Not to do with contracting or even computers, but the expertise on here is interesting sometimes.
Here's my requirement: I want to operate a 240V fridge from 12V. Actually it will be a 240V freezer used as a fridge: therefore I need to get an appropriate thermostat, and use an inverter. Keeping the power consumption down is the main point, so I won't keep the inverter on all the time. The ensemble must run unattended.
I'll put aside the question of the thermostat for the moment (use a fridge thermostat, or an electronic one?) because it may be influenced by the other question: how do I power up the inverter only when needed? Question: is it necessary to give the inverter some time (e.g. 1 or 2 seconds) before switching on the fridge? If so, what's a good way to do it?
1. Just spring for a demand-sensing inverter. They cost more but the problem is solved.
2. "you can do anything if you use enough relays". Thermostat provides a 12V signal. Apply it to a relay that switches on 12V power to the inverter. Also apply it to a relay that switches the 240V from the inverter to the fridge: but delay this switch-on. Simple method: small resistor in series with relay coil, sodding great capacitor across it. Problem: that will keep the fridge load on after the inverter supply is off. Is that a problem? Fix it by disconnecting the capacitor with a spare set on NC contacts on the relay (and discharging it slowly with a resistor across it, so that it doesn't buzz the relay when power goes off and the contacts get closed again).
3. "the 555, glue of the universe". Monostable to delay make for the 2nd relay.
4. Both of those switch off the fridge at the same time as the inverter, at best. Would it be better to switch off the fridge first, then the inverter? Maybe I could re-use the capacitor in no. 2 to hold the inverter's relay on for 1 or 2 seconds? But I think that needs another relay.....
Here's my requirement: I want to operate a 240V fridge from 12V. Actually it will be a 240V freezer used as a fridge: therefore I need to get an appropriate thermostat, and use an inverter. Keeping the power consumption down is the main point, so I won't keep the inverter on all the time. The ensemble must run unattended.
I'll put aside the question of the thermostat for the moment (use a fridge thermostat, or an electronic one?) because it may be influenced by the other question: how do I power up the inverter only when needed? Question: is it necessary to give the inverter some time (e.g. 1 or 2 seconds) before switching on the fridge? If so, what's a good way to do it?
1. Just spring for a demand-sensing inverter. They cost more but the problem is solved.
2. "you can do anything if you use enough relays". Thermostat provides a 12V signal. Apply it to a relay that switches on 12V power to the inverter. Also apply it to a relay that switches the 240V from the inverter to the fridge: but delay this switch-on. Simple method: small resistor in series with relay coil, sodding great capacitor across it. Problem: that will keep the fridge load on after the inverter supply is off. Is that a problem? Fix it by disconnecting the capacitor with a spare set on NC contacts on the relay (and discharging it slowly with a resistor across it, so that it doesn't buzz the relay when power goes off and the contacts get closed again).
3. "the 555, glue of the universe". Monostable to delay make for the 2nd relay.
4. Both of those switch off the fridge at the same time as the inverter, at best. Would it be better to switch off the fridge first, then the inverter? Maybe I could re-use the capacitor in no. 2 to hold the inverter's relay on for 1 or 2 seconds? But I think that needs another relay.....
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