design and operation

[EVcrf250x]

Good day . Ok i got a 3500 watt 12volt inverter /120 . I have a 12volt 168 amp hour(2KW) with a BMS . discharge current max 840amps, but charging current is only 10amps . 200amp BMS on it . so I have 2 small pumps for a total of 850 watts 120volts . So what i do not understand if I'm running them on the 12volts side the current would be about 70amps . If i have have 1000watts of solar panels and the MPPT on the unit what i do not understand what happens when the battery's drop ,and need charge current does the MPPT limit the current to only 10amps ? Also what i do not understand the MPPT based on the size of it and the current (70) amps the wire size never fit into the MPPT . I understand a lot of electrical wiring and understanding electrical equipment but this solar is confusing me . Can the solar array provide full current to the load at full sun ? Or is it only to provide power to charge the battery's?? I hope you all out there make sense of what i'm asking and did i provide data on what i want to do ? Also based on 2kW and the pumps running is only get about 2.3 hrs of running on the battery's (2KW/.850KW = 2.3hours ) . I do not want to burn up the MPPT unit . Anyone have the time to answer my questions greatly apricated it . I know the panels only put our so much current and i understand series and parallel set up wire size ect .
Thanks
EM

[EVcrf250x]

Hello all ,
I was wondering if i asked to many questions or not all the correct data ? No feedback yet . Maybe i need to do more digging on my own on the site .
If i understand the charging from the MPPT to my batterys i think my problem is my batterys max charge current is only 10amps so 10 X 13 = 130watts . so if my battery is near dead it would take 168 amp x 12 = 2KW 168 / 10 = 16.8 hours to recharge my battery bank ?? so i think my system using my battery bank and charging it with the solar and 1kw of panels is worthless based on the low charge current on them . Not sure if i can push to 20amps charge current

[chrisski]

If you have a 10 amp charge controller, than yes your 1000 watts of panels will only provide 10 amps,~120 watts of power under any circumstances.

Your battery spec sheet will tell you how much you can charge. Since you mention a BMS, I suspect this is a lithium battery and could be charged a lot more than 10 amps. Check the spec sheet or contact the manufacturer.

Your 16.8 hours is a bit optimistic and includes full power all day long. IME, from the limitations you listed on your charger, you’d only get 2 to 5 hours of good sunshine a day. So 120 watts X 2 = 240 watt hours a day in the winter to 5 hours X 120 = 600 watt hours in the summer. So in the winter, expect 9 days of good weather to charge, and in the summer, 4 days of good weather to charge.

I don’t think this 10 amps will provide enough power to anything you mentioned on your inverter to run it. I ave up to 80 amps of power my solar panels can produce at 24 volts, and without a battery, the inverter may power up, but will run nothing. Has to do with the MPPT does not deliver power on demand, but takes a few seconds to “Spool Up,.”

When I see a 3500 watt 12 volt inverter, I think danger. With low voltage cutoff and inverter conversion losses, I can easily see 400 amps going through there. Luckily, The 200 amp BMS on that battery can’t even power it. The idle draw on an inverter like that could use half of your 2 kWh battery per day.

For your calculation of 70 amps, does this include the inverter losses?

[EVcrf250x]

I have bought these junk batterys Daweikala 3.2 v 32700 12800mahr . But there is no way they are rsted for 12.8 amp hours . Tests i did i got about 5.5 amp hours .So did others on youtube . I cannot find a spec for max charge rate . They post max discharge which i dont believe . I bought 120 of these for my ev dirt bike before i found out they are not near rating and i could not get my money back .so now i put togther at 4s28p = 5.5 x28 = 154amp hrs x 12 = 1848watts of power . Not sure how many amps i can push for charging . Dont go cheap on batterys .

[EVcrf250x]

Anyone else used these batterys or can find the max charge current ?

[Ampster]

Hello all ,
............... i think my problem is my batterys max charge current is only 10amps so 10 X 13 = 130watts ......... Not sure if i can push to 20amps charge current

The charge controller is probably limited to 10 Amps. You cannot push more current that the loads, including charging can pull.

[EVcrf250x]

Hi thanks . So if the inveter doest drop out on low voltage and my inveter at 12volts is pulling more than 10amps it will try to pull it from the charge controller and if not fused will burn it up ? My load is about 850watts 120volts side . So 70amps on inverter side

[Ampster]

...... So if the inverter does drop out on low voltage and my inverter at 12volts is pulling more than 10amps it will try to pull it from the charge controller and if not fused will burn it up ? My load is about 850watts 120volts side . So 70amps on inverter side

No your charge controller will only deliver the 10 Amps it is rated for. If your inverter is dropping out because voltage sag, your batteries are not fully charged or just bad and not capable of putting out the 70 Amps to run the loads without the voltage sagging.

[EVcrf250x]

Thanks Ampster . So let me reword this if i.m runing the load in the daytime and the batterys will eventully run down to the point the charger wont be able to supply what the batterys need to keep the voltage up to supply enough current for the load on them . There must be some protection if i run my load till my batterys drop down so that they dont pull the load from the controller . Just based on how the output of the charge controller is wired to the battery is in parellell with the inveter input . I assume the inverter will drop out before the load on batterys starts to pull more than the controller output . So if i run my 850watt load at night it will just run the batterys down till the inveter drops out and recharge the next time the sun is out and the inveter will need reset . Im i still missing something in the running load down in the day once the batterys run down after a few hours of running ?

[Ampster]

..,. I assume the inverter will drop out before the load on batterys starts to pull more than the controller output . ....

It all depends on how much the load is and how much current the controller puts out. The load is going to be split between the battery and the controller. The inverter will drop out when voltage sags. It is not important which one occurs first since the controller output will be affected by sunshine and battery output will be affected by capacity.