component isolation for 12V RV system

Greetings, I've been setting up solar power for a small van RV, and I'm adapting the old power distribution center to handle multiple power inputs. I'm using a Sunsaver 10 (LVD) to charge an existing small deep-cycle battery with a 75 watt panel, and I'm feeding the battery power from the LVD (low voltage disconnect) terminals into my 12V disribution buss via a 10 amp fuse. Everything seemed okay feeding a 12V incandescent fixture from the PV system, then I threw the breaker on for the old 45A 12VDC converter and my 10 amp fuse failed immediately. So I did some checking and polarity was correct, + to + etc., but at the time, my power supply was ~1.5DC volts higher than the battery voltage, and I also read ~4 volts AC in the DC output, so I'm assuming this would qualify as "unregulated". I see that 10 amp blocking diodes are common in PV systems, would one of these prevent the 10 amp PV input fuse from blowing when switching to converter? AFAIK, I have isolated the deep cycle battery from the old (and non-working) charging system, with the exception of the electric starter cabling to the AC generator. Also, It is my understanding that I could use the standard alternator output to partially charge the deep cycle through an isolator when driving, correct? Another issue is getting an inexpensive but capable deep cycle charge controller to recharge when connected to AC or running the generator. Anyone else been down this road? Many thanks for providing this forum...

K.D.

Comments

  • mike95490
    mike95490 Solar Expert Posts: 9,583 ✭✭✭✭✭
    Re: component isolation for 12V RV system

    I'm not sure where you are getting 4VAC in the RV, are you connected to a AC power battery charger?

    What's a sunsaver 10, a charge controller, AC charger, ????

    RV shops have Vehicle battery isolators, which should be adequate - it's just a big 80 amp rated diode.

    Will 75W panel be enough, or are you having an aux generator kick in automatically? Skip the generator, and add more panels, get rid of the incandesent cabin lamps, and get LED lights.
    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: 33,431 admin
    Re: component isolation for 12V RV system

    Regarding the fusing... Fuses protect "down stream" small gauge wire (and equipment like solar arrays, chargers, appliances) from getting dangerous amounts of current in the case of a short circuit...

    Assume that the battery has almost unlimited current.

    You connect a 14 gauge copper wire to the positive post (or bus bar) through a 15-20 amp fuse... Any shorts (or current sources) in the 14 gauge wire that exceed the fuse rating will be prevented by blowing the fuse.

    If you attach the sun saver to your battery with, say, an 18 gauge wire, you would connect the fuse between the 18 gauge wire and the bus bar.

    --So, you should have one common bus bar connection with fuses and their respective wires going off of them...

    It sounds like instead, that you have a 10 amp fuse connected to the battery and some major loads/current sources (solar charger, 45 amp charger, etc.) connected to the "down stream side" of the fuse. So, if there are any loads (or current sources) that try to take from (or input into) the battery that exceed 10 amps, you will pop the fuse.

    The 45 amp battery charger will need both heavy gauge wire and, at least, a 55-60 amp in-line fuse for protection. I don't believe that there is anything wrong with the battery converter (as best as I can tell from reading your post--of course, it could easily be bad).

    The issue of measuring the output of the 45 amp battery charger with a meter while disconnected from the battery is that many chargers will give a rectified sine wave output which you will see as an "unregulated" voltage with lots of AC voltage too (what you will read exactly depends on both the type of charger and the type of meter used to read the voltage--DVMs and Analog meters will read differently).

    The solar charger should be able to connect to the battery bus/system (through the appropriate fuse) without any concerns (you should have no issues with other charging sources properly connected to the battery). Check the manual for the Sun Saver controller--it should already contain the equivalent of a blocking diode... You probably don't want to add a blocking diode to the Sun Saver battery terminal--it can cause the sunsaver to under charge your battery (by the diode voltage drop).

    Yes, you can charge from your vehicle generator--but given the long run of, relatively, small gauge wire, the voltage drop of the harness will probably limit the amount of current that will charge the trailer battery. Unless you do something special, your vehicle will probably not satisfactorily recharge your trailer battery using car/truck's alternator.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • System2
    System2 Posts: 6,290 admin
    Re: component isolation for 12V RV system

    Okay, to clarify, I'm revamping an old RV van, and the power center still supplies 45 amps at ~12VDC when powered by AC (grid or generator). I have wired the battery output of a Morningstar Sunsaver 10 LVD PV charge controller, taking advantage of the low voltage disconnect feature to somewhat "idiot-proof" the system, since it will remove the load when the voltage drops to the point that the battery requires recharging. (Anyone who has ever gone RV camping with a family will understand my motivation.) Since the amperage rating of the Sunsaver is 10, I put a 10 amp fuse in-line between the LVD output of the Sunsaver and the 12V distribution buss of the RV. Yes, this will mean that turning on too many loads will blow the fuse, but better that than my controller! This also means that my single deep-cycle battery cannot be subjected to unduly high discharge loads either. So, while I was testing the PV system, by running a dual-bulb incandescent light fixture that probably pulls about 2 amps, I switched on my backup power converter (whatever charge control features it may have once had are no longer functional), and there was enough current into the Sunsaver module to immediately blow the 10 amp fuse, despite the fact that the wiring polarity was correct. So I am assuming that the higher DC voltage of the converter, the ~4VAC present in the convert output, or some combination of those and other factors was responsible for blowing the fuse. Understand that I am not trying to feed power into the Sunsaver, I just assumed that it would not allow what I'm guessing is a reverse current to flow when the ~12VDC convertor power is present on the distribution buss. Putting it another way, I figured the Sunsaver would work and play well with the convertor. It don't. So, would a 10 amp blocking diode (or two if necessary) effectively isolate the PV system when the convertor is online without having to switch it out manually? The alternative charging issues are seperate right now, since I have not obtained a deep-cycle charge controller or a battery isolator for that purpose yet, but it would be nice to at least get a jump on recharging by using power from the alternator while driving. Assuming that the PV controller would be finishing the job, since the LVD won't allow current to be pulled from the battery until it is recharged anyway, I think I have a reasonably good chance of preventing premature battery death. With the addition of an AC charge controller, I think I can depend on the battery to extend the end of the waking day by a few extra evening hours without resorting to using the noisy generator. Again, thanks for the advice...

    K.D.
  • niel
    niel Solar Expert Posts: 10,300 ✭✭✭✭
    Re: component isolation for 12V RV system

    "So, while I was testing the PV system, by running a dual-bulb incandescent light fixture that probably pulls about 2 amps, I switched on my backup power converter (whatever charge control features it may have once had are no longer functional), and there was enough current into the Sunsaver module to immediately blow the 10 amp fuse, despite the fact that the wiring polarity was correct."

    if i'm reading this correctly it sounds like the 45amp converter(charger) is defective. if this is the case be sure your sunsaver is still functioning as an incident i had with a charger that passed ac blew out my ss10 i used to have. the fusing my have actually saved the ss10 from blowing out as you fused input and output from what i gathered. no charger, not even a cheapo, should be showing 4 volts of ac. please confirm this with somebody inspecting its operation and let us know the result of your inquiry of the converter.
  • crewzer
    crewzer Registered Users, Solar Expert Posts: 1,832 ✭✭✭✭
    Re: component isolation for 12V RV system

    Kristopher,

    If I correctly understand your system, your connections look like this:

    1) The PV module is connected to the SunSaver’s inputs.
    2) The battery is connected to the SunSaver’s battery connections.
    3) The SunSaver’s load output is connected via a 10A fuse to the RV’s distribution bus.
    4) The RV’s converter is connected to the RV’s distribution buss.

    Assuming this understanding is correct, the problem probably lies with the converter’s connection to the distribution buss. Instead, the converter, which like the SunSaver is just another charging source, should be connected to the battery (via a fuse or breaker, or course). It’s OK to have multiple charging sources connected to the battery. Also, placing a fuse between the battery (+) and the controller will help protect the controller as well as the loads.

    Your vehicle’s alternator might be a third charging source, but this typically doesn’t work very well. The combination of the relatively low voltage at the alternator less the voltage drop described by Bill makes for a low voltage at the battery terminals. Accordingly, the alternator may work as a deep-cycle battery maintainer, but not particularly well as a charger.

    HTH,
    Jim / crewzer
  • System2
    System2 Posts: 6,290 admin
    Re: component isolation for 12V RV system
    crewzer wrote:
    Kristopher,

    If I correctly understand your system, your connections look like this:

    1)  The PV module is connected to the SunSaver’s inputs.
    2)  The battery is connected to the SunSaver’s battery connections.
    3)  The SunSaver’s load output is connected via a 10A fuse to the RV’s distribution bus.
    4)  The RV’s converter is connected to the RV’s distribution buss.

    Correct. The reason that the converter is wired to the DC buss is so that the lighting etc. will still work when plugged into the grid or running the AC generator. I'm thinking that it would be a good idea to use a relay to switch out the PV subsystem when the convertor is active, especially since the electric starter for the generator also pulls from the deep cycle. I realize that a 75 watt panel isn't going to keep up all by itself, although I will probably add another to the mix down the road. Having an extra hour or two of evening power for a TV and a light without having to resort to the generator or running the engine is all I'm trying for, and I don't mind running the generator for a bit during the day to cool off with the AC, perhaps run a vacuum, and do some microwave cooking. With the addition of a high amperage charger that can take advantage of the AC generator power when it's running, the PV will mostly have a "topping off" and off-season charge maintenance function. It occurs to me that I might have to use a delay for the converter DC output, to make sure the PV is fully switched out, but I guess I can test it first, since my 10 amp fuse apparently prevented the Sunsaver from frying (it's still working). I'm a little concerned about the ~4VAC present in the DC converter output messing with electronic devices (ie. 12V TV) though, guess I'll read up on MOV's and whatnot, to see if I can filter it out without having to replace the whole unit...

    K.D., C.T. (Compulsive Tinkerer)

    ;^]

  • mike95490
    mike95490 Solar Expert Posts: 9,583 ✭✭✭✭✭
    Re: component isolation for 12V RV system

    Can you post a simple sketch here of what is what, and how it connects, entire system. On another group, I spent weeks trying to sort out a problem, then I finally got a sketch: saved a lot of words (and lives !)

    (DO NOT TRY TO BUILD THE FOLLOWING SKETCH )
    text with sketch: This is a sketch drawing of how we are thinking the batteries get connected….Does this look right? Is there a smarter way to do this? We are placing the batteries in the tongue of the trailer so we have this triangle space to work with….Ultimately we are going for 48 volts with 16 : 6 volt / 400 amph batteries

    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 ,

  • System2
    System2 Posts: 6,290 admin
    Re: component isolation for 12V RV system

    My (simplified) system:

    [external 120vac] [120vac generator]
    | |
    [75w PV panel] [120vac breaker panel]
    | |
    [Sunsaver 10 LVD Charge Controller]
    [12v deep cycle] |
    | |
    [10a fuse]
    [12vdc power bus]
    [45a12vdc converter]

    All connections to the Sunsaver are dedicated (I didn't bond the negative terminals directly to frame ground), and of sufficient guage to handle the intended ampacity. The Sunsaver is fully functional, including the low voltage disconnect feature, despite having blown the 10 amp fuse on my first test. Since then, I have not placed both the LVD output and the converter output on the DC buss at the same time. Looking ahead, I'm considering using a relay, with delay if necessary, to prevent the two power sources from interacting (ie. blowing my 10 amp fuse!). I might try my hand at filtering the ac current from the converter output, I doubt it is good for any 12v electronics (ie. AV equipment) that might encounter it, if I can't identify any component problems within the converter circuitry itself. Perhaps a better option would be to install a seperate regulated DC power supply for my electronics, keeping the existing converter output for the incandescent lights and various control solenoids that don't seem to be adversely affected. Thanks for the input, I'll keep you posted...

    K.D.
  • BB.
    BB. Super Moderators, Administrators Posts: 33,431 admin
    Re: component isolation for 12V RV system

    Maybe I am missing something here... s the 45 Amp 12 VDC converter a battery charger? It appears to be from your wiring diagram--although Xantrex and some others (I am sure) make inverter/chargers that can do both functions automatically, depending on the voltages applied (consume 120 VAC and charge battery, or if 120 VAC is missing, consume power from the battery and generate 120 VAC).

    So, assuming it is a charger, you should have the 12 volt converter attached directly to the battery and not go through the sunsaver LVD... You are, at best, limiting the converter to a maximum of 10 amps to charge your battery--and if the battery triggers the LVD (low voltage disconnect), you will not be able to recharge your battery with the converter because it is disconnected from the battery...

    The only advantage that I can see how you have connected your Sunsaver/charger/LVD is that if you have the converter plugged in, you can draw more than 10 amps from your DC power bus when the converter is plugged into 120 VAC... If this is true--it is not a great idea--but it could work OK for you... Is this what you are trying for?

    Also, I have an old trailer with a 12 VDC converter in it (looks like a large computer power supply), and as I have said before, it does not put out a clean filtered DC wave form, and if I power the interior lights with just the converter (batteries disconnected), I get "dim" lights and some buzzing (AC 120 hz noise on a lower than 12 vdc average voltage). Once the inverter is connected to the battery, everything is fine. The battery acts like a giant filter capacitor. May not be the best thing in the world, but it does work fine.

    I would suggest that you only power small loads (less than 10 amps) from the LVD on the Sunsaver. These could be things you might leave on unattended (lights, radio and such)... The heavy loads are probably best directly connected to the batteries (through appropriate fuses).

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • System2
    System2 Posts: 6,290 admin
    Re: component isolation for 12V RV system
    BB wrote:
    ..is the 45 Amp 12 VDC converter a battery charger?

    It was originally, now it just supplies the existing DC buss with power when running the AC generator or using the RV external power cord.
    It appears to be from your wiring diagram...

    I just noticed that the composition window is not using the same text format as the reader, so I tweaked the spacing so it aligns in my Linux Mozilla browser window, your result may vary, but I will provide a more detailed graphic soon, to avoid the proportional vs. fixed spacing problem.
    ...you will not be able to recharge your battery with the converter because it is disconnected from the battery...

    Correct, I gave up on that some time ago. I'm basically rebuilding the deep cycle charge control system from scratch, for now using PV, but eventually combining alternator charging via a battery isolator with a seperate dedicated AC to DC deep cycle charger for more rapid recovery.
    ...you can draw more than 10 amps from your DC power bus when the converter is plugged into 120 VAC...

    That is part of the original system, the problem arose when I activated the convertor with the Sunsaver LVD output attached, some sort of "backcurrent" blew the 10a fuse. I have yet to determine if the problem exists when the LVD has cut out, it was passing current at the time the fuse blew, but I'm leaning toward using a relay to automatically lock out the PV subsystem when using auxiliary power.
    I would suggest that you only power small loads (less than 10 amps) from the LVD on the Sunsaver.

    Yes, that is the intention. A single battery won't last long enough to be truly useful with heavier loads anyway, so the 10 amp limit is an acceptable limitation. I will make a more detailed diagram before I try to address some of the other issues I have mentioned, and provide a link to it in my next post. Thanks...

    K.D.
  • BB.
    BB. Super Moderators, Administrators Posts: 33,431 admin
    Re: component isolation for 12V RV system

    I read your diagram correctly (pre-edit)... So, your converter is simply charging the battery by backfeeding the LVD terminal on the controller (I do not believe there would be any diode in the controller to prevent this...

    Until you get a new battery charger (which should be bolted to the battery directly), you should just leave the converter attached to the battery too. If you are loads are not heavier than 10 amps, there will be no problem anyway. By the way, you can have heavy loads (like a water pump) that draw more than 10 amps but because of their short duty cycle are compatable with use on a storage battery system.

    Alternator charging--not quite sure what you are referring too... Is this the standard alternator from the truck (car/etc.)? If so, you may wish to approach this in two different methods... One would be to replace your alternator (or alternator voltage regulator, if you can) with one for a marine installation with a proper charge controller.

    I forget where, but somebody posted here a website from an alternator/controller manufacturer that seemed to have very good charge characteristics (high current until the battery was near fully charged, then dropped back to more limited charge current). Most car alternators are not designed and optimized charge a large storage battery bank (let alone have settings for different types of batteries).

    Also, if you stay in the ~10-15% recommended charge rate for standard flooded cell batteries, you would need to run the engine for 8-10 hours to bulk charge a battery bank discharged to 50%--that is a lot of driving/idling (and fuel) every day or three.

    Another way would be for you to get one of those 1,000 watt or so cheap inverters and bolt it into your engine compartment to the battery. And connect the 120 VAC output to your 120 VAC to 12 vdc battery charger... May be cheaper and, depending on what kind of RV this is (trailer, motor home, or whatever), easier to wire...

    I guess I am not quite sure what kind of RV this is, how much power you need every day, how much you would normally drive, etc... If you are planning on have a genset anyway--it would probably be better in the long run for you to use it to charge your battery bank directly instead of trying to use your alternator from your truck--in almost all cases, it will use less fuel (even if you are driving anyway) and, probably, charge quicker (and more accurately) than your standard vehicle alternator ever could.

    Lastly, if you will need to quick charge your battery bank (no local AC utility power available, and not enough sun/solar to fully charge), then you may wish to look into getting AGM type batteries... If you keep them cool, and monitor the temperature, you can charge then up to a 1 hour rate (instead of the 10 hour rate) (if I remember Niel's post correctly from elsewhere here). You can really save a lot of generator runtime (and noise) by being able to charge at a 1-2 kW rate for an hour or two vs a 100-200 watt rate for 10 hours...

    Sometimes it is better to start with the problem statement (what you have vs what you need, vs how much you can spend) and then design a solution... Sometimes I may be just chasing my interpretation of what you are trying to solve instead really understanding the problem itself.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • mike95490
    mike95490 Solar Expert Posts: 9,583 ✭✭✭✭✭
    Re: component isolation for 12V RV system

    Thanks for the sketch,

    Hook the 45A 12V charger (via its own 60A fuseable ink) right to the batteries, otherwise, you will forever blow fuses in your load controller.
    I assume you have it for "opportunity chargeing" when you have to kick the generator on, and want to dump a fast charge into the batteries ? The battery should filter out any odd ripple, maybe a radio or TV may show some 60 HZ hum.
    45A will always blow a good 10A fuse, unless the battery is full, and you don't need a charge.
    Do you only use 1 battery, or do you have several in parallel?
    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 ,

  • System2
    System2 Posts: 6,290 admin
    Re: component isolation for 12V RV system
    mike90045 wrote:
    Hook the 45A 12V charger (via its own 60A fuseable ink) right to the batteries...

    I'm jut using it for 12vdc supply when plugged into the grid or on AC generator. I would rather use a dedicated bulk-charger since the same battery is also connected to the Sunsaver controller. I've upped my PV to 150w now, a matched pair of 75w panels, do I need to use diode protection when running them in parallel?
    45A will always blow a good 10A fuse, unless the battery is full, and you don't need a charge.

    Yep, I found that out the sorta-hard way (blew the fuse instead of the controller) ;^]
    Do you only use 1 battery, or do you have several in parallel?

    Currently (pardon the pun) I have one reconditioned 95ah rv/marine type flooded "deep cycle", which seems a reasonable match to the 150w PV and the Sunsaver 10a charge controller, especially since I am routing the battery output thru low voltage disconnect so other people using the system won't unknowingly pull the battery down below 50%. I tried starting the GENSET with the deep cycle and the Sunsaver immediately cut power at the LVD, but once the starter was switched off the LVD was back online within a minute with no appreciable PV charge current available (it was evening). That means my battery was being pulled down to (or below) the 11.5 volt lower setpoint under load from the generator starter, and then bouncing quickly back to 12.6v. Perhaps I should consider using the engine starter battery instead, anybody have their $.02 to add?

    Another question, since my 65 watt (ac rating) TV/VCR combo stopped working on DC input, but still works fine with line voltage, would running it off a 100w inverter effectvely isolate it from the junk in my unregulated DC power supply? (including anywhere from 4 to 6 volts AC measured so far at various times) How robust are these "cigarette lighter" inverters? Just finished some testing and poking around my RV van, I'll diagram my system with detailed info and come back with a link. Thanks, more later...

    K.D.
  • BB.
    BB. Super Moderators, Administrators Posts: 33,431 admin
    Re: component isolation for 12V RV system

    Regarding starting of the genset... RV/Marine batteries are typically hybrids that are both "starting batteries" (short periods of high current) and "storage batteries" (storage batteries are designed for around 50% discharge before damage can occur, whereas starting batteries should not be discharged by more than 20% capacity before recharging).

    Take a volt meter and measure the voltage on the battery posts themselves to determine if the battery is good (compare with the voltage of starting your own car). How far the battery will drop is a combination of starting load and battery condition. It has been a long time since I have diagnosed starting problems but I can believe a battery will probably maintain 10volts or more during starting and a bad one will probably be below 9vdc...

    Another issue is the wiring itself and how much voltage drop there is when current is flowing... Ideally, you want heavy gauge wires directly from the battery to the starter. And, you want the sunsaver either directly to the batteries, or as close as possible to the battery bus bar (as little voltage drop as possible between the sunsaver and the batteries to ensure that the sunsaver is accurately measuring true battery voltage). Higher resistance between the sunsaver and battery will not only cause losses due to heating of the wiring (probably not much at 10 amps, but still it is a loss), but the voltage drop across the wiring will cause the sunsaver to prematurely reduce current flow to the battery during charging. And, also cause the LVD to prematurely detect low battery voltage.

    Lastly, I would still suggest that you move your 12vdc converter from the LVD directly to the battery. It sounds like it needs the battery to absorb or filter your "ripple" current (AC voltage). The farther from the battery you have the 12vdc converter connected (through small gauge wire and a 10 amp fuse), the worst your ripple voltages will be for your electronic devices.

    There really is no good reason (that I can see) for having the converter connected elsewhere than directly to the battery.

    If you isolated the RV DC Bus because you wanted the LVD to power the RV Bus--And the RV DC Bus is a good size piece of wire/copper/fuse block, you should probably reconnect it back to the battery bank as originally designed. And create your own little LVD bus for the low powered devices.

    Using the LVD like I think you are is probably causing you some of your problems you are seeing now. I would humbly suggest that you connect the 12vdc converter back to the battery. You can later remove the converter and replace it with a good quality battery charger.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • System2
    System2 Posts: 6,290 admin
    Re: component isolation for 12V RV system

    Okay, I have posted a simple .pdf diagram that I can update as I make changes:

    http://www.nmia.com/~barefoot/temp/diagram.pdf
    BB wrote:
    Regarding starting of the genset... RV/Marine batteries are typically hybrids that are both "starting batteries" (short periods of high current) and "storage batteries" (storage batteries are designed for around 50% discharge before damage can occur...

    Okay, since the cabling looks like 0 guage welding conductor, I'll leave it hooked up to the deep cycle for now, makes life simpler.
    Take a volt meter and measure the voltage on the battery posts themselves to determine if the battery is good...

    Yep, I do that with my regular batteries, but I suspect it is okay, given the fact that the LVD kicked it back online within seconds...
    Another issue is the wiring itself and how much voltage drop there is when current is flowing...

    I used dedicated cables for all my PV system hookups, both positive and negative, nothing left to chance that way.
    Lastly, I would still suggest that you move your 12vdc converter from the LVD directly to the battery.

    It's okay, I'm not getting much noise, and the pump, control solenoids and incandescent lighting don't seem to have any problems. Proceeding from the system as mapped out in my diagram, I'm going to try a Schottsky(?) diode on the LVD input to see if that will keep my 10 amp fuse from blowing when the DC converter is feeding power into the buss. If that doesn't work, I'll try to work out a relay, or maybe a MOSFET would work in this situation?
    There really is no good reason (that I can see) for having the converter connected elsewhere...

    Remember, that part of the system is the original configuration, allowing the DC components in the RV to contimue working when the AC generator or line voltage is active. The original charging section of the converter gave out some time ago, so I just yanked the leads and proceeded from there. I see no reason to ditch a 45 amp power supply that seems to be working fine otherwise.
    If you isolated the RV DC Bus because you wanted the LVD to power the RV Bus...

    Yes, that is my intention. I want this system to be transparent to all the other people who have been using this RV for the last two decades, so I don't have to think about it, or for them, when I'm off hiking or admiring the scenery.
    Using the LVD like I think you are is probably causing you some of your problems...

    Definately, but I want to make it possible for my battery power from the PV system to "work and play well" with the other sources, again so I don't have to retrain a bunch of other people how to cope with it. A little effort now will save me "some s'plainin to do" later, to quote Ricky Ricardo...
    You can later remove the converter and replace it with a good quality battery charger.

    I intend to add one in addition, that's the following step after I address the issue mentioned above. Just noticed Harbor Freight has a charger on sale that might do the trick...

    ;^]

    p.s. any thoughts on the portable 100w inverter for my TV? Do these "cheapo" units provide a clean enough signal for a CRT/VHS combo?
  • BB.
    BB. Super Moderators, Administrators Posts: 33,431 admin
    Re: component isolation for 12V RV system

    I am not quite sure how the converter still works but won't charger a battery (unless the voltage controller it out or something)... Be that as it may, a Shockty diode on the LVD output will probably work fine preventing the charging of the battery by the converter.

    The only issue that I can see may be that running the converter with 4 VAC of ripple may tend to discharge the storage batteries over time as the diode becomes forward biased on the bottom side of the ripple (assuming that the low side of the ripple is less than battery voltage - 0.2 VDC...

    Looking at your current PDF diagram--if you add a diode to the LVD, I am not sure how you will be charging the storage battery (via AC or Truck Alternator) unless it is via a separate battery charger/charging path that is not currently in the diagram.

    Regarding the small inverters running a TV and such... I have done it without any damage or problems (may have been some noise from the modified sine wave--don't remember now (was decades ago). I probably would not do it with my (not cheap) HD TV, but with a $100 TV and $30 DVD player--it is probably worth the risk (keep a nose out for "hot smells from the power supplies" in the first hour or so to see that all are happy with modified sine wave). Obviously, the TV and DVD have to add up to less than 100 watts (though, even 300 watt units out there are now dirt cheap).

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • mike95490
    mike95490 Solar Expert Posts: 9,583 ✭✭✭✭✭
    Re: component isolation for 12V RV system
    Kristofer wrote:
    Lastly, I would still suggest that you move your 12vdc converter from the LVD directly to the battery.

    It's okay, I'm not getting much noise, and the pump, control solenoids and incandescent lighting don't seem to have any problems. Proceeding from the system as mapped out in my diagram, I'm going to try a Schottsky(?) diode on the LVD input to see if that will keep my 10 amp fuse from blowing when the DC converter is feeding power into the buss. If that doesn't work, I'll try to work out a relay, or maybe a MOSFET would work in this situation?
    There really is no good reason (that I can see) for having the converter connected elsewhere...

    Remember, that part of the system is the original configuration, allowing the DC components in the RV to contimue working when the AC generator or line voltage is active. The original charging section of the converter gave out some time ago, so I just yanked the leads and proceeded from there. I see no reason to ditch a 45 amp power supply that seems to be working fine otherwise.

    I'll reinforce the thought, move the 45A converter to The Battery, not the load. Blowing the 10A fuse should be giving you a hint that it's wrong the way it is. I'm also a bit concerned that it (45A converter) is part of a fried charger system. And that it has a fair amount of ripple. I'd consider dumping it, and get one of those 45A super chargers from Vector # VEC1093A northerntool.com has a good price on it. Connect it to The Battery. The Battery.

    Running devices from the 100 - 300W modified sine (square wave) inverters. You have to try it, many things will work fine, some may show hum or buzz, and some wall wart or inline brick AC/DC converters will get frighteningly hot. If something is getting hotter than normal, it does not like the square wave output, and you should move on. I'd look for appliances that run off 12VDC, and save the losses you get with a inverter (most are about 70-80% efficient) They will have a statement on the package 90% efficiency at ____ some exact load. outside the 34.56w load, the efficiency drops way 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 ,

  • System2
    System2 Posts: 6,290 admin
    Re: component isolation for 12V RV system
    BB wrote:
    I am not quite sure how the converter still works...

    I haven't really looked that closely at it, ya know, if it ain't broke...
    Be that as it may, a Shockty diode on the LVD output will probably work fine preventing the charging of the battery...

    Which is what is (probably) blowing my 10a fuse.
    The only issue that I can see may be that running the converter with 4 VAC of ripple may tend to discharge the storage batteries over time as the diode becomes forward biased on the bottom side of the ripple

    Well, I was thinking of putting diodes on both terminals of the LVD for that reason, reversed in polarity to each other. I'm assuming that will double the voltage drop of using one, and the portion of the ripple current that might drive through would have the right polarity. Since the drop won't affect the PV charging, I think it is an acceptable tradeoff, unless I'm missing something here.
    Looking at your current PDF diagram--if you add a diode to the LVD, I am not sure how you will be charging the storage battery (via AC or Truck Alternator) unless it is via a separate battery charger/charging path that is not currently in the diagram.

    Correct. I'm going to (hopefully) solve my fuse problem, and then I'll add alternator charging via battery isolator so partial charging can occur while driving, and a seperate AC to DC deep cycle capable charger for bulk charging from the genset or AC power cord. My digram represents the "current" state of this work-in-progress...
    Regarding the small inverters running a TV and such... I have done it without any damage or problems...

    I'll give it a try, I can get a plug type for about $20, if it doesn't like the ripple voltage in my DC, I won't be out much anyway. Thanks for the feedback, keep you posted...

    K.D.
  • System2
    System2 Posts: 6,290 admin
    Re: component isolation for 12V RV system
    mike90045 wrote:
    I'll reinforce the thought, move the 45A converter to The Battery, not the load.

    That would prevent me from using more than 10 amps (fused) of DC power when I was running the GENSET or on AC power cord. Other than the possibility that the ripple voltage is what caused my DC input to fail on a TV/VCR combo, I haven't had any problems with this original factory unit. 45a power supplies aren't exactly cheap, and this sucker is built like a Sherman tank. The entire power center, including AC breakers and DC fuse bank is built around it, so the logistics of removing and replacing it would be difficult as well.
    Running devices from the 100 - 300W modified sine (square wave) inverters.  You have to try  it,  many things will work fine, some may show hum or buzz,  and some wall wart or inline brick AC/DC converters will get frighteningly hot.

    I'll try a 100w inverter to power a 65w TV/VCR unit, but the power circuitry is internal, so I guess I'll have to monitor it by nose. It might be too late by the time I notice, but hey, it's old, got my money's worth out of it already. Thanks for the tip...

    K.D.
  • BB.
    BB. Super Moderators, Administrators Posts: 33,431 admin
    Re: component isolation for 12V RV system

    I know that you want to use the LVD to prevent over discharging your battery--but voltage cutoffs are probably not the best way of doing this. The battery monitor which measures total current (and voltage) going into and out of the storage battery is a much better and more accurate method.

    Even the cheapest ones are probably more than you want to purchase at this time--but they are still worth a look to understand how they work and how they can help you to battery manage your storage battery.

    http://store.solar-electric.com/metersmonitors.html

    There is also a basic user Trimetric manual link (from Wind-Sun) that covers basic battery care and operations and why things are the way they are.

    http://www.bogartengineering.com/UsingTriMetMaintain.pdf

    Short term, you may wish to just get a simple amp meter (and shunt, assuming it is needed) to manually monitor the current flow to your storage batteries.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • System2
    System2 Posts: 6,290 admin
    Re: component isolation for 12V RV system

    To clarify, the LVD is a feature of the integrated charge controller I purchased from NAW&S:

    http://store.solar-electric.com/ss-10l.html

    I'm content to let the Sunsaver controller deal with the state of charge, it's temperature compensated and whatnot. I can understand the necessity of closely monitoring a large expensive array, but in this case, we're talking about a $35 reconditioned battery used for a relatively non-critical function, so the justification isn't there. I don't mind the time and effort this project has involved to become more familiar with the various concepts and components involved, since it is likely that alternative energy will be playing a significant role in my near future. But spending money to put a "Rolls-Royce" PV system in my "Ford" RV just isn't necessary. ;^]

    K.D.
  • System2
    System2 Posts: 6,290 admin
    Re: component isolation for 12V RV system

    Tested a single Schottky diode in line with my 10 amp fused input, seems to work fine. In fact the PV charged battery had a higher voltage than the converter, so the test light got brighter when I patched in the PV system. I'll wire everything up properly tomorrow and see if the genset and alternator input causes any problems. Later...

    K.D.
  • System2
    System2 Posts: 6,290 admin
    Re: component isolation for 12V RV system


    Updated my system diagram:

    http://www.nmia.com/~barefoot/temp/diagram.pdf

    So far, so good, the final step will be wiring in the battery isolator. The Schottkey diode is blocking current flow thru the 10a fuse into the Sunsaver, a $2.00 part, not bad. The Sunsaver seems to be unaffected by pulling current from the deep cycle battery while starting the GENSET or by the automatic charger kicking in when AC is present. Now the really fun part begins, figuring out how to stuff the battery isolater into the van's engine compartment...

    ;^]