Rabbit hole?

[Mollysdad]

I dipped my toe in the solar pond with a suitcase, but now I'm thinking bigger. Without falling all the way down the rabbit hole can I ask a few questions?
1. My stage two plan involves a Victron solar controller 50 amp. But it doesn't specify if it will charge lead acid batteries. People claim they work fine using the AGM settings. Yes? No? (The 400 w. panel I'm considering has no controller.)

2. Are there LiIonP batteries that fit in the battery box?
Group 24? Group 27? size?

3. Code requires a 'breaker' (disconnect) between the panel and the controller. (switches both legs simultaneously. )

4. It's recommended that there's a disconnect from the controller to the batteries.

My current suitcase has none of those things. It goes from the enclosed controller to the batteries.

Where's a good place to start? (Nothing is going on the roof.)

[uncle_bob]

Hi

All of the modern Victron solar gear that I've ever seen will do a fine job on lead acid batteries.

If you go to "Lithium" you want LiFePO4 batteries. Given how weird battery sizes turn out to be (they should be standard .... but ....) you need to check dimensions. There are a range of batteries out there running from $200 up to $800. The cheaper you get the more risk you take.

The code for a residential house has various requirements in it. That "code" does not apply to RV's or portable setups. A simple fuse should do fine for something like you are talking about. In a portable setup, you have connectors. They are the ultimate "disconnect" and (obviously) at least as easy to get at as any switch.

As mentioned in other threads, there are some advantages to a "full series" setup for something like you are thinking about. To do that, you would want a controller with a pretty good maximum voltage input rating.

When you go from the 100V max series (which the 50A device is part of) the current ratings change a bit. The 150V equivalent is a 45A device. You also could head up to 250V devices. They all appear to be happy dealing with 12V batteries.

A "full portable" setup is a bit unique in that you *should* be able to set it up and have every panel get the same sun all the time. That will never be 100% true, but it should be true enough of the time to be a reasonable design target.

The math:

Your typical 12V panel has a rated O.C. voltage of 21V. There are variations, so let's use 24V. (things like temperature also get into this ....).

A 400W setup with 4 panels gets you to 92V. Probably safe for a 100V controller.

A 600W series setup with 6 panels gets you to 144V. Probably safe for a 150V controller.

An 1KW setup gets you to 240V and you are "at limit" for that 250V controller.

Again: check the numbers for your actual panels !!!!! Don't just go with this math without a double check.

Fun !!!!

Bob

[Mollysdad]

I'm trying to stay with my lead acid batteries because they're relatively new and the BIG ticket item on any build.

I saw Battle Born has a 100 wh Lithium battery that's a group 27 dimensions, but mine are currently group 24 and have plenty of room, (until you try to remove one.)

The panel I'm looking at is the 400 w. Renogy folding with some rigid features and some flexible features. Folded it's 30 pounds! Aluminum frame, pretty minimal; rigid panels.
(It's 30 pounds unfolded, but never mind that right now!)

Thanks for the advice, keep it coming.

[uncle_bob]

Hi

If you "go cheap" the pair of lithiums are < $500. They give you 2X the capacity of the lead acid's. On a same / same basis that puts them in the "pretty darn cheap" range.

In terms of this solar stuff it's sorta kinda a "does not matter" sort of thing. The solar converter and panels will work with either one.

Why "sorta kinda"? Lead acid's charge much more slowly. Lithiums charge quickly. If you have a "big" solar, it's only useful if your battery can handle the power output.

So the math (you knew we'd get to math eventually ):

Two leads acid's have about 100AH of "usable" capacity. Once you charge up roughly half that, they slow down in terms of the power they will accept.

So we have 50AH of charging to do (if we're at the stop using point).

You have 400W of solar. You have a 50A controller. Whatever the panels put out will go into the battery. Two hours of "full sun" gets you up to about 67AH. You now are well into the slow down region. The rest isn't wasted, but you really don't get a lot out of it.

Go over to a pair of lithiums:

You have 200AH usable.

The charge process does not slow down.

Your panels can put 6 hours of energy into those batteries. That's quite possible on a good day.

Fun !!!

Bob

[richard5933]

I've got disconnects on both sides of the solar charge controller.

There is a disconnect between the panels and the controller so I can fully remove incoming power from the system, including from the controller, for times it's necessary.

There is a disconnect between the controller and the batteries so the controller can be isolated from the system.

I'd have to go look to remember which is which, but one of the disconnect is a circuit breaker and the other is a Blue Sea battery disconnect.

[Mollysdad]

Originally Posted by richard5933

I'd have to go look to remember which is which, but one of the disconnect is a circuit breaker and the other is a Blue Sea battery disconnect.

From what I read, the disconnect between the panel and the controller must cut both legs simultaneously, and so a double pole circuit breaker sized so large there's no danger of it tripping and you just use it as a switch.
I'd use the Blue Seas to open the positive leg to the batteries.
That's consistent with what I've been reading. None of those gadgets are terribly expensive, so why not?

[uncle_bob]

Hi

So just what is involved in the "move the panels" stuff I keep going on about:

Sun rises in the east, panels need to face east. Sun is low to the horizon, panels need to be at a fairly steep angle.

At noon those east facing panels are at right angles to the sun. That's not ideal. They get rotated to face south. They also tilt at a more shallow angle. You obviously make this change mid-morning.

Sun sets in the west. Mid afternoon the panel get rotated to face west and the angle gets adjusted again. At the end of the day or before sun rise, you get them back to their morning location. Otherwise you get pretty much nothing at all before noon.

Yes, this does sound like a lot of fun. .... errrr ... not (at least not to me).

If you have the space (with unblocked views of the sun) it is part of why the portables can indeed outperform the roof mounted stuff. Put them in one location and you are right back to a compromise in terms of output. The good news is that your 200W panel now should do a whole lot better if you do all these moves.

Bob

[richard5933]

Originally Posted by Mollysdad

From what I read, the disconnect between the panel and the controller must cut both legs simultaneously, and so a double pole circuit breaker sized so large there's no danger of it tripping and you just use it as a switch.
I'd use the Blue Seas to open the positive leg to the batteries.
That's consistent with what I've been reading. None of those gadgets are terribly expensive, so why not?

What could possibly be the reason to have to cut both legs? There is one positive and one negative, and on a DC system the without the positive connection I'm not seeing what danger could continue to exist.

Can you fill me in on why both?

[SuperTrouper]

"the disconnect between the panel and the controller must cut both legs simultaneously" Perhaps the text pertains to two strings of series panels? In my system, which has been happily running for over 10 years, I have a cut off switch between the panels (510 watts , 5 panels, all parallel on roof) and the Blue Sky controller. I have a 50 Amp breaker between the controller and the house DC buss. All switching is on the positive side. No need to switch both sides. I also have a master switch and shunt between the negative side of my 460AH LiFePO4 battery and the DC buss. I rarely need a generator, water is my main resource problem when boondocking for a long time. Uncle Bob nailed it on difference between lead acid and lithium. Faster charging and usable capacity sold me on lithium. We camp at non-hook up sites most of the time.

[gypsydad]

Originally Posted by Mollysdad

I dipped my toe in the solar pond with a suitcase, but now I'm thinking bigger. Without falling all the way down the rabbit hole can I ask a few questions?
1. My stage two plan involves a Victron solar controller 50 amp. But it doesn't specify if it will charge lead acid batteries. People claim they work fine using the AGM settings. Yes? No? (The 400 w. panel I'm considering has no controller.)

2. Are there LiIonP batteries that fit in the battery box?
Group 24? Group 27? size?

3. Code requires a 'breaker' (disconnect) between the panel and the controller. (switches both legs simultaneously. )

4. It's recommended that there's a disconnect from the controller to the batteries.

My current suitcase has none of those things. It goes from the enclosed controller to the batteries.

Where's a good place to start? (Nothing is going on the roof.)

Not sure if your following the post here:

https://www.airforums.com/forums/f44...-250359-5.html

My post #81 I list the Li batteries I am considering; Group 24, with built in BMs and Bluetooth, plus the Youtube posted takes them thru all the important limits with good results. As for Solar, I have a folding solar suitecase which has worked great for 9 years or so...has settings for all 3 batteries built in to the control panel in this unit from GoPower. Mine is only 80W but GoPower and others offer models with more watts today, should you want portable. I am considering a couple panels on the roof also...just not sure if my existing 2017 28' still has the wiring for this available on the roof; I had them install a roof vent cover and they told me at the time, it would interfere with the solar connection up there, but I told them go ahead at the time, thinking I had portable, and would not use the roof. (stupid me) (oh- just saw your not interested in roof.)

Anyway, keep us informed on your progress.

[OrangeCrush]

Originally Posted by Mollysdad

From what I read, the disconnect between the panel and the controller must cut both legs simultaneously, and so a double pole circuit breaker sized so large there's no danger of it tripping and you just use it as a switch.
I'd use the Blue Seas to open the positive leg to the batteries.
That's consistent with what I've been reading. None of those gadgets are terribly expensive, so why not?

No, only the PV+ needs to be switched and the PV- should be tied to chassis. I believe this was wrongfully proliferated by Nate of Exporist life. You can read my detail explanation in post #8 in the following thread and draw your own conclusion.

https://www.airforums.com/forums/f44...ml#post2661139

[uncle_bob]

Originally Posted by OrangeCrush

No, only the PV+ needs to be switched and the PV- should be tied to chassis. I believe this was wrongfully proliferated by Nate of Exporist life. You can read my detail explanation in post #8 in the following thread and draw your own conclusion.

https://www.airforums.com/forums/f44...ml#post2661139

Hi

On some controllers, both the + and - of the panels go directly to the controller. They do this or that "on both sides" (think of a Smart Shunt on a lithium battery ....).

On other controllers (though not any that go into RV's ....) the - side of the panels actually has "back fed" voltage from the controller. In that case, disconnecting the minus side makes sense.

So: The need for that double pole switch is a combo sort of thing. You need to both have a controller that isolates the - and the + and does something a bit odd with the -.

There is another possible case where you have a short to ground *within* the array. In a portable setup, getting a solid ground connection like that ... how???? In a home, it could happen.

The "rules" are written for a home setting and not an RV or portable setup.

Bob

[OrangeCrush]

Originally Posted by uncle_bob

Hi

On some controllers, both the + and - of the panels go directly to the controller. They do this or that "on both sides" (think of a Smart Shunt on a lithium battery ....).

On other controllers (though not any that go into RV's ....) the - side of the panels actually has "back fed" voltage from the controller. In that case, disconnecting the minus side makes sense.

So: The need for that double pole switch is a combo sort of thing. You need to both have a controller that isolates the - and the + and does something a bit odd with the -.

There is another possible case where you have a short to ground *within* the array. In a portable setup, getting a solid ground connection like that ... how???? In a home, it could happen.

The "rules" are written for a home setting and not an RV or portable setup.

Bob

I agree. Isolation is a very different case for the home and necessary for many safety reasons mainly due to the voltage achieved with series arrays.

In an RV application when you connect the PV- on a Victron charge controller it is directly connected to the Battery- in the controller which should be connected to chassis. I personally think keeping this connection at all times is a good thing for safety (i.e. lightning) but that is all arguable. I think as long as you are not connecting lot's of panels in series there is no good reason to isolate the PV- on an RV.

[uncle_bob]

Hi

From the Victron instructions for installing their controllers:

PV array grounding

The positive and negative of the PV array should not be grounded.

Ground the frame of the PV panels to reduce the impact of lightning.

Do not connect the solar charger to a grounded PV array. Only one ground connection is allowed, and this should be near the battery

Basically, they do *not* want you to ground the negative side of the solar panels.

Bob

[OrangeCrush]

I am not saying you should chassis ground the PV- and bypass the controller. Of course wire the PV+ and PV- to the controller inputs per instruction. I am saying Victron connected the PV- and Battery- inside the blue/smart solar controllers so they are not technically isolated in these designs. You can verify this with an ohm meter. Maybe there is a fuse between them but I doubt it.

[uncle_bob]

Originally Posted by OrangeCrush

I am not saying you should chassis ground the PV- and bypass the controller. Of course wire the PV+ and PV- to the controller inputs per instruction. I am saying Victron connected the PV- and Battery- inside the blue/smart solar controllers so they are not technically isolated in these designs. You can verify this with an ohm meter. Maybe there is a fuse between them but I doubt it.

Hi

Take a hammer to one and I believe you will find a current shunt in the negative lead coming from the solar panel. Bypass it and the controller can't do its MPPT math.

My only point is that I don't want folks running off and grounding the panel minus to just anywhere ....

Bob

[Mollysdad]

Originally Posted by richard5933

What could possibly be the reason to have to cut both legs? There is one positive and one negative, and on a DC system the without the positive connection I'm not seeing what danger could continue to exist.
Can you fill me in on why both?

I'm only the messenger. But, I've been watching this series on YouTube, and the guy seems pretty knowledgeable.

https://www.youtube.com/watch?v=HOXnWXvLXko&t=318s

Here's a inexpensive switch from Amazon:<$30
I considered adding this on my suitcase between the panels and the controller since the manual cautions to ALWAYS connect to the batteries before exposing to sunlight.

[richard5933]

Originally Posted by Mollysdad

I'm only the messenger. But, I've been watching this series on YouTube, and the guy seems pretty knowledgeable.

Here's a inexpensive switch from Amazon:<$30
I considered adding this on my suitcase between the panels and the controller since the manual cautions to ALWAYS connect to the batteries before exposing to sunlight.

I just watched his video, as well as his updated one. Also went down a few rabbit holes of my own on this one...

Best I can tell is that the double pole switch has something to do with either a) DC have a negative-to-positive flow of electrons, or b) some solar charge controllers being negative ground and some being positive ground, meaning that they don't all switch on the same side. With either scenario, having a double pole switch covers all bases.

Any electrical engineers out there that can explain this so that a non-engineer could understand?

[OrangeCrush]

OK, Bob is 100% correct, do not chassis ground the PV- leg. Connect the panels correctly using PV+ and PV- inputs on the charge controller. That said, I do not think there is a shunt in the negative leg as that would be useless circuit wise. An MPPT circuit is single ended, not differential, so all current sensing is done in the positive leg using a resistor, FET, or hall effect device. Even though the controller connects PV- to Battery- you never want to connect the panels PV- anywhere other than directly to the controller due to the possibility of ground loops that would wreak havoc on the MPPT control circuit.

I am an electrical engineer with over 40 years of R&D experience. I spent a lot of time thinking about this along with several phone conversation with Garret Towne of the now defunct AM solar. I tried to explain why this is an NEC requirement in the previous link post #8 but may not have done a very good job. In Nate's current and previous version of his video he says switching both legs is required by NEC with no explanation why. So first thing to make clear, he is 100% wrong, it is NOT required by NEC in an RV application. In the previous thread referenced I tried to explain why it is an NEC requirement which has to do with worker safety with large PV arrays. If it makes you feel comfortable then by all means do it Nate's way but it is not required and there are some negative trade offs IMO.

[uncle_bob]

Originally Posted by OrangeCrush

OK, Bob is 100% correct, do not chassis ground the PV- leg. Connect the panels correctly using PV+ and PV- inputs on the charge controller. That said, I do not think there is a shunt in the negative leg as that would be useless circuit wise. An MPPT circuit is single ended, not differential, so all current sensing is done in the positive leg using a resistor, FET, or hall effect device. Even though the controller connects PV- to Battery- you never want to connect the panels PV- anywhere other than directly to the controller due to the possibility of ground loops that would wreak havoc on the MPPT control circuit.

I am an electrical engineer with over 40 years of R&D experience. I spent a lot of time thinking about this along with several phone conversation with Garret Towne of the now defunct AM solar. I tried to explain why this is an NEC requirement in the previous link post #8 but may not have done a very good job. In Nate's current and previous version of his video he says switching both legs is required by NEC with no explanation why. So first thing to make clear, he is 100% wrong, it is NOT required by NEC in an RV application. In the previous thread referenced I tried to explain why it is an NEC requirement which has to do with worker safety with large PV arrays. If it makes you feel comfortable then by all means do it Nate's way but it is not required and there are some negative trade offs IMO.

Hi

The shunt is set up the same way as the Smart Shunt. It is a positive supply IC with an input voltage range close to the negative supply. This allows them to use very normal positive regulators to operate that IC. It's cheaper / simpler / more accurate than using an instrument amp to sense the current in the positive lead using a shunt there.

Cheaper / more accurate wins.

Simple way to demonstrate this: ground the negative straight to the chassis. See what goes wrong. There are indeed threads around here talking about those results .....

Bob