Author Topic: solar power to keep a battery up  (Read 1081 times)

Offline mountainmoma

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solar power to keep a battery up
« on: September 15, 2020, 03:15:10 PM »
I think I've got thsi right.

I bought 2 used 140W 12V used panels very cheap off a re-roof.  Then A morningstar charge controller, 20amp 12V is in the mail via Amazon.

Likely I only need one of the panels, not sure

The travel trailer has 2 100amp hour gel batteries.  When  I run this thing not on hook ups, ie end of this week maybe or next week (  if I can hook up the truck brake controller in the truck and drag it up the mountain, or someone at teh fair will do it just to get rid of us :)  )  There is alot of sun at my place, DC is only needed for sure for igniting propane to run fridge, second will be if I have enough power the DC lights,  3rd will be water pump, but I can shower elsewhere and I will be hauling water and can just as well set the 5 gallons on the counter by the sink as dump it in the fresh water holding tank

Anyways, I also ordered cables and I think all I have to do is hook a panel to the charge controller  and that to the battery

OK, I just noticed I did not order wire to go from charge controller to battery.  But, I bet the charge controller instructions will tell me what to get at the hardware store.

SO, those of you that connect solar to your trailer or RV -- does this sound right or am I forgetting something ?

Offline Bradbn4

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Re: solar power to keep a battery up
« Reply #1 on: September 15, 2020, 05:07:08 PM »
>> I bought 2 used 140W 12V used panels very cheap off a re-roof.  Then A morningstar charge controller,
>> 20amp 12V is in the mail via Amazon.

Mounts or stand for Panels.
Water proof location for controller hardware
12V - one panel 140 watts + one panel 140 = (1.167 amps * 2) = 2.334

My guess is that the batteries are in parallel  to simulate one large 12 volt battery.


------------
Fun thoughts .. .

1) You will never get 140 watts per panel - even at high noon
2) You will never point the panels at the perfect point in the sky to maximize charge rate.  It is very rare to have sun tracking hardware in a fixed location, let alone on a mobile.
3) every thing seems to use more power than expected
4) it will always be overcast when you need power the most
5) where all possible, run DC appliances (pump, light, etc)
6) The longer the power wires are, the more power you lose
7) The thicker the power wires are, the less power you lose
8 ) A 12 volt batter does not have 12 volts  8)  Fully charged it should be around 13 volts?




Offline Fixit

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Re: solar power to keep a battery up
« Reply #2 on: September 15, 2020, 07:36:59 PM »
In general you are right . Now. 140watts÷  12 volts=11.06 amps so you will only want to hook up the1 panel as your charge control isn't rated to handle both. Above post gives reason why that may no be a problem. Getting max  power is rare. It is easier to save power than to make more so switch all lights to LESs if they aren't already.
Just my 2 ends worth.

Offline mountainmoma

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Re: solar power to keep a battery up
« Reply #3 on: September 15, 2020, 10:09:22 PM »
>> I bought 2 used 140W 12V used panels very cheap off a re-roof.  Then A morningstar charge controller,
>> 20amp 12V is in the mail via Amazon.

Mounts or stand for Panels.
Water proof location for controller hardware
12V - one panel 140 watts + one panel 140 = (1.167 amps * 2) = 2.334

My guess is that the batteries are in parallel  to simulate one large 12 volt battery.


------------
Fun thoughts .. .

1) You will never get 140 watts per panel - even at high noon
2) You will never point the panels at the perfect point in the sky to maximize charge rate.  It is very rare to have sun tracking hardware in a fixed location, let alone on a mobile.
3) every thing seems to use more power than expected
4) it will always be overcast when you need power the most
5) where all possible, run DC appliances (pump, light, etc)
6) The longer the power wires are, the more power you lose
7) The thicker the power wires are, the less power you lose
8 ) A 12 volt batter does not have 12 volts  8)  Fully charged it should be around 13 volts?

yep, my thought too on unlikelihood to have too many amps -- and I like that brand so I ordered the 20 amp as I dont think they make a larger one, at least I couldnT find a larger one right now not much time to research.   

Yes, of course the batteries are in parallel, they are in a box, it is thick plasTic with a lid and a padlock and a disconnect to dissconnecT batteries from the trailer when not in use I guess

lights appear to be LED

Water pump is I think overly large and likely also then overly power consumptive, why I think it is oversized is that it has to cycle on and off when I run  a tap at the pressure I like

Offline Bradbn4

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Re: solar power to keep a battery up
« Reply #4 on: September 15, 2020, 11:29:54 PM »
yea, it looks like I did a typo on the conversion (or went to the wrong website  :o )

While I don't think you would max out real word on amps - it is way to close to consider it.    On some hardware I would like to make sure I have lots and lots of headroom as I can afford to make sure the equipment is not run at its max capability.

https://www.rapidtables.com/calc/electric/Volt_to_Amp_Calculator.html

There are a bunch of different hardware options available from Morningstar that might fit your need.   However, once you go up in amps the price of the hardware go's up.   There is a lot of cool hardware out there since the last time I looked at anything solar.

PS-30 might work, or the simple answer is you only need one panel and the controller you picked up will do just fine.

Real world testing would be needed to see if one panel configuration will meet your needs.

And you are right, the water pump will be the highest peak load; but if that happens during the middle of the day it should not be too much of an issue. 


Some of the higher end charge controllers will show you a current display on the health of the batteries.

Some solutions can be 'cheap'.  i need special mounting gear or - I only use the hardware a few times a year, maybe my saw horses can do the work for me.

Offline mountainmoma

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Re: solar power to keep a battery up
« Reply #5 on: September 16, 2020, 10:55:22 AM »
I will start with one panel

I am not looking at long term right now.

I am a fire evacuee who has been living at teh county fiargrounds for a month.

I am going to move back up to my property within a week, park the trailer in the driveway.  This time of year is alot of sun

Ironically, right after I got the panel and ordered the controller, I went up there and my solar in the house looks like it is working ! I have a 22 year old inverter that was manufactured in California, not cheap chinese junk.  Once it occured to me to turn off the 2 breakers ( there are 4 breakers that are powered by battery backup) that went out to completely burned down locations ( water pump, auxillery small room that used to be my ex's office -- both locations ashes right now) and hit on in the scroll thru menu, I had power to the other 2 circuits ( some interior lights and outlets) I cannot be in the house yet due to my asthma ( not just soot, it is mold from refrig too) .  I do not have a plug that the trailer can plug into, so right now I cannot hook it to house solar/battery power.  Our local electrician is swamped right now.  So's the well guy.

Anyway, could be I dont need the DC solar for long, but it could be handy for keeping batteries topped off when trailer is not in use.

But, for a while, maybe short, I will be an offgrid trailer homesteader

Offline fratermus

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Re: solar power to keep a battery up
« Reply #6 on: September 16, 2020, 11:33:04 AM »
Can't make any promises, but I suspect the 20A (PWM?) controller would be ok with both panels.  I would definitely run both into a 200Ah bank.  Too much panel is just enough, and 240w:200Ah is nowhere near too much panel for the bank,

If your needs really are that light I'd consider running 240w:100Ah and using the other battery for another project.  IMO the damage from chronic undercharging is greater than the damage from cycling deeper.  Your mileage may vary, of course.




Offline Bradbn4

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Re: solar power to keep a battery up
« Reply #7 on: September 16, 2020, 07:44:21 PM »
Thanks for the background info, sorry you are going thru what you are going thru.  However, it does give me a better idea on use of the Solar.

Usage would full time while you need it.  The hardware selection can support your limited needs.  For long(er) term full time use I would go with dual panel setup.  I would also consider that a nice DC radio would be useful, maybe fan and a few other items.

The hardware you picked up is good; and can allow  you to do a few things even when moving back.   I was looking real close to your setup for an out building that needed a bit of light along with a few other items.

Limit peak usage during the day so surge can be absorbed by the solar array + dipped into with the battery pack.  Get a cheap but good battery gauge to let you learn how good this hardware will work for you.  I assume you matched the cable connectors from the panel to the charge controller. 

You might even keep using the trailer and live out of that to manage smoke, and other bad things that can be in the air.

My setup was going to be 2 - 4 panels, 2 controllers, 2 batteries, one small dc to a/c (pure sine) to run a computer, etc.  An optional pad for a small genny to support high load items that would over tax the solar.   A transfer box that would let me move from genny to DC to zero power.   I would use gravity to pump up a 50 gal metal barrel (food grade), so I would have running water when I needed it.

MorningStar was one of the brands I was looking at; however, the hardware that I chose is obsolete.   



Offline Greekman

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Re: solar power to keep a battery up
« Reply #8 on: September 16, 2020, 10:09:40 PM »
how about connecting a smaller load parallel to the panels? Like a 12v charger or a 12v fan etc?
Ypu won't be using those extra energy anyway, since the charger controller is a choke to the system when it is in its peak