Large RV system questions

[esteban]

Hello everyone!

I'm going to be installing a 1,240w system on my 38' fifth wheel with residential fridge and I'm tired of lugging around (2) 3,500w Champion generators and running them in parallel. I'm installing soft start's on both AC units and expect I should have no issue running everything on one generator, possibly even going down to a Honda EU2000. The system details I've decided thus far are:

(4) 310w panels in 2 parallel strings
Midnite Classic 150 charge controller
Magnum MSH3012M 3000 Watt 12V 125A Inverter/Charger
Corresponding displays, shunt, BMK etc.

Currently the RV has (4) 6 volt golf cart batteries, I'm considering swapping to 3-4 lithium batteries but for sake of simplicity lets not cover that aspect now

I've opted to do 2 parallel strings rather than 4 panels in series due to voltage limitations with the Classic 150 controller. That said I'm trying to correctly size wire gauge from the roof to the charge controller. My general calculations show the panels have a max amperage of 8.53 at 36.3 volts, which if I'm correct should render 17.06 amps at 36.3 volts when configured as stated. Correct?

Regardless of the exact amperage/voltage (if I got that info incorrect) I believe 8 gauge wiring from the roof to the charge controller should suffice, I don't have an exact measurement but I'd think under 50 feet is realistic, obviously do my best to keep the run as short as possible. Am I correct thus far?

If I'm correct in the previous assumption, my next question comes down to the parallel connection, the easiest route seems to be branch connectors as I've used in the past on a pair of Renogy 100w panels. But on a system of this size should I be using a combiner box? I can if need be, I'm just trying to keep things simple and weather safe as it will clearly be exposed to the elements (unless I were to send 4 wires through the roof and do the combiner behind a cabinet or something to that effect).

And now, regardless of that setup, I need to throw in a breaker near the charge controller, what amperage breaker should I be using? I notice the panel cut sheet listing the same as most 24v panels I've seen at a max of 15 amps, but with two panels in series and then paralleled I'm expecting hitting a max amperage of 17.06 (which I'll clearly never actually see with panels flat mounted on an RV but regardless the theoretical amperage exists). This would tell me I need a breaker in the 20 amp range, but that is beyond the 15 amp max listed by the panels.

I appreciate you taking the time to read this! I've attached 2 screenshots, one of the panel information (again I'll be using the 310w variant), and a screenshot of the Midnite solar sizing calculator with the panel specs input and well within the limits of the Classic 150 controller.

[karrak]

Is there any reason for using 12V instead of a higher voltage? If you use 24V you will only need a 50A charge controller or if you use 48V you will only need a 30A controller. You will also be saving money on the expensive 12V cable and crimp connectors you will need from your battery to your inverter which will need to carry up to 600A.

For any battery based systems the batteries are at the centre of the system. To some extent you have to design the system around the batteries and not the other way around. If you are going to be drawing 3000W for any period of time you will need over 1500Ah of battery of lead acid batteries or around 300Ah of Lithium Ion batteries.

Lithium Ion batteries are a good choice because of their small size and weight, higher current capacity, simple charge requirements and lower overall cost because of their long lifespan.

8AWG cable will be fine from the panels to the charge controller and you could use MC4 combiner connectors to link the two strings together. As you are only running two strings you do not need any fuses or circuit breakers between the panels and the charge controller. You will need a fuse or circuit breaker between the battery and the charge controller.

Simon

Off grid 24V system, 6x190W Solar Panels, 32x90ah Winston LiFeYPO4 batteries installed April 2013
BMS - Homemade Battery logger github.com/simat/BatteryMonitor/wiki
Latronics 4kW Inverter, homemade MPPT controller

[esteban]

karrak, I completely agree with everything you've said and would absolutely go with a higher voltage system if it weren't an RV.

Being an RV it's already set up for everything using 12v including all the lights, heater, water pump, jacks, slides and much much more. That essentially makes the decision for me right there.

I also agree the batteries need to be addressed and certainly will be, they will only remain for initial testing and I really don't have any expectation of ever pulling a sustained 3000w from the batteries now nor even when replaced with lithium.

The cabling situation is mostly a non-issue, I have a good friend who works in the welding industry and I only need a few feet of 4-0 wire to run from the batteries to the inverter, beyond that I already have plenty of large cable for battery interconnects and charge controller. I expect my cabling cost to be sub $50, a mere drop in the bucket for a system of this size and certainly not something to sway me to another system voltage.

My main goal of the system is to be less reliant on generator power. We spend a lot of time tailgating and at the lake with friends and the entire time I run a pair of 15" PA speakers for music almost all day, this has me running a generator non stop I hate continually filling it with gas. I actually currently carry two generators I parallel to power the trailer and I'm quite tired of that. The reason for selecting this inverter isn't to run 3,000w loads off it, it's to give me the ability to only bring a Honda EU2000 generator for air conditioning, and yes I'll be stuck only using one AC unit but I'm fine with that. The hybrid ability to supplement shore/generator power with battery power is a huge plus to me, no more worrying if the refrigerator and air conditioning fire up at the same time causing a generator to go into overload while we're out on a boat and we come back to a hot trailer etc. Currently that makes me run both generators most of the day, again, rather annoying. Beyond air conditioning I don't foresee any time I'll ever need to use a generator. This system is FAR more capable than what we use power wise.

Another goal for me is to not have to get up and start a generator (albeit mine are already remote start units) every morning when we want coffee, or the microwave, or the lady wants to straighten her hair or whatever it may be. We constantly have friends and visitors in the trailer and it seems there is always a reason to fire up a generator. Having this inverter will simplify life, all outlets will always work and I won't have to think about it. More or less it'll be just like being at home, things 'just work'.

I could build a less capable system for less money no doubt. I'm lucky that Battleborn Batteries is located here in Reno, NV so I can easily go pick up however many 12v 100ah lithium batteries as I please. This weekend we're headed to Santa Cruz, CA and along the way we're stopping into a solar store in the San Jose area and picking up brand new tier 1 310w panels for $150 each making the decision to go larger very easy.

All in all I enjoy building things, and I think it will be a fun little project. Not including the batteries (a massive part of the cost) I'll be into the entire system roughly $2,000. Finding great deals, free shipping, sales and more has dropped my cost quite a bit, along with me being able to sell my existing generators and power inverters the trailer came equipped with makes the transition rather pain free for me.

[Mike90250]

... to give me the ability to only bring a Honda EU2000 generator for air conditioning, and yes I'll be stuck only using one AC unit but I'm fine with that. The hybrid ability to supplement shore/generator power with battery power is a huge plus to me, no more worrying if the refrigerator and air conditioning fire up at the same time causing a generator to go into overload while we're out on a boat and we come back to a hot trailer etc....

Then you should look at a inverter that is able to perform Generator Support. That's where, if the inverter senses the generator is about to exceed it's programmed load limit, it stops charging batteries and throws itself in parallel with the generator, till the load abates. Not all inverters perform this function well, so get some endorsements that are not mfg paid shills.
The Schneider XW series works properly. Check with RV forums if your planned model will work that way too.

[esteban]

Then you should look at a inverter that is able to perform Generator Support. That's where, if the inverter senses the generator is about to exceed it's programmed load limit, it stops charging batteries and throws itself in parallel with the generator, till the load abates. Not all inverters perform this function well, so get some endorsements that are not mfg paid shills.
The Schneider XW series works properly. Check with RV forums if your planned model will work that way too.

That is specifically why I've chosen the Magnum MSH3012 inverter: http://www.magnum-dimensions.com/pro...ger-msh-series

[littleharbor]

The Midnite Classic controllers have 3 fans which actively cycle on and off throughout the day. Hopefully the location of the controller will be somewhat isolated from living space as this sound can get annoying if you were to, say, want to take an afternoon nap. There are other silent choices, although with less output than the classic 150.

[Sunking]

Currently the RV has (4) 6 volt golf cart batteries, I'm considering swapping to 3-4 lithium batteries but for sake of simplicity lets not cover that aspect now.

You do not want to use LFP batteries. FLA are less expensive and last longer. I assume you have 225 AH 6-volt Batteries? If correct you have a bit too much panel wattage. Depends on what manufacture and model you have. If Trojan T-105's you should be OK

I've opted to do 2 parallel strings rather than 4 panels in series due to voltage limitations with the Classic 150 controller. That said I'm trying to correctly size wire gauge from the roof to the charge controller. My general calculations show the panels have a max amperage of 8.53 at 36.3 volts, which if I'm correct should render 17.06 amps at 36.3 volts when configured as stated. Correct?

Yes

Regardless of the exact amperage/voltage (if I got that info incorrect) I believe 8 gauge wiring from the roof to the charge controller should suffice, I don't have an exact measurement but I'd think under 50 feet is realistic, obviously do my best to keep the run as short as possible. Am I correct thus far?

8 AWG is more than enough

If I'm correct in the previous assumption, my next question comes down to the parallel connection, the easiest route seems to be branch connectors as I've used in the past on a pair of Renogy 100w panels. But on a system of this size should I be using a combiner box? I can if need be, I'm just trying to keep things simple and weather safe as it will clearly be exposed to the elements (unless I were to send 4 wires through the roof and do the combiner behind a cabinet or something to that effect).

No need for a Combiner or Fuses with 2 strings of panels

And now, regardless of that setup, I need to throw in a breaker near the charge controller, what amperage breaker should I be using? I notice the panel cut sheet listing the same as most 24v panels I've seen at a max of 15 amps, but with two panels in series and then paralleled I'm expecting hitting a max amperage of 17.06 (which I'll clearly never actually see with panels flat mounted on an RV but regardless the theoretical amperage exists). This would tell me I need a breaker in the 20 amp range, but that is beyond the 15 amp max listed by the panels.

You need two sets of fuses Installed directly on the battery Term Post. One fuse looking at the controller, and another looking at the load. Although the picture below does not show your exact configuration, th ewiring configuration is exactly what needs to be done. What changes is the size of the fuses and wires. Between the Controller and battery will require 100 amps (you have an 96 amp controller and with 1200 watts will use every bit of 96 amps). Now here is where you really messed up big time, using a 3000 watt inverter on a 12 volt battery. You are asking for a great big FIRE, but what do I care if you burn your RV up No skin off my nose. If it were me no larger than a 1000 watt Inverter. 3000 watt demands 48 volts. Anyway you will need at least a 300 amp fuse between the Battery and Inverter using copper wire as large as your wrist.

[esteban]

The Midnite Classic controllers have 3 fans which actively cycle on and off throughout the day. Hopefully the location of the controller will be somewhat isolated from living space as this sound can get annoying if you were to, say, want to take an afternoon nap. There are other silent choices, although with less output than the classic 150.

Sorry the site clips all my posts when coming from a phone. It is certainly isolated, in the bottom front of the trailer is the current plan (original location for batteries and inverter so wiring will stay simple and short).

[esteban]

Now here is where you really messed up big time, using a 3000 watt inverter on a 12 volt battery. You are asking for a great big FIRE, but what do I care if you burn your RV up No skin off my nose. If it were me no larger than a 1000 watt Inverter. 3000 watt demands 48 volts. Anyway you will need at least a 300 amp fuse between the Battery and Inverter using copper wire as large as your wrist.

While I agree 3000 watts on 12v does theoretically pull quite a bit of amperage, I have to question why this is such a 'horrible idea' and 'fire hazard'? I'm using top quality components, wired correctly, with short runs and proper fuses?

I may be wrong, but I've seen multiple 'well known' RV bloggers etc using this same inverter, as well as many RV's coming standard with similarly sized 12v inverters and not heard of these fires you speak of?

The requirement per the manual, and what I read online is 4-0 wire, capable of 300 amps to 15.8 feet with less than 2% voltage drop. One would think a 2-3 foot run from the batteries would be WELL within the safe zone for such a system?

Adding to that, I literally cannot think of a situation where I'll ever pull 300 amps from the batteries, other than when I first set it up "just because" to ensure it all works smoothly.

Realistic usage: The fridge coming on an off throughout the day (which the existing Magnum 1,000w inverter handles just fine), the occasional LED TV (again already part of the existing 1,000w inverter), maybe a blender here or there, a quick pot of coffee, microwave for 2 minutes (popcorn) or something similar.

It just doesn't seem to me (on the surface) to be that risky? I'm not at all saying you're wrong, but trying to understand the worry if everything is sized appropriately?

Additionally, why is it that I don't want the Lithium batteries? My understanding is they are far lighter, far more capable of fast charging/discharging and offer a much better depth of discharge. Albeit at a much higher price.

[Sunking]

I may be wrong, but I've seen multiple 'well known' RV bloggers etc using this same inverter, as well as many RV's coming standard with similarly sized 12v inverters and not heard of these fires you speak of?

Not a one of them really know squat about power. Not one of them ever had an inspection to pass or reviewed by a professional. Like I said I do not care what you do.

The requirement per the manual, and what I read online is 4-0 wire, capable of 300 amps to 15.8 feet with less than 2% voltage drop. One would think a 2-3 foot run from the batteries would be WELL within the safe zone for such a system?

OK first distance has nothing to do with what I am talking about. Makes no difference if the run is 1 or 100 feet. Distance only matters with respect to voltage drop.

How much current you can safely run on a conductor has to do with the size of the wire, what raceway is used, and temperature rating of the conductor insulation. In NEC use can be as low as 100 amps in a race way with 5 or more conductors using 75 degree C insulation and as high as 405 amps with a single conductor rated for 105 C in open air. Use the right insulation and yes you could use it with a 300 amp fuse. In an RV no one really cares.

Again that is not the real issue. The issue is surface contact resistance and properly terminating compression connectors onto the wire. To properly terminate a proper 4/0 conductor is going to require a hydraulic compression tool with the proper die set. Very expensive tooling that requires training and experience. Even if you get that right, I have never seen a 12 volt 3000 watt Inverter input terminals that use 2-hole terminals using 1/4-20 hardware. That is what it takes to handle up to 300 amps. Just one loose connection or improperly terminated cable and you have melted battery terminals, or melted copper dripping off the wires.

Adding to that, I literally cannot think of a situation where I'll ever pull 300 amps from the batteries, other than when I first set it up "just because" to ensure it all works smoothly.

Yeah and my 16-year Son promised if I bought a Corvete he would never bark the tires or go over the speed limit. I did not believe a word of it and I am not going to start with you.

Realistic usage: The fridge coming on an off throughout the day (which the existing Magnum 1,000w inverter handles just fine), the occasional LED TV (again already part of the existing 1,000w inverter), maybe a blender here or there, a quick pot of coffee, microwave for 2 minutes (popcorn) or something similar.

Then why do you need or want a 3000 watt Inverter?

Additionally, why is it that I don't want the Lithium batteries? My understanding is they are far lighter, far more capable of fast charging/discharging and offer a much better depth of discharge. Albeit at a much higher price.

For one is you have no experience with them, and that makes them very dangerous. Just one over discharge, and they are boat anchors and an extreme fire hazard. Over charge them and you can have a fire. Regardless if over discharged or over charged, if they catch fire, you cannot extinguish the fire. All a FD can do is watch and try to contain the fire to keep your neighbors from catching fire.

One thing you said is partly accurate, they can handle deeper discharges, and be charged faster and discharged faster. But to make that a true statement means you have to compare them to Flooded Lead Acid. However a completely false statement if compared to AGM batteries. Additional is a moot point for your application. You have 550 AH batteries. Do you plan on charging or discharging at 550 amps? The types is LFP batteries you are most likely talking about are Chi-Coms like CALB, GBS or Winston. Yep they are cheap, about twice as much as FLA per Kwh of storage, an dlast no longer than a good FLA or AGM. You as Joe Public cannot buy quality large format prismatic cells. If you could would cost you 4 to 10 times more than a good FLA and still have about the same cycle life. Still dangerous. Only way to get them is as part of a packaged unit with built-in safety features and limitations.

Like I said I really do not care what you do. All these blogs you speak of have not had to been scrutinized or ever pass an inspection. Largest I would dare go with 1200 watts of panels is 1000 to 1500 watts if professionally installed. Ideally you do not want your Inverter to be any larger than the panel wattage.

This is from a RV like yours. The bolt holding the terminal got loose from vibration.

[karrak]

Being an RV it's already set up for everything using 12v including all the lights, heater, water pump, jacks, slides and much much more. That essentially makes the decision for me right there.

Have you looked at the economics of using 24V and a 24V to 12V converter to run all your 12V equipment?

My main goal of the system is to be less reliant on generator power. We spend a lot of time tailgating and at the lake with friends and the entire time I run a pair of 15" PA speakers for music almost all day, this has me running a generator non stop I hate continually filling it with gas. I actually currently carry two generators I parallel to power the trailer and I'm quite tired of that. The reason for selecting this inverter isn't to run 3,000w loads off it, it's to give me the ability to only bring a Honda EU2000 generator for air conditioning, and yes I'll be stuck only using one AC unit but I'm fine with that. The hybrid ability to supplement shore/generator power with battery power is a huge plus to me, no more worrying if the refrigerator and air conditioning fire up at the same time causing a generator to go into overload while we're out on a boat and we come back to a hot trailer etc. Currently that makes me run both generators most of the day, again, rather annoying. Beyond air conditioning I don't foresee any time I'll ever need to use a generator. This system is FAR more capable than what we use power wise.

One advantage of Lithium batteries is there high peek load capability which means you can use the battery and inverter to provide high peak power and use a small generator to recharge the battery. The power output from the generator only needs to be slightly higher than the average load to charge the battery.

Simon

Off grid 24V system, 6x190W Solar Panels, 32x90ah Winston LiFeYPO4 batteries installed April 2013
BMS - Homemade Battery logger github.com/simat/BatteryMonitor/wiki
Latronics 4kW Inverter, homemade MPPT controller

[karrak]

While I agree 3000 watts on 12v does theoretically pull quite a bit of amperage, I have to question why this is such a 'horrible idea' and 'fire hazard'? I'm using top quality components, wired correctly, with short runs and proper fuses?

You are right, if you use the correct cable, connectors and the connectors are crimped on to the cables correctly a 3000W 12V inverter is just as safe as a 3000W 24V inverter. Both can have up to 3000W passing through the connectors and both can fail with a high resistance connection that causes similar amounts of heat being generated at the bad connection causing damage or a fire.

I doubt companies like Magnum or the number of other reputable manufacturers that manufacture 2500W-3000W 12V inverters would do so if they weren't safe.

Additionally, why is it that I don't want the Lithium batteries? My understanding is they are far lighter, far more capable of fast charging/discharging and offer a much better depth of discharge. Albeit at a much higher price.

You are correct, sure they have a higher up front capital cost but work out cheaper overall than lead acid batteries because of their longer lifespan, higher efficiency, simple charging requirements, and higher load handling capability.

If you use the Battleborn batteries you do not have to worry about the safety or overcharging or overdischarging them because they have an inbuilt BMS that will disconnect the battery if they are taken out of there safe operating zone.

Simon

Off grid 24V system, 6x190W Solar Panels, 32x90ah Winston LiFeYPO4 batteries installed April 2013
BMS - Homemade Battery logger github.com/simat/BatteryMonitor/wiki
Latronics 4kW Inverter, homemade MPPT controller

[Mike90250]

If you go camping in freezing weather, your Li batteries need to be kept warm . Below 40F they loose a lot of capacity, and below frost 32F they cannot be recharged till warmed up above freezing.

And the onboard BMS are suspect, if they don't warranty repairs/replacement to your RV from a battery fault. Lead acid batteries get hot, boil, can go bang, but rarely take out their container. If a Li based battery gets a fire started (think of a road flare), there is no stopping it till it's consumed the battery and everything around it.

If you want to be ahead of the "curve" and must have Li batteries, you need to learn all aspects of charging them because I do not trust the dolts that make most of the batteries or BMS in their garage. Most charge controllers or inverters don't have solid management systems yet either. Lead acid batteries have been very forgiving for many years.

[Sunking]

Estaban do your self a favor and do some homework. Start by looking at T&B product page here for 4/0 compression connectors. All those connectors are listed, tested, and approved for high current and high voltage application. You do not need to look at all 20 pages, you will get the idea real quick from the first page. Take note of the surface contact area, number of holes, and most importantly the Bolt Hole Size. On a single hole connector the minimum bolt is 3/8", and two-hole is 1/4". Additionally they tell you what die code is needed to properly terminate and make a Listed Approved Connection.

In a mobile application or anyplace where there is vibration and movement demands a 2-hole connection using locking hardware. Any single hole application requires no tools to break loose. You can take a 1-hole bolt off with your bare hands, no tools required. With vibration of the road, it will loosen.

Take note some of the connectors have long barrels requiring 4 crimps. Those are the connectors required for fine stranded cable like you intend to use right? Keep this in mind.

Now take a look at your Inverter DC power input. What do you see? Bet it is a mechanical compression connector? You cannot use fine stranded wire with a mechanical compression connector. It would cut the strands and loosen up in no time causing a melt down. The only wire you can use is Class B Stranded, and it takes a gorilla sparky to bend and shape 4/0 AWG Class B standing.

Think about your safety. If you put safety first takes care of operational issues as a side benefit. Consider a smaller Inverter.

[karrak]

If you go camping in freezing weather, your Li batteries need to be kept warm . Below 40F they loose a lot of capacity, and below frost 32F they cannot be recharged till warmed up above freezing.

How well LFP batteries operate at low temperatures is dependant on the size of the LiFePO4 particles in the cathode and other factors that will vary from manufacturer to manufacturer. I would use the recommendations of the battery manufacturer as a guide.

In their documentation Battleborn say that the BMS inside the battery will not allow charging below 25^oF.

And the onboard BMS are suspect,...

What evidence do you base this statement on?

If you want to be ahead of the "curve" and must have Li batteries, you need to learn all aspects of charging them because I do not trust the dolts that make most of the batteries or BMS in their garage. Most charge controllers or inverters don't have solid management systems yet either. Lead acid batteries have been very forgiving for many years.

For LFP batteries with an inbuilt BMS that will disconnect the battery from the outside world if anything goes wrong there doesn't have to be any "solid management systems" in the charge controllers or the inverters. The charge controllers and inverter will however have to cope with the battery being disconnected from them.

For LFP batteries with a BMS that will only signal that there is a problem to the charge controller or inverter and expect them to shut down you do need some sort of "solid management system". For an inverter this could be as simple as a remote off switch input that is available on a number of inverters. Some charge controllers have the capability of being turned off via a remote signal. The Midnite Classic can be told to stop charging via the AUX2 input. If the charge controller or inverter do not have this facility you will have to provide the extra circuitry to disconnect the battery from the charge controller or inverter when signalled via the BMS to do so.

Simon

Off grid 24V system, 6x190W Solar Panels, 32x90ah Winston LiFeYPO4 batteries installed April 2013
BMS - Homemade Battery logger github.com/simat/BatteryMonitor/wiki
Latronics 4kW Inverter, homemade MPPT controller