12v vs. 24v or both?

[daddyoften]

So I've been thinking.... ok, trouble I know 
I'm going to completely rewire our bus for the build, and I have some problems with the current generator on the engine.  I need to determine if it's 12v or 24v because it was doing fine on it's voyage home until I turned on the head lights and then it started frying batteries.  It's been sitting ever since and I haven't had a chance to look at it any further. 

Ok, so here is my thoughts. 
I want to run a large inverter, say like 4000w ish, and I'm probably going to run around 6-8 6v batteries to power that.  I know 24v inverter's of that size are much easier to come by and they require a lot less draw due to the higher voltage.  I'm pretty sure my starter is 12v on the engine.  If indeed my generator is a 12v with a problem that is fixable is it just as simple as changing the voltage regulator over to get it to run 24v? If so what about using it at 24v for the house batteries and then running a smaller and newer alternator off of the empty pulley on the front of the engine to charge and run the start batteries along with all of the bus exterior lights and dash lights?  I was orginally just going to run everything at 12v from the large generator that's in there now if It's fixable and just not have as much of an inverter setup.  But I like the idea of a 24v inverter but that causes a few minor problems with the 12v electronic devises I want to run in the house but I think either a converter or equalizer would work to solve that problem.  Your thoughts........

Eric

[TomC]

About the only reason buses have 24v is for the twin A/C blower motors. Virtually all over the road trucks are straight 12v. My transit bus is straight 12v-which is so much simpler.
I would suggest you switch to all 12vdc and make your life that much easier. The starters now are high torque gear reduction type. Magnum makes a 3,000watt hybrid TSW inverter. If you want more, buy two and stack them (they have to be designed for that).
I like having only 12vdc, I think you will too. Good Luck, TomC

[Iceni John]

A 4,000 watt inverter is BIG, really big!   Do you really need all that AC power?   It would need an equivalently large battery bank to power it  -  six to eight GC2s won't last long for sustained heavy loads before they're down to 50% SOC.   Even a 2,000W inverter draws about 260-odd amps from 12V batteries at full rated output, and that requires heavy 4/0 cable ($6 or more per foot).

You should calculate your foreseeable AC loads, but plan on not necessarily running them all at one time!   You should then be able to use a smaller inverter, in which case (as Tom explains) you can keep everything 12V to make it simple.   Simple is good, especially with electrics!

John

[daddyoften]

I've read that batteries are much healthier when run in series as much as possible, also the higher the voltage the lower the amps, thus smaller required wire and heat. I don't have any 24v items as of yet but was leaning towards the 24v inverter because of the above reasons. I agree that all 12v is simpler and I may very well just go with that but was just trying to not have to run such large wire and dual 12v inverters.
I'm planning on having around a 8k diesel gen, 3k-4k inverter, dual roof a/c, house style large fridge, along with the norm of led lights and radios. I don't want to rely on lp for much and wasn't the option of boondocking for a little while.
Eric

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[TomC]

When I bought my inverter (Trace 2500 watt MSW) 21 years ago, I asked the gal about stacking (using two synchronized) for 5,000 watts. She asked if I had a Diesel Generator. I said I had a 10kw. She said to just use the generator when you want heavy loads like A/C.
My inverter loads are all plugs, which include my toaster oven and microwave, the primary water heater (I have 2-10gal elec water heaters-one feeding into the next with the final one powered through the inverter for hot water going down the road), and the bathroom heater.
Items that are wired direct to either generator or land line are the three A/C's, refer, freezer (both 12vdc/120vac), washer/dryer, secondary water heater. It's such a good, reliable system, I'm repeating it in my truck conversion. I also only use one leg of the 50amp for straight 120vac only. Good Luck, TomC

[zimmysurprise]

Eric- I had the same question when I got my 4108. It was all 24v and I looked into changing it over to make things easier, just as Tom explained. There are some things like the refrigerator, water pump, sound system and GPS that are much easier to find in 12v. The argument to convert it was strong. However, I decided to keep it all 24v for several reasons. First, my existing wiring was designed for 24v with less amps. Running 12v doubles the amps and can lead to a catastrophic failure (fire). I was also surprised to find that buying 24v accessories is very easy on the internet because the military and much of the rest of the world use 24v. Gauges, linear actuators and even LEDs are inexpensive and easy to obtain. Finally, I plan on putting in solar panels, and they are far more efficient as 24v.

For the 12v, I purchased (3) 480w 12v knockdowns. Two are in the front of the bus for my radio, GPS, wipers, cell phone chargers and the fridge. One is in the rear for the water pump and 12v igniter on the hot water tank. In short- I vote both.

Don

[Gordie Allen]

Are you talking about having your start batteries (starter, lights, dash,etc.) running on 12 v and the house bank/inverter running at 24v? If that's your setup I don't see any issues with having both. Yes, 24v  allows smaller wiring, but the cost of 12 gauge for all low amp operations is, IMO, negligible in the overall cost of the project. And 2/0 is more than enough for distribution to fore and aft dc panels. I have my four 12v AGMs linked to a common heavy duty DIY buss made of 1/4" copper flat stock drilled and tapped with six 5/16 posts with equal length 4/0 connecting them to the inverter in parallel. If you want maximum battery life, keep battery cables equal length. I have 2-D8 wet batteries for vehicle needs (starter, lights, heater fan, and four 12" radiator fans) using a 160A alternator. With everything running, I'm at about 50% of the alternator rating. That's about where you want to be. We have a second 300 amp AC Delco alternator charging the house batteries on the road. I can turn this on or off via a 300 amp continuous rated solenoid to avoid over charging the AGMs. It's only charging when both air conditioners are running going down the road. As I said, I have four D8 AGM's with a total of 1000 Ahr. I have a 3000w - 120v Victron Multiplus inverter/charger (true sine wave, automatic switching, synchronized 60Hz boosting of shore power if needed). Since we wanted the bus to look original from the outside we have nothing on the roof. We have two 120v mini-split heat pumps which handle both heating and cooling. They draw a max. of 9amps AC each. Each is rated to cool 500 sq. ft. (the bus is 250 sq. ft.). They have kept us warm with ambient temps as low as 10*F. We normally run only one unless we're sitting with ambient temps above 85*F or below 15*F. We have an apartment size frig (9 cu ft). That's the max. AC components we run down the road or without shore power. Our shore line power is 50 amps with one side running through the inverter and the other bypassing it. On the bypass line we have the water heater, washer/dryer, dish washer, microwave and mini oven. If I want one of these when not on shore power, I can move the breaker over to the inverter side of the AC panel and ration the power (we have never had a need to do that). The only real boondocking we do is an occasional overnight at a truck stop. Hope this doesn't just add to the confusion, but there might be a nugget here or there you can use.

[belfert]

If you have no plans to run air conditioners off battery I wouldn't buy a 4,000 watt inverter.  Some will run air conditioners off the bus alternator if you have a big one like a 50DN.  I matched the primary voltage of my house system to the alternator in my bus which is 24 volt.  I also kept the original overhead lighting in my bus which is 24 volt.  24 volt requires cables half the size of 12 volt.  If you aren't going to use a big inverter and won't be powering the system from a 24 volt alternator then I would just go 12 volt.

There are some who don't ever hook to shore power who decide to just run their generator 24x7 instead of using batteries and inverter.  One bus owner decided the $3000 plus for inverter and batteries could buy a lot of generator fuel.  They did start looking at batteries and inverter after a few years of diesel being mostly above $4 a gallon.

[Iceni John]

We have two 120v mini-split heat pumps which handle both heating and cooling. They draw a max. of 9amps AC each. Each is rated to cool 500 sq. ft. (the bus is 250 sq. ft.). They have kept us warm with ambient temps as low as 10*F. We normally run only one unless we're sitting with ambient temps above 85*F or below 15*F.

What make/model are they?   Do you know what their starting current surge and Power Factor are?   (If running off solar, every watt and amp counts!)

Thanks, John