300ma - 400ma current. can i change the two 1R8 resisters and with what value resisters.
 
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