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Ideas for building a battery power pack anyone?

 
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Hello and thanks in advance!

Maybe it is hurricane Dorian in the news, but I am really thinking about building a battery backup power supply.  I already have a 5k generator so this would basically be a power supply for smallish electronics.

I have looked at several builds on YouTube, and some are quite sophisticated, while others are very simplistic.  I have an idea of what inputs/outputs I want, but I don’t really know how to assemble the components, especially in an electrical connectivity sense.

Among the outputs I want to include:
4 USB ports
1 12v cigarette plug
1 DC to DC buck convert

As far as inputs, I would like to charge by 120 a/c and eventually solar panels for emergencies.

I would like to start with a 30(ish) amp hour 12volt sla battery and have the whole thing fit into a plastic.50 cal ammo can.

Any good suggestions?

Thanks in advance,

Eric
 
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Since you already determined the battery and voltage, the rest is pretty straight forward:
The USB ports are readily available on all markets, just look for stuff to build into a car. Same with the 12v plug (although I cannot recommend cigarette plugs, they never work reliable for me).
What do you want from the DC-DC converter? (The USB ports will contain a buck converter already.)

Charger: 12V battery charger. Also available everywhere.
And then probably a 12V battery controller to protect the battery from over charge and discharge. And a fuse next to the battery in case you short it out.

EDIT:
Assembly: First you will have to determine the maximum current your system will see. That determines the wire size. (see AWG).
Battery connections: Hopefully your battery has something to screw a bolt into. Unless you need super high current, twisting the wire between two washers should suffice. If you want to to it properly, get some properly sized cable lugs. There are some for crimping and some for soldering. Crimping is faster, soldering has better contact … not that you would ever need that much current.
Other connections: I am a huge fan of screw terminals: Twist the end of the wire, insert and tighten the screw. To do it properly, use one of these as well. Also shrink insulation for the positive connections.
 
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only other tip i'd give besides above is considered price comparing the finished product versus building yourself. The margins on this stuff is small and so you often can find solar panels and electrical equipment below cost of building or assembling yourself. If you are going to run something critical like a cpap you might also want to consider a finished product.
 
Eric Hanson
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Lucas,

You make fair points.  However, when I have done an apples to apples, cost/benefit analysis, I always seem to come out ahead (mostly I am comparing to the Goal Zero Yeti series).  Also, I can customize as I see fit, a major reason I am attempting such an endeavor.

Most of all, I just like building these types of projects.  It’s a great exercise in creative reasoning and I just love the learning experience and satisfaction when I am done.

Eric
 
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Hi Eric,
Being the tinkering sort I completely support your endeavor. I've done that sort of thing, though never as a self-contained unit.

Since I'm cheap I'll start with batteries. If you can find someone who works on fire alarms, you might be able to acquire some small gel cells that are pulled after a couple years. Recently I got an old car battery from an auto parts store. I paid about $25 for the core charge. Car batteries aren't ideal for your situation. A deep cycle battery is better. (I can explain if you want) But if they're cheap....

I'm thinking an ammo can will be too small for a 30ah battery. I know they make plastic battery boxes for boat batteries. I think walmart has them for $17.

For your ports, I'd got for something like these:
https://www.amazon.com/Linkstyle-Charger-Voltmeter-Cigarette-Lighter/dp/B07JHH5YP4/ref=sr_1_4?keywords=usb+12+volt+outlet&qid=1569541926&s=gateway&sr=8-4
https://www.amazon.com/Upgraded-Cigarette-Splitter-CHGeek-Waterproof/dp/B07QR3C8N2/ref=sr_1_15?keywords=usb+12+volt+outlet&qid=1569541926&s=gateway&smid=A1ZQ83AKJ5ITK4&sr=8-15
You can also get USB & Voltage:
https://www.amazon.com/SunnyTrip-Waterproof-Aluminum-Voltmeter-Motorcycle/dp/B07MMHZDXY/ref=sr_1_16?keywords=usb+12+volt+outlet&qid=1569541926&s=gateway&smid=A3TPCJDGCPP8OK&sr=8-16
I would make sure you have an on-off switch since the USB chargers will probably have a phantom load. (A tiny load but it will kill your battery in storage.) I like to know the voltage, too.

For chargers you have options. Chargers for small car batteries could work if you only charge them a few hours and then unplug. I'd tend to go for a float chargers. It won't charge as quickly but in theory it'll make sure your battery is always ready. I think the charge controller in addition to a charger is a good idea. It gives you an extra level of safety against over-charging. Over-charging boils off the electrolyte and kills the battery, so you don't want to do that. Float charging shouldn't be above 13.8 Volts. This is one reason I like having the volt meter. If you're fast charging you can take the battery to 14.4 V but that's only for a few hours.

On the opposite end of things, over-discharging also kills the battery (the lead oxidizes, falls to the bottom and shorts it out). I've heard that you can run a battery down to 11 V but I try to never go that low. Some charge controllers have a built in safety against discharging it too far, called a low voltage disconnect.

I think that's about it. Heavy duty wiring is really good. Even if a thinner wire can handle the load, a thicker wire won't be as lossy. Probably not super critical for your little installation but important if you have long runs of wire.

Let us know how it goes.

Daniel
 
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Eric Hanson wrote:Hello and thanks in advance!

Maybe it is hurricane Dorian in the news, but I am really thinking about building a battery backup power supply.  I already have a 5k generator so this would basically be a power supply for smallish electronics.

I have looked at several builds on YouTube, and some are quite sophisticated, while others are very simplistic.  I have an idea of what inputs/outputs I want, but I don’t really know how to assemble the components, especially in an electrical connectivity sense.

Among the outputs I want to include:
4 USB ports
1 12v cigarette plug
1 DC to DC buck convert

As far as inputs, I would like to charge by 120 a/c and eventually solar panels for emergencies.

I would like to start with a 30(ish) amp hour 12volt sla battery and have the whole thing fit into a plastic.50 cal ammo can.

Any good suggestions?

Thanks in advance,

Eric



I personally like car batteries. Cheap, simple, abundant.

And a biomass gasifier to charge them.
 
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Hey Eric,
Just wondering if you have an update on your project and how did your cost to build vs. buying a unit turn out? Besides the obvious enjoyment and satisfaction of DIY did you realize any savings?

B
 
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Since you have a generator already, you might consider a desktop computer's power supply.
They have 12V and 5V outputs.
I have seen many video tutorials from makers on different things, and a lot of people had them on their bench / workshop as power supplys. Then again, their workshops were mostly on-grid situations.


https://computer.howstuffworks.com/power-supply.htm


https://stevenbreuls.com/2014/06/diy-pc-psu-to-a-bench-project-power-supply/
 
Eric Hanson
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B Henry,

Sadly, I have gotten caught up at work and I have not gotten much beyond the planning stage.

I saw a really good YouTube  series that details step by step directions for a much more elaborate unit designed for 120v a/c output among other things.  I love this idea, but I thought I would start small first.

I was thinking about a 35ah design because I saw a couple of designs that looked promising and I thought that 35ah would power a lot of smaller items.

Thanks for the inquiry though, and when I do get started I will definitely update this thread!

Eric
 
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