# automatically AC to DC Problem

#### blackredrobin

Joined Sep 14, 2011
9
hello pals I want to make a led light with super flash led with some 6 or 8 (say) and then modify the usual light bulb into both AC and DC.
In my place electricity failure is very common so I just want this light to connect to the light holder and FED on 230 v (AC Hz) and when their is electricity failure than its automatically send DC 6v 4.5 (rechargeable cell) AH to illuminate the LEDs (Sound like a bit like UPS or Inverter type) I have attached the initial circuit diagram for reference .

But the Problem is how to make the thing work i.e what will I need to make the cuicuit work when the 230V is cut and to sent current for the 6v cell vice-versa.

Thanks

Last edited:

#### blackredrobin

Joined Sep 14, 2011
9
Sorry I forget to upload the file

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#### #12

Joined Nov 30, 2010
18,224
There are several ways to do this. One is to have the 240 volts hold a relay on so that when the power fails, the relay switches to the battery supply. Another way is to design the circuit so that only a diode is used. When the AC power fails, the battery is allowed to send its currnet to the LEDs

#### Audioguru

Joined Dec 20, 2007
11,248
Your circuit has nothing to limit the current to LEDs L1 to L10 so they will be very dim (or not light) or they will all burn out.
You are limiting the voltage to L3 to L10 with the series diodes instead but LEDs need the current limited, not the voltage limited. A series resistor (like R1) limits current. L1 and L2 need their own series current-limiting resistor.

You don't need D1. Connect R1 to D2 and D3 instead.

You do not have a filter capacitor so the LEDs will flicker on and off at 100Hz.

Joined Dec 26, 2010
2,148
If the 6V battery is connected straight to the rectifier for charging, with 9V (?) AC input and no current restriction, transformer, rectifiers and battery will all fry.

#### Audioguru

Joined Dec 20, 2007
11,248
If the 6V battery is connected straight to the rectifier for charging, with 9V (?) AC input and no current restriction, transformer, rectifiers and battery will all fry.
I didn't notice that nothing limits the battery charging current except the little 1A transformer that will fry. I think the rectifiers and battery will be very hot but they will survive. But the battery will soon boil dry.

Joined Dec 26, 2010
2,148
Perhaps this all sounds very critical, but the point is that the circuit as shown is unlikely to work properly. It may also destroy expensive parts, or even catch fire. Depending on the technology used, if the battery became overcharged it might burst or leak, possibly giving off poisonous or corrosive materials.

In any circuit of this kind, you need to be able to be confident that all currents will be at predictable safe levels, allowing for any likely changes in components, temperature, mains voltage, battery charge state and so on.

For instance, what happens if the battery is dead flat? Someone may say that, as the battery may be beyond recharging, we may not care. Not so! A dead battery is bad enough, a dead charger is worse, but burning the house down is far worse still. Let's not have any accidents!

#### #12

Joined Nov 30, 2010
18,224
True, the design you presented is lacking in many ways. Be sure to check back here when you have tightened up the safety issues and we will check it for you.

#### blackredrobin

Joined Sep 14, 2011
9
thank you all for your invaluable suggestion. yes i know there are some potholes in this design. I think, I have to start again, since I did'nt dare to work after your all advices on this design. there is also one problem that I thought later that.
If the current circuit is given a rectifier it may switch the ac to dc and vice virsa but. in days the main ac fed to circuit will switch off so that i dont need light on days. this will cause the dc to fed to the circuit resulting illuminating the LED. which I dont want the circuit to behave that way. any good design on this I shall always be indebt to you all folks.

#### K7GUH

Joined Jan 28, 2011
190
I think you are making this much too complicated. Use a 230 v.a.c. to 12 v.a.c. transformer, rectify the 12 v.a.c. with appropriate current and voltage limiting to charge a 7.5 Ah sealed lead acid battery, and run the LED's off the battery. This should work whether the mains voltage is present or not. You can make it much more complicated and fancy to the nth degree, but why?

#### blackredrobin

Joined Sep 14, 2011
9
sorry to misguide for reversing the current form ac to dc it is not to use a rectify but relay