Batteries and the On Off Switch.

The FXL DATA loggers do not have any internal batteries.

The decision was made in 1996 during the early design phases not to have internal batteries, and the reasons are:

• Internal batteries will go flat and the users will forget to recharge them.
• Internal batteries if left long enough will corrode and ooze acid inside the logger.
• If the logger relies on the vehicle battery, and if the vehicle battery is flat, then the vehicle is not going to start, so it wont need the data logger anyway.

However, there are three factors that can cause problems.

• Batteries can fail under vibration but appear perfectly OK before and after the race. This is because the internal plates in some batteries touch together under the severe vibrations, but do not weld themselves together. They usually blow a small hole where they have touched. Over time, the plate area of the batteries reduces, and this shows up as poor starting. When this happens, the only cure is to throw the battery out.
• The On Off switch. In the past, this has caused major dramas. FXL DATA supply a locking On Off switch that has silver plated contacts. These small switches have never shown any failures under vibration. Part Number 319-594 available from RS Components Call 1300 656 636 It is a condition of sale that customers MUST use this on off switch. Do NOT use spot light switches. They will fail under vibration. They will appear to be OK when wired to a spot light, because a spot light will keep working even when there is a momentary loss of power.
• Early models of FXL DATA loggers would lose their recordings if they lost power for even 1/100 of a second. Later models have more input capacitance to maintain the recording for longer.

Having a dedicated channel to monitor battery volts is crucial. When the plates touch, the battery volts can be seen to drop two volts. We have seen four volt drops on occasion, meaning that two cells have shorted out simultaneously. If the battery volts drops any further, then the data loger will not be able to run because of low voltage. When the voltage drops to a critical point, the microprocessor will pick up a corrupted instruction and then lock up. The symptom of this happening is that the logger refuses to download.

I believe that this is the reason that 16 volt batteries have become commonplace in drag racing. If two cells of a 16 volt battery fail, then you will still have 12 volts left to run the ignition.

I also believe that this is why magnetos have remained dominant in a field where they are not mandatory. Drag racers can choose virtually any ignition system, yet if you have an ignition that relies on batteries and the batteries fail, then you will get missfires. If you have a magneto, then you are far less likely to have a voltage problem as the magneto has its own generator (alternator).

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15 November 2005