Electronic Circuit Breaker
- Thread starter Ray64
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nkaminar
Well-known member
The circuit breaker breaks when the amperage gets to the set level. It does not depend on the voltage. Could be 6 volts, or 12 volts, or 90 volts. Try your local automotive store or search online. Here is one for 40 amps at NAPA: https://www.napaonline.com/en/p/BK_CBF40?gQT=1
nkaminar
Well-known member
BadPuppy, I normally will not counter respond, but the heating element you refer to in Post # 3 is heated by current not voltage. It is the current squared times the resistance.
Here is what is found on the internet:
"Heating by I squared times resistance" refers to the concept of Joule heating, where the amount of heat generated in a conductor is directly proportional to the square of the current (I²) multiplied by the resistance (R) of the conductor, represented by the formula: H = I²Rt. "
The voltage is important in that too much voltage will break down the insulation. But a 12 volt circuit breaker should work just fine at a lower 6 volts.
Here is what is found on the internet:
"Heating by I squared times resistance" refers to the concept of Joule heating, where the amount of heat generated in a conductor is directly proportional to the square of the current (I²) multiplied by the resistance (R) of the conductor, represented by the formula: H = I²Rt. "
The voltage is important in that too much voltage will break down the insulation. But a 12 volt circuit breaker should work just fine at a lower 6 volts.
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rotorwrench
Well-known member
It's all about amperage as was mentioned. The only reason they associate them with 12-volts is to indicate a low voltage DC electrical system. 12-volts is the most common automotive voltage in the common era. 1956 was a long time ago as much as I hate to admit it. Short stop circuit breakers use a bi-metallic internal switch that is rated at the max safe amperage of the wire it protects. If a short to ground happens, a 6-volt system will be only slightly slower to trip but we are talking fractions of a second. All it has to do is trip before the wire burns up. If you don't think it will work then it's easy to test. Just short one with power on it to ground and see what happens.
Higher voltage systems can use smaller gauge conductor wire. A 12-volt system can use 18 gauge wire for average light duty circuits. 24-volt systems can used 20 gauge wire. Circuit breakers are sized with slightly higher amp ratings than fuses for the same gauge of wire since it will trip faster at overload. Wire is sized depending on what amperage is needed in the circuit. It can be larger but it can't be smaller. With fuses, they can be a lower rating on the average wire size but it can't use an amp rating that exceeds the rating of the wire or it won't protect the wire. Protection of the wire is the whole point of using circuit protective devices.
Higher voltage systems can use smaller gauge conductor wire. A 12-volt system can use 18 gauge wire for average light duty circuits. 24-volt systems can used 20 gauge wire. Circuit breakers are sized with slightly higher amp ratings than fuses for the same gauge of wire since it will trip faster at overload. Wire is sized depending on what amperage is needed in the circuit. It can be larger but it can't be smaller. With fuses, they can be a lower rating on the average wire size but it can't use an amp rating that exceeds the rating of the wire or it won't protect the wire. Protection of the wire is the whole point of using circuit protective devices.
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No argument, Neil. Power and heat are the same thing, same formula. I'm assuming the operator is a resistive heating element, could be wrong. If so, 6V across it would produce half the current of 12V, thus 1/4 the power (heat). Would require 4x the current to activate the same CB. Would require a variable PS to test this assumption.
rotorwrench
Well-known member
Don't forget that a dead short to ground is a lot bigger load than any wire can take for long. I watched a wire in an alternator control circuit burn up when it finally shorted to ground after 32 years in service with a police department. The whole wire burned within 2 seconds since generator and alternator control systems aren't short protected circuits. A person can weld with a 100-amp generator. A battery can store a lot of current too.
Bob Johnson
Well-known member
Here is some information:
If you calculate the resistance needed for 30 amps for a 6 and a 12 volt system you get 0.4 ohms for a 12V and 0.2 for 6V. So a dead short across a circuit breaker would require it have those resistance. But that is not how it works. The circuit breaker has a much lower resistance, typicality 0.02 ohms. Thus it will "see" a voltage of 30 X 0.02 = 0.6 volts when it triggers regardless of the overall voltage of the system. The number of watts (power) is what triggers the breaker. In this case it is 18 watts (30A X 0.6V).
Note that when the breaker triggers there is a difference in the "short" resistance for 6V vs 12V. In a 6V system it take a resistance of (6V - 0.6V) / 30 A = 0.18 Ohms for 6V and (12V - 0.6V) / 30 A = 0.38 Ohms for 12V. That would result from a 180 watt load for a 6V system and a 360 watt load for a 12V system. That is where the difference between a 6V and 12V system is seen.
Bob
If you calculate the resistance needed for 30 amps for a 6 and a 12 volt system you get 0.4 ohms for a 12V and 0.2 for 6V. So a dead short across a circuit breaker would require it have those resistance. But that is not how it works. The circuit breaker has a much lower resistance, typicality 0.02 ohms. Thus it will "see" a voltage of 30 X 0.02 = 0.6 volts when it triggers regardless of the overall voltage of the system. The number of watts (power) is what triggers the breaker. In this case it is 18 watts (30A X 0.6V).
Note that when the breaker triggers there is a difference in the "short" resistance for 6V vs 12V. In a 6V system it take a resistance of (6V - 0.6V) / 30 A = 0.18 Ohms for 6V and (12V - 0.6V) / 30 A = 0.38 Ohms for 12V. That would result from a 180 watt load for a 6V system and a 360 watt load for a 12V system. That is where the difference between a 6V and 12V system is seen.
Bob
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TomInCologne
Senior Member
But this one is 'automatic re-set' one, so you may not realize that your circuit breaker is tripping often. A wiring fault or other electrical fault may go unnoticed until the fire starts eating your A away...
nkaminar
Well-known member
Here is what the ad says:
"Type II - modified reset Type II circuit breakers will remain “tripped” by an internal resistor (in the OFF position) as long as the circuit is powered. Type II breakers can be reset by turning the circuit OFF, or by turning the ignition switch to the OFF position. These devices are sometimes called "non-cycling breakers."
If I read this correctly, if you were to somehow disconnect the circuit, like disconnecting the battery and then connect it again, the circuit breaker would then trip again. It appears that the circuit breaker would not allow the car to burn up.
"Type II - modified reset Type II circuit breakers will remain “tripped” by an internal resistor (in the OFF position) as long as the circuit is powered. Type II breakers can be reset by turning the circuit OFF, or by turning the ignition switch to the OFF position. These devices are sometimes called "non-cycling breakers."
If I read this correctly, if you were to somehow disconnect the circuit, like disconnecting the battery and then connect it again, the circuit breaker would then trip again. It appears that the circuit breaker would not allow the car to burn up.
TomInCologne
Senior Member
Hmm, not a native speaker here, but i would parse it as 'turning the main switch off and on' will re-set the fuse. I would rather keep the fuse in the 'tripped' position until i manually re-set it.
Ymmv
katy
Well-known member
Methinks we've gone "off track" here.
https://www.phoenixcontact.com/en-ca/products/device-circuit-breakers/electronic-circuit-breakers
feufeu
Member
hi all,
in al my cars i hide this part under the dash board.
https://fr.aliexpress.com/item/1005008144807659.html?spm=a2g0o.productlist.main.1.7dd56d2eKifQGV&algo_pvid=2924c92f-b94e-428e-a1e8-02e092fee969&algo_exp_id=2924c92f-b94e-428e-a1e8-02e092fee969-0&pdp_npi=4%40dis%21EUR%2113.42%216.69%21%21%2198.68%2149.21%21%40211b61d017367915637533294e8eb5%2112000043981120712%21sea%21FR%21844011223%21X&curPageLogUid=w7SrSZIX6L4q&utparam-url=scene%3Asearch%7Cquery_from%3A
in al my cars i hide this part under the dash board.
https://fr.aliexpress.com/item/1005008144807659.html?spm=a2g0o.productlist.main.1.7dd56d2eKifQGV&algo_pvid=2924c92f-b94e-428e-a1e8-02e092fee969&algo_exp_id=2924c92f-b94e-428e-a1e8-02e092fee969-0&pdp_npi=4%40dis%21EUR%2113.42%216.69%21%21%2198.68%2149.21%21%40211b61d017367915637533294e8eb5%2112000043981120712%21sea%21FR%21844011223%21X&curPageLogUid=w7SrSZIX6L4q&utparam-url=scene%3Asearch%7Cquery_from%3A
katy
Well-known member
That link doesn't doesn't work for me.
rotorwrench
Well-known member
The short stop circuit breakers that Ford used in the post war era were a simple bi-metallic switch. Heat is what reacts them. The bi-metallic strip gets hot real quick in a short situation. They had bi-metal switches down to a science pretty early on. King Seeley used this principle for their pressure and quantity indicator systems as early as 1936 when Ford started using them. They are very reliable but can be destroyed in a dead short situation.
Aircraft circuit breakers work on the same principle but they have a toggle mechanism that must be reset to restore current flow. If the short still exists after a trip then the bi-metallic switch won't allow it to reset as soon as it heats back up. A short stop automatically resets after the bi-metallic switch cools back down but will continue to trip as long as the short is still present. Bi-metallic switches are calibrated for the amount of heat they can take before bending. A smaller wire can take less heat so the switch is made to bend at a lower temperature.
Aircraft circuit breakers work on the same principle but they have a toggle mechanism that must be reset to restore current flow. If the short still exists after a trip then the bi-metallic switch won't allow it to reset as soon as it heats back up. A short stop automatically resets after the bi-metallic switch cools back down but will continue to trip as long as the short is still present. Bi-metallic switches are calibrated for the amount of heat they can take before bending. A smaller wire can take less heat so the switch is made to bend at a lower temperature.
feufeu
Member
nkaminar
Well-known member
BadPuppy, You are right that with the same resistance the power would be 1/4 with the 6 volt system as opposed to the 12 volt system. But the current with a dead short is going to be so great that the circuit breaker (or fuse) will trip in so short of a time that it does not matter where it is 6 or 12 volts. I did some very crude calculations in my head last night with lots of assumptions and the time for the circuit breaker to pop is about one millisecond. The wire in a 16 gauge electrical cable may heat up 1 degree F in that time, probably less.
An interesting experiment would be to test, using 6 and 12 volts, the tripping time of the circuit breaker and the time it takes for a 16 gauge wire of 2 foot length to burn up. An oscilloscope would be needed to catch the circuit breaker tripping. A stop watch could probably be used for the wire.
An interesting experiment would be to test, using 6 and 12 volts, the tripping time of the circuit breaker and the time it takes for a 16 gauge wire of 2 foot length to burn up. An oscilloscope would be needed to catch the circuit breaker tripping. A stop watch could probably be used for the wire.