# Multi Input/Output DC to AC Power Supply--Help Needed Please

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#### gizander

##### New Member
Hi all!
A friend of mine has this Nokia gadget that has 8 digital outputs that can put out 6-30 VDC. I was asked to help design and build a circuit/s to turn each output into 220-240 VAC to make 8 outputs, each capable of supplying a 500 Watt device. I've been looking at inverting circuits and done some price calculating and 8 separate inverter circuits would cost a great deal. I dont suppose there is any way around this since each 6-30V output needs to trigger a separate device (but if anyone knows of a cheaper solution or at least cheaper "inverter" circuits help would be appreciated). Basically, the thing I really need to ask is if each DC output gives 6-30V what kind of circuit would I need to design or look for that could take this variable input voltage and put out a steady 220VAC? Thanks!

#### Diver300

##### Well-Known Member
What you are asking is basically impossible, or at least extremely difficult. I also think that you actually want something different.

A device that has an input anywhere in the 6 - 30 V and outputs 500 W at 240 V would have to draw over 80 A at 6 V, falling to 16 A at 30 V.

When you say that the Nokia gadget outputs 6 - 30 V, that is a very wide range for a DC supply. I guess that the gadget can switch a voltage in that range, so if you provide it with say 12 V, you have 8 outputs that are either 0 V or 12 V. I would also be surprised if the Nokia gadget could switch or supply more than 2 A or so.

Then we come to power. Where is the power for this device coming from? 8 outputs at 500 W is 4000 W. If that is coming from a low voltage source, say 24 V lorry batteries, it's over 150 A which is a serious current and well outside the scope of an amateur. If the power is coming from a mains supply, it's plain stupid to transform it down to a low voltage, switch it, and transform it back to 220 V.

If you want to control 8 devices, each up to 500 W at 220 V, from a device that can switch a low voltage, you need a low voltage power supply, and 8 solid state relays.

#### schmitt trigger

##### Well-Known Member
Exactly what type of gadget is this Nokia device?

#### gizander

##### New Member
Thanks for the replies...i noticed a ton of members pass this over w/o replying...lol. Yes, it does seem impossible. The device is a Nokia 12. I think what my buddy needs is just to use it to control stuff with his mobile phone. What if I used mains electricity to supply the power needs of the 8 500W devices and just used the Nokia 12 to be the "switch"? Each output can be set to 12V (so its easier to work with and not variable) and each has a positive, negative and Trigger output. If i used 8 relays, each connected to a digital output from this thing, how would the circuits look like? I was thinking that each relay could be switched closed by one output (but where to connect what?) with a protector diode across the relay coil to protect the N12 from back EMF (?) and each relay would act as an electromechanical switch to close the circuit of a socket drawing from the mains. (???)
If this is the solution, could anyone help me with the design of the circuits? Would I need a resistor and transistor in series to amplify the signal that turns on the relay (since i assume the N12 outputs very tiny currents from its internal ICs...)??? Thanks in advance for any help folks!

#### Diver300

##### Well-Known Member
You seem to be getting the right idea.

http://www.control.com.sg/docs/Nokia_12_Hardware_Integration_Manual_V2_0.pdf

That might help.

The Nokia 12 doesn't seem to be made any more, but I'm not sure. Like all GSM modules, it can only output a small current, so you will need a transistor amplifier and then a relay to switch 500 W. I don't think that the Nokia 12 can output more than 5 V.

I'm not sure, but I think that you will need to programme the Nokia 12, or connect it to a microcontroller to get the outputs to switch in response to a text message.

#### gizander

##### New Member
@ schmitt trigger: the Nokia 12 has a sim card and 8 digital (and 3 analog) outputs and it can control devices by outputting 6-30V from each output...something like that...i'm not really savvy w/ digital stuff. It's basically a gadget, that when hooked up properly to other gadgets, can turn them on or off or send you text messages that a door or switch has been opened or closed, etc.
@ Diver300: Thanks for the link...i'll go through the document and see if it helps...if not, see you back here...lol...thanks all!

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