Hoping for some help in preventing a fire or getting electrocuted

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x_david_x
x_david_x Registered Users Posts: 8 ✭
in Solar Beginners Corner #1
Hello,

I hope this is the right place to post this. If not, please point me in the correct direction. There seemed to be a few forums that may be applicable.

I'm new to solar. I'm putting together a system for an RV (fish house/toy hauler/camper). I've done a bit of reading on the basics, but now that I'm getting closer to installation, the topic of protection has reared its ugly head. I figured I'd post what I intend to do and see if I get reprimanded, along with an alternative recommendation. :blush:

Here are the basics. I'm happy to supply more detailed specs if needed.

- 2 x 100 watt, 12 volt panels in parallel
- 1 x 30 Amp PWM Charge Controller
- 1 x 100 Ah AGM battery
- 1 x 40 feet of 12 gauge cable with male and female MC4 ends for between panels and charge controller (cable will be cut into 2 x 20 feet sections)
- 1 x pair of MC4 Y connectors (for connecting the panels in parallel)
- 1 x 16 feet of 12 gauge cable for between charge controller and battery (cable will be cut into 2 x 8 feet sections)

There will not be an inverter at this time. The RV has a converter/charger for use with a generator or shore power and has a 120 volt AC circuit breaker box/12 volt DC fuse panel. There is some question about what the two chargers will do when they are both active at the same time, but I'm taking a wait and see approach on that one and hoping that one scares the other away (makes it think that the battery is charged) rather than dueling banjos.

I plan to mount the solar panels on homemade, angle adjustable, aluminum brackets and the panels will simply be placed on the roof (not anchored down). They will be removed when the RV is being pulled by a vehicle. I'll probably have to have some sort of quick disconnect adapters between the panels and the charge controller to allow for easy removal of the panels (or more specifically, the cables), as needed. Any recommendations on good, weather resistant adapters? These will most likely be in the battery box, which does have an outside door on it, but still isn't completely out of the weather at all times. I know I could use MC4 adapters, but I'm guessing I'd need to get a special crimping tool. I suppose anything I get needs to be crimped, but I'd rather not have a single use, expensive crimping tool.

Now for my main questions/assumptions.

1) It is my understanding that I probably don't need fuses between the panels and the charge controller, since I only have 2 panels. True/False?

2) Regardless of protection need, I'd like to have a switch between the panels and the charge controller for when I need to work on something. I'm thinking a DC circuit breaker would be good, as then I'd be set if I expand in the future and do need the protection. Good idea/Bad idea? If good, can you recommend a breaker of the correct size and small breaker box? This will be mounted inside the RV and I don't want it to take up a lot of room.

3) It is my understanding that I do need some sort of protection between the charge controller and the batteries in the case of a short in the battery or charge controller. I was considering an ATC style fuse, but I thought I read that is not recommended for some reason. Something like that could have been installed close to the battery. If I go with a DC circuit breaker, then that will need to be installed inside, several cable feet away from the battery. Anyway, recommendations on type and size as well as specific makes and models for this would be good too.

If it does turn out that a regular fuse can be used, is there any reason for a disconnect switch as well (between the charge controller and battery), since I'll already have a disconnect switch (circuit breaker) between the panels and the charge controller?

4) Any special grounding requirements needed for the panels-controller-battery loop?

5) Any recommendations for nice looking, easy to use conduit, since I won't be running the wires behind a wall inside?

Thanks for any help you can provide! :D

David
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  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
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    Re: Hoping for some help in preventing a fire or getting electrocuted

    Welcome to the forum.
    x_david_x wrote: »

    1) It is my understanding that I probably don't need fuses between the panels and the charge controller, since I only have 2 panels. True/False?

    True: two parallel connections of equal panels can not present a condition where one is overloaded by the other should the first one short.
    2) Regardless of protection need, I'd like to have a switch between the panels and the charge controller for when I need to work on something. I'm thinking a DC circuit breaker would be good, as then I'd be set if I expand in the future and do need the protection. Good idea/Bad idea? If good, can you recommend a breaker of the correct size and small breaker box? This will be mounted inside the RV and I don't want it to take up a lot of room.

    Not a bad idea, even if not strictly necessary. But when planning for future think about how much power there might be there and put the wiring and breaker for that in now. The size of the breaker would depend on how much current that will be. Since this is not being installed for over-current protection the issue is mainly one of being able to handle the power.
    3) It is my understanding that I do need some sort of protection between the charge controller and the batteries in the case of a short in the battery or charge controller. I was considering an ATC style fuse, but I thought I read that is not recommended for some reason. Something like that could have been installed close to the battery. If I go with a DC circuit breaker, then that will need to be installed inside, several cable feet away from the battery. Anyway, recommendations on type and size as well as specific makes and models for this would be good too.

    Yes, output from the controller should have over-current protection. The ATC style fuses tend to be a bit 'flimsy' for this application. Your best bet is a Blue Sea battery post fuse, unless you feel you need the disconnect function offered by a breaker. You'd be surprised how often you don't have to shut off PV or battery. "Several feet away from the battery" could be a problem both for protecting the most circuit and because it indicates a long wire run which would add to Voltage drop and inaccurate charging.
    If it does turn out that a regular fuse can be used, is there any reason for a disconnect switch as well (between the charge controller and battery), since I'll already have a disconnect switch (circuit breaker) between the panels and the charge controller?

    Not really. Cover panels = no power output = disconnect a wire that has no power on it. You should not have to do this often.
    4) Any special grounding requirements needed for the panels-controller-battery loop?

    You don't really have any 'grounding' in an RV because nothing connects to Earth. You will have negative common chassis 'ground'. The main thing here is to avoid those few panels which want positive grounding. Fairly easily done since they are the exception not the rule.
    5) Any recommendations for nice looking, easy to use conduit, since I won't be running the wires behind a wall inside?

    I avoid RV's myself, but I know there are plenty of RVer's on the forum who will have tips for installation.

    Don't worry much about how the solar charge controller will interact with the RV converter; the outputs of either will not 'back feed' the other due to the nature of the semiconductors on their outputs.

    BTW quite often people with RV's upgrade to off-grid inverters and throw those converters out. Ironically the stand-alone battery chargers usually used are just a variation on these converters! As such if you decide to go "full inverter" go for one wit a built-in charger (which is vastly superior to the converter type).

    Hope this helps.
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  • x_david_x
    x_david_x Registered Users Posts: 8 ✭
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    Re: Hoping for some help in preventing a fire or getting electrocuted
    Cariboocoot wrote: »
    Welcome to the forum.
    Thanks and thanks for the ultra-quick help. I just happened to read a series of posts by you, helping someone else, after I posted my thread. Something tells me you end up repeating yourself a lot on here for beginners. Thanks for that.
    Cariboocoot wrote: »
    True: two parallel connections of equal panels can not present a condition where one is overloaded by the other should the first one short.
    If I go up to 3 panels and 1.56*Isc*2 is less than the maximum series fuse rating of a single panel, then I still don't need over-current protection? This is more academic for me, as the panels I plan on getting have an Isc of 5.75 amps and maximum series fuse rating of 15 amps, and 1.56*5.75*2 = 17.94 amps, so I'm already over the max series fuse rating (if I go to 3 panels), but I just thought I'd ask to make sure I have this clear in my head. I'd like to plan for a plausible expansion down the road (more on that below).
    Cariboocoot wrote: »
    Not a bad idea, even if not strictly necessary. But when planning for future think about how much power there might be there and put the wiring and breaker for that in now. The size of the breaker would depend on how much current that will be. Since this is not being installed for over-current protection the issue is mainly one of being able to handle the power.
    Do I size the breaker using a similar formula?

    1.56*Isc*number of panels

    In my case, that would be:

    1.56*5.75*4 = 35.88

    So that would round up to a 40 amp breaker?

    If I do that, for 2 x 20 feet lengths of cable from the panels to the charge controller, what size cable do you recommend as a good compromise between cost/flexibility (in cold weather, mind you) and power loss? 6 gauge? The vendor sells a 4 panel kit that seems to come with 12 gauge, which seems odd to me. It is two 10 foot sections in that kit.
    Cariboocoot wrote: »
    Yes, output from the controller should have over-current protection. The ATC style fuses tend to be a bit 'flimsy' for this application. Your best bet is a Blue Sea battery post fuse, unless you feel you need the disconnect function offered by a breaker. You'd be surprised how often you don't have to shut off PV or battery. "Several feet away from the battery" could be a problem both for protecting the most circuit and because it indicates a long wire run which would add to Voltage drop and inaccurate charging.
    The RV will be moved quite a bit and I need to take the panels down and disconnect things when I move it. But as long as I have a switch between the panels and the charge controller and can shut off the power coming into the system, I should be fine without needing a switch between the controller and battery, right?

    Is this what you had in mind?

    Attachment not found.Attachment not found.

    If so, does wind-sun sell those? I looked, but couldn't find them here.

    Regarding distance from the battery to the controller and cable size, what would you recommend? The battery is in a compartment accessible from outside the RV. I'm just guessing, but I'd guess it is has 2 x 5 foot sections of cable going from the battery to the RV converter/charger, which is at floor level on the side of a bench/bed. I was hoping to put the charge controller a few feet up on the wall so that I could see it better and so that it wasn't down where water would have an easier time getting splashed on it, etc. (happens in a fish house) That's where I got the 8 feet cable length.
    Cariboocoot wrote: »
    Not really. Cover panels = no power output = disconnect a wire that has no power on it. You should not have to do this often.
    Panels will be on the roof and I'd rather not get out a ladder and climb up there if I want to take the battery home to charge it. Now that may happen less often once I have the solar (and is the main reason to get the solar, so that I can overcome parasitic draws without having to disconnect the negative post before leaving the RV sit, as well as ability to power security systems and other devices when not at the RV (hence not running a generator)). :D

    In short, this is a portable system, hence the extra thought going into making it easy to disconnect.
    Cariboocoot wrote: »
    You don't really have any 'grounding' in an RV because nothing connects to Earth. You will have negative common chassis 'ground'. The main thing here is to avoid those few panels which want positive grounding. Fairly easily done since they are the exception not the rule.
    There was nothing mentioned about grounding in the literature for the panels, but I just thought I'd check to make sure I'm not missing something. As long as I don't try to run the circuit through the chassis of the RV, I should be fine? Negative wire goes from panels to circuit breaker switch and from there to the controller and from the controller to the battery and from battery to the existing DC fuse panel, which should already have things wired properly.

    Here are the specs on the panels in case there is something in here that sheds light on anything we're discussing:

    ...
    Electrical Specifications
    Optimum Operating Voltage (Vmp): 18.9V
    Optimum Operating Current (Imp): 5.29 A
    Open - Circuit Voltage (Voc): 22.5 V
    Short- Circuit Current (Isc): 5.75 A
    Maximum Power at STC: 100 W
    Operating Module Temperature: -40°C to + 90°C
    Maximum System Voltage: 600 V DC (UL) / 1000 V DC (IEC)
    Maximum Series Fuse Rating: 15A
    STC: Irradiance 1000 W/m2, module temperature 25°C, AM=1.5;
    ...
    Cariboocoot wrote: »
    I avoid RV's myself, but I know there are plenty of RVer's on the forum who will have tips for installation.
    Heh. If anyone has done this, I'd love to hear how you handled the wiring on the outside of the walls (still inside the RV, but not behind the walls).
    Cariboocoot wrote: »
    Don't worry much about how the solar charge controller will interact with the RV converter; the outputs of either will not 'back feed' the other due to the nature of the semiconductors on their outputs.
    That's kind of what I figured, but I've read everything from "they'll blow up" to "it will work perfectly". :D

    I figure if the chargers are smart enough to stop charging the battery when the voltage gets to a certain level, then if that voltage comes from another charger, they should just shut off. And it isn't like either charger is going to throw voltage at the other charger that is much higher than what the battery would at full charge, so I figure I'm safe. My only concern would be if they both wanted to go into float mode periodically, as I don't want to overcharge the AGM constantly.
    Cariboocoot wrote: »
    BTW quite often people with RV's upgrade to off-grid inverters and throw those converters out. Ironically the stand-alone battery chargers usually used are just a variation on these converters! As such if you decide to go "full inverter" go for one wit a built-in charger (which is vastly superior to the converter type).
    The converter/charger in there now is...well, let's just say it isn't all that great. I'm almost considering ripping it out and putting in a different brand that has better reviews. It is a multi-stage charger, but I don't think it ever goes into bulk mode, so it just takes too long to charge a battery. I end up taking my regular battery charger and plugging that into the generator to charge the battery, which is just silly, since the converter/charger is supposed to be doing that job! :grr

    If I want to be able to run a microwave and air conditioner (future additions), I think I'll need the converter, unless I add more batteries, which presents a problem, since the battery box only has room for one.
    Cariboocoot wrote: »
    Hope this helps.
    It is more than I expected and was a good deal of help, both from the advice as well as the sanity check. I really appreciate it! :cool:
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  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
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    Re: Hoping for some help in preventing a fire or getting electrocuted
    x_david_x wrote: »
    If I go up to 3 panels and 1.56*Isc*2 is less than the maximum series fuse rating of a single panel, then I still don't need over-current protection? This is more academic for me, as the panels I plan on getting have an Isc of 5.75 amps and maximum series fuse rating of 15 amps, and 1.56*5.75*2 = 17.94 amps, so I'm already over the max series fuse rating (if I go to 3 panels), but I just thought I'd ask to make sure I have this clear in my head. I'd like to plan for a plausible expansion down the road (more on that below).

    Don't do it. Whereas it may look safe because a single panel may have a "maximum series fuse" rating of 15 Amps and the combined short circuit current of two is only slightly over 10 Amps there's this little thing called insolation which under certain circumstances can push the Isc up just that bit more ... and then maybe the shorted panel holds against the current and maybe it doesn't. In my opinion it is better to use a smaller than maximum breaker/fuse so that will trip/blow before there's any risk of the conductor in the shorted panel frying.

    Here we are talking about individual panel fuses. Once they are combined you need to use wire and breaker that will handle the total current. So if you have Isc of 5.75 and three panels in parallel you're looking at 17.25 Amps. Although the NEC may disagree with me, there is no reason to 'derate' the system with the 1.56 multiplier. At that current level a 20 Amp breaker will suffice, and the wiring of course would need to be 12 AWG or larger.

    Next bit: if you're planning on further expansion wire for it now. It wouldn't hurt anything to have a 30 Amp breaker in there and 8 AWG wire if that is keeping with your expansion plans. Better than having to rewire it all later.
    If I do that, for 2 x 20 feet lengths of cable from the panels to the charge controller, what size cable do you recommend as a good compromise between cost/flexibility (in cold weather, mind you) and power loss? 6 gauge? The vendor sells a 4 panel kit that seems to come with 12 gauge, which seems odd to me. It is two 10 foot sections in that kit.

    You need to use the PV rated wire before the combiner box: anything exposed needs to have insulation that can withstand that exposure. This stuff is 10 AWG and that's nearly always sufficient for the current from a single panel or string over the distance to the combiner. Out of the combiner is another story; that is usually in conduit (even in and RV) and so can be almost any kind of wire so long as the size is large enough to handle the current and not create a lot of Voltage drop (rarely a problem with an RV install).
    The RV will be moved quite a bit and I need to take the panels down and disconnect things when I move it. But as long as I have a switch between the panels and the charge controller and can shut off the power coming into the system, I should be fine without needing a switch between the controller and battery, right?

    Rule-of-thumb for solar charge controllers: connect battery first, panels last; disconnect panels first, battery last. In this case you're only switching the PV in and out so it works. In practical terms disconnecting the PV may prove a bit more of a challenge. Some like to use Anderson connectors for this (polarized, heavy-duty, available in various capacities). Remember that PV is big hunks of glass and needs to be treated as such.
    Is this what you had in mind?

    Attachment not found.Attachment not found.

    If so, does wind-sun sell those? I looked, but couldn't find them here.

    Yes, that's the item. Handy things they are too! NAWS does not carry this item, but many Marine/RV dealers do. You can probably find them locally.
    Regarding distance from the battery to the controller and cable size, what would you recommend? The battery is in a compartment accessible from outside the RV. I'm just guessing, but I'd guess it is has 2 x 5 foot sections of cable going from the battery to the RV converter/charger, which is at floor level on the side of a bench/bed. I was hoping to put the charge controller a few feet up on the wall so that I could see it better and so that it wasn't down where water would have an easier time getting splashed on it, etc. (happens in a fish house) That's where I got the 8 feet cable length.

    Here you have another instance of needing to know your future expansion now; no sense wiring twice when once will do. The greater the current and longer the run the more Voltage drop you'll have. Try to plan a route that makes the run from the controller to the battery as short and direct as possible. The charge controller, btw, should be inside and definitely not getting anything splashed on it.
    Panels will be on the roof and I'd rather not get out a ladder and climb up there if I want to take the battery home to charge it. Now that may happen less often once I have the solar (and is the main reason to get the solar, so that I can overcome parasitic draws without having to disconnect the negative post before leaving the RV sit, as well as ability to power security systems and other devices when not at the RV (hence not running a generator)). :D

    In short, this is a portable system, hence the extra thought going into making it easy to disconnect.

    Not a bad idea at all. Several RVers have "portable panels" which they set up when camping to supplement charging. Security and safety are sometimes a problem with that, though. All you have to remember is the disconnect/reconnect sequence and you'll be fine.
    There was nothing mentioned about grounding in the literature for the panels, but I just thought I'd check to make sure I'm not missing something. As long as I don't try to run the circuit through the chassis of the RV, I should be fine? Negative wire goes from panels to circuit breaker switch and from there to the controller and from the controller to the battery and from battery to the existing DC fuse panel, which should already have things wired properly.

    Yes; avoid using a mass of steal as the negative side of the circuit. :D All switching and circuit protection is done on the positive side (wiring convention not a requirement for operation).
    Here are the specs on the panels in case there is something in here that sheds light on anything we're discussing:

    ...
    Electrical Specifications
    Optimum Operating Voltage (Vmp): 18.9V
    Optimum Operating Current (Imp): 5.29 A
    Open - Circuit Voltage (Voc): 22.5 V
    Short- Circuit Current (Isc): 5.75 A
    Maximum Power at STC: 100 W
    Operating Module Temperature: -40°C to + 90°C
    Maximum System Voltage: 600 V DC (UL) / 1000 V DC (IEC)
    Maximum Series Fuse Rating: 15A
    STC: Irradiance 1000 W/m2, module temperature 25°C, AM=1.5;

    I see nothing out of the ordinary there, so no cautions.
    If I want to be able to run a microwave and air conditioner (future additions), I think I'll need the converter, unless I add more batteries, which presents a problem, since the battery box only has room for one.

    Yes A/C is a big power hog anywhere. When you have limited battery space ... well, that's it! The reason for generators. :p

    Don't worry about me repeating advice: one of the downsides of old age is you start to repeat yourself anyway so might as well put it to good use. :D:p
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  • x_david_x
    x_david_x Registered Users Posts: 8 ✭
    #5
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    Re: Hoping for some help in preventing a fire or getting electrocuted
    Cariboocoot wrote: »
    Don't worry about me repeating advice: one of the downsides of old age is you start to repeat yourself anyway so might as well put it to good use. :D:p

    I will reply fully tomorrow, but I just had to say that this made me laugh. :D

    Have a good night (assuming it is night where you are),
    David
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  • x_david_x
    x_david_x Registered Users Posts: 8 ✭
    #6
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    Re: Hoping for some help in preventing a fire or getting electrocuted
    Cariboocoot wrote: »
    Don't do it. Whereas it may look safe because a single panel may have a "maximum series fuse" rating of 15 Amps and the combined short circuit current of two is only slightly over 10 Amps there's this little thing called insolation which under certain circumstances can push the Isc up just that bit more ... and then maybe the shorted panel holds against the current and maybe it doesn't. In my opinion it is better to use a smaller than maximum breaker/fuse so that will trip/blow before there's any risk of the conductor in the shorted panel frying.
    I guess my question was simply whether you could add up the Isc values of number of panels minus 1 and as long as that is a bit below the maximum series fuse rating of a single panel, you'd be okay? This is just academic. I'm just trying to figure out when you can and cannot do without the protection when wiring in parallel.
    Cariboocoot wrote: »
    Here we are talking about individual panel fuses. Once they are combined you need to use wire and breaker that will handle the total current. So if you have Isc of 5.75 and three panels in parallel you're looking at 17.25 Amps. Although the NEC may disagree with me, there is no reason to 'derate' the system with the 1.56 multiplier. At that current level a 20 Amp breaker will suffice, and the wiring of course would need to be 12 AWG or larger.
    My understanding was that the 1.56 is obtained from 1.25*Isc (because, as you stated above, under certain conditions, the panel will put out more than its Isc rating) and then because NEC wants to derate another 1.25 multiplier just to be extra, super safe. If we do away with the second multiplier and stick with just one, the theoretical 4 panels (I was only using 3 above in the context of one shorting out and getting the load from the other 3) would output 5.75 * 4 = 23 amps. 23 * 1.25 = 28.75, which would round up to a 30 amp breaker to handle the output of 4 of these panels, post-combining.

    Does that sound right?
    Cariboocoot wrote: »
    Next bit: if you're planning on further expansion wire for it now. It wouldn't hurt anything to have a 30 Amp breaker in there and 8 AWG wire if that is keeping with your expansion plans. Better than having to rewire it all later.
    Yes, that's what I'm trying to figure out now. With 2 panels, I don't "need" protection between the panels on the controller, but I do want a switch and I figured a DC breaker would work. By sizing that correctly, I'm all set for if/when I go to 3 or 4 panels. However, the end state wiring is starting to be a pain to do at this point in time.

    Is there any reason I can't do the following? (my own made-up diagram)

    Attachment not found.

    Do charge controllers also act as converters when presented with 24 volts instead of 12 volts? Here is the info on the charge controller I am considering:

    ...
    Rated Working Voltage :12V/24V
    Rated Working Current:30A
    Solar Input Voltage≤48V
    Float Charging Voltage (adjustable):13.8V/27.6V
    Low Voltage Protection (adjustable):10.7V/21.4V
    Low Voltage Recovery (adjustable):12.5V/25.0V
    No Load Loss:≤30mA
    Loop Voltage Drop:≤170mV
    Temperature Compensation:-4mV/Cell/°C
    Technical Specifications
    Max. Wire Size:AWG #7 (16mm2)
    Working Temperature:-10°C to 60°C (14°F to 140°F)
    Storage Temperature:-30°C to 70°C (-22°F to 158°F)
    Temperature Compensation:≤90%, No Condensation
    Dimensions:90x188x48 mm (3.54x7.40x1.89 in)
    Weight :360g (12.7 oz.)
    ...

    Here are the panel specs again:

    ...
    Optimum Operating Voltage (Vmp): 18.9V
    Optimum Operating Current (Imp): 5.29 A
    Open - Circuit Voltage (Voc): 22.5 V
    Short- Circuit Current (Isc): 5.75 A
    Maximum Power at STC: 100 W
    Operating Module Temperature: -40°C to + 90°C
    Maximum System Voltage: 600 V DC (UL) / 1000 V DC (IEC)
    Maximum Series Fuse Rating: 15A
    STC: Irradiance 1000 W/m2, module temperature 25°C, AM=1.5;
    ...

    The reason this would be nice, is because I can then get by with only two cables coming down from the roofs into the RV and it avoids the protection need again (I think). If I need to wire them in parallel, then I'd need to either put a combiner box near the panels, once again getting me two cables from the panel area to the inside of the RV *OR* I'd have to connect two panels in parallel and the other set in parallel and run 4 cables from the roof into the RV and combine them in the RV. With the former, I'd need a combiner box that is completely weather proof (assume it will be submerged in melting snow) and won't be mounted to anything. With the latter, I have more cables to mess with (although they could be smaller than the other approach, since they'd each hold half the current).

    So, can I do what the diagram indicates, or will that controller only pass 24 volts on to the battery, not downconvert to 12 volts?

    If there is no way to get around a combiner box, for 4 panels, can you recommend one that would be safe buried in snow? Do they make any that combine and have an on/off switch (or that have circuit breakers (more than 1 switche) and also combine)?

    Cariboocoot wrote: »
    You need to use the PV rated wire before the combiner box: anything exposed needs to have insulation that can withstand that exposure. This stuff is 10 AWG and that's nearly always sufficient for the current from a single panel or string over the distance to the combiner. Out of the combiner is another story; that is usually in conduit (even in and RV) and so can be almost any kind of wire so long as the size is large enough to handle the current and not create a lot of Voltage drop (rarely a problem with an RV install).
    What type of exposure are you referring to? UV? What is the difference between PV cable and regular, outdoor cable from the hardware store?
    Cariboocoot wrote: »
    Rule-of-thumb for solar charge controllers: connect battery first, panels last; disconnect panels first, battery last. In this case you're only switching the PV in and out so it works. In practical terms disconnecting the PV may prove a bit more of a challenge. Some like to use Anderson connectors for this (polarized, heavy-duty, available in various capacities). Remember that PV is big hunks of glass and needs to be treated as such.
    I'm not understanding what the challenge is? If I have a switch/circuit breaker inside the RV, between the panels and the controller, I should just be able to throw the switch and then work on/disconnect the battery. If you mean when I take the panels down to move them, yes, I need some good connectors that allow me to unplug the cables somewhere before the circuit breaker so that I can take most of the cables and the panels down and inside the RV for transport.

    On that front, do people just pad these if they are being moved in a trailer? I'm guessing most are in permanent installations, but wondering if anyone has any tips on how to deal with them when they are often transported.
    Cariboocoot wrote: »
    Here you have another instance of needing to know your future expansion now; no sense wiring twice when once will do. The greater the current and longer the run the more Voltage drop you'll have. Try to plan a route that makes the run from the controller to the battery as short and direct as possible. The charge controller, btw, should be inside and definitely not getting anything splashed on it.
    ;)

    If the future expansion causes a lot more headaches in the wiring, I may just wire it the easy way now and redo it later. I'd rather not do that, but I'd also like to get this stuff purchased and installed before too long. If it gets too complicated, then I may not achieve that goal. I'd still like to see what all *would* be involved with doing it in a way that will support 4 panels in the future, however, before making the decision. Your help really is greatly appreciated!
    Cariboocoot wrote: »
    Not a bad idea at all. Several RVers have "portable panels" which they set up when camping to supplement charging. Security and safety are sometimes a problem with that, though. All you have to remember is the disconnect/reconnect sequence and you'll be fine.
    The funny thing is that the panels will allow me to run security cameras to protect the panels (or at least catch someone after the fact). Security of the RV is one of the reasons for the panels -- so I can run a security camera inside.
    Cariboocoot wrote: »
    Yes A/C is a big power hog anywhere. When you have limited battery space ... well, that's it! The reason for generators. :p
    I noticed in your signature that you have the EU2000i. That's what I have. I may have to get the companion to run those in parallel for the A/C. If I can find an A/C unit that will start up from the single generator, that's preferable. Of course, that may not leave much room for running other things/charging the battery when the A/C is running. I may need 2 generators regardless.
    Cariboocoot wrote: »
    Don't worry about me repeating advice: one of the downsides of old age is you start to repeat yourself anyway so might as well put it to good use. :D:p
    I'm happy to help you put it to good use! :D

    Thanks again,
    David
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  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    #7
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    Re: Hoping for some help in preventing a fire or getting electrocuted
    x_david_x wrote: »
    My understanding was that the 1.56 is obtained from 1.25*Isc (because, as you stated above, under certain conditions, the panel will put out more than its Isc rating) and then because NEC wants to derate another 1.25 multiplier just to be extra, super safe. If we do away with the second multiplier and stick with just one, the theoretical 4 panels (I was only using 3 above in the context of one shorting out and getting the load from the other 3) would output 5.75 * 4 = 23 amps. 23 * 1.25 = 28.75, which would round up to a 30 amp breaker to handle the output of 4 of these panels, post-combining.

    Does that sound right?

    That is where the 1.56X multiplier comes from: NEC regs. The thing is they are about Voltage-based power sources even though they get applied to PV which is current-based. As such, and this is just my opinion, they tend to be somewhat inaccurate.

    Take the extreme example of a high Voltage panel which runs with very low current (<2 Amps). These oddballs use the same material to make the panel, and so as a conductor they can actually handle the same 10 Amps current. Which brings us to that tricky word "maximum" in the series fuse ratings, and the whole concept that current handling capacity is not quite the hard-and-fast thing some would believe it to be (just look at the discrepancies in various wire charts). So you may have a 175 Watt panel with an Isc of 5.5 and a series fuse rating of 15, but if you put two up against a shorted one you could have 11 Amps going to it - or perhaps a bit more. Will that fuse/breaker actually 'go' at 15 Amps? Nope. They need to be over current for a certain amount of time to actuate. In the meantime you have near maximum current heating up the shorted panel, and possibly some part of it failing sooner than expected and starting the fire.

    So instead you use a 10 Amp breaker on it. 2X Isc is > 10 Amps, breaker trips before you run into the questionable area of "will the circuit hold?"

    Yes, that's what I'm trying to figure out now. With 2 panels, I don't "need" protection between the panels on the controller, but I do want a switch and I figured a DC breaker would work. By sizing that correctly, I'm all set for if/when I go to 3 or 4 panels. However, the end state wiring is starting to be a pain to do at this point in time.

    Yes in that case you're using the breaker as a switch, and like any switch it has to be able to handle the current and Voltage involved. If it can only handle the power being fed through it 'now' it will need to be changed to handle the power fed to it 'later'.
    Is there any reason I can't do the following? (my own made-up diagram)

    Attachment not found.

    Do charge controllers also act as converters when presented with 24 volts instead of 12 volts? Here is the info on the charge controller I am considering:

    That depends on the charge controller. The one you indicate is either 12 or 24 Volt, PWM type. It is not an MPPT type and so can not down-convert the higher Voltage into current. With an MPPT controller you can put any Voltage on the input between the minimum for the system and the controller's maximum input and use it. So you could have a '24 Volt' array charging a '12 Volt' system. With the caveats that not all controllers have good specs in this regard (some limit output current based on V difference) and the higher the array Voltage is in respect to system Voltage the lower the efficiency of the controller (small loss, but they add up).
    If there is no way to get around a combiner box, for 4 panels, can you recommend one that would be safe buried in snow? Do they make any that combine and have an on/off switch (or that have circuit breakers (more than 1 switche) and also combine)?

    Most combiner boxes are weather-tight, although not water-proof. MidNite makes the best ones (no I do not work for them or NAWS). But if you change your controller choice you may not need one.
    What type of exposure are you referring to? UV? What is the difference between PV cable and regular, outdoor cable from the hardware store?

    Yes, exposure to UV and heat/cold/wet. This will probably not be a major consideration for you, as RV's aren't very large. Panels + some extension cables perhaps and you're good to go inside the box, as it were. Much of this depends on measurements. Difference to outdoor cable will depend on which outdoor cable, but basically that is what you're after; insulation that will stand up to the elements.
    I'm not understanding what the challenge is? If I have a switch/circuit breaker inside the RV, between the panels and the controller, I should just be able to throw the switch and then work on/disconnect the battery. If you mean when I take the panels down to move them, yes, I need some good connectors that allow me to unplug the cables somewhere before the circuit breaker so that I can take most of the cables and the panels down and inside the RV for transport.

    Removing and transporting panels may not be as simple as it seems. How it is mounted and what size panels will play a significant role in how practical this approach is. So many variables!
    If the future expansion causes a lot more headaches in the wiring, I may just wire it the easy way now and redo it later. I'd rather not do that, but I'd also like to get this stuff purchased and installed before too long. If it gets too complicated, then I may not achieve that goal. I'd still like to see what all *would* be involved with doing it in a way that will support 4 panels in the future, however, before making the decision. Your help really is greatly appreciated!

    I'm a big proponent of "wire now for later", especially for people without a garzillion systems under their belt. It's easier than having to change everything later and removes the "WHOOPS! Forgot to change that wire!" problem (i.e. suddenly 2X the current traveling down a conductor than it was meant to handle). I also have difficult explaining wiring because I don't even have to think about how to, until I try to explain it. :p
    I noticed in your signature that you have the EU2000i. That's what I have. I may have to get the companion to run those in parallel for the A/C. If I can find an A/C unit that will start up from the single generator, that's preferable. Of course, that may not leave much room for running other things/charging the battery when the A/C is running. I may need 2 generators regardless.

    I'm quite impressed with the Honda EU series. When I first heard about them I was doubtful, to put it mildly, and then I had to buy one as the only choice to replace a dead big unit. That's all it took. The fact you can parallel two small ones is a nice feature, although I've never used it. My goal has always been PV first, gen only when needed. This is because of the years I spent using gen first because PV was so expensive. I made the investment over 5 years ago. So far it's worked well. Curiously I had never planned on re-doing everybody and their brother's system and designing ones from scratch for places all over the world, but at least it's an interesting hobby. :D
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  • x_david_x
    x_david_x Registered Users Posts: 8 ✭
    #8
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    Re: Hoping for some help in preventing a fire or getting electrocuted

    Cariboocoot - With the website changes last night, we lost at least the two most recent messages from this thread. I also noticed it was down a bit today. I'll wait a day or so before replying, in the hopes things have settled down. :D

    Thanks,
    David
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  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    #9
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    Re: Hoping for some help in preventing a fire or getting electrocuted
    x_david_x wrote: »
    Cariboocoot - With the website changes last night, we lost at least the two most recent messages from this thread. I also noticed it was down a bit today. I'll wait a day or so before replying, in the hopes things have settled down. :D

    Thanks,
    David

    Good idea.

    I seem to be repeated myself all over the place under assumed names. :D
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  • x_david_x
    x_david_x Registered Users Posts: 8 ✭
    #10
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    Re: Hoping for some help in preventing a fire or getting electrocuted
    Cariboocoot wrote: »
    Good idea.

    I seem to be repeated myself all over the place under assumed names. :D

    Computers....can't live with them, can't live without them. Oh, wait....we did live without them for thousands of years, didn't we? *grins*

    David
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  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    #11
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    Re: Hoping for some help in preventing a fire or getting electrocuted
    x_david_x wrote: »
    Computers....can't live with them, can't live without them. Oh, wait....we did live without them for thousands of years, didn't we? *grins*

    David

    Yes, but try telling that to your kids! *LOL*

    Maybe we should keep up the casual banter to make sure the forum is working and try to turn up any other glitches without actually running the risk of wiping out several paragraphs full of technical information and mathematics.
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  • x_david_x
    x_david_x Registered Users Posts: 8 ✭
    #12
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    Re: Hoping for some help in preventing a fire or getting electrocuted
    Cariboocoot wrote: »
    Yes, but try telling that to your kids! *LOL*

    Maybe we should keep up the casual banter to make sure the forum is working and try to turn up any other glitches without actually running the risk of wiping out several paragraphs full of technical information and mathematics.

    Yes. It is funny how we take these sites for granted. I figured all that good information would always be there for me to go back to and refer to and now it is gooooone. At least most of the thread survived. I do have a fancy new diagram I put together that I'll share after this waiting period.

    Did you lose information on other threads too? You'll be repeating yourself even more than usual! :-)

    David
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  • x_david_x
    x_david_x Registered Users Posts: 8 ✭
    #13
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    Re: Hoping for some help in preventing a fire or getting electrocuted

    I still see the last message I posted on this thread. Does that mean that the site issues are resolved and we aren't losing posts anymore?

    Thanks,
    David
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  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    #14
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    Re: Hoping for some help in preventing a fire or getting electrocuted
    x_david_x wrote: »
    I still see the last message I posted on this thread. Does that mean that the site issues are resolved and we aren't losing posts anymore?

    Thanks,
    David

    Well, most of them have been resolved. Posts and threads seem pretty stable now. Error messages seem to be under control. New users are able to sign up again (immediately we got spammers). 90% success. :D
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