[Date Prev][Date Next][Thread Prev][Thread Next] - [Date Index][Thread Index][Author Index]

Re: Signatures on AMSAT-BB



>That reminds me, is there a simple electrical circuit I can connect
>between my van's battery and my radios to prevent voltage
>surges/spikes from reaching my radios and ruining them?

If you're worried about a failed voltage regulator and/or battery
allowing the voltage to get too high, you can try a crowbar circuit.

A very simple one consists of an inline fuse rated to carry the radio
load (which you should have anyway) *followed* (not preceeded) by a
big zener diode to ground. Pick a zener that turns on at the maximum
voltage you want to reach your radios, say 16 volts. If the battery
voltage ever gets that high, the zener will conduct and (hopefully)
blow the fuse.

This circuit also provides inherent protection against polarity
reversals.  Zeners conduct at their rated voltage in the *reverse*
(breakdown) direction; in the opposite (forward) direction they
conduct at .6V or so like any other silicon diode.

A better circuit would use a power SCR as the crowbar, triggered again
by a zener diode of the appropriate voltage rating. In this case the
zener need not be rated for much power, as it only has to trigger the
SCR. If you still want reverse polarity protection, put an ordinary
power diode in parallel with the SCR but reversed in polarity.

Obviously these circuits are intended as last-ditch protection against
voltage surges that hardly ever occur. You don't want to keep
replacing fuses. Many radios already include overvoltage/reverse
protection circuits like these; check your radio schematic.

Phil




AMSAT Top AMSAT Home