Battery Bank Size

luvrbus · February 10, 2016, 03:26:04 PM

I know this question has been asked time and time again so here goes we have a electric fridge,2 TV's, the normal lighting all LED's,micro wave and I am installing a 2 burner induction cook top 110v diesel fired heat and on demand hot water from the heating system.
I am redoing the system to be more manageable it's setup with 2-12volt battery bank ea with 3- 8D batteries in ea bank then they tie together for the 2- 24v stacked 4000w inverters for 8000w of AC inverter power.

I want to remove 1 inverter and drop it to 4000w which should be plenty shouldn't it ? now how much battery bank would I need for 2 days of camping without the generator.I have a Lifeline rep helping me, some things he tells me makes sense and some are just goofy. What works best or you guys ?with about the same equipment

Scott & Heather · February 10, 2016, 04:10:55 PM

What's your plan for the other inverter? Free bump for this thread

Sent from my iPhone using Tapatalk

solardude · February 10, 2016, 04:14:07 PM

Hi Cliff,

As I'm sure you already know that this is a very tough question to answer, if even possible. I get this question ALL the time when installing solar. There are some reasonably constant variables, but most are hard to predict on-going.
The fridge for example is fairly constant, depending on ambient air temp and fridge type, some are more insulated than others. Here is a link to a worksheet http://www.wholesalesolar.com/solar-information/start-here/offgrid-calculator#applianceTable Its not perfect by any measure but it is a good way to visualize the loads. I would agree you could probably make due with 4kw inverter, depending on surge capacity. Inverters are kinda like generators, they are more efficient depending on load. With that said 6 Lifeline 8D @ 210Ah = 630Ah @ 24Vdc Depending on how long you want your batteries to last you choose how far to discharge them. Off-grid solar for example for longevity I would say discharge to 70% and the batteries will last many years if taken care of (up to 15 years). However, MOST people will destroy batteries much sooner as the care and feeding become tiresome. With that said, figuring that if you get 5yrs out of a set, you will be lucky as inverters are severe duty for batteries. Especially in an RV situation. I have a similar size battery bank, I plan to use 60% discharge, but will probably go to 50% as I'm realistic about what to expect for battery life. In other words don't choose 70% (30% Discharged) because the batteries probably will not last beyond 5yrs anyway, so you might as well get good use of them. OK, so back to the numbers. 630Ah/ 50% = 315Ah (7560w) to work with. That will certainly power a fridge for two days, throw in the microwave now and again along with some instant hot water... Speculating here, but I think you should be good, as long as there are not too many constant draws. Make sure to put a balancer between the two 12V banks, you will get uneven banks when discharging down to 50% and when heavy loads are used.

Jeff

Seangie · February 10, 2016, 05:04:13 PM

Cliff,

Go with 6 or 8 of the L16s. They will last you a while. 8 of them will get you over 1200 amp hours at 12v. You can live like a king for 2 days in the desert. If you go with the lead acid they are 300$ a piece. That's about 2 bucks per amp hour.

Just drove past your house in AZ today. Waved out the window as we passed. Not sure if you saw us or not...we were moving pretty fast at 75

-Sean

Scott & Heather · February 10, 2016, 05:24:16 PM

Shanksy, hoping to see you guys in April

so, $300 times 8 batteries $2400 and they last 5 years? I'm thinking $2400 every 5 years....I could just run off my generator and call it a day. Forget the batts. Yikes.

Sent from my iPhone using Tapatalk

Seangie · February 10, 2016, 05:37:14 PM

Quote from: Scott Bennett on February 10, 2016, 05:24:16 PM
Shanksy, hoping to see you guys in April so, $300 times 8 batteries $2400 and they last 5 years? I'm thinking $2400 every 5 years....I could just run off my generator and call it a day. Forget the batts. Yikes.

Sent from my iPhone using Tapatalk

Scott - They would last you 10 years. Think of how little you would ever cycle through them. And really if you take good care of them they could last longer than that as long as those plates don't get all eaten up.

Headed to Texas now. Be there by Sunday.

-Sean

Iceni John · February 10, 2016, 05:44:52 PM

Why no solar? Some's better than nothing, and for less than $1 a watt it's affordable. Harvesting the sun makes sense where the sun shines most of the year, i.e the Southwest.

John

solardude · February 10, 2016, 06:14:07 PM

QuoteScott - They would last you 10 years. Think of how little you would ever cycle through them. And really if you take good care of them they could last longer than that as long as those plates don't get all eaten up.

Below is a link to a data sheet for what I would consider top-of-the-line batteries

Note the expected life of the Gel or AGM is about 4-6yrs @ 86 degrees service temp, 2-4yrs at 104degrees, unless you live and play 2 miles from the coast or stick to the Northern states 10yrs of service is highly unlikely.

https://www.victronenergy.com/upload/documents/Datasheet-GEL-and-AGM-Batteries-EN.pdf

Perhaps, some of you long time bus nuts can comment on how long your house batteries have lasted. If anyone says >10yrs please provide the recipe you used for success, including percentage of usage, and discharge limit.

Solardude.

solardude · February 10, 2016, 06:33:34 PM

Quote$300 times 8 batteries $2400 and they last 5 years? I'm thinking $2400 every 5 years....I could just run off my generator and call it a day. Forget the batts. Yikes.

I agree that batteries are crazy expensive currently. If I had to buy another set I would think about buying a Chevy Volt battery pack from a junk yard and splitting it up for about $2400 but the battery would be orders of magnitude more energy dense than the current AGMs.

Here is a look inside the Volt battery. https://www.youtube.com/watch?v=00tTckGUv7I

TomC · February 10, 2016, 08:48:53 PM

I would run 4 L16 (@ 400amp/hr ea) that would give you 400 amp/hrs at 24v. Have automatic start on the genset-and just make sure the generator is extremely quiet with air bags under the mounts.
I have 2-8D AGM. I simply run the genset 2hrs in the morning and 2hrs after dinner. Lots cheaper, and less weight than a giant bank of batteries. Good Luck, TomC

blue_goose · February 11, 2016, 01:31:06 AM

If you are using the inverters for your change over from gen. to shore power, what will you do for change over if you remove one of the inverters?
Jack

bevans6 · February 11, 2016, 02:08:42 AM

A typical modern fridge runs at around 400 watts or less when it is running. Guess at a 40% duty cycle and that is 160 watts per hour, or 7.5 AH at 24 volts nominal through your inverter. TV, lights, fans are almost incidental because you need to size the battery bank to suit the long load (the fridge) and the short high loads (the microwave and the induction cooktop) Microwave is around 1200 watts when running, and the induction cook top is around 1500 watts per burner when running. Presume you need to run both at once, plus the microwave as you cook your dinner and you have 4200 watts - which is why you maybe want to revisit the dual stacked inverter setup. I would personally ditch the induction cooktop or keep the second inverter, and since you already have the inverter and you know how good the cooktop will be, the decision is pretty easy.

This gives you a short term draw in the 4500 watt range, which is 200 amps near enough at 24 volts through the inverter. Over 48 hours you would be looking at say two hours of cooking, at say half that average rate, so 100 amps times two hours is 200 amp hours. The fridge is 180 amp hours over 48 hours. TV, and LED lights are maybe 50 amp hours. Total (not counting 12 volt loads and fans and pumps) is around 420 amp hours. Using the old 50% discharge rule of thumb (modern AGM and other high tech batteries can go a lot deeper) I would be looking at 800 - 1000 amp hours at 20 hour rate to be conservative.

How are you going to run your air conditioners? This looks mostly like running the kitchen with pretty power hungry devices, and the rest of the coach gets an electrical free ride, almost, but the air conditioners were not mentioned in your note. Other questions I would have are rate of discharge at 200 amps, will that rate hurt or overheat the batteries, and rate of charge. If I ran a bank down to 50% or less I would expect to take at least 24 hours minimum to recharge. an hour a day wouldn't touch it. Running the generator while you are cooking would change the situation drastically.

Brian

luvrbus · February 11, 2016, 02:20:19 AM

I don't plan on running the AC's off the inverters with 5 roof tops it wasn't going to happen any ways.I am just finishing up my dash air which is 45,000 btu they say, I should be good there.LOL ditching the induction cook top is not going to happen I lost that battle in the first round.I doubt the cooktop will be used much off the inverters we cook outside a lot

sledhead · February 11, 2016, 02:49:20 AM

as much as we think we are the boss..... the woman folk run the world !

dave

lostagain · February 11, 2016, 03:12:06 AM

The simplest and cheapest is lead acid batts, an inverter, and a generator. Start the genny when needed. Solar panels are nice to have, but they only work when the sun shines high in the sky, not if you are parked under a tree, or anywhere in the winter, even down South. Unless you point them at the sun, but that is too complicated on a bus.

Looking forward to see your bus Clifford. Next winter hopefully.

JC