Inverter/charger/switch question

[Newbob]

As mentioned briefly here - there are web sites that help with battery calculations but do not forget that most batteries have a recommended percent of usage or "draw-down" so you don't damage the batteries while discharging. Follow the manuf recommendations - they are pretty low percentage-wise so you will need much more capacity than you might think - although it sounds like some guys here, in actual experience - are getting away with much less battery.

[solodon]

bevans6.........slipstick.......How many people didn't know what you meant?   

[Oonrahnjay]

bevans6.........slipstick.......How many people didn't know what you meant?    

      Come on, Don.  Since most of the people here have dirt that's a lot younger than they are, the only ones who don't know what a slipstick is are the ones who only counted with pebbles in the dirt outside their cave.

[daddyoften]

So back to the inverter question.... 
I have been doing some reading and learning and it looks like the higher the voltage the lower the amperage and thus lower the heat and up the efficiency.  Now some of this info came from a solar-cell board and they are living off of these battery/inverters and are looking for the max.  So my question is since my bus is already a 12v system and I have nothing already for 24v would it be worth the effort to redesign things to accommodate a 24v house battery bank for inverter purposes?  My alternator and starter are 12v and all my lighting will be 12v so that introduces quite a bit of work to go from 12v to 24v back to 12v    I can't see that would be worth the trouble to save a few dollars on buying a 24v inverter versus a 12v one and then spending more money on converters.  Now I would also, in theory, gain more usable Ah's and have less stress on the batteries.  My goal isn't to live off the grid, my goal is to be able to run essentials while the occasional boon docking where I can't use my generator and maybe run 120v items while driving and short boon docking.  BTW, I have my eye on a slightly used 8kw Kobota diesel so this might just all be a moot point anyways but I'm trying to learn as much as I can ahead of time. 

My current idea for this bus will be 6 6v golf cart batteries, each at 230Ah, a 3-4kw ish Magnum Invertor/charger/switch, and the 8kw Kobota genset.  Maybe about 200w-300w worth of solar panels as well, haven't decided if they are worth it or not. 

I have another question about the battery bank as well.  I will just be using one 8d for the engine starting and maybe the coach lighting outside, like the headlights and such.  I plan on using the golf cart batteries for all of the rest of 12v needs including the inverter.  How is the best way to charge the golf bat's from the 200+amp alternator while driving and keep them separate from my starting 8d?  And should I have a way to charge/maintain the 8d while parked?  And lastly is there a good way to "jump" the 8d in the rare event it died and I need to start from the golf bat's?

Thank you all for the information.
Eric.

[Geom]

Eric,

I wrestled with the 12 vs 24 volt dilemma when we were buying our inverter as well. There are a lot of advantages to a 24v system --less heat, smaller wires, higher amperage capability. But with that comes the pain of the issues you mentioned --system is already 12v, alternator for 12v charging, having to have a fairly complicated battery layout to keep the 12 and 24 systems separate. While it is most certainly doable, I found that just sticking with 12v was the path of least resistance, and I attempted to minimize most of the 12v negatives by keeping the inverter as close to the battery bank as possible (much cheaper cable costs that way too ).

The inverter we decided on was the Victron Multiplus 3000va 50a. I've been fairly happy with it and I like a lot of its features like power-assist boost, the ability to be stacked with additional units for higher capacities, and all of the monitoring capability it has. It's price is inline with a lot of the other pure sine-wave inverters out there. And on that subject, if you don't know what a pure-sine-wave inverter is, do a google search and there will be a lot of useful info to read through; but short story, you want one
At least if you want to run traditional house appliances like a microwave.

Even if you have a huge generator, you'll still want something between it and the house AC systems. It allows you to buffer the load on the generator a bit and gives you future options for controlling shore power vs gen vs house batts. The inverter is not just for inverting a battery load, but for managing the whole system.

As far as batteries themselves, we have three different battery systems and we keep them discretely separate most of the time. We have the coach batteries for starting the bus and a few of the 12v coach systems, we have a house battery bank for inverter capacity and some 12v loads in the house, and a single car battery to start the generator.
My inverter manages charging the house batteries and it is quite adept at that.
I have a plugin type heavy-duty charger to maintain the coach batteries. I think you'll definitely want to keep a good (managed) trickle charge on those to keep them healthy.
For the gen battery, I have a switch that allows me to charge it with a timer from the coach charger. It only gets occasional use and I just put a top-off charge to it every few weeks or so.

As far as charging on the road, I installed a relay, with a switch inside the coach, that allows me to pair the 12v house and coach batteries to one another. By default the alternator (it's a generator actually but for ease of term reference ) is plugged directly only to the coach batts. The relay switch allows me to charge both going down the road. I would not recommend this as the only way to charge the house batts as they prefer a more "controlled" and "intelligent" charge, but it suffices for the relatively small amount of time we're running the air (or heat) while en route and still have good usable AC without draining the house batts.
Once we're at the new site, the inverter resumes its previous duty to manage them.

We have enough capacity to run the AC for about one hour on batteries and we have about an 800AH system. Keep in mind that with lead-acid you have both a maximum discharge amount and discharge rate to watch. The max you should discharge a lead-acid, regularly, is about 50% of capacity. So an 800ah system is in actuality 400ah usable.
The rate of discharge is also quite important and it's a function of the battery's ability to deliver the required power over a specified time. While you can discharge an 800ah system in 20 minutes, doing so will damage the batteries over time vs discharging it over several hours.

Hope that helps and sorry for the loooong post

Good luck!
George

[daddyoften]

Thank you George,
Why do you have a separate battery for your gen-set?  Why not just tie into your coach battery?  And do you have a way to jump the coach in the rare event they go dead?  Yes I plan on getting a pure sine wave inverter as I will be running a house fridge, a/c, and tv's, some of which if not all will be native 12v already and I'm looking at getting 3 of those radio/dvd head units for rv's to run in each room.  Plus the laptop's and printer.     Now I know most of these won't be necessarily running all at once on the inverter but I don't want to have to worry about plugging in something and frying it cause I don't have a good inverter.  I will have to look into the Victron.  The Magnum I'm looking at has some great things included with it, it has a built in charger for the batteries and a switch plus the power sharing as well.  The remote console looks handy too.  I think the Magnum had like a 100 amp charger as well, something very high and somthing like a 50 amp switch.  Your 800Ah system, how many batteries and what kind is that?

Thank you,
Eric.

[Geom]

Keeping a separate batt for the generator is an insurance policy in essence. If I run down my coach batteries, then I can at least start the generator and use it to recharge the coach batteries for another shot at starting the engine. It's the way the PO had it configured and I definitely like having it. Keeping them seperate keeps whatever caused the coach batteries to drain from taking the gen batt with it.

I'm glad you asked about jumping the coach batteries if they're dead
I actually do. I have another relay hooked up to a momentary contact switch (inside the coach) that allows me to temporarily pair the house batteries to the coach (different than the previously mentioned linkage). Doing so allows me to in essence use the house batteries to assist the coach batteries in starting the coach. Now this is not something I would do often, since deep-discharge batts are not ideal for starting, but they would suffice in the rare emergency situation. It's all about having options on the road , and when it's your home and shop and transport mode the more options the better

The magnum is a good unit as well and I looked into it too. Its power-assist functionality seemed less functional than on the victron and it doesn't have the ability to be paired like the victron can (although I'm sure there's a way to run a pair in some special parallel config).
The victron has a 200 amp charger that will actually overload the pedestal if you're not careful and it does a great job managing the varied requirements of deep cycle house batts.
The victron also has a 50amp (AC) switch. Make sure you get the 50mp model though. The 3000va unit is sold as a 50a and as a 25a.
The one downside is it only has one 50amp leg. If you're not aware, 50 amp from the pedestal is 2 x 50 amp lines and right now my line2 is just capped off and not used. Someday I might hook up a bay plug to it or something, but 50amps total has been more than adequate for our needs (2 air units, fridge, water heater, small oven, and a bunch of computer bits). Not all running at the same time of course, but time managed appropriately to not exceed about 40 amps at any one time.

On that subject, I'd also strongly suggest you get a "surge" protector; more appropriately called a line-condition tester. You never know what kind of power you'll get from an rv park and I've seen some crazy stuff that our unit has protected us from. We have a progressive industries inline 50amp protector and it's worth its weight in gold. There are also plug-in pedestal type protectors, but those seemed to have a big "steal-me" sign attached to them, lol. 

Our setup is 8 6v golfcart batteries at 200ah per, for a total of 800ah @12V. It's a whole bunch of big batteries stacked one next to the other. On our bus the PO placed the batteries in an area at the front of the bus ahead of the front bay. Really nice setup. Not sure if that's the way the 4107 was configured originally, but all of our batteries are at the front of the bus, as is the inverter.

I plan on replacing the lead-acid with lithium as soon as I find that bottomless bag full of cash that I've been looking for, lol. Seriously though the price of lithium is coming down so much that it's almost a direct competitor with lead acid and certainly AGM (if buying new); and it's a much better battery technology that is longer lasting, lighter, less maintenance intensive and is able to deliver 80% of its capacity without skipping a beat.

Baby steps though, but it's on "the list".

[Oonrahnjay]

Keeping a separate batt for the generator is an insurance policy in essence. If I run down my coach batteries, then I can at least start the generator and use it to recharge the coach batteries for another shot at starting the engine. ... I definitely like having it. Keeping them separate keeps whatever caused the coach batteries to drain from taking the gen batt with it. 

       Yep, me too, for the same reasons.

     

[eagle19952]

some worth while reading here:

http://www.busconversions.com/bbs/index.php?topic=24105.0

Specially here when you get to this part:

"If I were doing Odyssey over again, one of the very few things I would change would be to eliminate the chassis/start batteries altogether and go with a single bank, just as Bob suggests, with the proviso that the generator has its own separate start battery.  The generator, of course, can charge the main bank via a charger once it's started".

[daddyoften]

What compartment are you referring to?  The spare tire compartment? or the one right behind the drivers seat where the HVAC use to be?  I also have a 4107 and would love to see how you did your compartments.  Sounds like a very similar setup as I'm looking at doing.  I don't think I'm going to carry a spare tire.  The PO who started the conversion raised the floor inside along with the roof line but didn't try to utilize the space under the raised floor area up front.  It's just framed in with 1" steel tubing with plywood screwed down right now so it's very easy to redesign right now.  I'm thinking maybe fresh water tanks but that's just an idea.  I still don't have the bus with me yet, I plan on picking it up in a few weeks  

[Geom]

some worth while reading here:

http://www.busconversions.com/bbs/index.php?topic=24105.0

Specially here when you get to this part:

"If I were doing Odyssey over again, one of the very few things I would change would be to eliminate the chassis/start batteries altogether and go with a single bank, just as Bob suggests, with the proviso that the generator has its own separate start battery.  The generator, of course, can charge the main bank via a charger once it's started".

For my vote I like having the discrete systems in the "just in case" category. We've drained our house batteries on several occasions, when we've lost pedestal power and started inverting; without knowing it. In that scenario, I still like the option of being able to start the bus, independent of that event; or if the scenario in reverse having a reserve amount of CCA for starting, fed in from the house batts.

In addition to that, I intend on someday replacing the house batteries with a completely different technology (lith) and I definitely don't want to use those as starting batteries.

Using your house batteries as start batteries also necessitates having a whole bunch of batteries to buffer that high of a load demand. A starter can easily draw 400+ amps at cranking, if I understand it correctly.

While combo batteries are in theory capable of both duties, starting and deep-discharging require two completely different physical demands of the battery. A starting battery is great for high quick bursts of a whole bunch of power for very short periods, deep-discharge being the exact opposite. And each having completely different physical traits of the lead-plate layout.

Not to step on any toes, but I would most certainly not combine the two functions.
My 2 cents worth anyway.

[daddyoften]

I agree,
I understand and like the idea of a separate battery for the gen-set though, I will think about that one.  As far as combining the chassis and house together that might work for some but I have a very wonderful wife and 6 kids that are going with me, but with that said they don't understand all of this and I may not always be there, I might work else where from time to time, and I need this to be um.... wonderful wife and kids proof!    I'm going to stick with at least a single 8d for the chassis and a bank of 6v's for the house with an emergency start solenoid to start from the house if need be.

[daveola]

Yes I plan on getting a pure sine wave inverter as I will be running a house fridge, a/c, and tv's, some of which if not all will be native 12v already

I'm in agreement with robertglines1.  You are on a budget, most everything you want to run is either 12V (and doesn't need an inverter) or is too big of a load for the battery bank you are describing (and hence needs to run off the genset).

So why do you need a large battery bank or inverters that will cost $1000s?

I suppose an inverter could be useful if you want to run A/C while driving (if the bus A/C doesn't work anymore) and want to power it off the alternator (which is 12V).  In that case, get an inverter just for the A/C units, and then you probably don't need a battery bank that big, just enough to act as a sort of "ballast" for the energy going from alternator -> inverter -> A/C.

Furthermore, you don't even plan on boondocking regularly.  So why not just run the generator when you are parked to power A/C or the microwave or when you need to recharge 12V, and otherwise live off 12V or shore power as planned?

[Geom]

What compartment are you referring to?  The spare tire compartment? or the one right behind the drivers seat where the HVAC use to be?  I also have a 4107 and would love to see how you did your compartments.  Sounds like a very similar setup as I'm looking at doing.  I don't think I'm going to carry a spare tire.  The PO who started the conversion raised the floor inside along with the roof line but didn't try to utilize the space under the raised floor area up front.  It's just framed in with 1" steel tubing with plywood screwed down right now so it's very easy to redesign right now.  I'm thinking maybe fresh water tanks but that's just an idea.  I still don't have the bus with me yet, I plan on picking it up in a few weeks  

On our 4107 it's laid out as follows:

Driver side:
Behind the driver's seat is the gas tank and it runs the full width of the bus. I'm fairly certain it came from the factory that way.

Behind it is our Onan 7.5 KW diesel genset.
It consumes a good sizable chunk of space and is abutting the front bay.

Passenger side:

The area where the main wet/dry air tank is, immediately under it are the starting batteries.

In between the space for the genset and the air tank area is an empty space that is directly beneath the steps inside the coach. It's big enough for 8 220ah golf cart batteries. There is an access panel door from inside the front bay to get to them, or you can crawl under the air tank from the side. Getting inside that space is a bit tricky and not something I wish to do regularly (for battery maintenance for example). So I have also installed an automatic battery watering system that is a life saver. Taking the PITA chore of watering the batteries to a simple 2 minute process of squeezing a pump from a distilled water bottle a few times (Another item worth its weight in gold)

The inverter is inside the front bay towards the outside, passenger side.
There is a distribution panel under and slightly behind the air tank and it makes getting 12v into and out of that area very easy, clean, and logical and I highly recommend a similar setup.
There is a short, 300amp fused, cable run to the distribution panel from the inverter.

The PO actually lowered our floor (4" I believe) and it made a HUGE difference in the amount of headroom inside the bus (roof stayed the same) and a grown-man can stand in the middle of the bus without bumping into the ceiling or AC (air) vent.  

This is the way our Bus came, so I'm not sure what was originally in these spots, but we do not have functional bus AC (nor want it) and we still have our spare tire (which I DO want, even with a coachnet membership ).

Our water is as follows:

Fresh is 3 30 gallon tanks under the bed. I have mixed feelings about that, but it definitely has advantages. Less bay space used, less likely of a freeze in cold weather, easier accessibility for work on the water system. Its disadvantage is the large potential for a water leak (which has already happened to us and ruined the carpet In there). Granted, that was caused by my dumb-assery, but dumb-assery happens, lol! I intend on pulling those tanks and replacing them with a single 100 gallon, thick walled single-rolled-piece tank and redo some of the plumbing runs (also on "the list", lol) but it's functional as is for now.

Waste water is in bay 2 with separate gray and black tanks stacked on one another. They consume about 2/3 of that bay, leaving a still usable 1/3 for additional storage.

I had a friend build me a sliding tray in both bays to make getting to either storage space easier. One "drawer" is the full width of the bay1 and is just slightly less than the full length (with room for the inverter). The one in bay2 is fitted to the entire available space.

If you'd like I can snap a few pics to clarify if needed.

[Geom]

I'm in agreement with robertglines1.  You are on a budget, most everything you want to run is either 12V (and doesn't need an inverter) or is too big of a load for the battery bank you are describing (and hence needs to run off the genset).

So why do you need a large battery bank or inverters that will cost $1000s?

I suppose an inverter could be useful if you want to run A/C while driving (if the bus A/C doesn't work anymore) and want to power it off the alternator (which is 12V).  In that case, get an inverter just for the A/C units, and then you probably don't need a battery bank that big, just enough to act as a sort of "ballast" for the energy going from alternator -> inverter -> A/C.

Furthermore, you don't even plan on boondocking regularly.  So why not just run the generator when you are parked to power A/C or the microwave or when you need to recharge 12V, and otherwise live off 12V or shore power as planned?

Daveola brings up an excellent point. If you don't intend to boondock or intend on running a heavy AC (power) load while en route, then you can probably forgo the inverter and batts, for now. If you'll mostly be pedestal hopping, then just get a good line-protector and run that to a transfer switch with your genset on the other side as an input and your breaker box as the output.

When using the genset, make sure to allow sufficient time (upwards of a couple of minutes) for the generator ramp up to load. Don't apply a heavy load immediately after starting it. Most generators have controllers that do this automatically but a little extra insurance doesn't hurt.

We no longer have bus AC and do intend to boondock eventually, so large battery capacity and a solid inverter was a necessity for us.