Is it possible to make 12V to 48V boost dc-dc converter of 6kW power?

Question

I have 12V battery that can output 500A (LiFePO4). But all 220V invertors that I found need 48V input to work with high power (6kW).

Is it possible to make boost DC-DC converter that will allow to use 12V battery with 48V invertors? Is it possible to make it cheap?

Answer 1

Not at all entirely impossible, just very hard and ridiculous, but what on Earth are you planning to do with 6 kW?

Generally single phase 230V is limited to 3.6 kW, since most electrical cords are rated for 16 amperes. Even then, the Schuko connector isn't really ideal for 16 amperes continuous for long periods, so I wouldn't advise for example continuously charging electric car with single phase 3.6 kW using Schuko connector, every day, for a number of years. The connector will degrade and then there's a danger of the connector overheating.

The largest 230 V appliances I have are:

• Vacuum cleaner 2200 W (and that's very inefficient, today you could get a similar one with 700 W power once EU started to fight the ridiculous inefficient motors with better regulation)
• Electric kettle 2200 W
• Several electric heaters 2000 W
• Coffee maker 1500 W
• Portable air conditioning unit 1000 W

Not a single device I have consumes more than 2200 W.

6 kW single phase is insane. That would be better implemented by having several different inverters with different AC and DC circuits.

500 amperes (6 kW at 12 V) requires very thick wires. Not even 0000 AWG (107 mm²) would be up to the task as that can handle about 200 amperes continuous.

On the other hand, if you limit a single circuit to 2200 W AC, it requires just about 200 amperes at 90% efficiency and 12 volts so you can use 200 ampere wires.

However, even that would be ridiculous. 2200 W AC should be really produced by a 48 V system where the current would be limited to 50 amperes. I wouldn't advise using even 24 V systems to create 2200 W.

So you can create 2200 W AC (50 amperes at 48 volts) using 16 mm² and maybe even 10 mm² wiring without overheating the wire insulation.

So my advice: use a 48 volt system and create many 2000 - 3000 watt circuits, each with different AC and DC wiring.

Your boost converter approach is incorrect. Boosting 12 volts to 48 volts and then to 230 volts is just a very inefficient pathway to create 230 volts. It has higher losses than going directly from 12 volts to 230 volts. Also, where are you planning to find a 6 kW 12 volts to 48 volts boost converter? I'm sure that won't be easy to find, cheap, small, lightweight or efficient. Every single boost converter I have seen is actually more expensive than a modified square wave 230 volt inverter of similar power level. Actually, a boost converter might even be more expensive than a a pure sine wave inverter of similar power level.

Edit: I didn't notice who asked the question is for Ukraine. Here is my advice, how I'm prepared for an energy catastrophe in Finland.

My home is heated by district heating. However, if that's unavailable but electricity is available, I use numerous resistance heaters (small heat blowers that take very little space when I don't need them). I have 5.8 kW electric heaters total.

If electricity is unavailable, I will do this:

• I have a cheap flashlight in every room just in case I need a flashlight immediately
• I start a 1900 watt inverter generator to create electricity. I have some fuel in storage. This will run computers, refrigerators plus some floor lights. Unfortunately, it won't run my entire house due to lack of transfer switch. I can of course use any non-fixed appliance with long cable reels and extension cords.
• If the electricity break is long, I will use a propane fueled 5 kW heater to create heat. I have the ability to monitor carbon monoxide, carbon dioxide and propane levels to alert about dangerous gases.
• If it's summer, I use two 100 watt solar panels to charge 54Ah 24V lead-acid battery bank. I have modified the 100 watt solar cells for 24V operation (originally they were 12V).
• The lead-acid battery bank can be used to run computers (It's connected to a UPS), plus I have another 300W 24V-to-230V modified square wave inverter. Lead-acid batteries die suddenly and often, so just in case if the lead-acid battery bank fails at an inconvenient time, I have two 210Wh 300W true sine wave battery power stations by Ecoflow
• Cooking, heating and making coffee is accomplished by a camping stove with small propane bottles. I would never dream about using non-grid electricity for cooking, heating or making coffee. Fossil fuels are better for emergencies.
• If fuel runs out, I just ordered a Fenix HM23 headlamp powered by a single AA cell. My opinion is that headlamps are the best available light source for extended outages where fuel runs out, because they leave both hands free and very dim brightness is enough since they will always point the light to the direction where you are looking. It should run 100 hours with a single AA. If the headlamp breaks, I also have a second headlamp run by 3xAA cells that's too bright for extended outages (batteries run out fast). I also have two Fenix E20 AA powered flashlights, homemade bases for them to allow them to tailstand like a candle, plus two Fenix AOD-S diffusers to make them into actual "electric candles".
• I have a Nedis World Receiver radio that runs for 60 hours with two AA batteries
• I have ordered 180 AA alkaline batteries. AA batteries are the best power source for emergencies, since AAA costs about the same but AA has 2.5 times the amount of energy. My calculations show these are enough for 2 years. They have a shelf life of 10 years. If buying AA batteries, please do ensure you order name brand batteries with long shelf life.
• I also have numerous Sanyo Eneloop low discharge AA cells that I can charge whenever electricity is available
• I can convert the 24V battery bank to USB directly without an intermediate inverter, plus I have a USB-to-AA charger allowing me to charge my Eneloops directly from 24V and from solar cells
• Although I normally mostly use car, especially during the winter, I have several bikes, some electric, some not. One of them is an electric fatbike, so I have the possibility to do shopping with it in the middle of a winter with lots of snow. I have panniers for all bikes, so I can carry lots of groceries.

Maybe you should consider something similar? Not thinking that 3600 watt-hour batteries run your entire house, but using a suitable form of energy (propane, gasoline, AA batteries, solar energy, maybe charged grid energy for times when you have it) for different uses.

If you find out that yes, indeed, 600 watts continuous (maybe 1200 watts peak) is enough for the uses in which you actually want to use electricity where fossil fuels aren't better, then I'm very sure you can find a single 600+ watt pure sine wave inverter and use the 12-volt system you currently have, and the 3600 watt-hours probably are enough to cover long power outages. I think that 1200 watts peak is enough to start a refrigerator for example.

If AA batteries and AA battery powered headlamps are in a short supply, a candle is better than nothing, but for emergencies AA batteries and LED headlamps really win. They are cheaper, take less space when you need light for a very long time, and the brightness can be usually adjusted.

Answer 2

I see that you're in Ukraine, so I'll do a frame challenge.

You don't want to power your stove from batteries. That's plain silly; round trip efficiency will be south of 50% I'd bet.

What you want:

1. Lights should be powered from low voltage sources. AC inverters have quite large losses, which you avoid with LED flashlights with a diode fed by a PWM circuit.
2. For heating and cooking, use gas, diesel oil, kerosene or some other fuel source. They're fairly energy dense, and a liter of kerosene contains 3-4 times the energy of your battery bank.

Your battery bank contains ~3.6kWh of energy. Let's say 80% of that's practically usable without destroying your batteries. That's 2.8kWh, or 10MJ. That's the energy content of 0.25 liters of kerosene!

At full throttle your 6kW inverter will suck the batteries dry in 20-30 minutes - and probably even faster in practice due to internal resistance in the cells.

Use your inverter for powering the fridges and other 230V loads that you need. Use rechargeable flashlights for lights. Use some other fuel for cooking and heating.

Your batteries simply doesn't have significant amounts of energy when you start listing water heaters, air conditioners and other high power loads. For a small 100l water heater, with incoming water at 10°C and outgoing at 70°C, the energy required to heat the 100l is 25MJ - or 2.5 times your battery!

Answer 3

The simple way to convert 12V to 24V. Is to get two 12V batteries and place them in series. Doing 12V to 24V any other way (Inverter) will involve going via AC.

However, for this much power, you will be better off using the DC directly. Yes you will need different appliances, but the losses will be lower.