24 volt to 12 volt converter

dp

BFL13 wrote:
On the OP's MPPT controller which I ASSume is a Tracer 4210A rated current-40A ,rebranded:

Rated charge power 520w-12v, 1040w-24v; and max PV array power 1560w 12v,

Renogy/Tracer 40
Max PV input power: 400W @12V, 800W @24V

Source: Manual, page 22

I would go for TS MPPT 60 and 3*250W array. Possibly - 3*300W.

I love this new math where 1+1 = 2.5 and watts have nothing to do with "I" or "E" energy vanishes without a trace. Kirchoff, is rated higher than Polish vodka. Oh well...time to listen to a little Tom Petty.

On the OP's MPPT controller which I ASSume is a Tracer 4210A rated current-40A ,rebranded:

Rated charge power 520w-12v, 1040w-24v; and max PV array power 1560w 12v, 3120w 24v. This is because the controller can handle three times the rated charge power for its PV power before it will fry from going over that rated charge power.

520/40 = 13v and 1040/40 = 26v so these guys are using 13v at "12v" for their ratings. Morningstar uses 13.3v ISTR.

So as Old Smokey said, they are indeed using the output power for their rating by using "charge power" 40 amps at 13v = 520w

The OP is in no danger whatever of frying his controller, and as has been stated, is not much over-panelled either, and that bit of over-panelling is a good thing like Morningstar suggests. He will have a good set-up as planned.

OldSmokey wrote:

BFL13 wrote:


Wait a sec! My 12v system has 0.6v drop when pulling 120 amps from the 450AH, whatever , bank.

It does not matter what the starting voltage is, it drops 0.6v so from 12.5 it drops to 11.9, and from 12.2 it drops to 11.6 (as seen on the Trimetric) so right away the percentage is different within the same "12v" system. the inverter will alarm at 11v--it doesn't care where you started from.


EDIT-Ha! his 24v inverter will alarm at 22v, same as a 12v will alarm at 11v. So how do you get a percentage difference for low voltage out of that?

I know it's late and I need my meds... but I'm not sure what the inverter has to do with it though ? I gave you the % drop based on nominal batt V :?

The only voltage drop I care about is what gets me too close to inverter alarm at 50% SOC. Otherwise, I could care less how far the voltage drops under load as long as it bounces back afterwards. So it is all about the inverter for me.

There are other concerns with array to controller and controller to battery for losses, but I have fat wire both sides, so no issues with that. YMMV.

tdevery wrote:
Or i spend $500 on a new charge controller

I would just do that.
Getting 600W array and 4 batteries - with controller that has 3 fixed setpoints: #1, #2, and #3... Let's say, "it will get you there". Not sure - where.

BFL13 wrote:


Wait a sec! My 12v system has 0.6v drop when pulling 120 amps from the 450AH, whatever , bank.

It does not matter what the starting voltage is, it drops 0.6v so from 12.5 it drops to 11.9, and from 12.2 it drops to 11.6 (as seen on the Trimetric) so right away the percentage is different within the same "12v" system. the inverter will alarm at 11v--it doesn't care where you started from.


EDIT-Ha! his 24v inverter will alarm at 22v, same as a 12v will alarm at 11v. So how do you get a percentage difference for low voltage out of that?

I know it's late and I need my meds... but I'm not sure what the inverter has to do with it though ? I gave you the % drop based on nominal batt V :?

2oldman wrote:
No problem, but series wiring of all panels is much simpler.

Yes, 2 in series will be easier to wire. I wrote this earlier in another thread - on a short run (up to 25ft?) it is still possible to wire 2*300W in parallel, using a standard "MC4 solar wire", just slightly thicker - #8 instead of #10. Plus, a pair of standard MC 4 Y-splitters. Not sure whether parallel will be better though. Might not be worth extra few $ for #8 and splitters.

He doesn't need to convert anything from 24V to 12V anyway. His controller is "just about" the right size, there will be none or very little extra amps to cut off.
600W in, 48A @12.6V out, under ideal conditions. Realistically, less than 40A because of controller losses, pre-controller cable losses, and volts often higher than 12.6. Maybe - a little more than 48A if he camps at high elevations on a cold day.

MrWizard wrote:

600 watts in my book is right on the limit of 12 volt systems.
now, your 40 A controller is too small for a 12 V system unless you intend to throw those watts away.. 40A*12V=480W and you waste 120W ! not an ideal situation.

What are you thinking?
You don't charge at 12v you charge at 14+v
14*40 =560w if he can get it, there is next to zero loss
14.4 or higher is even better
When the batteries are low he will use every amp the solar can make
He probably won't get 600, but he sure will Not be throwing away 120w

yeh.. it's more of an academic response to highlight the CC is maxed out.. I should have worded it differently..

OldSmokey wrote:

BFL13 wrote:
"- battery V drop under load is halved on a % basis at 24v"

Is that true? It might be halved or doubled as such, but I would think on a Percentage Basis it would be the same. Please elaborate--my brain quit :)

assume T105RE with internal resistance of 0.001 Ohms per cell and 1200 Watt load

for 12V we have 6 cells so 0.001*6*100 A = 0.6 V
0.6/12*100% = 5 percent drop

for 24V we have 12 cells so 0.001*12*50 A = 0.6 V
0.6/24*100 = 2.5 percent drop

Wait a sec! My 12v system has 0.6v drop when pulling 120 amps from the 450AH, whatever , bank.

It does not matter what the starting voltage is, it drops 0.6v. so from 12.5 it drops to 11.9, and from 12.2 it drops to 11.6 (as seen on the Trimetric) so right away the percentage is different within the same "12v" system. the inverter will alarm at 11v--it doesn't care where you started from.

If I had a 24v system, it would pull half the amps, but the burning question is---what is the 24v inverter alarm at? Is it 22v no matter what? I don't know, so I am asking about that for a percentage comparison.

EDIT-Ha! his 24v inverter will alarm at 22v, same as a 12v will alarm at 11v. So how do you get a percentage difference for low voltage out of that?