How to know which battery to get

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How to know which battery to get

Postby attomica » Thu Oct 21, 2021 11:24 am

I'm starting to layout the electrical system for my cargo trailer conversion. 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 one, but it is physically much larger than the 100Ah one. 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.
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Re: How to know which battery to get

Postby Tom&Shelly » Thu Oct 21, 2021 12:48 pm

attomica wrote:I'm starting to layout the electrical system for my cargo trailer conversion. 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 one, but it is physically much larger than the 100Ah one. 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.


If we run our fan all night and use our lights reasonably we use about 5 Ah per day. But, we don't have a 12 v cooler, which I suspect will drive your requirements.

Tom
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Re: How to know which battery to get

Postby saltydawg » Thu Oct 21, 2021 3:34 pm

If you have solar and are in the sun full time 100 ah and 100 watts of solar is fine, from what my trailer used with the fridge I would feel safe at 2 days with no charging, maybe 3 but I have 120 ah of lifepo4.

If your not going to be in the sun, go for the bigger battery. If you really dont want to go bigger battery go way bigger for solar with a mppt charger. That way even with some shade you will get some charging, and I mean like 300 watts of solar. Or when you do have full sun you can dump some amps back in to it.

edit my draw when the fridge runs, is about 4 amps but that includes light etc. The fridge runs 3 times an hour for about 10 mins each time ( eco mode ). Figure the fridge is 3 amps, I am using 1.5 amps per hour on the fridge or 36 amps a day just on the fridge. Maybe a little less

I know the run times as the first week I had it running next to my desk and I heard it run.
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Re: How to know which battery to get

Postby TimC » Thu Oct 21, 2021 4:22 pm

No expert here, just a thought about conserving energy. If you are not into conservation just skip right on to the next post... :)

I don't have many of the high draw items you will have but when I had 144 aHr with an AGM bank I had to conserve a bit to make it though three cloudy days. That improved when I upgraded to MPPT. It was simple... I would use electronics charging and shower pump only during the day to help keep overnight draw minimized. If I could run during daylight while charging that is what I did. I'm thinking your shower, water pump and USBs could be used in a similar manner. The only night time draw was the 12v fridge, low draw case fans and maybe an hour or so of LED lights before the book would hit me in the forehead to let me know it was time for sleep.
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Re: How to know which battery to get

Postby RJ Howell » Wed Mar 30, 2022 6:46 am

Comes down to wattage used and recovery. Up in the Nor'east solar recovery is slower than southwest. We have trees & clouds, desert not so much..

My main draw is my 12v frig, then some recharging. I have a 60ah lithium and can go 2.5 days with frig only. Up here I rely om my DC/DC charger as my main recovery, but we don't stay more than 2 nights most anywhere. In the southwest we stay put longer and rely on the solar, cause you can.

Add up your wattage/amperage and use the factor with the length of time you stay and your location. Battery size will become apparent!

P.S. In the commercial trailer we ran 230ah off dual 6v's. Those things were heavy!!! You want a copy of my Power Audit (spreadsheet) PM me.
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Re: How to know which battery to get

Postby bdosborn » Wed Mar 30, 2022 9:00 am

RJ Howell wrote: You want a copy of my Power Audit (spreadsheet) PM me.


Too many people take the ready, shoot, aim approach when sizing their electrical systems. Doing a little homework up front will make it easy to make good choices on battery and PV sizes. :thumbsup:

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