By Albin Moore
This month, we feature a guest article, written by Mr. Albin Moore. Mr. Moore is owner of Big Wrench Repair, an ASE CMAT L1 technician, a frequent contributor to industry publications and forums and has 40 years of experience analyzing and fixing mechanical and electrical problems. We have highlighted his posts/articles in the past. Here, he provides an in depth look at the the need for clean power during on-vehicle repairs.
How many times have you had a vehicle in your bay for some diagnostic work or an electrical component replacement and had the vehicle’s battery run down? That doesn’t seem like anything more than an inconvenience, right?
How much of an inconvenience is it to relearn the memory that was lost in many of the electronic modules? In some cases, electronic modules can even lose their programming. Now what? Does your shop have the capability to do the needed programming and module relearns that will be required to return the vehicle to its normal working condition?
I would imagine most of us have attempted to solve this problem by hooking up a second battery with jumper cables, using a jumper pack, or better yet, hooking up a battery charger to keep the electrical system alive. This is all well and good, but if the power supply has too much voltage ripple, the electrical components of the system you are working on can be damaged.
Why the Need for Clean, Stable Power?
All electrical components have a few basic needs, such as proper ground and a good clean supply of power. When I refer to clean power, I refer to power with voltage and amperage changes that are within a range specified by the component.
The range can be large or small, depending on the component involved. For instance, a windshield motor will safely operate within a much higher current and voltage range than a body control module. A body control module will operate within a much wider current and voltage range than the body control module needs when it is being programmed. There is no simple formula for the range that any component requires. I would recommend to error to the safe side, and when working on electrical problems or programming electrical modules, use a power source that is clean and will supply the required current for the job.
All this talk about a clean power supply begs the question, “How do I know if the power supply I am using is clean?” Many different suppliers of battery chargers and power supplies have something for sale that is marketed as clean power. How about the charger that you use in your shop – what kind of power does it output? Looking at Figure 1, the information on the charger says it has an output between 2 and 35 amps, but it says nothing about the voltage it outputs, or what the maximum voltage output is. Yes, it says it is a 12 Volt charger, but how many electrical systems have you seen that operate at 12 Volts? Most systems I have seen start with an open circuit voltage of 12.6V and reach around 14V with the engine running.
Figure 2 shows two small portable battery chargers, two seemingly simple chargers. Are they any better at being used for a power supply, than the wheel charger in Figure 1? The only way to tell is to hook up a scope and take a look at the voltage and amperage output.
Figure 3 is a waveform from the large wheel charger. Notice the green trace: charging current. The current is being pulsed between 0 amps and 30 amps. The voltage is also being pulsed by 180 millivolts. The charging voltage also rises close to 16 volts. This is above the normal operating voltage for the vehicle’s electrical system. Can you imagine how an electronic component or module will react to a pulsing voltage when it was designed to operate on a clean, smooth power supply?
Figure 4 is a scope capture from a battery charger that produces a clean power supply. Both voltage and current are nice and smooth. This is the kind of power supply that allows the components in automotive electrical systems to operate properly. There is only one way to tell the kind of power your battery charger is producing and that is to hook your scope to a vehicle electrical system while the charger is charging it.
Consequences of Excess Ripple Voltage
I have observed many strange side effects over the years from using a battery charger with excessive AC ripple when running an engine while the charger is supplying electrical power. Things like the radio buzzing or the engine idling rough are just two examples that come immediately to mind.
Take a look at the waveform in Figure 5, which was captured at the left tail light of a Toyota pickup while a battery charger with excessive ripple was connected and the engine was running. Examining the waveform shows a voltage change close to half a volt (blue trace). This waveform shows that a dirty power supply, whether from an electric battery charger or from a defective generator, will infect the entire electrical system.
One of the stranger problems was on a Ford vehicle and the problem emanated from the driver’s power seat. After sitting overnight, when the engine was cranked, the power seat would start moving forward until it reached its most forward position. This could be a dangerous situation, since the vehicle owner was afraid of getting squeezed between the seat and the steering wheel. The problem was caused by a very low voltage spike when the starter was engaged. The voltage spike tricked the driver’s seat module by matching the voltage that commanded the seat to move forward.
Example of an Application Needing a Clean Supply of Power
A few years ago, I had a problem with a 2006 Ford Escape Hybrid vehicle that required the ignition key to be left on for an extended period of time while operating the antilock brake pump. This vehicle came to the shop with one of the front brake lines broken. This problem required the replacement of not only the brake hose, but also the master cylinder, to fix the problem.
Doing a brake bleed on this vehicle is not as simple as hooking a power brake bleeder to the master cylinder and opening the brake bleeders to let the air be pushed out.
Step one in any repair procedure like this should be to go to your vehicle service information and read up on the procedure. In reading down the list of things to do, I see several places where it says “WARNING” and “NOTE”. One of these notes says, “NOTE: The ignition key must be in the ON position when checking the brake fluid level and during the bleeding procedure. Another notes says, “NOTE: Adequate battery voltage is required during the system bleed. Connect a battery charger.” Here are two things mentioning the need for a clean, suitable power supply to be used during this brake bleeding procedure.
The ABS system on this vehicle is not like any other Ford Escape brake system. When doing the brake bleed procedure, everything MUST be done correctly, or the scan tool will stop the procedure and make you start over at step one. Proper electrical power and proper brake bleeder pressure are very important. This brake bleed procedure can take up to one hour and, each time the brake pedal is pushed to the floor, the ABS pump can come on for a few seconds. The brake bleeding procedure can take over one gallon of brake fluid. Having to do the procedure more than one time would be a costly waste of valuable time.
PRO-LOGIX Has the Answer
Each year, as new model year vehicles come to market, there are changes in electrical system technology, with the systems always becoming more complex. It is very important that shops and technicians update their tooling and training to keep up with the changes. One of the pieces of equipment that needs to be updated to keep pace with these changes is the battery charger. For today’s shop, there is a very real need for an up-to-date charger that is capable of charging all battery types (Flooded, AGM, Spiral Wound and Gel Cell) as well as supplying the clean power needed to perform a wide variety of repair and maintenance applications like the Ford Escape Hybrid brake job cited above.
The PRO-LOGIX PL2320 is an ideal charger/power supply for such situations. As has been referenced here and in prior articles, the PL2320 utilizes advanced microprocessor technology to deliver a precise charge in a very tight voltage window. This not only benefits batteries under charge, but is also exactly what the system wants when the charger is supplying power to maintain battery voltage during an on-vehicle repair. This makes it a great tool to use in the above referenced Ford Escape Hybrid brake job, as it will maintain system voltage through the repair without adverse consequences to electrical system components.