Odd voltage drop

[DaPutster 10+ year member]

I have a 1/0 awg dedicated line running to a distribution block in my trunk. Now this morning I go to drive my car & the amplifier won't turn on. The car starts up fine, the head-unit powers up, but nothing happens with the amp. Realizing I needed to get where I was going I held off looking more into it til this evening. So after going thru all the steps to see where the problem is (check voltage, check relays, check fuses, etc) things gets weird...

With the car ignition off the distribution block voltage is fine (12.8 volt avg), but as soon as I engage the accessory setting the voltage on that line drops to 300mv. This also stays the same when the engine is running as well.

The 1/0 awg line is not new (installed about 3 months ago) and has been working fine up until this morning. Does anyone have any ideas as to what else I should be looking for?

Click to read more...

 

[jrz126 10+ year member]

check/replace the fuse?

 

[DaPutster 10+ year member]

The fuse on it doesn't look blown. That being said, if it was the fuse, wouldn't the voltage drop be happening with the ignition off as well?

 

[ramos 5,000+ posts]

What's the voltage with the car running ? //content.invisioncic.com/y282845/emoticons/smile.gif.1ebc41e1811405b213edfc4622c41e27.gif

 

[DaPutster 10+ year member]

When the ignition is off entirely, the distribution block is reading ~12.86v.

When the ignition is on accessory or with the engine running, the block reads ~300mv.

 

[ramos 5,000+ posts]

What's the voltage up front ? Either your alts not charging or your battery is toasted. But let us know what the voltage is up front. If the alts charging it should be over 13v at least. //content.invisioncic.com/y282845/emoticons/smile.gif.1ebc41e1811405b213edfc4622c41e27.gif

 

[jrz126 10+ year member]

sometimes the fuse looks good but it really isnt

 

[ramos 5,000+ posts]

Yeah, but if the fues is blown. How does the block on the other side of the fuse have power ? //content.invisioncic.com/y282845/emoticons/smile.gif.1ebc41e1811405b213edfc4622c41e27.gif

 

[JimJ 5,000+ posts]

Wiring by sight is never usually a good thing.

That wire might not look like it has 350VDC on it, but before I put myself between it and ground, I want to see the proof of that on a DMM //content.invisioncic.com/y282845/emoticons/biggrin.gif.d71a5d36fcbab170f2364c9f2e3946cb.gif

The point? Use a meter.

 

[Chevyaudio 5,000+ posts]

Yeah, but if the fues is blown. How does the block on the other side of the fuse have power ? //content.invisioncic.com/y282845/emoticons/smile.gif.1ebc41e1811405b213edfc4622c41e27.gif

I've been totally stumped on an install where there was a 2channel and 4 channel amp. Only one of the amps would power up, turned out that the fuse was separated just enough to only let a limited ammount of current through. So a fuse can be blown and not look blown.

 

[ramos 5,000+ posts]

You guys are missing my point. don't look at the fuse. If it's blown where is the power coming from on the other side of it ? Where do you guys get these fuses that blow and break only part of the element. Everytime I have blown one it's all gone. Take the dmm up front where the wire is coming from and measure voltage. This way you can eliminate the battery and the charging system if they check out fine. It's always easier for me to trouble shoot If I start at the source and work my way down the chain. //content.invisioncic.com/y282845/emoticons/smile.gif.1ebc41e1811405b213edfc4622c41e27.gif

 

[crhye250r 10+ year member]

Listen to the man. Geez..

 

[jrz126 10+ year member]

What's the voltage up front ? Either your alts not charging or your battery is toasted. But let us know what the voltage is up front. If the alts charging it should be over 13v at least. //content.invisioncic.com/y282845/emoticons/smile.gif.1ebc41e1811405b213edfc4622c41e27.gif

That cant be the problem...The car would run at all on 300 mV

You guys are missing my point. don't look at the fuse. If it's blown where is the power coming from on the other side of it ? Where do you guys get these fuses that blow and break only part of the element.

what is your point? I dont know where the fuses come from, but it does happen. When no current is flowing through it, it conducts. Turn on the amps and start drawing some current, it opens up.

I'm about 99.9 percent positive that its a bad fuse.