Two Quick Questions

[BradKW]

Spending time with my new favorite hobby on a Saturday night...playing around with graph paper and a ruler 

1) Are batteries a potential ignition source? I have a possible design that places propane tank and batteries in a box with passive vent to outside through floor. Could grouping these together in a confined space possible cause trouble?

2) Why are shore power cords always the heavy and relatively expensive 30A ones? I would really prefer to use a good heavy duty 20A cord from HD if this doesn't pose some problem I'm not grasping. Also, what is the first piece of equipment that the shore power connects to? I understand that it needs its own 120v panel, but not what the cord actually plugs into...

I guess that's 3 questions... TYIA!

 

[B and C]

1) Are batteries a potential ignition source? I have a possible design that places propane tank and batteries in a box with passive vent to outside through floor. Could grouping these together in a confined space possible cause trouble?

2) Why are shore power cords always the heavy and relatively expensive 30A ones? I would really prefer to use a good heavy duty 20A cord from HD if this doesn't pose some problem I'm not grasping. Also, what is the first piece of equipment that the shore power connects to? I understand that it needs its own 120v panel, but not what the cord actually plugs into...

I guess that's 3 questions... TYIA!

1) Only through a loose connection that would cause sparking.  If wet cell batteries are used the off gassing might be a corrosion hazard for the propane tank.  I hope others chime in here  

2 & 3) Shore power cords connect to an AC/DC distribution panel with the actual power cord hardwired to the MAIN breaker.  Other breakers in the panel are for branch circuits.  Fuses are provided for the 12v distribution system.  A power converter/charger is wired into the panel to provide 12v for the circuits and a charger for the batteries.  Progressive Dynamics is a proven winner and recommended here.  30 amps is about what it would take to start/run and air conditioner and a microwave in an RV at the same time with a little left over for battery charging and lights without depleting the battery.  30 amp cords are also very heavy duty as they spend a lot of time in the elements.

Here is a link to their website: http://www.progressivedyn.com/ 

A wealth of knowledge there.  You may get by with a smaller system if your needs are not that heavy.

 

[highdesertranger]

well on travel trailers they usually place the batteries and propane tanks right next to each other on the tongue. however this is in the open air. on rare occasion batteries do blow up. I have had it happen once, when a positive cable grounded. I would place both in a confined space I would separate them. highdesertranger

 

[speedhighway46]

BradKW:

Can't speak to your first question, but as to the second (and third!):

I "designed" and built my shore power system in my truck conversion. All components came from Home Depot. I'll describe what I did; if I leave something out, or if there is something I need to explain further, please ask me.

Overview: my shore power system is designed around 30 amp capacity. I could never envision needing more capacity than that in my application, even though 50 amp service is available in some campgrounds. 30 amp components are more readily available. The system has been in use five years now and I have never had a problem with it. If you design your system around 20 amp capacity, you can save some money due to more modest components. For a van application, 20 amps would probably be okay as long as you aren't planning on running an air conditioner. But, the additional cost to have 30 amp capacity is modest; you should consider it as long as you system is going in "new" and will serve you for many years.

1> Shore power cord: HD sells these 10 gauge ugly orange power cords. I refused to purchase the expensive yellow ones from the marine stores. I cut the plug off the end and installed a three prong 30 amp plug which is "standard" at campgrounds.

2> What does the cord connect to? The socket end of the shore power cord was also cut off, and I installed a four conductor "twist lock" socket. On the side of my van box I mounted a matching "male" twist lock connector mounted in a weather-tight metal enclosure. This is where the shore power cord connects to the motorhome.

3> Inside the motorhome from the shore power connector, 10 gauge wiring runs to the service panel. I believe the one I used accommodates six circuits. I used 15 amp circuit breakers in all circuits. Both the panel and the breakers are Square D.

4> Wire the service panel for each of your branch circuits. I used a separate circuit for my refrigerator; 2 for the base plug socket circuits; another for the lights; one for the microwave; another with GFI protection for the outside base plugs.

Now, here is something which is very important. In standard household wiring, the white neutrals and the green ground wires are connected to the same buss inside the service panel. This is according to code because in a home installation there is a ground rod installed near the service panel. However, in a mobile installation, there is no actual ground; you are sitting on four rubber insulators called tires.

Therefore, the white neutrals and green grounds must be separated. This is called "floating neutrals." The green wires can be terminated at ground potential, and connected to the frame of the vehicle so they share the same ground as your 12VDC system. The white neutral wires can be terminated all together inside the service panel, but must not at any point contact a true ground. Further, when wiring all appliances and circuits inside your vehicle, make sure you do not let the neutrals and grounds join.

Its been long enough for my brain to have forgotten the details of this floating neutral requirement. I'll look through my construction notes and get back to you regarding this requirement. You can also do some Googling on floating neutrals.

I'll also takes some pics tomorrow and post them. All of my components came from my local Home Deport. Nothing special; all off the shelf stuff. This is abt as cheap as you can get!

Hope this helps.

 

[speedhighway46]

For more information about floating neutrals, go to:

www.beamalarm.com

Go to "RV Technical Help"
Go to "Electrical"
Go to "120 VAC in your motorhome"

 

[BradKW]

Thanks for the responses!

SpeedHwy, B and C talked about the converter/charger, pre-panel I believe. You don't mention this, so does this mean that your rig is designed to operate Only on 120v, or that your 12v items are segregated with no crossover possible?

B and C... does the design you describe require inverter use for any 120v appliance, regardless of running off shore or battery? Hoping you say yes, as that would mean I'm understanding things better

 

[SoulRaven]

Run an extension cord through the window, connect it to a 6 outlet power strip with built in breaker, and done.

 

[johnny b]

For question 1--Hydrogen gas is lighter than air, so it needs to be vented out the top of the box, not the floor.
The gas would accumulate in the top of your box, which is where the propane valve is!

I would bag this plan and start over. Keep the battery and propane apart and vent the battery box out the top...it can then turn no more than 90 degrees and go out a side wall....louvered grate with louvers pointed down to keep out the rain.

Safety first!

 

[GrantRobertson]

For question 1--Hydrogen gas is lighter than air, so it needs to be vented out the top of the box, not the floor.
The gas would accumulate in the top of your box, which is where the propane valve is!

I would bag this plan and start over. Keep the battery and propane apart and vent the battery box out the top...it can then turn no more than 90 degrees and go out a side wall....louvered grate with louvers pointed down to keep out the rain.

Safety first!

Agreed.

 

[B and C]

B and C... does the design you describe require inverter use for any 120v appliance, regardless of running off shore or battery? Hoping you say yes, as that would mean I'm understanding things better  

The design I am describing is how the RV manufacturers do it where there is a power center.  Can it be done different, sure.  An inverter is only needed if there is no shore power available.  Inverters run off of 12v to make 120v.  Can you run stuff off an inverter while on shore power?  Yes, but I don't know why you would want to.  Your battery charger would have to replace the power taken from the battery to run the inverter.  As many items that you can get to run off 12v, the better.  All the inefficiencies involved with using an inverter to power something that could be done with 12v natively is wasted energy and has to be replenished. You will need to figure out the amp draw of the 120v appliances to figure out how big a battery bank you need to run it.

The cheapest way for 120v is Off Grids way of doing it.

 

[speedhighway46]

BradKW:

I have two systems on my motor home: a 12VDC system and a 120VAC system.

The 12 volt system is in several parts.

1> A "starting battery" system which is pretty much unaltered as it was installed by Peterbilt when the tractor was built in 2003. It is fed by the main engine alternator when running or traveling down the road. It can also be fed by an on-board auxiliary power unit (APU) which is basically a 4000 watt generator and a heater, and also has a 12VDC output. The APU also circulates the main engine coolant to keep the block warm in cold weather.

2> A "house battery" system which I added. It is fed by four deep cycle 6V golf cart batteries, wired first in series and then in parallel; providing 12VDC with about 240 amp hour capacity. These batteries are fed from the engine alternator when the engine is running (going down the road), and from a built-in battery charger when I am connected to shore power. I hope to soon install a solar panel system which will also feed these batteries (in the spring, I hope!).

There is no interaction between these two system; they are completely independent and not interconnected in any way. I set the systems up that way for two reasons: they don't need to be; and secondly, when I take my truck into a Peterbilt dealer for service I don't want to hear any, "blah, blah, blah, we can't service your truck because you've messes with the electrical system." My replay, "go pound sand, they're not connected!"

You can see, so far I have not said anything about an inverter.

So, at this point the 12 volt stuff runs off of 12 volts, and the 120 volt stuff runs off 120 volts when I am connected to shore power, or when I have the APU running.

Hey, wouldn't it be great to be able to run the 120 volt stuff when boon docking and not have to run that blasted, noisy APU? You bet it would! Enter the inverter.

I'm sure you've read all about the various type of inverters because you are asking the right questions about designing your system. I purchased a pure sine inverter with 3000 watts continuous and 6000 watts peak output. It was cheap; its from China, it will probably poop out before I finish this posting. Still, it's done everything I've asked it to for the past five years.

Inverters take 12VDC and change it into 120VAC; that's it. No magic. For the inverter to provide any type of capacity to run your 120 volt stuff, you need to provide it with two things; proper operating voltage and lots of available current. Proper voltage is provided by using big honking cables between the battery bank and the inverter. The bigger the better; the only limit is your wallet. I use two gauge on most all my 12 volt runs; for the inverter I used two parallel 2 gauge feeds for both positive and negative. The second requirement, current, is provided by the batteries; that's why mine are deep cycle. Lots of amps over a long period of time.

My 12 volt control panel was home made. Very simple, works great. My 120 volt panel is basically just the service panel with the breakers. I have designed my system so I can manually connect the input of the service panel (which controls all the 120 volt circuits) to EITHER the shore power source, OR the 120 inverter source. NOT BOTH! This is done manually using a short jumper which can be plugged into either of the sources to feed the service panel. I can only plug into one output at a time, thereby avoiding a big senior moment screw-up.

Sorry this was so gassy. I'll take some pictures for you today of my system and post them.

 

[speedhighway46]

Attached is a .pdf file showing the electrical system I have installed in my motorhome. Pictures to follow soon.

Thanks.

 

[highdesertranger]

nice schematic speedhighway. highdesertranger