Posted on 08/29/2023 3:36:17 PM PDT by Rebelbase
Hello, I have a technical question for 12V solar folks.
In the process of building an off-grid solar set up for my camper trailer. Just need enough juice to keep the fan running in the propane fridge and to power the blower on the propane heater plus the lights and water pump.
Going to do a 200 amp hour gel battery and two 100 watt panels. A couple of months ago I bought a new-in-box 100 watt panel at an estate sale that I was told was for a 12V system.
Reading the back of the panel I don't see 12V anywhere on the spec decal, which is below.
Here is the question, when I buy the second panel does it matter if the voltage specs do not match up perfectly?
I looked at the Renogy website and do not see the exact specs on their current inventory. I suspect this panel is several years old as it came from a well stocked prepper who passed a few months ago.
I am fortunate when it comes to batteries. I am in the big rig repair business. Most trucks need all three batteries to be in very good condition to produce the cold cranking amps they need to start.
Every winter when the temps drop, usually one of the three will take a dump and stop putting out it’s share of the total amps needed. So standard practice is to just change out all three because the other two are not far behind. I keep these takeouts and turn in actual dead and good for nothing batteries or old batteries off my solar system to the vendor.
For a solar system that doesn’t need “cold cranking amps” they are still good to go for a few years. In fact, I have found having them on the slower charging solar system actually repairs most of the cold cranking amps they lost over a couple weeks. Why and how I am not sure, but it does... But when they start getting weak on my system I just swap them out again for fresher take outs.
I also had some great “Elmer's” who brought me along with building techniques. Old Ham's were inherently “cheap”.
Thank you, I hope they are decent for you. Please update how they do!
FYI a fully charged 12vdc battery should be 12.7 volts.
12.0 volts is about 80%. (don't want to go much lower)
Run them down below 11.8 volts on a regular basis and you will kill them quick.(inverters etc will auto shut down at 11.8v to help prevent battery death)
200 amp hour is a lot for 100-200 watts of panel. The 100 amp hour battery ought to do what you want just fine.
BTW, we lived off grid for 5 years using a 320 watt, 12 volt solar panel setup with 4 GC2 golf cart batteries which is about 200 amp hours. We made those batteries last almost 10 years which is pretty good for GC batteries and being first timers in solar. Everyone says newbies kill their first set of batteries in 2-3 years.
I still have the panels and was looking at Renogy charge controllers and batteries just a few days ago. We had a Xantrex C40 charge controller which are supposed to be bullet proof but it up and died. Died the day before we had electric service, pole and meter installed.
How many panels would I need to charge a 200ah battery?
If you have a 200ah battery, only 80% of that is usable due to depletion limitations, so you really only have 160 amp-hours of energy to draw on. If you learn that you typically can last two days with energy from that battery, that means you consume 80 amp hours a day.
Based on the earlier calculation, a 100 watt panel will produce an average of about 30 amp-hours per day (based on an average sunny day). This means you would need three 100 watt solar panels or one 300 watt panel to fully recharge your battery on the average day.
https://www.renogy.com/blog/what-size-solar-panel-do-i-need-to-charge-a-12v-battery/
” they basically have a “Buck Convertor””
Thanks for that and the link to Wikipedia. Huge article. Need to go back and actually learn how it works.
You have most of your questions answered by now.
The one thing I would comment on is if you do use two significantly different 100 Amp panels in parallel they many not share the load equally. The impedance of the panel will have an impact on how much current it will supply to a given load or to a battery charger that is shared in common.
Good luck.
Basically rather than being a resistor and just wasting that power as heat, it takes the voltage it removes and converts it to additional amperage output.
So most are around 95% efficient, what you lose in voltage is a gain in amperage. So you lose very little of the total power passing through it.
“We had a Xantrex C40 charge controller which are supposed to be bullet proof but it up and died. Died the day before we had electric service, pole and meter installed. “
We talked about this before, but lived off grid for over 10 years ourselves. And we lost a couple charge controllers and inverters from lightning striking within a hundred yards. One inverter was tested to work and new as a back up and the EMP field from lightening hitting next to the house killed it while it was in the closet not hooked to anything. lol
Close lightening strikes can kill controllers and inverters.
Thanks for the info. The estate sale panel was a spur of the moment purchase that I just found out won’t work for my situation. The camper roof is curved which requires flexible panels be used for the best aerodynamic. So, I’ll be buying a matching pair of those.
I can sell the rigid panel for what I paid for it with no problem.
I ordered that book a few days ago and it was delivered today.
Watts = Voltage x Amperes
Most important equation you need to figure out how to wire your system.
No.
But if you are looking to leave something hooked to it perpetually to maintain a car battery, that $20 charger is a DEAL! :)
Yes, thanks, but are you saying that even the 10 Watt 12 Volt Solar Trickle charger should have a controller?
So sorry I misunderstood. No, when you get a complete charger like that it will have the controller built in with it.
It will control the voltage and go on float (idle) when the battery is topped off. When the battery drops to a certain voltage it will kick back into charge mode again.
It will repeat to maintain it.
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