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I am a novice in electronics. Doing it as a hobby. In one of my projects, I am facing an issue whereby I see arcing whenever I connect my 12V lead acid battery to my circuit. The reason I say this is because I can see a brief flash of 'spark' at the point of contact and alittle bit of sound at that instant. Then one of my sensors (INA219) will blow (specifically the R100 resistor of the INA219) and I can see smoke arising from it. My thoughts are that the circuit is suddenly drawing too much current in that instant when I physically connect the wires causing a spike in current. This does not happen when I use my power supply from my wall socket which passes through a fixed 12V 5A DC regulator. As I am not an expert on this, and might be incorrect in my judgement, I would thus like to ask for advice on this. I am thinking of using a resistor at the point of the connection between the wire from the battery and the wire from the circuit, to prevent this 'spike' in current. What kind of resistor should I be looking at (if a resistor should be used at all)? I trialled with a 1.5 and 4.7Ohms, but that doesnt seem to provide enough power to the components in my circuit. Ideally, I would like a resistor that can allow 5A of current to pass from my 12v lead acid battery. Otherwise, what other ways can I do try to minimise this arcing?

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closed as unclear what you're asking by Olin Lathrop, Michel Keijzers, Finbarr, laptop2d, Dmitry Grigoryev Apr 17 '18 at 9:10

Please clarify your specific problem or add additional details to highlight exactly what you need. As it's currently written, it’s hard to tell exactly what you're asking. See the How to Ask page for help clarifying this question. If this question can be reworded to fit the rules in the help center, please edit the question.

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    \$\begingroup\$ Fix the wall of text, cut the chit-chat, and show a schematic of your circuit. \$\endgroup\$ – Olin Lathrop Apr 14 '18 at 12:40
  • \$\begingroup\$ At least a block diagram to start with. You mention a Pi Zero which use 5V supply, so somethings are missing from your description. \$\endgroup\$ – Dejvid_no1 Apr 14 '18 at 13:15
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Difficult to judge without knowing the circuit. I'd suggest you add one.

A 12v lead acid battery (if one from a car) can provide a lot of current. You might be having problems with inrush current, which is mostsly a current peak needed to charge all the capacitance in your circuit. Do you have a lot of capacitance?

A common strategy to prevent this is using an NTC (negative temperature coefficient), which will have a high resistance initially and then drop as you have some current running.

Take a look at: http://www.mouser.com/ds/2/168/920-325D-LR-245176.pdf

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  • \$\begingroup\$ I am not sure if there is alot of capacitance. The main load in my circuit is actually just the Raspberry Pi Zero and a few relays (coils). But thanks for the NTC suggestion, I will look into it. \$\endgroup\$ – Craver2000 Apr 14 '18 at 12:44
  • \$\begingroup\$ I am thinking of getting an Inrush Current Limiter rated at 2ohms 25A. That way the current can be limited around 5A, which would be enough for my circuit, and the current is also limited to a relatively safe peak level of 25A. Do you reckon I can go with this? \$\endgroup\$ – Craver2000 Apr 14 '18 at 12:59
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The problem is with your circuit, not your power source. The circuit evidently has a problem in that it can't handle the power input rising quickly, and then be able to deliver essentially infinite current. Fix that.

The difference between the car battery and the power supply is that the car battery doesn't have current limiting. It can supply a few 100 A. The power supply probably has a capacitor on its output, but other than that can't supply more than some maximum current.

Your circuit apparently draws way more current than it should when first turned on. This may be due to something like a FET gate that floats when power is first applied. Without a schematic, there is little more to say.

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  • \$\begingroup\$ Thanks. I now understand why the two power sources behave differently in the initial power output. I am using a AGM battery actually, one that is more suited for deep discharge than a conventional car battery, but as you mentioned, I suspect it still can supply a very high amount of current compared to my regulated power supply. \$\endgroup\$ – Craver2000 Apr 14 '18 at 12:47

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