DC/AC Power Distribution Panel Part 2

 DC/AC Power Distribution Panel Part 2

This is an entry in our current non-fiction writing contest  By DanW

Read part one here.

panel 300x225 DC/AC Power Distribution Panel Part 2 Intro:

This part deals with more about component selection, preparation and installation for my Power Distribution Panel project.  Part 3 is a summary, component functional description, and parts list.  Part 4 is my Construction Notes. So, read on! Thanks in advance for your patience ………. Hope you like my efforts!

Once again: A note of caution: When working with anything electrical you should always pay heed and follow all safety procedures to prevent harm to yourself or others. I suggest you do not attempt to build and/or use one of these units unless you have a good working knowledge of basic electricity.

Individual Component Selection, Preparation, and Installation:

AC Power Strip - A 10 Socket 120 vac Power Strip is included on the lower wooden front panel.  It is switched and has a small LED power indicator light.  I chose this particular strip as the outlets are spaced further apart for use with multiple small plug-in type transformers.  Placing the 10 Socket Panel lower on the wooden part of the front panel keeps its weight, and the weight of the cables, adapters, and small transformers that will probably be plugged into the 10 socket strip, in a more manageable location.  With these components plugged in at the bottom of the Power Panel they will be easier to keep out of the way.  I drilled out the original rivets holding the two parts together and re-routed the AC input wire through a hole I drilled in the socket strip back panel. This makes the assembly much neater and facilitates wiring the 10 socket strip to the control switch S8. I mounted the back to the wood face plate and then attached the body of the socket panel using small sheet metal screws.

Meters - In addition to the integral Ammeters on each Tenma unit I have added other digital meters to be able to monitor the various voltages. I was a bit torn between using digital versus analog meters.  In the end I chose digital due to their compact size and very low current draw.  I purchased several extra meters for use as spares. My entire finished Power Panel will be stored in my Faraday cage so the somewhat delicate meters should be shielded from EMP damage.

If my design criterion of a total current draw on the Battery not exceeding 5 amps is to be followed, it is important for me to know what the total load is at any time.  I chose a dual Voltage/Ammeter for this function that will show the Battery voltage and the total amperage being drawn from the battery. This type of meter requires a “shunt” (included with the meter).  The shunt must be mounted so as to be insulated from all other components and voltages.  It will dissipate some heat so it should be mounted on short non-metallic standoffs to provide some ventilation. Be sure you install this shunt in the 12 vdc Negative line per the manufacturer’s schematic (found on Amazon at the link below). This Meter will not read anything below 1 amp however the ammeters on the Tenma units will read below an amp of current flow. The AC Voltmeter will read accurately for grid or generator supplied voltages but will read low when the Inverter is supplying the AC.  This is primarily due to the fact that the Inverter chosen for my panel is not a true sine wave generator and the meter isn’t designed for a square wave.

Four digital voltage meters monitor the voltage for each circuit.  They have an operating range of 3 to 30 vdc. In order to shut off these Meters (to minimize the current load when the circuit is not in use) I purchased some automotive style SPST rocker switches.  Rated for 12 vdc @ 16 amps, these are more than adequate for this application. These switches have small green LEDs that may be wired or left unconnected. Should you choose to connect them, the current draw will be negligible but since they are designed to be used on 12 vdc circuits they may not operate properly in the 9 and 6 vdc circuits.  The current draw of each Meter is also rather negligible but all of these small current loads can quickly add up.  Each switch fits in a ¾” diameter hole and is a single pole rocker style. The switch is connected in series with the 12 vdc Positive (Red) wire going to the meter. These Meter switches are not necessary and could be eliminated if you choose to do so.

AC Power (Grid/Inverter and the 10 Socket Strip) -  Since it is possible that I will have 120 vac being available from our generator (or the grid), I added a switch (S9) that would allow me to choose the source of AC power for the 10 Socket strip.  This switch is a triple pole triple throw (On/Off/On) allowing selection of the source of AC power to the 10 Socket Power Strip (Inverter or Line) or to disconnect its input voltage completely.  This is important as we don’t want the Inverter output accidentally connected to a live grid or generator power ………….. This might produce smoke!!! The idle (no load) DC current draw of the inverter is .5 amps.  This translates to roughly 6 watts of non-productive DC power drain on the battery.  To eliminate that waste, I put in a switch (S8) to disconnect the 12 vdc input to the inverter when it’s not in use.  A panel mount fuse holder (with a 5 amp AGC fuse) is installed to protect the Battery as well as limit the maximum amount of current the inverter can draw.  The value of this fuse may have to be adjusted later. This Inverter is capable of producing 1100 watts of continuous 110 VAC output power. (Wattage = Voltage X Current)  That wattage translates to 10 AC amps (peak current) being produced by the Inverter at its max rated continuous output. In reality, since the Inverter is not 100 % efficient there are probably more than 10 DC amps being drawn from the battery to produce 1100 watts of AC power. The Inverter I chose has the capability to produce much more AC Power than I plan for its intended purpose. At the max load I expect to need it will be virtually idling along.  If needed, it could always be removed from the Power Panel and used to run power tools.  A lower wattage Inverter would save a few dollars.  Due to the physical size of the Inverter it was mounted to the wooden bottom panel behind the 10 Socket power strip. Be sure you mount it where you have unimpeded access to the controls, fuses and connections for your Inverter as well as space for the fan to exhaust.

Keep in mind that this Power Panel is not designed, nor intended, to be able to provide you with a way to plug in a bunch of power hungry appliances!  It would work …….. But there are other more suitable means available to do that.

Inverter Type - As a side note: The Inverter I chose has a “modified sine wave” output.  This type of output characteristic (square wave) is not recommended for use with computers, laptops, or other such devices.  If you think you will need or want to run a computer, notebook, or some other such device then I suggest you select a Pure Sine Wave Inverter that is more appropriate to your application.  Keep in mind that this type of inverter is much more expensive, watt for watt, than modified sine wave models.  I selected this type of inverter because, if my Power Panel is in use, that means that the situation here is such that there isn’t any internet, email, or that type of service available.  Besides, if I do need to power up my computer I can always fire up my generator.  When you are installing the Inverter keep the 12 vdc input wiring as short as possible.  Use wire of a gauge that is similar to the input wire found on the Tenma units, and route the wire away from other components if possible.

Accessory Sockets - Four 12 vdc accessory type sockets are included. They are connected to the main 12 vdc buss via a 5 amp AGC fuse mounted on the Panel.  One switch (S5) controls the set.  This is a convenience since many of the things I will want to connect to the Powder Panel come with an automotive 12 vdc connector or adapter.  I chose Marine style sockets since they are installed in the metal panel and their outer body is non-conductive. They require a 1 1/8” diameter hole (see Optional Parts List for a step drill).  By the way, I found a small battery charger (C, AA or AAA) that comes with an automotive type plug so I can conveniently charge 2 C or 4 AA/AAA batteries at a time.  (See the Optional Parts List).

Fan - This entire unit is going to have several heat generating components. The Inverter, potentially one of the bigger heat generating sources, has its own cooling fan. Even though the Power Panel will not have a back to close it in, I decided to splurge and get a small cooling fan to move some air across the components.  The fan I chose is a 12 vdc model and only draws .1 amps.  (See the parts list).  It is mounted using standoffs so it blows down on the top of the voltage reducers on the wooden top panel.  The fan comes with quick disconnect plugs so the top panel can be easily removed if necessary.  Of course I added a switch (S3) to turn it on/off.

Electrical Wiring - I used two standard Electrical Breaker Panel grounding bars as “tie points” for connecting the various circuits to the 12 vdc.  (These are not suitable if you’re going to mount them on the metal panel)  Mine are installed on the wooden parts of the Power Panel and therefore electrically isolated.  These bars can be purchased in different lengths and are an easy way to wire this unit.  I used one each for 12vdc Positive and 12 vdc Negative connections.

Another consideration is the connection of wires to the switches and other components. Rather than solder, I have used crimp style slide-on wire lugs (available at most all hardware stores) that slide on and off the switch blades.  The wires are soldered to the slide-on fittings.  If you find yourself in an off the grid situation it is easier to repair and replace components if no soldering is required.  It will also make it easier for you to assemble, troubleshoot and repair this Power Panel.  You may not always be around to be consulted on how it is wired so, if you build one of these units, put your design plans in an envelope, and save them for future reference.

Wire, Cables & Routing - Quick-route cable holders will contain the various cables and keep the front panel tidy when the load devices (radios, etc.) are connected. I like neatness and ultimately it will be less confusing with the device power cables are bundled and routed out of the way!

You will need to have two heavy gauge primary connection wires with large alligator clips or lugs for connecting the Battery to the Power Panel. An automotive jumper cable has alligator clips on both ends, is relatively inexpensive, and would work fine (Just remove the alligator clips from one end.)  There is also plenty of extra heavy gauge wire that will be left over from the Tenma units once they are installed in the Panel. I was able to completely wire the 12v circuits using this left over red and black wire.   You will also need a standard grounded three conductor AC Cord that can be plugged into a nearby wall outlet. After you’ve hard-wired the 10 Socket Outlet Strip, and cut off the excess wire, there’ll be a long piece left over that can be used.

Additional wiring will be needed to interconnect the various circuits.  When you are wiring these circuits be careful not to confuse the black 12 vdc wire with the black 120 vac hot wire.  This is another good reason for separating the AC and DC circuits on the Panel.

The Tenma Power Panels come with standard Banana Plug connectors so you will want to have some compatible connectors to adapt to your device power cords.  I use the Red and Black Banana plugs I found on Amazon (see parts list below).

Select wire gauges for the interconnect wiring that exceeds the anticipated amperage and limit your interconnect wiring distances to be as short as possible yet still functional and serviceable.  Excessive lengths of wiring will reduce the efficiency of your Power Panel.

 

FusesA word or two on fuses:  If it seems like I have gone a bit over the top as far as fuses go ……… you’re right.  Fuses and fuse holders are cheap and the best form of insurance against accidental overcurrent situations.  You might want to eliminate some of the fuses I’ve put into this design.  It will still work as intended, but all it takes is one misconnected wire to destroy a non-replaceable (post SHTF) component. Just remember that it’s better to put in a lower value fuse, and have to replace it, than to wait for the smoke to tell you where the problem is!  Buy plenty of extra fuses.

To protect the battery I added a 30 amp automotive style automatic-reset style breaker. It is installed in series with the battery positive input lead.

Load DevicesThese are the Radios, CB’s, Battery Chargers, Home Defense System, etc. that you will connect to the Power Panel.  More than likely each one will have an AC power cable and a cable or jack on the back that can be connected to an alternate voltage. The user’s manual will give you details on the devices input voltage requirements and may also list accessory cables available. If a device uses a small transformer that plugs into a standard wall outlet check out the transformer to see what it provides in the way of voltage. It’s probable that you will be able to power your device, without using the transformer, directly from one of the Tenma unit’s outputs.

 

Battery Charger - I decided that it would be good to have the ability to charge the 12 vdc Battery from the Power Panel if grid or generator power was available.  To accomplish this I have a small Battery Tender charger (see parts list).  Note that the Battery Charger may be used (in a grid up or generator running situation) while the Power Panel is in use. If the charger is not in use it should be disconnected from the battery.

 

Roll-Around Base - A few years ago I built a custom “lift assist” mechanism for a dear handicapped friend.  She used it in her kitchen and, when she passed away, it was returned to me.  I modified it for use as a roll-around base for my Power Panel.  The Power Panel is mounted to the base using quick release clamps.  Designed to place the Power Panel at a height of 30” for easy access, there is a low shelf strong enough to support the 50# weight of the deep cycle 12 vdc battery.  I also put in a shelf to hold a plastic toolbox for spare parts, adapters, transformers, cables, etc.  A storage area for cables, manuals or binders, accessible from the rear of the unit, is included.  Casters (the two front casters lock) allow the entire unit to be easily moved around.  The entire Power Panel may still be used as a desk top unit without the stand and, when removed from the base, fits in my Faraday cage.

To Be Continued:  Part 3 will be published soon and contains a summary, component functional description and the parts list.  

Prizes for this round (ends May 24 2014) in our non fiction writing contest include…

  1. First place winner will receive –  A $150 gift certificate for Hornady Ammo  courtesy of LuckyGunner, a Wonder Junior Deluxe grain mill courtesy of Kitchen Neads, a one year subscription to the Personal VPN service courtesy of unspyable and Three Survival Seed Vaults courtesy of LPC Survival.
  2. Second place winner will receive – Brand New, Sealed Case of Military MREs (Meal, Ready-To-Eat)  a $119 value courtesy of Campingsurvival.com and a Survival Puck  courtesy of Innovation Industries.
  3. Third place winner will receive – a copy of my book ”31 Days to Survival: A Complete Plan for Emergency Preparedness“ and “Dirt Cheap Survival Retreat” courtesy of TheSurvivalistBlog.net a copy of “The Survival Medicine Handbook” courtesy of www.doomandbloom.net and a copy Herbal Antivirals and Herbal Antibiotics .

Comments

  1. Very Good part 2. Looking forward to the rest. I must say that you not only made this thing robust, safe and versatile, but pretty as well.

    Thanks

  2. Big Bear says:

    Sorry the photo is on it’s side. I probably forgot to rotate it before I sent it to MD …..oops! All in all I’m pleased with how it turned out. I spent way more time in the design process than I actually spent in building it. I like things neat, organized and functional! Once the schematic and the rear view is posted it’ll all be much easier to see how it’s wired.

  3. Chuck Findlay says:

    Power strips are a must-have item as the phantom load many of today’s electronic items have can keep an inverter powered up when it really should not be. This can run a battery down fast and for no useful reason as the device is not really being used but still consumes power. A power strip isolates these devices from the system and actually turns them off 100%.

    I understand the use of digital meters for the low insertion (sp?) loss, but I like analog meters for the ability to read them at a glance and I grew up with them. Also many digital meters have a separate 9-volt battery to power the display and just when you need it, the battery could die on you. I buy used analog meters usually for a buck or two at Hanfest, I have probably 30 of them waiting to be used in some project. Probably beyond what most people would want to do, but if you had a small solar system and wanted to save every bit of power you could. A switch could be used to power up or down the meter to save the bit of energy it uses. A momentary contact and a normal switch could be used.

    This is why I would never have an electronic safe, a U-Tube search will prove digital locks have an unacceptable failure rate and do suffer battery death. A analog (dial lock) can sit for decades and work every time. And another thought: I don’t know if an analog meter would survive EMP, but I would bet a digital one would not. Not that I worry about EMP as I see it as a super low probability.

    .

  4. Chuck Findlay says:

    For fans I use old computer fans, the run on 12-volts, draw little power (some draw more, but the rating is listed on the fan.) and I seem to accumulate a lot of them. Again Amateur radio hamfest are where I find a lot of things (fans being one item) for electronic projects.

    P.S. The biggest hamfest on the planet is coming up shortly in Dayton Ohio. (May 16-18 2014) “The Dayton Hamvention” http://www.hamvention.org You can find anything electronic at Dayton, it’s a great place to find old electronic items. I plan on going to it and coming home with a lot of useful junk for future projects. If you go, take a lot of money as there is always lots of things to buy.

    Not too much of it is wife-friendly…

    It’s been said that if mankind made it, it’s been sold at The Dayton Hamvention.

    .

    • Chuck,
      All through the 80’s and 90’s I never missed the hamvention. It’s barely a 2-hour drive which always made me feel very lucky. When the DD completes college and we have some spare cash again, I’ll once more be attending; although I suspect some of the old tube stuff and real boat anchors are no longer available.

  5. Big Bear says:

    The fan I used only draws 0.1 amps @12 vdc and is small. I have several fans that I’d pulled out of computer cases that could’ve worked but they all drew more current. I rarely throw anything away without going through it first to remove parts that can be used on some other project. I even save the screws!

  6. Chuck Findlay says:

    You sound like a hoarder, or I should say a fellow hoarder…

    .

    • Big Bear says:

      Waste not …. want not. My folks were children during the great depression. Although they weren’t hoarders they were always hesitant to throw things away. Must have rubbed off on me. Things used to be made to last and be repaired if they broke. A nation obsessed with consumerism has changed all that for the worse. Planned obsolescence ensures future sales!

      • It all depends on your definitions.
        A hoarder is one who saves junk.
        A collector is one who repurposes junquie.
        I am the later, and suspect both of you are also.

  7. Jersey Drifter says:

    Big Bear, I like this project. Thanks for taking the time to write it up.

  8. Big Bear says:

    You’re welcome! Glad you took the time to read it. Part 4 should be posted soon.