question

dittaspank avatar image
dittaspank asked

how to use 12V inverter on 24 volt (2 battery) system

I am using a Victron 150/60 Smart Charger powered by 2 x 450W solar panels. 2 LIFEPO4 batteries making 24V and 200A total. I have a 12V to 120V Inverter (1800 Watts). So have to go with 24V for 2 PVs to get more power (1300W max I think)

- What is the best way to connect it? Straight to a 12 volt battery, thinking battery bank imbalance issues will not be good, or use a 24V to 12V step down converter? 90% efficient so lots of losses but can manage.

Amazon = (https://www.amazon.com/uxcell-Converter-Regulator-Transformer-Waterproof/dp/B01LYK6G2Y/ref=sr_1_3?crid=1W9CSRGD6CE31&keywords=24V+Step+Down+to+12V+40a&qid=1706035581&refinements=p_72%3A1248879011&rnid=1248877011&s=electronics&sprefix=24v+step+down+to+12v+40a%2Caps%2C83&sr=1-3)


Is there a better way?

Thanks a lot!
Andreas Gadmer

battery chargingMPPT SmartSolarLithium Battery
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4 Answers
prein avatar image
prein answered ·

Option 1: keep the 24v, sell the inverter and buy a 24v one.

Option 2: make the entire system 12V. If you don't have more parts connected, it's as simple as connect the battery in parallel and connect everything. (Make sure to use thick enough cables). The mppt is also 12v capable.


A step down converter will not work, or you will need a much more beefy one, which will not be cost effective at all.

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kevgermany avatar image kevgermany ♦♦ commented ·
@dittaspank

1800W at 12V is 150A. Might be better sticking to the 24V setup.

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dittaspank avatar image dittaspank kevgermany ♦♦ commented ·
I will go to 48V when the house is built but I only have a 12V 1800W Inverter for now and do not want to buy another, for now. Using what I got.


I guess a step down converter will do for now. I will make a by-pass circuit with 3 way switches so I can use the 2 batteries in parallel and also disconnect the Victron charger. Thus I can use all my full battery power when needed and then just switch back to charging after. All for the power tools that will build my house. A generator for backup also.

Thanks


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dittaspank avatar image dittaspank commented ·
unfortunately the Victron Smart 150/60 only hands 900 Watts at 12 volts. so only 1 PV so not acceptable for power. Need to panels min for 950+ Watts. so for 2 panels one must use 24V.


So I need the right amount of power. I hv a 720W, 60A 12V step down and that will charge all I need including a battery charger for a 3rd deep cycle 60A that I can use the inverter on independently. Temp solution but need 24V min for both panels. So stuck a bit.

Thanks for the info. All very true.


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prein avatar image prein dittaspank commented ·
I don't understand you. Why can't you hookup 2 pv panels on the mptt?

It will deliver max 900W, ok, but that's like 95% of max power. So what is the issue of putting 2x pv panel in series in het mptt and go for a 12v setup?

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dittaspank avatar image dittaspank prein commented ·
Look at the spec sheet for the 150/60. 800 watts max with 12 volt systems. 1700 watts when it's 24 volts. Limitations of the victron. Correct me if I am wrong. My panels are 460 Watts each. 50.6 volts oc. With my step down converter I'll have enough power to run enough devices and get enough power for 2 panels. One is not enough.
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honu avatar image honu commented ·
Not possible, you got to make a choice : 12V or 24V.

Sell the 12v inverter, buy a 24v one.


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dittaspank avatar image dittaspank honu commented ·
I'll post my design and results from next weekend. I hear ya but like to try stuff before tossing.
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JohnC avatar image
JohnC answered ·

@dittaspank

It limits the output, just the same as if the batteries were full. The power is left in the panels, like the tin roof next to them. Your 150/60 could easily handle >4000W of panel, as long as wiring rules are followed. The 2x you have you could wire series or parallel. You won't break it.

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dittaspank avatar image dittaspank commented ·
Getting tight writing here. Makes sense. I will try and let you know. Should workout at 12V then. Thank you for the clarity.
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uguraladag avatar image
uguraladag answered ·

If you ask me, connect the batteries in parallel and stay at 12 volts, when you will increase the system panel power, your charging power will double with an additional mmpt 150/60 and 2x450 Watt panels..

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honu avatar image honu commented ·

12V systems are not good for 1800W inverters, 12V is really for small systems.

12V : UpTo 1500W system
24V : UpTo 3000W
48V : UpTo 10kW

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dittaspank avatar image dittaspank honu commented ·
I know. It just for basic security camera, wifi router, cell extender. Not that much so 12V will do for now. Chainsaw and drills work well with the 12V inverter. I hv great cables. For my house I will go 48V, but we are slowly building it this spring. Thanks for the info. Very true but I am limited and expanding this summer.
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honu avatar image honu dittaspank commented ·

I was just saying that to uguraladag... :D

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dittaspank avatar image dittaspank commented ·
  • So pong as the charger limits the power unlike the max VOC limit that can blow the box. I hope that is true because the, yes, I can stay at 12V and the power is safely limited and no smoke. Thanks
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dittaspank avatar image
dittaspank answered ·

Final answer is the Victron 150/60 Smart Charger system can handle 60A max. It limit that current and not blow up like when the Voc is over the 150V max. That will cause burnout. Not the current max. So the unit will just never go over 60A causing 12V = 12Vx60A=720W, 24V = 24Vx60A=1440W, 48V = 48Vx60A=2880W.
So the panel power will be clipped and only the max current and power will flow.

A huge thanks to all that explained this and were super polite.
AG

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honu avatar image honu commented ·
Current is not forced intol the MPPT, MPPT ask for it like a lightbulb draw current as much as it need and not more. Like when you drink in a bottle, your mouth take the water it need .. there is no surpressure.. if it make sense.


BUT you can't go over the max voltage, it's 150V but in fact.. do not go over 130V cause this max voltage depend on physical parameters like temperature.

Reason i said .. go the 24V way ...

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