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I have a household mini fridge connected to my off grid electrical system, and recently I bought a smaller inverter just for the fridge so that I can turn my larger inverter off to reduce power consumption. However the problem is that when the fridge compressor starts, the power surge flickers the lights and other DC devices and risk turning off completely.

Question is: Is there something I can buy or build that's relatively inexpensive to put between my inverter and slightly insufficient buck converter to supply the surge power for the first few seconds?

Buck converter ---> ? ---> Inverter ---> Fridge

Here is my setup: 120v AC mini fridge (Hisense 4.4 cu. ft.) that starts up to 450 watts for 2 seconds, 45 watts running --> 300w Bestek pure sine wave inverter, 750w surge --> 414w step down 24v to 12v buck converter --> 24v, 230ah LiFePo4 battery bank (self built from cells and BMS)

electrical setup to fridge

Would something like a capacitor work? E.g. stores energy needed until the discharge and once the discharge occurs, the power just flows through it until the device has stopped. Then it builds its charge up again, waiting for the next surge.

Unless there is an affordable small 24v inverter available, I can't justify buying an additional expensive inverter for the amount of power saved. I could revert back to plugging in my fridge to my 2000w inverter but the goal is to reduce the standby power consumption and usage of a less efficient large inverter. Also, I could buy a larger buck converter but I was hoping that I won't have to spend extra $ on a 2nd buck converter and also won't a larger converter increase power consumption?

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  • \$\begingroup\$ Hi there, and welcome to EE. Can you draw a diagram and upload to your question, it will help to get a visualization of the setup. Oh and also write what gear you got there, model numbers etc. Better to add more than less. \$\endgroup\$
    – MiNiMe
    Nov 15, 2023 at 23:25
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    \$\begingroup\$ Rather than spending money on a larger buck converter, look for a small inverter which can run from your 24V supply instead and get rid of the buck converter stage in the chain. \$\endgroup\$
    – brhans
    Nov 15, 2023 at 23:43
  • \$\begingroup\$ @MiNiMe Included a diagram and more info. For the sake of brevity or preventing information overload, if there's anything specific that is unclear or necessary to answer the question, I'd be happy to include it! \$\endgroup\$
    – jechen95
    Nov 15, 2023 at 23:52
  • \$\begingroup\$ @brhans That's what I've considered but so far all the 24v inverters are very large (at least 1000w) which could defeat the purpose of having a small inverter to minimize power consumption, and they are much more expensive. Do you have any recommendations on smaller affordable 24v inverters around 300w or less? \$\endgroup\$
    – jechen95
    Nov 15, 2023 at 23:54
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    \$\begingroup\$ A 12 / 24 V fridge would solve a couple of issues here. And thanks for updating the question. \$\endgroup\$
    – MiNiMe
    Nov 16, 2023 at 0:14

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You're likely to need quite a large capacitor to start the fridge, but not as extreme as those capacitor banks you see people use for starting cars.

But the first thing to check would be to try the small inverter powered from a 12V battery and conform that it is capable of reliably starting the fridge.

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  • \$\begingroup\$ Good point on verifying the inverter quality with a 12v battery! and do you have any specific recommendations on a capacitor? I'm not familiar with them so any type or size? \$\endgroup\$
    – jechen95
    Nov 16, 2023 at 6:03
  • \$\begingroup\$ I would be guessing too, the good thing about capacitors if you can add them in parallel if you don't have enough. I think the ones that were starting cars were about 50F so maybe 1F might be a good first try, \$\endgroup\$ Nov 16, 2023 at 11:45

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