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shunt/ current sense resistor question
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Jezebels_couz
Dec 1, 2020, 9:41:44 PM12/1/20
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In the process of finishing a 0-12 VDC @ 0-10 A switching power supply.
Fairly new at this and wanted to ask about the shunt resistor. It will
be in the ground line. Plans mentioned two options: either a custom
shunt made from constantan wire or similar, or simply two 5W 0.1 ohm
power resistors in parallel. Since I wanted to keep costs down, I am
going with the power resistors, but I have a concern: I will be running
12 gauge wire for the output lines, but when the ground wire reaches the
shunt, even the two resistors in parallel combined are far less than 12
gauge. Should I be concerned, or is the tiny resistor/ 12 gauge wire
distance (basically just for the 12 ga wire to resistor wire connection)
irrelevant to heating and losses?
Fairly new at this and wanted to ask about the shunt resistor. It will
be in the ground line. Plans mentioned two options: either a custom
shunt made from constantan wire or similar, or simply two 5W 0.1 ohm
power resistors in parallel. Since I wanted to keep costs down, I am
going with the power resistors, but I have a concern: I will be running
12 gauge wire for the output lines, but when the ground wire reaches the
shunt, even the two resistors in parallel combined are far less than 12
gauge. Should I be concerned, or is the tiny resistor/ 12 gauge wire
distance (basically just for the 12 ga wire to resistor wire connection)
irrelevant to heating and losses?
Johann Klammer
Dec 2, 2020, 2:47:18 AM12/2/20
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On 12/02/2020 03:41 AM, Jezebels_couz wrote:
> In the process of finishing a 0-12 VDC @ 0-10 A switching power supply. Fairly new at this and wanted to ask about the shunt resistor. It will be in the ground line. Plans mentioned two options: either a custom shunt made from constantan wire or similar, or simply two 5W 0.1 ohm power resistors in parallel. Since I wanted to keep costs down, I am going with the power resistors, but I have a concern: I will be running 12 gauge wire for the output lines, but when the ground wire reaches the shunt, even the two resistors in parallel combined are far less than 12 gauge. Should I be concerned, or is the tiny resistor/ 12 gauge wire distance (basically just for the 12 ga wire to resistor wire connection) irrelevant to heating and losses?
If it's not too long, the heat might dissipate through the adjoining traces.
> In the process of finishing a 0-12 VDC @ 0-10 A switching power supply. Fairly new at this and wanted to ask about the shunt resistor. It will be in the ground line. Plans mentioned two options: either a custom shunt made from constantan wire or similar, or simply two 5W 0.1 ohm power resistors in parallel. Since I wanted to keep costs down, I am going with the power resistors, but I have a concern: I will be running 12 gauge wire for the output lines, but when the ground wire reaches the shunt, even the two resistors in parallel combined are far less than 12 gauge. Should I be concerned, or is the tiny resistor/ 12 gauge wire distance (basically just for the 12 ga wire to resistor wire connection) irrelevant to heating and losses?
(if they didn't lie about the resistor wattage, that is)
Bob Engelhardt
Dec 2, 2020, 8:11:29 AM12/2/20
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resistance is .0008R - <2% of your shunt & negligible.
* - https://www.engineeringtoolbox.com/copper-wire-d_1429.html
Ralph Mowery
Dec 2, 2020, 9:51:08 AM12/2/20
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In article <rq6ut4$jh7$2...@dont-email.me>, jb...@three.net says...
The small wire of the resistors should handle it just fine. The main
reason for # 12 wire on the circuit is for the voltage drop.
reason for # 12 wire on the circuit is for the voltage drop.
Jezebels_couz
Dec 2, 2020, 12:45:02 PM12/2/20
to
very clear, so hopefully the diagram will better relate:
https://i.imgur.com/pYSRxiX.jpg
Jezebels_couz
Dec 2, 2020, 12:45:36 PM12/2/20
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Jezebels_couz
Dec 2, 2020, 12:45:56 PM12/2/20
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Ralph Mowery
Dec 2, 2020, 2:47:12 PM12/2/20
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In article <rq8jsg$ne0$3...@dont-email.me>, jb...@three.net says...
To put your mind at ease Astron that makes power supplies has a 20 amp
one that has two pass transistors. That means that each one would be
good for 10 amps. They use only one .1 ohm 10 watt per transistor.
I have larger ones that do the same thing and they have worked for years
with no problems.
Each of your resistors will need to be less than 3 watts at a 10 amp
current if a quick calculation is correct.
>
>
> Here's a diagram of what I was trying to explain. I wasn't sure I was
> very clear, so hopefully the diagram will better relate:
>
> https://i.imgur.com/pYSRxiX.jpg
>
>
I understand what you are going to do.
>
> Here's a diagram of what I was trying to explain. I wasn't sure I was
> very clear, so hopefully the diagram will better relate:
>
> https://i.imgur.com/pYSRxiX.jpg
>
>
To put your mind at ease Astron that makes power supplies has a 20 amp
one that has two pass transistors. That means that each one would be
good for 10 amps. They use only one .1 ohm 10 watt per transistor.
I have larger ones that do the same thing and they have worked for years
with no problems.
Each of your resistors will need to be less than 3 watts at a 10 amp
current if a quick calculation is correct.
Jezebels_couz
Dec 2, 2020, 2:57:16 PM12/2/20
to
through those small areas and I wanted to minimize heating and loss. In
my mind, it sort of defeated the purpose of using 12 gauge wire
everywhere else to have a bottleneck at the end, but if all is well then
no longer concerned. There will be two 5W resistors in parallel, so
good to go on wattage. Thanks again.
Transition Zone
Dec 5, 2020, 8:59:59 AM12/5/20
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