Solar Panel Addition Questions

capewoods · April 2015

My wife and I recently purchased a 2006 T@B Clamshell that we're very excited about. As we plan to be without shore power quite a bit, I have been researching replacing the existing battery with two 105A Lifeline deep cycle batteries wired in parallel. I'm going to mount two (and eventually four) 100W bendable panels from Renogy on the roof. Between the panels and the battery bank, I plan to use a 40 amp MPPT charge controller (also from Renogy). I'm going with the 40 amp, because when I eventually add the two additional panels, I'll put the two panels on each side of the roof in series and the pairs in parallel. I understand that this will feed the controller 24 volts (which it will step down to 12) but allow greater amperage to flow into the batteries -- thereby shortening the charge time. I hope this is correct, but I'm not sure.

I'm also planning to install a Trimetric TM-2025-A battery monitor rather than using the charge controller add on unit as I've heard it's more accurate and just a nice piece of equipment to have.

Questions I've got for those who may have done this already or are just more knowledgeable about T@B wiring and living off grid are as follows:
1. Does this make sense?
2. Is the 200A battery bank enough? (I've heard that you should be at least up around 300A for 400W of panels?
3. Do I have to do anything special with my original converter box or will the solar installation cause it any problems?
4. Were I to install a pure sine wave inverter into the mix, would 500 watts be sufficient for most camping needs and if it is attached to the battery bank as well, how does it get wired? 5. Would an inverter replace the converter somehow for all ac power in the camper?

As you can tell, I'm new to all this and just trying to get as full an understanding before I start ordering equipment. Thanks to all who might be able to provide any thoughts or recommendations.

Bgkirk · April 2015

Capewoods,

Congrats on the T@B purchase. My wife and I have a 2015 T@B Clamshell and love it. We have similar battery amp-hour capacity (220 ah - two 6 volt lifeline batteries). This has proven to be ample for 5 days without any charging and 50% draw down on the batteries. The lifeline battery will have no problem with the charge rate from the 400 watt panel as they accept 250% of the rated capacity each or over 500 amps for both. That being said, I think your original 200 watt panel capacity will meet all of your needs. This would allow you to use the TM-2030 and the SC-2030 together for a really nice charge/monitor setup that will do an excellent job of charging your batteries and protecting them from damage. This is what we have and love how it works. You shouldn't have to do anything to your original converter.

Not sure what you want to power with your inverter so the size question is tough. Inverters are separate from the converter and the existing AC outlets in your trailer (unless you do some major and expensive rework that is probably not practical given the size of the T@B). Inverters of this size would need to be wired directly to the battery. 500 watts is approximately 45-50 amps at 12 volts with the efficiency of an inverter. This is a big wire and the length of wire would need to be considered prior to determining the wire size.

I hope this helps and happy camping.

Rad · April 2015

You must wire the batteries in series to have 12v. In parallel will result in double the amp hrs but only 6v. That will not operate the T@B.

If I misread your post, sorry

Bgkirk · April 2015

I think the 105 amp batteries from lifeline mentioned are 12 volts. I am using 6 volts in series in my setup. I believe the series/parallel description was related to the solar panels themselves. Same sorry if I misread.

capewoods · April 2015

BGkirk,

You are exactly right about the batteries being 12v and therefore wired in parallel. Your insights are exactly the kind of input I need. Thank you. I had considered the TM2030 and SC2030, but was thinking I would go with the Renogy 40amp charge controller because it is MPPT. You wouldn't use both that and the 2030 would you? Or, are they doing different things. Perhaps the MPPT just isn't necessary, but it seemed like this could increase charge rates by as much as 30% and would also help if sun was getting to one panel but not the other. Again, your thoughts would be welcome. By the way, did you get the bendable panels and if so, how do you like them? Did you mount them with tape, silicone, or industrial velcro? The batteries in our clamshell are located under the bench seat and I figured the inverter could be right beside them with an outlet just a few inches away and essentially on the floor. That's also the reason we're going with AGM batteries. So if we're hooked to shore power, doesn't the converter try to charge the batteries and is that an issue while they are getting charged by the panels?

Bgkirk · April 2015

Capewoods,

MPPT controller is a more efficient controller and will deliver more of the rated output of your panels to your batteries. I liked the flexibility and programability of the the TM-2030/SC-2030 combo so sacrificed some charge current. I do have the flexible panels but don't have them mounted. I like to be able to move them into the sun while the trailer is in the shade. There is certainly advantages to having them mounted too.

Your inverter plan sound easy and simple given the batteries are close.

The converter does charge the batteries while plugged into shore power but there will be no problem with the solar panel charging at the same time. You may want to invest in a new converter that is a smart charger (not sure what converter was in use in 2006). Smart chargers in converters have serveral modes to increase charge rate when needed and float charge when plugged into shore power for long periods of time. Also not sure what the amp rating of your current converter is, but it may not meet your needs.

Lisa33 · April 2015

I have 2 Trojan T-105 6v batteries wired in series for a total of 225Ah. I've paired them with 300 watts of solar. Basic rule of thumb is 1w of solar per ah of battery capacity. I've mounted my panels because I want them working for me all of the time whether I am stopped at an overlook, taking an impromptu hike, eating lunch on the road, etc. I've been the portable route with an 80w Zamp unit, but found it impractical for my needs (plus too small). I've intentionally oversized the panels to the batteries (300 watts to 225 Ah) to compensate for my complete refusal to park in direct sun when it can be avoided.

I am running a Norcold 2-way refrigerator (which, by the way, I consider the better choice for anyone who wants to dry camp extensively) along with an ARB fridge in my TV. I've upgraded my fan to the low amp model (currently the 7350). All of my lighting is LED. I used a Renogy 300 watt solar kit, which included a PWM controller. The solar set up allows me to boondock indefinitely without any real concern over power. My last cross country trip was 6 weeks long without shore power. Since I was boondocking wherever I could, my average cost per night for camping fees was $2.50. I figure I saved about $25-30 per night by avoiding the "need" for campsites with hookups. Over that 6-week trip, I figure the solar set up paid for itself.

Bgkirk · April 2015

Great comments Lisa33. A combination of minimizing what you use and maximizing what you generate is the key to boondock success.

Nomad · April 2015

Good info Lisa - Even though I have just 120w, I consider it the best investment I made. I've only been hooked to shore power 5-6 times in 6 months. Use the generator 5-10% of the time but some of that is by choice - Sunday morning breakfast just ain't right without toast :-).

capewoods · April 2015

Bgkirk said:

Also not sure what the amp rating of your current converter is, but it may not meet your needs.

Bgkirk:

It looks like I've got a WFCO 8725 converter which seems to mean that I've got a 30 amp main AC breaker and three 20 amp circuits. The online specs also show "25 amps DC output." I'm not sure if this means 25 amps to the battery bank when charging or just to the four DC circuits? If it is 25 amps to the battery, would this be sufficient to charge my battery bank? I saw maximum ratings on amperage inputs to the battery, but not minimum. Again, this would only be charging when on shore power and I think I understood your earlier post to suggest that there would be no problem with the converter and my panels both charging the batteries at the same time.

Also, would it not be possible to take a small inverter and feed the the AC circuits somehow? I was reading about the Go Power TS-30 Transfer Switch which says:

"The TS-30 is a two-pole 30 Amp AC Switch that automatically connects shore power (when available) to your vehicle load center (breaker panel). If you unplug from shore power, it then connects your inverter output to power your circuits. The GP-TS includes a cable with built-in plug to connect the inverter output, and a receptacle that powers your converter only when shore power is available. "

This sounds like a possible solution to get AC to my existing AC outlets in the T@B trailer -- assuming I'm not overloading my wiring. I do notice that the breakers in my Converter are all 15 amp for some reason?

Any thoughts you or anyone else can provide are very much appreciated as I'm a newbie when it comes to electricity -- and camping!

Bgkirk · April 2015

The converter essentially does three things for you. 1) It passes shore power through circuit breakers to A/C 120 volt accessories and plugs throughout your RV, 2) Coverts A/C 120 volts to D/C 12 volts passing it through fuses to accessories and plugs throughout your RV and 3) Provides a charge to the batteries.

The 25 amp capacity on the WFCO 8725 is related to the D/C 12 volt aspect of the converter. This is the maximum amount of amperage the converter can produce for items 2 and 3 above combined. The current WFCO 8725 model provides a basic level of smart charging.

The transfer switch is an option and is used in many (typically larger RV's). You are limited by the capacity of the inverter and batteries when not connected to shore power. Also inverters use some amount of power all the time, even when no A/C accessories are being used. If wired this way, I would make sure you could turn the inverter off.

I would also recommend the A/C wire work be done in accordance with the National Electrical Code Article 551 or by someone familiar. The mobile wiring system has unique issues that are not found in a home. Grounding all of these accessories in a very particular way is very important and is just one item that comes to mind.

Bgkirk · April 2015

My Recommendations for you to get started:

Start with your 200 watts of solar and controller of your choice
Upgrade your batteries to the lifeline
Install the TM-2025 or TM-2030
Install a standalone inverter of the size to meet your needs

Give this a go for a couple trips and see if you need to adjust anything from there. Happy T@Bbing.

capewoods · April 2015

Thanks. I am going to start by just installing two 100 watt panels, but I am genuinely torn now about whether to use the TM-2030 PWM charge controller or an MPPT charge controller. I spent some time yesterday speaking with Bogart Engineering (who was very helpful and very generous with his time). I had been under the impression that when I went to four panels, there was a charge time benefit by combining a couple of panels in series to produce 24 volts going into a 12 volt battery bank. The theory, as I understand it, is that the MPPT controller steps the voltage down going into the batteries -- but more amps are being fed to the batteries thereby producing a quicker full charge. Since the 2030 will not accommodate this higher voltage setup, an MPPT was the only option. However, maybe that's not the whole story.

I'm told that if all panels are run in parallel, the power to the batteries is the same as in the above partial parallel/partial series approach. Given the short distance on the T@B, running the panels all in parallel is not a big problem. Moreover, the shading cutout problem seems to be addressed since any one panel being obscured should not affect another panel still in the sun. This seems to leave the only benefit of the MPPT controller as helping when the temperature of the panels is so cold as to reduce output. This is something a PWM controller just doesn't adjust for. While I live in Maine, the general use of the panels will be in very pleasant spring, summer, and fall temps!

So it may be that the 2030 does almost everything I need -- as long as all panels are wired in parallel. It does seem to be a simpler and cheaper approach, but I'd like to make sure I'm correct about this and not missing some significant benefit of the MPPT controller. It does seem like larger systems now gravitate toward MPPT and away from PWM, but maybe that's my newbie impression. Do others agree or am I misunderstanding "the electrics" here. Thanks again.

jcfaber1 · April 2015

The folks at Bogart engineering are very helpful and are trustworthy. I have their 2025-RV meter and find it very helpful in managing my batteries. They were helpful with programming the meter. I have 2 6V batteries wired in series. Regarding the PWM / MPPT decision you need to decide how you want to wire your system. On my system I originally purchased a 260W grid tie panel which outputs at 32V. 32v is regarded a higher voltage and required MPPT controller. I have Midnite Solar Kid charge controller and it works quite well. MPPT can yield about a 10% boost. The other benefit of higher voltage output is that thinner or longer wire can be used with less voltage loss. My setup is portable and I use a 50ft 8 guage cable. You want to have less than 3% of voltage drop. Southwire has a nice voltage drop calculator to help you figure out what cable to use.

http://www.southwire.com/support/voltage-drop-calculator.htm

I think you are going to use the Renogy RNG-100DB panel. ( I am converting to these panels as well with my 200W solar suitcase) It outputs 17.7V @5.7amps. Therefore if you wire the two in series (35.4V), you will require the MPPT controller. Since you are going to permanently install on the roof, you need to be very concerned with shading. If the panel gets shaded it will not output. Therefore I would wire each of them in parallel to the controller so that as the sun moves through the sky on any shading will not shut the whole system down. If you use heavy enough wire, with such short runs, I would just use the Bogart PWM charge controller. It is designed to work with the meter and will be a nice setup. I would install breakers between the panel and the controller and between the controller and the batteries.

Check out this persons blog, there is a lot of good information:

https://handybobsolar.wordpress.com/the-rv-battery-charging-puzzle-2/

Have fun now!

John

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