bigcountry

I have a mrp m650 Alpine mono power amplifier powering one 12" Alpine type r sub. My question is that the wiring kit it came with came with a 100a fuse on the power cable, however, the manual for the amp recommends only 40a. In anyway is it hurting anything by having the 100a fuse?

Thanks for any input!

Glide

Remember, the fuse is basically protection.

When you have a circuit that draws X amount of current under normal operation, you'd know something was wrong if it suddenly started drawing 2x current. The fuse's job is to melt when something like this happens, stopping the current almost immediately.

Your amp is supposed to draw no more than 40A under normal operation, so if something went wrong, the 100A fuse wouldn't be able to do a thing about it.

Short answer: Get a fuse with the same rating as the amp. (But I hope the full answer helps you understand how they work...)

bigcountry

Thanks for the explanation. I have an 80a laying around but i guess i should try and find an ANL 40a - Does anyone know where i can get one of these?

Piston_Head

Just remember, the fuses built into the amp are for protecting the amp.

The main fuse (the one I believe you are talking about) is to protect the wire between the battery and the amp. The main fuse can be sized at whatever the max draw of the amp is, as long as it does not exceed the capability of the wire.

I can't find the chart I usually use, but after a quick search, here is a link that should explain it fairly well.

http://sounddomain.cardomainwiki.com...tery+fuse+size

So really, without knowing what size of amp wiring kit you have, I wouldn't know what size fuse to recommend.

Hope that helps.
Later,
Brad

bigcountry

I have 4awg wire...and thanks for that link, still kinda confusing though

Piston_Head

If you do have an 80 amp fuse laying around, it will work fine.

No need to buy another one.

Later,
Brad

EmperorJJ1

iTrader: (5)

u wont find a 40amp anl fuse... agu or atc both offer 40a thou

Glide

So I guess you'd use a breaker rated for 2x the amount of current in your house as well?

The reason that the manufacturer recommends that fuse, is because they don't want to get sued when somebody burns down their car by installing, say... an 80A fuse instead of a 40A.

Fuses are for protection. If you seriously want to gamble a $20K ride over a $2.00 fuse, it's your money.

The way to calculate the fuse rating is as follows:

You need to calculate how much current the amp will draw. Look at the RMS rating. (Not counting peak current, as this is usually supplied by power banks inside the amp itself).

This needs to be divided by the efficiency of the amp. (This takes into account how much of the amp's draw is being converted into heat). For example, an class-D amp that's 80% efficient, will require 1000W of input current to produce 800W of output. The rest becomes heat. If you divide 800 / 0.80 (RMS / Efficiency) you obtain the input wattage (1000W)

In your case, your amp has an RMS rating of 400W into 4Ohms at 14.4V. 75% is usually a good estimate for the efficiency of a class D amp.

So for your amp, input wattage would be: 400W / 0.75 = 533W (Input)

Next, you calculate current for a certain voltage (By Ohms law current = power/voltage)

so 533W / 14.4V = 37 A
So your fuse would need to protect you against a 37 A draw (40 A is the closest commercial fuse size). The number might change a bit depending on what the actual efficiency is. I just ballparked 75%.

Source: Understanding current and power

EmperorJJ1

iTrader: (5)

right but the actual fuse he puts on the wire may vary if his amp has an internal fuse (like many do).... if your amp is fused at 40a then the fuse at the battery is no longer nessicary to protect the amp but it protects the wire. In that case you could fuse as large as the wire can hold without burining. Im not sure what wiring kit you got (im assuming larger then 4g because of the anl fuse) but even 8awg can take more then 40 amps

Glide

again no...
If your circuit has an expected draw of X Amps, your fuse should be rated at X Amps, regardless of what wire's being used.

An amp's ]internal fuse protects against an internal peak. If you read the specs, you'll see that it actually has two 30A fuses, protecting two internal circuits rated to 30A each. These circuits have nothing to do with the amp's total draw (They're probably protecting the capacitor banks use for high current discharges).

Fuses are safety measures that only work when used properly.

EmperorJJ1

iTrader: (5)

im sorry but the fuses in an amp protect the amp. While an amp has seperate componants it doesnt have specific "circuits" that need to be fused (power supply or output stage). And when a cap is charged the fuse isnt going to help (when a cap blows it either stops working or literally blows up, its a simple componant) I didnt read the specs because in reality i dont care that much.... ill give advice and all but im not going to look up every componant in everyones setup (if you ask ill be more then happy to do so)

While you can fuse the wire to really whatever you decide if your amp has a fuse (i said internal so it would be less confusing but in all reality there is no such internal fuse in the amp case. They are all on the outside were the user can remove them so they are external to the board and amp componants) then it is redundant to try and fuse to that amps rating. You can safely fuse up to the point of the wire melting and you will be fine

Spun

iTrader: (1)

Alright so let me ask a question
Remember before everyone jumps down my throat, I'm asking not telling, mainly because now I'm unsure and confused after reading the last few pos.

If the fuse on the wire is smaller then the fuse (or sum of the fuses) on the amp, will this cause conflict. ie: will the fuse on the wire blow alot easier?

Piston_Head

**** edit **** No you should not increase the breaker size in you house. It is already sized for the wire **** edit*** forgot this part What can I say, it was early and I was heading to work !!

This is exactly my point. The breaker in your house is to protect your houses wire. It does not matter what you plug into the outlet at the end of the wire. The home breaker size is determined by what wire you have. If you have a 15a circuit at home and plug in an alarm clock, everything works perfectly well. Then you add an electric kettle to the same circuit. Everything is still O.K. Then you try to add something like say a 110 volt welder that draws say 13 - 14 amps. If everything is going at the same time, pop, the breaker opens to protect the wire from damage (possibly fire). This is because you have exceeded the safe capacity of the wire and the fuse is there to protect you from doing this.

You can run a smaller fuse in your car's system (or house for that matter), it will still protect the wire.

Hope that helps, and doesn't just confuse you more.

Check my previous link or go to 12volt.com for more info.

Later,
Brad

EmperorJJ1

iTrader: (5)

yes the smaller fuse should always blow first. Reason i said should and not will is because the actual "rating" on any fuse is never 100% exact. What a fuse actually is is a piece of metal that literally burns after a certain amount of heat. So assuming you didnt have a cobalt and your fuse by the battery was in the engine bay of a car and the amp is chilling nicely in your a/c car on the back of the seat (folded down).... your wire fuse which may be rated higher then the amp fuse (40a and single amp fuse of 30a) may still pop first.

Your never really going to get into a "conflict" persay with using small fuses. Only problem you will have is blowing them constantly and whatever your fusing not working due to no power.

Ill give a real good example.... I had my giant T30001bd amp repaired by my boss at one point and at the time he only had his smaller power supply hooked up not his 400amp or whatever power ten power supply... so he couldnt test it to its full potential and we didnt want to just throw it in the car and see what it would do. but we sorta had to due to lack of power supply power. What we did was physiclly hold a fuse inbetween the power wire and the battery so we could "test" it.... we kept on poping fuses liek crazy because it took 50a on the power supply for my amp to turn on and it was just eating the smaller 40a fuses. I had to use the red 50a fuse that came stock for the pcm or bcm or whatever it is to get the amp to turn on. Moral of the story was no damage was done by me using 30 and 40a fuses on my amp that has an "internal" 300a fuse because the fuse is always the weakest link and as long as you actually use them correctly they should blow before you have problems.

Spun

iTrader: (1)

Now that I understood
Thank You

Glide

When was the last time you looked at you house fusebox?

Seriously, go and take a look at it. You will find that you have different rated breakers for different circuits even though the wire size is the same. You fuse based on the expected draw of the circuit.


Ok, here's a hypothetical:
Say that this amp is screwed directly to the sub enclosure. The heat and vibration cause a part to come loose, causing an internal short that draws 59 A (Just 1 A short of the 60 A of internal fusing). Your suggested 80 A wire fuse just sit around helpless while the amp's circuitry melts filling the car with smoke, driver panics, car crashes, etc etc...

Driver decides to sue alpine for producing a faulty amp, alpine says, hey our amp's good. We told you to fuse it at 40Amps... Sorry! Good luck with that permanent disfigurement.

Maybe a bit extreme, but you get my idea.

Anyway. I've stated my point of view. For me, it's not really a worthwhile gamble.

EmperorJJ1

iTrader: (5)

in the rare occasion your amp starts to fry it doesnt usually just do a little bit. And many times an amp will "blow" without smoking out at all... Im not trying to act like i know everything but my boss does amp repair and ive seen quite a bit come thru even unfixable damage like burning the board along with most of the internal componants. i realize how fuses help and can/will prevent damage and if you feel safer fusing to whatever the amp draw is thats fine as long as its the same amount or lower then the max current rating of you wire

Piston_Head

For the sake of ending the confusion, I'll skip everything else. This quote pretty much covers it.

If you want a good place to learn all kinds of info about car audio, check out http://www.bcae1.com . It covers everything under the sun.

Later,
Brad

EmperorJJ1

iTrader: (5)

damn i was looking for that link too. I never can remember it

Glide

Just to prove I'm not that hard headed I did go through the website's fuse section (I'm always open to learning something new).

Two quotes from that very same website on the topic of fuses...

Number one, a better example than the one I posted.

Number two:

Anyway... Enough on this topic really. Up to the readers to form their own concussion...