12v Circuit Breaker in a 24v System - Team Camaro Tech
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post #1 of 14 (permalink) Old May 8th, 12, 05:23 PM Thread Starter
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Al
 
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12v Circuit Breaker in a 24v System

So there I was last evening mowing my lawn and minding my own business when my rechargeable 24 volt electric lawnmower quit. The batteries are only a year old so I didn't suspect them. So I took it apart - fixed a few things that didn't need fixing - then discovered that the circuit breaker had failed. It's one of those 2-stud auto-reset types, 40 amp, 24volt.

Went to my local auto parts store this morning and as close as I could get was the same design, but 40 amp 12 volt. A brief discussion with the parts man and we both decided since amps is amps, it's only $3.49 and it oughta work. So Installed it and it does work and has one mow under it's belt.

Dug around on the web today and found the correct 24v rated 40a breakers and ordered a few of them, and I will swap it out when they arrive.

My main question - I guess - is what effect does voltage have on a circuit breaker, and what would likely happen were I to leave the 12v rated breaker in place?


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post #2 of 14 (permalink) Old May 8th, 12, 06:23 PM
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Re: 12v Circuit Breaker in a 24v System

Well it's been awhile since I dusted off my OHM's law for DC circuits, but basically by using a fuse rated at half the voltage and equal amperage the fuse is only rated at half the wattage capacity. So the fuse won't likely last if in fact the circuits sees anywher near max power usage, which it probably won't.

OHM's law is P= E x I (watts = Volts x Amps), so I guess you go from a fuse that will handle 960 DC Watts @ 24v to 480 DC Watts @ 24v. If my memory serves me from my apprenticeship days. If I'm wrong someone will surely correct me.

Worst case as I see it is the fuse will kick early, but you won't damage anything.

Run it and lets see how long it lasts....

Sean

1968 rs with an old school 354" SB2.2 pump gas motor.

Repetition does not transform a lie into a truth.

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post #3 of 14 (permalink) Old May 8th, 12, 06:49 PM
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Re: 12v Circuit Breaker in a 24v System

As stated above twice the volts = twice the wattage but amps are what melts the wires.

Fuses/breakers trip off of amperage... A 40A is 40A so both should trip at the same amperage regardless of the voltage.

Wire & fuses are strictly amperage rated.
The insulation quality is what you have to watch for with high voltages... but 24 in not that high.


As long as it is of good quality it should work fine.
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post #4 of 14 (permalink) Old May 8th, 12, 06:59 PM
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Re: 12v Circuit Breaker in a 24v System

I am inclined to agree with Lonnie to a point.
I'm not a DC guy and voltages I deal with are AC and much higher, buuuut, I don't buy that the amperage is the only issue here. It's rated at 12 volts only for a reason I would say, and most likely the reason is the sustained wattage (power seen at the device) and the fuse will be pushing the edge because of the materials it's built with. Otherwise the mfg would rate it at 12-24-48- etc. etc. volts, they can sell more that way.

I do know that;
Quote:
Wire & fuses are strictly amperage rated.
Is not a true statement with AC voltage, and likely DC is the same. But the amount of difference is small in your case AL, so it may be fine.

I could be wrong but in my electrical field what it's rated at is everything, any deviation that goes beyond the rating is an issue. I could be wrong here though, it's happened before....

Sean

1968 rs with an old school 354" SB2.2 pump gas motor.

Repetition does not transform a lie into a truth.

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post #5 of 14 (permalink) Old May 8th, 12, 07:30 PM
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Re: 12v Circuit Breaker in a 24v System

Quote:
If my memory serves me from my apprenticeship days.
Yep and the alzimers hasnt..
Unless the mower is chinese and works right on the limit of the breaker..u should not have an issue too soon...generally there is reasonbley genrous rated saftey margin.
If u load up the mower it will just switch the breaker sooner.

Quote:
Wire & fuses are strictly amperage rated.
AT a given Voltage....which at the end of the day amounts to the amount of watts that go thru. on DC VxA=W ...and why appliances are rated in Watts
So if u run anppliance at a voltage 1/2 what rated it will draw more amps, but not blow the fuse.

My Spelling is not incorrect...it is creative

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post #6 of 14 (permalink) Old May 8th, 12, 07:57 PM
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post #7 of 14 (permalink) Old May 8th, 12, 09:03 PM Thread Starter
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Al
 
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Re: 12v Circuit Breaker in a 24v System

.


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post #8 of 14 (permalink) Old May 9th, 12, 08:08 PM
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Re: 12v Circuit Breaker in a 24v System

Quote:
Originally Posted by Steptoe View Post
Yep and the alzimers hasnt..
Wait... what were we talking about again?....

Sean

1968 rs with an old school 354" SB2.2 pump gas motor.

Repetition does not transform a lie into a truth.

Franklin D. Roosevelt
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post #9 of 14 (permalink) Old May 9th, 12, 08:25 PM
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Re: 12v Circuit Breaker in a 24v System

Amp is an amp. For instance I have used 32v rated fuses in 110v circuits with no problems. I have never paid attention to the voltage rating.When sorting fuses they went to the appropriate size amp bin. There is a BIG difference between slow blow and fast blow, though. This spans a 27 year electronics career.
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post #10 of 14 (permalink) Old May 9th, 12, 09:03 PM
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Re: 12v Circuit Breaker in a 24v System

Quote:
For instance I have used 32v rated fuses in 110v circuits with no problems
There is also a big difference between AC and DC...not a good idea to mix them up, the fumula between the 2 are different.

My Spelling is not incorrect...it is creative

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post #11 of 14 (permalink) Old May 10th, 12, 12:03 AM Thread Starter
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Al
 
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Re: 12v Circuit Breaker in a 24v System

fumula.....Kiwispeak for formula. Or perhaps Stepspeak?


Thanks for the replies fellers - interesting topic, at least to me. As said, the 24v rated breaker is in the mail.....though I'm tempted to leave the 12v one in and see what happens.

I did dig around on the web a bit and one guy said the diff is in the quality of the materials and the number of on/off cycles, and that a lower voltage rated breaker could fail due to excessive voltage and theoretically "weld" itself into the closed position. But it's one opinion. What's the worst? - it's just an effin lawnmower.


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post #12 of 14 (permalink) Old May 10th, 12, 02:50 PM
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Re: 12v Circuit Breaker in a 24v System

Quote:
fumula.....Kiwispeak for formula. Or perhaps Stepspeak?
IMAO yeah sorta m8....seriously bit of dyslexia..damn think got that right??
I used to try the spell checks, but they come up with big lists of words, have trouble choosing the right one...which very often was wrong then changed the whole meaning of what I was saying...in the long run you guys seem to understand misspelling far better than the, correct spelling but incorrect word lol
...plus spell check real time consuming......with that many words lol

I do not mind open comments made with no malice like Al above, usually in inocence or humour...which ever creates a smile ....
I do get very angry when ppl treat deaf or blind people as retarded, or things like dyslexia and things like that as an insult... stuff like that shows who the retarded morons really are

Quote:
I did dig around on the web a bit and one guy said the diff is in the quality of the materials and the number of on/off cycles, and that a lower voltage rated breaker could fail due to excessive voltage and theoretically "weld" itself into the closed position. But it's one opinion. What's the worst? - it's just an effin lawnmower.
circuit breakers , fuses these days have alsorts of parameters built in for alsorts of applications...Chances are idf it us underrated it is just going to throw earlier...come to a halt when the full rated would not.
Hell I would have , and have done so on my welder and a few other things over the yrs, as a temp fix till the correct part arrives.
Quote:
it's just an effin lawnmower.
Nope its an effin electric lawnmower... cant go past a good old B&S reel mower cica 1950s lol

My Spelling is not incorrect...it is creative

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post #13 of 14 (permalink) Old May 10th, 12, 04:41 PM
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Sean
 
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Re: 12v Circuit Breaker in a 24v System

Quote:
Originally Posted by Moonpie View Post
Amp is an amp.
Ok, we are talking about a freaking (effing... ) electric mower rated to 24 volts, but that statement is not true when certain voltages are concerned.

Now when speaking of small electronics items the worst case of going to a lesser rated fuse is probably going to be shortened fuse life if anything, but when speaking of larger voltages the wrong voltage rated fuse (like using a 250 volt fuse in a 600v rated circuit) can be a disaster and deadly, they can create an arc blast when tripped and thats a bad thing... and besides that it's not accepted by code.
Thats why they rate them, they are designed to effectively operate at a certain maximum voltage.

Of course this is all like picking fly crap out of pepper because it will most certainly never matter to Al when he's mowing his yard (or paying some neighbor kid to....), and it will probably last a long time since it isn't operating at max.
But for all intents and purposes it is bad practice to consider the fuses rated voltage as unimportant especially when considering larger voltages. This is when using a lesser voltages in a greater voltage circuit of course.

Interesting topic however, (probably only to us taking part in it though... )

Sean

1968 rs with an old school 354" SB2.2 pump gas motor.

Repetition does not transform a lie into a truth.

Franklin D. Roosevelt
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post #14 of 14 (permalink) Old Aug 9th, 12, 07:41 PM
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Re: 12v Circuit Breaker in a 24v System

The voltage rating of fuses and breakers has mainly to do with how much voltage it is rated to withstand when it has opened the circuit. It's kind of like voltage ratings of wire insulation. If the insulation isn't rated high enough, electricity just goes right on through.

Zeke
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