Trying To Get It Right 2nd Time - Permanent Boondocking

LastcarLastcar Registered Users Posts: 9 ✭✭
Hello all,

I have scoured the forum over the past three days and reluctantly post this. I hate to bug folks when I feel like I could find more on my own. But I am starting to head in circles and am back to being confused.

This is a very generous community on here and I admire your willingness to help no matter how much new members seem to end up giving back in future. You all deserve praise for that. I will do my best to be an ongoing contributor here if doing nothing more than sharing my experiences.

Anyways...onto my situation.

We have a travel trailer we leave in a permanent spot outside of Logan Lake BC. https://www.google.ca/maps/place/50%C2%B032'03.9%22N+120%C2%B038'18.2%22W/@50.534426,-120.638377,17z/data=!3m1!4b1!4m2!3m1!1s0x0:0x0

Able to position panels at various tilts and a static angle as desired toward sun's path. Minimal shading from trees for first hour or so of sun. No other shading.

Its new to us as of last week. It is a 2006 34 foot bunkhouse model with the factory battery bank at the front. Replacing an older 5th wheel. Don't yet know its phantom draw at "idle". Which I recognize could impact our amp hour needs as our current rig's phantom draw is 0.3a.

After years of use we have determined our power needs to be just shy of 100ah a day on the colder and less active days. Summer time when everyone is out and about much less. But this time of year the demand goes up naturally. More lights, some furnace time although we use a catalytic for primary heat, more down time using computers, tablets, TV etc. We are around 89 amps with most of that having to run through an inverter so we have our loss bringing it up to roughly 100amp hours.

Now when I am there alone which is more common this time of year I can converse and get no where near this. But when all four of us are up there of course the creature comforts come into play and we use more power.

Summer time we usually do two 8-10 day trips, long weekends and regular weekends. Spring and Fall we mostly do weekends with a few week long trips by myself. So for the most part not long stretches but certainly long enough if fussy weather. As a rule though bright and sunny in summer. Spring and fall can have some amazing days as well. Although by this time of year we are seeing more cloudy days than sunny days. To date no use after end of November.

In mid to late October we start to see temps dip below freezing with the real cold coming in November. Below freezing every night and up to 10 degrees below from time to time.

Currently using a system that seemed to serve us well but in some reading I have done can see why it came up short. Mostly my poor understanding of certain things, some bad advice followed and a few incidents such as a failed water pump running 24/7 for two weeks...or well until the batteries would hit the "load off" point. Neither here nor there now...lots learned and will hopefully do better this time around. I am sure there are experiences I have from the last three years that will help this conversation and I will chime in with them as asked or seem relevant.

No generators allowed where we are, which we love. And I have already bought some more stuff in the past few weeks that I wish I had waited but I knee jerked due to needing to get things on track before the Canadian Thanksgiving weekend.

Existing components from current system:

All LED lights

3 x 100 Watt panels

Voc 22.60v
Isc 5.53a
vmp 19.53v
Imp 5.17a


Charge Controller seems terrible. Was part of a package. No name and have no specs...other than was 20amp.

Batteries - just purchased 4 Trojan T-105s to replace three AGMs that seem to have failed. Two actually seem fairly functional after all but neither here nor there now.

I have since ordered two Renogy 100w panels and have those in the box still. Part of the knee jerk assumptions I was making.

Now realize the best thing you can do is come up with a heck of a solid plan based on some facts and not assumptions. I 100% acknowledge I am have made a bunch of mistakes...some as recent as 2 weeks ago in the purchase of more panels without having a plan other than spending more money...

Power needs are about as accurate as we are going to get. Until next year but in the short term I need to get something in place for November as I will be spending about 15 days up there and I have some help available to wire things up as needed that may not be around in the spring.

So again at peak we require just shy of 100ah per day. Have 5 100w panels. Committed to buying a new charge controller, battery meter, another panel.

My plan to date, which I am second guessing the heck out of:

5 100w panels wired in parallel

Morningstar Tristar TS-60 PMW (OR Morningstar Tristar TS-MMPT-45 but haven't figured out why, not saying I shouldn't just don't know if I need to)

Trimetric 2030

Wiring from panels will be able to be under 14 feet. All other wiring will be able to be minimal as well. Currently plan to use factory wiring from stock battery bank area to get power into the trailer.

Traditionally what I have done for AC is plug the shore power into the inverter and toggle it using a RF toggle i installed on the inverter.

Will add all needed fuses, shunts etc. Although could use some advice on this but have found some pretty good drawings from other sources. More than willing to use a combination box. And of course any other tips.

Planned to build a frame and place panels on the roof. Will adjust the tilt for spring/fall and summer. Will be placed on the roof in a way that creates no shading and is close to the factory battery bank as possible.

And open to what other feel is ideal. Doesn't have to match what I have...although suggestions on how to get the best out of what I have appreciated of course.

Thanks in advance.

Kye

Comments

  • CariboocootCariboocoot Banned Posts: 17,615 ✭✭
    Re: Trying To Get It Right 2nd Time - Permanent Boondocking

    Welcome to the forum Kye.

    Well any off-grid system starts with loads, but unfortunately that's somewhat of an unknown here.

    But you have got four T105's so maybe we better start there. No doubt it's a 12 Volt system. Any inverter & 120 VAC loads?

    The T105's at 225 Amp hours and 6 Volts each (450 Amp hours @ 12 Volts total) will give you a fair amount of power: up to about 2.5 kW hours. The issue is recharging them, especially without a generator. But you do have shore power available, yes? That would be a big help.

    First off the 20 Amp controller is a no-go even if it were any good. You've got 450 Amp hours and that means you want a target of 45 Amps at 12 Volts minimum. That would be at least 700 Watts of array on an MPPT charge controller. As our sunlight drops to negligible in Winter even that will not be enough. Certainly your five 100 Watt panels won't do it.

    So there are a couple of questions such as how sure are you about your power usage and battery bank size? Using 100 Amp hours from 450 would be about right. Another question would be how committed you are to avoiding shore power for recharging? Frankly with the right equipment it would not be too difficult to use the shore power as a "generator" input if the battery Voltage falls too low and needs to be boosted up.

    If I were you I'd avoid buying any more equipment just yet. You need to know what to buy first, and we're not at that point.
  • LastcarLastcar Registered Users Posts: 9 ✭✭
    Re: Trying To Get It Right 2nd Time - Permanent Boondocking

    Thanks for the quick reply!

    I guess the better question ask is there a good "How to build a system" article or book? Not to say I don't appreciate everything you guys may provide, just want to to the heavy lifting and have you guys top up the information to my exact needs. I'll stop calling myself a burden if you guys are into it though. I am happy to have you help all the way. :) Solar is a tough subject to find quality info on!

    Loads are not 100% accurate but they are close. Using either the change in draw on the CC or using my mid grade meter. I converted the AC draw to amp hours using I=W/V then x10 to get to DC amps. Not as precise as a proper assessment but I did do it as properly as I could, albeit with potentially less than ideal equipment.

    Again open to this being flawed.

    Yes, 12V.

    Inverter 600w (likely some chinese made model but pure sine wave and seems to be of decent quality)

    Ac loads: Macbook Pro, Macbook Air, iPad, couple iPhones, iPods, Magic Bullet, TV

    No shore power of any kind in proximity to the trailer.

    Although could place batteries in utility trailer to get me through the fall and run them down to an AC outlet bank available for charging and charge them that way. Leave them there while I am out during the day and tow it back up and reconnect. Although not convenient, seems like short term pain for long term gain vs building a poor solar system out of haste.

    Had contemplated also rigging things up so that it would be moderately easy to do this anytime of year. i.e. build batter bank on a sliding platform that could with some ease despite weight be transferred to utility trailer and moved down the hill for a charge from AC. Certainly wouldn't want this to be an everyday thing but a few times a year as needed would be the back up plan.

    Come fall may be a more regular activity.

    No intention to keep that 20A CC. It has days have been numbered for some time.

    One other thing, on the old trailer and will do on the new one is to disconnect the charge portion of the built in converter so when plugged into shore power we are not creating a charging loop. Assuming this is a valid step?

    For peace of mind...cause it is killing me trying to solve this. Let's say my needs are 100ah a day, what set up is recommended? Assume we are stuck with the panels (but can add more) and batteries. Everything else I am willing to purchase. And Cariboocoot we certainly share the same climate give or take. Not that far apart relative to the sun.

    I promise to buy nothing and do some load testing! I'll pick up a Kill-A-Watt or whichever device you all suggest. I'll opt for the manual charge process by dragging the utility trailer down the hill during the day while I am off fishing and not using power. Don't want to be the guy who asks for advice and then goes rogue and does what he wants. You know...like our kids all do. ;-)
  • CariboocootCariboocoot Banned Posts: 17,615 ✭✭
    Re: Trying To Get It Right 2nd Time - Permanent Boondocking

    There are some book recommendations in the reference section. I haven't read any of them. I haven't written any of them either. Not yet anyway. :D One thing about "how to" and off-grid is that every system is different, so the only thing that really can be covered in a book is the basics.

    If we can go with the loads being good enough then the battery bank size is also okay. It then becomes a matter of how to recharge them. Not having generator or shore power available is a big drawback because of those 6 hour Winter days. You really can't cram the power back that fast:

    45 Amps over a normal 4-5 hour charging day becomes 90 Amps trying to get it done in the 2 hours of good sun you have in Winter. The batteries will not take that kind of current. Nothing to be done about that except change the batteries or change the charge source. It doesn't matter how many Watts of panel you put up, no sun equals no power.

    So what happens if the power fails? How much of a disaster is it?

    The idea of loading at least half of the batteries up and taking them for a drive to Kamloops (or wherever) isn't unrealistic. In fact with the right set-up they can be charged from the vehicle while driving.

    A Kill-A-Watt is good for measuring AC loads and certainly worth it even when you're on grid and looking for what's running the bill up. The RV is mainly DC loads though, so it won't be as big of a help.

    Running the panels up to the max you can fit and using a good MPPT controller that can limit the current to the batteries will buy you some charge time on less-than-perfect days.

    My system is not in use all year. Frankly if I were there now (and I have been) the generator would be on about 2 hours a day to make up for the sun we already are missing. This is not a good locale for year-round solar. :cry:
  • LastcarLastcar Registered Users Posts: 9 ✭✭
    Re: Trying To Get It Right 2nd Time - Permanent Boondocking
    My system is not in use all year. Frankly if I were there now (and I have been) the generator would be on about 2 hours a day to make up for the sun we already are missing. This is not a good locale for year-round solar. :cry:

    Mine is May to November. Which to be fair is pretty much approaching winter sun in Nov. Luckily I just have go about 300 yards to where I can connect them to a traditional charger. So maybe that is the best bet for this time of year.

    Losing power would not be ideal but very manageable. I can keep the two AGMs from the previous system topped up and swap them in to get us through the time needed to get the Trojans back up to speed.

    If I was able to cut the power needs in half in late October and November (which may be dreaming with the need for the furnace a bit more) then would 6 x 100w panels with a 60 watt MPPT be a start? When it is just me I am pretty diligent on power usage. But do like watching hockey or football on the laptop in the evenings. So one laptop for 4 hours would still be on the docket. I can live with no furnace over night so it'd be just for a bit of top up in mornings and evenings before heading off for the day.

    Really for 80% of our season the "proposed" system is probably overkill but I guess that is never the point of solar. Always plan for the leaner times. It does get 4 or 5 days of no demand other than phantom load while we are back home. Giving it some breathing room to top back up. But again, October and November we may get very poor sunlight days.

    I am somewhat second guessing my power numbers as well...which I think you guys all probably did from the beginning. ;-) May be a bit high...while my draw numbers are based some measurements with potentially flawed tools, my time of use per day may be flawed. Too high.

    Any advice on how to measure load from DC draws that is actually accurate?

    And so far if I can draw some conclusions from our conversation where we've assume my power needs are close to right:

    go MPPT

    go to at least 6 100w panels if not 7

    sure as heck figure out my actual power needs

    build the battery housing to make a trip to the AC charging location relatively easily and be willing to lean on that in low sunlight times
  • CariboocootCariboocoot Banned Posts: 17,615 ✭✭
    Re: Trying To Get It Right 2nd Time - Permanent Boondocking

    DC loads can be measured with a DC Ammeter (clamp-on), battery monitor (uses a shunt to measure all power going in to and out of batteries), or a small "loads only" meter like the Doc Watson. Ultimately the battery monitor will be the most useful for you.

    You probably won't be able to reduce power usage as sunlight fades in the year as inevitably that's when you need more for lights and furnace. I think you will have to rely on being able to cart the batteries off for a charge from time to time.

    600 Watts of panel would work but >700 would actually be best. To that end you might want to reconsider the panel choice now, instead of investing in more 100 Watt 12 Volt units. Unless you are getting them at a really good price these small panels may not be much of a bargain. As you increase the number you increase the complexity of the wiring: more than two parallel connections and you should be using a combiner box with breakers or fuses per string.

    This points toward the use of GT style panels, which are usually much cheaper per Watt. They are generally over 200 Watts too, so fewer panels to get the power you need. The MPPT controller will take care of the Voltage difference.

    For example I bought two 260 Watt Conergy panels from a place in Kamloops this year for $300 each. How does that compare with your 100 Watt Renogy units?
  • LastcarLastcar Registered Users Posts: 9 ✭✭
    Re: Trying To Get It Right 2nd Time - Permanent Boondocking

    For example I bought two 260 Watt Conergy panels from a place in Kamloops this year for $300 each. How does that compare with your 100 Watt Renogy units?

    $120 USD shipped and I pick them up in Blaine. I declare everything but don't often have to pay duty. Very open to paying it, just doesnt seem to happen much.
  • CariboocootCariboocoot Banned Posts: 17,615 ✭✭
    Re: Trying To Get It Right 2nd Time - Permanent Boondocking
    Lastcar wrote: »
    $120 USD shipped and I pick them up in Blaine. I declare everything but don't often have to pay duty. Very open to paying it, just doesnt seem to happen much.

    Well that's $1.20 per Watt vs. $1.15 per Watt, going to Blaine vs. going to Kamloops, and seven panels with a combiner vs. four without. Your choice.
  • AuricTechAuricTech Solar Expert Posts: 140 ✭✭
    Re: Trying To Get It Right 2nd Time - Permanent Boondocking

    If it's feasible, you might want to consider running two PV arrays: one with your original three panels and a PWM charge controller, aligned facing southeast (to begin charging as early in the morning as possible), and a second with 600-800 Watts worth of GT panels (or more Renogy panels wired in series) and an MPPT charge controller, aligned facing south (to maximize charging during the time of peak insolation).
  • LastcarLastcar Registered Users Posts: 9 ✭✭
    Re: Trying To Get It Right 2nd Time - Permanent Boondocking
    Well that's $1.20 per Watt vs. $1.15 per Watt, going to Blaine vs. going to Kamloops, and seven panels with a combiner vs. four without. Your choice.

    We live in Vancouver and are down across the line a few times a month. So while not ideal not the end of the world. Its an hour each way to Kamloops from our place up there as well. So these even out.

    Its closer to 1.30 per watt for the 100w renogy though with exchange. But remember 3 of 100W panels are already bought and paid for 4 years ago. But would need to add 2 more to go with the 2 just purchased. I am sure I can sell the 2 Renogy's in the box for what I paid so not likely to be any financial loss there. Selling the other three used to end up with better system is A OK with me. Very open to the idea of selling off what I have and starting fresh for sure. So your advice is not falling on deaf ears.

    What brand are the ones you are referring to? Just so I can sort out dimensions as I am still hoping to roof mount these. Much prefer what you are suggesting, just have to weigh all the pros and cons.

    Also like the idea of more voltage per panel...but may be for flawed reasons. Does an 18.5 volt panel lose its ability to generate enough volts to charge a battery properly in low light? I.e. cloudy days can the voltage drop below 14.8v and in turn be doing little to give you much of a charge? Or I am out to lunch on this?

    I did order the Trimertic 2030-RV meter with cable and shunt, so I will get some much better numbers for my needs through the next month. So come spring when its time to make the final purchase decisions we'll know exactly what we are dealing with.
  • LastcarLastcar Registered Users Posts: 9 ✭✭
    Re: Trying To Get It Right 2nd Time - Permanent Boondocking
    AuricTech wrote: »
    If it's feasible, you might want to consider running two PV arrays: one with your original three panels and a PWM charge controller, aligned facing southeast (to begin charging as early in the morning as possible), and a second with 600-800 Watts worth of GT panels (or more Renogy panels wired in series) and an MPPT charge controller, aligned facing south (to maximize charging during the time of peak insolation).

    Thought about that too. I will probably at some point start to take some heat from my other half if I turn our place into a solar farm. But if it can all be roof mounted she will be ok with it. New rig has sky lights...so I will have to make sure those aren't blocked. They do make up for the lack of windows in the kitchen area.

    I think we'll have a much better idea what we are up against once I get some bette usage numbers. I absolutely get now why that matter so much. Taking stabs in the dark (no pun intended) is pointless, expensive and setting one up for frustration and lack of power. There is no way one can accurately guess what they need. I should have known better.

    I'll rock the battery wagon as mentioned in early posts to charge them as needed for the balance of this season then we'll have all winter to sort what I need. Heck, maybe one can even get better deals in the winter?
  • AuricTechAuricTech Solar Expert Posts: 140 ✭✭
    Re: Trying To Get It Right 2nd Time - Permanent Boondocking
    Lastcar wrote: »
    Also like the idea of more voltage per panel...but may be for flawed reasons. Does an 18.5 volt panel lose its ability to generate enough volts to charge a battery properly in low light? I.e. cloudy days can the voltage drop below 14.8v and in turn be doing little to give you much of a charge? Or I am out to lunch on this?

    I'm pretty sure that what drops in low-light conditions is current, not voltage. However, as panels heat up, they produce less voltage, so that might come into play in your application.
  • CariboocootCariboocoot Banned Posts: 17,615 ✭✭
    Re: Trying To Get It Right 2nd Time - Permanent Boondocking
    AuricTech wrote: »
    I'm pretty sure that what drops in low-light conditions is current, not voltage. However, as panels heat up, they produce less voltage, so that might come into play in your application.

    This is correct: low light = low current because PV is a current source. The slightest bit of illumination will give you Voc, but nothing usable when you put the load on.

    Higher Voltage is only an asset if you have to overcome V-drop in long wiring or have an MPPT controller that can down-convert higher array Voltage to greater charging current. Otherwise it can be detrimental - as I just explained to someone else showing two panels on an PWM controller where one panel is "higher Watts" but the actual power available for charging is the same because they have identical Imp ratings and the greater Watts comes from higher Vmp rating.
  • LastcarLastcar Registered Users Posts: 9 ✭✭
    Re: Trying To Get It Right 2nd Time - Permanent Boondocking

    So I have my Kill-A-Watt meter and my Trimetric 2030-RV in hand. Off to the trailer Thursday through Sunday. Will do my best to get a read on all the various draws and come back with some #'s that will help us sort out demand a bit better.

    Assume I should use the Kill-A-Watt when drawing power through the inverter at the trailer? Or can I be testing those items at home as well/instead? As in are the numbers going to look the same at home on grid vs at the lake on batteries and inverter?

    One thing I did notice (at home) when the laptop was plugged in the amps jumps around quite a bit. From about .24amp to .55amps. Assume this is also normal? I left it on and either charging, floating or in use for 20 hours and it was at .2 KWh. Came out to an average of 0.1KWh per hour. Which seems to work back into 4.55amps DC.

    But jump in on my bad math here.

    Anyways, any tips or guidance when measuring things this weekend?
  • CariboocootCariboocoot Banned Posts: 17,615 ✭✭
    Re: Trying To Get It Right 2nd Time - Permanent Boondocking

    You can test things with the Kill-A-Watt anywhere as the power source doesn't matter; you're looking at how much the load actually consumes. Quite often you can test 'similar' items at home before planning the off-grid build just to get an idea how much power you'd use under 'normal' conditions - and to see how far off the calculation method really is.

    Don't get hung up on the Amps, especially with a computer; their draw changes depending on what they do. Every time the hard drive activates the current demand increases for one thing. Running accessory connections will do the same thing. You're really looking for total Watt hours over a normal usage time and the combined maximum of everything you want to run.

    How the AC Volt Amps or Watts converts to DC is not quite as straightforward as a factor of 10 for a 12 Volt system; in between you have the inverter efficiency and consumption. If the inverter is operating at 95% efficiency then 100 Watts AC becomes 105 Watts DC. If it's 85% the change is to 118 Watts DC. The inverter will draw a consistent amount on top of that. Both of these factors depend on the particular inverter.

    The TriMetric will show fairly accurate current flow to/from the battery. If the batteries are new and fully charged and the monitor is programmed correctly it will also give you a good indication of SOC during cycles. If not, it will be inaccurate for that function. It has to know the battery is 100% and a capacity of 'X' with an efficiency of 'Y' to begin with in order to approximate SOC as current goes in and out.
  • Alaska ManAlaska Man Solar Expert Posts: 252 ✭✭
    Re: Trying To Get It Right 2nd Time - Permanent Boondocking
    Lastcar wrote: »
    We live in Vancouver and are down across the line a few times a month. So while not ideal not the end of the world. Its an hour each way to Kamloops from our place up there as well. So these even out.

    Its closer to 1.30 per watt for the 100w renogy though with exchange. But remember 3 of 100W panels are already bought and paid for 4 years ago. But would need to add 2 more to go with the 2 just purchased. I am sure I can sell the 2 Renogy's in the box for what I paid so not likely to be any financial loss there. Selling the other three used to end up with better system is A OK with me. Very open to the idea of selling off what I have and starting fresh for sure. So your advice is not falling on deaf ears.

    What brand are the ones you are referring to? Just so I can sort out dimensions as I am still hoping to roof mount these. Much prefer what you are suggesting, just have to weigh all the pros and cons.

    Also like the idea of more voltage per panel...but may be for flawed reasons. Does an 18.5 volt panel lose its ability to generate enough volts to charge a battery properly in low light? I.e. cloudy days can the voltage drop below 14.8v and in turn be doing little to give you much of a charge? Or I am out to lunch on this?

    I did order the Trimertic 2030-RV meter with cable and shunt, so I will get some much better numbers for my needs through the next month. So come spring when its time to make the final purchase decisions we'll know exactly what we are dealing with.

    When you wire the shunt ALL negative connections go to the shunt, only one cable goes from the shunt to the negative on your battery bank. In case you didn't know, because I didn't and had all my connections going to the bank then to the shunt and wondered why my readings were wrong. Doah...........


    CC mentioned charging from an alternator. Can you run a vehicle with an over sized alternator to help with your charging? Or is the "No generator" rule also mean no idling vehicles?
  • LastcarLastcar Registered Users Posts: 9 ✭✭
    Re: Trying To Get It Right 2nd Time - Permanent Boondocking
    Alaska Man wrote: »
    When you wire the shunt ALL negative connections go to the shunt, only one cable goes from the shunt to the negative on your battery bank. In case you didn't know, because I didn't and had all my connections going to the bank then to the shunt and wondered why my readings were wrong. Doah...........


    CC mentioned charging from an alternator. Can you run a vehicle with an over sized alternator to help with your charging? Or is the "No generator" rule also mean no idling vehicles?

    Certainly this time of year I can run the vehicle. And plan on it as needed if I get into a pickle.

    On that note, with the batteries in the utility trailer they'll be a bit far from the connections on the trailer. Am I off my rocker to use jumper cables to complete the connection? From batteries directly to the trailer wiring which has lugs that normally connects to the battery posts?

    It'll only be for this 4 day trip.

    On Sunday I will be able to do things differently as I will have pulled the wiring from the old trailer and be able to wire things in a bit better.
  • BB.BB. Super Moderators, Administrators Posts: 29,518 admin
    Re: Trying To Get It Right 2nd Time - Permanent Boondocking

    Charging from an automotive alternator to a remote battery bank can be problematic.

    First, a standard alternator is designed to output around 13.8 to 14.2 volts or so... A typical flooded cell lead acid deep cycle battery is really happy in the 14.4 to 14.8 volt range (when actively charging).

    Second, the voltage drop from the alternator back through 10-20 feet or so of cable/coupling at hitch, etc... Many times, that will limit a typical installation to around 10 amperes maximum current from the alternator to the battery bank. What gauge wiring is your charging connection, how long is the run (one way), and how much current do you wish to pass (5-10% minimum of battery bank capacity would be a good start... 220 AH battery bank, ~11 to 22 amps minimum).

    Third, you need to install a relay (or electronic relay) to isolate the trailer bank to vehicle battery to prevent RV use from discharging the vehicle battery.

    Fourth, automotive/light truck alternators tend to only output rated current when cold--As they get hot, the maximum output current tends to fall quite a bit.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • LastcarLastcar Registered Users Posts: 9 ✭✭
    Re: Trying To Get It Right 2nd Time - Permanent Boondocking
    BB. wrote: »
    Charging from an automotive alternator to a remote battery bank can be problematic.

    First, a standard alternator is designed to output around 13.8 to 14.2 volts or so... A typical flooded cell lead acid deep cycle battery is really happy in the 14.4 to 14.8 volt range (when actively charging).

    Second, the voltage drop from the alternator back through 10-20 feet or so of cable/coupling at hitch, etc... Many times, that will limit a typical installation to around 10 amperes maximum current from the alternator to the battery bank. What gauge wiring is your charging connection, how long is the run (one way), and how much current do you wish to pass (5-10% minimum of battery bank capacity would be a good start... 220 AH battery bank, ~11 to 22 amps minimum).

    Third, you need to install a relay (or electronic relay) to isolate the trailer bank to vehicle battery to prevent RV use from discharging the vehicle battery.

    Fourth, automotive/light truck alternators tend to only output rated current when cold--As they get hot, the maximum output current tends to fall quite a bit.

    -Bill

    Ya...read a fair bit about this. Seems decisive but I want to err on the side of caution for sure. So on second thought I won't do it.

    I should be fine, will charge them via an AC outlet a few hundred yards away and cart them back up the hill at the end of the day when I get back to the trailer.
  • BB.BB. Super Moderators, Administrators Posts: 29,518 admin
    Re: Trying To Get It Right 2nd Time - Permanent Boondocking

    There are ways it can be done... One is to put a 120 VAC inverter in the engine compartment and send AC power to a battery charger in the RV.

    Another option would be to install a marine alternator on the engine and you can adjust its output to better charge the battery bank. For example:

    www.balmar.net

    Even though the Balmar (appears) to have a 1 lead remote voltage sense--I am not sure that it would still be "easy" to get a reliable charging connection from the alternator in the two vehicle to the RV trailing. Sending 12 volts longer distances at high current is just ugly.

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