What's going bad?

[Kindred]

All right, I haven't had the time to get under the hood yet, but let's see what more knowledgeable people think before I start tearing parts out of my car.

First of all, I only have a little 300W class A amp. It's nothing special, but it's all I'm going to spend stereo-wise until it breaks, and it's just enough to power my 10s and 6x9s (rated at 100rms a piece). Here's the problem. If I cut the sound up beyond about halfway, whenever I hit a hard note the amp cuts out for a second as if I was trying to start the car. The problem becomes much worse at idle. Sometimes if I'm sitting above 1/4 volume, the sound will cut out. My first thought was I need a cap, but is it a possibility that my alt or battery are going bad instead?

[darpien]

maybe the alternator but i doubt it check the wiring for loose connections if that isn't the case then make sure that your connections aren't redneck(wiring nuts and the like) if you can solder it then use shrink wrap that's the best way to do it. other than that maybe its a faulty ground or its just that your pulling too much power and you just need to ditch the 300w amp if your gonna use that much power and it cuts off like that a capacitor isn't gonna help much your just gonna drain your battery til it dies. The capacitor only holds electricity for quick discharges like if the sub hits very loud for a second but if its cutting out at idle then its the amp that's pulling too much.

[Kindred]

Well I'm not thinking it's a connection issue as the problem goes away a bit as the engine revs higher. If I'm driving at 3500rpm on the highway, I can turn it up as much as I want with no real problems. Someone brought up the fact that it may be my amp (an old ass JVC piece of shit) going out. Again, this looks to me like a current issue. Is there a safe way (see: without electrocuting myself) of checking the alt's output while it's mounted to the car?

[darpien]

well if you rev the engine higher you will have more output from the alternator since the magnet is spinning faster which induces a higher current to move through the copper wires so if it was a current issue then the faster your engine revs the less you would notice it duh!!! its simple science the faster the generator spins the more power you get at idle it is spinning slow=less current at 3500 its spinning faster=more current.

[Kindred]

Yes, but even the meager festiva alternator should be able to juice a meager 300W amp with no problems, right?

[darpien]

whats the rms of your head unit if its around 50 then you could be screwed. i was told by gro that i should be fine with a 200w amp but he wasn't sure if it could handle a whole lot more plus my head unit was putting out 60w rms. That's just what it runs at not including the highest it can go so yeah if your listening to it at a relatively low level and the bass isn't hitting hard every 2 seconds then you should be fine i mean don't play it loud and turn the bass boost down a bit so the sub matches the speakers db level and you should be alright. i would tell you to take off the alternator belt and spin the pulley to see how much resistance there is if its going bad it won't spin much mine spun about 2 revolutions with almost no problem i would say if it doesn't spin more than 1/2 without considerable force then your screwd and need another alternator. I believe it puts out hrrm about 50 amps maybe up to 60 but no more than that. If the connections are fine and the only time it idles funny is when you connect the amp then its drawing to much current away from the engine and you need to get a lower wattage amp.

[Kindred]

You know, now that I think of it the idle speed drops about 100-200 rpm when the stereo hits and doesn't cut out. I've got a Sony 4 channel, 50w peak/channel head unit, a pair of kicker comp 10"s, a pair of sony 6x9 threeways, and my single 300w JVC amp. I'm guessing my alt is either going out or I'm trying to pull too much juice and need to upgrade. If the latter is the case, are there any alternator upgrades that are compatible with the B3 setup?

[darpien]

unless you use a different pulley setup like pulling them all off an mx-3 then no i don't know if it will bolt up so you would be doing something no one else has tried and i am not sure of the fitment of the alternator itself but hey it wouldn't hurt to try. oh yeah and cut the connectors and bring them with the alternator i believe they are a little bit different but i am not sure. if you need help with figuring out which of the wires goes to what im me i have the b6 out of the mx-3 and i am using the alternator. oh yeah and i am not sure but you might have to test fit different length belts i believe the stock mx-3 one is way to long. but the cool thing is you can adjust the alternator by turning one bolt to tighten it instead of using a pry bar and then tightening down the side 12mm bolt. and if it does work hey there is something the festiva guys can do to get more power out of the car for higher wattage systems. oh yeah the stock mx-3 alternator is 65amp and the stock festiva is 50 so you would have way more than enough power to do whatever you wanted to do with the car audio. oh yeah i forgot you should get them off a 94-95 mx-3 dohc 1.6l that's the one i used i think you could easily use it but to make sure test fit it to a festiva or aspire at the jy no use in actually getting it if it won't work. and make sure the alternator pulley spins easily if it doesn't don't get it, should spin about 2 revolutions with little effort. oh yeah and don't say you will blow the fuse links since every one who has done the b6t swap as well as me with my b6ze use the fuse links.

[aithanmier]

just replace it with a high amp gm alternator...cheap and powerfull. hell you can get a chromed one for like 100. then get creative on the pulleys. stock one off your stiva might fit it who knows. if not a trip to the machine shop will fix that. then just fab up some bracket adapters. Thats what i'm planning on doing anyway.

[Kindred]

I've been doing some looking around, and Ait's suggestion sounds more reasonable. I'll check into that.

[Kindred]

All right, I took a DMM to my battery, and here's what I found. Tell me if this is indicative of my alt going out (it's a little oil encrusted), or a sign of my equipment being too much.

Car at idle: 13.8V
Car with all lights (including aftermarket foglights) on: 12.2V
Car with lights and system on: ~8-10V.

I wouldn't think my 300W would cause that much of a voltage drop.

[studdyhalllooser]

i had problems with power when i had my last amp but i got 2 cheepo 250w xplode amps and a 50x4 pioneer head unit now and have no problems. oem alternator and 2 year old walmart battery....id still check your connections. maybe do the big 3 wire upgrade...wouldnt hurt.

[FB71]

alternator output is rated/measured at 1500rpm, not idle. Most alts are not capable of their rated output at low rpms. If you get below 12.6 volts at 1500-2000 rpm, then your system is too much for your alt.

[EricZKC]

add up the amperage at idle and the amperage at max volume of ALL your accessories (lights, heater, ac, etc) then find out what the amperage of the alternator at idle and the max output amperage of the alternator. if the accessories are higher than what the amperage is at idle from your alternator, then you would have problems like what you are describing.
Wattage is not the determining factor, It is amperage.
Also, try to got with the thickest power and ground wire that you can get away with. This will help in current transfer. Make sure that you use the same Gage power wire and Ground wire.

[aithanmier]

just for a quick and dirty upgrade order a alternator from a 90's model protege with the bp engine. it's rated output is 80A instead of the stock festiva 60A, bolts right up too. they probably make a higher output version for the protege as well. on'y downside is that it's slightly larger so it's a bit more difficult to put in, i'll be doing a write up on it tomorrow after i pick up the new alternator (o'reilleys had to order it).