How to eliminate arcing in a switch?

  • Thread starter Thread starter Topher925
  • Start date Start date
  • Tags Tags
    Switch
Click For Summary

Discussion Overview

The discussion revolves around methods to eliminate arcing when connecting a 36V battery to electronics with capacitors. Participants explore various approaches to mitigate the effects of inrush current that causes arcing during the connection process.

Discussion Character

  • Technical explanation
  • Debate/contested
  • Experimental/applied

Main Points Raised

  • One participant suggests using a pre-charging method with a resistor to limit current and prevent arcing when connecting the battery.
  • Another participant proposes using a large value inductor in series to oppose the input current initially, which could help manage inrush current.
  • A different viewpoint mentions using a SPDT switch to manage the connection and suggests a specific time constant for charging the capacitors to reduce arcing.
  • Another suggestion is to place the switch after the capacitors to potentially avoid arcing issues altogether.
  • One participant discusses the reliability of using a power MOSFET as a switch, highlighting its advantages over traditional switches at low currents and suggesting a circuit design for smooth turn-on.
  • There is a mention of shifting the arcing issue to when the switch to the battery is opened, indicating a potential trade-off in solutions.

Areas of Agreement / Disagreement

Participants present multiple competing views on how to address the arcing issue, with no consensus reached on a single solution. Various methods are proposed, each with its own considerations and implications.

Contextual Notes

Participants express uncertainty regarding the effectiveness of different solutions, particularly in terms of the implications of shifting arcing to other points in the circuit. There are also discussions about the specifics of component values and configurations that may affect performance.

Topher925
Messages
1,563
Reaction score
7
I'm working on a project where I'm connecting a big 36V battery to some electronics which contain capacitors on the power input. Of course when I connect the two I get some major arcing which likes to weld and stick connectors together. Does anyone know of a simple or easy way around this? The only thing I can think of is pre-charging by first powering up the electronics from the battery using a big resistor (~100Ohm) to prevent arcing and then connecting the battery (without resistor). Is there an easier way that doesn't involve me using two connectors?
 
Engineering news on Phys.org
Sounds like the arcing is caused by an inrush of current. A suitable large value inductor connected in series will initially oppose the input current until steady state is reached.
 
what said:
Sounds like the arcing is caused by an inrush of current. A suitable large value inductor connected in series will initially oppose the input current until steady state is reached.

So that shifts the arc to when the switch to the battery is opened... :wink:

Maybe use a SPDT (make before break) switch for the connection, and choose an appropriate resistor to give you about a 100ms time constant for the inrush charge-up of the caps. Just pause briefly in the middle switch position when turning the device on...?
 
Maybe you can simply put the switch after the capacitors?

General tip: if the current is not too big, for reliability you can also use a power MOSFET as your actual switch (make resistive voltage divider for gate voltage, use switch on that, switches are considerably more reliable at low currents).
Nowadays a power MOSFET costs under 1 euro. I got 10 of these for something around 5 euro:
http://www.irf.com/product-info/datasheets/data/irfz44n.pdf
the on resistance is 0.017 ohm, which can easily beat your switch, the off leakage is under 0.025 mA so that's not a concern either. You can make circuitry to ensure smooth turn on, with a capacitor that has to charge through resistor to bring gate voltage up on turn on, but is discharged immediately at turn off. That'd dissipate half the capacitor's energy at the mosfet during charging, i don't know how big your capacitors are but that may well be acceptable. I can draw you the circuit if you need.
 
Last edited:
berkeman said:
So that shifts the arc to when the switch to the battery is opened... :wink:

It sure does without adding a diode across the coil.
 

Similar threads

Replies
37
Views
7K
Replies
30
Views
3K
  • · Replies 12 ·
Replies
12
Views
2K
  • · Replies 31 ·
2
Replies
31
Views
5K
  • · Replies 17 ·
Replies
17
Views
3K
Replies
6
Views
4K
  • · Replies 9 ·
Replies
9
Views
2K
  • · Replies 10 ·
Replies
10
Views
3K
  • · Replies 33 ·
2
Replies
33
Views
5K
  • · Replies 10 ·
Replies
10
Views
2K