[Rover] Power Droop

[n2mh at n2mh.net]

Hi Ev,

During engine start, there are actually two conditions that you need to
protect against:

The first is voltage droop as you have experienced.

The second is the very real possibility of a voltage spike due to the
collapsing field of the starter solenoid or the starter motor. I say "very
real" because this blew out the dial lights in one of my radios once.

The only real way to avoid bad things to your equipment during engine
start  is to disconnect it completely from the auto's electrical system.
This begs the issue of keeping the equipment running when it is
disconnected from the car battery. The answer here is to have an auxiliary
battery or two that runs the equipment all the time and to have the car
alternator charge the aux battery when the engine is running.

I tried the series diode approach at first, but found that the voltage
drop across the diode never fully charged up the aux battery. I finally
settled on a conventional 20 amp wall switch. You turn on the switch after
the engine is started and you turn it off before you stop the engine. Nice
and simple but you need to be disciplined for this approach to work ok. I
bought mine at Home Depot (My Favorite Antenna Store [TM]). Just make sure
that you get one that is not rated AC only. And, I use a couple of
"Marine" batteries from Wally World.

BTW, I did try the big-honkin' capacitor trick once to try to prevent
voltage droop on SSB transmit peaks. I used a 1 Farad capacitor but found
that with my 100 watt radio on 6m (an FT-847), the cap pooped out before
the  peak was finished. You also have to be very careful with those caps.
You must charge them up to 12 volts slowly before connecting them directly
across your 12v line. I use a tail-light bulb in series for that. It
lights up real bright at first but goes dim then goes out. When it goes
out, it's safe to connect the cap across the 12v line. Also, very
important, fuse the capacitor. If it gets discharged and you suddenly put
12v across it with no fuse, nasty things could happen. Ditto for a rapid
discharge condition - they don't like to supply a lot of current all of a
sudden. Just remember that there's a lot of Joules stored in there that
must be kept safe.

73, Mark, N2MH

PS, you might find some other suggestions in a piece of spam mail or two. :=)

>
> Hey Guys...I have a couple of vehicles that apparently have enough voltage
> drop during engine start that it causes my transceivers to reset.  Without
> getting into all of the ugly details, I wonder if anyone has experience
> with "droop protection". (be nice)
>
> I'm thinking that maybe something as simple as a big-ol' honkin' capacitor
> (like what is used for mobile stereo bass boosters) might be all I need,
> but I thought I'd ask the pro's first.
>
> Ev, W2EV