Battery bank for your Occupation.  In the end we will go through a battery and cable sizing exercise.

Occupy Baltimore (OB) organized a meeting at a local church which brought about 200 concerned citizens together.  It was decided then to occupy McKeldin Park in the Inner Harbor of Baltimore, MD at 12 noon on October 4th, 2011.

www.occupybmore.org

Occupy Philadelphia (OP) spilled out from an organized meeting at a local church with more than 700 people.  Committees and list serves began that night to prepare for the 9am occupation of City Hall on October 6th, 2011

www.phillyoccupation.org

Occupy Baltimore, Occupy Philadelphia, Occupy Wall Street, OCCUPY EVERYTHING

First we wanted to build some battery back-up power boxes for Baltimore.  After buying the parts and taking them down to OB we found out that they had power.  So we built the boxes and drove them up to Philadelphia.

The Tech Tent also had power at Philly for the computers, speakers and stage.  So the first two battery boxes went to the Medical Tent at Philly to keep their walkie talkies, cell phones and laptops charged up.

I have detailed the parts, prices and effort below in hopes that more people find a way to keep the computers, networks and live stream up for those of us who cannot attend every night.

WARNING:  Batteries pack a punch so do your homework before working with anything electric.

ITEM - Description (PRICE) – WHERE TO BUY
BATTERY – 55Amp-hour, SC34DU, Optima Yellow Top AGM Lead Acid ($150) - INTERNET
BOX - Stanley Roller Tool Box ($20) – LOWES
INVERTER – 500Watt Inverter includes two 120VAC outlets and one USB ($40) – LOWES
MISC - Wood and Screws ($15) – WHEREVER

• 4x4 at 13.75” long
• 4x4x4 block
• 2x2 at 17.25” long
• Screws, 1”

TOTAL $225 USD

Tools Needed
Drill with 1/4” drill bit
Screwdriver and/or screwdriver bit for drill

Fortunately you only need one charger for all the battery boxes you make so I will not incorporate it into the base cost of each unit.

OPTIONAL ITEM - Description (PRICE) – WHERE TO BUY
CHARGER – 10A Battery Charger with AGM Battery Option ($50) – PEPBOYS
POWER STRIP – Six (6) 120VAC outlets ($5) - LOWES
INVERTER - 800W Inverter includes two 120VAC outlets, one USB and Display ($80) – LOWES
INVERTER - 750W Inverter includes two 120VAC outlets, one USB and Display ($75) – NAT'L AUTO
INVERTER - 500W Inverter includes two 120VAC outlets, one USB ($40) – HOME DEPOT
INVERTER - 800W Inverter includes two 120VAC outlets ($80) – HOME DEPOT
INVERTER - 400W Inverter includes two 120VAC outlets and two USB ($60) – PEPBOYS
INVERTER - 3000W Inverter ($350) – PEPBOYS
BOX – Big Roller Tool Box to hold multiple batteries ($50) – LOWES
MULTIMETER – Voltage, Current and Continuity Checker ($25) - KMART

Now that you have the parts and the tools begins the fun part.  You have to open up the front of the Stanley box to get the battery in because it's just a little bit too big.  Be careful not to break the chintzy plastic tabs holding the tool box together.  Pull the sides out while pulling the front piece forward.

First put the 4x4 block in the bottom against the back.  Put four screws through the rear bottom of the box to hold the 4x4 in place.  It is much easier on your wrist to put some pilot holes for your screws in and then sink the screws into the 4x4 with your screwdriver.

Now put the battery in the box on top of the 4x4.  Put the 2x2 piece across the top of the battery, behind the terminals (+ and -) and in front of the raised plastic area on top.  Push the 2x2 piece down snug and place one screw in each side of the tool box to keep the wood fixed.

Now slide the battery to one side and place the 4x4x4 block beside the battery to keep the battery stable and in place.  Remove the block and VERY CAREFULLY drill two holes through the back of the tool box where the block will sit.  Then put the block back beside the battery, turn the toolbox around and put two screws into the block to hold it in place.  The battery should not be able to move at all.

Next is putting the inverter into the top of the battery box.  Open the top of the box and take out the top shelf.  Drill two 1/4” holes from the top to the bottom where the battery is located.  Now carefully use the 1/4” drill bit to open up the holes wide enough to feed the RED and BLACK inverter cables through the box.  Be careful not to break your drill bit as I broke all my smaller bits making these boxes.

Pull the cables up through the holes from the battery compartment up to the inverter compartment.  Connect the RED to the positive terminal of the inverter and the BLACK to the negative terminal of the inverter.  ALWAYS CONFIRM THE + AND – TERMINALS ARE CONNECTED CORRECTLY BEFORE CONNECTING TO ANY BATTERY.

Connect the Red clamp to the positive terminal on the battery first and then connect the BLACK clamp to the negative terminal.  You will see a little SPARK as those electrons just can't wait to complete the circuit to your inverter.

Now you can turn on the inverter and watch the green light comes on.  CONGRATULATIONS, you now have 55A-hr battery connected to a 500W inverter (2 x 120VAC outlets with one 5VDC USB slot) ready to power your OCCUPATION.  If the green light blinks and the inverter stops working, simply turn the inverter off and on and the green light should come back on steady and ready to go.  You can also plug in a power strip to get more outlets for low power electronics.

If you have any questions, do not hesitate to contact me, Matt Weaver, This e-mail address is being protected from spambots. You need JavaScript enabled to view it

DON'T BE LEFT OUT IN THE DARK WHEN WE TURN THE POWER OFF!

BATTERY CHARGING

When the inverter gives out the batteries are below their operating voltage, 11.2VDC.  You can use the multimeter to check the voltage.  Set the multimeter to the 20VDC range and touch the red lead to the positive terminal and the black lead to the negative terminal.  The battery is full at around 12.8 VDC, discharged at 11.2VDC and completely empty at 10.4VDC.  Do not run the battery below 11.2VDC or it will not recharge correctly and it will greatly reduce the life and charge capacity of the battery.

Voltage is the potential, like the pressure in a water hose helping the water move.  Current is the size of the hose, allowing you to move more water.  Without sufficient voltage you cannot move the current, same as you need pressure to push the water through the hose.

Optima Yellowtop (AGM) Batteries can be charged with the Schumacher model charger pictured here.  First you want to disconnect the inverter from the battery.  DO NOT PLUG IN THE CHARGER.  Connect the RED charger clamp to the positive terminal and the BLACK to the negative terminal.  Now you can plug in the charger.  You will have to select the AGM battery option and then the 10A charging option.  If you are using another charger make sure the equipment is capable of charging AGM batteries and use the 10A charging rate.  These are the requirements of the manufacturer, Optima.

http://www.optimabatteries.com/optima_products/yellowtop/index.php

Each Yellowtop is 55A-hr (fully charged).  The charger is 10Amp (current) so intuitively it should take 5.5 hours to charge but the Optima manual says it will take 6.5 hours.

BATTERY SIZING

Now that we have the basics down of hooking up, running and charging a single battery let's discuss the options of battery banks.  These AGM (lead-acid) batteries are heavy so the first considerations are where they are going and if you want them to be mobile.  The Big Roller Tool Box in the OPTIONS above was identified because it can hold three or more batteries to increase the OCCUPATIONS power.  Keep in mind the big tool box is over 3 feet wide and with three batteries will weigh over 100lbs.  Now transporting the box to the charging station is a two person operation but it is on wheels.

When you are assembling bigger battery banks you will need to decide what the required voltage is.  Different inverters have different input voltage requirements.  Chargers also have different input voltage requirements, so keep that in mind when you are looking at solar panels for charging options.

BEFORE YOU CONNECT ANY BATTERIES TOGETHER YOU MUST CONFIRM THEY ARE THE SAME SIZE, TYPE, MODEL AND HAVE THE SAME CHARGE (VOLTAGE).  IF THE VOLTAGE IS DIFFERENT THEN FULLY CHARGE THEM AND CHECK THE VOLTAGE AGAIN.

You can wire batteries in PARALLEL (+ to + to +) and (– to – to –) to add up the current and keep the voltage the same.  If you wire three Yellowtop batteries in PARALLEL you will have 55A-hr*3 = 165A-hr of charge at 12VDC.  Clamp the inverter to a battery at the end of your bank and now you have three times the Amps of one battery.  WHEN YOU WIRE BATTERIES IN PARALLEL AND INCREASE THE CURRENT YOU MUST SIZE THE CABLES CORRECTLY TO HANDLE THE CURRENT, SEE BELOW.

You can wire batteries in SERIES (+ to -) to add up the voltage.  Some inverters operate at a higher input voltage, ie 24VDC or 48VDC.  You can wire two (2) 12VDC batteries in SERIES to get 24VDC.  Power is voltage * current (indirectly proportional) so by increasing the voltage you are decreasing the current.  And with a lower current you can use smaller cables.

http://www.otherpower.com/otherpower_battery_wiring.html

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Now let's assume that you are going to use all of the power from the 500Watt Inverter with 120VAC electronics.

Power (Watts aka VA) = Voltage (V) * Current (Amps)
500Watts = 120V * (Amps)

The Amps you are pulling are approximately 4.2A.  This is derived from 500W/120V = 4.2A

And you have a 55A-hr battery.  Well 55A-hr / 4.2A = 13 hours.  You should get 13 hours of operation from the single Optima Yellowtop battery.

Keep in mind batteries are effected by temperature and there is always power lost in conversion.  Batteries are DC (Direct Current) power and the inverter makes AC (Alternative Current) power.  The loss from this conversion DC to AC will result in heat, which you can feel coming from the inverter.  ENERGY IS NEVER CREATED OR DESTROYED.

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Now if you have three 55A-hr batteries in parallel you will have 165A-hr total.

Assume the same 500W inverter supplying 120VAC and a load of 4.2A.

Then you will get 165A-hr / 4.2A = 39 hours of operation from the Big Roller Tool Box.

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And if you choose a larger inverter, let's say 1500W for more lights, internet, network and live-streaming of the OCCUPATION.

1500Watts = 120V * (Amps); 12.5Amps
Three batteries at 165A-hr will run for: 165A-hr / 12.5A = 13.2 hours

AND PLEASE CONSIDER THE AC AND DC SIDE WHEN SIZING THE POWER CABLES.

The 1500Watt example above using a 12VDC battery bank is pulling 12.5A on the AC side.  So you need a cable capable of handling at least 13A.  Size AWG 8 cable can carry 24A so that should work fine.

Now the DC side in your battery box is operating at 12VDC, so to get 1500Watts through those batteries you need to size accordingly.

1500(VA)/12V = 125A

1/0 (0) AWG cable can handle 150A and 2/0 (00) AWG can handle 190A.  I would opt for the larger 2/0 cable or anything larger that you can find, but never smaller cables.

You may recognize the standard 4/0 cable in the hardware store which is used in larger power supplies.  It's about 1” diameter.

Now consider the DC side in your battery box is operating at 24VDC, so to get 1500Watts through those batteries you need to size accordingly.

1500(VA)/24V = 63A

3 AWG cable can handle 75A and 2 AWG can handle 94A.  I would opt for the larger 2 AWG cable or anything larger that you can find, but never smaller cables.

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Copper is expensive so if you plan on using a lot of cable for a big battery bank keep this in mind.  The copper conductor in 2/0 AWG cable is 0.37 inches in diameter and it's 0.26 inches in diameter for 2 AWG cable. 

So the physical cross sectional area of the two cables are:
Area (2/0 AWG) cable = π*radius^2 = 3.14 * (0.185in) * (0.185in) = 0.107in2
Area (2 AWG) cable = π*radius^2 = 3.14 * (0.13in) * (0.13in) = 0.053in2

Now you can see that 2/0 AWG cable has twice as much copper as 2 AWG cable.  So you will pay a lot more to run a higher current system than you will with a lower current system.