Comments on RV configuration

I got the bug to add solar to my truck camper to make those stays in the ski resorts more comfortable and less stressful. We take the camper up to the mountains about once a week in the winter, and we're always concerned about how much charge is remaining before and during the trip. We charge during travel and a generator during the day. The solar panels would be good to charge the batteries during the time it is parked in storage.

Being the impulsive person I am, I ordered 2-60 watt sunwize SW60 panels (17 volts), and a BZ250 MPPT controller. Right after that, I read the terrible reviews about the BZ product on this forum. I am glad for the smart input from members here. I just ordered a morningstar 15 amp MPPT controller instead.

First all, I'll like to know if any folks have any general comments about this equipment.

The 2 specific questions I have are:
Should I attach a remote battery temperature sensor? I think yes since the batteries are isolated from the main cabin.

Should the panels be connected in series to take advantage of the MPPT?

What gauge wire is appropriate for a 15 foot run?

Thanks.

Comments

  • mike95490mike95490 Solar Expert Posts: 9,583 ✭✭✭✭✭
    Re: Comments on RV configuration

    Yes, get the remote temperature sensor.

    But I don't understand the rest. A 10 or 15 W panel will keep the batteries topped off in storage - you would not need 120W.

    If you are currently running a generator, you may be able to reduce that to just a short run in the AM, and let the solar PV top of the batteries the rest of the day, I don't think 120W of PV will make a large dent in your generator run time. Use the gen to run the microwave & coffee pot and charge the batteries (while you are using the high power loads) and then shut down the generator.

    Do you have an accurate voltmeter or charge totalizer for the existing battery ? You will need to experiment with this for a couple days, to see how much you withdraw from the batteries, and what the solar vs genset replaces.
    Powerfab top of pole PV mount | Listeroid 6/1 w/st5 gen head | XW6048 inverter/chgr | Iota 48V/15A charger | Morningstar 60A MPPT | 48V, 800A NiFe Battery (in series)| 15, Evergreen 205w "12V" PV array on pole | Midnight ePanel | Grundfos 10 SO5-9 with 3 wire Franklin Electric motor (1/2hp 240V 1ph ) on a timer for 3 hr noontime run - Runs off PV ||
    || Midnight Classic 200 | 10, Evergreen 200w in a 160VOC array ||
    || VEC1093 12V Charger | Maha C401 aa/aaa Charger | SureSine | Sunsaver MPPT 15A

    solar: http://tinyurl.com/LMR-Solar
    gen: http://tinyurl.com/LMR-Lister ,

  • BB.BB. Super Moderators, Administrators Posts: 32,804 admin
    Re: Comments on RV configuration

    At this panel / controller size... It probably does not matter if you do the panels in series or in parallel...

    Personally, I would choose series connection and just use 14 AWG house wiring between the panels and the controller. Less wire to run.

    As always, make sure you have appropriate fusing between battery and the controllers/loads.

    And the RBTS should be bolted to the battery (per instructions)... Batteries are a big thermal mass and will not always be at the temperature of the air around them (keep batteries cool in the summer and warm in the winter--in the 70's F is the ideal range). Keep your batteries well charged in the winter to prevent freezing/case splits.

    A 120 watts of solar panels will probably run LED/Florescent lighting, plus a radio/small TV/fan very nicely... For trickle charging during off season, you only need around 5-10 watts per 100 amp*hours of battery capacity. (small panels, no need for charge controllers... If you have a lot of panels, then you will want a good quality charge controller with "float" mode).

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • System2System2 Posts: 6,290 admin
    Re: Comments on RV configuration

    That's the thing. We've been running blind with the battery levels.

    It's not clear that we are totally replenishing the batteries after each trip, so the 120 watts should definitely ensure that the batteries are full before the next weekend and provide enough power to replace the furnace draw.

    The generator feeds a progressive dynamics 40 amp converter. The batteries are two 105 ah flooded.
  • BB.BB. Super Moderators, Administrators Posts: 32,804 admin
    Re: Comments on RV configuration

    Read this battery FAQ first (if you have not already).

    If these are flooded cell batteries--then you need a temperature compensated hydrometer--the only 100% accurate method to measure battery state of charge (especially under load or charge) other than getting a battery monitor.

    Assuming Flooded Cell batteries, you want to ensure they spend as little time below 75% state of charge as possible. Below 75%, sulfates begin to harden (within hours) and you lose battery capacity (harden sulfates do not ever recover).

    So, that tells you how much power your can draw from your batter bank...

    210 AH * 25% = 52.5 Amp*Hours (1 amp for 52 hours, or 52 amps for 1 hour, etc.).
    52.5 AH * 12 volts = 630 watt*hours

    ...before you want to fire up the generator and begin recharging...

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • System2System2 Posts: 6,290 admin
    Re: Comments on RV configuration

    Checking the specific gravity would be brutal at 15 deg fahrenheit outside. Will the solar charge controller give an indication of charge level?
  • BB.BB. Super Moderators, Administrators Posts: 32,804 admin
    Re: Comments on RV configuration

    If the battery has sat with no current flow (charge/discharge) for 3+ hours, and you know the true temperature of the battery, you can use an accurate DVM to estimate the state of charge... Note that the difference between 80% and 70% state of charge is only 0.1 volts... So a calibrated digital volt meter and thermometer is absolutely necessary.

    Remember that a cold battery has much less capacity vs a warm battery. And a discharged battery freezes at a much "warmer" temperature than a charged battery.

    At ~-15F, a battery that is at 40% SOC (or less) will freeze (AGM will freeze, but will not be damaged, a flooded cell with break the case--don't recharge a frozen battery--warm it up first). A battery at 15F will only have about 65% of its capacity when warm. So--knowing temperature, how much power you are using, how much charge is left, etc. is all very important to make sure that you don't damage your batteries.

    The Xantrex LinkPRO also includes a battery temperature sensor--may be too expensive for your application (~$350?)... But, if you are in extreme conditions and would be in a world of hurt if your battery system failed--it may be worth the money to you.

    -Bill

    Some solar charge controllers estimate the battery state of charge--but it is not very accurate. A battery monitor is as close as you can get to a "gas gauge" for your battery that can give accurate answers in any conditions (under load, under charge, etc.).
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • nielniel Solar Expert Posts: 10,300 ✭✭✭✭
    Re: Comments on RV configuration

    i agree for you to get the bts and you may wish to enclose the batteries and give the enclosure some insulation. allow for a bit of room as you don't need a tight fit and i don't recommend a tight fit, especially at the top where you will want more room for the batteries to breath and make the connections easily.

    as to the 2 60w pvs, they can charge those batteries given enough time, but a long time it will be as each pv is rated at 3.3a. with 2 batteries rated at 105ah, this is 210ah battery capacity total and a rough max of 3.3a x 2 = 6.6a total pv charge current. one doesn't always see the max current from pvs and what you do have is boosted somewhat with the mppt. anyhow, 6.6a/210ah=3.14% for a charge percentage and we generally recommend in the range between 5 and 13%. in theory that would be 30hrs of full sun minimumly. this can be used to top off the batteries just fine with other charge sources providing the bulk charge.

    to properly comment on the batteries i really should've asked if they are 12v each or 6v each and i made the assumption they are 12v each. i also assume your needs to be 12v so stay with a 12v configuration on the batteries with 2 12v batteries in parallel. you could have the 2 pvs in series if you like or in parallel for the controller could handle it either way. if you go to add another pv into the mix then i'd suggest paralleling another of the same pv (all pvs in parallel for 3) as the max for the controller with a 12v battery configuration is 200w. these 3 pvs will be 9.9a and with 210ah of capacity this is a charge rate of 4.71%. this is still on the low side for a charge percentage, but is near the max wattage for that controller.
  • System2System2 Posts: 6,290 admin
    Re: Comments on RV configuration

    The batteries are enclosed and insulated. The battery box protrudes into the kitchen cabinet from the outside, so there is some heat to the batteries.

    The two 105 ah batteries are in parallel. From total output, does it make a difference between series and parallel. Does the MPPT convert the extra voltage to extra current for equivalent power?

    From a sulfation perspective, if the solar panels are slowly charging a discharged battery is sulfation prevented or do I need to quickly bulk charge?
  • BB.BB. Super Moderators, Administrators Posts: 32,804 admin
    Re: Comments on RV configuration

    To a degree, as long as you have the battery temp sensor and don't cook (over ~120 degrees) or freeze solid your batteries--you should be fine (aiming for ~70-80F would be ideal).

    In parallel, the Amp*Hours add, and the voltage remains the same (still 12 volts, but 105+105=210 Amp*Hours). If they where in series, the voltage would be 12v+12v=24volts, and the Amp*Hours would remain 105 AH total--still the same amount of stored power/energy--just available at a different voltage (to a degree, higher voltages require smaller wires and electronics, because the current is cut--remember P=I*V, double the voltage and 1/2 the current, same amount of power).

    From a sulfation perspective... If you pull your flooded cell lead acid batteries below 75% state of charge--you would want to that (or the next) day recharge them to above 75% state of charge... Using your genset to do bring the SOC up to 80-90%, then letting the solar bring up the last amount is a good way to do it (fuel efficient and less noisy--"bulk" charging the battery is much faster because the battery takes a lot of current... Finishing off the battery charging is slower as the charge controller starts to taper down the current flow--good time to let solar do its part). Hence Mike's recommendation to run the genset (and AC charger) first thing in the morning to make coffee and such... Then let the Sun pick up the charging after ~9:00am...

    Very roughly, # of hours of direct sun times panel rating (in watts) * 1/2 will tell you how much power you can get out of your solar panels per day...

    Say, 4h*120Watts*1/2=240 Watt*Hours in one day

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • icarusicarus Solar Expert Posts: 5,436 ✭✭✭✭
    Re: Comments on RV configuration

    Snowranger,


    Checking the sg at 15f is a piece of cake! Try doing it at -40f!

    Seriously, a couple of things to remember. While battery CAPACITY goes down with temperature, battery LIFE goes up, so in the long run, if you can keep your batteries cooler they may not have as much capacity but they will have greater longevity. If your batteries are in an insulated box you won't have any problem.

    After a while, through a series of trips you will begin to get a pretty good bal park idea of how you are loading the battery, and how you are are (re) charging it. I agree that a meter such as the Trimetric is a handy tool. quite simply you can see amp/hours out versus amp/hours in in real time so you can adjust either the loading or the charging as needed. For the kind of weekend trips you are talking about, you will find that on an average weekend you will use about the same amount of power week in and week out, so you will know how much you need to put back in.

    Tony
  • System2System2 Posts: 6,290 admin
    Re: Comments on RV configuration

    Thanks. I have a pretty good idea. We've done this for the past two seasons. However, I am always concerned about having enough stored power before the night since it is pretty rude to run the generator late. There have been a few occasions where the battery was unusually low. I think the solar will give that extra measure of storage over the week.
  • nielniel Solar Expert Posts: 10,300 ✭✭✭✭
    Re: Comments on RV configuration

    having the pvs seriesed or parallel is your choice. if parallel then any shading on 1 pv will not affect the output of the unshaded pv and in series shading would degrade the whole string. on the other hand the higher voltage with series helps overcome wiring losses and can start and maintain a charge going to the batteries sooner and longer unless shaded. understand that you aren't getting more power miraculously in either case. odds are it will be better in parallel as tree branches and leaves would cause the series shading at some time unless you're in a wide open clearing.
    edit to add:
    understand that a battery that is maintained even at 80% will still sulphate as what bill is saying with 75% is somewhat misleading. sulphation is something that occurs in nearly all batteries, but the degree of which is determined by how long a battery is not at full charge in its overall life. a battery that is topped off once a week will have more sulphation than one topped off every day. this is a process that occurs in the uncharged areas of a battery's cells. it also goes without saying that the deaper the discharge, the longer it is in an uncharged state in areas of the cells as it takes time to recharge. this is why having an average state of charge that is higher over a battery's life (or lower average dod) creates a longer life for the battery. having a full charge on a battery can almost guarantee that any given spot in the cells is not continueing that process. a battery maintained at 99% will develope sulphation in that 1% area over time. let's face it if a battery after 10 years has sulphation in 1% of it's cells' area, that is doing excellent. to achieve that the battery wasn't drained very far very long.
  • System2System2 Posts: 6,290 admin
    Re: Comments on RV configuration

    Thanks Niel. That last post was most informative about sulfation. I am glad that lead batteries are relatively cheap.
  • nielniel Solar Expert Posts: 10,300 ✭✭✭✭
    Re: Comments on RV configuration

    i wouldn't call any of them cheap in cost even if cheap in quality as the cost of metals have skyrocketed.

    edit to add:

    it seems i'm wrong as the spike in metals came down in the spring and is even lower now. i wonder when the batteries will start coming down in price to reflect the market downturn on these metals?
  • mike95490mike95490 Solar Expert Posts: 9,583 ✭✭✭✭✭
    Re: Comments on RV configuration
    snowranger wrote: »
    2-60 watt sunwize SW60 panels

    With your 120W of PV, I'll make a few assumptions, to provide an optimistic charge expectation from them. Real life may be a bit less.

    1) wired in series (~30V)
    2) MPPT charge controller w/Remote Battery Temp sensor

    5 hours of good, strong direct sunlight, with panels tilted to the sun {less if just flat on roof}

    Then you can expect to get about 80 - 90% of the nameplate power from the panels

    @ 90%, 120W = 108W * 5 hours = 540 watt/hours of power harvested
    in amps:
    108W / 14.5V = 7.44A * 5 hours = 37amp hours of charge
    (14.5V = charging voltage at battery terminals)
    Flooded cell batteries, only charge at 80% efficiency, so this 37AH would replenish 30AH of used battery charg.

    With 2, 105 A batteries (210A total) this is a marginally small amount of power, and so you would need to use some other source to bulk charge your batteries.

    What 30AH represents:
    (I'll use 12.5V as the battery voltage for calculation purposes)
    a 15w (1.2A) CF lamp running for 25 hours

    a 60W (4.8A) laptop running for 6.25 hours

    You can scale this to your other appliances.

    So while the 2 PV's are good for some light loads, and light topping off of the battery charge, it will take them over 3 perfect charging days to completely recharge a pair of batteries depleted to 50%, and sulphation will have already begun to set in. Don't get rid of the generator yet.

    Mike
    Powerfab top of pole PV mount | Listeroid 6/1 w/st5 gen head | XW6048 inverter/chgr | Iota 48V/15A charger | Morningstar 60A MPPT | 48V, 800A NiFe Battery (in series)| 15, Evergreen 205w "12V" PV array on pole | Midnight ePanel | Grundfos 10 SO5-9 with 3 wire Franklin Electric motor (1/2hp 240V 1ph ) on a timer for 3 hr noontime run - Runs off PV ||
    || Midnight Classic 200 | 10, Evergreen 200w in a 160VOC array ||
    || VEC1093 12V Charger | Maha C401 aa/aaa Charger | SureSine | Sunsaver MPPT 15A

    solar: http://tinyurl.com/LMR-Solar
    gen: http://tinyurl.com/LMR-Lister ,

  • mike95490mike95490 Solar Expert Posts: 9,583 ✭✭✭✭✭
    Re: Comments on RV configuration
    snowranger wrote: »
    We charge during travel

    Most automotive systems are set to about 13.8V, so as to not over charge the vehicle starting battery.

    Are you using a battery isolator (so your cabin lights don't drain the starter battery) ?

    Many isolators have a volt of drop across them.

    I would not be sure your vehicle is fully charging the camper battery bank, unless you are on a long, 15 hour trip. It will, however, at least supply a bulk charge, and get the battery up to about 80 or 90% of charge in a couple of driving hours.

    The PV panels will provide the top-off charge for you, and may even be enough to provide an equalize charge after a week of topping-off.
    Powerfab top of pole PV mount | Listeroid 6/1 w/st5 gen head | XW6048 inverter/chgr | Iota 48V/15A charger | Morningstar 60A MPPT | 48V, 800A NiFe Battery (in series)| 15, Evergreen 205w "12V" PV array on pole | Midnight ePanel | Grundfos 10 SO5-9 with 3 wire Franklin Electric motor (1/2hp 240V 1ph ) on a timer for 3 hr noontime run - Runs off PV ||
    || Midnight Classic 200 | 10, Evergreen 200w in a 160VOC array ||
    || VEC1093 12V Charger | Maha C401 aa/aaa Charger | SureSine | Sunsaver MPPT 15A

    solar: http://tinyurl.com/LMR-Solar
    gen: http://tinyurl.com/LMR-Lister ,

  • System2System2 Posts: 6,290 admin
    Re: Comments on RV configuration

    The isolator is a sure power one. I upgraded the charge line to the camper to 8 gauge I believe. Each weekend, we probably drive for 4 hours.

    It sounds like these panels will be for topping purposes, especially since this will be during winter. If I get the inkling to add more panels, can I get any kind? Are my limits 200 watts with panels in parallel and 400 watts with panels in series?

    I made the comment about lead being cheap since I just bought a bicycle lifepo4 battery for much more.

    Thanks.

    BTW-why do post appear backwards in the threads?
  • BB.BB. Super Moderators, Administrators Posts: 32,804 admin
    Re: Comments on RV configuration

    Regarding displaying your posts... Go to the top of page and look for "User CP" and click... Then scroll down on the left to Settings & Options, then click on edit options and scroll down 2/3'rds of a page to near the bottom. Thread Display Options, and click on pull down (mine is set to Linear--oldest first).

    You can try this link--it may take you directly to the "edit options" page (if you are already logged in--or have keep me logged in checked):

    http://forum.solar-electric.com/profile.php?do=editoptions

    Your question on limits... 200 watt vs 400 watt... The answer is--it depends on your charge controller... For example the Morning Star MPPT controller's maximum battery charging current is 15 amps, and it can charge either a 12 volt battery bank or 24 volt battery bank. So it is ~200 watts maximum of solar panels for a 12 volt bank or ~400 watt maximum for a 24 volt battery bank.

    Regarding charging using your truck's electrical system... You might have a better chance installing an Inverter in your truck, and running the 120 VAC back to your camper and plugging in your AC charger.

    In general, using the vehicles alternator+battery isolator is not a great way to charge deep cycle storage batteries. Using and inverter+charger or a 12 volt to 12 volt charger (don't know anything about the company or the product) (and here is another link to the product in a UK shop with more information and other models) would probably be better (although, more expensive).

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • System2System2 Posts: 6,290 admin
    Re: Comments on RV configuration

    The battery to battery charging is very interesting. It claims 5 times faster charging. My diesel engine at idle would consume .5 gallons per hour producing 50 amps compared to the ONAN at .3 gallons at 40 amps. This is not such a big difference, and the diesel engine is much quieter. Also, the instructions said that solar panels could be connected to the charger.

    Hmmm....maybe I shouldn't have bought the MPPT controller and bought this instead?

    Perhaps a 600 watt inverter may also fit the bill.
  • BB.BB. Super Moderators, Administrators Posts: 32,804 admin
    Re: Comments on RV configuration

    Or a Honda eu2000i running at 400 watts (~25 amps or a bit less charging a 12 volt battery) is 1.1 gallons per 15 hours or 0.07 gallons per hour...

    Even at full power (1,600 watts, 100+ amps at 12 volts--if you could find a charger that capable--probably not), 1.1 gallons / 4 hours or 0.275 gallons per hour... Matching a Xantrex TC-10 or TC 20 to the Honda eu1000i (10 amp) or TC-20 (eu2000i) would be an efficient setup. Or, running the same TC-xx off of a a vehicle supplied inverter, would also be good while driving.

    A ~20 amp +/- charger would match your current 210 AH battery bank pretty well (~5-13% of 20 Hour "AmpHour" rating is the rule of thumb for typical recommended battery charging).

    Don't know what will work best for you--but generally, finding a small, fuel efficient, genset that matches lower power (such as 3-15 amp max, 120 VAC) devices is pretty difficult outside the few Honda/Yamaha and inverter/generators and the knock-offs...

    Generally, running a vehicle motor to charge batteries/operate appliances is not a good use of fuel.

    A number that I use is around 5kWhrs (~400 watt) to 5.4 kWhrs (~1,600 watt) per gallon of gasoline for the Honda eu2000i (one of the most fuel efficient small gensets out there (in my humble opinion).

    Your diesel 50 amps * 14 volts / 0.5 gallons = 1.4 kWH/gallon
    Your Onan 40 amps * 14 volts / 0.3 gallons = 1.87 kWH/gallon

    The dedicated genset is around 3x more fuel efficient than either of the above (you will have some losses converting your 120 VAC to 12 volts for battery charging).

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
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