Building Uninterruptible Power Supply for Medication Fridge

[Alan Lightstone]

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.

[Frank Pratt]

I would just buy a suitably sized UPS. Done. No need to plug and unplug anything.

[George Yetka]

Ive purchased some refrigerators for medical jobs that have these features. But at the price of those you can put in a whole house generator and reduce this issue.

Something like this may be a better purchase (im not sure of the temp your looking for)
https://ivyxscientific.com/products/minus20freezer?variant=42755340501158&currency=USD&utm_medium=product_sync&utm_source=google&utm_content=sag_organic&utm_campaign=sag_organic&srsltid=ASuE1wSGuTNMFhfQJJ9FurTxSPOLyxRUsm65YG4g1y wj5Y4cbeFQigSmjS0

[Alan Lightstone]

Ive purchased some refrigerators for medical jobs that have these features. But at the price of those you can put in a whole house generator and reduce this issue.

Something like this may be a better purchase (im not sure of the temp your looking for)
https://ivyxscientific.com/products/minus20freezer?variant=42755340501158&currency=USD&utm_medium=product_sync&utm_source=google&utm_content=sag_organic&utm_campaign=sag_organic&srsltid=ASuE1wSGuTNMFhfQJJ9FurTxSPOLyxRUsm65YG4g1y wj5Y4cbeFQigSmjS0
Looking for a relatively inexpensive solution. Since I already own the battery and inverter, it's now just about the electronics to make it switch over to the inverter when the power fails.

The fridge is to keep the medications 36-46°F (2.2-7.7°C). So while that freezer is really interesting, what we need is for insulin and biologics.

Do you just hook up the relay coil directly to AC current? That's my biggest question. The rest of the wiring I think I can figure out.

[Doug Garson]

Not an electrician but how about if you run the fridge off the inverter powered by the battery full time and keep the battery charged with a charger plugged into the wall? What am I overlooking?

[ChrisA Edwards]

In the RV industry, i.e motorhomes, 5th wheel trailers etc, we have transfer switches that detect being plugged into the electrical grid.

If not plugged in, i.e. when we are traveling, it transfers to an inverter which powers the fridge from the battery.

Expensive; I have a 270AH lithium battery that would probably power that fridge for several days.

[Alan Rutherford]

Reply deleted

[Alan Lightstone]

Not an electrician but how about if you run the fridge off the inverter powered by the battery full time and keep the battery charged with a charger plugged into the wall? What am I overlooking?
May be nothing, and I do have all the equipment to do that so an interesting idea. Does that wear out the battery quicker though? Certainly uses more power, as less efficient.

[Alan Lightstone]

Something like this?

Sounds like the solution.
https://www.amazon.com/AC120V-Automatic-Transfer-Switch-HD060/dp/B0BRQ7KQQ7/ref=sxin_21_pa_sp_phone_search_thematic_sspa?conte nt-id=amzn1.sym.ef491751-6e4f-407c-96ed-c531e185f804%3Aamzn1.sym.ef491751-6e4f-407c-96ed-c531e185f804&cv_ct_cx=rv+transfer+switch&keywords=rv+transfer+switch&pd_rd_i=B0BRQ7KQQ7&pd_rd_r=114e89a0-acd0-44c4-9f21-63d470938179&pd_rd_w=ltp5s&pd_rd_wg=FotVO&pf_rd_p=ef491751-6e4f-407c-96ed-c531e185f804&pf_rd_r=SPC5140VG99CQXGXVTJJ&qid=1690909552&sr=1-2-2b34d040-5c83-4b7f-ba01-15975dfb8828-spons&sp_csd=d2lkZ2V0TmFtZT1zcF9waG9uZV9zZWFyY2hfdGhlbWF 0aWM&psc=1

[George Yetka]

Something like this?

Alan your battery would be DC, so you'd also need an inverter before going into this and have a way of charging the battery

[Lee Schierer]

Why not purchase a RV fridge that works off of 120 volts or 12 volts and propane. Ours maintains temperature pretty well as long as you don't open and close the door frequently. It will operate for days off a 12 volt battery and a tank of propane. Norcold makes a wide variety of sizes.

[Alan Lightstone]

Alan your battery would be DC, so you'd also need an inverter before going into this and have a way of charging the battery

I already have both, and they are already wired up. Right now I have to switch over manually, and the inverter needs its power switch turned on to work.

[Alan Lightstone]

Why not purchase a RV fridge that works off of 120 volts or 12 volts and propane. Ours maintains temperature pretty well as long as you don't open and close the door frequently. It will operate for days off a 12 volt battery and a tank of propane. Norcold makes a wide variety of sizes.
Already have the fridge. Interestingly, I have a very accurate Bluetooth temperature disc/thermometer I use to look at the temperature of the fridge (I use this when traveling to monitor the medicines temp in our insulin cooler). This fridge I bought is great at staying in range. Our full size kitchen fridge - terrible at it.

[George Yetka]

I already have both, and they are already wired up. Right now I have to switch over manually, and the inverter needs its power switch turned on to work.

Oh you really are there then. That should work.

[Jim Becker]

One "modern" solution is one of the ever-popular and growing products from the "battery generator" industry with solar charging as an option in addition to from the main power supply. They are basically similar to a UPS, but have more smarts and can even talk to you about their status. There are a whole bunch of brands.

[Doug Garson]

You also need to monitor the battery to make sure it is charged when you need it. We have very infrequent power outages, (last one to last more than a few minutes was over a year ago) and last time we had one at night I connected my CPAP to my backup battery and dead :mad:. I need to remember every few months to plug it into the charger. In your case you might also consider keeping a few ice packs in your freezer as a second backup method.

[Brian Runau]

Would solar with batter backup work?

[Paul F Franklin]

Lot of replies here and I didn't see an answer to your questions...So, ahem...

If it's a 120 volt ac coil on the relay, you just connect it directly to 120 volt line. Even a fairly large relay will draw less than 100 milliamps current from the 120 volt line to keep the coil energized, so less than 12 watts. Smaller relays will be even less, and a solid state relay, even less than that.

I'd probably put a 1 amp 120 Volt rated fuse (so not an automotive fuse) in series with the relay coil so in the very unlikely event of the coil shorting out, the fuse will blow.

I assume you are switching the DC to the inverter, so you need a relay rated to switch DC. It should be rated to switch DC current of at least twice what your inverter draws fully loaded to ensure long life of the contacts (although it won't switch very often, so not much of an issue).

[Ed Aumiller]

What Doug said.... buy a 12v charger that stops charging when battery is full..(almost all today are that way)... put it on a quality deep cycle (marine?) battery ... connect a small inverter (300watt??) to it.. plug refrigerator into inverter..
The battery will always be close to full charge and the charger will use minimum current except when the refrigerator is running and then only about what the refrigerator is using...
I did this for years to make an UPS for our house wifi modems and laptops... the battery never wore out !!!
With the modern batteries you probably would never have to replace it!!

Just remembered that my house alarm system uses same setup, except it uses a small motorcycle battery and it is almost 25 years old and still working !!!

[Steve Demuth]

I think you're looking for one of these: https://www.amazon.com/Switch-Battery-Controller-Automatic-Emergency/dp/B07RS48WTH.

[Keegan Shields]

For our business, we use off-the-shelf UPS to cover power interruptions for critical equipment.

The cost depends on capacity needed and the battery needs to be replaced periodically, but they take care of the battery charging and switch over to battery power when grid power is lost.

Something like this:

Server UPS (https://www.amazon.com/Tripp-Lite-Line-Interactive-Protection-SMART1500LCDT/dp/B009TZTGWK/ref=sr_1_1_sspa?crid=PKU1RF0F9U42&keywords=server+ups&qid=1690928316&sprefix=server+up%2Caps%2C149&sr=8-1-spons&sp_csd=d2lkZ2V0TmFtZT1zcF9hdGY&psc=1)

[Alan Lightstone]

I think you're looking for one of these: https://www.amazon.com/Switch-Battery-Controller-Automatic-Emergency/dp/B07RS48WTH.
Just looked at the specs. The voltage of the power source, battery, and charger must be equal. All DC.

[Alan Lightstone]

Would solar with batter backup work?
That would work out great for our whole house solar array. But for $37K or more, have to pass on that.

Also, no way to have solar wired to the room it's in.

[Alan Lightstone]

Lot of replies here and I didn't see an answer to your questions...So, ahem...

If it's a 120 volt ac coil on the relay, you just connect it directly to 120 volt line. Even a fairly large relay will draw less than 100 milliamps current from the 120 volt line to keep the coil energized, so less than 12 watts. Smaller relays will be even less, and a solid state relay, even less than that.

I'd probably put a 1 amp 120 Volt rated fuse (so not an automotive fuse) in series with the relay coil so in the very unlikely event of the coil shorting out, the fuse will blow.

I assume you are switching the DC to the inverter, so you need a relay rated to switch DC. It should be rated to switch DC current of at least twice what your inverter draws fully loaded to ensure long life of the contacts (although it won't switch very often, so not much of an issue).
Thanks, Paul. Was wondering about that as a safety issue.

Actually, since the particular inverter I have won't automatically turn on when energized (stupidly, they have an solid state on/off button on it), I'll be switching the AC output from the inverter.

It sounds like the RV automatic transfer switch will be the way to go. It will switch the AC output from the inverter when the AC line power fails. Since the inverter will always be getting 12V DC from the battery, I'll just turn on its switch, and it will stay on, but producing no power as it has no load until the transfer switch closes the contacts. I'll keep the charger hooked up to it. Presently I have it on a timer to trickle charge it once a week. It sounds like I can just keep it on, and it will stop charging when the battery is full.

[Steve Demuth]

Just looked at the specs. The voltage of the power source, battery, and charger must be equal. All DC.

Sorry, my bad. I was looking for DIY alternative to an off the shelf transfer switch, and didn't read the fine print. This is the link I was originally looking for: https://www.amazon.com/AC120V-Automatic-Transfer-Switch-HD060/dp/B0BRQ7KQQ7. Understand that it's probably a bit pricy compared to what you're trying to do.

[Alan Lightstone]

Sorry, my bad. I was looking for DIY alternative to an off the shelf transfer switch, and didn't read the fine print. This is the link I was originally looking for: https://www.amazon.com/AC120V-Automatic-Transfer-Switch-HD060/dp/B0BRQ7KQQ7. Understand that it's probably a bit pricy compared to what you're trying to do.
I purchased one. On paper looks like a perfect solution. I'll hook it up in a couple of days and see how it goes.

[Leo Graywacz]

Looking for a relatively inexpensive solution. Since I already own the battery and inverter, it's now just about the electronics to make it switch over to the inverter when the power fails.

The fridge is to keep the medications 36-46°F (2.2-7.7°C). So while that freezer is really interesting, what we need is for insulin and biologics.

Do you just hook up the relay coil directly to AC current? That's my biggest question. The rest of the wiring I think I can figure out.

Don't do any of that. Hook up a charger to the battery and that's it. The battery charger keeps the battery up to snuff and the inverter powers the fridge. When the power goes out the charger no longer charges the battery but that's it, the battery keeps the inverter working so the fridge keeps working. When the power returns it will charge the battery back up again.

[Alan Lightstone]

Don't do any of that. Hook up a charger to the battery and that's it. The battery charger keeps the battery up to snuff and the inverter powers the fridge. When the power goes out the charger no longer charges the battery but that's it, the battery keeps the inverter working so the fridge keeps working. When the power returns it will charge the battery back up again.
An interesting, simple approach. My concern is which approach is more susceptible to failure, when we're not at home to notice it (or at home for that matter, and the battery/charger fails and we don't notice that).

Of course, in the outdoor scenario here in Florida, car batteries tend to die in 2 years. The brutal heat takes its toll. This battery, while it did live outdoors for a few weeks, lives in a constant 74°F, so it has an easier life. But if/when it fails, there is no backup if it is the usual power source for the fridge, and the medication is ruined. Unless the inverter can carry the load of the refrigerator on its own, and it's not designed to do that.

Which is the most likely part to fail? The inverter (which will not restart if it loses power)? The battery charger (not the most expensive one, but not garbage either)? Duke Energy providing energy to the house? The RV transfer switch (which is a cheap part, but how likely is it to fail when power goes out and its coil stops the contacts from staying attached to the AC part of the circuit)?

With the RV transfer switch, the fridge runs off utility 120V AC for 99+% of the time. In case of a blackout, the transfer switch needs to flip over to the battery system, and the fridge stays powered. My hunch is that this is the most reliable setup (it is, after all how typical UPS systems work). Essentially, this is replicating a UPS system.

What do you all think? Which is likely to be most reliable?

[Leo Graywacz]

So you need a back up for your back up?

I understand you overthinking this but there are going to be situations beyond your control. How far do you plan on going? The inverter can fail, the refrigerator can fail, the charger can fail. If you put in a UPS it is essentially what I described. An inverter working on a battery with a charger so that when the power fails the battery just continues on providing power until the battery is depleted. The bigger the battery the longer the protection.

Put a power alarm on the device so when it fails the alarm sounds. If you aren't around to notice it's going off it won't really matter.

You want to do this with items you have instead of going with a specialized dedicated system. Well dedicated systems are specialized to protect and have other safety features, but they cost an arm and a leg. You want the shortcut to reduce the cost. I'm not sure you can have it both ways.

So it's up to you to decide the risk factor. Use a LIFePO4 battery with a charger and hook it up to your inverter and it should provide you with good protection. Not perfect, nothing is unless you have countless redundant systems as backups.

Good luck.

[Jim Becker]

That would work out great for our whole house solar array. But for $37K or more, have to pass on that.

Also, no way to have solar wired to the room it's in.

Just a program note that this is different than I was suggesting...which was something like a Bluetti or Jackery portable "battery backup generator" and power supply that can be recharged with solar panels if necessary or desired.

[Steve Demuth]

To be reliable and long lived systems, including the batteries, need to be designed for the charge and discharge cycles they follow. A typical car battery is designed for frequent relatively shallow discharge cycles, and is probably not a bad match for the way your refrigerator uses power in that respect. But it's going to be the equivalent of starting a car a couple dozen or more times a day (assuming your fridge has to run for a few minutes every hour, at minimum). The battery life will affected accordingly. You would also need to consider the charger = it should be regulated to only charge when the battery is discharged, and to throttle off when the battery is fully charged. Overall, unless you're into designing charging circuits and regulation, just hooking a charger and inverter to an automotive type battery and letting it run is not an optimal solutio Yourn. If you're looking at any other type of battery, same considerations apply, but with different parameters. Your case, e.g., is somewhat similar to what the drive battery in a hybrid car experiences in stop and go traffic. There is a reason for the elaborate electronics and software that manage those batteries.

On the other hand your battery + inverter + transfer solution isn't perfect either, but it's close to the way a lead acid powered UPS would work. As long as you check the battery periodically for ability to sustain a discharge, and top it up as needed, it's a pretty simple solution - not quite fire and forget, but minimally complicated. If it were me, I'd have gone out and bought a real UPS, but short of that, your solutions with the ATS is pretty sound.

[Rick Potter]

Back to what Leo suggested....battery backup with a battery MAINTAINER instead of a regular charger. Deltran Battery Tender is the best known, and what I use to keep car batteries up. They, depending on model, can charge a low battery, but normally cycle on and off as the battery starts to get low, charging at a slow rate to maintain the car battery, keeping it ready for your power outage. After the outage the maintainer will automatically recharge the battery.

I have gone as long as six months without starting an old car, and it they have always started. Got four in use right now. About $40.

[Leo Graywacz]

You can put a solar charger and a outlet fed charger on the battery at the same time. If the AC one dies the solar will continue to charge.

I have a solar/inverter setup in my truck. 3KW sine inverter and a 125AH AGM battery. It'll make almost anything go. I've run my house on it during power outages. Obviously the essentials. But the solar chargers are pretty reliable and you could likely get away with a 50w panel. At least that way there is a redundancy.

[Alan Lightstone]

Back to what Leo suggested....battery backup with a battery MAINTAINER instead of a regular charger. Deltran Battery Tender is the best known, and what I use to keep car batteries up. They, depending on model, can charge a low battery, but normally cycle on and off as the battery starts to get low, charging at a slow rate to maintain the car battery, keeping it ready for your power outage. After the outage the maintainer will automatically recharge the battery.

I have gone as long as six months without starting an old car, and it they have always started. Got four in use right now. About $40.
Is that better than the one I'm presently using? It's this. Seems to be a battery maintainer also:
https://www.amazon.com/Automatic-Maintainer-Desulfator-Detection-Motorcycles/dp/B08L4BGJLC?th=1

[Alan Lightstone]

You can put a solar charger and a outlet fed charger on the battery at the same time. If the AC one dies the solar will continue to charge.

I have a solar/inverter setup in my truck. 3KW sine inverter and a 125AH AGM battery. It'll make almost anything go. I've run my house on it during power outages. Obviously the essentials. But the solar chargers are pretty reliable and you could likely get away with a 50w panel. At least that way there is a redundancy.
Solar isn't an option. The fridge is in an interior room 35 feet off the ground.

[Rick Potter]

Same type, different brand, Alan. Sorry, I must have missed where you mentioned you had one.

[Alan Lightstone]

Well, really glad I put the system together. We went out of town for 5 days, and the utility cut our power twice for over an hour as they are replacing many electric poles. I had finished and hooked up the system the night before we left town (and made a deep cut on my finger needing me to test out the Nexcare I had just bought). Really glad I did it.

The backup power, RV transfer switch, charger, battery worked great. When I got home, I checked history on the temperature disc in the fridge and the system kept the medication at optimal temperature the entire time with ease.

Thanks for all the information, guys. Really helped and saved us from a real mess.

[Leo Graywacz]

A hour outage shouldn't have caused much issues as long as the fridge is kept closed. But glad it worked out and the feeling of not having to worry really makes it worth while.

[John Lifer]

For those suggesting a UPS, at 80 or so watts, it could run 30 minutes on that most expensive UPS ($230 one listed) And if the house is in FL, and the AC was off for several hours, it most probably run way more than what you think. And if power off in August for say 48 hours, that UPS would be long dead. Bad solution for what you are looking for. I like the switch and you can ALWAYS put two batteries in line or more if you wanted longer time. (I'd sure test it to see the time it would keep things cool) I would for sure add just a battery maintainer, heck I use a $15 option from Harbor freight on my tractor in the winter. Has worked for 5 years.
As long as you are charged when you leave, you would be fine.
And fwiw, you can get alarm to a smartphone if your power goes down. Not to expensive an option to at least know it's down.

[Bert McMahan]

Three pages in and only one person replied to your original question- "can you just hook up the relay directly to the AC line voltage"?

Yes, you can. I think you must've misread the datasheet for your relay, because 75 ohms is WAY too low for a 120V relay. That's a reasonable value for a 12V relay, but not 120V. Check out page 3 of this datasheet:

https://cdn.automationdirect.com/static/specs/78relays.pdf

I just picked the first one in the list. Their 120V coil relay has a resistance of 4.43 kOhms, meaning it consumes under 2 watts of power. That's going to be fine to be left on all the time. If you add a power resistor, you'll reduce the voltage across the coil and it won't work.

Also, I doubt you can measure the resistance of the coil with a normal multimeter. Maybe you can, but I suspect the "resistance" they're quoting is the AC impedance at 60 Hz. (Basically, the AC version of resistance is impedance, so the math still works with Ohm's Law). If you measure an AC relay coil using a normal multimeter, you'll get the actual resistance of current to flow to DC voltage, which isn't what you want.

I'd do your original plan- hook up the relay to mains power, then if mains drops out it connects in the battery/inverter solution. Make sure to test it a couple times per year to make sure the battery is still working. This is a better solution (IMHO) than letting the battery run it full time.

If your house power dies, you will know it immediately. If the battery dies and you don't have an extra alarm, you won't know it until your fridge stops working.

Basically, the "critical failure" point here is for the fridge to lose power. With your relay solution, you reach critical failure with *two* things going wrong- your house power dies, AND your battery dies. With the "let the battery run it all the time" solution, you reach critical failure with just *one* thing going wrong- the battery failing.

Now, in any given case you could argue that having option two means that you can detect the battery failure *while you still have house power* and can therefore fix it. With the relay solution, there is potential for you to not notice the battery failure until both items fail.

You can only plan for so many contingencies, but I think I'd still go with the relay solution and put an alarm on the battery itself. Then you're not worrying about the inverter and battery providing fridge loads 24/7, and will notice when the battery dies.

Either solution will work- you can just decide which failure scenario seems less risky from your point of view.

[Alan Lightstone]

Three pages in and only one person replied to your original question- "can you just hook up the relay directly to the AC line voltage"?

Yes, you can. I think you must've misread the datasheet for your relay, because 75 ohms is WAY too low for a 120V relay. That's a reasonable value for a 12V relay, but not 120V. Check out page 3 of this datasheet:

https://cdn.automationdirect.com/static/specs/78relays.pdf

I just picked the first one in the list. Their 120V coil relay has a resistance of 4.43 kOhms, meaning it consumes under 2 watts of power. That's going to be fine to be left on all the time. If you add a power resistor, you'll reduce the voltage across the coil and it won't work.

Also, I doubt you can measure the resistance of the coil with a normal multimeter. Maybe you can, but I suspect the "resistance" they're quoting is the AC impedance at 60 Hz. (Basically, the AC version of resistance is impedance, so the math still works with Ohm's Law). If you measure an AC relay coil using a normal multimeter, you'll get the actual resistance of current to flow to DC voltage, which isn't what you want.

I'd do your original plan- hook up the relay to mains power, then if mains drops out it connects in the battery/inverter solution. Make sure to test it a couple times per year to make sure the battery is still working. This is a better solution (IMHO) than letting the battery run it full time.

If your house power dies, you will know it immediately. If the battery dies and you don't have an extra alarm, you won't know it until your fridge stops working.

Basically, the "critical failure" point here is for the fridge to lose power. With your relay solution, you reach critical failure with *two* things going wrong- your house power dies, AND your battery dies. With the "let the battery run it all the time" solution, you reach critical failure with just *one* thing going wrong- the battery failing.

Now, in any given case you could argue that having option two means that you can detect the battery failure *while you still have house power* and can therefore fix it. With the relay solution, there is potential for you to not notice the battery failure until both items fail.

You can only plan for so many contingencies, but I think I'd still go with the relay solution and put an alarm on the battery itself. Then you're not worrying about the inverter and battery providing fridge loads 24/7, and will notice when the battery dies.

Either solution will work- you can just decide which failure scenario seems less risky from your point of view.
I essentially went with the relay thing (bought ready made RV transfer switch. I also thought the resistance of that relay couldn't be that low.

Is there a power outage monitor that would tell me if the power was out (my utility, Duke Energy, does send out texts, and their outage map, while usually not terribly accurate does give the big picture of the area)? I would have to be able to receive the message with no power and no internet, so that seems difficult.

Also, how would you know if that battery fails? I can monitor that in the house with the inverter (it has a digital readout of battery voltage, as does the charger). I know my solar inverter measures battery voltage and if you are close to it you can see a reading via Bluetooth, but it's also very inaccurate.

The system is done now, and seems to be working great, so this is more intellectual curiosity, and possible help to others.

[alan weinberg]

thread drift—backup power is great but don’t forget temperature monitoring. My SensorPush sends me a text and email if wine cellar temp or humidity rise over set numbers. There are other systems but this one is reliable and cheap.

[Alan Lightstone]

thread drift—backup power is great but don’t forget temperature monitoring. My SensorPush sends me a text and email if wine cellar temp or humidity rise over set numbers. There are other systems but this one is reliable and cheap.
I use SensorPush sensors also. Didn't realize it could send me a text and e-mail. Never used that function. Wouldn't work here with a power failure as we'd lose internet access and wifi, but their sensors have been great for traveling with portable insulin fridges for medications.

Actually, just looked on their website. You need their wifi gateway and I think their higher-end sensor, but again a non-starter for me with the prospect of losing internet with a power failure, but a nice option.

[ChrisA Edwards]

So back to he RV stuff, we also use a device called Waggle. It's a small device that uses a battery and communicates via cell(Verizon, $20 per month). In the camper it stays plugged into an outlet. If the power goes out, it sends me a text message. When power is restored, I get a text message.

It also has high and low temperature limits that also cause it to send a text message.

We use this mainly when we leave our dogs in our camper for a few hours. We are never far away, but if camping in a hot State and our RV has a power outage, we can either rush back to the camper or call the campground to let our dogs out.

[Alan Lightstone]

So back to he RV stuff, we also use a device called Waggle. It's a small device that uses a battery and communicates via cell(Verizon, $20 per month). In the camper it stays plugged into an outlet. If the power goes out, it sends me a text message. When power is restored, I get a text message.

It also has high and low temperature limits that also cause it to send a text message.

We use this mainly when we leave our dogs in our camper for a few hours. We are never far away, but if camping in a hot State and our RV has a power outage, we can either rush back to the camper or call the campground to let our dogs out.
That Waggle is interesting, though pricey, especially considering monthly coverage. That's for my usage in a fridge. To protect your pet in an RV - worth every cent. https://mywaggle.com/

I wonder if the temperature alerts can be set to the needed range for a medication fridge (36-46°F). Can you look at your Waggle app and see if that's possible?

[ChrisA Edwards]

The Waggle can be set to a temperature range of -4F to 140F, so 36F-46F would be well within range, but not familiar with a medical fridge, I assume you would have to put the Waggle device inside the fridge and therefore, I would be a little concerned about the cell signal that could be sent from inside the fridge.

[Alan Lightstone]

The Waggle can be set to a temperature range of -4F to 140F, so 36F-46F would be well within range, but not familiar with a medical fridge, I assume you would have to put the Waggle device inside the fridge and therefore, I would be a little concerned about the cell signal that could be sent from inside the fridge.
Thanks, Chris. Looks very useful, but wouldn't work for my particular application. Nice to know about it, though. Also not sure about a cell signal inside a fridge. I might throw my cell phone in there for kicks to see if it answers a call. Of course, during a blackout with potentially no cell service and no internet...

[Maurice Mcmurry]

An interesting thread. I and several of my clients have situations where the home sewer is dependent on a pump. My backup is a battery bank and inverter. I have not solved the automatic need as my inverter’s solid state on switch is also the reset and requires a manual touch. Rather than getting inside the inverter and redesigning the circuit I am buying a ready made unit that will control the transfer, maintain the battery bank, and create the AC. Pump Spy or one like it.

[Jim Becker]

An interesting thread. I and several of my clients have situations where the home sewer is dependent on a pump. My backup is a battery bank and inverter. I have not solved the automatic need as my inverter’s solid state on switch is also the reset and requires a manual touch. Rather than getting inside the inverter and redesigning the circuit I am buying a ready made unit that will control the transfer, maintain the battery bank, and create the AC. Pump Spy or one like it.
That was one of the reasons we got the generator at our previous residence...no power meant both no water and no septic because the latter had to pump up the hill. (although there was certainly some leeway for shorter outages since the pump tank was 500 gallons and normally at a relatively low level) Here at the "new" place, water is similar since we have a well, but we do have public sewer. But Alan's need is certainly more critical than water and septic in most aspects!

[Maurice Mcmurry]

Alan's need is certainly more critical than water and septic in most aspects!
For sure! Good job well done Alan!