I recently bought an expensive amateur radio - an IC-7000. This radio runs off 12v, and draws up to 25A when transmitting. Asume the radio puts a lot of nasty HF noise and high voltage spikes back into the power rails.
I've been warned that the radio is very unforgiving to reverse voltage, and I've seen pictures of a completly blackened main board due to reverse polarity. Apparently the repair cost is >£250 - not something I want to risk!
So, I can think of four possible solutions to the problem of protecting the radio from reverse polarity connection (see attachement). For the high power diodes (solutions 1 and 2) I would use a D83-004 schottky diode (30A continuous, 150A surge, Vf = 0.55v @12.5A). For solution three I would use a 30A continuous, 40A peak relay (150mA coil current).
So, the advantages and disadvantages:
Series diode:
+: Doesn't blow the fuse if connected wrongly
+: Simple to install
-: Wastes power (and gets hot)
-: The radio gets les voltage (so transmits with less power)
-: The electrical noise of the radio gets amplified (due to the non constant voltage drop)
Crowbar diode:
+: No negative effects when the radio is connected with connect polarity
-: Blows the fuse (a pain to replace)
-: Trusting the diode to work (if it fails O/C, no protection)
Relay:
+: When switched on, the radio sees full supply voltage
+: Doesn't care about noise/spikes on the supply rail
+: Doesn't cause any damage or blown fuses if radio is connected backwards
-: Draws the coil current (150mA) at all times (waste of power)
P channel FET:
+: When switched on, the radio sees full supply voltage
+: Doesn't cause any damage or blown fuses if radio is connected backwards
+: Doesn't waste/drop any power
-: Gate voltage has low limit (20v) - could be damaged by spikes
-: Might not be happy with HF electrical noise
I'm leaning towards solution three (the relay) to protect the radio - but any thoughts or suggestions are most welcome!
Thanks,
Andrew
I've been warned that the radio is very unforgiving to reverse voltage, and I've seen pictures of a completly blackened main board due to reverse polarity. Apparently the repair cost is >£250 - not something I want to risk!
So, I can think of four possible solutions to the problem of protecting the radio from reverse polarity connection (see attachement). For the high power diodes (solutions 1 and 2) I would use a D83-004 schottky diode (30A continuous, 150A surge, Vf = 0.55v @12.5A). For solution three I would use a 30A continuous, 40A peak relay (150mA coil current).
So, the advantages and disadvantages:
Series diode:
+: Doesn't blow the fuse if connected wrongly
+: Simple to install
-: Wastes power (and gets hot)
-: The radio gets les voltage (so transmits with less power)
-: The electrical noise of the radio gets amplified (due to the non constant voltage drop)
Crowbar diode:
+: No negative effects when the radio is connected with connect polarity
-: Blows the fuse (a pain to replace)
-: Trusting the diode to work (if it fails O/C, no protection)
Relay:
+: When switched on, the radio sees full supply voltage
+: Doesn't care about noise/spikes on the supply rail
+: Doesn't cause any damage or blown fuses if radio is connected backwards
-: Draws the coil current (150mA) at all times (waste of power)
P channel FET:
+: When switched on, the radio sees full supply voltage
+: Doesn't cause any damage or blown fuses if radio is connected backwards
+: Doesn't waste/drop any power
-: Gate voltage has low limit (20v) - could be damaged by spikes
-: Might not be happy with HF electrical noise
I'm leaning towards solution three (the relay) to protect the radio - but any thoughts or suggestions are most welcome!
Thanks,
Andrew
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