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marco.rc.santos

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Reply with quote  #21 
My smaller UPS would go to bypass mode and use direct power from the grid (or power off if being supplied only from the batteries).
So the charger will power off if the system demands more power than it (or the panels) can handle?

stmbtwle

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Reply with quote  #22 
That's how it's supposed to work, anyway. If the grid is down the UPS will provide power from the batteries as long as they last. Once the battery voltage drops below a certain point if the grid is still not available it will have to shut down. If solar panels are connected the solar array will (within limits) keep the batteries charged, so in actuality you're using power from the array. Once the sun goes down, you start depleting the batteries. If the array comes back up before the batteries die you're good, but now the solar array has to charge the batteries AND provide power for you. If it can't, sooner or later you'll run out of power.

IF your solar array AND your batteries are big enough, you don't need the grid at all. My houseboat will operate for months like this. However in sustained bad weather or wintertime I may have to connect to the grid. If no grid is available I'll start the diesel and go for a ride. If worst comes to worst I shut down all loads for a while.

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marco.rc.santos

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Reply with quote  #23 

Still, my worry is the one below:
If the UPS consumption is at its maximum, then it's gonna demand the maximum from the DC connection (Iu). At that point I wonder what will be the current distribution: batteries (Ib) vs charger (Ic); given that the charger maximum power is lower than the UPS' demand and that the panels maximum power is lower than the charger's maximum supply power, which is lower than the UPS' demand. Even if the battery can supply what the UPS requires, how can I be sure that the charger will not supply higher current than it can? Does the charger limit the current output, considering the panels' maximum output and its own maximum output?

Max power.png 
I'm sorry to insist on this, but better safe than sorry.


Rick H Parker

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Reply with quote  #24 
Pmax = 2.5kW? ... I thought you had seven 250 Watt panels for a total of 1.750Kw.

The UPS would draw current from the Charge controller up to whatever the Solar Panels can supply at that time, then the remainder would come from the batteries.
In the example above, with full sun, the UPS would draw 2.5kW from the charger and 9.5kW from the batteries.

Power in Watts = EMF in Volts * Current in Amps.
Ic = 2500W/192V = 13A.
Ib = 9500W/192V = 49.5A.

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Rick H Parker
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stmbtwle

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Reply with quote  #25 
Pretty much agree with Rick, though I think solar pmax would be in the ballpark of 2kw with all 8 panels, but that's minor.

If by "charger" you mean the Charge Controller, it doesn't matter that it is "rated" for 9.6 kw, the solar panel output is only 2kw, so all you're going to get is 2kw.  You're limited to the PV output + the battery output regardless of the size of the UPS.  While you MIGHT get 12kw total I'd say it's highly unlikely for more than a few minutes before the batteries go dead, the voltage drops and likely the unit will shut down.

The UPS should be designed to handle overload situations.  If it overheats it should shut down.  At worst you may trip a breaker or blow a fuse.

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Rick H Parker

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Reply with quote  #26 
"with all 8 panels"

The numbers indicate he has ten 250W panels.

From #1.  "They are 60 cells panels (Vmp=30.7V; Imp=8.15A; Voc=37.4V) "

Vmp: Voltage at Maximum Power.
Imp: Current at maximum power.
Maximum Power = Vmp * Imp = 30.7V * 8.15A = 250W
2500W/250W = 10.


"I believe so is the charger, so it's capacity is moot"

In the drawing above, by charger he meant Solar Charge Controller ... see the solar panels attached to it.

"you'd probably be lucky to get 30 minutes of run time before the batteries go dead"

He not going to be running continuous 12Kw loads, The reason he upgraded to a 12Kw UPS is to cover peak loads. He is trying to make sure he got all his T's crossed and I's dotted this time so he does not have problems covering peak loads such as as motors starting up. 

What need to be looked at is the peak power that the batteries can deliver. If the batteries cannot cover the peak loads on their own, he will have problems when the grid is down and the sun isn't shining. He has not posted enough information on the batteries to determine what the peak battery current/power is.


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Rick H Parker
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stmbtwle

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Reply with quote  #27 
Not picking. I think the original post said 8, and he disconnected one, leaving 7. Could be 10, now, but I don't remember any mention of it. I think the controller could handle 32 or more, depending on configuration.

Yeah sorry about the misunderstanding. I believe the UPS has it's own charger, as well, and that's what I originally thought of.

I'm aware that he won't be running 12kw loads at least not for long. To be honest I think the original UPS would have been enough, IMO the problem is the batteries, not the UPS.

The batteries are 38ah. A decent 38ah battery can easily put out 100a for a few seconds, and 16 of them should handle a 12kw startup load with no problem, but at a 700w continuous load they probably won't last overnight.
Two sets might.

38ah @ 20 hr rate (given) is only 1.9 amps. At 192v (16 batteries) that's only 365 watts.



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Solar is like the wind. It may be free, but putting it to work isn't!
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Rick H Parker

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Reply with quote  #28 


I think the original post said 8, and he disconnected one, leaving 7.

He tried 8 bareback and was smoking, most likely boiling the electrolyte, knocked it down to seven after that.

"I think the controller could handle 32 or more."


The controller he is looking at could handle the peak power of 38 250W panels in a series-parallel array, I would cap it at 40 panels.

IMO the problem is the batteries, not the UPS.

That is a possibility I have been thinking also. That why I nudging the conversation towards the batteries.

A decent 38ah battery can easily put out 100a for a few seconds

A good 38Ah could do about 500A for 5 seconds, 100A for about 5 min because 100A would discharge it that quick.

No clue how good his are.

700w continuous load they probably won't last overnight.

Perhaps 10 hours, but one would be buying new batteries often because, 10 hours at 700 watts is 100% DOD ... that is hard on batteries. Because they are gel, they should not be discharged below 80% DOD, so 8 hours max at 700W avg. 




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Rick H Parker
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stmbtwle

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Reply with quote  #29 
Agree with everything.

38 (2 x 19) would be way over the voltage limit.  36 or 40 could work, but that much power is probably overkill.  The issue is still the batteries.  

As 32 batteries have already been bought, I think I'd put them in 2 strings of 16 and pray.  When they eventually need replacing I think I'd go with 16 x 100ah (or bigger if available).

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Solar is like the wind. It may be free, but putting it to work isn't!
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marco.rc.santos

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Reply with quote  #30 

I originally said 8 panels and then 7 connected only, but I have a total of 11 panels. I wouldn't connect them all at once if it was to directly charge the batteries, but since I'm thinking about acquiring a battery charge controller (a "charger" as I put on the drawing) that can handle up to 400V, I can increase the number of panels connected to the system. With 11 panels of Voc = 37.4V each, I'd get a total Voc = 411.4V; so I'll connect only 10 and get a total Voc = 374V.

If overloaded, the UPS will handle for sometime and then shutdown.

"He is trying to make sure he got all his T's crossed and I's dotted this time so he does not have problems covering peak loads such as as motors starting up."
Exactly!

Regarding the batteries, the aim was to have 2x (16x 38Ah), but half of them came damaged. Now, since Angola is having a lot of problems of import, the supplier doesn't have enough 38Ah batteries to replace the ones I bought and cannot have them in country any time soon, so he's suggesting to replace 2x (16x 38Ah) by 1x (16x 65Ah) that it's what he currently has. My original concern was how to charge the batteries, not properly how long they last, because I was already considering the increase of capacity, but all the tips are welcome!
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