Which battery would be best, 100Ah or 206Ah?

[attomica]

I'm starting to layout the electrical system for my CCT. It'll be purely 12v - a LiFePO4 battery charged by solar panels or shore power. I'm wondering how to select between 100Ah or 206Ah batteries.
Items that will require current include...
- Eight LED ceiling puck lights
- A Fantastic Fan
- A few USB charging ports for iDevices, bluetooth speaker, etc.
- A 12v water pump for the sink
- A 12v shower
- A socket to power a 12v cooler/fridge
- A diesel heater
I'm inclined to get the 206Ah, but it is physically much larger than the 100Ah and we know how tight space is. So, would a 100Ah one sustain regular living for a couple days before needing a charge? Of course, I understand it depends how much any of these things are used, but I imagine most people use them in similar ways. I'm not experienced in trailer camping, so I'd be grateful for any guidance.

[flboy]

If you can afford it, I'd go with the larger battery. It buys you a lot of margin assuming the 100aH would be adequate. You really don't want to go down less than 10% on a regular basis for longevity, so with the 100aH, you need to plan for 90aH available.

Based on what you said, I tend to think you'd be caught short with the 100aH in anycase.

With similar draws, I run through 100aH quickly.

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[John61CT]

Yes the fridge and the heater could draw you down in not much over one 24 hr cycle.

Do not use ciggie ports, go Anderson plugs

[cluttonfred]

Well, I don't mean to be flip, but have you run the numbers? Amp-hours at a given voltage are like water in a bucket. You have a list of items you want to power...look up the current draw of each item (X amps at 12v times the number of hours it needs to run) and add it all up for 24 hours. If the energy usage is in watts or the current draw is quoted at a slightly different voltage, then use a simple online watts-amps-volts calculator to make everything consistent. That's how much water you'll be using in 24 hours. Now, how many days do you want to go without needing a charge? 24 hours? 48? 72? That's how much water you need in the bucket, plus about 25% reserve for modern LiFePO4 batterie (more for ordinary lithium and a lot more for lead-acid). Yes, solar panels will put some water back in the bucket, but often not as much as you expect unless you have lots and live in the desert.

[John61CT]

You can't just use vendor nameplate current ratings.

Need to actually measure IRL usage at your DC voltage, how many Ah per 24hrs.

So if your laptop uses 9Ah per hour with your usual activity / usage level, and you figure average 3hrs/day

that line item in the budget gets 27Ah/24hrs

The freezer averages 40Ah/24hrs because its duty cycle in hot weather is 70%

need to account for worst case not just average temperatures

So now up to 67Ah/24hrs.

[flboy]

It is not exact and mileage varies depending on many factors. Plan your best, but I'd recommend you to carry a small generator you can run a few hours here and there. I have 520aH and ended a 4 day trip with about 230aH in reserve (45%), but I did run my Honda 2000 about three hours on day 3 just to bring it up some. I have 420W of solar panels which are useless in an Oak Hammock. I could have went the whole weekend without replenishment, but I like to run the generator from time to time just to keep it up.

I do not conserve power at all for the most part and just use what I use and replace it as needed ( solar usually keeps up if not in shade). I do like to keep generator usage to a minimum, but I think it is a good compromise.

So, IMO , if you have to make a choice between another (extra) 100aH cell and a small generator, I'd get the generator first as it will cover a multitude of scenarios. Frankly, a 100aH and a small quiet generator cost about the same these days. If you can afford both, then great.



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[attomica]

Great advice! I am immensely grateful and will try to calculate current draws per device. I do have a small generator that will come along on trips, but I too prefer to use it sparingly. I'm weighing the possibility of just using a cooler versus a constantly running refrigerator, but I suspect that may be more of a hassle than I want to deal with and the diesel heater is a "maybe" too.

So, I ordered the 206Ah battery and now I'm on to researching solar panels, charge controllers, etc.

Is there a recommended way to be able to charge the battery with either solar or shore power/generator? Like, do you have a charger connected to the battery and a device to switch between methods?

[Socal Tom]

Great advice! I am immensely grateful and will try to calculate current draws per device. I do have a small generator that will come along on trips, but I too prefer to use it sparingly. I'm weighing the possibility of just using a cooler versus a constantly running refrigerator, but I suspect that may be more of a hassle than I want to deal with and the diesel heater is a "maybe" too.

So, I ordered the 206Ah battery and now I'm on to researching solar panels, charge controllers, etc.

Is there a recommended way to be able to charge the battery with either solar or shore power/generator? Like, do you have a charger connected to the battery and a device to switch between methods?

The 12V freezer/fridge are pretty efficient power wise, the 12V "coolers/Warmers" eat power like it was candy at Halloween. I love my 12v fridge, the 12V coolers are a waste of money and space.

The power draw calcs are good advice. Once you have those work out how many days between charges and you will have a idea what makes sense for you.
Tom

[flboy]

Is there a recommended way to be able to charge the battery with either solar or shore power/generator? Like, do you have a charger connected to the battery and a device to switch between methods?

Connect all the chargers to the 12VDC bus bar (solar, shore power, etc. ). The devices will regulate their output based on what they see on the buss bar. You can run solar and shore at the same time with no issues. They tend to balance their outputs to accommodate the battery charging draw and will not "hurt" one another. That has been my experience.


For instance, I have my 40A MPPT Solar Controller, LiFePo4 45A Charger/Converter, and the 20A DC to DC charger (configuration for LiFePo4) from the truck all connected to the same place and could run any single or all at same time.

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[TheOtherSean]

The 12V freezer/fridge are pretty efficient power wise, the 12V "coolers/Warmers" eat power like it was candy at Halloween. I love my 12v fridge, the 12V coolers are a waste of money and space.

The power draw calcs are good advice. Once you have those work out how many days between charges and you will have a idea what makes sense for you.
Tom

I mostly agree.

Those "cooler/warmer" devices are Peltier-effect thermoelectric devices with a maximum coefficient of performance (COP) around 0.7 but typically lower than that. That means for each watt of electrical power you get less than 0.7 watts of heating or cooling power. Peltier effect is very simple and compact and easy to work with, but it isn't very efficient. I got one of those cooler/warmer bags very cheap, and it works fine if I need to keep some food warm or cool while driving to a picnic or pot luck or such, or keeping beverages cool on a long road trip. It uses way too much power to be powered off a battery for long, so not much use for camping purposes.

The 12v freezer/fridge units are typically compressor-based, and have a coefficient of performance of at least two and possibly greater than three. Thanks to the miracle of the vapor compression cycle, you get multiple times the wattage of cooling power than the wattage of electrical power that runs it. This compressor cooling can be well over five times as efficient as thermoelectric cooling. Great for camping.

Put another away: Relatively speaking, thermoelectric cooling gulps power. compressor cooling sips power.

[Socal Tom]

The 12V freezer/fridge are pretty efficient power wise, the 12V "coolers/Warmers" eat power like it was candy at Halloween. I love my 12v fridge, the 12V coolers are a waste of money and space.

The power draw calcs are good advice. Once you have those work out how many days between charges and you will have a idea what makes sense for you.
Tom

I mostly agree.

Those "cooler/warmer" devices are Peltier-effect thermoelectric devices with a maximum coefficient of performance (COP) around 0.7 but typically lower than that. That means for each watt of electrical power you get less than 0.7 watts of heating or cooling power. Peltier effect is very simple and compact and easy to work with, but it isn't very efficient. I got one of those cooler/warmer bags very cheap, and it works fine if I need to keep some food warm or cool while driving to a picnic or pot luck or such, or keeping beverages cool on a long road trip. It uses way too much power to be powered off a battery for long, so not much use for camping purposes.

The 12v freezer/fridge units are typically compressor-based, and have a coefficient of performance of at least two and possibly greater than three. Thanks to the miracle of the vapor compression cycle, you get multiple times the wattage of cooling power than the wattage of electrical power that runs it. This compressor cooling can be well over five times as efficient as thermoelectric cooling. Great for camping.

Put another away: Relatively speaking, thermoelectric cooling gulps power. compressor cooling sips power.

\

Those coolers are also limited to about 30F below ambient temps, so 60F milk on a 90F day. Not good enough for me.
Tom

[TimC]

...
The 12V freezer/fridge are pretty efficient power wise, the 12V "coolers/Warmers" eat power like it was candy at Halloween. I love my 12v fridge, the 12V coolers are a waste of money and space.

The power draw calcs are good advice. Once you have those work out how many days between charges and you will have a idea what makes sense for you.
Tom

Not to hijack this thread, I just thought I would pass on data from my 12v fridge. I've got some consumption numbers in the post that starts on the following page with "I've been trying to do a test of amp hours used by my Alpicool fridge..." Alpicool is a knock off brand but has served me well and is very efficient. There are a number of decent fridges like this. If you have the money go with the Dometic.

http://tnttt.com/viewtopic.php?f=2&t=71874&hilit=what+size+fridge&start=60

Bottom line is it uses less than 14 aHr per 24 hours in my climate. Solar keeps up with it and more during the day so my battery is probably down seven or eight aHr each morning. Keeps frozen meat frozen in the bottom covered with Reflectix as a divider and vegis cool in its smaller compartment away from the coils.