So, here's my latest project. We get occasional blackouts here, and certainly have the risk of them with hurricanes (although no power loss with the last hurricane). We had one yesterday for two hours when they were replacing the poles and someone must have screwed up because 1900 homes lost power.
We have a fridge that we keep some expensive medications in. When the compressor is on, it consumes 80 watts, and otherwise near zero, cycling on and off. So really small electricity usage which is nice for this, and does a great job controlling the temperature in the safe range for medications.
I just took a marine deep cycle battery and hooked it up to a pure sign wave inverter and plugged the fridge into it. It works great, and keeps the medication at a safe temperature. Should run about a day on its capacity.
Now, if we're away from the house, there is no way I'm going to be able to talk someone over the phone into unplugging the fridge from the wall, plugging it into the inverter, and turning the inverter on. In the dark. So, I figured, lets build a homemade uninterruptible power supply. Far, far more capacity - run time than a typical computer UPS (battery is massively bigger, about 90AH).
Still a little iffy about how to wire it, but I think I've got it. I do have some questions for our electricians.
I bought a relay with a 120V AC coil. I haven't measured the resistance on the coil yet, but have been wondering how much energy it will consume just in standby, plugged into the wall, waiting to flip if the power fails. Just looking online, it looks like some of these relays have a 75ohm resistance. If that's so, the relay will consume 192 watts. That seems like a ton. Would it be helpful to add a power resistor inline to reduce the energy consumption? Would the relay still work?
Also, is the correct method to essentially just plug the coil into the wall AC current, or is that a short circuit that will fry the relay, tremendously heat up, or flip a breaker?
Lots more questions to come, but let me start with those important ones.