Solar and Inverter System - Design Check

We are doing a Solar and inverter upgrade in our Sprinter based RV.

Currently I have a lot of bins and parts taking up most of the garage with the hope that they will come together over the next few days into a great install. The major components are already purchased, some of the 'balance of system' components are still to be picked up.

Attached is my system block diagram: View attachment System Diagram - Sep 15, 2014 1852.pdf

Any suggestions?

Wiring sizes and breaker / fuse considerations are likely the most critical.

Thanks much!

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Measure twice, cut once.

Diagram change: You show 120 volt from shore generator going to batteries through a 300 amp fuse and a disconnect. What you probably meant is 12 volt coming from battery bank to the Magnum with fuse close to battery and then the disconnect between the fuse and the Magnum.

I confess to being tired from a 4 day trans continental trip, but I am seeing (or not seeing) a couple of things. It is not clear to me from your block diagram how you are going to take the PV/battery power into the inverter. I also would consider increasing the wired size in the PV leads, especially if you are ever going to add additional panel capacity. Also parallel PV arrays ought to be fused between panels, (but seldom are!) When ever you have three or more panels wired in parallel they should be fused, as the potential current of any two is potentially big enough to cause a problem in the event of a flaw in the third.


Perhaps more later,

Icarus

Thanks much for the comments, I'll do another update in a bit.

First, I made a major error when moving things around in the drawing and had the 300 amp t fuse coming off the receptacles & appliances. Fixed in this version.

Updated: View attachment System Diagram - Sep 15, 2014 2009.pdf

That is better. Now change the arrow directions so 12 volt power goes from battery bank to the inverter. How big a battery bank? 2000 watt Magnum may require more than two batteries? Magnum lists MS2012 as 2000 watt not 1200.

Do not know your power usage, but 350 watts of solar should be enough. I have a 205 watt panel and do not need to use shore or generator or connect to the Sprinter 12 volt system. It has been 10 months since I changed from a 135 watt panel to the 205 watt panel. Only solar charging since the change.

icarus said:

I also would consider increasing the wired size in the PV leads, especially if you are ever going to add additional panel capacity.

Click to expand...

I am very open to thoughts here, and would greatly appreciate knowing how to properly calculate these values.

Our system maxes out - due to roof real estate - at 4 panels or 600 watts with our current panels. Panel specs can be found in the attached PDF.

Wire gauge was calculated using the BlueSea calculator found Here.

And the following assumptions:

• Max current applicable to the Kid (30 amps) - which should be more than we can produce with 4 panels if my numbers are correct.
• Closest voltage in calculator which is less than Vmp (more loss)
• A couple extra feet of conductor (more loss)

Then I chose one standard wire size larger than the value returned.

A copy of the calculator values can be seen here:
View attachment 62446

Graphite Dave said:

That is better. Now change the arrow directions so 12 volt power goes from battery bank to the inverter.

Click to expand...

Thanks, I made them bidirectional - for invert and charge

Graphite Dave said:

How big a battery bank? 2000 watt Magnum may require more than two batteries?

Click to expand...

Four batteries would certainly be better, and will likely happen in the future.

Graphite Dave said:

Magnum lists MS2012 as 2000 watt not 1200.

Click to expand...

Yup, thanks for that.

Graphite Dave said:

Do not know your power usage, but 350 watts of solar should be enough.

Click to expand...

We use the unit for both recreation and mobile office with our laptops, etc. While working we can easily pull 250-350 watts at any given time.

Latest version: View attachment 62447

I am not an expert on system design so would call Magnum to see if they have any recommendation for size of the battery bank to support their 2000 watt inverter.
I have a Magnum MMS1012 1000 watt inverter with one 255 amp-hr 8D AGM battery. I also have the Magnum ME-RC50 remote and the Magnum ME-BMK shunt.
When I set up the system I used the remote to tell the Magnum what size battery I had, type of battery and charge rate. (maybe some other settings, but I forget) Can you do the setup without the meter? I have been very pleased with the 3 components and how they work together to keep me informed of my SOC. I could care less about amps in/out or any other information. I just set the meter to SOC and use that to tell me what to do. I did notice you have a Trimetric TM-2030 shunt and not the Magnum shunt and meter.

Did just see you are in the Pacific NW so you need more solar panels than I due to the weather.

Graphite Dave said:

I am not an expert on system design so would call Magnum to see if they have any recommendation for size of the battery bank to support their 2000 watt inverter.

Click to expand...

They are very helpful. I'm lucky in that both Magnum and MidNite Solar are within about an hour drive.

Our battery configuration is reasonable at the moment, we rarely pull more than 350 watts. For the sake of increasing capacity, we will likely add 2 more batteries in the future, and/or switch out the type/chemistry. Also, probably add a small true sine inverter such as the MorningStar 300 Watt (suggested on Wind & Sun forum) to decrease the overhead of the larger inverter when possible.

Another suggestion from the Wind & Sun forum was to increase our battery cables to 4/0. The latest drawing shows that update. View attachment System Diagram - Sep 16, 2014 1430.pdf

Yes, we are in the Pacific Northwest... If only PV worked from rain....

There is a new post "sprinter AC/DC house electrical diagram" where some one stated that you can not program the Magnum charging profile with out the RC-50 remote. I also found the remote to be very useful to monitor the house battery SOC. I did use the remote to setup my system so charging profile matches my 255 amp-hr Lifeline AGM battery requirements.

The key is to design is a balanced system. That means the solar, batteries and inverter (power needs) need to match. You're only as strong as your weakest link.

Do you really need 2000W inverter? What's driving that? The microwave? You may need 6 batteries for that.

600W solar is huge! I just have 130W, & 2 x 6V bats. The charge controller is usually in absorption mode by 1pm. At this time the batteries don't want all the current that the 130W panel can supply. 600W and 4 x 6V's doesn't seem balanced to me. Depending on your power needs, get more batteries or less solar.

You want a disconnect switch between the panels and the charge controller, not a breaker. If you're really concerned about safety then install a 10A fuse for each panel. If you have 5 panels, then you need 5 10A fuses. BTW, you can only fuse 3 or more panels in parallel. Two panels can not be fused.

Cal

Thanks Dave,

Ended up getting the ARC-50 remote for just that reason, as it allows much more configuration.

calbiker said:

You want a disconnect switch between the panels and the charge controller, not a breaker. If you're really concerned about safety then install a 10A fuse for each panel. If you have 5 panels, then you need 5 10A fuses. BTW, you can only fuse 3 or more panels in parallel. Two panels can not be fused.
Cal

Click to expand...

Thanks Cal,

The breakers are also rated as disconnects, just added a note on that. The fuses are already in.

Here is the latest version: View attachment ScoCan - Charging & Solar System Block Diagram - Sep 16, 2014 1910.pdf

I agree with CalBiker. The trick is to have a balanced system design where all the components are the correct size relative to each other. The size of the system needs to match the needs of the user. One size does not fit all. What I build may be entirely inappropriate for someone else who does not have the same requirements.

To start a reasonably accurate list of what electrical items need to be listed with their amperage and then a reasonable length of time they run needs to be estimated. From the chart a system then can be designed. A big help here is to review what others have done for a similar use. Another useful tool is the "Kill-a-Watt" meter. Plug the items in at home to see the actual amperage they draw.

Somehow I lucked out with my system. It fits my use very well. I was a bit short on solar so fixed that with a change from 135 watt panel to a 205 watt panel. I probably have too much battery capacity because I seldom get below 86% SOC. I dry camp without access to shore power and have excess capacity so I can travel without being concerned about lack of power.

One mistake that is made is "more is better". A larger system has added cost, space and weight. OK if your needs require it but a larger system can be worse than a smaller system. All inverters have about 85% efficiency. The 15% loss on a large inverter is more than the 15% loss on a smaller inverter. Leaving my inverter on overnight will use 8% of my battery capacity without any 120 volt loads. I only turn inverter on when I need 120 volt power.

A 2000 watt inverter and large battery bank is not required to run a microwave. I run a 600 watt microwave on a 1000 watt Magnum inverter and 255 amp-hr. battery. Microwave use reduces the battery SOC by 1% for every two minutes of operation. I tried a 700 watt microwave initially that worked once but not again. Replaced with 600 watt and have run that for 10 minutes straight. I am into the surge capacity of the inverter but it does work.

Hi Scocan,
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Download free e books on multiple subjects and learn plenty along the way from a long established business building top end products, that puts out extensive and valuable info for everyone's benefit. Doubt that you will be disappointed.

In my conversion I used 1000W Magnum converter. The only use for this inverter is the 600W Microwave, for me an absolute corner case. High power inverter increased complexity of the conversion significantly. It was my mistake. So think thoroughly about your key AC needs in off the grid situations, there is a major tradeoff of high power off the grid AC needs versus complexity.

Another point is that the standby current on small inverters is lower than on large inverters http://www.morningstarcorp.com/products/suresine/ 55mA and http://magnumenergy.com/wp-content/uploads/2012/08/64-0036-Rev-A-MMS-Series.pdf is 5W in the search mode – 420mA and a whopping 19W – 1.6A in no clicking standby. Very likely I will get the Morningstar 300W unit due to lower standby draw as a primary unit (Icarus’ point).

For my actual needs a 300W sine inverter would be sufficient to power computers and camera chargers. A good 30-40A charger with a good battery monitor (like Link 10) would be good enough for me and it would fulfill the KISS principle.

George.

My balance goal is simple. I want a system that is Onan generator and propane free with no need to make a decision whether to seek shore power and be able to use all systems such as coffee maker, microwave and 120v AC outlets at all times. Air conditioning is a secondary concern as we by experience have successfully followed the seasons and the climate in our RV to avoid the need. We have a Class B with back door screen, side sliding door screen and five operable windows that will keep heat from building up inside at a campsite. Not many RVs have that capability. However, if we do need air conditioning during short stops in public places during the day when we can't open up with screening, the other desired requirements would allow a couple of hours to run the air conditioning.

I made an error in suggesting 10A fuses. If you start with 3 panels and get a short in one of the panels, the 10A fuse will probably not blow.

2 * Isc = 5.9A * 2 = 11.8A

A 10A automotive fuse may not open at 11.8A. I believe 10A current is guaranteed not to open a 10A fuse. It's better to go with a 7A fuse. Even if you add another panel later, stick with 7A fuses.

Cal

ScoCan said:

The fuses are already in.

Here is the latest version: View attachment 62467

Click to expand...

Taking a look at your solar cable sizing (I don't use on-line calculators, just my TI-85):

1. Calculating from combiner to charge controller: 12 ft, 8 awg

Imp = 5.5A

Total current = # panels * Imp = 4 * 5.5A = 22A

Resistance of 8 awg = 0.63 m ohm/foot

Total resistance = 0.63 m ohm / ft * 24 ft = 15.1 m ohm

Power loss = I^2 * R = 22A^2 * 15.1 m ohm = 7.3W

2. Calculating from charge controller to batteries: 8 ft, 4 awg

(Neglecting converter efficiency)

Charging current = 600W / 12.5V = 48A

Resistance of 4 awg = 0.25 m ohm/foot

Total resistance = 0.25 m ohm/ft * 16 ft = 4 m ohm

Power loss = I^2 * R = 48A^2 * 4 m ohm = 9.2W

If you're going with 600W then both cables are marginal. I think the goal is to keep power losses to less than 1%.

You got:

7.3W / 600W = 1.2% for the upper cable
9.2W / 600W = 1.5% for the lower cable

Cal

Any chance you have a parts list? I am building almost the exact same system, but not as learned as you on the exact components. Question specifically do you have a separate module that acts as a combiner or is that just a logical call out?
Question two for anybody. I am hooking three panels in parallel and they have blocking diodes to prevent current flow between panels in case of damage or a zero output situation per Kyocera documentation do I still need to fuse the individual panels with 7amp fuses?

Thanks everybody

Regarding your loads and inverter, I would first try to see how much of your load can be run DC. Laptops, game systems, audio, video, lighting, can all be done DC. The cost of a few DC-->DC adapters is far cheaper than upsizing batteries and inverter to cover the 15%-25% loss your 12vDC-->120vAC-->DC.

Is there any reason to fuse the solar panels, like it's not as if you'll get a solar flare and get super power surge? The only consideration I could see is if there is fault in the charge controller and power flows from the batteries into the panel cells in reserve, but they usually are diode protected. Using the MC4 connectors on the solar panels and running them into your van from parallel connections to maintain the 12volt system to single pair should be the way. It would be messy and costly to fuse at each joint.

Also could you forego a breaker at the charge controller since turning one off will be effective? Having two would only help to turn off the charge controller from obtaining any power.

Note I'm no expert, so if you're been advised by others then over read what I posted!