DC - DC converting causing sparks/arc?

[UCYT5040]

So I have a 48v battery as well as 48-36 converter. Whenever I connect the wires ( I did it twice ) it is causing either sparks or an arc (I can't really tell because I remove the connection so quickly).

Have I harmed my lithium ion battery?

I think the issue is that the converter has no load. But also, I worry that once I connect a load I will suffer from more damage to the battery.

I attached a photo:


Thanks for helping

[indeterminate]

The battery will be fine
your 48-36 converter will have sum large input capacitors that are causing a large inrush current and hens the arching.
you need to use a suitable rated switch & fuse between the battery and converter.
the switch needs to be rated for 100v DC

[UCYT5040]

The battery will be fine
your 48-36 converter will have sum large input capacitors that are causing a large inrush current and hens the arching.
you need to use a suitable rated switch & fuse between the battery and converter.
the switch needs to be rated for 100v DC

Could you recommend a switch? I couldn't find anything like that on AliExpress

Where do I setup the switch? If it's easy to do, I'd like to setup the switch to the main 48v so I can turn on/off everything I have hooked up to that. There will be an additional 48v>9v converter wired in parallel.

And is this okay for the fuse: https://a.aliexpress.com/_mtNF5Wy ?

[T3sl4co1l]

A switch rated for capacitive inrush can be used, or a precharge circuit (perhaps as a complete electronic solution e.g. eFuse, solid-state power controller, etc.) can be used to prevent arcing.

Tim

[Phil1977]

As mentioned, the sparks are quite normal. For larger systems (like in EVs) you usually switch on in two steps: First a small relay switches on a pre-charge-resistor, then a big contactor shorts the resistor.

Could you recommend a switch? I couldn't find anything like that on AliExpress

Where do I setup the switch? If it's easy to do, I'd like to setup the switch to the main 48v so I can turn on/off everything I have hooked up to that. There will be an additional 48v>9v converter wired in parallel.

And is this okay for the fuse: https://a.aliexpress.com/_mtNF5Wy ?

The fuses are definitely too small. Such an 48V-battery can easily deliver 100A for several seconds, these are about 5kW of arc power! Short-circuit current may be even factor 10 higher, but then (hopefully) the BMS in the battery pack trips.

I´d take at least fuses like this

https://nl.aliexpress.com/item/1005006286904138.html

Though Aliexpress shouldn't be considered as the best source for fuses. They may look beefy, but do you know what´s inside?

For the switch I´d take something like this:

https://nl.aliexpress.com/item/1005007481463049.html

It´s only gut feeling, but I´m quite sure this switch also survives the inrush current without any pre-charging.

[UCYT5040]

I´d take at least fuses like this

https://nl.aliexpress.com/item/1005006286904138.html

That link isn't working in the USA, could you please tell me the specifications of those fuses? Thanks

[Phil1977]

Yes, the link is not active anymore. As I said, Aliexpress is not a good place to buy fuses. If you order at mouser you could get a link of something reliable.

If you want to get it at Aliexpress:
- Take fuses with ceramic body, not glass
- Avoid 5*20mm, prefer 6*25mm or 6*30mm
- "Sand-filled" is better
- Avoid purely automotive fuses for more than 24V

I honestly think about discharging a "little" capacitor bank (I have 400mF <=> 400 000uF @25V available) into a 5*20mm glass fuse and record it with the fastest camera I have available. It´s always nice to see controlled explosions and I can stress my recently acquired 800A-thyristor.
And yes, a Li-Ion battery as shown by the OP can deliver similar peak currents like the capacitor bank. But the capacitor bank rarely catches fire when misused.