A couple of years ago I bought this for occasional backup use when we get power outages here (Eastern Arizona).



However I never got around to buying any batteries but want to address that, we recently bought a deep freeze that's in a spare garage and I want to be ready to switch the freezer into this unit if we get an outage that looks like it could be many hours.

Naturally I'd need a charger to go with the batteries.

The way I'd do this is keep the batteries on charge all the time and when we get a problem, connect the batteries to the unit (or perhaps have them already connected) and then unplug the freezer from wall and plug it into the inverter and switch that on.

There are several kinds of batteries though, RV, Boat, etc and Lithium, Lead Acid and so on, I've read several articles but most are pushing this or that product so its hard to get an objective view. I know this isn't rocket science but nothing beats first hand experience from others who might have done something like this themselves.

 

How often do the power cuts occur?
If it is a rare occurrence, then VRLA batteries designed to spend their entire life on float charge would be a good choice, but the number of full discharge cycles would be quite limited. You would get 12 years’ life, if the number of power cuts is only one or two per year.
For more frequent power cuts, you would need deep cycle batteries, but they don’t like continuous float charge anywhere near as much. For the longest life, Top up the charge once every month and then disconnect.
I would only recommend Lithium if you need to save weight.

 

How often do the power cuts occur?
If it is a rare occurrence, then VRLA batteries designed to spend their entire life on float charge would be a good choice, but the number of full discharge cycles would be quite limited. You would get 12 years’ life, if the number of power cuts is only one or two per year.
For more frequent power cuts, you would need deep cycle batteries, but they don’t like continuous float charge anywhere near as much. For the longest life, Top up the charge once every month and then disconnect.
I would only recommend Lithium if you need to save weight.

Actually yes, we're talking one or two, perhaps three a year and these often align with the monsoon rains that cause all kinds of disruption. Often power is back within a couple hours but we've had a twelve hour outage here once too.

 

I'm wondering how the inverter's output voltage behaves as the DC supply slowly falls during discharge, I need to look at the manual...

 

My UPS (used for PC and DSL modem) uses smaller lead acid batteries like this.



The UPS gets the same use as these new batteries and inverter would, two or three times a year.

 

Freezer consumes 300W or so too.

 

This Yuasa unit seems a good pick, I also know of the brand, used smaller Yuasa batteries in a small 6502 based robot I built in the late 70s and the batteries were reliable and well made.

https://www.digikey.com/en/products/detail/yuasa-battery/NP65-12FR/13171157

I could buy two and have them both on charge and use one for the first say 15 or so hours and then swap that out with the other, could likely run the freezer fine for some 40 hours or more.

Can these batteries be left on continuous charge using a basic car battery charger?

 

You need a basic but "smart" charger that is designed to be left connected continuously. It might be reasonable to use a solar panel and charge controller. A 10 amp PWM solar charge controller with LCD voltage display is only about $10 from China. 5 to 20 watts of panel should be plenty.

On the other hand, if you're willing to spend real money, a name brand combination charge controller/charger/pure sine-wave inverter could be the right solution. Maybe this:
https://renogy.com/2000w-12v-pure-sine-wave-inverter-charger-w-lcd-display/

And on the other other hand, freezers may not need continuous power. Powering it up in the morning and evening could be enough. The freezer compartment in my mini fridge recently survived several hours of scheduled outage without defrosting. It wouldn't be too inconvenient to fire up a generator twice a day, though for long term reliability, propane or natural gas would be preferable to gasoline.

I'd investigate LiFePO4 batteries; they should have more usable capacity than lead batteries, and last much longer. Alternatively, just buy whatever wet lead-acid battery gives the most capacity for the buck, or that you can find surplus or free. RV owners are switching to lithium and selling off their old batteries cheap ($30 for 235Ah from a local ad).

 

Can these batteries be left on continuous charge using a basic car battery charger?

I wouldn't recommend it. Yuasa recommends a very precisely regulated and temperature compensated float voltage for maximum life. Basic car chargers are designed to get enough charge into the battery to start the engine and nothing more sophisticated.

 

If you are after long service life, Nickel Iron batteries may be worth a look. They have lower capacity and higher internal resistance than most others but can last for many years. When I worked at Radio Australia, there was a bank of them in use for over 40 years and still going strong.
Whatever type of battery you chose, the correct charger/management system will need to be used for that battery chemistry otherwise damage will result.

 

I'm all for the idea of charging the battery once a month AND for switching the inverter on only long enough to complete a freeze cycle, then leave it off until it needs another freeze cycle. To do that you might want to have a thermocouple added into the freezer to monitor temperature. When, and only when a re-freeze is needed - the inverter comes on. And stays on long enough to complete the cycle. You'd have to experiment to know at what temperature the built-in thermostat switches on and at what temp it switches off.

Suppose it switches on at 28˚F and off at 22˚F. Leave it alone and use the thermocouple to switch the freezer back on when the temp reaches 29˚ and off at 23˚. That way the freezer will be on and ready to freeze when the inverter powers up, and switch off before the freezer would normally switch off.

One thing that just popped into my fuzzy head - - - what's the start up current draw of the freezer? If it's more than the inverter can handle then it will go into overload protect mode and not power the freezer compressor. Make sure your inverter can handle the load. Otherwise you've done some experimentation and construction for a project that might not work. You MAY need a bigger inverter. Or a soft start circuit for your freezer. And I don't think the compressor would like a soft start.

One more thing in my fuzzy head - - - if the freezer were in a freeze cycle when power went out then the compressor won't start back up until the freon pressure equalized enough for the compressor to overcome the back pressure. That could take several minutes. Switching the inverter on at that time will certainly draw max current and likely send the inverter into overload protection.

Just a few things to be considered.

 

I just tried to ask Yuasa about recommendations for chargers for these batteries, and as is all too common these days I was met with failure:



This has likely been broken for ages and because it doesn't work nobody can report it !

 

Here’s a copy of the manual.

 

A couple of years ago I bought this for occasional backup use when we get power outages here (Eastern Arizona).

View attachment 268373

However I never got around to buying any batteries but want to address that, we recently bought a deep freeze that's in a spare garage and I want to be ready to switch the freezer into this unit if we get an outage that looks like it could be many hours.

Naturally I'd need a charger to go with the batteries.

The way I'd do this is keep the batteries on charge all the time and when we get a problem, connect the batteries to the unit (or perhaps have them already connected) and then unplug the freezer from wall and plug it into the inverter and switch that on.

There are several kinds of batteries though, RV, Boat, etc and Lithium, Lead Acid and so on, I've read several articles but most are pushing this or that product so its hard to get an objective view. I know this isn't rocket science but nothing beats first hand experience from others who might have done something like this themselves.

AGM Lead Acid is a good fit for most backup energy projects. It's fairly cheap, simple, rugged and easy to charge.
https://forum.allaboutcircuits.com/...c-controlled-battery-array.32879/post-1438996

https://www.batteryequivalents.com/...ybrid-gel-12v-200ah-deep-cycle-batteries.html

 

Here’s a copy of the manual.

Thanks, that's interesting, so they do make "charging units" (just need some basic additional components) but they seem almost impossible to obtain, here is the 6V standby unit:



No sign of anyone selling the 12v unit anywhere!

The one above is from a site I never heard of before - Bonanza.

 

You need a basic but "smart" charger that is designed to be left connected continuously. It might be reasonable to use a solar panel and charge controller. A 10 amp PWM solar charge controller with LCD voltage display is only about $10 from China. 5 to 20 watts of panel should be plenty.

On the other hand, if you're willing to spend real money, a name brand combination charge controller/charger/pure sine-wave inverter could be the right solution. Maybe this:
https://renogy.com/2000w-12v-pure-sine-wave-inverter-charger-w-lcd-display/

And on the other other hand, freezers may not need continuous power. Powering it up in the morning and evening could be enough. The freezer compartment in my mini fridge recently survived several hours of scheduled outage without defrosting. It wouldn't be too inconvenient to fire up a generator twice a day, though for long term reliability, propane or natural gas would be preferable to gasoline.

I'd investigate LiFePO4 batteries; they should have more usable capacity than lead batteries, and last much longer. Alternatively, just buy whatever wet lead-acid battery gives the most capacity for the buck, or that you can find surplus or free. RV owners are switching to lithium and selling off their old batteries cheap ($30 for 235Ah from a local ad).

Thanks, yes LiFePO4 seems to be all around, Amazon have tons. My worry though is these brand names mean nothing to me, Yuasa has been around for years and are established. All too often these days I buy something cute from Amazon only to find its cheap, poorly made by some low tech shop in China and poor quality.

It doesn't help either that there are Lithium Ion and Lithium Iron batteries, talk about confusion...

 

I would talk to local solar (and battery) suppliers; they may have trustworthy brands of LiFePO4, or deals on used batteries.

 

Inverters like you have are generally powered by a SLA (Sealed Lead Acid) battery. My bike battery I just keep on a Battery Maintainer all winter long. I go out every now and then and the bike starts right up. Anyway I would look towards a SLA battery with a good enough AH rating for as much time as you need. I would just run with a SLA and battery maintainer common for SLA batteries. That will keep your battery topped off. NE Ohio winters are not fun and having the bike ready to run is nice.

Next, I am not sure how your freezer compressor will like the inverter out. Problem is many low cost inverters output a modified sine wave and not a true sine wave. Make sure your freezer compressor will run on what your invertor outputs as to waveshape. May or may not matter but something to consider.

Ron