DC - DC converting causing sparks/arc? - Page 1
Forum section: electronics / beginners

author: UCYT5040
author_rank: Newbie
timestamp: August 12, 2024, 09:54:45 pm
content: 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

author: indeterminate
author_rank: Regular Contributor
timestamp: August 12, 2024, 10:53:32 pm
content: The battery will be fineyour 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

author: UCYT5040
author_rank: Newbie
timestamp: August 13, 2024, 03:08:02 am
content: Quote from: indeterminate on August 12, 2024, 10:53:32 pmCould you recommend a switch? I couldn't find anything like that on AliExpressWhere 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?

author: T3sl4co1l
author_rank: Super Contributor
timestamp: August 13, 2024, 04:21:32 am
content: 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

author: Phil1977
author_rank: Frequent Contributor
timestamp: August 13, 2024, 07:20:53 am
content: 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.Quote from: UCYT5040 on August 13, 2024, 03:08:02 amThe 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 thishttps://nl.aliexpress.com/item/1005006286904138.htmlThough 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.htmlIt´s only gut feeling, but I´m quite sure this switch also survives the inrush current without any pre-charging.

author: UCYT5040
author_rank: Newbie
timestamp: August 13, 2024, 11:09:21 pm
content: Quote from: Phil1977 on August 13, 2024, 07:20:53 amThat link isn't working in the USA, could you please tell me the specifications of those fuses? Thanks

author: Phil1977
author_rank: Frequent Contributor
timestamp: August 14, 2024, 06:02:57 am
content: 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 24VI 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.