Solution for intermittent high wattage needs?

BackToBasics

I'll be moving to my property next spring / summer and it is completely off grid. I'm very excited, except for one aspect- the high amperage 120v tools I own. I don't want to sell or trade them, but I don't want to spend a ton just to power them occasionally.

For my house batteries, I will have 450ah @ 12v with 690 watts of panel plus a 1200/1500 watt Champion generator and a 45 amp smart charger.

What I would like to do is take my generator, smart charger and buy a used 2500-ish watt MSW inverter and a (tested) used/refurbished starting / marine battery.

Generator < 45a Charger < Battery < 2' 2/0 Cable < Inverter < Tool (15a air compressor, 15a table saw, etc)

I figure in an average hour the tools themselves would be running for about 20 minutes at most. (.33 * 15a * 120v) 594 watt hours = 43 amp hours @ 13.6v

In that same hour, the charger should produce the 45 amps it's rated for. I realize that 100% of this won't actually be replaced / stored in the battery, so I would top the battery off with a 2a "battery tender" i have using my house batteries and my tiny inverter.

I have several reasons I would prefer to go this route over a larger or additional generator:

1) The 45 amp charger loads my generator to a very constant 60%-65%. That is a very good load to be at for generator fuel efficiency and longevity.

2) Inverters have start up surge rating twice their continuous rating where as a generator's is lucky to be at 125% of it's continuous rating. I would have to vastly oversize a generator just to get my tools to start

3) The sporadic use of the tools overall and the 33% duty cycle when I actually use them don't seem to warrant the maintenance and storage of a second generator.


Please discuss.

waynefromnscanada

Re: Solution for intermittent high wattage needs?

The short answer to "occasionally" running your 120 volt power tools is an answer you don't want to hear, but it will save you a lot of future stress and disappointment, and that answer is to forget the MSW inverter, and the used marine battery, even a new marine battery. Your present generator may well start and run your power tools, and even if it won't, you'd still be far ahead to get a new, larger generator for your stated needs. Oh, and do not assume an inverter will put out twice it's continuous power for motor starting. Some will, yes, but many will not, and motors don't like MSW.
I won't tell you what you want to hear, because it would not be fair to you, and it would make me a liar.
As for storage and maintenance of a generator, I bought a 1200 watt Homelite generator when I built my house in 1982. It ran all the power tools used in construction and has been used whenever needed ever since. Yes, I changed the oil a few times, but that's it. I have NO idea how many hours are on it after 30 years. And yes, it still operates and puts out power as it did when new. Not Kidding!

icarus

Re: Solution for intermittent high wattage needs?

Buy a generator to run your toos efficiently, and you could probably use it for batty charging as well.

We run our shops off of gennies, using the right genny for the tool in in question. A Honda eu 1000 for sanders and drills and small routers, a 2900 for table saws, grinders, skill saws, planer etc.. a Honda eu 2000 is barely able to start a 13 amp worm drive saw. The few gallons of rule you burn is cheap compared to the PV, battery, inverter required to run shop tools.

Tony

Wayne,, I got you beat. I still occasionally use a 3.5 kw Onan cck, bought used in 1947! Aside from points, plugs, and an oil change, and converting it to an electric fuel pump, it still runs as new! It even has an auto start function. Turn a light bulb on, and it starts. I seldom use it as it burns way to much gas, unles fully loaded, and then I don't have the loads for it.

T

waynefromnscanada

Re: Solution for intermittent high wattage needs?

icarus wrote: »

Wayne,, I got you beat. I still occasionally use a 3.5 kw Onan cck, bought used in 1947! Aside from points, plugs, and an oil change, and converting it to an electric fuel pump, it still runs as new! It even has an auto start function. Turn a light bulb on, and it starts. I seldom use it as it burns way to much gas, unles fully loaded, and then I don't have the loads for it.T

Wow! Guess ya do have me beat! But then, I still have my Grandmothers 1947 Bendix front load automatic washer, but I confess, it hasn't been used for about 10 years, lol
http://www.automaticwasher.org/VID/47BENDIX/Bendix_Wash.wmv

icarus

Re: Solution for intermittent high wattage needs?

My mothers 1962 Viking wringer washing machine just gave it up last year,, stripped drive gear, no replacement to b found. Replaced with another Maytag wringer I found in an abandoned bush camp.

T.

PS. I could talk about my outboard collection that runs back to the 1920s!

vtmaps

Re: Solution for intermittent high wattage needs?

What you want to do is not unreasonable. Victron energy advocates that approach in this document:
http://www.victronenergy.com/upload/documents/Book-EN-EnergyUnlimited.pdf
Look in section 8 for "The DC Concept".
--vtMaps