Can a DIY Power Supply actually work?

Consider this for a moment nearly all ICE (internal combustion engine) vehicle modules run on direct current. Normally these control modules start with battery open circuit voltage Of 12.6v ( just for sake of a example.) As a technician brings a vehicle in for repair in the midst of diagnosing one concern the battery runs down. Creating the potential for new concerns due to memory/parameter data lost along with implausible data corruption from modules trying to communicate with a low battery. This is somewhat of a extreme scenario but I have actually seen it occur more often than you would think. Where more issues develop from run down batteries and automotive technicians attempting to repair and diagnose a vehicle in this state. I have also seen how if a shop does have a battery charger or power supply for a vehicle it is either not used or it is a inadequate piece of equipment . That sends "dirty power" through the vehicles control modules.

Dirty Power

To explain dirty power. I must first define well what it is, dirty power is basically anything that falls short of supplying a vehicles modules with voltage and amperage within its specifications to operate in a healthy manner. Another way to describe it would be any electricity that deviates from its normal standard by exhibiting spike, surges and dips. That can be caused by electromagnetic interference (EMI) or damaged power source i.e.,. alternator. Also since it can not supply a vehicles ecu's with what it needs, dirty power can cause a lot of damage. For instance a driver window regulator motor vs a driver door module both will start with 12v or more but the amperage requirement for one vs the other will have a distinct difference. This possible damage can occur when the supplied voltage and amperage is not stable or way above what a component can handle. A regulator motor would be able to handle electrical spikes, surges and dips better than a control module.

To make this comparison more vivid you wouldn't run the same amperage required for a starter motor through a PCM. Neither would a vehicle perform well if the alternator supplies erratic voltage and current from a shorted diode on its rectifier bridge. If this did happen get ready for the magic smoke show and burnt embed circuit board components.

During my time in the dealership world as a service technician nearly 80% of the vehicles l serviced would have some type of software update available. That depending on the customer concern or vehicle symptoms maybe it's modules would need it. Not to mention all the tsb (technical service bulletins) that are pushed out every month sometimes weekly to fix quality control concerns on the manufacturers newest products. While in every tsb or software update available the first instruction issued is make sure vehicle is hooked up to a clean power supply. During diagnostic procedures especially on those relating to module communication. There is usually a line about checking health of battery and vehicle charging capability. For me personally just as I check a generator ac ripple, voltage output and duty cycle. I also do the same for battery charger or vehicle power supply. This is because I'm aware of the havoc of what running way too much AC voltage through a vehicle electrical system can do. Generally speaking no more than 50mv ac is accepted in the automotive world.

What to look for in a Power Supply

A good power supply should be able to put out up to a 100 amps. Maintain control over voltage output not fluctuating all over the place. While the output voltage should of course have a very low voltage ripple to not disturb a programming event. Along with being able to respond accordingly to the vehicles current draw load requirements.

Can a clean power supply be built or modified for automotive use?

So out of sure curiosity I wonder if it was possible to modify something like a server power supply for automotive use. This question was so perplexing I decided to do a little research first to see if anyone had already attempted to do it. To my surprise I found several diy tutorials on creating a automotive power supply but what I noticed immediately nearly none of them were tested after the build.

This made me think well how do you know if the build is any good if you don't compare it to a power supply that can be purchased?

This led me to conduct a experiment and build one myself for comparison. My results were shackling good from my DIY version in contrast to the IOTA DLS-90, 12V 90A Power Supply. Both easily produce a voltage output of 13.3v to 13.5v and while the amperage output at the time of testing. Steadily is a 19amps up to 40 amps with all user controlled loads on in a 2002 Chevy Avalanche.

Prolong use and Various loads

These results are taken after 1hr of continuous use with every load possible switched on in the Chevy Avalanche. While the ready made and unmodified power supply maintains a steady 84°F from its exhaust fan and 110.6°F from its exhaust vents on the case.

Steady Voltage for ECU Programming?

My next test was to see the over all dc voltage ripple basically I was checking to see if there were any sudden surges or dropouts in current output. In the first picture above measurements were taken with Curien N2 providing a close up of more detail on the actual voltage output. Where a peak voltage of 14.25 to a low of 14.10v is observed. While a similar tool Pocket Pro shows only a 4mv difference after 30 minutes of continuous use.

So after all this there was only one thing left I was concerned about and that was if my DIY power supply was pumping out any AC volts? If so was it at acceptable level or not in comparison to the pre fabricated ready to buy Iota unit.

AC Voltage Ripple Test Results

To conduct this test a AC pass filter was used to filter out the DC (steady) portion of the signal so I could focus on the AC signal portion of a voltage reading.

The data was taken after 30 mins with all available user control loads on in the test vehicle. At minimum I knew my DIY Power Supply hovered around 1.58mv but at its peak it could reach 37.52mv. Still well below the 50mv threshold so there was no cause for alarm here but this DIY unit is a decent build for Automotive diagnostics and programming /reflashing ecu's.

The ready to buy Power Supply revealed quite shocking results, so much that I ran more test and used other pieces of Equipment I stop short of using a Pico scope. Once I realized my findings were pretty consistent. The ready to buy unit from peak to peak had a surprising 129.8mv and after 20 mins it spike at 250mv then even 2 volts at the 30 min interval. This was definitely not what I expected to find but it was clear the data gather pointed to the DIY Power Supply as the more efficient unit.