Continue to Site

Welcome to our site!

Electro Tech is an online community (with over 170,000 members) who enjoy talking about and building electronic circuits, projects and gadgets. To participate you need to register. Registration is free. Click here to register now.

  • Welcome to our site! Electro Tech is an online community (with over 170,000 members) who enjoy talking about and building electronic circuits, projects and gadgets. To participate you need to register. Registration is free. Click here to register now.

Reverse voltage protection for a radio

Status
Not open for further replies.

cowana

New Member
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
 

Attachments

  • Reverse voltage protection.png
    Reverse voltage protection.png
    21.1 KB · Views: 155
Last edited:
Asume the radio puts a lot of nasty HF noise and high voltage spikes back into the power rails.
I would hope that the engineers at Icom would put some decent filtering on the supply lines, especially the price they charge for that thing!

However, I digress...
Use solution 3, and miss out the fuse in the negative lead.

Fusing the -ve does not add any protection when used with a fixed power supply.
Fusing of -ve supply leads is a carry-over from days gone by.
Also when used in a vehicle, and powered from the vehicle battery, the possibility exists for large fault currents to flow through the radio in the event of a fault in the battery/starter wiring in the vehicle. The -ve line fuse protects that situation.

JimB
 
Thanks for the thoughts.

I think I'm going to go with option three as it the most robust way of doing it - although there is the additional power consumption.

As for the fuse in the negative lead, that's already been done by Icom - they put one in each of the power supply leads.

**broken link removed**

Andrew
 
Last edited:
Last edited by a moderator:
I guess they are covering positive ground applications. A few 120/12V supplies ground the positive by default. e.g. The Kikisui PAD series.
 
Status
Not open for further replies.

Latest threads

New Articles From Microcontroller Tips

Back
Top