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Forum Index : Electronics : 240V timers, persistion paid off
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Tinker Guru  Joined: 07/11/2007 Location: AustraliaPosts: 1904 |
I required a timer to control solar RE equipment I'm building at present. The choices were mechanical or digital timers, I bought one of each and commenced testing them. The mechanical timer (24 hour type with setting pegs @ 15 min) was a rather poor time keeper, too inaccurate for my liking. The digital timer was very accurate, it has a minimum on time of 1 min (I only need <10 sec), 24hr/7day/ 14event per day, just perfect for my intended use. However, when I measured their power consumption I was in for a surprise. In standby (switch off) the plugged in mechanical timer would consume about 9KWh per year. The digital timer consumed a whopping 50KWh per year. Way too much for a solar system where one aims for the lowest consumption in all parts in the power producing circuit. That digital timer bothered me. I eventually managed to take it apart (a small feat by itself) to find out where the power went. From the 240V side it has a simple series capacitor/ resistor, followed by four diodes connected as a bridge rectifier, a small smoothing electro cap and a 24V 1W zener diode to regulate the output. The timing electronics are fed of this, via another zener circuit, regulated to a 3.5V operating voltage. The switching relay is 24V DC operated. The power gobbling was done by the 24V zener across the bridge rectifier. I decided, after studying the traced cicuit, that the best option was to remove all 240V components and power the timer from my 24V battery bank. Big surprise again, it now consumes 1.27KWh per year, powered from fully charged batteries (28V). That is a reduction of 39 times! The final consumption might be closer to 2KWh/year when one includes the relay on time & associated LED. I should point out that I am a licensed electrician and fully aware what tampering with mains operated timers involves. Klaus |
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GWatPE Senior Member  Joined: 01/09/2006 Location: AustraliaPosts: 2127 |
Hi tinker, I am planning on using a time clock to reduce the night time consumption of one of my older Solar Grid connect inverters. The SunProfi unit has 18W static load it seems. The Latronics unit has 5W, and will need to look at other options like DC activated SSRelay system. May end up with this type on both inverters. The new SMA SunnyBoy inverters consume nothing at night. Gordon. become more energy aware |
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| davef Guru Joined: 14/05/2006 Location: New ZealandPosts: 499 |
I bet you'd be losing a lot more in whatever series resistor there is to drop the mains voltage. If you want REALLY low power consumption in a timer that could do anything you wanted, look at the ATMEL AVR Pico series microcontrollers. |
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| GWatPE Senior Member Joined: 01/09/2006 Location: AustraliaPosts: 2127 |
I doubt that making a dedicated unit to just replicate an off the shelf unit that consumes 1.5W[mechanical type including ON/OFF switches and CE rated 240VAC connections] or 0.5W[Arlec digital with relay and CE rated 240VAC controls and connections]. Dropping the mains voltage with a resistor is not how you power these units. It is the capacitor that drops the voltage. The resistor gives current limiting. The mechanical timer I have has a synchronous motor 240VAC and a mechanical switch. No electronics. The SSRelay powered from the 5V internal inverter rail looks the best option still. Gordon. become more energy aware |
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| davef Guru Joined: 14/05/2006 Location: New ZealandPosts: 499 |
I'd have to refresh my real and imaginary power theory. What is the resistor value and how much current is flowing through it? Or, how volts across it? That will tell us how much real power is lost in the resistor. The reactive current still has to flow through the resistor. Please, tell me if I have this wrong. |
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| Tinker Guru Joined: 07/11/2007 Location: AustraliaPosts: 1904 |
The resistor is only 100 Ohm. You do have it wrong, as Gordon said, its the mains rated capacitor that does the voltage dropping. The DC voltage measured at the bridge output was around 33V. I played around with series resistors to the zener diode (there is provision to insert one on the board) but it makes no difference to the current drawn. The relay requires 24V, its coil is in series with a LED which obviously lights up as current flows through the relay coil in the 'ON' state. I suppose this current is around 20mA to light the LED. But the timer draws 23.7mA @240V *all* the time, the zener shunts this current to regulate the voltage to 24V. Gordon quotes a much lower consumption for his Arlec digital timer, my HPM draws over 5W but its the only timer I found that has the program I require. Klaus |
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| davef Guru Joined: 14/05/2006 Location: New ZealandPosts: 499 |
Thought the resistor would be much bigger, so point taken. 23.7mA through a 33V zener is 0.7821Watts. Circuit draws 230V * .0237A = 5.451W, so the remaining 5.451 - 0.7821W = 4.6W is required to operate the timer and hold the relay ON. Seems reasonable. Would a latching relay do the job for you? |
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| Tinker Guru Joined: 07/11/2007 Location: AustraliaPosts: 1904 |
FYI we have 240V mains here in Oz and the zener is a 24V type. If you read my first post above again you will read what my solution to the problem was. Thanks for your suggestions but I feel one really needs to study the circuit to quote figures, descriptive words are not always enough. I was basically just mentioning that digital mains timers do draw current, much more than anticipated in my case. Klaus |
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electricme Newbie  Joined: 14/01/2009 Location: AustraliaPosts: 5 |
@ Tinker, Have you ever tried to draw voltage out of the earth using a copper pipe and a zinc nail? If so, what success have you had. jim |
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| Fernanda Newbie Joined: 05/02/2011 Location: United StatesPosts: 2 |
Some of the resistors have 100 ohm only. The DC voltage can be measured by the bridge in the output around 33v. The relay should also be 24v and higher so you will not experience some problem. My Sports Timer |
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KarlJ Guru Joined: 19/05/2008 Location: AustraliaPosts: 1178 |
Nice one I have a HPM timer that I use for the solar water heater for the pool 10mins off 2mins on etc during peak sun hours only. however this time of the year pump doesnt turn on as its too warm already. just saved me 24 x 5 W = 100W a day 
Thankyou I'll take it. Now switched off until the adding heat is required again and when that is over will be off again until next adding heat period. Regards Karl Luck favours the well prepared |
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