Where can I find a 12v 20AMP circuit breaker?

Recently I bought myself a HUGE 800 watt power inverter. When you buy an inverter this big, it doesn't come with a cigarette lighter adapter, but battery cables. When I'm running something small off of it, (my laptop) I don't want to have to hook it up to my car battery, so I am going to add a cigarette lighter cable. Where can I find a 12v 20 amp circuit breaker to add to this? I don't want a fuse, because I don't want to replace it every time it burns out.

You should be able to get them at any auto store or junk yard.
However, your cigarette lighter IS (normally) fused. So, if its a 20A circuit (a lot are 15A) you need a considerably smaller circuit breaker. A thermal breaker will heat up and break in about 1 sec at 200% rating, 10-20 seconds at 150%, and probably never pop at 125%.

Don't forget that cigarette lighter circuits are commonly shared with radios, door locks, or other equipment that may help pop the fuse.

Your notebook takes probably 40 watts. You would probably be better off getting one of the small 75 watt inverters. Xantrex makes one that is very small. One end is the cigarette lighter plug and the other end is an outlet. Your 800 watt inverter (depending on technology) may waste more power than its driving at those levels.

I wouldn't call 800 watts huge. I have a 2500 Watt inverter from a T.V. Station and it is a real sine wave inverter (60 hertz controlled) its really heavy >200 lbs. Mine already had a circuit breaker on it. I would go to a custom car stereo installer to pick one of those breakers your looking for.

What about getting a nice surge protector with a built in circuit breaker?

If you still want a 12V 20amp circuit breaker, any marine chandlery will either have one or can get one for you. Most medium sized pleasure boats are on 12 volt systems and the breakers are used for protection as well as often being the only switch on the circuit ( running and navigation lights, auto bilge pump, etc.)

- Don

Thanks...my laptop uses about 165 watts from the power adapter when it is charging - 2 huge lithium batteries. I've got a 140 watt inverter...and that is not big enough. The closest thing I could get is probably a 300 watt...and that's starting to get rather expensive. I'm thinking about permanently mounting the inverter under the seat in my truck...then running a dedicated wire to the battery for it...

I would seriously look at the Jazz 300w unit. It comes with both alligator clips and a cig lighter plug. It is quite small and will run 280w continuously. As for price you can get them for under $35 on ebay all the time. I got mine for $29 including shipping. It is a great little unit, very small and will put out up to 500w in a pinch. I didn't get mine from here, but it is a start.


http://cgi.ebay.com/ws/eBayISAPI.dll?ViewItem&item=3020935521&category=1498

If you do still want to install your inverter I would suggest running a dedicated wire about 8 gauge and use a 40A fuse, but if you really want a circuit breaker any marine place should have them. Try westmarine.com

The 800 watt uses about 75 amps a full output... /ubbthreads/images/graemlins/grin.gif /ubbthreads/images/graemlins/ooo.gif

Um, stupid question coming. Why wouldn't any CB rated at a voltage higher than 12V work? Does the 12V rating mean that it is a smaller CB? Why not 28V 20A or 120V 20A?

I think it would probably be best to hard mount it.
If it doesn't have a control line or doesn't shutdown at a reasonable input line voltage, you can add a relay powered by one of the spare ignition on circuits. Make sure you DO appropriately fuse your install or use a non-resetting breaker. There is a lot of energy flowing....

Shankus, the big deal is it needs to be rated for DC. Yes you could use a 24vdc or 48vdc 20A breaker on 12vdc. The problem is AC breakers sometimes don't open far enough to stop the large rushing current of DC.

zmoz I ran a dedicated #8 line from the battery to my trunk and just fused it at 40A for my 300w inverter. Yes if you might pull the full 800, you would need about a 100 amp line, maybe #2 or 2aut to reduce line loss.

I used to have a #2 running from my front battery to a battery in the trunk. Then I ran a 2400w inverter from the rear battery. I needed the rear battery to reduce line loss. I also had the two batteries connect together when the ignition was on with a 100a contactor and disconnect when it went off, way overboard, but I was messing around and could run anything that would plug in to a 120v outlet /ubbthreads/images/graemlins/smile.gif

I have seen contradictory information in both labelling and application.

So-called "thermal" circuit breakers should not care what the circuit voltage is, or if it is AC or DC. However, I have seen breakers (and even switches!) marked as "AC Only" which may have something to do with contact deterioration being less when you are switching AC because the average damage done to the contacts will be less than if you were switching 120V DC.

There are other circuit breaker designs which employ magnetics or sometimes active circuitry--these are usually found only in certain complex industrial or special application circuit breakers (such as GFCI). These, of course, must not be used for anything but their intended appliation.

I have seen a PCB-mount 4A, 120V circuit breaker used in a 14.4V battery circuit for a pro video camera. Since that works, I don't see why a 15A or 20A panel mount breaker wouldn't work. I do think, however, that there are other limiting factors involved, especially the wiring going to the cigarette lighter. I have seen wire as small as 16AWG used for a 20A cigarette lighter circuit!

Hello there,

Another idea would be to construct a solid state
circuit breaker using a high current, low resistance
MOSFET and a fast acting control circuit.
This type of circuit could be made so fast it actually
protects the fuse. I guess this isnt really saying that
much though, but it will protect transistors too.

Good luck with your LED circuits,
Al

i use a lot of these in my setup.
i bought them in bulk and they are bout 3.00 ea.
mount in a 3/8 or so hole.
depending on how many you need i may have a few extras.

If snakebite does not have what you are looking for, post here again or email me. I have a decent quantity of DC CB's in various sizes from 1A up past 100A, price for one or two to a CPF member for a worthy cause would be...free /ubbthreads/images/graemlins/smile.gif
Only catch is, they are either used outtakes or will have cosmetic defects ie chips or scratches.
Most smaller ones have a #10 stud for input & output, 100A & up have 1/4 or 3/8" depending on size.

i doubt a 20a breaker is of any use for his app.
maybe 100a?

There's a couple of insights worth mentioning. One already has been, for a number of reasons breakers often have entirely different 'trip points' for DC and AC.

Another is the bit about current handling (in this case interrupting) capacity. AC favors contacts since the arc on opening automatically starts, stops, reverses direction, and starts again 120 times a second. There is no such 'reset' in the DC case. This generally means tougher contacts for DC as well as a different profile. The usual result of ignoring this is contact welding.....not what we're looking for.

I'd suggest sticking to the makers ratings.

Doug Owen

Well, I think I've decided just to permanently mount the inverter under my seat...so I won't be needing a breaker. Thanks everyone...

In my car I have a 100amp breaker which I use for my audio system running about 2000watts through 2 amps (1 for 2 12" subs and 1 for my component speakers). If you're looking for high amp circuit breakers, companies selling car audio products should have what you're looking for.
-ERiC

I guess my price was too high /ubbthreads/images/graemlins/ooo.gif