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1  Using Arduino / General Electronics / Re: Going from 120VAC to Arduino VDC on: December 11, 2012, 08:38:44 am
Transformers are the easiest, you can salvage them from old hardware or buy them quite easily you want one with 120v primary and 12v secondary.

You can connect like this to a bridge rectifier and a capacitor:

This will give you approximatly 12v DC, you will then need a regulator. The 78xx linear regulators are good and I have used them for years, however they are not that efficent and they generate quite allot of heat at higher loads. If you are only powering the arduino and a few other small components the 7809 would give you 9v that you cold feed into the arduino Vin, the arduino would then use its own internal regulator to get its 5v.

You could instead use a 7805 and connect this to the 5v pin on on the arduino and leave Vin disconnected, if the 7805 is attached to a heatsink you can take upto 1A from it.

What I tend to do is use small DC-DC converter modules like this:

I adjust them to 5v and connect directly to the 5v pin on the arduino, these can give you as much as 3A and have a very wide input voltage.

I have managed to buy these boards from "direct from china type online stores" for about £1.50 each. If you need higher loads these are far more efficent than the linear regulators.

I am guessing for your application, you could select an appropriet transformer, rectifer(could just be 4 diodes), and capacitor and connect the supply to the Vin pin this will make use of the on board linear regulator.

2  Using Arduino / General Electronics / Re: Filter circuit for Arduino controled water heater on: December 11, 2012, 04:11:57 am
I will give that a try, the only thing I am worried about is making the lights flicker each time it is turned on and off.

The input circuit has a couple of large 260 micro Farad capacitors on it so not sure if they would smove lower frequencies out.

I have some more pictures si I will try and upload them on my lunch break.

3  Using Arduino / General Electronics / Re: Filter circuit for Arduino controled water heater on: December 10, 2012, 01:18:27 pm
Thanks for the replies.

I am using a standard emersion heater in a domestic water tank, so I would like to avoid non standard elements. The idea of using multiple elements is interesting, however I think I would struggle to get the fine control that is needed for charging the battery. I am also not keen on bringing high current wires into the house.

The inverter is also used to power the lighs and computers/tv, switching for longer periods of time would probably cause flickering so I would like to avoid that.

Changing the PWM frequency is definitely an option, so I will take a look at doing that.

Does anyone have any sugessgions for a filter design with the PWM at a higher frequency?

As for the last point "Has anybody pointed out that switching a heater on/off at 10kHz is silly...?", in what way would you sggest modifying the program?

Thanks for your time.
4  Using Arduino / General Electronics / Re: Filter circuit for Arduino controled water heater on: December 10, 2012, 09:43:56 am
The power comes from an inverter it is then rectified and filtered to prevent noise getting back to the ac line, the inverter is used to power the lights and small ellectrical appliances. In tests so far it does not seem to make the lights flicker so I guess the filter in the rectifier is working fine.

The circuit is in the garage close to the inverter, batteries generator etc the switched power then goes down 8 meters of wire to the hot water tank in the hose.

The inductor would be in the garage so it could sing to its harts content (I cant hear it there) the line going into the house would be far better if it is DC as I guess it would make quite an antena for the rf interferance.
5  Using Arduino / General Electronics / Re: Filter circuit for Arduino controled water heater on: December 10, 2012, 09:36:56 am
I have solar panels charging deep cycle batteries, on bright days the pannes produce more power than the batteries can take so the voltage regulator on the panes just cuts them off.

This is obviously a waste of power, but also its better to keep the battries at a constant 28V. So the idea with this circuit is to divert the small amout of excess power from the solar panels to the hot water tank. This should result in better charging of the batteries, and free hot water.

6  Using Arduino / General Electronics / Filter circuit for Arduino controled water heater on: December 10, 2012, 09:04:24 am
Hi All

I have been working on a circuit for diverting excess power from solar charged batteries to a domestic emersion heater. The circuit measures the battery voltage, when it starts to approch 28V it increases a pwm output on the Arduino this then goes through an opto isolator into an IGBT switching 240V DC. This is all working fine, I have a web page with images and a description here:

The problem with this circuit is that it makes the heater element wine, quite loud and I am a little worried that it may fatigue the coil in the element. So I am thinking of adding a filter circuit with an inductor, capacitor, and a free wheel diode.

I have very little experience selecting inductors, would anyone be able to advise what would be sensible?

The element is 3kw 240v, I am planning on switching upto about 50% duty cycle.

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