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Old 07-31-2018, 03:13 PM   #1
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Trying to grasp electric..

So, I've been researching. And researching. And researching.

I'm trying to wrap my head around everything as it relates to power.

Shore. Generator. Engine.

AC and DC.

I started compiling a list of what we want as far as needing power in an effort to understand what size generator, and maybe additional batteries for DC we would need.
  • Two rooftop air units for when on generator/shore (bus has engine powered air for transit)
  • TV
  • Laptop charger
  • ~4 phone chargers (thinking ahead of having people with us)
  • Smallish fridge
  • Hot water heater, but could be propane. Not against it. Then would also have gas avail. for stove and space heater
  • Space heater? See above
  • Induction cook top? See above
  • Composting toilet vent fan - DC
  • Water pump - DC
  • ~10 outlets. Maybe the "fancy" kind w/ USB plugs
  • Ceiling lights, prefer LED, but does that have to be DC? Bedroom, toilet, kitchen, eating area, sitting area. In 2 bunks, maybe 3rd bunk
  • Accent lights maybe running in hidden trough above windows (LED)?

I've tried to tally up, from what I could find and am around 7000 running watts, 9000 starting.

Now, what I'm struggling with, is the transfer switches, the inverters, etc.

How do I run the ceiling lights while on engine power, then switch them to the stored battery power?
How the hell do I charge the battery? From the chassis battery? From generator? Both?
Can run generator while we are traveling to power everything as if we were parked, I guess thats a thing?

I'm not really bothered by the shore power inlet, and the wiring I think as I can understand most of that and have someone check my work or help me.

I just dont know what all the different components would be. Dont care to make it super complicated, but also dont want to dumb it down to make it unsafe or cumbersome to use

Not full timing. Weekend warrior (sparse).

Am in South Florida, will be going around South East area, maybe up Eastern Coast. Never when its freezing cold will we be there, at least, I dont think.

Started a google doc to log everything
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Old 07-31-2018, 03:30 PM   #2
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Howdy and Welcome Chris!

All good questions. Everyone 'learns' differently but I'd suggest finding a reasonably simple RV wiring diagram to start learning from - maybe even morph it into 'your' diagram.

In the case of DC power, it is easiest/best to have a chassis battery (for the engine) and a house battery (or battery bank). It may help to think of that battery bank as a "tank" that has a bunch of stored energy in it.

Your house lights (the DC ones) always draw from the house battery. Some people also install AC lights but ignore that for now. These lights (and water pump and misc. other items) draw from the battery "tank".

To fill that battery "tank", you have several options - and you may be filling while also consuming from it. You may have a battery charger (or charger/converter) that operates from shore/generator power, a solar charge controller (and panels), or maybe even charge the battery from the engine alternator (though this has some issues and isn't as simple as it sounds - save that for later).

Yes, if installed that way, you can run your generator while driving (to power the A/C) or whatever.

Most people would also have an inverter (creates AC power from DC battery). These suck a lot of power from the battery so be careful. However; they can allow you to power small-to-medium sized AC loads from DC battery (when there is no shore/generator power). Some of us want to be able to do this for long periods or power large loads so we end up with large battery banks.

Lots more could be said but let's see where that takes us.
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Old 07-31-2018, 03:38 PM   #3
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Thanks JD

Right, I've looked at a lot of schematics. In fact, I think I've looked at yours several times (is that the Missy one?)

Its helped a lot.

For the DC batter tank, I can handle that nomenclature. So, The theory would be perhaps, I'm only going to drive the bus for say 8 hours max a day. So my battery tank should be able to supply whatever for as close to that as possible, so I can run the ceiling lights, water pump etc. Then, when I get somewhere to either park or plug in for the night, I can do whichever and it would be running my air conditioner (since its separate than my driving powered one, whatever thats called lol), charging my batteries up while theyre also being drawn from at the same time.

Am I correct in my logic so far ?
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Old 07-31-2018, 03:49 PM   #4
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Originally Posted by ChrisFL View Post
I think I've looked at yours several times (is that the Missy one?)
Yes, correct. However; mine is too complicated - let's start a bit easier. I bet someone here has a good one but, in the mean time, take a look at this.

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Originally Posted by ChrisFL View Post
For the DC batter tank, I can handle that nomenclature. So, The theory would be perhaps, I'm only going to drive the bus for say 8 hours max a day. So my battery tank should be able to supply whatever for as close to that as possible, so I can run the ceiling lights, water pump etc. Then, when I get somewhere to either park or plug in for the night, I can do whichever and it would be running my air conditioner (since its separate than my driving powered one, whatever thats called lol), charging my batteries up while theyre also being drawn from at the same time.
Yes, exactly right. You could also change the scenario to one where you are going to camp one night without shore/generator power. In that case, you may want your battery tank and inverter to be sufficient to run your essentials. That includes the lights/pump you mentioned but maybe also your refrigerator (and whatever else). It's these "use cases" (scenarios) that slowly lead us to the decisions that we make about the hardware we require. Of course, these are much different for the style of use you have planned than for someone living in their bus.
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Old 07-31-2018, 04:53 PM   #5
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as you plan......

I like to break things down into a systems......

every time you go from battery, DC voltage, to house wiring kind of stuff, AC voltage, you are going to loose some power in the conversion.. same thing going from AC to DC. So, some things that use DC power, like laptops, cellular telephones and the like... DC connections may be the most power saving. I did not say convenient.



things that are 12v operated --

Like RV water pumps. 12v dc --could be 110v ac too, but 12v dc is harder to hurt some one with voltage/amperage

interior lights - could be 110v ac or 12v dc or 24v dc if they are all 12vcd LED light ing then only one kind of wiring would be needed

you could buy 12v refrigerator. is it cheaper in the long run to use a small inverter just for the fridge and buy 110v ac unit?

stereo-music system could be 110v ac or 12 v dc. -- car stereos

If you keep systems like this 12v then -IF needed - you can connect into the engine battery or batteries of the truck and gain power that way.
I Like the idea of using a small inverter just for the fridge. If needed the power can taken from an outlet run from another inverter.

Now, if you had two big honkin batteries for the truck engine and two or four big honkin "house" batteries, you can have a set up with some thing called an "isolator" This device separates or turns off the truck batteries in order to ensure you keep enough power to start the truck. That allows you luxury of using all the batteries for some of you power needs with out being stuck not being able to start the truck.

now if you discharge four of the big batteries down to one level, and two of the truck batteries are at a different level, you are going to have some sort of odd problem charging "the good way"... if four house batteries are very low and two truck batteries are pretty well charged... and the truck alternator does what ? I think now you are going to need something called a charge controller... this thing can have inputs from solar cells, alternators, ac power from an outside source- and extension cord!

and this controller then puts out to each battery for charging. so each battery has an input from the controller.

There are finer points about this part I still have to learn but that is a part of the system.

110v -- I would have some outlets run from "shore power" only. and those would be all one color...like black. and some outlets would be inverter, a big inverter that would not be able to kill the charge in the "house" batteries, and those would be some color other than black -- white, green, gray, orange...

so you would know at a glance what outlet would use battery and what would use shore power.

Now that I am thinking of it, if you had roof vent fans, that would be on dc house batteries. but I might have a small window unit on an ac inverter circuit.

So now two inverters,, one small one to run the fridge, shoot for an inverter that runs at about 50% of rated power. and one big mongo inverter that can run a 110v things like hair driers, welders, tools, etc

So now you can look at things that input power to the charge controller, solar panels, engine alternator, generators, shore power, and something I have never seen talked about... wind turbine.

does this help you at all? It is just my way of looking at things...

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Old 08-01-2018, 05:58 AM   #6
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... in the mean time, take a look at this.
Thanks JD and magna.

I love it. The only change to my "envisioned" plan, would be to have shore in.

I was looking thru the gallery on the site you linked, and this one seems pretty fitting as far as high level? Also includes some of what magna responded with as far as isolaters, I think.

Not really sure why the fridge has propane going in.

The 12vdc would need some tweaking, no hood, add water pump. Poop vent.

Coach battery = battery tank we've been referencing? And before the battery tank after the isolator would be the charge controller?

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Old 08-01-2018, 06:36 AM   #7
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Coach battery = battery tank we've been referencing? And before the battery tank after the isolator would be the charge controller?
Yes, "coach battery" and "house battery" are synonymous. "Truck battery", "chassis battery", "engine battery", and "starting battery" are also all the same thing. In the case of RV's/buses, when we refer to the "house battery" we are almost always talking about a bank of batteries. On the chassis side, that can vary - many rigs have a single battery (for engine starting) but quite a few have a "bank".

Most RV refrigerators are absorption units which use heat to cool. They run on either 110VAC or propane (to produce the heat). Usually, the control board is ran from 12VDC.

Be a little careful with the idea of combining the house and chassis batteries as well as charging the house battery from the engine alternator. Usually, the two battery types are very different. A chassis battery is designed for infrequent but high voltage draw (starting the engine) whereas a house battery is designed for slow/constant draw to a much lower level (no more than 50% SOC). There is more to it, of course, but this is why a 12V starting battery is not ideal for a house battery and why a 6V golf cart battery is not ideal as a starting battery. When it comes to charging that house battery, an engine driven alternator is not very smart so it is easy to charge the house battery 'incorrectly' and do damage (reducing it's life). When you invest many hundreds of dollars in a house battery bank, it is good to take care of it (and that includes a "good" battery monitor).

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Originally Posted by ChrisFL View Post
The 12vdc would need some tweaking, no hood, add water pump. Poop vent.
If you install a 12VDC fuse panel and a 110VAC breaker panel, you can easily add circuits as required. It's always nice to have the full design before starting work but things change (ask Dwight Yoakam!) and adding electrical circuits is pretty common.

Note that the diagram you referenced is missing a number of key components (for simplicity, I assume). The biggies include the shore/generator power transfer switch, inverter, and it kind of overlooks fusing for 12VDC circuits. It also combines the idea of 12VDC distribution (fuse panel) with the 12VDC charger/converter - that is a bit misleading. Just be aware...
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Old 08-01-2018, 06:54 AM   #8
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Quote:
When it comes to charging that house battery, an engine driven alternator is not very smart so it is easy to charge the house battery 'incorrectly' and do damage (reducing it's life). When you invest many hundreds of dollars in a house battery bank, it is good to take care of it (and that includes a "good" battery monitor).
Completely agreed and understood. I thought that was why theres the isolator on that schematic, that would keep the power contained on its leg? I guess a better depiction would just have it completely removed as its only function is to stay connected to itself for sole use by engine needs, while the battery tanks would be for amenities

Would want to charge battery tanks from generator or shore only.

I think I'm starting to get a grasp on this. Really appreciate the help
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Old 08-01-2018, 07:19 AM   #9
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Oh... I forgot. Many motorhomes use an isolator between chassis and house batteries so they can (manually, via a dash mounted switch) connect the two if the chassis battery is ever so low as to be unable to start the engine.

Excellent - very welcome! There is a learning curve to all of these systems - and I'm not sure it ever really ends! Always something new to learn!!
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