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Old 03-12-2013, 10:44 AM   #1
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Just starting: electrical system question

Hey All, we've been studying all of the information we can read about the conversion process. Our bus is partially converted by the PO. But his work was focused on gutting and cleaning up the interior. There is no permanent plumbing or electrical systems. On the one hand, this is good because we can do it ourselves.

So, we figure that the mission for our bus is going to be roadtrips with a few stops with 1 or 2 night stays for riding/hiking/paddling/etc. We can also see using it for a week straight up at our family's place in the Adirondacks - it would be sweet to have a place of our own to sleep, rather than festival sleeping on the loft. At any rate, we do not plan to live in this full time.

We're planning a decent sized battery bank - 4 or 6 220Ah 6-volt batteries. We're planning on a small Honda genny: the EU2000 is the top pick. Solar seems cool, but it is expensive, and here in New England we will be using every oppurtunity to park in the shade.

We're planning on installing a 9000 btu mini-split HVAC up front in the "travel area." Our plan is to be able to seal off this area from the rest of the bus when underway to cool it. I do not see using the HVAC during the actual "camping" portion of the trips.

With that, I'm a little confused about a few items, hopefully you guys can shed some light.

So, I have some AC and some DC loads. The AC loads include the HVAC, the frig, and the battery charger, TV/DVD, and perhaps a couple of AC outlets. The DC loads include the lights, the water pump, radio and inverter.

The AC loads can be powered via the genny, the inverter or the shore power.

I'm thinking of powering the HVAC from the genny when underway. Should I provide a dedicated line right from the HVAC to the genny, or should I wire HVAC to AC panel and then feed AC panel from genny? I can see the HVAC and the frig and the TV being powered up when underway. If the HVAC has a dedicated line, the frig could run off the inverter. This kind of seperates the 2 big loads. If they're both fed from the AC panel, they might not be able to be seperated...and could be too much of a load for my genny.

Can the AC panel be fed from both the inverter and the genny at the same time? Or should I intall an either-or switch for AC panel feed?

What will be the result of powering DC loads when underway while the alternator charges the batteries. Will the alternator effectively power the DC stuff, and then whatever power is left over goes to charging the batteies?

Do I gound both the house battery and engine/chassis battery to the chassis?

Do I run a single hot DC feed to the lights and other DC loads, and ground the negative to the chassis at the load? Or, do I run 2 wires to each of the lights and then gound at the DC panel?

Alrighty, I think that is about it for now. If you've made it this far, thanks very much for your interest! Good day!

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Old 03-16-2013, 12:08 AM   #2
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Re: Just starting: electrical system question

Lot of questions. Rich is right, size the generator to start the ac. Typical on a bus/RV system is to tie the house bank and start batteries together when the engine is running, by either a diode block or solenoid. The alternator then provides the voltage and current that provides the power to charge batteries, or power stuff. What the heck do they call those diode things anyway? They drop the voltage by 0.7 volts, which equals a big power loss in a 12 volt system. My 160 amp alternator on my bus could realistically provide about 10 amps of 120 volts ac (maybe) through an inverter, with some engine R's,(maybe again.)

Standard is to run your battery bank to an inverter-charger. Most switch from battery to shore power automatically. Size your inverter to run your ac when on the run. Big money, big money, but cool. Cover the top of your bus with solar panels and get free electricity. Really--after twenty thousand dollars.
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Old 03-16-2013, 09:55 AM   #3
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Re: Just starting: electrical system question

I agree with the others I think your EU2000 will be a little too small to power the full load of what you have on your plate. I just looked at the specs on a sanyo 9k btu mini split and it looks like it takes close to 8 amps (i am assuming is the highest draw) when the compressor kicks in and close to 3 amps running. I know a refridgerator is going to be a larger draw also when its compressor comes on also. Since the honda doesnt have multiple legs to connect it to it will have to bear the whole load of both if they come on at the same time.

I think you have thought a lot of your design out I just think your a little shy on the input sizing. I would sit down and take a HARD look at the power numbers and reconfigure. Power is one of those things you cant have enough of at times. I plan on running 2 AC units in my bus along with a lot of the same things you have going on in yours... Mine is to be powered by a 7k Onan propane generator.

As for grounds and neutral bonding.. I think there is a whole thread dedicated to that very discussion. I think there were some feathers ruffled with in it but it is a good read. I am not too far out on this part of my build so I can only offer theortical advise and not real world for the moment.

Good luck
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Old 03-16-2013, 10:20 AM   #4
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Re: Just starting: electrical system question

why not just get a good converter lot less hassel, that way you have 120v 12v and a battery charger all in one, when you are driveing you plug you power cord into the generator, when camping you can plug it into shore power, or into a inverter. also you need at least a 3000 generator, this is the set up I have but i dont plug into a inverter, I just use a small on for my tv and sat dish if Im not on shore power. my generator has command start on it so when im driving i can start it and run the ac
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Old 03-16-2013, 04:08 PM   #5
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Re: Just starting: electrical system question

Mixing AC and DC power takes a while to wrap your head around but it's not rocket science (at least once you've figured it out ).

An INverter makes AC from DC and consumes about 15% of your battery power in the conversion. For this reason I've installed as few AC appliances as possible.

A CONverter makes DC from AC shore power. It consumes some power also but you've got a lot more shore power available so wasting a bit isn't such a big deal.

As Bus-Bro said, the diode based battery isolaters do drop the voltage coming from the alternator quite a bit. This means your peak charging voltage goes from 14.4v or so down to the 13.7v neighborhood which will prevent the batteries from ever getting a full charge on alternator power. Your converter/charger should still give you proper charging volts (if it's properly designed) but it only charges when you're plugged into shore power.

I'm using a simple shutoff switch on the positive battery cable between the chassis batteries and the house bank. It's simple and cheap but I do have to remember to disconnect the two banks when parked to avoid draining the chassis batteries. The battery disconnect relay switch is a more fool-proof way to go but requires a bit more wiring.

Take a look at the Progressive Dynamics Intellipower power centers. They have AC breakers, DC fuses, an AC to DC converter and a three-stage battery charger in a nice small package.

As far as grounding goes, if you're using alternator power to charge batteries you'll have to ground the house batteries either to the bus frame or run a ground cable back to the chassis batteries. Grounding back to the chassis batteries is preferred (gives you a single-point ground) but both methods work and grounding to the frame takes a shorter (less expensive) battery cable. Your AC breaker box should be grounded to the steel bus body. DC device grounds can be to the bus body or back to the DC fuse box. My bus has a fiberglass body so all my grounds have to be wired back to the panel.

If you will be using a house-style AC breaker box get a branch breaker box with the ground and neutral bars separate. AC grounds and neutrals should only come together at the main breaker panel at your house or the campground.
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Old 03-17-2013, 01:23 AM   #6
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Re: Just starting: electrical system question

Quote:
Originally Posted by BelltownBikes
. . . . We're planning a decent sized battery bank - 4 or 6 220Ah 6-volt batteries.
Each battery stores 6v x 220 Ah, or 1320 watt-hours. For 12 volts, two 6v batteries in a series string are still 220Ah, but 12v x 220A= 2640 watt-hours. Four batteries (two strings) are 5280 watt-hours, and six batteries (three strings) store 7920 watt-hours.

Please note that most deep-cycle batteries have their capacity rated at a C/20 rate. This means a 220 Ah battery is rated to provide 11 amps for 20 hours, but cannot be expected to last a full hour at a continuous 220-amp draw. I have seen a few C/10 rated batteries, which will supply high current longer than C/20 rated ones of the same capacity.


Quote:
. . . . I'm thinking of powering the HVAC from the genny when underway. . . .
Where are you going to mount the portable genny? On the back bumper, or maybe underneath the body? It can be done, but please consider the exhaust fumes, vibration, etc.

Quote:
. . . . Should I provide a dedicated line right from the HVAC to the genny, or should I wire HVAC to AC panel and then feed AC panel from genny? . . .
It will work either way (if the genny is strong enough), but having the feed run through the panel will make it easier when connecting to an outside source via a shoreline.

Quote:
. . . . I can see the HVAC and the frig and the TV being powered up when underway. If the HVAC has a dedicated line, the frig could run off the inverter. This kind of seperates the 2 big loads. If they're both fed from the AC panel, they might not be able to be seperated...and could be too much of a load for my genny.
Try to get a high-efficiency fridge, or even convert a chest freezer as others here have done. Every time you open the door on a conventional fridge, all the cold starts pouring out onto the floor. Remember, you still need to provide the same amount of watts (volts x amps) whether from the genny or an inverter.

When using an inverter, as a rule of thumb multiply the AC amps times 11 for the DC amps drawn. A 1200-watt AC appliance (10 amps x 120 volts) will still need 1200 watts (100 amps x 12 volts) into the inverter, and add about 10% for wire losses and inverter losses. That would be 110 amps. As the batteries start to fade, a well-regulated inverter will draw even more current to keep up the output (for example 132 amps at 10 volts). Make your DC wires big and keep them short. Run long lengths at AC, wire losses are ten times less at the lower current draw.


Quote:
Can the AC panel be fed from both the inverter and the genny at the same time? Or should I intall an either-or switch for AC panel feed?
Their outputs cannot be tied together, but if you had a 240-volt panel, one 120-volt leg and its branches could be sourced by the genny, and the other leg and its branches could be sourced by the inverter. If the inverter was not designed with a change-over relay, you would need a switch or disconnect plug arrangement when using a shoreline.

Please note: a panel in a vehicle is a sub-feed of the outside source when connected to a shoreline. Keep the AC neutrals insulated from the safety grounds. If you plug the shoreline into any GFCI outlet, a ground-to-neutral bond will trip the protection. The inverter or genny may tie the ground to neutral when they are the source of power, but never the shoreline.

Another idea: what many vehicles (and buildings) use when there is a transfer arrangement present, is to have a main panel plus an emergency or protected panel. The main panel would have the air conditioners and other external-power-only loads, and one breaker in the main panel would feed the transfer relay for the inverter and its few protected circuits in the "emergency" panel. If the transfer were an automatic relay, the inverter could be armed to start whenever the commercial power fails or the genny stops for refueling.


Quote:
What will be the result of powering DC loads when underway while the alternator charges the batteries. Will the alternator effectively power the DC stuff, and then whatever power is left over goes to charging the batteies?
This works for many people, but depends on the size of the alternator and the size of all the loads. Unfortunately, you will have to do the math.

Quote:
Do I gound both the house battery and engine/chassis battery to the chassis?
The engine/chassis battery is required to be grounded by the vehicle manufacturer's design. It up to you to make a choice for the house battery system. But obviously, if you are charging them with the alternator and not solely with a converter-charger or integrated inverter-charger, you will have to ground those batteries to the chassis as well.

Quote:
Do I run a single hot DC feed to the lights and other DC loads, and ground the negative to the chassis at the load? Or, do I run 2 wires to each of the lights and then gound at the DC panel?
If you opt for an isolated house system, you need to run returns for all the house loads. If you opt for a grounded system, you can do it either way, sort of belt and suspenders.
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Old 03-17-2013, 12:56 PM   #7
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Re: Just starting: electrical system question

I thought of posting an answer but had far more questions. I don't think the OP has really thought things out. So my response is one I had posted before. Read thru it all. It's what I think everyone should do before they start converting. And when I say write it down, I really mean put it on a piece of paper that you can make corrections, add to, scratch off, pass back and forth with your SO. It is to make you think about things and to discuss options. There are other things that I have thought of since posting it (like look at campground directories to see what type of power & hookups is available in the types of campgrounds you normally would stay in) but I decided it was long enough of a post. You have to stop somewhere.

http://www.skoolie.net/forum/viewtop...=54466#p143767
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Old 03-17-2013, 04:39 PM   #8
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Re: Just starting: electrical system question

Airconditioning just kills your electrical consumption. It can also make you want to do crazy stuff like multiple sub panels, split shore systems, etc.

Are you _sure_ you can't live without it?

We have no aircon.

Our inaugural outing was last summer during august. We drove from ND to California, via Wyoming, Nevada, etc. We were driving through the southwest in august during a drought. We had a 5 year old and two two-year olds. We used fans and open windows to make the bus managably cool during bedtime so that we could fall asleep. We had windows open while underway to keep air moving through the bus.

Our electrical goals were to be able to run our fridge, microwave, coffee maker, griddle, lights, laptops, etc, for a couple days of boondocking with batteries only and no solar panels. We have no LP in the bus.

I set it up so that our 120v circuits are always coming off of the Magnasine 2812. The Magnasine chooses the appropriate way to power things -- battery, shore power, or generator.

We don't have a generator.

I think I have it wired so that MS2812 will pass-through two legs of 50A to the breaker box when on shore power, but when on inverter, both hots are tied to the same leg, so you could only really use 240v loads when on 50A shore connections. we don't have any 240v loads.

I installed the Blue Sea Systems "Add A Battery" kit, which gives a nice isolator/combiner between the house and the chassis DC systems. Since we never stay in one spot for more than a couple days, and our driving stints are pretty long, we get good recharging of the house batteries while underway.

I figure if we ever want to add aircon, I may add one of those in-room AC units and just build a panel to fit in one of the bus windows that holds the venting hose. Easier than cutting the roof.

http://www.mattevans.org/~matt/bus/electrical.html
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Old 03-17-2013, 08:32 PM   #9
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Re: Just starting: electrical system question

Thanks All, some very good points to ponder. Thrash, your site is most helpful.

From looking around, I think our conversion will be on the "simplistic" end of the spectrum. We have thought a lot about what we need - how to do it correctly is the point of my questions. Our AC loads are pretty small. No TV. No stove. We'll need a couple of outlets to recharge batteries and phone and run computers and such. The frig will be a converted chest freezer. We will cool it off before leaving and then leave it off when travelling.

We will use our bus as "weekenders" aside from a couple of longer (4 - 6 week) roadtrips in the coming years before the kids get too old. We build custom bicycle frames for a living (note that both my wife and I are engineers for the *real* paying gig - the frame building is a passion, but it doesn't pay a lot of bills). The bus will support our travels to festivals and races and plain adventuring. We will more often than not be dry camping.

I want to run off batteries primarily, but have a way to re-charge besides the engine alternator. Also, I do know that the hVAC will drain the life out of the batteries quickly...hence the genny. I'm conflicted about the size of the genny. I think that one honda 2000 will run one of those little mini-split HVACs...but there is so much conflicting info out there that you don't know until you set it up. If one doesn't do it, we'll just get another and run them in parrallel. I'd rather have redundant smaller gens anyway.

I think the HVaC will only be used when over the road - and then minimally. Our Vanagon has no AC and we've been dealing with that forever. But it sure would be nice to be able to cool off some hot and tired racers on the way home. Or stay coolish when stuck in traffic at the Tappan Zee bridge in August. We are planning two roof top vents, and I believe that they will be able to keep us cool enough most of the time. We're not really AC people anyway - but still want to be prepared.

It looks like I can run a inverter/charger and essentially let it figure out what to do with the incoming and outgoing power. The Magnum units look nice and I like that they are made in USA.

Thanks for the pointer on battery isolation and grounding. Does anyone have an opinion of this isolator?:

http://www.powerstream.com/battery-isolator.htm

Best of both or worst of both worlds? I do think that I can handle a switch...but keeping things simple is important.

We're all very excited for this project here. It'll actually hit the driveway in 2 weeks - assuming the pile of snow is out of the parking place. Then the real fun begins.

Again, thanks for the advice. B
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Old 03-17-2013, 09:13 PM   #10
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Re: Just starting: electrical system question

The relay you link to looks like a good way to go. Since it senses the charging voltage you wouldn't have the hassle of wiring your relay back to the ignition switch. I may have to re-think my manual switch plan. One thing I do like about the manual switch is that I can easily connect the two banks for starting if the need ever arose.

Keep in mind that your deep cycle batteries shouldn't be discharged much more than 50% (about 12.1 volts) for good battery life, so only half of you total available watts are actually available before recharging. Deep cycle batteries will only take about 150 deep cycles (from fully charged to fully discharged). If you recharge at 50% discharge the batteries will take maybe 500 cycles. The lesson is to charge early and charge often.
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