Adding solar for charging, I have grounding question for MPPT in an RV

EagleOneEagleOne Posts: 16Registered Users
Hello all, I'm new here (first post) but I have been reading for awhile. I searched but didn't find an exact match. I currently have two banks of batteries (500AH each) that I obtained from the unused stock years ago from my work. I have them in a 'step van' (some call it a bread van) and I have a Samlex 60A charger and an OnBoard Solutions 2500W MSW inverter. I also have DC lighting and outlets to run smaller TSW inverters. I have the switches/disconnects and appropriate fuses already in place.

I am going to be adding two Kyocera 315GX-LPB panels using a MorningStar TriStar MPPT60 c.c. I am reading the MS manual and it states that there is no internal GFDI, and it also states "Do not connect the system negative conductor to this terminal" when it is referring to the chassis ground on the MPPT. My 'system' currently has a vehicle chassis ground on a four post terminal on the negative side of the battery bank. My MSW inverter also has the chassis grounded to the vehicle chassis, with about three feet between the two grounds. Also, the 'system' is completely independent from the engine system (other than being grounded to the same chassis in a different location).

This vehicle is all aluminum/steel and it has 'electrical continuity' EVERYWHERE. Some of the posts that I have been reading have the term 'magic smoke' in them and I do not want to practice my magic skills.

I can mount the MPPT in a way that it is not in direct contact with the vehicle chassis if needed. Can you experts provide some advice about the proper way to ground the panels and the MPPT c.c.? Any advice will be more than helpful.

Thanks,
- Chris J.

Comments

  • CariboocootCariboocoot Posts: 17,615Banned ✭✭
    Re: Adding solar for charging, I have grounding question for MPPT in an RV

    Welcome to the forum.

    The Morningstar warning about not connecting the negative to the case ground is a reference to installing the NEC required DC ground-fault system (where it mentions there's no internal GFDI). Since yours is a mobile application there is no real Earth ground and so there's no need. With the GFDI negative has to be kept isolated from ground at all points (save one small resistor in the GFDI).

    I've been having a bad day, so I could be confused about this. But in standard off-grid installs (non GFDI) negative is connected to ground and all is well.

    Make sure the AC out from the MSW inverter is isolated from chassis ground and there is no neutral-ground bond there, otherwise the magic smoke is sure to come out.

    630 Watts of panel will work well on 500 Amp hours of battery. Not so well on 1000 Amp hours (the two together).
  • icarusicarus Posts: 5,108Solar Expert ✭✭✭✭
    Re: Adding solar for charging, I have grounding question for MPPT in an RV

    Also note, that in any mobile application, yr PV performance will drop considerably from "normal" due in large measure from the fact that the panels are rarely if ever properly oriented.

    Tony
  • EagleOneEagleOne Posts: 16Registered Users
    Re: Adding solar for charging, I have grounding question for MPPT in an RV

    Thanks Cariboocoot. I think it was you that posted "that's not enough panel" in some of the threads I was reading before. I have the two banks wired to a BlueSea 1/2/1+2/Off switch so I will have to gain experience on the actual solar charging compared to the AC charging capabilities. Icarus - I am expecting to not get full potential from the solar system (especially in the Seattle area), but I am guessing it will provide for my needs to start with. My system is just intended to provide the modern luxuries and is most likely overkill in many people's opinion. But at least I have enough roof to add another 'kit' in the future. I just ordered the 630W kit from NAWS and will be installing it after delivery. I absolutely refuse to ever have the 'need' to use a generator just to charge my batteries so I can have modern conveniences while camping and roughing-out power outages, although it would be cheaper!
  • ShadowcatcherShadowcatcher Posts: 228Solar Expert ✭✭✭
    Re: Adding solar for charging, I have grounding question for MPPT in an RV

    One thing to realize is that frame grounding as a connection is not a good idea. Our teardrop trailer has an all aluminum frame and nothing relies on the frame for grounding period. You are asking for trouble down the road (pun intended) with corrosion. If you use copper attached to the aluminum you are really asking for galvanic action problems. Part of this equation needs to be conservation, i.e LED lights low draw fans... I use an Espar diesel heater and we use AC only when on shore power.
    One of the better sources for RV solar is Handy Bob, nothing if not opinionated but what he does works. http://handybobsolar.wordpress.com/
  • EagleOneEagleOne Posts: 16Registered Users
    Re: Adding solar for charging, I have grounding question for MPPT in an RV

    Shadow - I am not sure exactly what you mean by 'frame grounding as a connection is not a good idea'. I am guessing that you are refering to using the frame as part of the DC return circuit, rather than an actual return wire run? My intentions are to provide proper grounding, and to have dedicated returns for each circuit in use.

    I have been reading about the corrosion issues with copper/aluminum mating connections. I have 'tinned' connections to bond my current ground to the chassis. I also ordered the GBL4-DBT lugs for grounding the panels to the chassis. I have read a good amount from the HandyBob pages. I am hoping to have a decent 'boondocking' setup for when I want to use it, and HandyBob has some good info for accomplishing this WITHOUT the need for a generator.

    Would any of you happen to have advice on MC4 connectors? Can I have them exposed to the elements up on the roof, or do I need to enclose them in a weatherproof box? I have made 'custom' mounts for the panels using UniStrut/SuperStrut so there are no roof penetrations but the 40" leads from the factory panels are not long enough to make it 'inside' the van where I will have all the c.c./Disconnects/Breakers etc. I am also planning on grounding the panels to the chassis, do you have any input on this? Is it safe to assume you have some type of solar setup on your teardrop? I am trying to avoid the need to use AC 'shore power' as well as a generator.

    Thanks,
    - Chris J.
  • CariboocootCariboocoot Posts: 17,615Banned ✭✭
    Re: Adding solar for charging, I have grounding question for MPPT in an RV

    Chris;

    You've got it right about the use of the vehicle chassis for conducting current. Run separate negative wires.

    The MC4 connectors are as weather-tight as you can get.

    I wouldn't bother grounding the panel frames to the chassis. Since there is no actual connection to Earth you won't gain any measure of safety by doing so.

    Disclaimer: it's early in the morning here, and I may have written all of that backwards. :p
  • EagleOneEagleOne Posts: 16Registered Users
    Re: Adding solar for charging, I have grounding question for MPPT in an RV

    Coot -

    Thanks for the reassurance. We are in the same time zone, and it is now late in the morning here and I am still working on my morning coffee so I might just be backwards as well.

    If you don't mind me asking, do you have 'real-life' stats on how many amp-hours of recharging you can get out of your 700W's of panel at different seasons of the year. I am guessing you are not putting your system under heavy discharge, but if you did drop it to 50% DOD and give the system some 'room-to-work', what could you get out of the BC weather? My Seattle area seems to be notorious for rain and cloudy weather. But when the sun shines here, I don't think the area can be beat!

    Thanks again,
    - Chris J.
  • CariboocootCariboocoot Posts: 17,615Banned ✭✭
    Re: Adding solar for charging, I have grounding question for MPPT in an RV

    Chris;

    I'm up in the Cariboo (hence the name) and that gives me two advantages: one, we don't get the horrible endless rain that dampens the spirits of coast dwellers; two, 3200 feet of elevation makes the panels run over 80% efficiency.

    Spring-Summer-Fall is no problem; usually everything works from May to October with minimal generator supplement. Winter is impossible: when you're down to 6 hours of daylight and can only use two that's just enough to keep the batteries up. We pack up and go in to town.

    I can in fact get over 2400 Watt hours per day, providing I time things right. My battery capacity is minimal; designed to see the essential loads run through the night. I have pulled the batteries down to 50% on purpose and there is no problem recharging them in a single day of good sun. I can hit 23 Amps peak current. It usually takes less than 2 hours for Bulk, and there's almost always one hour or more spent in Float.

    One big improvement has been replacing the desktop computer with laptop: more than 100 Watts difference over 8-10 hours. Another change will be made in the water pump department, as some people keep turning it on "after hours".
  • EagleOneEagleOne Posts: 16Registered Users
    Re: Adding solar for charging, I have grounding question for MPPT in an RV

    Thanks for the info Coot. It sounds like you are getting about as much as can be expected during the good times. And thanks for the watt-hours comparison, I noticed by your tag line that you have a 24V system?

    Otherwise, I might have compared my Amps to your Amps and my head might have increased in size. I need to finish the mounting and hook everything back up, looking forward to the numbers.
  • CariboocootCariboocoot Posts: 17,615Banned ✭✭
    Re: Adding solar for charging, I have grounding question for MPPT in an RV

    Yes, my system is 24 Volt. When you convert to Watts and Watt hours it makes it easier to compare different systems.

    Never should have said anything about rain: the forecast is solid downpour for the next week! :cry:
  • solarvicsolarvic Posts: 1,048Solar Expert ✭✭✭
    Re: Adding solar for charging, I have grounding question for MPPT in an RV

    Mark here in Pa we have a deficite of near 3 inch rainfall so need the rain and it is raining here today. Expecting cool and rainy weather for a week. Over memorial day weekend we had 92f temp like july in May. :Dsolarvic
  • EagleOneEagleOne Posts: 16Registered Users
    Re: Adding solar for charging, I have grounding question for MPPT in an RV

    Cariboocoot, et al -

    Thanks for the advice, I know that I appreciate it and I am sure other newbies do as well. I just thought I would pass along a status update now that the panels have been running for a few weeks.

    Last week I used my friend's RV (and my ice maker) to put a load on my 'mini-van' and it discharged it 300+ AH (12V) after about 10-12 hours. My inverter was the 'shore-power' for his RV. We had one day of somewhat cloudy weather, and a second day of decent sun. I was able to gather 1530 WH and 3090 WH over the two days to recharge the batteries. I did the same experiment this Tuesday night to drain the batts over 350+ AH, knowing the forecast for Wednesday was supposed to be sunny all day and temps in the mid to upper 60's, maybe a tad over 70. I collected 4180 WH with the 630W of panels. The TriMetric battery monitor shows 53 AH remaining and about a 95% SOC. The clouds are supposed to be back on Thursday, but I should be able to get them to float stage (hopefully).

    I haven't done the math to see how well my batteries are doing, but considering that they are about 11-12 years old (2000-2001 vintage, I forget?), I would put my mindset into the 'happy camper' category. Again, a big thank you to all the long-timers on the forum that take the time to help all of us rookies. All of this solar stuff isn't the 'golden child' that some make it seem to be, but it is definitely interesting and useful.

    May the sun shine brightly on everybody and the cool winds blow (or at least those with solar needs),

    - Chris J.
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