Car audio Class D amp cut only in cold weather

[Doctorbass]

Hey guys i need your help and opinion about this:

I have a great car audio Polk Audio Amplifier 5ch classs D model PA-D5000.5. 100x4 +500x1

The problem is that it cut when it's cold outside ( it's still winter here) and i would say i only get about 25% power before it cut.

It cut mostly during peak of bass or mid bass on the sub channel.

And for those of you who would think it's because of the speaker coil that get hot and change resistance, i have to say i tested that with resistive dummy load that are at ambiant and it does not change anything so it's not the load the problem. I used 1.0 ohm 1500W load and when amp is warm it dont cut and i can get even about max 28A output continuous!.

at first i did not know it was due to the temp of that amp.... i just tought that the amp was just unable to drive low 1 ohm load as the spec say... but here is what hapenned: when i decided to test the "official" rms power using non inductive load, a scope and a freq gen... the power numbers i got was simply increasing over the time i repeated that test! :| so i concluded that the temp was affecting the amplifier..... so i tought it was due to the speaker coil that just increase in resistance as they get hot so i tested with a 1.0 ohm resistor load that was cold but while the amp was warmed... and i got full power no prob and amp did not cut...

Problem is that the run i drive each morning to my work dont last long enough to get that amp warm to give full power..

Any idea what could cause a class d amplifier to cut at low temp?

is there transistor bias adjust to correct? caps to replace?

oh btw i'm driving it with my Chevy Volt witch use a DC-DC to charge the 12V battery and give a perfect 14.8V at 185A availlable so the amp is more than perfectly supplied in term of electrons! as it only need 80A max

Thanks for any help guys!

Doc

 

[liveforphysics]

Sounds like a good reason to step up your rig to an amp that switches off your Volt's traction pack.

Sometimes controllers or amps that use the expected RdsOn drop across the FETs to measure current can behave a bit funny when cold and showing less than the expected voltage drop.

 

[Doctorbass]

Sounds like a good reason to step up your rig to an amp that switches off your Volt's traction pack.

Sometimes controllers or amps that use the expected RdsOn drop across the FETs to measure current can behave a bit funny when cold and showing less than the expected voltage drop.

Oh that would make sense Luke... so they use the fets RdsOn as current shunt?..... i guess i would have to find witch resistor in a divider and vref that i could tweak a bit...?

actually i'm driving 4 cheap bose sub of 5.25" dia It's my "winter subwoofer" that i built 10 years ago and i get 143.7dB with 400Wrms.. ( tested for fun!) but i have to say that the chevy Volt trunk shape is just like the old great CRX !!! it ack like a horn and keep the wavefront uniform and the phase remain really uniform in the cross sectional of the cabin so it get more efficient. it's just a custom ported 3cu ft box with 2 aero port of 4" dia by 11" long... i get pretty nice bass, kick and down to 35Hz presence with low harmonics ( acoustics i mean)... these 5.25" bose are very efficient and have low mms and great BL. their Xmec is about 18mm one way!

 

[amberwolf]

It could also be something as simple as a bad solder joint on a PCB or connector pin/wire, or bad crimp on a connector.

I can't count the number of things I've fixed over the decades with those kinds of issues (cold failures, intermittent, etc.).

 

[Lebowski]

could it be the internal power supply of the Amp is busted ? I cannot imagine the amp running directly of the 14V ?

 

[flathill]

Open it up on the bench under load and starting spraying freeze spray to find the problem

Target only a small area or one part at a time

 

[Doctorbass]

could it be the internal power supply of the Amp is busted ? I cannot imagine the amp running directly of the 14V ?

Yeah i know it's a switching that probably boost from 14V to 28 or 30Vdc. It is rated 500W at one ohm so it's about 22V.

Doc

 

[Doctorbass]

Open it up on the bench under load and starting spraying freeze spray to find the problem

Target only a small area or one part at a time

That's a good aproach, however the problem is more like proportional and not ON or OFF... the warmer the amp become the less it cut.. .

Doc

 

[marty]

My truck - 2012 Isuzu Reach. Similar problem. Cold winter mornings. Radio lights up and makes no sound. No sound till around 11:00am to 2:00pm depending on temperature. Under warranty, dealer replaced Jensen JHD3620 radio with similar radio JHD3630BT. Problem not fixed. Still no sound when cold. To diagnose I removed radio and speakers from truck and put everything in my car with a 12V wire going to cigarette lighter. By replacing speakers with some different ones, found problem to be speakers. Cheesy Jensen speakers. Called Jensen. They sent me new speakers. I sent the bad speakers back to Jensen. Everything works now.

Dream for the future.... Spend a few months redoing the inside of this truck. Sound proofing and a nice sound system. Now the truck sounds like a big noisy bumpy truck. I want sound insulation so the inside of the truck is silent. Engine and road noise is causing me to have mental issues.

First I would try a different music source and some different speakers temperately hooked up on the rear seat of a car in cold weather to be sure amp is the problem. Call Polk Audio and tell them about problem. See if they will send you a new amp?
http://www.polkaudio.com/pa-d50005/d/1162