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Old 05-24-2015, 05:24 PM   #1
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How big is your battery? Is it big enough?

I'm seriously considering buying a LiFE (lithium iron phosphate) battery for my bus. They are very pricey, to be sure, but they have some nice advantages over lead-acid batteries.

Anyway, the biggest I can afford would be about 150Amp-hrs, but I'm not sure it's enough. It should be, but I'm curious how much capacity others have and whether they think it's enough or if they had to install more after living in it for awhile.

I've read and I understand the 12V and solar recommendations here and elsewhere. What I want to hear is actual experiences of other schoolies.

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Old 05-24-2015, 08:05 PM   #2
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the main concern with a bus battery (batteries, 2 in mine) is the output needed to start the bus, if the battery cannot output something like 1000 amps for engine startup, then is worthless no matter the cost, unless you are planning to use it as living area power, not for starting and running the bus.

also there is an issue in that Lithium batteries require controlled charging with a temperature sensor on the battery, over heating a lithium battery causes fires
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Old 05-24-2015, 08:33 PM   #3
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Quote:
Originally Posted by Kubla View Post
the main concern with a bus battery (batteries, 2 in mine) is the output needed to start the bus, if the battery cannot output something like 1000 amps for engine startup, then is worthless no matter the cost, unless you are planning to use it as living area power, not for starting and running the bus.

also there is an issue in that Lithium batteries require controlled charging with a temperature sensor on the battery, over heating a lithium battery causes fires
The battery I'm looking at supplies 1500 CCA for starting. I looked up some 8D lead-acid replacements and found they had lower cranking amp ratings, so I'm sure this LiFE battery would work fine.

Lithium-ion batteries that use cobalt chemistry (like those found in cell phones and computers) are prone to overheating and fire if overcharged. Lithium iron phosphate (LiFE or LFP (lithium ferrophosphate)) are chemically stable and cannot catch fire if overcharged. Obviously, overcharging isn't good for the batteries, but at least they aren't a fire hazard.

So, how much battery capacity do you have on your bus and have you found it to be enough for your use?
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Old 05-24-2015, 08:55 PM   #4
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My two group 31's provide 1900 cca.
For $75 they are awesome!
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Old 05-24-2015, 10:21 PM   #5
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I'm with Cal on the Group 31s.... but holy cow $75 is a bargain.

i have 7 of them. 4 are the house battery for about 500AH. thats enough for my fridge and lights to run 30ish hours before recharging @50%.

its all gonna depend on your loads, but 150AH isnt much IMO.
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Old 05-24-2015, 10:45 PM   #6
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For a house battery on my trip two years ago I used a pair of Trojan J305P-AC. These are 6 volt lead acid, rated 330 AH at 20 hours. They didn't come to me new, however -- they were take-offs from some kind of floor cleaning machine and I guess the reason they were replaced is that they didn't hold a charge like new anymore. So I can't say how many AH mine are actually good for.. In any case, I ran a residential freezer-fridge, about 22 cubic feet, 24/7 on those batteries. The Black & Decker 40 amp charger ran on a generator 3-4 hours a day to recharge. Maybe we used 80-100 AH/day for the fridge and a small amount of lighting..? I'm not sure.
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Old 05-24-2015, 11:52 PM   #7
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My chassis batteries are both 8D's rated at 1300 CCA each and the truck
mechanic two doors down says that if the weather gets down cold the
engine will need that much amperage to get it started. I was thinking it
was a bit of overkill myself but the batteries that came out were 7 year old
NAPA batteries so I replaced them with the same for $350.00 a pair.
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Old 05-25-2015, 12:21 AM   #8
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All I'm running yet is one 8D 1600 CCA, a 7 watt amorphous solar panel.

It runs my two 3 watt led lights for more than 24 hours without going under 50% DOD.

Nat
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Old 05-25-2015, 12:25 PM   #9
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I have a fairly normal 1180cca starter battery and 3x XC2 12v deep cycles for house batteries. The house battery bank is 455Ah. With the ~600w panels the house batteries give us enough power for everything we've thrown at them so far.

Typically we don't run the bank down beyond 80%. On occasion we may go lower. Yesterday, for instance, we had several friends over and were running an electric raclette for over an hour in the evening. That brought the bank down to 70% SoC.

For battery longevity I think we're in a good situation. When running the table saw or pancake air compressor for a busy day of building we may get close to 50% SoC, but as long as I'm working when the sun is shining the solar panels are directly contributing to the power output..

So far I'm very happy with our system. We haven't sacrificed any electrical devices to be living off-the-grid (note that we don't have or need A/C, though).
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Old 05-25-2015, 12:42 PM   #10
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That sounds promising, Jazty. What kind of fridge and/or freezer are you running?
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Old 05-25-2015, 01:22 PM   #11
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A dinky 12vdc/110vac Edgestar: Amazon.com: 43 Qt Portable Compact Refrigerator Freezer - EdgeStar: Appliances

It works very well and is quite efficient. When the compressor kicks in it uses ~5amps on 12vdc. I'd estimate that the compressor is on for about 10 minutes or less every hour, so ~0.83Ah.

I did a test with water in a bowl and in the fast-freeze mode it could make ice in an hour. We only use it as a fridge, though.

The price is $469 on amazon, but we got it on sale at another camping website (don't remember which one) for around $360.

They also make a 80qt unit, but it was too big to fit in the space I designated and I didn't want to pay $600 for a refrigerator.
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Old 05-25-2015, 01:29 PM   #12
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Cool. We use a 63-qt unit for a home freezer. It's been running for over three years without a hitch. Even survived a 1000-year flood in 2013.
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Old 05-25-2015, 01:36 PM   #13
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Oh yeah, almost forgot: Compactappliance.com has a scratch and dent section that's very much worth watching. We got our FP-630 for about what you paid for the 43-quart one, with free shipping.

Thanks for the DC draw numbers. I keep forgetting to put our on the Kill A Watt for an AC measurement.
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Old 05-25-2015, 04:19 PM   #14
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I have two chest-type freezers with one being used as a fridge. According to the user manual, one of them draws 1.3A @115VAC or 105 watts and is assumed to use about 210kwh per year. Extrapolated down, it uses about 580 watts per day, so the manufacturer is assuming it runs about 20% of the time. My other freezer is a glass-top version so it is likely less efficient, but I'm using that one as a fridge so it should run even less.

The 6000BTU window air conditioner draws 5.2A @ 115V or 560 watts. It's rated for a 260 sqft room and my rig will be roughly half that (with almost no windows and the walls heavily insulated) so I'm hoping for efficiency there, too. When I've run it during the summer, it cycled on for about ten minutes less than twice an hour. It has an Energy Saver mode that shuts down even the fan between cooling cycles and runs the fan for a few seconds every three minutes to check the air temp.

The only other major draw will be the computer, but I'll be using that only when I need to edit photos. Reading email and browsing the web will be mainly done on my phone. House lights are all LEDs. I'm also hoping to install at least one 200W solar panel, maybe two.

The microwave, while a huge draw, is really less significant because it runs for only a few minutes at a time, maybe once or twice a day.

This is the battery I'm contemplating: 12V 150AH Li-ion Smart Battery. Like I said, pricey. I still need to call to verify at what state of discharge they rate the AH capacity.

I think I stated earlier that this is 1500 cold cranking amps. That was wrong. It's 2000. Should be perfectly useable as a starting battery for the coldest weather I plan to encounter.
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Old 05-25-2015, 04:40 PM   #15
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Quote:
Originally Posted by PDBreske View Post
I have two chest-type freezers with one being used as a fridge. According to the user manual, one of them draws 1.3A @115VAC or 105 watts and is assumed to use about 210kwh per year. Extrapolated down, it uses about 580 watts per day, so the manufacturer is assuming it runs about 20% of the time. My other freezer is a glass-top version so it is likely less efficient, but I'm using that one as a fridge so it should run even less.

The 6000BTU window air conditioner draws 5.2A @ 115V or 560 watts. It's rated for a 260 sqft room and my rig will be roughly half that (with almost no windows and the walls heavily insulated) so I'm hoping for efficiency there, too. When I've run it during the summer, it cycled on for about ten minutes less than twice an hour. It has an Energy Saver mode that shuts down even the fan between cooling cycles and runs the fan for a few seconds every three minutes to check the air temp.

The only other major draw will be the computer, but I'll be using that only when I need to edit photos. Reading email and browsing the web will be mainly done on my phone. House lights are all LEDs. I'm also hoping to install at least one 200W solar panel, maybe two.

The microwave, while a huge draw, is really less significant because it runs for only a few minutes at a time, maybe once or twice a day.

This is the battery I'm contemplating: 12V 150AH Li-ion Smart Battery. Like I said, pricey. I still need to call to verify at what state of discharge they rate the AH capacity.

I think I stated earlier that this is 1500 cold cranking amps. That was wrong. It's 2000. Should be perfectly useable as a starting battery for the coldest weather I plan to encounter.
I would say that 150Ah is not enough to be running all those appliances. You might be able to get away with 300Ah Li-ion or LiFePo4 bank; or a higher Ah flooded bank for longevity.

You have to remember the conversions here.. An A/C unit running at 5.2a @115vac will be pulling 50a @12vdc + inefficiencies from the battery. So you could get 3 hours of total run time with a 150Ah battery bank, but that would be pulling the bank down to 0% state of charge which is bad for batteries of any chemistry.

The fridge isn't that bad, really. 1.3a @115vac is 11.5a @12vdc. Add in inverter inefficiency and you're looking at (just guessing) an additional 15%, so 13.2a @12vdc..
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Old 05-25-2015, 07:07 PM   #16
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Thanks for bringing up the conversation regarding the feasibility of using LiFePo as a starter battery. I hadn't considered it before, not realizing that they could so easily handle that much surge current. My starting batteries are tired and I'll be needing house batteries too.... There's something to be said for combining house and starting batteries and using the cost savings to upgrade to lithium (and to install some kind of battery management system to avoid excess discharge).

The linked Smart Battery seems a little on the expensive side though I confess to having done extremely little shopping of my own. Knowing nothing about this vendor or their quality, here are 100 AH cells for $170. Four in series with some connector hardware builds a battery pack similar to the Smart Battery for about $700. The Smart Battery is 150 AH to the 100 AH of this solution, so multiply the price by 1.5 to compensate and the DIY battery comes in about $1050 compared to the Smart Battery $1900.

I wonder whether the Smart Battery has extra stuff inside.. charge balancing circuits or something.. to justify the price difference? Or does the arbitrary vendor I found sell low-quality cells? I dunno.
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Old 05-25-2015, 07:47 PM   #17
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One thing that has not been mentioned is the flooded lead acid battery's we are using are highly inefficient.

We never get the power we put into them back. It gets lost as heat, ect.

The LiFePo4 packs give all back that was put into the battery's.

Also, the LiFePo4 packs don't mind being discharged to the 80% DOD.

So all in all, I feel that we can get away with a LiFePo4 pack 30% to 50% smaller than the flooded lead acid packs we have been using.

Nat
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Old 05-26-2015, 08:15 AM   #18
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Quote:
Originally Posted by jazty View Post
I would say that 150Ah is not enough to be running all those appliances. You might be able to get away with 300Ah Li-ion or LiFePo4 bank; or a higher Ah flooded bank for longevity.

You have to remember the conversions here.. An A/C unit running at 5.2a @115vac will be pulling 50a @12vdc + inefficiencies from the battery. So you could get 3 hours of total run time with a 150Ah battery bank, but that would be pulling the bank down to 0% state of charge which is bad for batteries of any chemistry.

The fridge isn't that bad, really. 1.3a @115vac is 11.5a @12vdc. Add in inverter inefficiency and you're looking at (just guessing) an additional 15%, so 13.2a @12vdc..
The Smart Battery manufacturer claims 99.1% efficiency.

Quote:
Originally Posted by family wagon View Post
There's something to be said for combining house and starting batteries and using the cost savings to upgrade to lithium (and to install some kind of battery management system to avoid excess discharge).
I know the Smart Batteries have circuitry to avoid excess overcharge/discharge. They cutoff at 16V/8.0V.

-----

Still waiting to hear about people's real world setups and whether they have been adequate or needed to be upgraded over time.
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Old 05-26-2015, 08:22 AM   #19
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Found this on the page for the 200ah Smart Battery. The feature set is the same for all the batteries from this manufacturer:

FEATURES

•Fully automatic built in battery protection system
•Automatic low voltage cut off - 8v
•Automatic over voltage cut off - 16v12V 100AH Lithium Ion Battery
•Automatic short circuit cut off - instant
•Automatic internal cell balancing
•High quality bolted cylindrical cell design
•Built in cell safety fuse " Nano Cell Fuse Technology "
•Long life 3000 - 5000 cycles
•Lightweight - up to 70% lighter than lead
•No voltage sag - faster cranking for motors and higher voltage for continuous consistent power.
•Dry Battery - no toxic lead or acid
•Zero Maintenance
•No venting or gassing
•Heavy duty stainless steel bolts, washers and flat washers included
•99.1% efficient
•Green ROHS compliant - No Lead
•Use 100% of rated capacity
•Does not heat up during use
•Connect in series or in parallel
•One battery for 12v, 24v, 36, or 48v applications
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Old 05-26-2015, 09:15 AM   #20
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Quote:
Originally Posted by nat_ster View Post
One thing that has not been mentioned is the flooded lead acid battery's we are using are highly inefficient.

We never get the power we put into them back. It gets lost as heat, ect.

The LiFePo4 packs give all back that was put into the battery's.

Also, the LiFePo4 packs don't mind being discharged to the 80% DOD.

So all in all, I feel that we can get away with a LiFePo4 pack 30% to 50% smaller than the flooded lead acid packs we have been using.

Nat

It was alluded to, but not quantified. I don't know the numbers well enough.

Quote:
Originally Posted by jazty View Post
I would say that 150Ah is not enough to be running all those appliances. You might be able to get away with 300Ah Li-ion or LiFePo4 bank; or a higher Ah flooded bank for longevity
Preliminary research states that (as you mentioned, Nat) safe levels are 50% DOD for flooded lead acid vs 80% DOD for LiFePo4. So essentially a 400Ah FLA bank is in the same realm as a 240Ah LiFePo4 bank.

I must say that I'm disappointed to see that even LiFePo4 batteries lose capacity in the cold... I was hoping they would magically perform well in sub-zero temperatures.

Here's a fun little presentation on the subject: http://www.bruceschwab.com/uploads/li-vs-la.pdf
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