In need of basic knowledge to calculate power and recharging needs

[Smoky]

It's clear that almost all people here are familiar with 12v systems, have an unconscious understanding of the term amp hour, and can quickly calculate their battery and solar power needs. I, on the other hand, am a neophyte at electricity-related things. Consequently, I’m struggling to calculate my power and recharging needs based on the accessories I’ll want to locate in the truck cap camper I’m building (fridge/freezer, laptop, LED lights, 12v fans, etc.). So, my questions are these -- First, what are amp hours? Second, how do I read, interpret, and apply accessory specifications for watts and/or amps in determining my power and recharging requirements? Anybody out there have a simple, neophyte-friendly explanation?

Thanks, in advance, for your help.

Smoky

 

[verdesardog]

Power = amps multiplied by volts.
1 amp hour =1 amp for the duration of one hour
Battery charging is dependent on battery type, available charging methods and how much the battery was discharged.
There is way too much information to be taught in a simple forum post.
Add up all the current requirements and make sure you have enough battery to handle that for the amount of time between charges.
Wire size is important to make sure you don't have voltage drops or over heating of wires.
Fuses are required for safety.
Etc, etc, etc
Maybe you need a good local person to help with your design and install needs.

 

[Smoky]

That's helpful, verdesardod, thanks.

If no one has yet done so, it would be of GREAT help to people like myself (those who know little to nothing about the electrical side of vehicle mods) if someone would be willing to put together a basic glossary of terms and maybe a few quick tutorials and/or system design guides to help us better understand what we need to consider and plan for as we think about various electrical/solar system options.

 

[jonyjoe101]

One thing that is often overlook is how much amp hour you can get out of your battery. For instance a 100 amp hour battery isnt really what you will get out of it. You never want to go below 50 percent of your battery rating.

So for a 100 amp hour battery, you can actually only use 50 amps out of it. Using only 50 percent will let your battery last years, drain it to 90 percent every time and you will "cycle it", each battery can only be cycle so many times before it starts losing capacity (it wont last long before you need to charge it again).

So if your needs use up 100 amp hours every day, that means you will need 2 x 100 amp hour batteries or a large 200 amp hour battery.

In your list of things you plan on running, the fridge / freezer will be the one using the most power. The fridge set to 40 degrees will use about 25 amp hours in a 24 hour period, but set it to zero and it might go up to 50 amps or more.

I use a small netbook which I can literally run 24 hours without it using too much power. But the larger 15 inch laptop Is a powerhog and I only use during the day when solar is available.

Led lights and fans wont use too much power, fans you usually run during the day when the sun is out. At night I usually use a small 120mm 12 volt fan that uses less than 1/2 amp. Thats 1/2 an amp per hour, if i run it for 4 hours it will use 2 amps total.

Since everything is 12 volts you just add up how much amps each item uses.

One quick way to do it is just get a dc wattmeter (cost about 15 dollars). And just measure how much amps something use during an hour of use. Thats how I find out how long I can use something with the battery I have. You quickly find out what your power hungry devices are.

 

[Smoky]

Many thanks, jonyjoe101...VERY helpful!!

 

[workerdrone]

I'd add that just as it's better for (traditional lead acid) batteries not to be drained below 50% of their capacity, it's even betterer for them to be drained less than that - so a battery that's cycled between 90 and 100% and kept at a nice constant temperature (not likely in a mobile application I know), might last 10 years or more.

It's very nice to have some extra capacity on hand too - depending on your charging method (alternator, solar, generator, shore power), you'll need to charge less often, and as the batteries age and capacity diminishes they'll still be effective for you. We're 100% solar and just spent 4 days in the shade and our batteries were still at 75% or so which was pretty nice - probably got a 5% charge or so each day from the filtered sunlight. When we're parked in the sun and running 14+ volts off the solar I'll plug a bunch of stuff in (laptops, battery chargers etc) so everything starts at 100% when the sun goes down

 

[Smoky]

Thanks, workerdrone...what's the wattage of your solar system?

 

[SnoViking]

I have seen some decent power consumption spreadsheets for purchasing generators (google them). You can select all the devices you have, either pick or manually enter the amp draw (at both startup and consistent running; ie. a fridge may pull 5amps when the compressor kicks on but only 1.5 whilst running) and for how long you're planning on using each item within a period of time. From there you can get your max draw and constant draw. I've used them in the past to figure out what size generator I needed. Using one of those charts/spreadsheets you can first determine what your overall power need it. From there you can put that into your equation of what battery and solar capacity you have.

 

[Smoky]

Tnanks, SnoVikig...I'll get on that post haste.

 

[workerdrone]

Thanks, workerdrone...what's the wattage of your solar system?

We're 300 watts with another 100 we can throw out on an extension cord but we never do

 

[IdaSHO]

That's helpful, verdesardod, thanks.

If no one has yet done so, it would be of GREAT help to people like myself (those who know little to nothing about the electrical side of vehicle mods) if someone would be willing to put together a basic glossary of terms and maybe a few quick tutorials and/or system design guides to help us better understand what we need to consider and plan for as we think about various electrical/solar system options.

What you seek is within one of the stickies in this forum.