Amp cut only in cold temp but load is the same

Hi all,

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 wold say i only get about 25% power before it cut.

It cut mostly during peak of bass or mid bass.

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!:confused: 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
 
There can be an electrolitic capacitor with higher ESR cold, or 14.8V is on the upper limit of the overvoltage protection which also can be temperature dependent, or problem can be caused by any specific part of the amplifier and/or power supply. Im not sure if your 14.8 is really stable. A high specified current doesnt ensure this. Partly because the amplifier is also specified and failed, partly because PSU (DC/DC) is probably not specified for current rate of change (and/or cold operation), and partly because you didnt write anything about the input source of your PSU. The problem can be very short and not only drop, overshoot can also happen. There are many possibilities.

the power numbers i got was simply increasing over the time i repeated that test
Not clear what you experienced. What was the limitation? Distortion? Shutdown?
 
There can be an electrolitic capacitor with higher ESR cold, or 14.8V is on the upper limit of the overvoltage protection which also can be temperature dependent, or problem can be caused by any specific part of the amplifier and/or power supply. Im not sure if your 14.8 is really stable. A high specified current doesnt ensure this. Partly because the amplifier is also specified and failed, partly because PSU (DC/DC) is probably not specified for current rate of change (and/or cold operation), and partly because you didnt write anything about the input source of your PSU. The problem can be very short and not only drop, overshoot can also happen. There are many possibilities.


Not clear what you experienced. What was the limitation? Distortion? Shutdown?


Hi

Thanks for your input. The amp output just cut and comeback after about 3 sec and it will cut as long as i keep the volume to that level with amp in cold conditions. no distorsion, just output that cut.. probably a 30A relay inside that is connected to the output.
I can say that the dc-dc of the chevy Volt ( witch is like an "alternator" but for electric vehicule) is VERY STABLE. it keep 14.8V at any amp below 185A i tested it... but that's not the problem... the problem is the amp protection circuit is sensitive to low temperature even just zero celsius make it cut...


DOc
 
Hi

Thanks for your input. The amp output just cut and comeback after about 3 sec and it will cut as long as i keep the volume to that level with amp in cold conditions. no distorsion, just output that cut.. probably a 30A relay inside that is connected to the output.
I can say that the dc-dc of the chevy Volt ( witch is like an "alternator" but for electric vehicule) is VERY STABLE. it keep 14.8V at any amp below 185A i tested it...

In situ, cold, with load transient and oscilloscope triggered to load step? No drop, no overshoot for some ms duration?

but that's not the problem... the problem is the amp protection circuit is sensitive to low temperature even just zero celsius make it cut...
DOc
It's obvious that low temperature alone doesn't trigger the protection. It only sets the protection threshold too low, or sensed signal too high. But which protection? There can be protections at many places. 1: output current. 2: under/overvoltage lockout of gate drivers. 3: over/undervoltage lockout of supply rails. 4: over/undervoltage lockout of input power. 5: temperature protection.

And you know only that signal becomes higher than threshold, but there is no information whether the threshold becomes too low, or corresponding signal becomes too high at low temperature. Yes, signals may be really too high/low. You didn't check them, except maybe the output current, however you didnt share any useful quantifiable result about low temprature behaviour.

If you discard some of the possibilities without actually checking them, then maybe you will never find the cause of the problem. You can choose possibility to check first, but don't reject something without real reason!

You have also many possibilities to find the problematic part/parameter. But first thing is always to check input power. You can place a battery into the car, and test the system, or measure voltage by oscilloscope, and find the moment of the cutoff (you can trigger to a small overshoot).

Or you can test amplifier for input limits. Is it specified?

Etc..