Switching off Chartplotter/radar

[lumphammer]

I have a Raymarine C80 classic chart plotter and 2KW radar that is operated through the chart plotter. By default the radar comes on in Standby mode when the chart plotter is turned on. Turning the radar off using the chart plotter displays a message "Shutting down in 60, 59, 58 ...... secs".

Is this shut down time important, because I usually switch off the chart plotter from the plotter isolation switch on the switch panel and not from the power off button on the plotter, so the radar turns off immediately from standby without the time delay.

I have to say though that I have been doing this since we installed the plotter about 6 years ago and nothing seems to have stopped working.

I wonder why Raymarine have the delayed switch off?

 

[pvb]

I have a Raymarine C80 classic chart plotter and 2KW radar that is operated through the chart plotter. By default the radar comes on in Standby mode when the chart plotter is turned on. Turning the radar off using the chart plotter displays a message "Shutting down in 60, 59, 58 ...... secs".

Is this shut down time important, because I usually switch off the chart plotter from the plotter isolation switch on the switch panel and not from the power off button on the plotter, so the radar turns off immediately from standby without the time delay.

I have to say though that I have been doing this since we installed the plotter about 6 years ago and nothing seems to have stopped working.

I wonder why Raymarine have the delayed switch off?

During the countdown to off, you can't re-power the scanner.

 

[johnalison]

I was told that you should never turn the power off the radar without going through the power down process first. The fact that you have been doing this and the radar still works suggests to me that this may not be as critical as I had thought, but I doubt if it is a good idea. It may also be that the new generation radars are different.

 

[macd]

It may also be that the new generation radars are different.

They're very different: no magnetron, instant on and off.

From what I've read magnetron warm-up in conventional radar is far more critical than cool-down, but I'm far from being an authority. Compared to new-gen, the reason for the much higher standby consumption of conventional radar is presumably partly due to the maintenance of magnetron temperature. Anyone know if this is so?

 

[rszemeti]

The heater current in a typical 2kw magnetron is arounf 0.5A at 6.3V. Assuming it is using a reasonably efficient switch-mode PSU to derive the 6.3V from the 12V boat system, that will be around 1/4 of an Amp for the heater. or 3W

When running, the maximum input power to the anode of a typical 2kw magnetron is just 10W ... so I don't think the magnetron itself is the power hungry bit, I suspect it is the support circuitry and power supplies that are less efficient than more modern designs. Older units with a CRT for the display probably uses more power than the scanner does.

 

[BelleSerene]

It’s an excellent question. I have done the same as you for years - although I suppose it’s very rare that I hit harbour with the radar still on (I’m a sailing boat and don’t want the battery drain), so I will rarely have depowered it from hot.

I have failed to find any mention that you shouldn’t turn the unit off without first turning it to standby. There’s none in the manual. I therefore assume that powering down from hot isn’t a problem.

 

[tjbrace]

My old Furuno radar is not via my Garmin mfd and its LCD screen blanks as soon as the power off switch on the unit is pressed (not the switch on the distribution panel). It may still go through cool off under the cover. However, the Garmin kit records ‘unexpected power loss’ in its operational log when powered off from the distribution panel rather than the mfd. Other than the log entry I see no other effects.

 

[Lon nan Gruagach]

The heater current in a typical 2kw magnetron is arounf 0.5A at 6.3V. Assuming it is using a reasonably efficient switch-mode PSU to derive the 6.3V from the 12V boat system, that will be around 1/4 of an Amp for the heater. or 3W

When running, the maximum input power to the anode of a typical 2kw magnetron is just 10W ... so I don't think the magnetron itself is the power hungry bit, I suspect it is the support circuitry and power supplies that are less efficient than more modern designs. Older units with a CRT for the display probably uses more power than the scanner does.

Do you think that a power down time is in order to drain the HT supply?

 

[dunedin]

So you don’t switch the chart plotter off by the power down button on the plotter, but simply slam the power off at source?

If so, that is rather unkind to the electronics. They are pretty robust, but that would be mistreating it needlessly - certainly lacking engineering empathy with the computer innards. Bit like stopping the engine by dropping the clutch in gear rather than using the ignition button.

 

[rszemeti]

Do you think that a power down time is in order to drain the HT supply?

For power up, the sequence is normally something like cooling on, filament on, wait 3 minutes, HT on ... for power down, I think it is less critical. As soon as the cathode heater id turned off, the supply of electrons dies and that should stop everything. I can only imagine it is a "safety" thing to ensure the HT supply is dead before anyone fiddles with it.

There is a phenomenon in thermionic devices known as "cathode poisoning" .. it can happen when the cathode is left heated for long periods without HT current (basically ion drift allows all sorts of crud that would normally be stripped off the cathode to accumulate), I tend not to turn mine on unless I intend to use it, but long periods in standby might be best avoided. it is normally the heater that fails first in Magnetrons, which is what comes on in standby mode anyway, so I doubt it saves the tube much wear.

There is an excellent and now probably hard to find pamphlet called "The Care and Feeding of Power Grid Tubes" that gives much useful information on looking after thermionic devices in general, if you are interested in that sort fo thing.

 

[johnalison]

For power up, the sequence is normally something like cooling on, filament on, wait 3 minutes, HT on ... for power down, I think it is less critical. As soon as the cathode heater id turned off, the supply of electrons dies and that should stop everything. I can only imagine it is a "safety" thing to ensure the HT supply is dead before anyone fiddles with it.

There is a phenomenon in thermionic devices known as "cathode poisoning" .. it can happen when the cathode is left heated for long periods without HT current (basically ion drift allows all sorts of crud that would normally be stripped off the cathode to accumulate), I tend not to turn mine on unless I intend to use it, but long periods in standby might be best avoided. it is normally the heater that fails first in Magnetrons, which is what comes on in standby mode anyway, so I doubt it saves the tube much wear.

There is an excellent and now probably hard to find pamphlet called "The Care and Feeding of Power Grid Tubes" that gives much useful information on looking after thermionic devices in general, if you are interested in that sort fo thing.

With my original RL70 radar/plotter the radar was switched on each time the plotter was, as the OP's is. For most trips I would have to de-power the radar before continuing, but my current set-up e7 has a separate power supply to the radar, which makes things a lot easier. I still have the red plastic that I wrapped round the plotter power switch to remind me not to switch it off without running down the plotter or radar.