diy solar

diy solar

What would be more optimal

ericfx1984

ericfx1984

Solar Enthusiast
Joined
Oct 10, 2021
Messages
741
So I've got a bit of an issue... I need to start bringing my new system online...

Need to build the new battery... I need to do all the things... Lol. I need to test the inverter.

Here's the problem... I don't have a place to put the new solar panels yet

However currently I have one system that is 12 volts... With 22 kW hours of lithium iron phosphate batteries

I'm running a total of five MPPT solar charge controllers with a total of 3,400 Watts of solar panels spread between them with a 3000 low frequency inverter... I rarely see more than 1,800 Watts coming in through the solar charge controllers to the battery.. a lot of that has to do with the fact that it's been very hot and the panels are hot which creates a significant drop in efficiency


What I'm considering doing is this

I have nine 250 w panels setup on my shed... What I'm thinking I might do is disconnect those from my 12 volt systemc and connect them to my 48 volt all in one.

At that point I could build my 280ah 16s battery and use the 48 volt setup with the 9 250w panels to charge it

The problem is I am relying on those panels to keep the 12 volt system functional

But I'm thinking perhaps I could connect the AC output of the 48 volt system to the AC input of the 12 volt system

The other option that I've considered is that I could offload some of my loads to the 48 volt system... And then little by little bring the 48 volt system to full capacity. (which would consist of a pair of 16S batteries One would be built with 280 amp hour cells the other one with 304 amp hour cells... And 10,000 Watts of solar panels).

Basically I need to start building this...
 
ericfx1984 said:
But I'm thinking perhaps I could connect the AC output of the 48 volt system to the AC input of the 12 volt system
Click to expand...
This is the least obtrusive changeover option imho. You can test and maintain uptime all at once
 
When you say that you are depending on those panels to keep the 12volt system functional, what does "functional" mean? From the context of the post (where you mention moving loads over) it sounds like it means you'd keep it up and running with loads. If so, your idea of connecting your AC output of the 48v to the input of the 12v is probably the easiest method, assuming you think you can get the 48v built, tested, and functional soon enough to supply power to the 12v system before the batteries are depleted.


The suggestions will vary a bit if "functional" just means keeping the 12v system batteries charged vs, powering household loads off of it.


Off the top of my head

If you just need to keep the batteries charged:
- buy a 20a DC-DC converter, powered from your 48v batteries. Once the batteries reach float, 20a is a bit "excessive", but allows enough headroom that if you did want to use it occasionally for loads, it'll top them off too.

If you also need to power loads,
- buy a normal AC to DC charger. power the charger from your 48v system. The eg4 chargeverter can provide a significant amount of power (and adjustable, so you can also limit the max output.. and IMO is not a bad thing to have onhand should you need to charge batteries from a generator or something)

If you intend to eventually completely replace the 12v with the 48v system, you could do a manual generator transfer switch. feed both the 12v and 48v outputs to the transfer switch input. Feed it's output as the AC input to your electrical panel, and move the loads from 12 to 48v as needed for testing.



Depending on what specifically it is you are trying to do with the 12v system.. there may be other options/ideas
 
Last edited:
I guess I should clarify a little more The 12 volt system is in the RV

The RV is stationary... But the house is permanent as we just got the roof on it a few weeks ago

Temporarily the RV has solar panels on its roof (1200ish) as well as about 2,400 Watts of panels on the roof of a shed with temporary connections

The biggest problem I find is that if I hook the RV 12 volt system up to grid power... The inverter charger goes into charge mode... Unfortunately there's no way to keep it on inverter mode with grid/generator support
 
ericfx1984 said:
I guess I should clarify a little more The 12 volt system is in the RV

The RV is stationary... But the house is permanent as we just got the roof on it a few weeks ago

Temporarily the RV has solar panels on its roof (1200ish) as well as about 2,400 Watts of panels on the roof of a shed with temporary connections

The biggest problem I find is that if I hook the RV 12 volt system up to grid power... The inverter charger goes into charge mode... Unfortunately there's no way to keep it on inverter mode with grid/generator support
Click to expand...

Thanks for the clarification!


I guess in that case, can you limit how much current the 12v inverter draws, to charge with? assuming the 48v system is working as it's supposed to, is the output enough to handle the demand of the 12v? If so, I think your own idea of using the 48v AC output into the 12v input makes a lot of sense.

If not (either the inverter can't reduce the charge current, OR the 48v can't handle the demands of the 12v) then I'd consider doing the 18a charger from eg4, or if budget allows.. the chargeverter. that way, the draw shouldn't be above the 48v systems capacity.
 
n2aws said:
Thanks for the clarification!


I guess in that case, can you limit how much current the 12v inverter draws, to charge with? assuming the 48v system is working as it's supposed to, is the output enough to handle the demand of the 12v? If so, I think your own idea of using the 48v AC output into the 12v input makes a lot of sense.

If not (either the inverter can't reduce the charge current, OR the 48v can't handle the demands of the 12v) then I'd consider doing the 18a charger from eg4, or if budget allows.. the chargeverter. that way, the draw shouldn't be above the 48v systems capacity.
Click to expand...
Oh yeah it can handle it... The 48 volt unit produces up to 6,000 Watts out but whereas the 12 volt unit is only a 3,000 w set up... And I think it's max charge is 100 amps at 12 volt nominal
 
ericfx1984 said:
biggest problem I find is that if I hook the RV 12 volt system up to grid power... The inverter charger goes into charge mode
Click to expand...
I think you meant converter not inverter….
Turn off the dang converter. I’ve never had an active converter for more than a few weeks before I removed it. They are like 50% lossy.
 
Seems like a workable idea.. especially since i cant see why youd exhaust 22kwh of battery on the 12v side before you finished setting up the other system. I mean, youll be too busy sweating somewhere else to burn up all that power in the rv, right?
 
12VoltInstalls said:
I think you meant converter not inverter….
Turn off the dang converter. I’ve never had an active converter for more than a few weeks before I removed it. They are like 50% lossy.
Click to expand...
No I meant what I said... Aims Power 3000w inverter/charger. It's an inverter with a charger built in
 
Vigo said:
Seems like a workable idea.. especially since i cant see why youd exhaust 22kwh of battery on the 12v side before you finished setting up the other system. I mean, youll be too busy sweating somewhere else to burn up all that power in the rv, right?
Click to expand...
Well between a 12,000 BTU mini-split and a 5000 BTU window unit it doesn't take long
 
You must log in or register to reply here.

Similar threads

T
Optimal Panel Placement
Replies
5
Views
210
timselectric
T
S
More Batteries or More panels? What is the tactical approch for expansion?
Replies
9
Views
303
labeeman
labeeman
J
Optimal alternator setup?
Replies
12
Views
328
justinm001
J
BjornM
What would your next charge controller be?
2
Replies
24
Views
1K
Steve_S
Steve_S
T
Some pointers for newbie would be helpful.
2
Replies
25
Views
469
tj07161990
T
Back
Top