What voltage?

[Jim Blackwood]

Kind of a strange question because my bus is pretty flexible in terms of power. I has a Vanner on the batteries, there is wiring in place for both 12v and 24v DC and some wiring for 110v AC, I have 2 24v battery chargers and a bunch of smaller (900w) 24v inverters. I guess what the question really goes to, is what makes the most sense to use when adding devices, such as the water pump.

Now those come in 12v, 24v, and 110. I'd say the 110 is out because it would require an inverter to be powered up all the time or else switched on by the pump's pressure switch, meaning it would be run on DC anyway. Leaving the choice of 12v or 24v. (some things will pretty well have to be run on 110 but those are special cases)

Why should I pick one over the other? So far:

-24v wiring doesn't have to be as heavy, but under 10A does that really matter?
-24v devices tend to cost more. The water pump is about $20 higher in 24v.
-I'm not going to consider changing the whole bus over to 12v, so the 24v stays.

Is there a reason why I shouldn't just go ahead and run everything I add on 12v? Do I risk overloading the Vanner by doing that? Other thoughts?

Jim

[richard5933]

We left the bus chassis 24v. No need to even think about switching that over to 12v.

Our house system is 12v. Why? Because it's much more common in the RV world, so many of the little convenience devices are sold in 12v format. Yes, it's possible to use converters to have 12v available on a 24v house system, but I chose 12v for convenience.

Another thing we considered was availability of replacement parts while on the road. For example, likely one could find a replacement 12v water pump at any RV store. A 24v pump might be a problem and require a wait.

That said, the inverter would certain require smaller gauge wiring on a 24v system. We kept the cable length fairly short so it wasn't a problem, but for someone that can't keep the inverter within a few feet of the house bank 24v would make the need for oversized cables less.

The other place where wire size seems to be an issue is the chargers, both the 120v charger and the solar charge converter. Both of our can output about 75 amps @ 12v and require adequate wire gauge size. Obviously on 24v the current is half so the wires could be smaller gauge.

Other than the inverter, there really aren't any single devices which have a high enough current draw to make that much of a difference in the wiring department, and those that might can be wired with relays to avoid much of the issue.

Even with the chassis system at 24v and the house system at 12v, it is still possible charge the house batteries from the chassis system easily using a battery-to-battery smart charger.

[luvrbus]

Kind of a strange question because my bus is pretty flexible in terms of power. I has a Vanner on the batteries, there is wiring in place for both 12v and 24v DC and some wiring for 110v AC, I have 2 24v battery chargers and a bunch of smaller (900w) 24v inverters. I guess what the question really goes to, is what makes the most sense to use when adding devices, such as the water pump.

Now those come in 12v, 24v, and 110. I'd say the 110 is out because it would require an inverter to be powered up all the time or else switched on by the pump's pressure switch, meaning it would be run on DC anyway. Leaving the choice of 12v or 24v. (some things will pretty well have to be run on 110 but those are special cases)

Why should I pick one over the other? So far:

-24v wiring doesn't have to be as heavy, but under 10A does that really matter?
-24v devices tend to cost more. The water pump is about $20 higher in 24v.
-I'm not going to consider changing the whole bus over to 12v, so the 24v stays.

Is there a reason why I shouldn't just go ahead and run everything I add on 12v? Do I risk overloading the Vanner by doing that? Other thoughts?

Jim

Lot of folks use the 12v supply tap on the Vanner to provide 12v power I think it is 60 amps.I never tried it others have told me the 12v on the blade cutoff is not that stable for a house supply 

[buswarrior]

Every time one changes voltages, there are losses, and/or expensive equipment involved.

I would pick a voltage and streamline to that, and then the rest of the electrical design may be focused, as far as redundancy, or recovery, from failures.

My bias is the "real" voltage of the coach, 24 volts in the case of a DL.

Motors/pumps die from starvation. There's nothing in the way for the water pump to get the best of what's available, if you get a 24 volt one.

And, it is easy enough to rig up a 12 volt emergency replacement to save a vacation, if such a disaster does occur...

Pairing pumps, in parallel, has been done, for those times one wants lots of water, and is easily justified as redundancy...

Happy coaching!
Buswarrior

[luvrbus]

My Country Coach is 12v and all blowers motors on the heating and dash air are 24v motors when I asked I was told they been doing it for 25 years because the 24v motors wired to 12v last twice as long,a 24v starter will work on a 12 v 4106 the solenoid needs to be 12v though or they don't work   

[ccbmster]

I had a 12v house battery system with a 12v inverter for many years.  I just had to replace my inverter, and my batteries were toward the end of their life cycle, so I decided to switch to 24v and LifePo4 batteries.  I am all 110v-120v for everything except my stove, which is propane, and my water pump which is 12v  but a cheap step down converter takes care of the water pump.

[Jim Blackwood]

Good replies, Thanks. I'm leaning towards the 12v pump just because it is cheaper and more common. Good chance I can repair this other one with JB Weld and either keep it for a spare or plumb it in parallel to boost the flow.

Have any of you tried to reverse the inlet and outlet? Seems like it might not be hard to do.

Jim

[dtcerrato]

Our chassis is 12 volt. It used to be positive ground. When we performed the conversion back in 79 the  house system was 12 volt neg. ground for obvious reason - RV appliances don't come in positive ground. When we had a positive ground chassis (recently converted the chassis to neg ground) you could have 24 volts by tapping the house & chassis banks. Yes we have to run large cable on our current 2800 watt inverter upgrade - it is what it is. As far as demand potable water we run a 12 volt dc pump & have a brand new one in a box that can plug & play. We know some bus nuts that have plumbed two 12 vdc demand pumps in parallel with valves so if one fails the other is immediately ready which we're contemplating on doing - heck we're carrying a spare anyway why not just plumb it in. I guess we take our potable water pressure for granted. Imagine running out in the middle of a shower in the middle of a pandemic in the middle of a hurricane (which we're about to be in too!) if there wasn't a spare on board - shame on us. Done.

[windtrader]

As stated earlier, th higher voltage the battery bank, the smaller wire required for distribution. Step-down DC-DC converters are very common and loss efficiency is minimal. One option would be a 48v the battery and step down as desired to 24v or 12v with cheap and reliable converters.


Additionally, as more convert to solar the higher voltages are more common and more efficient.

[luvrbus]

His DL3 has several wired 12 v step downs in place it is not like the older MCI with only stud 55 

[Jim Blackwood]

I haven't really gotten into the electrical system much yet, though I do know there is 12v available because it had a bunch of cigar lighter sockets in the package shelves below the overhead bins. The water pump will only be running constantly during showers so it isn't a real big current draw but if I have 2 pumps connected that could be 15 amps. I'll want to run 12 ga for that, although 14 ga should also work. Not much difference in cost there. I can decide when the time comes to run the wires. And that is probably something I should put off until it's time to install the house wiring. I suspect that will be after the plumbing and cabinetry is done, the genset is mounted, and most of the rest is near completion. Tanks, leveling, and framing come first naturally, and I've begun the sketches for the waste tanks which is why I have to know where the pump is going, as well as certain lines and connections. Today's task is finding a good 2" dump valve.

Jim

[luvrbus]

You won't have any trouble finding 12v supply on your bus,the DC supply for my 5 roof top thermostats and water pumps were tied to the factory 12v wiring 

[richard5933]

You won't have any trouble finding 12v supply on your bus,the DC supply for my 5 roof top thermostats and water pumps were tied to the factory 12v wiring

Wait a minute - are we talking about setting up a house system or just tapping 12v off the chassis system?

Sounded like the question was whether to set up a 12v or 24v house system, not how to tap the chassis system to get 12v. For many reasons, it seems that having a totally independent house system is the ideal setup. Whether to go with a 12v or 24v house system depends on various issues, such as what appliances/devices one plans to power from it as mentioned earlier.

If the desire is an independent house system, then where/how to tap the chassis system for 12v is a moot point.

[Jim Blackwood]

Yeah I hadn't thought it through. Of course the pump should be 12v.

Jim

[freds]

I am probably an extreme case with my bus:

1. Tesla house batteries 18-24 volt, charged by solar and shore power when available or the diesel generator
2. Bus start batteries 22-28 volts charged by bus alternator and DC to DC converter from the house batteries
3. 11-13 Volt battery for RV stuff and diesel generator start, charged by separate bus alternator and DC to DC converter from the house batteries.

Newer house systems like computers and LED lighting run off the Tesla house batteries or in an emergency can be switched over to the bus start batteries.

AC Line power devices run off of shore power when available, 6KW split phase inverter or the diesel generator.