Appliance Power Math

[rffffffff]

Originally Posted by jackdebear

I'm lost in the RV power maze too. For what is worth here's where I am just now. I have a 100A lithium and a 2000W inverter. And a dedicated 10A AC charger. I'm using this to run tests in my house. So far it looks like I can run my wifi router and my freezer forever like this. The wifi draws next to nothing. The freezer about 1A 120V intermittently. That means the battery draws down from 14.5 to 13.5V and then recovers. So the 10A charger is just keeping up. I tried adding the fridge and it slowly ran the battery down. I'll be getting a second battery and charger so that will be 20A charging and 200A storage. I expect that will mean the 3 devices will be semi-off grid. In the event of a power outage I should not have to worry about food spoiling for a good long time. By the way I did happen to be at my battery meter when the freezer kicked in. I saw almost 70A DC get used for a few seconds.

200ah at 20a charging is 10 hours to refill your batteries from dead, if you’re on a generator it’s a little annoying. Bumping up to a bigger charger could make life a little easier depending on circumstances, I use a 55a charger for my similar sized battery bank and it’s great. Obviously will depend on your use but 10a or 20a seems a bit small.

[jackdebear]

My batteries come with 10A chargers. Anyway right now I'm just in the head scratching phase of testing. The equipment is for an RV install but mid winter in Ontario eh? I figure using the batteries in some way is better than letting them languish for the 10 months of the year they won't be in the RV. The current arrangement isn't ideal. I don't think keeping them at almost full charge continually is the best plan. I expect to put some more load on them to run them down a bit every month or 2 and use a transfer switch to put the load on grid while they recharge. Slowly slowly.

[rffffffff]

I could be wrong and you have to check your specific chemistry but my understanding of lithium is that they do best NOT fully charged or fully dead, but someplace in the middle, which is why a lot of people use then at 80% capacity, taking 10% off the top and bottom to keep them in the happy range. Double check so you don’t mess them up before you really use them.

[jackdebear]

That's roughly my understanding. I'll be aiming for 80% - 20% in the long run.

[Rivetboy]

These two items will greatly help any electrical adventure you might find yourself in. That is also assuming that you already have your Handy Dandy Jungle Jim TS 352 B/U multimeter test set with leads or a Home Depot equivalent Guurnteed to make you smrt..

[jackdebear]

I have 3 multimeters and 2 electricians I can pester if I get stuck. Getting there is most of the fun so I'm trying to muddle forward on my own with much help from YouTube and folks like you. Thanks.

[Rucker]

The thread title being 'Appliance Power Math', this might help (and I think is posted elsewhere in this forum, available with a search), fridges use induction motors, which draw a huge initial current, then afterwards draw very little.

So when calculating inverter or battery sizes you need to be able to support the inrush current (8 amps on my dorm fridge) as well as the normal draw (about 3 amps). The 'normal draw' is periodic, and probably can be calculated from the energy usage sheet that comes with the fridge, like other folks above have done.

Every once in a while the fridge turns on, and for a few seconds draws lots of current, then settles down to it's normal draw. An amp meter (clamp type meter) with a max or 'inrush' button will help you capture the initial surge.

You can also buy pretty cheap devices on Amazon that track watt usage. I bought one, but never bothered to experiment with it.