diy solar

diy solar

max load with small battery for day usage?

kaizday

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May 27, 2021
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i have 2x 20ah (for now) rating lifepo4 and approximately 1kw array, what is the max load can i power during the day? beside the inverter and charge controller, is the battery still my constraint in regard my max load?

for instance, i am planning on getting a 60a mppt, a 24v 1000w PSW inverter, can i run something as much as 800w continously during peak hour?

tia
 
Are those 12 volt batteries? For best service discharging at half the capacity is recommended. 2x 20ah = 40ah x 50% = 20 amps x 12v = 240 watts. Same wattage in parallel or series. Can go more to run maybe 500 watts however to do this day in day out will reduce the life some. At 240 watts the battery will only last 1.5 to 2 hours. That is just from the battery. You can add all the solar power actually produced and 800 watts will be fine while the sun is strong mid day.
 
i have 2x 20ah (for now) rating lifepo4 and approximately 1kw array, what is the max load can i power during the day? beside the inverter and charge controller, is the battery still my constraint in regard my max load?

for instance, i am planning on getting a 60a mppt, a 24v 1000w PSW inverter, can i run something as much as 800w continously during peak hour?

tia
So you have two 12V 20Ah (240Wh) battery packs, correct?
So two 12V in series you will then have 24V 20Ah (480Wh) battery bank.
So if you have 800W of AC load, then you may be able to run the load for about 20 minutes at best at night, but during the day the solar will supply most of the power to the load.
 
So you have two 12V 20Ah (240Wh) battery packs, correct?
So two 12V in series you will then have 24V 20Ah (480Wh) battery bank.
So if you have 800W of AC load, then you may be able to run the load for about 20 minutes at best at night, but during the day the solar will supply most of the power to the load.

i see. yeah, i guess my question should have been whether a typical inverter would offset the required power directly from the mppt controller or it depends entirely on the battery only.
 
Whoa! You have a 1KW array? Under best conditions that's capable of about 55a charge.

Will your 40ah bank stand that kind of charge? Or maybe the better question is will your BMS fold-up and disconnect with too high a current inrush? Check your bms specs to see what the current rating is.

And you didn't specify which battery. If they are Miady's, they will smoke with a 1Kw array.

While you *can* charge LFP if they are high quality with up to 1C, I would cut that back to no more than 0.5 to 0.75C max. In this case, that would mean an array that is only capable of about 20 - 30A max. That would be about a 500w array in the case of a 12v setup.

Heh, you are one of the lucky few where we recommend scaling BACK your solar! :)
 
I agree the battery seems a bit undersized. I would want the battery large enough to fully drive the 1000w inverter for several hours minimum.
 
Whoa! You have a 1KW array? Under best conditions that's capable of about 55a charge.

Will your 40ah bank stand that kind of charge? Or maybe the better question is will your BMS fold-up and disconnect with too high a current inrush? Check your bms specs to see what the current rating is.

And you didn't specify which battery. If they are Miady's, they will smoke with a 1Kw array.

While you *can* charge LFP if they are high quality with up to 1C, I would cut that back to no more than 0.5 to 0.75C max. In this case, that would mean an array that is only capable of about 20 - 30A max. That would be about a 500w array in the case of a 12v setup.

Heh, you are one of the lucky few where we recommend scaling BACK your solar! :)

yeah i know that the current battery cant accept that high current, but i thought it is the negotiation between the charge controller and the bms, ie if the battery doesnt want to draw that much current, then the controller wont put out too much, is that a wrong assumption?

i want to start w something i currently have in hand right now while saving up for a larger battery, maybe i have no choice but to wait altogether lol
 
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