Is this Costco kit a good match for basic RV setup?

Re: Is this Costco kit a good match for basic RV setup?

'Morning Ken,

You have two questions--what amount of power does your RV need to properly recharge the battery bank and what about the Costco system.

Lets assume you use the batteries to 20% state of charge (80% discharged--while this is a heavy discharge and not great for long life--you don't wan to go any deeper because you may permanently damage the battery bank). The amount of AH you have used is:

• 225AH * 0.80 = 180 AH

Lets assume that are somewhere in BC Canada, mount the panels flat, and are using this mostly during the summer months. Assume that you get >5 hours of "noon time" sun a day. Also that your battery bank is 80% efficient.

The panels are 2x80 watts = 160 watts and Imp=9.34 amps.

• 180 AH * 1/5 hours of sun per day * 1/9.43 amps * 1/0.80 = 4.77 days of sunny weather

So, based on your requirements, this system would meet your needs...

Now, batteries tend to sulfate when kept below ~75% state of charge--So, their life would be longer if you could get them >75% SOC quickly (within a day or so) and let the solar panels finish them off. Generator, using towing vehicle to charge, etc. would all help.

Will your batteries last you 1-3 years or 3-5 years depending on how you take care of them (less deep discharging, getting them above 75% quickly, etc.)--maybe (I cannot foresee the future ). But, as long as you know the "costs"--Do what works best for you (not going camping and staying home for better battery life is not the end game here).

Regarding the Costco system... The panels and charge controller PDF Manual) are probably fine and will do what you expect of them.

Regarding the price--I would certainly shop around... I know that Canada is not cheap for solar products--and perhaps a trip to the US and some hand tools to install the system may be worth your time and trouble:

First the solar panels... Generally, the panels over 100 watts tend to have a much better $$$/watt based pricing (if you can fit them on your RV). For example, you can get two Kyocea 135 watt panels for $720.

The charge controller--there are two major types available. One is a PWM (as in the Costco kit), which work fine and are less costly.

The other are MPPT (Maximum Power Point Tracking) which have several advantages. In cold weather, solar panels output higher voltage, and the MPPT controllers can convert that extra voltage into more current into the battery bank (maybe 10-15% on average, in subzero weather, maybe 20% or more). Also, you can wire the solar panels in series and run the panels farther away with smaller gauge copper wire (for example, you put the panels on a 25' cord and position them in better sun than where your RV is parked--remember panels need to be protected against wind gusts--or you end up with shattered glass).

Lastly, see if you can get a Solar Charge Controller that includes a Remote Battery Temperature Sensor option. Will help ensure that the batteries are quickly and properly charged (pretty much mandatory for the Morning Star 15 amp MPPT charge controller). Batteries are very sensitive to temperature and properly charging voltages.

A Morning Star PWM controller is around $80-$160... The smallest MPPT is $235 (plus more if you want the meter or PC Interface kit).

Finally, the inverter... You can get inexpensive MSW (Modified Square Wave) inverters for almost nothing ($20-$30 or so). I would suggest a TSW (True Sine Wave) Inverter. If you are going to be charging your cell phones, running a laptop, TV, video player, etc.--Many of the small wall wart type transformers overheat when run on MSW Inverters.

A really nice 12 volt 300 watt TSW inverter from Morning Star. Efficient, and goes into low power standby if loads are turned off... $260

You did not ask--but some other nice to have options. If you will be using a fair amount of AC loads--get a Kill-a-Watt meter to measure them. It is also handy for use around the home to look for smaller energy hogs. If you will be doing a lot of DC loads--a DC Amp*Hour/Watt*Hour meter is nice.

A good Hydrometer for the battery bank. And I like to recommend a Battery Monitor to keep track of your battery usage. Almost manditory for sealed batteries.

Some FAQ's to read up on:

Deep Cycle Battery FAQ
www.batteryfaq.org
All About Charge Controllers
Read this page about power tracking controllers
All About Inverters
Choosing an inverter for water pumping

Pretty much the whole point of having a good system with long life revolves around properly managing the battery bank.

By the way, many of the above links are to our host's site as a starting point. However, you are more than welcome to look around for the best source for your location.

-Bill

Re: Is this Costco kit a good match for basic RV setup?

Kamala wrote: »

160W * 5hr = 800WH (640 if derated 20%)

800WH / 12V = 67AH (or 640/12=53)

Am I doing something wrong here Bill?

OP says he uses 10% of battery per day, or ~ 26AH.

I used the Imp current because this is a PWM controller... Vmp (as long as it is >Vbatt charging) is not useful... The actual Power going into the battery (before deratings):

• 9.34 amps * 14.4 volts (batt charging) = 134 watts
• 5 hours * 9.34 amps = 46.7 amp*hours

If this was a MPPT controller--then I would do the calculations in Watts.

Yes, I assumed maximum battery discharge as a worst case condition, and I did not add any derating for the panels (although, temperature derating is irrelevant for current (in fact, current increases a little bit as the panels get hot). For his original loads, this system is sized fine. I used 5 hours as a minimum--should be a bit more for BC--depending on a whole bunch of weather factors).

-Bill

Re: Is this Costco kit a good match for basic RV setup?

kshopper wrote: »

There is also a concern that if the batteries are very low (below 50%?) when put in storage that it would be better to charge them to 80% via plug-in (or tow vehicle) quickly (the first day back) rather than let solar recharge more gradually over several days to avoid the risk of sulfication. Does that sound right?

The less time the batteries send below 75%, the less sulfation... In the end though, RV use is a tough service... Lots of temperature swings and sometimes deep discharge.

Golf cart batteries properly maintained are probably good for 3 years or so... What you are doing to them is not going to take that much life away (unless you let them sit for days/weeks/months below 75% state of charge). Watch the water levels--running them dry (exposing the plates) is probably #2 on the battery hit list (right after #1 -- too much load, too little charging = deficit charging). (note--I am trying to be conservative here--if your system does better--be happy )

Another question, will the solar alone be enough to *properly* top up the batteries. Will they provide enough voltage etc.?

• Vmp>Vbatt-charging + 2 volts

Flooded cell batteries, when equalized need 15+ volts, so, Vmp + 2 volts (controller and wiring drops) is generally fine for anything but very hot days and very cold batteries (Vmp>17 volts).

If this system was in a hot desert--we would be looking at putting two panels in series and using an MPPT charge controller to allow you a wider operating range.

Current wise, the normal recommendation for charging is ~5%-13% as a reasonable min/max charge rate based on 20 Hour capacity:

• 225 AH * 0.05 = 11.25 amps
• 11.25 amps * 17.5 volts (panel Vmp) = 197 watts minimum panel
• 225 AH * 0.13 = 29.25 amps
• 29.25 amps * 17.5 volts (panel Vmp) = 517 watts maximum panel

The above numbers are just rough rules of thumb... So, you could easily add more solar panels and still be within a comfortable operating range for your battery bank.

Economically, it may not be worth it. Using alternative power for charging will make up for the occasional deficit.

Steca PR 1010 Solar Charge Controller, 10 Amp, 12/24 volt $126.00

I don't know much about the Steca controller. Nice integrated unit... Looks like it may even include an internal load shunt for keeping track of AH into and out of the battery--very cool.

One thing to watch those is that the maximum Load Current appears to only be 10 amps max (for the 10 amp charge controller). 10amps * 12 volts = 120 watts may not be enough power for your loads (laptop+inverter+various others)... May not handle inverter/AC load surges well.

Also, a 10 amp controller may be too small if you want to add more panels later.

If I could ask one more question, does anyone have a link to a resource that would explain in detail the proper way to connect the PV controller to the battery, along with the existing AC/DC/charger converter in the trailer? From what I've read, seems like you basically hook the solar controller onto the battery in addition to whatever is already connected, but I'd like to see a more comprehensive overview/example. Is it okay to be charging the battery using the tow vehicle and solar at the same time, what about the solar and the plugin-converter/charger in the trailer?

For connecting the charge controllers, following the manual is always a good start (www.stecasolar.com).

Here is a nice nice thread with video from Keven in Calgary Canada discussing many of the issues with installing panels on a small trailer. Even includes a video or two.

Yes, you can charge the same battery bank with multiple charge controllers... Basically, the one with the highest voltage set-point "wins".

Charging with a tow vehicle (DC cable from battery, through isolator, to trailer, to battery bank) usually does not do a good job of pumping amps into a battery bank. The resistance of the wiring, the voltage drop of an isolator, the 13.8-14.2 volts that most vehicle alternators are set at, etc., usually limit the useful charging current to less than 10 amps (just a guess).

If you have a long drive, you could setup an inverter in the tow vehicle and run 120 VAC back to the trailer and run a 12 VDC battery charger into the bank--You will be able to charge the bank with a vehicle much better with that setup (obviously, the extra costs for a vehicle inverter, AC battery charger, etc.).

In the case of longer stays and not enough sun, it is almost always better to bring a small genset (Honda eu1000i or eu2000i type) and a good AC charger than to attempt to charge with a tow vehicle (really fuel inefficient to charge with the tow vehicle).

-Bill