Solarex MSX 120, questions??

Re: Solarex MSX 120, questions??

That should be around Vmp=17.1 volts and Imp=7 amps... It will parallel fine with the Kyocera 135 watt panel when you are ready.

Kyocera 135 watt panel:
Voltage at Max Power (Vmpp) 17.7
Current at Max Power (Impp) 7.63 Amps

If you had to--You could run them in series for a 24 volt battery bank or for use with a MPPT type charge controller (Maximum Power Point Tracking)...

However, if you are going to mount the panels directly to the RV and the runs are short--a less expensive PWM type Charge Controller would work just fine (somewhere in the 20-30 amp range).

It is important that you mount the charge controller close to the battery bank with appropriate (heavy) cabling and fuse/breaker. You don't want much voltage drop between the controller and the battery bank.

A charge controller from Morning Star (PWM or smaller MPPT) or from Xantrex (PWM) would be fine.

Recommend the Remote Battery Temperature Sensor Option.

Also, if you have the interest, a Battery Monitor is a nice tool for monitoring your battery bank's state of charge.

Here is a nice thread with video from Keven in Calgary Canada that shows designing and installing solar PV in a small RV trailer. He eventually went with a MPPT type charge controller--but the rest of the information is pretty much the same for any type charge controller.

Do you have any specific questions that we did not answer?

-Bill

Re: Solarex MSX 120, questions??

Crossroads,

You are very welcome--We all try to help here.

crossroads wrote: »

I don't mean to be a pain in the....rear, but I'm just now getting in Solar Power for my RV home. It's just too expensive for an old coddger like myself to have to run my onboard genny to charge my 4-6volt batteries all the time. And seeing as I was fortunate enough to get this panel for free, it appears that I'm going to be able to save a pocket full of $$ recharging my batteries. At least I hope so.

Be aware, that most people underestimate their loads and over estimate what solar panels can output...

For folks with gensets, the recommendations that we use are:

• Run the genset first thing in the morning until the battery is 80+% charged, then let the solar panels finish of the charge. This reduces generator runtime and lets the solar panels finish off the rest of the charge... Ideally, you want to avoid having your batteries below ~75% state of charge for days/weeks/months at a time, and you want them >90% state of charge once or twice a week at least.
• Look at the size of your genset, battery charger, and battery capacity... Generally gensets are not very efficient if operated below ~50% output load... And batteries generally don't like to be charged much faster than C/8 or ~13% of their 20 Hour Amp*Hour rating...

Lets say you have a 12 volt bank and 4x6 volt 225 AH batteries... The recommended charge rate (flooded cell rule of thumb) runs from 5%-13% (numbers are approximations--4.5% or 14% is not going to kill anything ):

• 450 AH bank * 0.05 rate of charge= 22.5 amp minimum charging
• 14.4 volts charging * 450 AH bank * 0.05 rate of charge * 1/0.80 charger efficiency = 405 watts min load from genset
• 450 AH bank * 0.13 rate of charge= 58.5 amp minimum charging
• 14.4 volts charging * 450 AH bank * 0.13 rate of charge * 1/0.80 charger efficiency = 1,053 watts min load from genset

So, your battery charger should be rated around 20-60 amps and your "maximum" "optimal" genset would be around 800 to 2,100 watts (depending on battery charger rating)...

If this works out the way I hope it dose, I'll probably want to add that 135 watt. Kyocera panel a little bit later on after I save a few more $$. I was going to go with the Morningstar TS 45 PWM charge controller now, that way I probably won't have to worry about adding in a large controller later on, and if I decide on adding a third panel to my new system. I hope that sounds like good reasoning, Bill, and I do want to thank you for all your help.

Ideally, if you can plaster between 400 watts and 1,000 watts for solar arrays--you can only use the genset when your loads exceed your daily panel charging capacity (5-13% rate of charge comes only from solar panels).

The TS 45 PWM controller will be very nice--Get the Remote Battery Temperature Sensor and use the Battery Voltage Sense Leads too (more accurate battery voltage readings)... Morning Star seems to one of the few solar charge controller vendors that has Remote Voltage Sense Leads--Very Cool! (yes, I am a boring engineer--why do you ask?).

-Bill

Re: Solarex MSX 120, questions??

crossroads wrote: »

...the Solarex MSX 120 watt panel coupled with the Morningstar Ts45 controller will help me with my charging problems, right?

You are going to hate me. :roll:;)... The answer is yes and no--The solar panel + MS TS45 will certainly charge your battery bank.

With several "it depends"... First is what size are your batteries... I guessed a 12 volt bank with 4x6 volt 225 AH (golf cart sized) batteries.

While you will get somewhere around 7 amps or so (full sun, nice day) out of the battery charger combination--You will still probably need your generator to more fully charge the batteries a few times a week (at least).

The second also depends on your loads... For a very rough rule of thumb, you will get some where around:

• 4 hours of day full sun * 120 watts of panels * 0.52 overall system efficiency = 250 Watt*Hours per reasonably sunny non-winter day.

This assumes you are using a small AC inverter to power your loads... For example, a 30 watt laptop + 13 watt CFL + 10 watt radio:

• 30w + 13w + 10w = 53 watts
• 250 watt*hours / 53 watts = 4.7 hours

So, using my made-up numbers, your 120 watt solar panel would be able to keep those loads running for a bit more than 4 hours per sunny day.

Drawing any more power than that will force you to run the genset (every few days in the AM?) to keep up.

And if I add in the remote meter, will that give me a battery monitor as well? Or should I get a separate monitor, like the Xantrex?

If I understand the MS charge controller (and virtually every other "simple" PWM/MPPT charge controller) correctly--The Amp/Amp*Hour/Watt*Hour meter is only logging the power output from the solar panel.

The battery meter actually logs the power/current flowing into, and out of, the battery bank. Basically, it is like monitoring the amount of fuel level of your gas tank by measuring the fuel flow over time of the gas line.

Besides the Xantrex Battery Monitor, there is also the less expensive Trimetric which a few people (like Tony/Icarus) have and are very satisfied.

Solely living on social security is a living hell, and it might take me some time to acquire all the necessary goods to finish off my Solar system properly, like a separate battery meter and battery sensor, but in due time I will get around to adding them in. But for starters, is there anything else you can think of in your vast storehouse of knowledge regarding Solar power I might need to get my system up and running properly.

Otherwise, you should be using a hydrometer + thermometer to measure the specific gravity of your batteries once in a while anyway (see that they are properly charged and, if the cells SG is miss-matched, then run an "equalization" charge to get them all back to "full charge"--Stop equalization when the SG stops increasing). Many RV's, it is difficult to measure specific gravity (door on side of battery box an no top access for hydrometer).

The other thing to watch out for is safety... Every wire that leaves the battery bank positive bus point should have a fuse/breaker in to sized to the wire leaving the battery bank. You don't want a short somewhere melting the wires and starting a fire.

In the end, the batteries are the single most susceptible component of your solar / RV power system to poor operation and maintenance. Focusing on keeping them "happy" will the batteries last as long as possible.

If you want to see the detailed questions about designing a small off-grid power system (not much different than an RV system)--Here is a nice long thread with lots of discussions:

Emergency Power

It may help you better understand the pieces and help answer some of the questions you may have even thought about yet...

-Bill