battery question

[djconklin]

I'm looking to convert a bus into an RV. I found a good portable generator that puts out 4,000 watts. I'd like to store the excess power into some marine batteries. How many do I need? What do I look for in batteries? I was thinking of using Sears Die Hard Marine batteries.

[westend]

smkettner wrote:
For best value look at Costco or Sam's Club golf car batteries.
Get four.

Go with LED lamps, about 200w+ solar panel, small 300w inverter for quiet time.



http://www.solarblvd.com/Solar-Panels-&-Systems-12-Volt-Solar-Kits/c1_272/index.html

Go Power 300w sine wave inverter

http://www.ebay.com/itm/10X-48-SMD-LED-Panel-Light-Lamp-Warm-White

I get jealous every time I see your wiring skills, nice job!

[Veebyes]

This is not a question that can be answered in one nice tidy short paragraph.

You need to learn yourself up on the 12V & 120VAC worlds especially as you are embarking on the major project of a bus conversion.

The genny does not charge the battery bank. A charger charges the bank. The capacity of the battery bank depends on many variables, primarily how much space is available for it & what type of batterys.

The size of the inverter depends on the size of the battery bank & what is intended to run off the inverter & for how long. A 300W inverter is just a toy. I would not consider anything less than 1000W.

With a bus conversion, where weight is not so much an issue as a towable I'd be looking at the capacity of 4, preferably 6, 6V golf cart batterys or similar capacity in multiple 4D or 8D batterys. I'd be looking at a pure sine wave marine 2000W inverter/charger with remote controller.

This set up would allow long periods of normal 120VAC, no air, water heater on propane, use without the clatter of a genny.

Do it right the first time, the only time. Trying to skimp will only cost more in the long run.

[tatest]

djconklin wrote:
...

Well since I was planning moving out to a desert I don't think I'll need a furnace! Now the AC ... I just checked; that uses 810 watts, 7.3 amps.

Look into low cost, low energy desert living.

Most deserts in the U.S. get cold, at least when the sun is down, for part of the year. Even in the Southwest. High deserts, which are most of our desert areas, can get very cold. People build well insulated desrt homes (think about thick mud brick walls) with high thermal inertia, to smooth out daytime heat and nightly cold to a livable daily average.

Outside urban areas, desert living can still mean learning to live without mechanical air conditioning. What you really need outside the city is shade, insulation or thick walls to hold down the daily peak temperatures, and adaptation to living in dry air that is close to body temperature. I've worked outdoors, all day in daytime, in the desert, finding that air conditioning just gets in the way of my adaptation.

A/C lets people live and work in LasVegas or Phoenix as if they were in St Louis, Chicago, or New York, same types of buildings, same high energy lifestyles. But that lifestyle is not necessary to live in the desert, it is possible to slow down and live with the heat (natives have been doing it thousands of years).

What you do have to have is a source of heat when the desert gets cold, something to burn and a stove can be enough, furnace is more tech than what is necessary.

[westend]

Download for spreadsheet that calculates usage, bank size, and solar charging.

[wa8yxm]

FORGET marine/Deep cycle, go for REAL deep cycle

As to how many you need.. That is a job for a math major (Which I happen to be) with a whole lot of info I don't happen to have.

Basically, figure out how much you use

I would start with two pair of golf car batteries or two fairly big AGM Deep cycle (Make sure they are DEEP CYCLE with no manention of Marine) and if you need more, add more

Six Volt Golf car batteries, though "High maintenance" are the best value for your dollar.

[djconklin]

>That 7.3 amps is at 120V. If you are planning on running it when off the grid it will draw about 80 amps at 12v using an inverter. I don't think you will run that off batteries.

There's always a fly in the ointment!

Have to check on RV AC's.

[djconklin]

For best value look at Costco or Sam's Club golf car batteries.
Get four.

Go with LED lamps, about 200w+ solar panel, small 300w inverter for quiet time.

Good to know, posted in my file. Thanks!

[tenbear]

Oops.

[tenbear]

djconklin wrote:
>...Now the AC ... I just checked; that uses 810 watts, 7.3 amps.

That 7.3 amps is at 120V. If you are planning on running it when off the grid it will draw about 80 amps at 12v using an inverter. I don't think you will run that off batteries.

[time2roll]

For best value look at Costco or Sam's Club golf car batteries.
Get four.

Go with LED lamps, about 200w+ solar panel, small 300w inverter for quiet time.



http://www.solarblvd.com/Solar-Panels-&-Systems-12-Volt-Solar-Kits/c1_272/index.html

Go Power 300w sine wave inverter

http://www.ebay.com/itm/10X-48-SMD-LED-Panel-Light-Lamp-Warm-White

[djconklin]

>Look at Costco for batteries

Good idea!

> Many of us have switched to LEDs to reduce the energy used for lighting.

Yep, that was a good idea I gleaned some months ago.

>The furnace and water pump both draw substantial current

Well since I was planning moving out to a desert I don't think I'll need a furnace! Now the AC ... I just checked; that uses 810 watts, 7.3 amps.

[tenbear]

Look at Costco for batteries.

The fridge uses about 18-20 AH per day running on propane. The lights can be an energy hog if you are using incandescent lights. Many of us have switched to LEDs to reduce the energy used for lighting. The furnace and water pump both draw substantial current, in the 6-8 amp range so if they run very long they can use considerable power.

[djconklin]

Thank you!

Even as I was typing in the question I realized some of the variables that you mentioned! But, since I haven't even started I couldn't figure out how to answer them!

The only real energy hogs I can think of would be my fridge and computer.

[tatest]

You store energy (watt-hours). You put it in and take it out as power (watts) over a period of time.

How many batteries depends on how much energy you plan to store, or use. How many watts do you need to draw from storage, for how many hours? Different types of usage have radically different answers.

Most small RVs store 1200 to 2400 watt-hours, e.g. 100 to 200 amp-hours at 12 volts, with the expectation of using no more than half of that during one charge-discharge cycle, which might be a day. Using more than half the batteries' capacity greatly shortens the number if cycles available.

Larger RVs running a number of large electric appliances from stored power may store 4 to 10 KW hours, might have 400 to 1000 pounds of lead-acid batteries to do that. But then they need much larger charging systems to keep those up, or need to be charging for long periods of time.

You need to figure out your own electricity use and storage goals.

My need was for marine (rather than deep cycle) batteries, because I have some short-term high amperage loads, but I passed on the DieHards. Those were priced way higher than equivalent batteries from discount stores, auto stores, and even the overpriced Interstates at RV and boat dealers. If you have smaller loads over a longer period of time, you should look at golf-cart batteries.

A consideration for me is package size. You might get the same capacity in four 60 pound batteries, two 110 pound batteries, or one 190 pound battery. Fewer bigger batteries can save you a little weight (and sometimes quite a bit of cost), but what can you lift and wrestle into the space?