Power box build (eventually will add solar)

[jharkin]

I was chatting offline with @woodgeek about this one and I figured I would post a short thread to share.

I've been wanting to make a small portable DC power station for a while now. Mostly this is an excuse to play with small solar by eventually adding a 50w panel and charge controller to make it completely self contained. To start with I am just charging off line power.

The primary practical application of this is to have a portable power system for hobby use (I fly R/C models) so I can power battery chargers and related items at our club field without being tethered to the truck. Secondary use will be to backup power for phone,tablet, flashlight, etc charging during blackouts at home when I don't feel like running the big genny.

Requirements:
* Reasonably portable (ie. not weigh a hundred lb)
* Enough battery capacity to run 12 volt battery chargers for loads ranging from small nicads up to medium size lithium batteries (6s 3ah packs or so) with enough capacity for a half dozen charges of the large sizes.
* multiple outputs for 12 volt DC and USB charging
* low maintenance battery


Basically we are building something like a Goal Zero power pack, at a fraction of the price. Read on...

 

[jharkin]

So to build this system I decided on a 50Amp-hour Absorbed Glass Matt (AGM) sealed lead acid battery. I got an inexpensive china made UB12500 by universal battery. This is a true deep cycle battery (not starting or marine/hybrid) so its safe use down to 80% DoD (though cycle life will be reduced). They run just under $100 shipped and it weighs about 30lb. Being an AGM design you can also charge them up to 0.35C (18A), mount it in any orientation, and never worry about it freezing.

You can spend a lot more for very high end US made deep cycle like Trojan, Concorde, etc... or for similar or less money get a flooded marine battery of bigger capacity (heavier, needs watering and ventilation). All depends on your application.


The battery will be housed in an old 20inch plastic tool box I had laying around and all the wiring will be done with marine 12 volt components.

 

[jharkin]

First step was modify the box to hold the battery. I made dividers with dowel wrapped in foam to pad the battery.


Then install a 12 volt fuse panel and start wiring outputs.



Once everything was wired up it looks like so:



The right side of the box is all output wiring, left side is left open to store chargers and eventually add the solar controller.

 

[peakbagger]

Sounds like a fun project. I have a few 12 volt panels left over from my old array sitting in the garage waiting for excuse to get used. I also have cute little English Lister Petter 12 volt generator from one of those old flashing road signs. Kind of tough to justify spending money since my gas generator has not been run since 2001 but its a great way to learn solar

 

[jharkin]

The battery is wired to the fuse panel with 6ga automotive cable protected by a 30A auto reset breaker. I wired up 5 cirucits

(2x) bananna jacks with 20A fuse wired on 10ga
(2x) marine cigarette lighter sockets with 15A fuse wired on 16ga
(1x) circuit that controls 2 dual USB outlets and a 12v cooling fan (PC scrounge)

I also added a 12v meter hardwired to the battery.

The fan, USB outlets and meter are all switched. Both USB outlets havea status LED that draw about 10mA as does the meter so any of them left on permanently would draw the battery down over a few months.

 

[jharkin]

I did some load tests. 24 hours after a full charge the battery was resting at 13.1. I hooked up a USB tablet and a small 6 volt NiMH pack to a charger. The total 12v load was around 2amps.



Another use is that for winter operations at the rc flying field we use insulated transmitter mitts with home made electric heaters. The heater draws about 3 amps. Last weekend I ran it on and off for 4 hours on the 50Ah battery. A few hours after end of the day it was resting at 12.58 volts unloaded and it took back about 9Ah on recharge, or about 20% DoD. Used like that this deep cycle should be good for over 1000 cycles.

 

[jharkin]

I mentioned a fan, you can see it on the end, will be useful in the summer on hot days running big loads.




And for now to recharge I hardwired a plug in adapter for my NOCO smart charger (I already had this). This is a smart 4 stage (bulk ,absorb, float, equalize) charger that can be left hooked up all the time and will properly float the battery for max life. In AGM mode it charges it up to the 14.7v absorption limit and then drops to 13.2v float. I tested it with a kill-a-watt and it draws 5w while in float mode.

 

[jharkin]

The final weight of the setup was 38lb. Its a bit heavy to be carrying by hand to distant campsites but is manageable going from garage to truck, etc.

Total investment was:
Battery - $99
Toolbox - free
12 volt fuse panel, meters, sockets and wire - about $75~100
Total around $200.

For comparison, Goal Zero makes a similar box with a smaller batter (30Ah) and a small AC inverter and sell it for nearly $500.

There are other things you will need like a battery charger (get a good 3/4 stage smart charger) and good electrical tools ( a quality ratcheting crimper is key) so figure on quite a bit more if you are starting from scratch. All the wiring is automotive cables with crimped terminals I got at the local electronics shop. The fuse panel, 12volt sockets, etc are all marine components from outfits like Blue Sea Systems, etc - easily available online.




Eventually I'm going to add a 50watt panel and charge controller. Probably these:

• panel http://www.amazon.com/gp/product/B00DVPPFDS?keywords=50 watt renogy&qid=1450981431&ref_=sr_1_1&sr=8-1
• charge controller http://www.amazon.com/Morningstar-SunSaver-SS-10-12v-Charge-Controller/dp/B002MQW3H8/ref=sr_1_1?ie=UTF8&qid=1450981455&sr=8-1&keywords=sunsaver
• power input meter http://www.amazon.com/gp/product/B017FSED9I?psc=1&redirect=true&ref_=oh_aui_detailpage_o05_s00

For anyone interested in making something similar here are some useful resources:

• http://www.solar-electric.com/deep-cycle-battery-faq.html
• http://batteryfaq.org/
• http://forum.solar-electric.com/categories

 

[begreen]

I love this project. Think I am going to do the same. Thanks for documenting it so nicely. We also have frequent short outages of a few hours when I don't want to hook up the genny. One mod I may make is to install this panel instead. I have put it in our RV and really like it. The panel is small but includes a DC voltmeter, cigar lighter and a pair of USB jacks. This unit is designed for motorcycle installation and supposed to be waterproof or at least water resistant. It can be installed horizontally or vertically.