Help with sine wave inverter charging

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Joeadeoye

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I made a pure sine wave inverter using a low frequency transformer and full bridge mosfet configuration and it's working fine. Now I want to include a charging function in the same inverter.

The transformer used is 7v-220v and 4 IRF3205 mosfets were used to form the full bridge.

Talking about the charging, if 220v AC mains is applied to the transformer, the secondary side will give 7v AC which is too small to charge a 12v battery.

I have seen some commercial inverters do this, but I don't know how the voltage was boosted from 7v to 13.8v needed to charge the battery.

I have seen some threads discussing the same issue I am having but none of the answers in the thread worked for me.

H-Bridge Battery Charging Concept

Dear All, Can anyone help me to know H-bridge charging.Can we charge a battery using H-bridge?? Thnaks in Advance
www.edaboard.com

Charging Principle in Sine wave Inverters

Which charging technology is used ,in sine wave inverters or home UPS, by leading companies? Thanks
www.edaboard.com

The above links discuss the same issue I am trying to resolve. Please I need help
 

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I used a mower which had electric start built-in (Lawn Boy brand). The battery was 6V and the charger read something like 5V with my old-fashioned VOM. The system worked for years.

For a long time I puzzled that the charger could make do at charging on that low voltage. Eventually I realized it had no smoothing capacitor. It produced peaks which were higher than the battery voltage therefore the charger's peaks were sufficient to do the job.

With 7VDC input you can do likewise by a voltage multiplier or boost converter. One is based on capacitors, the other is based on an inductor. You can build either type to double 7V and produce sufficient voltage to charge a 12V battery.
 

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A voltage multiplier will not work for me because it can't produce the required current to charge battery. A boost converter on the other hand can do the job, the leakage inductance from the transformer can be used, but the question is how?
 

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In sine wave inverter design, we use pwm signal s too switch the H-bridge alternately thats why we use 7v transformers because its SPWM signal and is not 50% duty cycle, during charging to High side mosfet will go off and the two low side mosfet oscillate which in turn makes transformer to work as boost converter and by doing so the voltage can go up to 14v, note :when the High side mosfet go off during charging it act as a Rectifier.. Hope this helps..
 

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Thank you for the reply. I want to know,

1. The low side oscillate together or one after the other? I mean both will ON and OFF at same time, or one will ON while the other will OFF

2. What frequency will they oscillate?
 

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The challenge in making your converter bi-directional is to design a step-up ratio that makes up for losses, then also making the identical transformer have a step-down ratio that makes up for losses in the other direction. Either direction causes losses. To find the correct winding ratio seems like the impossible dream.

To create the charging function, it might merely require winding a few more turns on the low voltage winding. Just sufficient turns to change the ratio and obtain a higher voltage produced by the battery side. The rest depends on how your transformer behaves with 50 Hz AC or PWM.
 

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Hello
Why you not look online for a UPS service manual where is a schematic diagram of the whole circuit, I am into UPS field and try all the time get manuals from the internet
The small capacities UPS have data online
Look at this link, there are many types similar to design you work o I think

UPS Schematic Diagram - AliSaler.com

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Look at the circuit and see how the designer made the charging circuit and use as a reference for your design
I talk about the transformer based UPS, small capacity, as there are many types and different capacity

I have a manual for some machine at work, I’ll try to photo and send you here
--- Updated ---

They often use relay to be triggered when ac plug in
 

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