Fifth Wheel 12v system

Normok · December 2012

Ok guys heres the next phase of my project. I want to install flexible solar panels on the roof of my fifth wheel to charge 12v dc loads only. The fifth wheel is 41' so I have a good amount of space for some panels. I used the load calculator provided by wind/sun and in the winter using the furnace I use an average of 4863 watt-hours per day. This includes the furnace, lights, tank heaters, water pump, radio, and misc loads like the gas sensors. There will not be a need for an inverter as this will only power 12v loads.

I think 6 2v 1050ah batteries wired parallel should be enough but not sure.

My question is what charge controller and how much/many solar panels do I need?

Thanks again for all your help.

Cariboocoot · December 2012

Re: Fifth Wheel 12v system

4.8 kW hours on a 12 Volt system? That's pretty horrible. You might think about dividing it up so there's some system redundancy just in case.

Otherwise you're looking at using 400+ Amp hours for that power, so your estimate of a 1050 Amp hour 12 Volt bank is not unreasonable for approximately 40% DOD. Charging it will be a bit of a struggle, as no charge controller could handle 100 Amps @ 12 Volts (a 10% rate) although the MidNite comes close at 90+ Amps. Another reason to perhaps divide it in half.

Total panels using the 10% rate would be around 1600 Watts.

BTW you mean to wire the 2 Volt cells in series, not parallel.

westbranch · December 2012

Re: Fifth Wheel 12v system

well I cant remember phase 1, so going at this blind... assuming that you do use those batteries you will need between 53 and 105 Amps (say 50 - 100) from your panels to get you in the 5% - 10% charge rate. A 140w 12V panel will have ~7.8A so you would need between 7 and 14 panels for starters.

Those loads are quite high, especially for a small 12 v battery, if it was 24 V it would be close to meeting those needs.

What loads are critical and what are optional? IMHO you need to lower that total battery load.

hth

Photowhit · December 2012

Re: Fifth Wheel 12v system

Gosh, don't know where to start, lets start with Tesla, he won the battle for AC over Edison who wanted DC many years ago...

12 volt DC has a lot of voltage drop over small wires, so you'll end up buying lots of heavy gauge wire...

Nearly 5Kwh is a lot of power! Where are you located? (helps us figure out solar isolation, or how much the sun shines) and how many days do you want storage for? (the sun doesn't shine every day in most places)

To your questions, You will likely need 3 Midnite classic Charge controllers and 3Kw array minimum depending on your answers to my questions...

Photowhit · December 2012

Re: Fifth Wheel 12v system

Ooops after reading others responses I forgot to add, IMHO you will want more storage(battery) unless your in a sunny area, using 400 amps at 12 volts per day a normal battery bank this would represent 20% of your battery capacity so Your looking at closer to 2000Amp hour 12 V battery or about double what you have speced...

Give us more info and we can give you better info!

Cariboocoot · December 2012

Re: Fifth Wheel 12v system

I kind of got the impression this is a pre-wired RV where everything is 12 Volt to begin with, so changing to AC and/or upping the DC Voltage is not practical. So he is looking for capacity and solar charging to keep from running the gen so often.

As always, the devil is in the details. :roll:

Normok · December 2012

Re: Fifth Wheel 12v system

Ok here is my load break down:

Constant load for gas and co2 sensors and stereo idle is 30.7w x 24hrs = 736 watthours (this load will be reduced as some of this power is loast in the converter.
Heated Tanks use 36w x 8hrs for night time use = 432watthours
Furnace used at most 20hrs on cold days 150w x 20hrs = 3000watthours
water pump used 3hrs 85w x 3hrs = 255watthours
lights 280 watthrs
stereo used 2 hours a day 80w x hours = 160watthours

total load = 4863 watthours

I live in South Dakota Black Hills

Yes I meant series for batteries thank you for the correction.

Cariboocoot · December 2012

Re: Fifth Wheel 12v system

And this is all 12 Volt existing equipment? There's no inverter presently? No 120 VAC anything? Voltage converter to turn 120 VAC to 12 VDC?
What about a generator?

Will this be at a fixed location or mobile? If fixed, where?

Yes it can all make quite a difference to the design.

Normok · December 2012

Re: Fifth Wheel 12v system

Yes this is all standard equipment for the trailer. Currently, I run my 11kw Miller pipepro welding machine to charge the batteries (through the factory converter120v to 12v) and run 120v loads. The furnace is propane.

I really just wanted to get the 12v dc loads covered before moving to 120v ac loads. Also it didnt seem very efficient to run a 48v ststem through and inverter and then back to the converter. I might be wrong.

As far as the battery bank size if it is an excessively cold day and the furnace run longer than anticipated or its a day without sun I can run the welder to charge everything.

Cariboocoot · December 2012

Re: Fifth Wheel 12v system

What has it got for battery capacity now? Obviously not big enough.
I can see why you'd want to cut down on running an 11kW gen!

It might make sense to go with a higher DC Voltage if more of the equipment could be converted to AC (if you're planning on adding an inverter anyway). The conversion to 12 VDC from 120 VAC powered by 48 VDC doesn't make much sense, though, even with the improved efficiency of the 48 Volt system. The difference would come from how much could be shifted from 12 VDC.

There's more than one way to accomplish meeting this power requirement.

Normok · December 2012

Re: Fifth Wheel 12v system

Ive got a 200ah battery currently and unless I have to use the furnace a lot does a pretty good job. I have a small array of panles on the ground hooked to classic 150 that helps charge the 12v system currently but I wanted to make the 12v system self sufficient and indepenent.

I usually fire up the generator when the battery gets low and then turn on all(4) of my 1500w AC heaters plus use all my opportunity loads. Running this for about 2hours charges the battery and get the trailer nice and toasty so I dont have to fire up the furnace immediately after turning off the generator.

Normok · December 2012

Re: Fifth Wheel 12v system

Also I cant really shift any of the 12v loads to AC without significant changes to the trailer...which Im hoping to avoid. Also these loads I have indicated are highest usage and would not be average. Obviously in the summer this would be cut in half if not more so.

Photowhit · December 2012

Re: Fifth Wheel 12v system

If your willing to run the welder/generator every day you don't have full sun, you could likely go with 'Coot's 1600 watt array and your battery bank as proposed. Since I think the Classic tops out for practical array of @1300 watts at 12 volts (I didn't run over and check, they have a sizing tool Here) so you'll need 2 Charge controllers, I would go with a slightly larger array. This might give your the extra you need on somewhat close days.

While it doesn't always seem effiecent, often you mitigate some of the effcientcy loss in inverter with effiecientcy loss in wires in voltage drop. A DC motor designed to run at 12.7 volts will likely run at 11.4 volts but draw more amperage to make up for it, so if you have voltage line loss you will actually use more power than rated.

Might put a wood stove in your trailer, I had a small box stove in mine for 3 winters and I have a friend who's a logger who has a pot belly stove in a 16' camper! You have to loose some space, I placed mine right next to the door and took out a built in there and one of the built in seats and table. In Missouri i didn't worry about not having combustion air from outside, I needed to leave a window cracked, it would chase me out until it got near 0.

westbranch · December 2012

Re: Fifth Wheel 12v system

OK, as I suspected your furnace is the KILLER>>> so why not give it some honkin big batteries for dedicated use, say the biggest GC's you can get, and that brings you down to ~1600 Watts for the rest?

Normok · December 2012

Re: Fifth Wheel 12v system

Thats a good idea however changing the wiring in trailer will be a really tough. This trailer has an insulation package with rigid underbelly plating. This makes it very difficult to access some of these areas, areas I would need to access to make such a change. As it stands I dont think it will be a problem to just run off the 1050ah battery bank and charge with genny when necessary. Also once my main PV system is completed I can always charge my 12v system from that just flip the breaker for my internal battery charger converter.

Cariboocoot · December 2012

Re: Fifth Wheel 12v system

Your existing battery charger-converter was not designed to charge 1000+ Amp hours of battery. Chances are it's capable of about 30 Amps max, and it will just "go flat" when connected to that large of a bank with a low SOC. Coming up with a stand-alone battery charger capable of putting out enough current to affect that much battery would be difficult.

If you're going to go the big bank route and install an inverter anyway, I'd lose the converter and do the necessary re-wire to handle the heavy current demands even if they have to be run in external conduit somehow. With an inverter-charger you could have 80 or 100 Amps of charging from the AC which would just about handle that much battery.

You're going to need space to do this: space for all that battery (very heavy too) and space for the inverter-charger and space to run the wiring. You can not force heavy current down small wires, so if the existing DC side isn't large enough to handle the charge current for that much battery (extremely doubtful) you'd have to change it anyway.

And when it comes to wire size, single 4/0 would definitely be needed for up to 100 Amps @ 12 VDC.

Normok · December 2012

Re: Fifth Wheel 12v system

Coot I just checked the charger on the trailer and its a 65amp. Do you think this would be good enough to charge the batteries? If so I can buy and install them now and add the CC + solar later. This would give me longer run time before needing to run the generator. What do you think?

westbranch · December 2012

Re: Fifth Wheel 12v system

CAUTION, you are dealing with AGM batteries, and they will , in all likelihood need a different charge regime than that that converter will put out... check the manufacturers site for their charge regime, particularly the Absorb V and Float V.

Blackcherry04 · December 2012

Re: Fifth Wheel 12v system

Normok wrote: »

Coot I just checked the charger on the trailer and its a 65amp. Do you think this would be good enough to charge the batteries? If so I can buy and install them now and add the CC + solar later. This would give me longer run time before needing to run the generator. What do you think?

Here is the deal, once you are away from 100 % charge you end up in the 50% to 85% SOC range to utilize, that 35 % is what you have to put back on every cycle you charge minimum . A 65 amp charger will take about 3 hrs or so, depending on the loads you run in conjunction with the charging. I have that size bank, if I am at say 12.2 volts I have to charge back to around 13.8 charging voltage to have enough to get through the night, the batteries will be at about 12.5 V. This something you'll learn after a few cycles, depending on your loads. The lower you pull it, the more you have to put back. So, I charge in the evening, to get through the night, in the morning, I'll look at the voltage and decide how much charging I need for the day and the anticipated solar. Doing a bulk as early in the morning will set you up for a absorb on solar and you'll know where you stand in the evening.

Normok · December 2012

Re: Fifth Wheel 12v system

westbranch wrote: »

CAUTION, you are dealing with AGM batteries, and they will , in all likelihood need a different charge regime than that that converter will put out... check the manufacturers site for their charge regime, particularly the Absorb V and Float V.

Ok - here are the specs on the charger:
Bulk = 14.4vdc
Absorb = 13.6vdc
Float = 13.2vdc

Here are the specs on the proposed batteries:
Absorb/bulk = 15-14.16vdc (depending on temp)
Float = 13.4vdc

It seems as though I should be good...Im a little light on the float. Do you think this will be a problem?

westbranch · December 2012

Re: Fifth Wheel 12v system

Absorb is the most important phase as this replaces the last 10 - 20% of your charge and you are .5 v too low. Absorb is generally 1 to 4 or longer hours long. I would contact the manufacturer and discuss the implications of a 13.5V Absorb cycle. You need to also think about how many watts you are using and replacing each cycle, the lower V means more time is needed to get the same watts. Overall you will need to replace 110% - 115% of what you remove from the battery.

Cariboocoot · December 2012

Re: Fifth Wheel 12v system

Normok wrote: »

Ok - here are the specs on the charger:
Bulk = 14.4vdc
Absorb = 13.6vdc
Float = 13.2vdc

Here are the specs on the proposed batteries:
Absorb/bulk = 15-14.16vdc (depending on temp)
Float = 13.4vdc

It seems as though I should be good...Im a little light on the float. Do you think this will be a problem?

I'm going to be redundant here and say "don't use that charger with a bunch of big, expensive deep cycle batteries". As has been pointed out, the current is low for getting that bank fully recharged in short order and the Voltages don't match up either. There probably is zero adjustment on that charger as well. If you sink big $ into batteries, sink $ into charging them exactly as recommended by the maker. Otherwise you'll be buying new ones sooner rather than later.

Normok · December 2012

Re: Fifth Wheel 12v system

Alright so I have been looking at upgrading the charger and I found the MS2012 Magnum and it looks like it would do really well for charging my battery. Except while I was looking at the spec sheet I noticed a different model the MS2000 and for the life of me I cant tell the difference excpet for $400 and some dimension difference. ???? I'm sure its something stupid I just overlooked. Any ideas?

Also is it necessary to have 4/0 cable? Thats what the specs say but thats massive compared to the 6awg I currently have and seeing as the loads arent really increasing seems odd.

westbranch · December 2012

Re: Fifth Wheel 12v system

look carefully at the certifications for those 2 inverters, you might find one is for RV use and the other is home use. I asked about a similar difference of larger inverters..

BB. · December 2012

Re: Fifth Wheel 12v system

The wiring for a typical 2,000 watt 12 volt inverter should be rated for:

2,000 watts * 1/10.5 volt cutoff * 1/0.85 inverter efficiency * 1.25 NEC safety factor = 280 amp branch circuit wiring+breaker/fuse rating

Using the NEC table 310-16 for copper wire with high temperature insulation, 4/O wire is rated for 260 amps continuous (in conduit I believe). NEC is on the conservative side, and you will see other wiring tables that will support the use of smaller gauge wiring.

If you do not plan on running at 2kW (typically inverter should be good for near 4kW peak), you can down size the wiring/breakers (the breakers may trip when operated at higher than planned output).

Breakers are designed to run at 80% of maximum rated load (1/1.25 NEC safety factor) and will trip at 100% of rated load (may take minutes to hours to trip).

-Bill

inetdog · December 2012

Re: Fifth Wheel 12v system

Normok wrote: »

Alright so I have been looking at upgrading the charger and I found the MS2012 Magnum and it looks like it would do really well for charging my battery. Except while I was looking at the spec sheet I noticed a different model the MS2000 and for the life of me I cant tell the difference excpet for $400 and some dimension difference. ???? I'm sure its something stupid I just overlooked. Any ideas?

Looking at the data sheet from Magnum , the only difference that I see is that the 2000 has only a single pole 30 Amp transfer switch built in while the 2012 has a two-pole 30 amp transfer switch. That means that the 2012 can be used with a 240 volt generator or service to allow all of your 120 volt loads to be powered regardless of which phase of your distribution box the load is on. But it will not deliver power to a 240 volt load, of course. And there may be problems if you have multi-wire branch circuits with a common neutral.
Although there seems to be a typo in the spec sheet on this detail, the 2012 can be used with either a 30 amp 240 volt or 60 amp 120 volt shore/generator power connection, while the 2000 is limited to 30 amp 120 volt. There is no difference in the output of the inverter, just in how it is compatible with your alternate AC power system. If you have a 60 amp shore power connection, you could not feed it through the 2000. So it would limit the loads you could drive when connected to shore or generator power.
I also get the impression that the 2000 is an older model and may be different in other ways.
Since an automatic transfer switch (ATS) is an expensive item, it may justify the difference in price all by itself if you need that two pole feature.

Normok · December 2012

Re: Fifth Wheel 12v system

inetdog wrote: »

Looking at the data sheet from Magnum , the only difference that I see is that the 2000 has only a single pole 30 Amp transfer switch built in while the 2012 has a two-pole 30 amp transfer switch. That means that the 2012 can be used with a 240 volt generator or service to allow all of your 120 volt loads to be powered regardless of which phase of your distribution box the load is on. But it will not deliver power to a 240 volt load, of course. And there may be problems if you have multi-wire branch circuits with a common neutral.
There is no difference in the output of the inverter, just in how it is compatible with your alternate AC power system. If you have a 60 amp shore power connection, you could not feed it through the 2000. So it would limit the loads you could drive when connected to shore or generator power.
I also get the impression that the 2000 is an older model and may be different in other ways.
Since an automatic transfer switch (ATS) is an expensive item, it may justify the difference in price all by itself if you need that two pole feature.

Ok I am not entirely sure I understand what you just said. Let me put it in terms I understand and you tell if I get it:

On my trailer I have a 50a 240v plug that is wired into the distribution panel. There are 2 hot wires that go into a 50a break (1 wire in each slot of the breaker, the breaker has 2 switches locked together) it also has a neutral wire that goes to a bus bar that appears to common for all loads and a ground(unshielded wire)

I was plan to wire the inverter/charger to the distribution panel via a spare breaker slot (15a breaker). I could then flip the breaker on when I wanted to use small AC loads thereby energizing the panel.

The charger (AC in) would also be hooked to the on the current breaker labeled (converter)

The DC portion of the inverter would be wired exactly the same as the existing charger.

Ok now all that being said this is my plan when chagering the battery bank with a generator I would turn the AC 15a breaker for AC loads off and turn the converter breaker on allowing the batteries to be charged.

I hope I didnt confuse you but this is at the edge of my knowledge base as of now. I getting a little deep.

BB. · December 2012

Re: Fifth Wheel 12v system

I have to go right now--But quickly--Is not the MS series a 120 VAC only inverter? The two pole AC transfer switch (in my humble opinion) would allow the proper "switching" of AC neutral/ground bonding. Pass through L/N from the AC shore power, or switch over both L/N to the inverter, and have the local Neutral/Earth bond at the inverter/RV electrical panel.

Of course, these all gets more complex if you want to through an RV generator into the mix.

-Bill

Normok · December 2012

Re: Fifth Wheel 12v system

Ok so this is a very crude diagram of what Im thinking, its only the AC part of the wiring. Also I would like to know if it is necessary to shut off the right breaker while running the generator as there will be 2 sources of AC power at the panel when the generator is on. Damn I really dont understand AC power at all.

Attachment not found.

inetdog · December 2012

Re: Fifth Wheel 12v system

BB. wrote: »

I have to go right now--But quickly--Is not the MS series a 120 VAC only inverter? The two pole AC transfer switch (in my humble opinion) would allow the proper "switching" of AC neutral/ground bonding. Pass through L/N from the AC shore power, or switch over both L/N to the inverter, and have the local Neutral/Earth bond at the inverter/RV electrical panel.

Of course, these all gets more complex if you want to through an RV generator into the mix.

-Bill

Yes, the output of the MS 2000 series is always only 120 volt AC.
But given that, there are three circumstances where the dual-pole ATS makes sense to me:

1. When you need to switch the AC neutral as well as the hot side. This is a somewhat special case which does not often come into play for a PSW inverter. But if you need it, it makes the difference between working and smoking.

2. When the shore connection is 240 volt 30 amp plus neutral, going into a 240 volt, 30 amp, split-phase distribution panel in the trailer. (And there are no actual 240 volt loads, or they do not need to be used when on PV power.)
The two poles will allow you to either connect the two 120 volt phases from the shore power to the two busses in the distribution panel and then when the switch goes over to PV to connect both busses in the distribution panel to the single 120 volt inverter output. It will not give you any more inverter power, but it could avoid the need to rewire the distribution panel and will let you use more shore power when you have it.

3. When the shore power is 120 volt 40-60 amp. In this case you would use both poles of the 30 amp transfer switch in parallel to allow the distribution panel to get up to 60 amps from shore power but switch automatically to getting up to 30 amps when on the inverter.

Cariboocoot · December 2012

Re: Fifth Wheel 12v system

You do not want two sources of AC available at the same time. However it is wired, it needs to be "either/or" never both.

It gets complicated with this sort of set-up where you can have two 120 VAC Hot lines fed either from the ends of a 240 VAC feed or from the same 120 VAC source. One mistake and you short the 240 VAC power.

There are also potential problems with duplicate Neutral-Ground bonds when connected to shore power. Especially if there are any GFCI outlets on board.

Fifth Wheel 12v system

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