In inverter designing, one of the most required tasks is a good charging system. A good inverter charger will increase battery life span and will also increase the run time of the inverter.
Many inverter chargers exist but one that will keep the battery always fully charges is the best. These type of chargers are known as float chargers.
A float charger is a charger that keeps the battery always under its float voltage level or fully charged level without over charging it.
Many poor or basic chargers consists of relays that disconnects the power supply line when the battery reaches its full state. This is not best because the relay contacts may stack and the battery will be overcharged and even swell up.
Many home made inverter chargers also lacks current regulation and also make heavy humming noise during charging.
The circuit below shows an inverter charger circuit for all battery sizes. The circuit is based on Iron transformer, SG3524, Mosfets, fast switching diodes and filter capacitor.
Many inverter chargers exist but one that will keep the battery always fully charges is the best. These type of chargers are known as float chargers.
A float charger is a charger that keeps the battery always under its float voltage level or fully charged level without over charging it.
Many poor or basic chargers consists of relays that disconnects the power supply line when the battery reaches its full state. This is not best because the relay contacts may stack and the battery will be overcharged and even swell up.
Many home made inverter chargers also lacks current regulation and also make heavy humming noise during charging.
The circuit below shows an inverter charger circuit for all battery sizes. The circuit is based on Iron transformer, SG3524, Mosfets, fast switching diodes and filter capacitor.
INVERTER CHARGER CIRCUIT FOR ALL BATTERY SIZES
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| CLICK TO ENLARGE |
INVERTER CHARGER CIRCUIT OPERATION
The power conversion technique employed here is bridgeless boost power factor correction (boost PFC). This technique ensures minimum parts count and high reliability.
One adorable advantage of this circuit is that, a smaller transformer can charge a battery of any ampere hour (AH) rating.
The circuit is based on SG3524 PWM IC. The datasheet of the SG3524 can be downloaded from here.
The inverter float charger works by supplying 220V or110V AC to a step down transformer T1.
This produce a stepped down voltage at the secondary side of the transformer.
D1, D2, Q1 and Q2 forms a bridge circuit which is connected to the secondary side of the transformer. The secondary winding coil forms an inductor connected to the bridge circuit. This means that if we are able to switch Q1 and Q2 alternatively at a higher frequency, the circuit will behave as a boost converter which will boost the stepped down AC to a high voltage DC.
Example, if a 12V transformer is used, more than 36V DC can be obtained from the output. This means that, a small 12V transformer can be used to charge 24V battery bank or 36V battery bank.
Best practice is to use a transformer with half of your battery bank ratting for charging or little higher than half. That is select 6V-10V for 12V battery banks, 12V -18V for 24V battery banks, 28V to 19V -24V for 36V battery banks etc.
D1 and D2 can be any fast switching diode which can handle your desired output current.
Q1 and Q2 is any N-mosfet which can handle your maximum charging voltage and current.
NB. the mosfet voltage should be higher than your floating voltage by minimum of half.
The duty of the SG3524 is to switch Q1 and Q2 alternatively at a frequency set by U4 and R12.
U4 is 103 fixed capacitor and R12 is 100K. This set the operating frequency to f = (1.3/RtCt) where Rt =100k and CT = 0.01uf.
If the value for RT and CT does not work for you, you can use 104 capacitor and 4.7k
If the value for RT and CT does not work for you, you can use 104 capacitor and 4.7k
T2 is a current transformer which is used for setting the maximum charging current. The current transformer is done by removing all the secondary winding of any transformer (smaller ones preferred ) and using a cable to rewind the part you removed by 2 turns. After winding, connect it as shown in the diagram above.
The output from the current transformer is rectified using normal diodes and fed to pin 10 for current regulation. U3 is used for setting the charging current. PLEASE ENSURE THAT U3 IS CONNECTED BEFORE TESTING YOUR CIRCUIT IF NOT, THE HIGH VOLTAGE FROM THE CURRENT TRANSFORMER WILL CAUSE THE SG3524 TO FAIL.
U2 is used for setting the floating voltage or battery full level.
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I want to make UPS battery charger mentioned in your blog using sg3524. In all the charger circuits I have seen so far, when I connect a 3A charger to a 60Ah battery immediately the terminal voltage crosses 13.8 (that is before battery getting fully charged) and my cut off relay gets activated.
ReplyDeleteif I use this circuit in sinewave inverter project, will I be able to charge battery 24V 60AH, in 6Amp without crossing 27V(terminal), till it is fully charged. I mean can I independently set floating voltage and charging current? is there any issue if I use 24V charger winding of my inv transformer to charge 24V battery. (blog says less than 24)
If I use sg002 to build 2000VA (1500w) ups, can I use irf540n 4 numbers in each leg (total 16) in H bridge?
It would be very helpful if you could mail me the H bridge pcb diagram so that I can print, toner transfer and build one.
And I request you to post one article for AVR using the extra tapping in secondary with relays and transistors. I mean the function of auto transformer.
Hello, if 3A is getting 60A battery crossing 13.8 instantly, then its one of the signs that your battery has become very weak. Because a good 60AH battery will need 1/10th of the 60AH which is 6A to get it charged over a period of 10hrs. so first check your battery.
DeleteYes you can set float charging at 27V or any desired voltage and that will be the maximum voltage of the battery.
Each IRF540n is rated 33A maximum so divide the wattage you want to produce by your battery minimum operating voltage. This will let you know how many of the mosfets you need to connect in parallel in other to get the maximum current you want and some gab.
Example. if you want to produce 1500W using 24V, Your low battery turn of voltage will be 20V.
so divide the wattage (1500W) by the minimum battery (20V) and you will get 75A of maximum current transfer. Multiply your maximum current by 2 so that your system can survive 3000W of surge. This brings your max current to 150Ampres.
But each IRF540 is rated 35A meaning that you will need 150A/35A number of mosfets. which is 4.2. This means that a minimum of 4 mosfets will work well for the system in our example.
Request well noted.
how out current and voltages are controlled in Boost pfc. Does changing duty cycle changes both ?
ReplyDeleteYes duty cycles reduces as battery is getting fully charged
DeletePls what is the highest amp ur inverter battery charger can handle I an looking for 0 to.100amps charging current
ReplyDeleteThe highest current will depend on your transformer size and the mosfets used. You can connect several mosfets in parallel
DeleteThanks. I did it but the mosfet was heating up when i plug it. I guess i wil increase mosfets in parallel
ReplyDeleteThanks for the design but please which fast switching diode should I use
ReplyDeleteAny fast switching diode which can stand your current.
ReplyDeleteCan I still use mosfets , instead of the fast switching diodes.?
ReplyDeleteYes. Remember to connect the gate and the source together so that it will always be off. Also use mosfets which has internal body diode
Delete