universal auto matic relay circuit to disconnect charger from supply in ful charging

hi iam new to this field.i need help..

hi iam new to this field.i need to design a universal automatic relay circuit (that can be used for different batteries) which will disconnect charger from supply in the case of full charging.i need to make just a relay circuit not a charger.i have no idea how to make it...pls help me.thank u

So it’s a complete solution: charger + ‘’automatic relay’’ or just the ‘’automatic relay’’ only?

just the relay.can you help me?

Maybe this simple timer circuit can help you :
AVR Project – Relay Timer with ATmega8 AVR MCU | eXtreme Electronics


Or if You need time schedule Clock ControllerV1.1 :
**broken link removed**

I consider that we need to have a different approach about : ''the automatic relay’’. This it’s not necessary a programmable timer, more often a smart battery monitor, comparing the voltage on batteries and to decide the status: ''charged/ not charged’’ and based on this information to disconnect the batteries if necessary.
But this is not a simply process to do, for a universal device, microprocessor-controlled, we must impose to adapt the alarm values to be configured to match different type of batteries. For example a more complex system, in addition to voltage, the internal resistance and temperature are constantly monitored and compared with preset thresholds. When any of the threshold values are exceeded, corresponding alarms will be communicated . The automatic controlled charging method with I-U characteristic provides a gentle charging of the accumulator, if possible.
But here, to put in practice for a simple circuit, we need more details about battery voltages, battery chemistry and capacity.

which will disconnect charger from supply in the case of full charging.i need to make just a relay circuit not a charger

Click to expand...

He say no charger needed! Maybe he need just voltage comparator?

Maybe you need this :

tpetar said:

He say no charger needed! Maybe he need just voltage comparator?

Maybe you need this :

Click to expand...

what type of battery are you charging?

the old nicd's you charge until the batteries heat up to a preset limit, then stops charging, much like the wheller cordless soldering irons (I have a few they use a reset able thermal fuse. I remember it opening at 108 deg F. Others use a constant current, and charge for a spcific time at that current rate. You need to get the data sheet for the batery manufacturer to see what current time is approperate for your battery.

when NiMH, came out, a hole new approach was used. and still is, using a current pulse, as the battery fills, The current pulse off time gets longer, then stops. There is a common chip, dont recall the name, was introduced for charging thogh the usb port, but you need the battery recommended specs, to deliver the correct current to the battery.

for usb check here h**p://www.maxim-ic.com/app-notes/index.mvp/id/3241

hope this helps

---------- Post added at 17:35 ---------- Previous post was at 17:15 ----------

A universal circuit will have to detect the difference in what type and style battery is placed upon it.

in current chargers as the battery charges, the current from the charger decreases.

You would have to design a circuit that engages a relay to charge the battery, as the current to the battery decreases, the relay would disengage. The problem with a universal automatic relay, is to encode the different styles of battery and encode the release current.
a 12v lead acid battery will have a diferent release current then a AA battery. Limiting the charger to car battery or AA batterys will simplify things.

vidyalakshmy said:

hi iam new to this field.i need to design a universal automatic relay circuit (that can be used for different batteries) which will disconnect charger from supply in the case of full charging.i need to make just a relay circuit not a charger.i have no idea how to make it...pls help me.thank u

Click to expand...

---------- Post added at 17:36 ---------- Previous post was at 17:35 ----------

tpetar said:

He say no charger needed! Maybe he need just voltage comparator?

Maybe you need this :

Click to expand...

what type of battery are you charging?

the old nicd's you charge until the batteries heat up to a preset limit, then stops charging, much like the wheller cordless soldering irons (I have a few they use a reset able thermal fuse. I remember it opening at 108 deg F. Others use a constant current, and charge for a spcific time at that current rate. You need to get the data sheet for the batery manufacturer to see what current time is approperate for your battery.

when NiMH, came out, a hole new approach was used. and still is, using a current pulse, as the battery fills, The current pulse off time gets longer, then stops. There is a common chip, dont recall the name, was introduced for charging thogh the usb port, but you need the battery recommended specs, to deliver the correct current to the battery.

for usb check here h**p://www.maxim-ic.com/app-notes/index.mvp/id/3241

hope this helps

what if we can limit the use to 2 or 3 devices?,say a mobile phone and a laptop or a camera.all are li ion batteries but with various current & voltage limits...i want to use a 1020mAh,3.7v,3.8Wh mobile battery.a camera battery of 3.6v,730mAh& a 10.8V,61Wh / 6Cell lap top battery.is there any way i can design the circuit by measuring the change in current?

How often do you need to charge the phone/laptop battery outside the device?
Yes, you can modify a charger diagram in order to work with different batteries. Easy to do for batteries with similar voltages. See for example the schematic presented here:
**broken link removed**
This simply charger can by adapted to different Li-Pol batteries capacity by modifying only one resistor : ''Rx''.

Warning! Li-ion and Li-pol cells may explode if a shorted, overcharged, charged or discharged eith too high currents, exposed to high temperature, mechanically damaged or otherwise improperly treated!

Click to expand...

@estefan2020 in original message he say that he dont need battery charger part, just voltage switch or timer, you see original first post was edited by vidyalakshmy; 25-01-12 at 21:12. my post corespond to original message. Now he say that he need battery charger 8-O

Part of first and original question, also I citate in my post #7 :

which will disconnect charger from supply in the case of full charging.i need to make just a relay circuit not a charger

Click to expand...

New version and edited thread question is :

hi iam new to this field.i need to design a universal automatic relay circuit (that can be used for different batteries) which will disconnect charger from supply in the case of full charging.i need to make just a relay circuit not a charger.i have no idea how to make it...pls help me.thank u

Click to expand...

Based on that drastically changed new question my answer is :
You can make universal battery charger, but that battery charger must be smart, and must have capability to set or recognize which battery is on charger, and acording to that must set charging procedure and phases.
NiMh can be charched with constant current, Lithium-Ion battery need voltage and themperature control, Lead Acid also need voltage, and current control.... Some batteries like lead acid can be charged in several phases. Pay attention specially on lithium-ion batteries when charching, that batteries can explode or cause big fire like some lpg canister.
For LioIon use dedicated battery charger for lithium or adequate charger for that, dont improvize if you dont know what are You doing!

Battery charger dont need to use relays. Smart battery chargers often use microcontrolles as heart of device.


I thise thays working and experimenting with crazy charging of alkaline batteries 1,5V. I must say In last 3 days I charge about 20 AA and AAA with success 99% only one is bad (0V), 0 leaked, 0 exploded. During charge no heatup. Charged alkaline works like new. Also thise day experimenting with garden solar lamp cells charging alkaline / NiMh and powering some device like SMS alarm, iButton Lock, Alarm centrale,....


Best, tell us what type of batteries you have in plan to charge ? And acording to that we will supply some adequate battery charger solution.

mister_rf said:

How often do you need to charge the phone/laptop battery outside the device?
Yes, you can modify a charger diagram in order to work with different batteries. Easy to do for batteries with similar voltages. See for example the schematic presented here:
simple Li-Ion and Li-Pol cell charger
This simply charger can by adapted to different Li-Pol batteries capacity by modifying only one resistor : ''Rx''.

Click to expand...

yea its simple, lm317t and inefficient, what happends to the chip, with excess voltage, its converted to heat, yea it will work in a crunch, but bad design if you plan on marketing and selling

LT1510 - Constant-Voltage/Constant-Current Battery Charger
LT1510 - Constant-Voltage/Constant-Current Battery Charger - Linear Technology

This will atleast be more efficient, and use a switching PSU so the energy used will be placed into the charger, and not wasted in heat like the lm317t or constant voltage regulators does.

If you are going with non automotive battery chargers, there are plenty of switching power supplys that will deliver 1amp to charge with, making it possible to be charged from the mains or in transit, without wasting energy

here is another link to chargers **broken link removed**

Good luck, charging non rechargeable batteries, They are not designed to release the hydrogen buildup when recharging, However, I would suggest using a 555 with your charging circuit , with a changing duty to let the battery time to catch up.

50% of charge at 100% , 50% duty for 75% of time charged, and 25% duty to 85%, and then 25% duty for the remainder.
This should keep the battery cool and less likely to swell. Would also use masking tape to indicate how many times they have been charged. try not to fully deplete the batteries to zero before charging.

I was going though s few links and found a nicd car charger schematic, using a voltage regulator 5v, connected as a constant current, with taps for different current levels. The schematic was from a ham operator, and it looks like it sends current pulses at a rate of 1.5khz to charge batteries.

**broken link removed**

one can use a 4017 Johnson counter, a slow running 555 to change the dutyand have a 9 step charger that can change the 555 in the above circuit to sequentially slow down the charger. one can then reset the 4017 to at the end of the charge time.and auto stop the charger, or set it for a trickle charge.

**broken link removed**

hi iam now designing the circuit..pls note my circuit is not a charger it comes out side charger,and in between charger and supply..so current and voltage at the supply side to charger are the measuring values.the problem is due to load fluctuations these two are not constant.so i have to use two comparators for these two and one more..making a total of 3 for a load (charger).this creates much error.so can any one suggest any way to compare power...please replay thank you..

1) Amp meter
2) Volt Meter
3) Watt Meter

you hit the 3 types of meters.

By initiating latching reley with a 10ohm 100w resistor (10 100ohm 10w in parallel) may give additional load to the battery under charge, and when battery is full, the amp meter will reduce, possibly cause the relay to de-latch and stop the charge.

by monitoring the amp meter with an Adreno processor one could have specific current stops within a pre-programmed 8/16 position dip switches, one could also create 8/16 different battery stations in which different battery bays are constructed, in order to separate battery types, so they would each be able to be monitored, and serviced to the correct current rating so one can recharge each type of battery to the manufacturers recommendations.

vidyalakshmy said:

hi iam now designing the circuit..pls note my circuit is not a charger it comes out side charger,and in between charger and supply..so current and voltage at the supply side to charger are the measuring values.the problem is due to load fluctuations these two are not constant.so i have to use two comparators for these two and one more..making a total of 3 for a load (charger).this creates much error.so can any one suggest any way to compare power...please replay thank you..

Click to expand...

My friend use this to monitor voltage, amperage, circuit resistance (good when charging batteries) and Ah (you can see how much battery receive Ah or how much power supply give) :

Power Supply Unit Multimeter

For power supply use LM338K circuit.