Introduction: DC Mini Circuit Break Box

Picture of DC Mini Circuit Break Box

I bought Extremeaire Air compressor for my truck. It has a superb motor, solid cable and top quality. However, it has two problems. It does not have fuse box for safety and switch to turn it on and off. Once hooked to car battery, you will see an electric spark and motor is running. It is just too dangerous for me. Manufacturer advised me to use quick connector to switch it on and off. The quick connector is very hard to pull apart and hookup. It is simply not designed for switching. Also this unit does not have fuse box to protect circuits. If shorted, it will damage car battery right away. Anyway, i need a fuse box and switch for this superb air compressor.

Step 1: Build Circuit Break Box

Picture of Build Circuit Break Box

once figuring out the Amps of compressor, I put up a fuse box, composed of 2 circuit break to protect both wires. Remember, it should be a DC circuit break. Its internal wiring needs to be adapted to DC power, resulting in a little bit complexity. Wire has to be thick enough for enough electrical Amps. It needs to be calculated first.

Step 2: Build Connector

Picture of Build Connector

I built two quick connectors on each end of break box. It needs to be soldered, primed, shrink wrapped properly. We are talking about unto 120 amps of electric current here. So everything needs to be solid.

Step 3: Integrate Circuit Box Into Package

Picture of Integrate Circuit Box Into Package

Next step is to put circuit/switch box into original box. Again, circuit box size needs to be calculated first. I secured box into big carrying box by 2 screws. Remember, if these 2 screws get loose and falls into circuit box, they should not short wiring inside.

Comments

tutdude98 (author)2016-07-23

Didnt know there are dc circuit breakers like that

Just make sure your battery can put out enough amperage to trip breaker or you might damage it

jcweicom (author)tutdude982016-07-23

do not understand. would you please clarify? amperage depends on compressor. initially it is around 120A for half a second, then it drops to 30A at 0 PSI and 50A at 150 PSI. So at normal working condition, breaker will not be tripped.

tutdude98 (author)jcweicom2016-07-24

When battery is low it cant provide same current as it can when is fully charged

When you want to start a car but battery is empty, it will rotate a starter few times but wont start car becouse it cant deliver same current as it would when is fully charged, so in case your battery is empty, compressor might work slower but if short circuit happens and battery can only deliver 30A then you will damage battery, but circuit breaker wont trip becouse theres only 30A drawing

jcweicom (author)tutdude982016-07-24

oh. now i see your point. thanks. first, i have to run the car while running compressor. otherwise, it will drain battery quickly. car's generator could output 130 Amps as max. car itself takes 40A, and compressor takes 30A. So the battery is not drained when car is running. Secondly, if short circuit current is under 60A (you mentioned 30A as example) and would not trigger breaker, I guess battery is able to take it. I could be wrong. I think any short circuit is in hundreds of AMPS, and the heat it generates damages the battery. If short circuit AMP is only 30Amps, the heat it generates is in this normal design capability. Correct me if i am wrong.

tutdude98 (author)jcweicom2016-07-26

If you are running it with car alternator then its probably fine

I had battery that was short circuited and it was drained till it was empty, battery swelled up and looked like a ballon becouse when you short curcuit it, it will produce gas (hydrogen i think) and if it doesnt have release valve like motorcycle batteries it will contain all that pressure until it blows up (or just caps)

memjr73 (author)2016-06-25

You're trying to protect thing with a 60A breakers? How big of a compressor is this? The 28 gallon compressor in my garage doesn't eve use 10. I have a compressor like that in my truck too. Id'd be surprised if it used more than 5 amps at start up.

You also need to protect just the hot (positive) wire, as the entire car body is a huge ground plane.

fjr_scoot (author)memjr732016-06-27

Electrical energy is measured in watts.

Your garage compressor is probably 120 volts x 10 amps = 1200 watts.

This heavy duty car compressor is 12 volts x 60 amps = 720 watts.

memjr73 (author)fjr_scoot2016-06-28

Yes. I failed to realize the OP had the bad ass version or the compressor that looks just like my dinky one.

jcweicom (author)memjr732016-06-25

The compressor has 3/4 HP motor, is using Car's 12V battery. I use power meter checked its AMP. The starting current is 120 amps, and running current is 30 Amps at 0 PSI. Its specs says that it is drawing 50A when at 100 PSI. So 60 Amp fuse is good enough. Your 28 Gallon is using 120V wall power. So it is 120x5 = 600 W power consumption. Mine is 12x30 = 360 W power consumption. I put 2 circuit breaks in the box. One is protecting hot, and one is protecting ground. Also, if you pull wire hard and force it break, hot line will be detached inside box, preventing it from shoring the circuit. The wire is top marine grade at 6 gouge, good for unto 60 Amps.

memjr73 (author)jcweicom2016-06-28

Yes, my bad. I have a similar compressor. It looks just like that except black instead of red. I failed to realize your had a bad ass one instead of one like my dinky one.

rafununu (author)2016-06-27

You don't need the ground protection, there are only two wires so intensity cannot go elsewhere. A breaker is not a switch and it is not designed to act as a switch, but for occasional uses it can fit. I've never seen distinction between AC or DC for breakers, only intensity matters, but there are different kind of curves with a special curve for motors that permits the breaker to accept the starting overcurrent.

jcweicom (author)rafununu2016-06-27

you are right. I do not need 2 circuit breakers. i put two in case 1 is bad. i put many safety features in, such as what if a wire is forcefully pulled out from the box, what if screws inside box get loose, etc. also, breaker is not switch. i should put a solenoid and remote wireless control in. but they are probably already too big for the box. another reason is that i have already spent $200 on this box since i used all the top of the line material (all material are made in the USA). For occasional use, it is good enough. i just stop this project since it is already above my budget target. But you might be wrong on DC, AC breakers. They are different in structure internally. They should be be mix used. The breaker i used has some "delay" effect. It tolerates initial current spike to 120 amps up to few millisecond.

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