Choosing the Right Fuse for a DIY Home Battery

Steps

1. 1

   Step 1: Understanding the mega fuse mistake

   I built my home battery for 1200 euros and the video went viral. I made a real mistake by protecting the battery pack with a mega fuse because its stop power is not enough. My lithium battery is 300 amps, and during a short circuit, it can let ten times as much current flow, reaching 3000 amps.

   The fuse must be able to handle and stop this power.

2. 2

   Step 2: What determines fuse sizing

   A fuse must not be calculated based on the total battery capacity. The fuse determines the cable thickness, ensuring no more amps flow than the cable can handle without getting hot. Even with a 300 amp battery, if the connected equipment only asks for 200 amps and the cable can handle 300 amps, I use a 200 amp fuse so it trips much earlier.

3. 3

   Step 3: Key fuse ratings explained

   When choosing a fuse, we look at the maximum voltage that can pass through it and the amperes it must disconnect. We also look at the AIC, which stands for Amperes Interrupting Capacity. The AIC tells us how many amperes the fuse can actually stop when it blows.

4. 4

   Step 4: Glass fuses

   Glass fuses are often found at the bottom of equipment or in line to protect devices like a servo. They work on various voltages up to 250 volts and higher, but usually have a maximum voltage of 40 amps. They have an AIC of 1000 amps, meaning they can stop a 1000 amp short circuit current.

5. 5

   Step 5: Blade fuses

   Blade fuses are the small fuses found in cars and car fuse boxes. They handle various voltages and range from 1 to 40 amps. They have an AIC of 1000 amps, which means they can stop a 1000 amp short circuit current.

6. 6

   Step 6: Why glass and blade fuses do not work

   Glass and blade fuses are useless for our home battery setup because they handle a maximum of about 32 amps. Our 48 volt home battery goes up to 52 volts and higher, which is too much for them. My 314 amp home battery will generate a short circuit current over 3000 amps, so these fuses are not suitable.

7. 7

   Step 7: Maxi fuses

   Maxi fuses come in 32 volt and 58 volt versions, where 58 volts could work for our home battery. However, they have a maximum amperage ranging between 20 and 80 amps, which is too low for our needs. Despite this, they can stop 1000 amps.

   They are identical to blade fuses but made for slightly higher power.

8. 8

   Step 8: Midi fuses

   Midi fuses have a voltage range between 32 and 70 volts and power ratings from 30 to 200 amps. The 70 volt version could work on a 48 volt battery pack, and my pack is protected at 150 amps. However, they have an AIC of 2000 amps, which is not enough since my short circuit current exceeds 3000 amps.

9. 9

   Step 9: Block fuses

   Block fuses are usually made up to a maximum of 58 volts and power ratings from 30 to 300 amps. They have an AIC stop power of 10,000 amps, which is enough for our home battery since our short circuit current is around 3000 amps. An advantage of block fuses is that they are easy to install by screwing down one side and attaching the regular connection.

10. 10

    Step 10: ANL fuses

    ANL fuses have maximum voltages of 32 volts and 80 volts depending on the model. Their power ratings vary from 60 to 500 amps, and a 200 amp version costs about 7 euros. They have an AIC of 6000 amps, which fits within my range since I need around 3000 amps and want a 150 amp rating.

    I could use an ANL fuse in my home battery.

    What I used

    Item	Amount	Notes
    ANL fuse	1	200 amp version costs about 7 euros

11. 11

    Step 11: Mega fuses and my critical error

    Mega fuses come in 32 volt and 58 volt versions and range from 60 to 500 amps, costing about 10 euros for a 200 amp version. However, I made a huge mistake here because a mega fuse has an AIC of only 2000 amps. With a short circuit current over 3000 amps, the internal wire gets hot and burns through, but the fuse may fail to properly disconnect and jam up internally.

    What I used

    Item	Amount	Notes
    Mega fuse	1	200 amp version costs about 10 euros

12. 12

    Step 12: Class T fuses

    Class T fuses handle a maximum voltage of 125 volts and power ratings from 110 to 400 amps. They feature an exceptionally high AIC of 20,000 amps, meaning they can easily stop a 3500 amp short circuit current. The downside is the purchase price, which ranges between 50 and 80 euros per piece, and they are ruined and must be thrown away after one short circuit.

    What I used

    Item	Amount	Notes
    Class T fuse	1	Costs between 50 and 80 euros

13. 13

    Step 13: Using a Class T fuse in the busbar

    For my busbar, where all my battery packs come together before going through the shunt and to the distribution, I placed a Class T fuse. If anything goes wrong on the distribution side, the Class T fuse will stop it immediately. This is why reading viewer comments is great, as it helps me catch oversights and research the correct facts.

    What I used

    Item	Amount	Notes
    Class T fuse	1	Placed in the busbar distribution

14. 14

    Step 14: Adler EF3 fuses as a drop-in replacement

    A viewer mentioned Adler EF3 fuses in the comments, which I had never heard of before. They handle up to 250 volts, range from 150 to 750 amps, and have a massive AIC of 50,000 amps. They share the same terminal pattern as mega fuses, making them a direct drop-in replacement with a 200 amp version costing about 20 euros.

    What I used

    Item	Amount	Notes
    Adler EF3 fuse	1	200 amp version costs about 20 euros

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    Step 15: Circuit breakers as a reusable option

    Circuit breakers are available up to 250 volts, range from 160 to 400 amps, and have an AIC of 20,000 amps. The advantage is that they are reusable, so if a fault happens, you can just click them back on, and they also double as a switch to easily turn off the battery pack. However, a 400 amp version costs around 180 euros, making them considerably more expensive.

    What I used

    Item	Amount	Notes
    Circuit breaker	1	400 amp version costs around 180 euros

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    Step 16: Calculating my battery and cable requirements

    My battery is 314 amps at 58 volts and can charge and discharge at a maximum of 0.5C, which is half of 314 amps or 157 amps. It is connected with a 50 square millimeter cable that can safely carry up to 150 amps. As a margin, I plan to draw a maximum of 100 amps from the batteries, which is better for the cells and the BMS.

    What I used

    Item	Amount	Notes
    50 mm square cable	1	Can tolerate a maximum of 150 amps

17. 17

    Step 17: Selecting the final fuse for my setup

    With a voltage above 58 volts, glass, blade, maxi, and midi fuses are ruled out. Based on my short circuit current of 3140 amps, the mega fuse fails because it only stops 2000 amps. This leaves the block fuse, ANL fuse, Class T fuse, and Adler EF3 fuse as viable options.

18. 18

    Step 18: Mounting the Adler EF3 fuse

    Physical placement and housing space are important factors when choosing a fuse. My battery pack and link distribution use mega fuse holders, and the Adler EF3 fuses have the exact same form factor. Because they fit right into the existing mega fuse holders and meet all electrical specifications with a much higher AIC, the Adler EF3 fuse is the most suitable choice for my setup.

    What I used

    Item	Amount	Notes
    Adler EF3 fuse	1	Fits into existing mega fuse holders

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    Step 19: Takeaways

    • Fuses must be chosen based on cable thickness and expected short circuit current rather than battery capacity alone.

    • Mega fuses have an AIC of only 2000 amps, which is insufficient for a 3000+ amp short circuit current.

    • Glass, blade, maxi, and midi fuses cannot handle voltages above 32 to 70 volts.

    • Adler EF3 fuses serve as a drop-in replacement for mega fuses with a much higher AIC of 50000 amps.

    • Circuit breakers offer reusability and a switch function but come at a much higher price.