Low Battery Light comes on with fully charged battery.

The yellow LED illuminates when the voltage at the DewBuster™ controller falls below 11.0 volts. Any electrical wiring will lose voltage (voltage drop) as current travels through it and the higher the current the more voltage loss occurs. Normal resistances in the DewBuster™ controller's power cord and fuse may result in as much as 1/2 volt loss, meaning the low battery light could begin to illuminate when the battery is at 11.5 volts.

Many of us use elaborate battery setups that include switches, fuses, and other connections so there will be a voltage loss as current passes through each one. The worst is a silicon diode because it has a 0.7 volt loss. If you have multiple batteries connected with diodes, use high current Schottky diodes since they only have about a third as much voltage drop as silicon diodes.

To locate the problem causing the voltage losses, do the following:

Do not plug any heaters in yet. Unplug the temperature sensor and turn the control knob to maximum so the DewBuster™ controller will send full power to the heaters. Keep the DewBuster™ controller in this setup for all of the following troubleshooting because you will only see voltage drops when maximum current is flowing.

Plug each of your heaters into the AUX heater jack, one at a time. If any heater caused the yellow light to come on, then check it with an ohmmeter for shorts. A 14" heater will measure about 2.5 Ohms, 8" to 12"  heaters 4 to 8 Ohms, 3" to 5" heaters 10 to 20 Ohms, and small heaters 20 to 100 Ohms. As you can see, the larger the heater the lower its resistance should be, but if any heater reads less than 2 Ohms then it has a short in it.

If no individual heater causes the yellow LED to come on, plug all the heaters in and see if the yellow LED comes on when the control knob is turned to maximum. If it does, the following steps will locate the problem.

All heaters must be plugged in (maximum load) and the control knob must be turned to maximum while taking the following voltage measurements.

1. Measure the battery voltage directly at the battery posts. This voltage should be above 12.5 volts on a fully charged battery under load. If the battery posts are below 12.0 volts then the battery needs to be recharged before continuing. If you are using a power supply and the voltage is dropping then it is unable to supply enough current. If this is the case, try testing the controller from the cigarette socket in your car to see if the problem disappears.

2. Next measure the voltage at the DewBuster™ controller by measuring as shown in the diagram above. The + is the inside terminal of any heater jack. The - is any mounting screw of the plastic heater jack panel. Later model DewBuster™ controllers do not have plastic side panels, in this case use the outside of the RCA jack as the negative.

3. If the voltage at the DewBuster™ controller is less than battery voltage by 0.5V or more then you have a voltage loss somewhere in the wiring. If so, then measure the positive and negative side voltage drops as shown in the diagram (from battery post to DewBuster™ controller). With a large dew heater strip the positive side may read up to 0.4V drop and the negative side may read up to 0.1V drop. If it reads more then there is a problem. By measuring the voltage across each connection, switch, fuse, etc. you can determine where the voltage loss is. The fuse in particular will cause a voltage loss due to it's internal resistance, and the smaller the amperage the higher the resistance will be.

Solutions to common problems: