12v to 5v regulator beginner problem

[English]

I have a 12v to 5v DC regulator in a vehicle PCM that gets hot and outputs 7v and shuts down the car.
Can I add an external 12v to 5v regulator to bypass the problem?
I am going to mount a cooling fan to help with the temperature.
This is a link to the problem
http://dodgeforum.com/forum/2nd-gen...-dakota-durango-no-bus-pcm-for-under-5-a.html
although my output jumps from 5v to 7v and shuts down the vehicle rather than in this case where it drops to 0.4v
Thanks for any advice, I could really do with the help.
I have a basic 12v to 5v 3 pin regulator that I was thinking of trying to use.

 

[Gryd3]

That link you provided is a very shoddy hack... It may work but I would never recommend it.
Do you have any specifications on what the 5V source is used for?
Is this line supposed to be constantly on, on with accessory, on with ignition, or on with some other control mechanism?
Do you know what to expect for the current draw on this 5V line?
Will tapping into a controlled 12V source cause further issues with devices on that 5V source if that 12V source is no longer available? (Say a fuse goes, or the on-board computer shuts off that particular 12V supply)

The only thing I can tell you to do, or recommend for you is to use some of the brain cells in your head and do any non-oem repair to your vehicle in a safe manner.
If you do not understand the repair, you should not do it with third-party or home-brew equipment. Take it to a qualified tech, or do more research into your own vehicle, and remember that no-one anywhere on the internet is liable or at fault for anything you stick in your ride.

On another note, if you are sure you can use your regulator... remember that the 3-pin device you are planning to use may be sensitive to noise on the 12V line (Which can vary typically up to 14.4V) Make sure the device you want to use can be used reliably, and that you take the proper precautions to ensure your replacement part is protected from the elements, and from the voltage you supply to it or you could do further damage.

*One more word of warning: I have a feeling this topic may be locked by a moderator if any of them get the feeling that you are putting yourself or anyone else at risk by doing this hack type of repair. Hopefully I've covered as much as I can in this first post.

 

[English]

Thanks for the reply, I will read a lot more. This was a huge problem for the 1999 and 2000 year Dodge Durango with multiple problems suggested and often multiple answers suggested too. Unfortunately no single answer was ever provided. The PCM has been replaced but has the same problem now, the 5V output supplies multiple engine sensors, but when the PCM gets hot, which is everyday in Southern California, the PCM shuts down. I am going to vent the PCM area and add a 12v fan which will be wired through the ignition circuit. The regulator will also be wired through the ignition circuit to supply a constant common 5v to the sensors. I will check the draw on the output and find a suitable regulator. Any additional comments would be appreciated.
Thanks

 

[Gryd3]

As long as you can determine a current draw, or expected current draw, you should be fine. It sounds to me like you know what the behaviour of the 5V line should be.
If you end up building your own 5V regulator from the ground up, be sure to include a filter capacitor on the output to help reduce ripple and noise that could mess with your sensor readings. Many of the 3-pin regulators as you have put it... have a grounded metal tab.

http://www.fairchildsemi.com/ds/LM/LM7805.pdf

This could be a huge advantage for you as you could use the chassis as a heat-sink for the voltage regulator which will help prevent overheating.
If at all possible, be sure you inject your own 5V source in such a way as it will not inadvertently connect to the faulty 5V line.

I would like another's opinion on using a filter capacitor on the input side as well... but to prevent the filter capacitor from discharging back to the automotive supply by using a diode.

 

[English]

As long as you can determine a current draw, or expected current draw, you should be fine. It sounds to me like you know what the behaviour of the 5V line should be.
If you end up building your own 5V regulator from the ground up, be sure to include a filter capacitor on the output to help reduce ripple and noise that could mess with your sensor readings. Many of the 3-pin regulators as you have put it... have a grounded metal tab.

http://www.fairchildsemi.com/ds/LM/LM7805.pdf

This could be a huge advantage for you as you could use the chassis as a heat-sink for the voltage regulator which will help prevent overheating.
If at all possible, be sure you inject your own 5V source in such a way as it will not inadvertently connect to the faulty 5V line.

I would like another's opinion on using a filter capacitor on the input side as well... but to prevent the filter capacitor from discharging back to the automotive supply by using a diode.

Thanks for the reply I really appreciate it.
In the http://dodgeforum.com/forum/2nd-gen...-dakota-durango-no-bus-pcm-for-under-5-a.html link this guy appears to connect the new regulated 5v supply to the original 5v output wire? This seems strange as the problem is not constant and until the PCM overheats the output would now have two separate 5v power supplies? Am I reading this correctly and does that seem likely to work?
Thanks again, and best wishes, Steve.

 

[Gryd3]

Thanks for the reply I really appreciate it.
In the http://dodgeforum.com/forum/2nd-gen...-dakota-durango-no-bus-pcm-for-under-5-a.html link this guy appears to connect the new regulated 5v supply to the original 5v output wire? This seems strange as the problem is not constant and until the PCM overheats the output would now have two separate 5v power supplies? Am I reading this correctly and does that seem likely to work?
Thanks again, and best wishes, Steve.

Your right. From the description of the problem on his post, there is initially 5V on that line, and he has connected another 5V source to it. I don't like it as I have no information on how the PCM generated it's own 'internal' 5V supply. I would be much more comfortable if you could disconnect the original supply instead of running a faulty supply in parallel with your proposed replacement.
Are you able to get a circuit diagram for the PCM or a picture that would show us? Perhaps there is an LM7805 in the PCM that has failed XD

 

[cjdelphi]

Anything over 500ma from > 12v and you should consider a switching power supply rather than a linear one like the 7805