Need some power at the cabin

**Mike90250** · 10-26-2019, 02:16 AM

600w of solar PV is only 13A @ 48V, so a 30A controller would allow for future growth.

Sadly, I don't know of any MPPT 30A controllers for less than $100. junk on amazon only has a sticker that says MPPT, without the real innards.

**Fordtrucksforever** · 10-26-2019, 10:57 PM

Thanks for your input. Is there any disadvantage to getting a larger than needed controller, besides the cost? Would just adding another smaller one work as well when increasing the number of panels?

Can I tap into three of the 4 battery bank for 36 volt use without any serious issues?

**Mike90250** · 10-27-2019, 12:21 AM

Originally posted by Fordtrucksforever

Thanks for your input. Is there any disadvantage to getting a larger than needed controller, besides the cost? Would just adding another smaller one work as well when increasing the number of panels?

A larger controller allows for addition of more panels

Adding a 2nd controller, you loose some control over charge setpoints, one controller will likely remain in Absorb for extra 30 minutes, you know the "Man with two Watches" never knows the right time.

Can I tap into three of the 4 battery bank for 36 volt use without any serious issues?

NO ! NO !

**PNW_Steve** · 10-27-2019, 04:11 PM

Originally posted by Mike90250

600w of solar PV is only 13A @ 48V, so a 30A controller would allow for future growth.

Sadly, I don't know of any MPPT 30A controllers for less than $100. junk on amazon only has a sticker that says MPPT, without the real innards.

I used the Renogy 40 amp MPPT. I paid just a bit over $100. I have been happy with it so far. Even with just one 300 watt panel has significantly reduced generator run time.

**Mike90250** · 10-27-2019, 05:20 PM

Originally posted by PNW_Steve

I used the Renogy 40 amp MPPT. I paid just a bit over $100. I have been happy with it so far...

Great, thanks for the info

**Fordtrucksforever** · 10-27-2019, 06:33 PM

The only ones from Renogy I am aware of even close to $100 were 12/24 volt. Otherwise could have been a possibility. Any 48 volt chargers were around $300. I may just roll the dice on one of the off brands that has some support and decent reviews.

**PNW_Steve** · 10-27-2019, 06:43 PM

Originally posted by Fordtrucksforever

The only ones from Renogy I am aware of even close to $100 were 12/24 volt. Otherwise could have been a possibility. Any 48 volt chargers were around $300. I may just roll the dice on one of the off brands that has some support and decent reviews.

You are correct. I overlooked the mention of the 48 volt battery bank.

**Fordtrucksforever** · 10-28-2019, 12:30 AM

Just want to thank everyone for their input. With just a little bit of fill in the blank, I have a lot more insight about what my project will require to become a reality. One thing I was curious about regarding some inverters at hand. Two of them are 24 volt at 1000 watts. Another is 36 volt at 700 watts. Is there any way of making work with a 48 volt bank? I was hoping to tear into the 36 volt inverter and see what is needed to alter the battery voltage. May be a waste of time. But without trying something with these will never know what might work out. If they go boom, then to the scrap pile with them.

Another dumb thought....maybe connect each of the 24 volt inverters to a pair of batteries in the 48 volt bank. Is this another really bad idea?

**Mike90250** · 10-28-2019, 02:15 AM

I don't think there is a viable way to change inverter DC voltage. It appears it's easy to make charge controllers operate over a wide voltage range, but inverters have so much feedback happening because of variable loading and needing to greatly vary the input amps to keep the output voltage stable, the control circuits are tuned to just 1 voltage..

Because of the rapid variation of input current, even 2 inverters wired in series to use a higher battery voltage, each powering a simple incandescent bulb, will quickly begin to oscillate in a bad way.

**Fordtrucksforever** · 10-28-2019, 04:50 AM

I am trying to make use of existing components that have been collected so far. Maybe drop down to a 36 volt battery bank, then use inverter from one of the ups units until the demand exceeds what power is available. My immediate goal is to have lights and some other conveniences so I keep working on the cabin after dark as the days get shorter. Then build the system up when spending more time there. For the out of pocket expense so far, I will be way ahead on what the generators have cost just on fuel consumption in the past few months. If something crashes, then just fall back to generators until fixed.

**Fordtrucksforever** · 11-02-2019, 06:52 PM

Just asking on what might be the best approach with what I am working with right now. The 4 12 volt batteries are either going to be series/parallel at 24 volts to use a 1000 inverter or 3 batteries in series and use the 36 volt 700 watt inverter. With exception to wire size, is there much issue with one over the other?

**MichaelK!** · 11-02-2019, 10:20 PM

I did a bit of research into your 12HX540 batteries, and what I'm seeing is that they appear to have specifications similar to Trojan's SAGM12-135 battery. That might give you a guide as to how much power you can expect out of them and how they should be charged. They have an 8 hour capacity of 123AH, so their 20hr capacity is about 140? That's why I mentioned the Trojan comparison. If you want to charge them at about 20% of C, that would mean 140AH X 0.2= 28amps. Now you just plug in that number into a formula to see the solar needed.
28amps X 50V X 1.25 effeciency conversion ~1800 Watts. That's triple the amount your panels are using now. Keep in mind these numbers are a guestimate, because you are using the batteries for an application they are not meant for. If you want to adher to the standard admonishment of never depleting your batteries more than 50%, that gives you about 3.4kwh of power.
140ah X 48V X 0.5capacity =3360watthours. I'd say that's enough for a lights, a TV/computer, and a small 15-17 cuft refrigerator. my guess though is that these batteries will not last long, being used in a way they are not designed for.

Later in time, you can upgrade your system with more capable electronics, better inverter, better batteries. If you went with 24V instead of 48, your numbers would be exactly half. You could raise the 24V capacity by having two parallel strings of 2 batteries. The charging voltage would go down, but the amps would need to be doubled, so the watts is the same. Cobbling together components now is going to be a problem for future expansion. I'd say try to zero in on either a 24 or a 48V system. All the major companies make components to match those voltages. If you go with 36V, you are pretty much limited to using Outback equipment. Outback makes high quality equipment, but it would be your only choice for 36V. If you want to power nothing bigger than a frig, you can get by with 24V, but serious power needs 48V.

Keep in mind these numbers are estimates for what's best for batteries other than what you've actually got. You really won't know until you get it up and running, and trash at set. For sure you can get by with much less solar if you are limiting yourself to just lights and a TV. The frig however raises electrical demands an order of magnatude.

**Fordtrucksforever** · 11-02-2019, 11:52 PM

WOW! Thanks so much for all the info. I have been getting a headache every time trying to run the numbers. Reading all of the stickys just made it worse. I know its not that difficult, after working with it. You broke down the basics really simple enough. I do have a new charge controller that was within my budget, and works for whatever battery combination. Currently for the minor needs at hand, one of the inverters in question is what will be used. I am still in the dark on so much. But have some basic understanding to know whats within my limitations. I will likely stay with the 24 volt bank until the load demands are exceeded. Then pay the big bucks and get a 48 volt inverter and more panels.

The roof on by cabin is facing just a little south of due west and steep enough in pitch to take advantage of sunlight until it sets. I want one set of panels there and another set on front of cabin facing south. My cabin is deep under the trees, so trying to make best use of available sunlight when shows itself. Watching where the sun shines during the day, this seems to be a possible plan.

The reasoning for those batteries is simple enough. They cost almost nothing. Actually, these four cost $30 a piece. For the life I can get out of them, then sell back for scrap at $25 a piece, makes my net cost negligible over the next few years. What really gets me, is I had, tho many years ago, several electric forklifts for the taking. These were very old and powered by Edison cells. I wanted to keep the batteries around, just in case of a use might arise. I was not familiar with them at the time. No internet back then either.

There were some hard back volumes of manufacturing companies information books. They were light green and huge. Cant remember the name of them tho. They are called Thomas Register. I spent weeks making phone calls all over the country,but running into dead ends. Finally found some old timer guy in retirement years that gave me the lowdown. I added some water to them, then charged overnight with a dc welder, per his advice. For something that had been left outside neglected for 20 plus years, came right back to life and worked great. But too much time passed and they are gone.

Thanks again for your help.

**Mike90250** · 11-03-2019, 02:45 AM

Originally posted by Fordtrucksforever

There were some hard back volumes of manufacturing companies information books. They were light green and huge. Cant remember the name of them tho. I spent weeks making phone calls all ovr the country,but running into dead ends. Finally found some old timer guy in retirement years that gave me the lowdown. I added some water to them, then charged overnight with a dc welder, per his advice. For something that had been left outside neglected for 20 plus years, came right back to life and worked great. But too much time passed and they are gone.

Thanks again for your help.

Edison cells are seldom "gone" unless they rust away. New electrolyte and they are good as new. The electrolyte is ALKALINE - KoH Potassium Hydroxide very much like lye, which could be used in a pinch.

Need some power at the cabin

Need some power at the cabin

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