Given the choice, 1 limited system or 2 systems?

[Rednecktek]

So I'm pondering my options for my cabin and I can't decide if I want 1 system nerfed on panels or do 2 completely different systems. My cabin has an existing 12v system powering lights and heaters and fans, so I MUST retain 12v in there. I'd like to throw an inverter in so I can turn off the generator at night, but I'd want to keep my inverter comparable to the generator I have to make math easier, which means a 2000w inverter and all the fuses and shunts that entails. I have the physical space for 6x 120Ah FLA batteries on the shelf before things start hanging over the edge, 4 installed in parallel now.

I was looking at the specs on my MPPT controller and it says that on a 12v system I can only have a max VoC of 80v and a max wattage of 720w. I'm planning on buying a pallet of used panels for a few projects and they're 36.3VoC as listed which means if I did a 2s I'd be right on the edge of frying my controller when the winter hits. To avoid frying things I'd have to limit it to a 3p setup which would only give me a MAX of 600w. Unfortunately I can't find a max input amps for my controller so I'm guessing that the 21.3a max would still be OK.

So it seems I have to choose between adding 2 batteries and a 12v 2000w inverter OR reducing my 12v bank to 2 batteries and going with an AIO 24 or 48v unit separately to power the 120v systems. I can find 24 and 48v PWM controllers to parallel in to keep the batteries topped up while disconnecting the batteries from the AIO to avoid drain on them for the 6+ months at a time I'm not up there, so that's a thing. It seems to me that going with a separate system for the 120v would be more expensive as I'd be building a complete new system rather than modifying the one I have, but would be safer (less amperage involved), be easier to top up with the generator, and allow larger arrays and more PV input.

Down side is that I can only have 4 batteries involved, either 120Ah@24v or 60Ah@48v and due to finances LiFe's aren't an option at this time so I'm stuck with FLA's and hopefully AGM's (unless LiFe's become significantly cheaper in the next couple years) for the foreseeable future.

So, oh Hive Mind, I ask of you: 1 system or 2?

What I have:
40a MPPT Controller, 20-80VoC input @12v system, 720w max PV
4x 120Ah FLA batteries
2x 100w Poly panels
Pallet of 200w (170w certified) panels (shipping soon)
25a battery charger

 

[Wellbuilt]

You are way better off going 48 volt with one system
the only time I would stick with 12v is on a RV .
The 48volt system should have a 80 amp cc with voltage of 150v
you can add 4000 plus watts of solar , maybe up it to 5000?
If you want to keep the 12volt equipment you can use a doctor dc converter 48vdown to 12volt .
A converter for lites is easy they use them for golf carts in assuming you are using a RV heater run off propane
the blower uses a lot of power .
I would make room for 8 6v GC battery’s from Costco
the 170 watt panels are to small , to many connections and wires I would get larger panels 300watt range with 40ish volt out put you can use 3 in series for 125ish total volt out put and you would be safe to -125 +- ?
but you have to do the math .
Costco , sams has a 8 volt agm battery so you could use 6 in series for 48 volt .
The real up side to AGM for is you could charged them up and leave for 6 months and they would still be charged up
When you return they have a low self discharge rate especially if you keep them cold.
I would rather have FLA if I get snowed out it’s only for 31/2 months and I can snow shoe in to charge the system .

 

[Rednecktek]

So throw away everything I already have and buy all new batteries AND a rectifier that can handle the 40a of 12v I need to fire up the heaters? That'll put me WWWAAYYY over budget. I work for a living. :D

 

[Wellbuilt]

We’ll spend the money now or spend it later ?
You could use your battery’s ? But the way you said it , it seamed like you where replacing them any way .
The all in one unit has a charge controler so you don’t need it .
The AIO has a charger .
here is a 48to 12 converter 100 bucks dosent seam like a deal breaker .
using solar to do any kind of heating is not cost effective .

You brought up the new system 24/48 volt
You asked one or 2 systems ?
You could use 24 volts
but in a cabin it is best to be able to series all battery’s run at a higher voltage series parallel panels
You just won’t need your existing system ?
Just sell the components.
There are lots of ways you can go , but why not build something that would be easy ?

 

[Rednecktek]

OK, let me clarify with this:

I'll be keeping all the things I already have
I'm working with a budget of about $1000
The camp is unoccupied 49 weeks a year and it gets butt-nuggets-COLD out there
I have a 3500w (peak) generator I currently use to feed my 120v system and it's really overkill for my needs

Due to budget constraints I'm really, really not wanting to throw away my batteries. I can upgrade in the future but even at the cheapest I'd be over budget just buying LiFePo4's and then I'd be under volted AND have none of the other parts to make anything happen for at least another 6 months.

I'm planning on upgrading in the future to LiFe batteries and the rectifier and such, but unless someone here is willing to mail me 4 big LiFePo4 batteries or a big check it's just not in the picture.

 

[Red Squirrel]

Since you already have a 12v system wired I'd lean towards two systems myself, do a 24 or 48v system for all the AC stuff and that would be your main system. Have the solar panels charge that system up only, then have that system charge the 12v system. Consider the 12v system as basically a backup. When the big system is off, you still have basic 12v power such as lights or whatever is on it now.

For the batteries for the new system if you go with golf cart batteries you'll blow your budget right there as they are usually a bit over $200 per battery so for now I would just use some cheaper 12v batteries like marine/RV ones and you can always upgrade later. I find batteries never go to waste as you can always find a use for them later.

 

[chrisski]

I have a 12 volt RVI’m converting to a 24 volt system. I’m keeping the 12 volts with a Victron Orion 24 volt tP 12 volt step down converter With 70 amps. You probably don’t need that much. Maybe 10 or 20 amps. Less than $100.

For the panel limitations you mentioned, you can use multiple Charge controllers to hook those up. THe Victron charge controllers can be $120 for a 74 volt 15 amp, which would handle 1 or two panels. So many different options for SCCs and some like Epever are cheaper. I have three VIctron SCCs on my RV build.

As I look at your budget, multiple SCCs for a 24 volt or 48 volt build and a Step Down converter to run the 12 volt stuff would come in well under your $100 budget, provided you already have the hardware and other components. I‘m thinking there’s room in there for a $200 for some PV Cable and MC4 connectors also.

 

[Wellbuilt]

Ok here you go , add 24watt inverter charger for 829 and one step down converter for 100 bucks 50 bucks for a fuse and 2 power cables , and use your 4 existing batterys in a 24 volt figuration .
I did not look to see how much sOlaf you can hook up but I’m thinking 2/3000 watts .
Thoughts ?

 

[Rednecktek]

Funny, I actually based this idea around the MPP 3048LV-MK which is the 48v version of that same inverter. I figure that at $700, 2 more batteries at $100ea and some wire should put me about the $1000 mark. If something goes wrong with either system I still have lights and heaters running from the other one.

 

[Wellbuilt]

I’ve had a few people tell me that the mpp brand is not to good
but I don’t know first hand . I think I would go with a 2000watt 24 volt system but did not see one in my search .
It would save some power just being on .

What’s with your heaters ? I think any thing that makes heat will really drag down you battery’s fast and my not work on the system .
So you are thinking to add 2nnew battery’s to your 12v system and using the 4 old battery’s in a 24or 48 volt configuration?

 

[Rednecktek]

The heaters are propane (12v fan) and diesel (glow plug and fan) so there's a 10a draw on each diesel heater while the glow plug warms up then drops down to 1a to run its fan & fuel pump once it's lit off. The propane heater has a 12v fan that's pretty heavy all the time.

Yeah, 2 new batteries for the 12v system, slap the other 4 into a 48v setup.

 

[chrisski]

I will add I wish I’d considered some all in one when I built my system. Even with my 24 volt upgrade, that growwatt is $200 cheaper than the SAMLEX 3000 watt inverter I ordered yesterday.

For my next RV build, I will seriously consider an all in one.

 

[Wellbuilt]

samlex equipment is good stuff , but you really can’t go wrong the aio inverter chargers , they we’re not around when I bought my system
I use a out back all in one , I think it was 2800 bucks 4 years ago works great

RNT I see no reason to keep the 12 volt system .
You could save some battery money and put it towards the power converter 48 to 12 volt .
With the extra solar panels you will have plenty of power for day time .
And be full charged at dusk .
I think the 48 volt system can take 4500 watts of solar .

 

[Rednecktek]

OK, so just go straight to a 48v system, throw in a 12v 70a rectifier for all my 12v needs, and solo it up. That's a thought. I can throw a couple of panels on the old MPPT in parallel to keep the batteries topped up while I'm gone since I'll be disconnecting the batteries from everything when I leave.

Which brings me to another question. When I get back and go to turn the batteries on there'll be the big surge to the AIO. I was planning on Step 1 being a push button around the breaker through a 50ohm 10w resister to pre-charge the AIO before Step 2 turning on the battery breaker and Step 3 turning on the AIO.

I've seen Will and others demonstrate the pre-charging but they ALL do the same thing and connect the resister then the video jumps. How long does the resister need to be connected (Step 1 button held in) before it's safe to go to Step 2?

I have to make this system idiot friendly since my nephews are sportsballers and I don't trust them to "Just Know" how to do it right. ?

 

[Wellbuilt]

70a seams like a lot , the larger the converter the more power it will use
hmmm I know nothing about pre-charging a inverter?
this is the first I’ve heard about it .
I just flip the breaker on my system and it comes to life there seams to be a automatic start sequence
where I can’t get power immediately I’ll check it out .
It seams like a big power serge at first .

 

[Wellbuilt]

Just a thought , you could have different 48/12 v converters .
I’m not sure about the power needed to run your 12 volt equipment but lites / fan could be on one small converter
And the heater on a second one . Converting power is the same as inverting power it uses Energy

 

[wiseacre]

OK, so just go straight to a 48v system, throw in a 12v 70a rectifier for all my 12v needs, and solo it up. That's a thought. I can throw a couple of panels on the old MPPT in parallel to keep the batteries topped up while I'm gone since I'll be disconnecting the batteries from everything when I leave.

Which brings me to another question. When I get back and go to turn the batteries on there'll be the big surge to the AIO. I was planning on Step 1 being a push button around the breaker through a 50ohm 10w resister to pre-charge the AIO before Step 2 turning on the battery breaker and Step 3 turning on the AIO.

I've seen Will and others demonstrate the pre-charging but they ALL do the same thing and connect the resister then the video jumps. How long does the resister need to be connected (Step 1 button held in) before it's safe to go to Step 2?

I have to make this system idiot friendly since my nephews are sportsballers and I don't trust them to "Just Know" how to do it right. ?

FilterGuy has posted a pre-charge switch build in the resources section.
https://diysolarforum.com/resources/inverter-disconnect-switch-with-precharge.60/

 

[Wellbuilt]

Way to go filter guy ?

 

[chrisski]

70a seams like a lot , the larger the converter the more power it will use

That’s true and if the OP does not need that power, sizing down would be good. I have a 70 amp converter only because of my RV leveling jacks. Without that, I would have 20 amps. The converter I chose is more efficient than my inverter.

https://www.amazon.com/gp/product/B01BF5BQLA/

I know nothing about pre-charging a inverter?

Will has a video of pre-charging. On a huge inverter like a 3000 watt I’m installing, the spark is big enough to shoot molten metal which he shows where it took a chunk out of his $1000 battle born battery. He used a pretty big resistor which I did not find a link for, but am using this one:

25 Watt Ceramic Cement Power Resistor, 30 ohms: Amazon.com: Industrial & Scientific

25 Watt Ceramic Cement Power Resistor, 30 ohms: Amazon.com: Industrial & Scientific

www.amazon.com

I can throw a couple of panels on the old MPPT in parallel to keep the batteries topped up while I'm gone since I'll be disconnecting the batteries from everything when I leave.

Take a look at the battery manual. You may just need to disconnect based off how long you’re gone. Two months for me is fine, longer than that, I’d need to charge my FLA batteries. When I do long term charging, I do it with 300 watts of panels, only because that is the smallest of three sets panels I have a circuit breaker for. I just leave the otero two breakers off.

 

[Wellbuilt]

I’m thinking my out back inverter charger must have a built in pre charge switch thingy , I’m going to check it out .
I can all most do any thing , with practically nothing at all , but I’m not much good at making electrical parts ?
You would think some one would make a battery switch with the built in resistor if it was needed .

My battery’s stay @ 90% all winter from before Christmas to aprial , so I don’t bother with the extra controller and panels . It’s cold so the battery box gets down to zero .
The one year I left my controller and panels on my Chinese controller died and wiped our the battery’s