12V Current sensing

By power rating. P = R I^2, for 0.01ohm that'd be 490mW, so sensible would be a 1W resistor.

I went ahead and studied some ohm's law while waiting.
With a possible maximum power draw of 140w

14v*10a fuse=140w

that would mean that a 0,01ohm resistor would need a powerrating of 196w to function
since I^2*r=p (140^2*0,01=196)

I calculated that a 0,0002ohm resistor with a 5w rating could withstand being in series with a load up to 158w with sounds to be well within margin for what I need.
Or tell me If I'm completely wrong please

I think I severely mixed up my numbers. hold on a minute

>>1210814
God I'm fucking stupid, disregard my other post. I mixed up watt and amp in my earlier calculations. You're ofc correct. Thank you sir

>>1210769
>>1210814
>>1210853
>>1210859
>>1210865
what the fuck is this


(70W/14V)^2*0.01 ohms=0.25W -> 1W resistor

you don't want to have to read 50mV FSR though so use a 10W 0.1 ohm which will give you 0.5V FSR.

>>1210897
Should specify based on 10V, not at 14V.

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>>1210853
>14V drop across a 10 milohm resistor

>>1210897
>what the fuck is this
Obviously you're not a golfer.
There's nothing wrong with amplifying the signal at the load point using an appropriate opamp with rail-to-rail inputs. Any milliohm-range resistor would work well as long as the leads are sufficient to handle the current. 0.03 ohms at 3W would provide for a 200mV FS which you could amplify or compare as you like. Also resistors of 10W and above are spendy.

>>1210904
To be fair, I mixed some numbers up

>>1210769

Why are you measuring the current, OP?

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Shit's pulling a healthy amount of current, and you (probably) don't need sub-mA resolution out of it.

String a wire through a current coil, amplify/measure voltage as needed. No xboxhueg resistors necessary, no permanent modifications to wiring harnesses.

>Pic extremely related.

>>1211643
Where the hell do you get a DC current transformer?

>>1211643
Not gonna work for DC unless you spend a lot on a hall effect current sensor, regular coils only work on AC, they're a transformer.

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Use a hall sensor. A resistor is very unefective too much current passing through it, is going to be a high power loss. A transformer isn't effective because its DC not AC. A hall sensor is cheap, isolated, linear, doesn't consume too much energy, works with AC and DC, etc, etc. CHeck de ACS712

70W/10V = 7 Amps

I'd guess the wire to supply it is around 16 gauge (good for ~20Amps)
>http://www.engineeringtoolbox.com/wire-gauges-d_419.html

16 gauge has a resistance of ~.0132 ohms/meter
>http://www.daycounter.com/Calculators/AWG.phtml\

>the resistor has to be about 0.01ohm or something around that.
Measure the wire to find the gauge, calculate the length of wire needed for 0.01 ohms, then tap the wire at the appropriate length to measure the voltage drop. Electrical noise could be a big problem though, trying to measure ~70mv in an automotive environment. Maybe shielded wire would help.

>>1211759
You have to add your own AC signal and then you can figure out the DC component. Look it up, it's pretty neat.

>>1211769
This is also a very sensible option.

>>1211769
>40A current handling capacity at 40degC die temperature rise
Bretty gud, and does the amplification for you, if a bit spendy in single quantity.

>>1210769
I would opt for minimal intervention. Use the fuse itself as your series resistor and measure the drop directly across it, Kelvin contact style. The corresponding current can be measured once with an AC/DC clamp ampere meter or determined from other data. Now you have R_fuse=V_drop/I_lamp and I_lamp=V_drop/R_fuse.

>>1211798
Oh I know this I'm just trying to guage ops and this users level of retard. We already got a few winners trying to do math with their ass and DC CTs are not exactly cheap. Hall effects are better but again not cheapo. Without purpose it could all be for not and expensive.. So this is the last time I ask before I abandon this mystery faggotry.

Why does he want to measure the current?

>>1211891
>Why does he want to measure the current?
He doesn't. His job is to start threads and leave. There are many such threads. It has to do with the post-moot business model. All that counts is the number of posts. Scan the /sci/ catalog now and then to see where it will lead. Can you recognize the pattern of pseudo questions?

>>1211961
Indeed I have noticed such a pattern but I refused to believe it.

>>1210769
> google current voltage panel meter with shunt
these are like 10$ on ebay
some are good for 100V 50A