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Old 06-03-2018, 03:45 PM   #1
Skoolie
 
Join Date: Aug 2017
Location: Conneaut, Ohio
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Chassis: International CE 300
Engine: DT466E
Rated Cap: 71 passenger / 12 window
Generator + battery bank combination?

Okay, here's a wild idea for y'all, and let's see if anyone has experience with this. I'm trying to figure out what size generator I'll need, and since I REALLY don't want to mount a genset to the bus (I hate those things jackhammering away when I'm trying to sleep - had it on the Class C, don't want to have it again), I'm looking at a portable inverter generator.

Yes, I know that means I will have to get out of the bus and start the thing, and that fuel may be a concern unless I can rig up an auxiliary tank (diesel bus + gas generator = auxiliary tank if I need more runtime between fuel-ups than the generator's tank would provide)... but I'll take anything if it means I can sleep peacefully with the generator running.

For portability and price purposes, I'd like to stick to a 1,000 Watt inverter generator. I don't anticipate using much more power than that at one time without being connected to shore power, but in case I do, here's my thought. I wire up a bank of 12V deep-cycle batteries to an inverter, and run everything off of that inverter. I charge the batteries with a generator, using a charging device that can put out, at most, an amount of power comfortably beneath the capability of the generator. So, for instance, at some point my battery bank may be putting out 1,200 Watts, while the generator charging it is only putting in 800 Watts. The battery bank would draw down at a rate of 400 Watts under this scenario. Then when the power draw is not as large (such as after the "startup surge" is overcome), the generator would be putting in more power than the inverter from the battery bank is putting out, meaning that the battery bank is charging up.

From a simplistic standpoint, this seems to make logical sense. I know that on my tablet computer, which requires more running power than the charger puts in, the effect is that the battery draws down much more slowly than it would if it weren't connected to the charger.

Are there any flaws in my thinking? If yes, point them out and tell me why. (A better suggestion would be helpful, if there is a better suggestion that isn't "buy a bigger generator". I know I can buy a bigger generator, but then I'm spending all of that money on a bigger, heavier, and more fuel-thirsty generator.)
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Old 06-03-2018, 04:24 PM   #2
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There's lots of options for generators. You might consider optional fuel source (propane, diesel) for your generator so your not storing an additional fuel. I'm looking at a remote start genny, so I don't have to go outside to start/stop it.
They're a bit more expensive but Honda and others make some super quiet units that are powerful, yet compact.
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Old 06-03-2018, 05:21 PM   #3
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The Honda EU generators are the quietest. You could get a small one and link it to another one if you need more in the future. For charging the batteries you need a three stage converter between the generator and the batteries. Also, we all use six volt in parallel and series depending how many you want use. They hold their charge longer and are more efficient than 12 volt batteries because of the extra plates inside them.
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Old 06-03-2018, 07:22 PM   #4
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Yamaha 2000 mounted under the bus with a small door access. Extended exhaust, 10g remote tank gives up to 100 hours run time. Barely audible inside unless it's running full rpm.

Open the door, pull the cord, shut the door. Time to stop?...Switch inside does it.

Powers everything...One thing at a time. 1000w water heater, 5k btu ac, 8k btu ac, 1000w micro.

We will be boondocking soon and I leave it run all day if need be. Where we go our 200w solar is shaded.
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Old 06-03-2018, 08:57 PM   #5
Skoolie
 
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Quote:
Originally Posted by o1marc View Post
There's lots of options for generators. You might consider optional fuel source (propane, diesel) for your generator so your not storing an additional fuel. I'm looking at a remote start genny, so I don't have to go outside to start/stop it.
They're a bit more expensive but Honda and others make some super quiet units that are powerful, yet compact.
I don't want to use a mounted generator, so it hardly matters what fuel source I have. On our Class C, we had an unusually quiet diesel genset (compared to the gas gensets I'd heard in the past), and it was still much too loud for us. My current intent, though it is admittedly up for change if need be, is to get a portable generator, set it on the ground when it's in use (under the bus if need be to protect it from rain) and connect it to the bus's electrical system. We'll still hear it, but it won't telegraph anywhere near as much vibration through to the bus if it is not mounted to the bus.

Truth be told, I don't want our bus to be set up to have all of the amenities of home. We had that in our Class C and all that happened was that we spent too much time inside of the motorhome when we could have been outside (had we been more creative with where we parked). Okay, you don't want to be sitting in camp chairs outside of a motorhome in a Wal-Mart parking lot, but you can go to the local park and sit there until it's closed, and then go to Wal-Mart when it's dark and you'd be inside anyway.

I want the generator and battery bank setup to be able to run only a few small things - one 5,000 BTU window A/C unit if need be, one compact (~1.7 cubic foot) refrigerator if need be, a water pump, and some random electrical device chargers. The way I see it, the A/C uses approximately 600 Watts while running, the refrigerator uses 30 - 120 Watts while running, the water pump would probably run off of 12 Volts so it wouldn't even have to be connected directly to the generator, and the other random electrical stuff would use a total of 100 Watts at most. So, even with everything running at one time (which we hope not to have happen), we're still below 1,000 Watts of running power. The problem is the startup surge of devices like an air conditioner and refrigerator. Another thread I read on a trucking website said that the startup surge of even a small refrigerator can hit or top 1,500 Watts even if it only requires a small fraction of that amount of power to run.

I'd like to use a 1,000 Watt generator if I can, and I don't necessarily want to be running my generator at near-peak power constantly. That's why I said that I might use a battery bank charger to put power into the battery bank, then draw the requisite power from the battery bank, so that the generator is running at a constant level while the power draw on the batteries varies.

Quote:
Originally Posted by Thomas1985 View Post
The Honda EU generators are the quietest. You could get a small one and link it to another one if you need more in the future. For charging the batteries you need a three stage converter between the generator and the batteries. Also, we all use six volt in parallel and series depending how many you want use. They hold their charge longer and are more efficient than 12 volt batteries because of the extra plates inside them.
"We all"? I'm willing to use 6 Volt batteries if I must... it wouldn't be hard to wire them up properly, I imagine. I know a few things about electricity, but I'm not exactly a master of automotive or motorhome electrical systems. Really what I'm trying to figure out is whether or not my plan will work. Is there any reason why I couldn't put a set amount of electricity into the battery bank (less if the bank is fully charged, though I imagine the charger would handle that) through a generator, while the electrical devices being used draw their requisite power through the bank? Somehow that has to be how it works in a motorhome...... or is it? (After all, devices that ordinarily run on the battery when the motorhome is not connected to shore power or its own generator will also run when connected to one of those two power sources, so one of two things is true - either the device pulls its power from the battery, and the power source charges the battery... or there is some switch that disconnects the battery entirely from being the power source whenever the motorhome is connected to another power source. I figured it was the former.)
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Old 06-03-2018, 09:00 PM   #6
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Engine: DT466E
Rated Cap: 71 passenger / 12 window
Quote:
Originally Posted by 2kool4skool View Post
Yamaha 2000 mounted under the bus with a small door access. Extended exhaust, 10g remote tank gives up to 100 hours run time. Barely audible inside unless it's running full rpm.

Open the door, pull the cord, shut the door. Time to stop?...Switch inside does it.

Powers everything...One thing at a time. 1000w water heater, 5k btu ac, 8k btu ac, 1000w micro.

We will be boondocking soon and I leave it run all day if need be. Where we go our 200w solar is shaded.
Ah yes, a water heater. I may have to consider that... but as you said, it wouldn't have to run at the same time as everything else. (We rarely used ours in the motorhome - just when we showered or washed dishes.)

Do you have any vibration dampening material underneath your generator - stuff like that thick rubber used on fitness center floors? I would imagine that something like that would reduce the transmission of vibration through to the interior of the bus.
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Old 06-03-2018, 09:34 PM   #7
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"Do you have any vibration dampening material underneath your generator - stuff like that thick rubber used on fitness center floors? I would imagine that something like that would reduce the transmission of vibration through to the interior of the bus."

My Yamaha 3000 watt inverter genny is mounted in a drawer under the floor. It is lined on all sides with 2, 5/8" thick layers of gym mat which knocks down the low frequency racket that is so bothersome. The generator itself is mounted on isolators made from half a dozen engine valve springs set up in cages top and bottom thereby not requiring any other direct connection between the genny and the drawer. If I had all the money in the world I'd have used liquid filled engine mounts rather than the springs-----. I knew I had it figured out when I showed a guy at the camp ground how the remote start worked and after firing up the genny he asked "How much noise does it make when it is running?" Made my day!

I monkeyed with the exhaust some as well. If you'd like to hear more drop me a PM and I'll share what I learned. Jack
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Old 06-03-2018, 09:45 PM   #8
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I think I might try a slightly simpler plan. . .run the AC from the generator at night, run everything else from the batteries. Those new Hondas are small and quiet, and putting it 50 feet away, I doubt you'll hear it over the AC. Adding an aux gas tank to get 8 hour run time (all night) should be pretty simple.

The generators are small and light enough to easily move or stow on the bus somewhere when not being used. If you had the extra capacity (or time), you could always use it to top off the batteries.

Also, if you plan on running everything off the house batteries, that just increases the size of the inverter you need hooked up to the batteries.
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Old 06-03-2018, 09:58 PM   #9
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First things first: yes, your plan to run all your loads out of a battery bank, and to refill the battery bank with a generator, is sound. You have a good grasp on the concept that if you're running more load than the generator is providing then the charge of the battery bank will decrease; if your load is lighter than the generator/charger's capacity then the battery bank charge will increase. Of course there are some efficiency factors we've glossed over (1000 W out to a load is going to require say 1200 W from the generator due to losses in the charger, the batteries themselves, and the inverter) but the point is, your idea is sound and you can make it work.

I'm a little curious about the preference for a 1000 W generator. When I was at the point of generator shopping, Honda's EU6500 was the quietest on the market -- it beat out their EU2000 and EU1000 too. If absolute quiet is what you're after, don't assume the smallest-rated unit is going to be the quietest. Granted, an EU1000 at 100 yards is going to be perceived quieter than an EU6500 sitting right under your feet! If I remember correctly the EU6500 had better quarter-load efficiency than any other in Honda's lineup too, but it's not so easy to extrapolate whether the EU1000 or the EU6500 will burn less fuel for a given 800 W load for example.

One other thing to throw into the ring: a boost or hybrid inverter-charger. In general, these draw up to some maximum from their AC input (whether shore power or generator) and use it for charging battery or pass it through to the output. When more power is demanded than what's allowed to come from the input, it draws the difference from the battery. It's an all-in-one implementation of the scheme you've asked about. See technomadia, Victron MultiPlus, MasterVolt Mass Combi, and Magnum MSH3012M for instance.
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Old 06-04-2018, 12:26 AM   #10
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A multistage charger is important because you can damage your batteries by pumping to much voltage into them for too long. Also this may fluctuate the voltage going to your other devices like a cell phone charging off your batteries at the same time and damage that. You can use resistors on those items you're worried about. Some are built in.
Multi-stage chargers generally have three stages: Bulk, Absorb and Float.
In the Bulk stage, the battery is given as much current as the charging system can deliver. As the batteries accept this charging current, their voltage slowly rises. Eventually the batteries reach the “Bulk Voltage” which is something in the range of 14.3 to 14.8 volts.
The idea in the Absorb stage is that rather than force feeding the batteries all the current the charging device can deliver, the batteries are given just enough to keep them at the Absorb voltage.
Float Stage will hold the batteries at a much lower Float voltage in the range of 13.3 to 13.6 volts. They are pretty nearly fully charged. If the charger is turned off at this point, the batteries will eventually settle down (after a few minutes) to their own internal voltage, and that voltage will be around 12.7 volts, indicating that they are fully charged.
I decided to make a 12 volt DC System to prevent energy loss form an inverter. For example there are USB outlets for charging devices that are DC already, DC lights, water pumps, and small auxiliary fans that you can wire up with no inverter.
My air conditioner will run directly off generator or shore power and when either of those are on my converter will charge the batteries.
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Old 06-04-2018, 10:15 AM   #11
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Other than the A/C part, your plan is generally "typical." I'd suggest some more research - especially on batteries and which are better for RV type use.

I'm like you and just can't stand to hear a generator running (yes, even a "quiet" one). So, I don't own one. I do live in an "electric coach" (meaning, everything in it requires electricity - residential refrigerator, induction cooktop, microwave/convection oven, etc.) that is VERY rarely connected to shore power. That illustrates the power of that bright orange ball that is often in the sky during the daylight hours.

Some reading of recent A/C threads here will shed a lot of light on what it takes to run A/C from battery. Not to start that topic rolling again, it can be done but is not necessarily cheap/simple/etc.

You might look into the soft start add-on devices for A/C units to help with the startup power requirement.

I've seen some inverter-generators that have a wireless remote control/start thingamabob. Can't recall what brand it was.
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Old 06-05-2018, 12:45 AM   #12
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Motorsnorkel.com makes propane conversions for most generators. A 2000 watt predator from Harbor Freight is cheap and small. They have a conversion for that.
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Old 06-10-2018, 10:48 AM   #13
Skoolie
 
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The reason for my plans is that I'm looking to do this on the cheap, without using propane. I don't like the idea of propane, because my last experience with propane showed me two things: 1) you can't always get it when you need it, 2) it STINKS!. Plus, then I'd have to plumb everything in for gas... and now we're into more time and more money... I'd rather keep it simple.

Ideally I would have an electrical system that can run off of batteries, and a generator, and shore power, and solar power. It would start out running on only a generator or shore power, as I imagine it would be fairly easy to wire up a bunch of outlets, even if on multiple circuits (though that probably wouldn't be necessary given that I hope never to have to run more than 15 amps through my entire electrical system at a time), and then have the electrical system fed by what would effectively amount to the male end of an extension cord. Plug that into the generator or shore power, and boom... electricity. (Heck, if I wanted to, I could always just use extension cords in this phase!)

The next phase would be to add an on-board battery bank, and I'm thinking I will start a new thread about how to add a house battery charger that works off of the bus alternator while still leaving the alternator enough power to charge the engine batteries. (I just read an article about an isolator that can be switched back and forth to allow the alternator to charge either the engine batteries or the house batteries, but not both at the same time. Using such a device would require frequent switching, as far as I can imagine, because the engine batteries would be drawn down from running the engine even if no other chassis electrical devices were being operated concurrently.)

After everything were set up so that the electrical system could be run from either generator, shore power, or batteries (through an inverter), then, if I had the money, desire, and time, I could add solar panels to the roof and wire them into the electrical system. I have no desire to do all of this at once... nor do I have the money and time to do it all at once.

I don't want to run a 12 Volt DC main system, because I intend to run things such as a microwave, stove / hot plate, and water heater off of electricity. I imagine that all of those devices require 120 Volts. Furthermore, larger devices that can run off of 12 Volts but usually require 120 Volts (such as refrigerators) are significantly more expensive in their 12 Volt capable form compared to the form that only runs off of 120 Volts. So, I doubt I'd save any money going that route.

Why the preference for a 1,000 Watt generator? A few reasons:
1) Cheaper.
2) Lighter weight. (Both my back and my wife's back are in questionable condition, and given that we're only in our 30s and we hope not to be reliant upon strong pain medications by the time we're 50, if we can reduce the amount of weight we're slinging around on a regular basis, that'd seem wise.)
3) Quieter. (I have researched these, and it seems that although there are larger generators that are nearly as quiet, at the top of the list of "quietest generators", you still find 1,000 Watt models.)
4) Less fuel-thirsty. (With the oil companies deciding that a few billion dollars a year just isn't enough profit and therefore they have to squeeze the "little guys" for three bucks a gallon again, a fuel-sipping unit is preferable over a fuel-guzzling unit! Not to mention, I could install a smaller auxiliary tank and it'd last just as long.)
5) The less "creature comforts" we have aboard the bus, the more likely we are to enjoy the great outdoors. In my previous stint full-timing in a Class C with all the comforts of home, there were many days when we could have been outside but instead sat inside wasting time on our electronic devices.
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Old 06-13-2018, 05:55 PM   #14
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Have you thot about a PTO operated generator? Fire trucks have them too.
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Old 06-13-2018, 10:47 PM   #15
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Originally Posted by Dirtdoctor View Post
Have you thot about a PTO operated generator? Fire trucks have them too.
I'm thinking the bus engine is going to be louder than a good inverter generator, and long idling is bad for diesels.
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Old 06-14-2018, 12:34 AM   #16
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Yes and no, utilizing the proper size of generator you could charge your appropriately sized battery bank. Diesels run for hours and hours powering generators, setting the pto- is done with gears, setting a 10-15kw generator to run at 1250 engine rpm (depending on engine size etc). Charging the battery bank while driving or during off times. It is done regularly. It would depend on several factors - battery storage and properly specifiying wattage and amperage for your needs. I use two 3000 pound batteries to power two houses and run 10 freezers off of solar panels. So sizing a small food truck is really doable. Especially with the new technology in batteries. I went old school but many lithium ion battery set ups are being developed. Plus with 325wayt panels on the huge roof area on food trucks /buses makes for a good combination.
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