Some great resources to consult for assembling your system would be:

www.amsolar.com

and

www.jackdanmayer.com/rv_electrical_and_solar.htm


Also, I wouldn't get too attached to being able to run your fridge off solar much. Those propane/electric fridges are really most efficient off propane - and can really suck down the electrons otherwise. That's just how they are optimized. If you want to run a fridge off solar regularly, would recommend switching out to one optimized for electricity... and you'll probably need more panels and/or battery capacity too.

- Cherie

I would never EVER let an RV dealer install a complete implementation of an electrical system like you are describing. NEVER. The chances of them getting it right are "slim and none". There may be a dealer or two in the country that could do a decent implementation, but I sure would not roll the dice on most of them. I cannot tell you how many rigs both Bob (aka "Handy Bob") and I have fixed for people that have gone this route.

My advice is to NOT buy components yourself, and to take you coach to someone that knows what they are doing. There is a list on my website. Plus, I believe that Howard and Linda now endorse someone in PA, so you might want to check with them.

I no longer do installs....

A 30a controller is too big for one panel and too small for two. Unless there are features on the 30a version that are not on a 20a version, you could save money and space by going with the smaller.

This line of Tracer controllers are fairly new but from what I've read they seem to be functional. The only complaint I've heard is that the remote panel isn't all that accurate. For a few years now I have been using a inexpensive yet functional 20a MPPT controller that goes for $102 shipped. It has done fine but when I get around to mounting my panels this year I have decided to go with a more feature packed controller for the long haul. Features like a remote battery temperature sensor and voltage sensor plus software settings will make it worth the extra cost. ( my system is a pitiful 490w mounted and 230w portable)

MPPT vs PWM should be the last thing you worry about when you design a system. What fits on your roof and in your budget will determine that. One large 24v panel will need a Mppt controller and that's all that matters. There are other considerations like what conditions you camp in but in the end it is splitting hairs.

I'm with Bill.......after you calculate your needs, Double that!!!!

or go to AM Solar or a reputable solar installer and let them tell you what you need......trying to save a buck in the start will cost you double in the end.

Does this look like a good battery?
www.amazon.com/Vmaxtanks-VMAX-Rechargeable-Solar-Inverters/dp/B00DDYM1UC/ref=pd_cp_e_3

155 amp hours seems like a lot for a battery this size.

Jack Mayer wrote:

---

I would never EVER let an RV dealer install a complete implementation of an electrical system like you are describing. NEVER. The chances of them getting it right are "slim and none". There may be a dealer or two in the country that could do a decent implementation, but I sure would not roll the dice on most of them. I cannot tell you how many rigs both Bob (aka "Handy Bob") and I have fixed for people that have gone this route.

My advice is to NOT buy components yourself, and to take you coach to someone that knows what they are doing. There is a list on my website. Plus, I believe that Howard and Linda now endorse someone in PA, so you might want to check with them.

I no longer do installs....

---

 I never said I was going to let the RV dealer do the install. I said I was going to hire an electrician to do the install. Turns out my best friend set me up with an RV repair guy who is experienced in adding solar panels in RV's and is $40 cheaper per hour than the RV dealer. BTW, i'm in Montana.

-- Edited by phinfan on Monday 19th of May 2014 11:15:58 PM

phinfan wrote:

---

jimindenver wrote:

---

A 30a controller is too big for one panel and too small for two. Unless there are features on the 30a version that are not on a 20a version, you could save money and space by going with the smaller.

This line of Tracer controllers are fairly new but from what I've read they seem to be functional. The only complaint I've heard is that the remote panel isn't all that accurate. For a few years now I have been using a inexpensive yet functional 20a MPPT controller that goes for $102 shipped. It has done fine but when I get around to mounting my panels this year I have decided to go with a more feature packed controller for the long haul. Features like a remote battery temperature sensor and voltage sensor plus software settings will make it worth the extra cost. ( my system is a pitiful 490w mounted and 230w portable)

MPPT vs PWM should be the last thing you worry about when you design a system. What fits on your roof and in your budget will determine that. One large 24v panel will need a Mppt controller and that's all that matters. There are other considerations like what conditions you camp in but in the end it is splitting hairs.

---

 If the grape solar 250 watt panel is rated at 8amps, how is the controller too small for two panels? I wanted the larger controller so I could add more panels in the future and your saying its not enough? How did I screw up when figuring this out?????

---

You are correct, the panel is rated for 8 amps but at close to 40 volts. Once the controller converts the extra voltage, the output amps will be closer to 20 amps. Two of those panels will require a 40a controller.  On paper it looks like you can add another 120 watts to the 280 watt panel and be within the 30a controllers abilities BUT finding a 120w panel that matches up with the voltage specs of the bigger panel isn't going to be easy if at all possible. You really need to be with in a volt in Voc and Imp to not confuse the tracking of the controller.

Add into that my 230w 24v panel with a 8.33a rating  at 9-10,000 ft on a sunny day will put out over 13a in PWM mode. The air is denser at sea level where the panel was rated. Up there the air is much thinner and cleaner resulting in higher output.

That is one advantage of a PWM system. It is easier to add panels at a later date. A 150w 12v panel runs at close to the same voltage as a smaller panel so you can put a big one here and a smaller one over there, even add a new one in 5 years and they will all still be 12v panels. Also a 12v poly can be matched with a 12v mono with no ill effects. My 220w mono panel and 230w poly panel can't be used together as the mono has big swings in voltage in different light while the poly is more consistent.

As I said, MPPT vs PWM is the last thing that should determine what is bought. Knowing your needs, how much solar to properly handle your battery bank, how much room do you have to mount and in what configuration of panels, what is your budget and what is available will come into play first. Climate may be a consideration as I have read that in a sunny locale like AZ. MPPT has no advantage.

Now if your roof was filled with 12v panels and you absolutely needed that extra 10 %, switching to a mppt controller can help you. Just remember that you can be paying a lot for a few amps a hour. If you had extra room for another panel, you would be better off doing that. It would result in a bigger gain. 

My roof is perfect for two huge panels. I could go 12v but that would mean more panels, more work to mount, more holes, more wires, more connections and heavier wire to the controller. The big panels are cheaper per watt but the controller will cost me $500 by the time I add a remote display, sensors, etc. Even considering the portable 230w panel has a $100 controller, I will still spend twice as much on controllers as I did the panels.

-- Edited by jimindenver on Wednesday 21st of May 2014 08:08:26 AM

Okay, just got off the phone with Grape Solar and they confirmed that with that mppt charge controller and their 250w panel, i'd be pushing out 20amps. So, i'll be sending this controller back and purchasing a larger 45amp controller. I'm pretty sure at some point i'll be throwing on another 250 watt panel, so better to plan ahead now than be stuck with this controller with no return thru amazon.

so, i'm now sending back the 30a charge controller for this one:
www.amazon.com/gp/product/B00E7NI9PE/ref=oh_details_o00_s00_i00

I elected to go with the same brand as the remote panel would still be compatible and quite frankly, I like the price better than the more expensive Morningstar.

Grape solar engineer confirmed that this 40a one will be fine with 2x 250w panels.

Still waiting on the charge controller but the installer came out and installed everything else. Interesting thing here is that the 2000 watt inverter won't run the 800 watt microwave. Low voltage alarm comes on after about 2 seconds and shuts off the microwave. He used 6awg wire from inverter to the batteries about 6 feet away. The batteries are 2 Trojan t-105's wired for 12v and have 225amps. Did he undersize the wire?

As the panels are not yet hooked up because we are still waiting on the charge controller I haven't been able to test those yet but he used 12awg wire for that. Is this okay?

(Removed on edit since the other Bill has better info.)

On top of the issues Bill said, it might be the batteries.  Four T-105s can handle 1500 watts, so two should be able to handle 800 and still have enough voltage to not fault the inverter.  How good are these T-105s and how well charged are they?  

I also wanted to say that most electricians only know AC rules and are not that familiar with DC.  

-- Edited by bjoyce on Monday 26th of May 2014 02:09:48 PM

-- Edited by bjoyce on Monday 26th of May 2014 02:11:35 PM

Chris, the cable from the inverter to the batteries needs to be able to handle at lease 225 amps because the batteries are 225 amps each at 6 volts.
Don't so much look at the size of the cable but how much amps the cable can handle, the finer the wire the more amps the cable can carry because most of the amps travel on the outside of the cable not the inside, the finer the wire the better off you will be.

This is the cable that can handle 300 amps, I recommend from the inverter to the batteries.

And the second cable can handle 140 amps for battery to battery and from batteries to controller also from controller to solar wires on roof.

If you do not believe me go to RVillage and look at my site and my pictures, it works for me.

                                                       
                             Inverter to Batteries 
http://www.wireandcabletogo.com/2-0-Welding-Cable-Class-M-UL-CSA.

                                   and   

http://www.wireandcabletogo.com/4-AWG-Welding-Cable-Class-M-UL-CSA.html
                             

Lonney

-- Edited by Lonney Wade on Monday 26th of May 2014 02:44:39 PM

-- Edited by Lonney Wade on Monday 26th of May 2014 02:48:49 PM

-- Edited by Lonney Wade on Monday 26th of May 2014 02:51:06 PM

As Bill said, #6 is not going to work under heavy load....as you have discovered. #2/0 is what I would use, as well.

The run from the roof combiner to the solar controller is properly determined only one way. Calculating it using one of the online tools (or by hand). There is info on my website on doing so. Anything else is a guess. But I would use no smaller than #4 - as a good practice. But the real answer is to calculate it. I run the numbers for a 2% loss and usually go a little heavier.....and be aware that with an MPPT controller you "might" need heavier cable between the battery bank and controller because of the boosted current at 12-volts nominal. This connection is the most important to get right. Tenths of volts matter.

nevermind, I see my mistake. I was looking at the %5 loss chart.

I was also thinking you tested the microwave to get 800 watts. A 1000 watt microwave uses closer to 1500 watts of electricity to supply 1000 watts of heat, so an 800 watt microwave could easily use 1200 watts out of the wall. 1200 watts is too much for two golf cart batteries.  You need to test the microwave with a Kill-A-Watt or a this, http://www.amazon.com/Floureon-TS-836A-Voltage-Electricity-Monitor/dp/B00E945SJG, which will also save maximum watts.    

phinfan wrote:

---

2000watts = 166 amps. Shouldn't a 225amp battery handle a 225amp load for 1hr? if so, 166amps should go longer 1.35hr. And lets say the 800 watt microwave is pulling 1200 watts. That would be 100 amps. So if I didn't mind draining my batts down to zero, I should get a couple of hours. At 50% drain, I should be able to run the microwave at 1200 watts for 1hr, right?

-- Edited by phinfan on Monday 26th of May 2014 03:54:48 PM

---

The voltage drops too far when you pull more than about C/3, which is 225/3 or 75 amps.  I looked for simple charts, but this one, http://www.knowyourplanet.org/off-grid/batteries/deep-cycle-battery-voltage-and-discharge, is all I came up with.  Your battery was not discharged, it just can't handle too many amps without the voltage going too low.  If you look at production RVs, they use 4 batteries with a 2000 watt inverter and 6 batteries with a 2800 or 3000 watt one.  Voltage drop under load is a major reason.

bjoyce wrote:

---

phinfan wrote:

---

2000watts = 166 amps. Shouldn't a 225amp battery handle a 225amp load for 1hr? if so, 166amps should go longer 1.35hr. And lets say the 800 watt microwave is pulling 1200 watts. That would be 100 amps. So if I didn't mind draining my batts down to zero, I should get a couple of hours. At 50% drain, I should be able to run the microwave at 1200 watts for 1hr, right?

-- Edited by phinfan on Monday 26th of May 2014 03:54:48 PM

---

The voltage drops too far when you pull more than about C/3, which is 225/3 or 75 amps.  I looked for simple charts, but this one, http://www.knowyourplanet.org/off-grid/batteries/deep-cycle-battery-voltage-and-discharge, is all I came up with.  Your battery was not discharged, it just can't handle too many amps without the voltage going too low.  If you look at production RVs, they use 4 batteries with a 2000 watt inverter and 6 batteries with a 2800 or 3000 watt one.  Voltage drop under load is a major reason.

---

 

Bill J, good explanation and link.  Doing the math and even at 800 watts of draw (and the microwave is probably much more actually as you commended) that would be just barely below the C/3 point let alone the #6 wire I/R loss.  (Resistance = voltage drop)

I’ve run a microwave that drew 1,400 watts off a 2,000 watt inverter.  But it was drawing ~120 amps DC.  It worked because of the bank size and I was using 4/0 wire and the runs to the inverter were under 3 feet.  Point is, IMO, you don’t really want to think about actually running these high wattage units off the typical inverter as a normal occurrence.  Even if they bank holds, unless you have a bank like Jack’s, it will kill the batteries so quick the solar will never recharge them on a practical basis.  We’re talking minutes to flatten the bank to 50%, not hours as you well know.  That’s what they make generators for, IMO.  It’s really just math but the math needs to be understood.  225AH is not a large battery bank.

Sometimes it is difficult to make these posts as they can be disappointing. But the math, chemistry and physics are-what-they-are and all that can be done is to provide the best factual information possible.