I pass this along to you. It is from an electrical engineer friend. It is in regards to some subtle issues involving our so called low power devices. It is one more argument for not skimping on wire size. Mike Chuck wrote: > A lot of solid-state equipment such as GPS receivers may not draw much power > in normal operation. But, at initial power-up it can draw substantial > surges. This is called "In-Rush Surge." It's caused primarily by charging > the device's main capacitors. It's become more of a problem in recent years > as capacitors have improved and have lower internal series resistances. > Many modern electronic devices have switch-mode power converters internally > to convert the nominally 13.5V input to 5V or 3.3V for use by the internal > logic. These switch-mode converters are operating at higher and higher > frequencies these days which requires input capacitors with lower and lower > internal resistances. > > There are several problems that can be related to in-rush surge. First, > that same equipment may have a low-voltage cut-off circuit that > automatically shuts it down if input voltage is to low. So, the surge may > cause the voltage received by the device to drop triggering that cut-off > circuit. This will cause the device to turn on with sort of a studder. > This stutter, can create surges in the system that can confuse your main > voltage regulators. It can also create electrical noise in your system that > can interfere with other equipment. Copper and Aluminum both undergo what > is called "work hardening." Electrical pulses and surges can accelerate > work hardening causing the wire to literally become brittle. > > Of course, an ordinary voltmeter will never see these very brief stutter > pulses. > > The solutions possible are: Bigger wire. Even though your GPS receiver > only draws 500mA when operating, you might want to size the wire for the 10A > in-rush surge that it may draw. The other option is a capacitor placed near > the receiver. 10,000mFds at 35V, for example, placed near the receiver > would dramatically reduce the amount of in-rush surge seen by the boat's > electrical system. > > Chuck > > > Capt. Mike Maurice Tualatin(Portland), Oregon.