Solar, it just can't be that complicated?

[dznf0g]

Originally Posted by KJRitchie

Yes, I'm more than likely going to go that route. Not sure if I'm going to remove the controller to inside the Airstream. My batteries are in the A frame. So I would have to mount the controller under the front bed and run two sets of cable from the controller, one pair to the batteries and one pair to an Anderson cable to plug in the panel. Not sure its worth all that to gain a little voltage. I'm thinking of spending a little more for the 200w panel kit and just use better cabling like you did from the panels to the batteries but leaving the controller on the panels.

Kelvin

With the Anderson connector configuration I used, I can re-install the controller
to the panel bracket and plug it back in, in a matter of two minutes. Flexibility is the name of the game.

[Minipad]

Zamp has assured me that the diodes to prevent reverse flow are indeed installed on the back of their panels. Also keeps the panels from draining the batteries at night. In my 2013, Airstream pre-wired with 10 ga. wire. Someone should be able to tell you whether or not 10 ga. wire will be sufficient copper for the wattage and distance you are moving the current. I believe (haven't looked it up) that for the wattage you are intending, you should be fine running both panels through the same wire. I would make sure the connection is made above your trailer and that both panels are fused. (The Airstream factory seems to have missed that detail on my install. Not to mention that they put a screw through one of the wires.) I have two 150W Zamp panels running through my controller and it works great. However, someone suggested above that more batteries may be a good solution to consider. I would say both. In a thread I read just the other day, I saw another suggestion that is spot on. If you are running a generator at times, use the 12V (direct connected to your batteries) output function of the generator and pound your batteries with a full 8 amps for a period of time that is consistent with the depth of discharge in your batteries. My experience with wet Interstate batteries is that they lie to whatever controller available about their existing charge. They are too quick to report higher voltages (surface voltage readings) than what is actually true of their state of charge. The best way to really know the condition of your batts is by checking the specific gravity.

I do a lot of boondocking and here is the method that gives me the best results:

I check the stated voltage in my batteries before the sun hits my panels in the morning. If you have the SRM24 Interstates you have about 85ah available in each battery. You should try to never let them go below 50%. So with two, you really have 85ah overall available. For every 8ah you deplete from the batteries, give them a full hour of generator charge from the 12V function of the generator. (Unfortunately, your onboard converter provides them with less.) By the way, at 50%, your controller will tell you that you have 12.4 volts. (Again, this is a surface voltage reading and is generally optimistic. Especially shortly after a charge of any kind.) When mine are at 50%, I bulk charge with 8 amps for about 5 hours without any issues. Then my solar panels, converter from shore power, etc. do the rest.

With roof (flat) mounted panels, and depending on the weather, your latitude, the season, etc., the panels you have stated, may only produce about 30 to 60 amps of replacement charge to your batteries during a normal day. That being the case, if you see morning readings below 70%, you may start the next night at less than 100%.

Don't forget when you are hooking any charge directly to your batteries, put the negative wire on the negative post of one battery and the positive wire on the positive post of the OTHER battery. This ensures all cells in both batteries see the juice.

One other note: I have a sturdy, vented tool box, into which I mounted another SRM24. On the end of the tool box is a RV plug just like the one on my tow vehicle. At night, I set the box by my trailer and plug my trailer into the box. This gives me three batteries (actually, because of the routing of the wiring, more like 2 2/3.) That is usually enough to get me through a night of 15°F to 25°F lows without any issue. This box is charged during the day, either with the generator or another 150W solar panel and a separate controller which are both mounted above the bed of my truck. Of course the trailer is disconnected from the box before the charging begins to avoid the controller conflicts you have already learned about from others.

Maybe Lewster can give you the information of the voltage drop you will see by running both panels down the 10 ga. wire you already have installed. If you are going to pull new wire, at least do your best to get more wattage on the roof.

Just last night, I was boondocking near Steamboat Springs, CO and have finally finished a list of the amp draw on every thing in my trailer. I was surprised to find that my fridge, running on propane, still draws 0.78 amps per hour. That's almost 19 amps per day. The good news is that I learned that by using the dimmer switches on the LED lights in the ceiling, I can reduce the amperage draw by over 75% from full bright to the dimmest setting.

If you're still reading by this point, I hope that helps!

Cheers

[lewster]

What you are doing may be working for you, but at what level?

I'll place my comments in red. As always, take what you want, but after installing over 100 solar charging systems, I go with my experience and the specifications that battery and component manufacturers deem to be the best way to utilize their specific devices to properly charge their batteries.

Originally Posted by Minipad

Zamp has assured me that the diodes to prevent reverse flow are indeed installed on the back of their panels. Also keeps the panels from draining the batteries at night. In my 2013, Airstream pre-wired with 10 ga. wire. Someone should be able to tell you whether or not 10 ga. wire will be sufficient copper for the wattage and distance you are moving the current. I believe (haven't looked it up) that for the wattage you are intending, you should be fine running both panels through the same wire. I will use 10 AWG only for a single 100 watt panel. We also use 10AWG for the connections between the solar panels on the roof and the roof top combiner box to a maximum length of 15 feet per panel. I use the following for connections and tolerate no more than a 2% voltage drop in any of my systems and preferably less: 200 watts-8AWG, 200+watts to 500 watts-6 AWG, 500+ watts to 700 watts-4AWG. I also use multiple charge controllers and wiring harnesses for any system over 700 watts. You want as little voltage loss as possible in your wire runs, as every connection made in the system and any charge controller that you use will also show some voltage drop. I would make sure the connection is made above your trailer and that both panels are fused. (The Airstream factory seems to have missed that detail on my install. Not to mention that they put a screw through one of the wires.) I have two 150W Zamp panels running through my controller and it works great. What type of controller, PWM or MPPT?However, someone suggested above that more batteries may be a good solution to consider Any battery bank should be properly sized to either your anticipated or actual power usage patterns with the solar array and charge controller large enough to fully support the batteries. I would say both. In a thread I read just the other day, I saw another suggestion that is spot on. If you are running a generator at times, use the 12V (direct connected to your batteries) output function of the generator and pound your batteries with a full 8 amps for a period of time that is consistent with the depth of discharge in your batteries. This is a BAD IDEA and is no better at charging your batteries than using the original Parallax single voltage converter that Airstream supplies. Your batteries want complete 3 stage charging, NOT a constant voltage input from a generator. You would be far better using the 120VAC output from the generator to charge the batteries from a 'smart' 3-stage converter of better yet, a fully programmable inverter/charger. My experience with wet Interstate batteries is that they lie to whatever controller available about their existing charge. They are too quick to report higher voltages (surface voltage readings) than what is actually true of their state of charge. The best way to really know the condition of your batts is by checking the specific gravity. Get a better battery monitor and definitely better batteries! Actually, the VERY BEST way to check the condition of your batteries is with a conductance meter. It gives you the actual condition and health of your batteries at almost any voltage present in the batteries by sending an energy pulse thru the cells and interpreting the reading thru a proprietary processor. Very accurate and very high tech. No error from a specific gravity reading that is not temperature compensated.

I do a lot of boondocking and here is the method that gives me the best results:

I check the stated voltage in my batteries before the sun hits my panels in the morning. If you have the SRM24 Interstates you have about 85ah available in each battery. They are listed at 80 amp/hours each. You should try to never let them go below 50%. So with two, you really have 85ah overall available. For every 8ah you deplete from the batteries, give them a full hour of generator charge from the 12V function of the generator. (see above why single voltage charging is not a good way to properly charge your batteries) (Unfortunately, your onboard converter provides them with less.) Have you actually put a DC amp clamp meter on the charge line from a converter to the batteries to measure the amperage output? By the way, at 50%, your controller will tell you that you have 12.4 volts. Different batteries have differing 50% SOC readings, from 12.0-12.4 VDC. every charge controller uses a different method to determine SOC. The Blue Sky systems that I use have a very accurate shunt that gives you much better information than a simple charge meter. (Again, this is a surface voltage reading and is generally optimistic. Especially shortly after a charge of any kind.) When mine are at 50%, I bulk charge with 8 amps for about 5 hours without any issues. At what voltage? Then my solar panels, converter from shore power, etc. do the rest.

With roof (flat) mounted panels, and depending on the weather, your latitude, the season, etc., the panels you have stated, may only produce about 30 to 60 amps of replacement charge to your batteries during a normal day. A single 100 watt panel run thru a quality MPPT charge controller with temperature compensation should give you 30-40 amps per solar day, depending on the solar radiance it receives. Tilting the panels in lower latitudes can increase this amount by 20%. A properly sized solar charging system should (and does regularly) produce enough charging amperage (with full, temperature compensated 3 stage charging, to have the battery bank at 100 % SOC by 2:00-3:00 PM. That being the case, if you see morning readings below 70%, you may start the next night at less than 100%.

Don't forget when you are hooking any charge directly to your batteries, put the negative wire on the negative post of one battery and the positive wire on the positive post of the OTHER battery. This ensures all cells in both batteries see the juice.

One other note: I have a sturdy, vented tool box, into which I mounted another SRM24. On the end of the tool box is a RV plug just like the one on my tow vehicle. At night, I set the box by my trailer and plug my trailer into the box. This gives me three batteries (actually, because of the routing of the wiring, more like 2 2/3.) That is usually enough to get me through a night of 15°F to 25°F lows without any issue. Without temperature compensation on your battery charging voltage, you probably are severely under-charging them at these low ambient temperatures. This box is charged during the day, either with the generator or another 150W solar panel and a separate controller which are both mounted above the bed of my truck. Of course the trailer is disconnected from the box before the charging begins to avoid the controller conflicts you have already learned about from others.

Maybe Lewster can give you the information of the voltage drop you will see by running both panels down the 10 ga. wire you already have installed. If you are going to pull new wire, at least do your best to get more wattage on the roof.

Just last night, I was boondocking near Steamboat Springs, CO and have finally finished a list of the amp draw on every thing in my trailer. I was surprised to find that my fridge, running on propane, still draws 0.78 amps per hour. That's almost 19 amps per day. The good news is that I learned that by using the dimmer switches on the LED lights in the ceiling, I can reduce the amperage draw by over 75% from full bright to the dimmest setting.

If you're still reading by this point, I hope that helps!

Cheers

Have you been reading Handy Bob's blog (excuse me, he now goes by 'Solar Bob'). Much of what you have written seems vaguely familiar.......

[lewster]

Originally Posted by dznf0g

Thanks, Lew

Just out of curiosity, and maybe this isn't the place for it....what is the advantage of the system you describe with 3 controllers in parallel and running through an iPN panel...as opposed to three panel (arrays?) wired in parallel to a single large capacity controller? Is there no controller large enough for the load desired in the above system?

Rich,

Larger solar charge controllers for RV use are either not practical or not available for use in a 12VDC (nominal) environment. Plus, the cable size for the 2000 watt system that I installed, if there was a single 120 amp controller available, would be extremely cumbersome and likely in the 1/0-2/0 AWG range. Plus, by utilizing essentially 3 separate systems linked thru a single remote central control, you have more versatility in the event of shadowing, which at some point in the day will be a reality.

I used to use 60 amp controllers from Morningstar, but linking them in parallel is quite cumbersome and requires lap top programming of their router device. The Blue Sky system is far easier to connect, will control up to 8 solar charge controllers and also includes a full function battery monitor that is integrated into the iPN-PRO remote.

Each individual charge controller can be accessed thru the iPN-PRO remote for specific charging data, but all work together to place as many charging amps to the batteries as possible using the MPPT algorithm of each controller.

PM me if you want to go into more depth and detail.

[dznf0g]

Thanks Lew. That actually makes sense, not that I am even considering anything like that, but I find it interesting.

[MaineStreamer]

I may be exposing my ignorance, but with all these electrical systems, how does one achieve a "ground" when both the trailer and tow vehicle are separated from the ground by rubber tires? Or is a "ground" not important?

[lewster]

Originally Posted by MaineStreamer

I may be exposing my ignorance, but with all these electrical systems, how does one achieve a "ground" when both the trailer and tow vehicle are separated from the ground by rubber tires? Or is a "ground" not important?

Marty,

Grounds provide a common reference point for electrical measurement and a return path (classic electrical theory) for the current passing thru a circuit.

'Earth' grounding is not necessary in a vehicle or RV's DC electrical system, as the chassis ground connections provide the common point for all grounding leads, including the 120VAC system and the batteries.

In a residential application, the circuit breaker box will have a neutral to ground bond in one location ONLY, but this is not the case in RVs. When using a quality inverter, the inverter will actually have an automatic internal relay that will provide the neutral to ground bond inside the inverter when it is operating from the batteries (inverting).

When on shore power and using the inverter's pass-thru feature, the neutral to ground bonding relay is open (no connection), as there will be a single neutral to ground bond found in the 120VAC power post or residential breaker box.

Hope I haven't totally confused you ..........