Need help with electrical design

[Gordie Allen]

Hey all you experts,
I've gutted my bus (4104) and installed all new structural floor.  I'm getting ready to start the wiring, and I've read all the back issues on a "Balanced System", plus most of the posts in  the Archives.  Unfortunately, I'm no closer to making decisions on my system due to information overload and new technology.  I know there is no one answer here, but I need help on choosing components.  This was a previous conversion and it came with a 6000w Onan gas powered gen set which runs great and I'm keeping. The starting batteries are in good condition.  The 30' shore line is in good shape, I installed a new plug (50 amp).  I haven't pulled the alternator yet – the DIY bracket is not aligned correctly  and has to be re-fabricated.  I don't know the alternator's output until I pull it.
1. What is ideal alternator output?
2. I'm installing an Electric Fan Engineering 9,000 cfm fan which draws 70 amps.  This engine has blown two crank driven fans, so I'm buying a new viscous damper, but I've decided to go with electric to eliminate any inherent fan imbalance and increase cfm over crank driven fans.
3. My AC demands are 1500w microwave, washer/dryer, refrigerator (propane for on the road), air conditioning (est. 25 amp draw for two mini splits), and TV.  I plan on DC only lighting.  No 220v stuff.
4. I don't want to use the generator any more than I have to.  Can I power two 12 amp air conditioners with battery bank and alternators on the road, or will I have to run the generator?
5. What is the best choice for inverter/converter that has 3 or 4 stage charging and AC source management ( shoreline vs.  inverter, vs generator)?
6. Proper battery management is top priority.
7. I want full sine wave AC
8. Are there inverter/charger units that include remote control/monitoring panels?
9. I'm planning on sealed gel deep cycles for my house batteries, a separate start battery for the gen set.  If I can power A/C through the inverter how do I calculate size of house bank, or is this even possible?
10. I'm willing to spend to get the best system.
11. All my wiring will be in an accessible raceway inside the living quarters for easy trouble shooting and add-ons.
If this were your project how would you put all the pieces together?  Any advice would be greatly  appreciated.

Gordie

[Mex-Busnut]

Sounds like a great plan. How about some pictures to help us get an idea what you are doing?

[Lee Bradley]

What is the engine driven alternator output?  Most of your questions are based on that.

[Cary and Don]

Some general information on things you will want,  if not now then later.  You will want more than one way to charge batteries,  bus to charge house,  inverter to charge gen set battery,  aux start to jump bus batteries.  Run lots of extra wires.  If you are going to run one,  run four.  Extra runs from front to back,  front to panel area,  back to panel area, etc.  If you think you might want something in the future,  fancy monitor panel for you inverter,  run the wire now.  Label everything with tags and draw diagrams of what you did.  You will not remember what you did next year.  Have fun with your project.

Don and Cary
1973 05 Eagle
GM 4107
Neoplan AN340

[Gordie Allen]

Lee,
Alternator - 110 amps
Delco

[Gordie Allen]

Don,
I plan to run a raceway down both sides from back to front.  Hinging the top along the way, so I can troubleshoot, add on, etc.  All wiring will be in a raceway and branch off as needed.   Extra wires is good idea, Thanks!
Gordie

[Len Silva]

With only a 110 amp alternator, there is no way you are going to be able to run that 70 amp fan and another 250 amps or so for the air conditioners.

The next consideration is that with the limited horsepower of that little 6-71, you may have to turn off the air conditioners when you need the power for hill climbing.

Personally, for the money you are going to spend for a large alternator, battery bank and inverter, I think you would be much better off with a good generator.

You also need to be careful about how much you spend to convert a 4104.  As much as I love that bus, it will never be worth more than $20K or so, no matter how much you put into it.

[Gordie Allen]

Mex Busnut,
Here are some shots of floor in progress.









Floor is 13 ply Russian birch with both sides finished with heat pressed plastic.  Very smooth and durable.  No wood grain texture to surface.
Gordie

[Geoff]

If you are going to run one alternator (12v) I would recommend at least a 200 amp truck alternator, and a Trace SW2512MC inverter (pure sine wave).  And if your system gets overloaded there is no way you are going to get around running your 120v generator-- for one or especially two air conditioners.  If anyone tries to convince you you should go 24v I suggest doing the math.

--Geoff

[gus]

Just use your genset for the ACs, 6KW is plenty for two ACs plus the frig, I did it all the time with my 4104 and 6KW genset.

When I used the MW I turned off one of the ACs or frig if I had all three going, but I almost never used two ACs at the same time.

My battery bank was two Gp 31s. I really see no need for a huge, heavy battery bank unless you do a lot of dry camping and even then the genset is better.

[belfert]

I have 600 lbs of AGM batteries.  I got them cheap.  I figure it costs at least $2 an hour to run the generator.  If I save 350 hours of generator operation I've paid for the batteries.  My generator is reasonably quiet, but I still prefer not to listen it to it 24x7 especially just to keep the fridge and few other things going.

[Gordie Allen]

Len,
Thanks for the feedback.  I know I'll never get a return on my investment, but I'm building this for my wife and me.  I plan on owning it until I die or can't drive anymore.  I'm 65, so it only has to last 20 years or so.  We plan on putting $30,000 to $40,000 into it.  We have kids and grandkids in San Francisco and New York.  We live in Michigan, have a great house on 13 acres of woods that's paid for.  We just retired.  I'm a physical therapist and my wife is an occupational therapist.  We owned our own clinic up until two years ago.  We sold it to a rehab hospital so I think we have sufficient income to last us the rest of our lives barring any unforeseen catastrophe.  I caught the bug looking for a decent motor home.  The more I looked the more I learned about the difference in construction and longevity.  That's when I decided on the bus.  We built our own 3500 sq ft home from scratch - way back in '77 - when I was young.  I did all the carpentry, wiring, plumbing, custom cabinets, etc. myself.  I've also played with cars my whole life - built a '39 street rod with my oldest kid when he was in jr. high.  Built lots of dune buggies too.  I've got a 2000 Corvette that I customized and had a former patient do the final finish and paint.  He's a master body man and painter.  He painted planes for 8 years at Duncan Aviation.  They refurbish and customize business and private jets.  He's doing the exterior of the bus, and with his painting skills and work with airframes, the bus should be sweeeet.  I also have a good friend (my age) who was an electrician in the Navy.  He rewired a submarine!  So, he is capable as long as we know what we need to put together.  My number one priority is quality and reliability.  Since I'm not going to be in any big hurry, I think the 671 will be OK.

[Gordie Allen]

Thanks everyone,
So this is what I'm thinking so far. 
1. Get a 300 amp alternator. 
2. Plan on shore line 90% of the time for AC's when parked.
3. Install two 10,000 BTU (ea.), single zone, 110v heat pump AC's.  One on each leg of AC panel.  Advertised 950W ea. at 110v = 8.6 amps AC.  About 90 amps DC each
4. Two AC's (180 amps DC) plus radiator cooling fan (70 amps) = 250 amps
5. 50 amp reserve for lights and charging.
6. 6000w generator backup (has it's own starting battery)
7. All interior lighting DC
8. What size house battery bank?
9. Is 20,000 btu enough heating (I don't think it is) I have restored on the road heat.
10. It appears that heat pumps are more efficient than conventional AC, but air to air heat pumps are less efficient as ambient air temp rises.  Any opinions?
Gordie

[pvcces]

Hi, Gordie.

I don't know what kind of ACs you are looking at, but the modern mini-splits are real easy on power and you can get some that will work as heaters right down to zero and all the way up to 125 degrees as ACs. This would be high SEER models. 13 SEER models will work down into the teens.

Two one ton units would provide up to 24,000 BTU heating or cooling and you wouldn't need much for back up heating. They are very quiet. Larger units are quite a bit noisier, about 3 db.

I did see a report that some units lost their circuit boards running them on inverter, so it would be good to plan to figure out that side of it.

Your electronics are going to have problems with different battery chemistry. The problem is that you will likely recharge for a single battery profile and you will be tempted to use two different ones.

As a practical matter, with the right choices, you can get away with different batteries as long as you choose for compatibility. Some combinations will not work at all well together. If your interconnect can be set up right, it should work OK. We're using a Pathmaker and a substitute relay, which works most of the time.

We use liquid lead acid house batteries and we have some old gel cell start batteries. The system always wants to charge the house batteries.

Good luck on your venture!

[Uglydog56]

Something I got from another site about alternator sizing:  A standard brush-type alternator doesn't put out power the same as a permanent magnet alternator, and you should divide the output by 3 when sizing a brush-type alternator.  A 70 amp PMA charges about the same as a 220 amp brush type.  I am also looking to run my mini-splits off the alternator when I eventually finish the install, and I still don't have the definitive answer here.