Blowing fuses in power cable

[Nick1234]

Ok so i have a kenwood 800 watt amp and i recently bridged the wires between the amp and the subs. Now, ever now and then i keep blowin the fuse in the power cord. Any idea why?

 

Rockford 400 watt max 200 rms 10'' subwoofers

 

nick

[jeremy]

bad ground or pos/neg wires touching each other .....

[Nick1234]

what if i try putting a bigger fuse in there. Right now it is a 25, what if i go to a 30.

[gtphill]

Ok so i have a kenwood 800 watt amp and i recently bridged the wires between the amp and the subs. Now, ever now and then i keep blowin the fuse in the power cord. Any idea why?

 

Rockford 400 watt max 200 rms 10'' subwoofers

 

nick

 

Hey Nick,

 

As well as being a W-body owner, I also have done professional audio mixing, system tuning, and loudspeaker design for a number of years.

 

A quick bit of work with ohms law will show that 800 watts on a standard car battery is about 60amps of current. Also, typical Class A/B amplifiers are only about 60% efficient.

 

If you amp is actually capable of producing 800 watts (most car audio amps output is exagerated), then a fuse on the order of 100amps in order for you. What are the internal fuses on the amp itself?

 

Fuses, of course, work by heating up and breaking, so they often can withstand substantial short term bursts well in excess of their rated ampacity. Because music is so transient, the fuse holds most of the time. HEAVY usage for the large professional amps at major concerts corresponds to an integrated power output of only about 15% of peak.

 

Your 800 watt amp should be using at least #6 interconnect wire, and a fuse of approximately 100amps.

 

Before bridging your subs, the current demand on the amplifier was lower, but no that they are bridged, you have increased that demands. "Watts" is actually a terrible misnomer for amplifiers, as they are inherenlty VOLTAGE sources, and merely suck as much current as they need from the power supply (up to their thermal/mechanical) limits.

 

Hopefully this answers your questions!

[THe_DeTAiL3R]

I've got an 800w Kenwood amp.. (460w RMS bridged @ 4ohms, and 150 or 125w RMS x 2 @ 4 ohms.).

 

I have a 60 amp fuse by the battery, and 30 AMP fuse in the trunk before the amp. The amp itself has 2x30 amp fuses built in, and I believe the amp draws 45 AMPs or so. I've only got one sub hooked up though, so I'm not driving it very hard at all.

 

You might want to try a larger fuse, or make sure you have a fuse up front by the battery as well as in the trunk. I'm using 8 guage wire as well if that makes any difference.

 

Which fuse is it blowing? And you have your amp bridged? Or you have your subs connected in parallel (2ohm load on the amp?).

[Nick1234]

that info helps, but it kinda hard to understand, as you can amagine. First i have the 25 amp fuse after the battery in the power cable. Then the 2 30 amp fuses in the amp. Now i do NOT have the amp turned up all the way on the deck, and on the amp. There is a negative and a positive marked "bridge" on the amp. I took a pos wire from the pos port, went to the first sub, then took another pos wire and went from that sub to the other. Same with the negative. Now it is wierd cause i can have them pounding for 20 minutes without a problem, but today, i turned up, turned it up, and then turned it down again for some reason, and that is when it blew. I don't have a problem with diming lights, and i do have a capacitor, but it is not in the car. I guess what i need to know is what do i have to do to stop this problem.

 

Nick

[THe_DeTAiL3R]

so you are blowing the 25amp fuse by the battery? I would try upping it to a larger one. On my car I have a 60 amp fuse by the batt- maybe a bit bigger that I need for the 800w amp, however I also have a 250w amp connected as well. I've also got 30amp fuses for each amp in the trunk, in addition to the fuses that are built in the amps. I've got my amp set at like 1/3rd, bass boost off. Just one sub and I could easily blow it with that power.

 

Also, make sure you have a good ground. I've got 8 guage wire connected to the seatbelt bolt. (thanks Kyle).

[musthavemuzk]

if the 800 watt kenwood amp has 2x30 for fuses on it then the power wire needs to also have fuse(s) with the same rating as what is on the amp.

soooo

 

within 18 inches of battery the fuseholder needs to have a 60 amp fuse on it. provided that power wire only goes to the one 800 watt kenwood amp. if there are more amps on this power wire then the fuse by the battery needs to be the total of all the amps on that wire.

 

http://www.bcae1.com/ for some basics in car audio.

 

Monty

[god910]

Okay, wow, don't put a 100 amp fuse anywhere there. Unless gtphill is gonna buy you a new amp. If the amp fuses are rated at 60 then that will be fine anywhere on the power wire. So, 25 is to small, I have 1 time, ONE, used a fuse bigger than the OEM rated load BUT, that was after many talks w/ an ORION rep, and that was w/ an HCCA amp rated at 1 ohm mono 1/2 stereo.

[musthavemuzk]

dem der HCCA amps are just that HIGH CURRENT.

 

Monty

[gtphill]

that info helps, but it kinda hard to understand, as you can amagine.

 

What I described is fairly basic, and only requires a working knowledge of ohms law and its permutations. Voltage=Current*Resistance

 

Then the 2 30 amp fuses in the amp. Now i do NOT have the amp turned up all the way on the deck, and on the amp.

 

That confirms my supsicions about the true power output of your amplifier. Each of those thirty amp fuses covers 1/2 of the voltage swing of the amplifier (i.e. one for positive, and one for negative). Based on this information, the proper value of the line fuse for you should be 60amps, in an appropriate holder. The input signal attenuator on your amp does not influence its ultimate output ability, only how hard you have to drive it from the head unit to reach full output.

 

There is a negative and a positive marked "bridge" on the amp.

I took a pos wire from the pos port, went to the first sub, then took another pos wire and went from that sub to the other. Same with the negative. Now it is wierd cause i can have them pounding for 20 minutes without a problem, but today, i turned up, turned it up, and then turned it down again for some reason, and that is when it blew. I don't have a problem with diming lights, and i do have a capacitor, but it is not in the car.

 

On an amplifier running in "bridge" mode the speakers will be connected to both positive leads. In bridge mode the output from one of your original channels is inverted to all the effective amplifier voltage swing to be twice what it would be normally. Additionally, you have wire your subs together in parallel. The net result is a substantial increase in current needed to drive the lower impedance, and to supply current for the increased potential voltage swing.

 

Okay, wow, don't put a 100 amp fuse anywhere there. Unless gtphill is gonna buy you a new amp. If the amp fuses are rated at 60 then that will be fine anywhere on the power wire. So, 25 is to small, I have 1 time, ONE, used a fuse bigger than the OEM rated load BUT, that was after many talks w/ an ORION rep, and that was w/ an HCCA amp rated at 1 ohm mono 1/2 stereo.

 

Jay, using a larger fuse will not cause damage to the amplifier, which is protected by it's internal fuses. What it will do is increase the current needed to protect against the power wire shorting to the chassis of the car. This would be an issue if the power wire is of insufficient ampacity rating (not likely) and/or the battery was unable of supplying burst current sufficient to pop the fuse (also not likely). However, given that we now know the amplifier has two 30 amp internal fuses, a 60 amp protective fuse would be the appropriate value.

 

Hopefully this straightens you all out, Nick and Jay!

[lilloon]

gtphill and musthavemuzk--im impressed. you are the first people ive ever seen that knows what the fuk they are actually talkin about as far as audio. did u take the mecp course? anywho, its nice to see not everybody is mindless.

[slick]

Rule of thumb- Whatever size fuse(s) are in the amp, use the same size in your power cable also.

[musthavemuzk]

no mecp course taken here.

simply real world experience as well as membership on many many car audio forums and alot of reading.

 

not all amps have internal fuses.

in that case then you need to read the manual as there is usally info in there pertaining to recomended wire size and fuse ratings.

if not then you need to do some calculations on proper wire size and fuse ratings.

 

i am kinda confused on all this voltage talk from above.

why are you talking about one 30 amp internal fuse for negative and one for positive?

 

as well as your reference to voltage when bridging?

 

not calling your bluff just confused as i have never heard of this info before.

 

Monty

[THe_DeTAiL3R]

Nick put a 60amp fuse up front, and might be a good idea as well to get a distribustion box with fuse(s) (you can get them real cheap) and pop another fuse in there.. that will just add a little more protection for your amp. Even though they have fuses built in them I still don't trust them 100%. :? I'm no car audio expert by any means- this is my first setup, I set it up all myself too.. and have had no problems.

[gtphill]

gtphill and musthavemuzk--im impressed. you are the first people ive ever seen that knows what the fuk they are actually talkin about as far as audio. did u take the mecp course? anywho, its nice to see not everybody is mindless.

 

Lilloon, the last time I did anything semi-serious with car audio was about eight years ago, while I was in high school. Even then it was only a way of making money on the side of my real audio interests, which are professional audio related. I am currently working on my Doctoral degree in engineering, so I have a good background in the basic physics underlying all of this. Thanks for at attempting to answer my other problem down the board.

 

not all amps have internal fuses.

in that case then you need to read the manual as there is usally info in there pertaining to recomended wire size and fuse ratings.

if not then you need to do some calculations on proper wire size and fuse ratings.

 

i am kinda confused on all this voltage talk from above.

why are you talking about one 30 amp internal fuse for negative and one for positive?

 

as well as your reference to voltage when bridging?

 

not calling your bluff just confused as i have never heard of this info before.

 

Hey Monty, nothing wrong with being skeptical. This is more detail than the rest need, but here goes.

 

The power output leads on your amp (pos and neg) are slightly misleading. The negative posts are actually referenced directly to ground, and both the positive and negative voltage swings are on the positive lead.

 

In normal two channel operation there is one fuse for each channel, and the line fuse is sized to be 2x this value on the assumption that both channels are driven equally.

 

In "bridged" mode, the output is sent equally to both channels of the amplifier, only it is inverted in the second channel. So if there is a +10v swing in channel one, there is an equal -10v swing on channel two. Now, you connect your speakers to both positive inputs, and you see an aggregate voltage swing of 20v. So an amplifier that has 40volt rails in stereo mode can be made to appear to have 80volt rails through the bridged technique for a minimal amount of additional circuitry (an inverting opamp in signal path of channel two). In bridged mode the speaker may be thought of as having a floating ground reference.

 

Since you have 2x the voltage swing, you now need to have 2x the maximum current supply to keep the amp linear (V=I*R). When most amps (car/home/professional) are run in standard mode, they become nonlinear when they need to swing a greater rail voltage than available(voltage limited). In bridged mode, however, it is generally the limited current supply of the amplifier that makes it go nonlinear (current limited).

 

In the original poster's case he bridged the amp, AND wired the subs in parallel. Impedances in parallel sum by 1/(Z_total)=1/(Z_1)+1/Z_2)+...

So two identical subs in paralle will have half the impedance of and individual sub. So, by ohms law again, he needs to supply 2x the current to the subs for a given voltage swing as he did when one sub was wired to each channel. As you can see, between the reduced impedance, and the greater voltage swing available, his system's need for current has increased dramatically, resulting in the popping of his line fuse.

 

I am not sure how good the overcurrent protection is on car audio amplifiers (it's very good on profesional amplifiers, which will protect themselves against a dead short), but it is fair to warn him that if he starts popping the internal amp fuse, he should turn down some, as there may not be good internal protection circuitry on his amp for overcurrent, which could eventually cause his amp to experience a thermal failure.

 

Whew!

[musthavemuzk]

hmmmkkkk

 

Monty

[god910]

not all amps have internal fuses.

in that case then you need to read the manual as there is usally info in there pertaining to recomended wire size and fuse ratings.

if not then you need to do some calculations on proper wire size and fuse ratings.

 

HCCA High Current Competetion Amplifier, which didn't (might now that they aren't the same company anymore) have fuses, and have frighteningly small pos. leads. (10 gauge for a 40 amp line, okay but scary) Here's a link to a I vs. gauge/ft chart for copper wire.

http://users.bestweb.net/~tomh/Car/Current%20Capacity.html

 

As far as the 100 amp fuse goes, I know it's 60 that's why I said 60, if your gonna use 100 then why use one at all (always use a fuse for heaven's sake) Because as stated, the internal fuses will protect it sufficiently. (VS. a fuse WAY to big) I usually use those crappy fuses from Radio Shack for 1 main reason, they are VERY fast acting. It's annoying sometimes, but in comp. when you are pushing close to the limits (OR above them) as it is, it's good to have a little extra protection. I've been doing custom/competition installs for about 10 years now on and off. I took a long leave when one of my installs was torn out after 2 weeks, and I never even got pics of it. Only about 20 people saw it, and I was very pissed. It was 4 JL Audio 12's in a 4 door Civic. an RF Punch 800a2 and 2 250a2's. Eclipse Point Source all around. It really was awesome. This jackass paid me, about 2500 to do the install, (Complete car, everything custom) and then decided he wanted to go w/ different components, next thing you know, he was selling all the equipment off piece by piece. :gone2far:

[gtphill]

hmmmkkkk

 

Monty

 

Regretting asking?

 

Seriously though, if this an area where you'd like to know more, and/or feel like you've maxed out on the car-sound forums, send me a PM, and I can point you in a whole bunch of new directions.

[musthavemuzk]

not regretting asking at all.

if you knew me you would know i am always trying to learn something.

not sure if i totally believe or agree with what you typed is all.

 

mayb if i understood it better i could say i agree or disagree.

 

i do not understand without looking at the schematics for the specific amp that you can say there is one fuse for each channel. yet in bridged mode it can use both fuses. :?

not all stereo amps have onboard fuses let alone one for each channel.

my sub amps are mono and have 3 30 amp fuses on board for each amp. they are Tsunami DB1100D amps. i ran 2 in the SPL lanes last year. the amp i ran my fronts with is a PPI Art series A404 which is a 4 channel amp 50x4 actually. it has a single 40 amp fuse onboard. the predecessors to these amps were both PPI PC series amps. a PC450 (50x4)and a PC1400 (400x1 at 4 ohms and 800x1 at 2 ohms) with no onboard fuses.

 

i am guessing the fuses are in series or parallel if there are multiple fuses onboard an amp.

 

nowhere did i recall specs on the speakers in regards to their impedance.

 

there is a chance he was going below recommended impedance thus drawing too much current and the amp trying to protect itself blows a fuse.

not all amps can do 2 ohm mono. especially a stereo amp.

 

but anyways.

feel free to throw me linkage to things educational.

 

Monty

[gtphill]

not regretting asking at all.

mayb if i understood it better i could say i agree or disagree.

 

i do not understand without looking at the schematics for the specific amp that you can say there is one fuse for each channel. yet in bridged mode it can use both fuses. :?

 

You might be missing a crucial piece of how amps are built. In car amps, there is a switch mode power supply that is used to step up the car rail voltages. This supply takes your car's DC, converts to AC, runs it through some step up transformers, and then rectifys it back to DC again. This is establishes the DC rail voltages that the output transistors then draw from.

 

You are, of course, right in that I can't say for sure that there is one fuse per channel. It may very well be one fuse for the positive rail, and one for the negative, or one per leg of a rectifier, or half dozen other configs. I probably should have said that the sum of the ampacity of the internal fuses is a good metric for the design limits of the current draw for the weakest link, which will generally be the output transistors, or the stepup transformers.

 

i am guessing the fuses are in series or parallel if there are multiple fuses onboard an amp.

 

Fuses are a series element to do their jobs. A fuse in parallel is of no effect. Think of kirchoff's voltage and current rules.

 

there is a chance he was going below recommended impedance thus drawing too much current and the amp trying to protect itself blows a fuse.

not all amps can do 2 ohm mono. especially a stereo amp.

but anyways.

 

feel free to throw me linkage to things educational.

 

I will put some links together for you in the morning.

[musthavemuzk]

YEAH linkage for me.

 

thank you

 

Monty

[THe_DeTAiL3R]

Did Nick fix his car yet????

[rudefyet]

gtphill and musthavemuzk--im impressed. you are the first people ive ever seen that knows what the fuk they are actually talkin about as far as audio. did u take the mecp course? anywho, its nice to see not everybody is mindless.

 

hey i install car stereos ....i know what i'm doing...i just can't explain it to people....i never was good at that

 

a state record in car stereo competitions won't lie and no one has ever had a problem with a system i hooked up