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Thanks William.. I learned something new!! Now I need to find some
of these DC ssr's for my cnc mill... the mechanical relays are a pain in
the long run due to well.. their mechanical nature. Gonna have to research
this some more. Is DC SSR's a new development from recent years? Every EE
I've talked to about these in the last 3-4yrs has always spoke of them as AC
relays.
Thanks!
Jarrett
On Tue, 23 Aug 2011 10:10:31 -0600,
William Wilson wrote:
Not all SSR's require AC current. A DC SSR is,
effectively, a giant MOSFET transistor. There is, however, a difference
between a DC and AC SSR, so you need to get the right kind. An AC SSR will
not switch DC current correctly, and a DC SSR will pass half of an AC
wave. Ed's description of the pros and cons is pretty accurate.
SSRs also tolerate vibration much better, and as long as you manage their heat,
generally fail less often. The heat situation is different, as it depends
on the current flowing, vs. a conventional relay which pretty much generates the
same heat whenever it's closed based on how much current you activate it
with. Although we tend to think of solid state electronics as being more
delicate, SSRs can be made as big and tough as you need. They are used in
power substations and industrial motor controllers, among other things.
The only real reason to use a mechanical relay is for cost, or possibly heat
reasons.
On Tue, Aug 23, 2011 at 9:25 AM, Jarrett Johnson <hjjohnson@sasktel.net>
wrote:
Kelly... first things.. I'm
no 'EE'... just have used these before. Bottom line is they
are only good for switching AC current. To turn on or off they need a zero
crossing voltage [when the AC sinoidal wave goes from + to - or VS ] since
DC doesn't have that same waveform [or at least not a zero crossing
wave] they don't work with DC. You are pretty much stuck w/ a smaller 'ice cube'
type mechanical relay for anything DC. The other issue
with these SSR's [if you should have a used for them in the AC side of things]
is they can and often do, fail 'closed' such that you cannot turn off what
ever it is that your switching. I've had this happen a couple times [I
used these on my cnc mill] and it can be.... a bit
scary.
Fwiw
Jarrett
ps- I think my summer
flying schedule is starting to wind down to the place where I could actually get
some laser scanning done... I've been home a grand total of less than 1/2 the
weekends since the start of spring due to flying. I'm not complaining but it
doesn't make my other projects run too smoothly! Currently have my mill
all torn appart while I upgrade some electronic's and servo drives/motors on
it. If I was ever to look like the mad scientist, now would be the
time. Complete w/ hair sticking out every which way, wires sparking and
the odd release of the 'magic' smoke.. :D [ok.. sparking and smoke hasn't
happened yet but... ya just never know when it might!!]
On Tue, 23 Aug 2011 08:12:00 -0700 (PDT), Kelly
Troyer wrote:
Ed & Group,
I brought up the question of
possible use of Solid State Relays (SSR) to replace the
electro-mechanical contactors most of us use in
our flying electrical systems but I need
to depend on the smarter "EE" (Electronic Engineer) types
of our group to tell me if this
would be a good idea...........To the electrically challenged (Me) they
look good.......Light
weight, small, low operating voltage (down to 3 volts), low current draw,
low voltage drop,
high surge amp survival, etc..............They do require a heat sink to
utilize their maximum
amp capibility............They do cost considerably more than
the contactors but do not wear
or degrade and if used within their limits will probably last longer than
me...........
I have included a link to the company
that made the SSR that I have purchased on
blind faith that it would serve as my master relay........It is
a "Power-IO" model HDD-06V75
which has been upgraded since my purchase by the HDD-06V75E
which will operate at
a lower voltage,lower drop and lower current draw............Both versions
will stay operated
at down to 1 volt..........Looking forward for a critique of this idea pro
or con...............<:)
Kelly Troyer
"DYKE DELTA JD2" (Eventually)
"13B ROTARY"_
Engine
"RWS"_RD1C/EC2/EM2
"MISTRAL"_Backplate/Oil
Manifold
"TURBONETICS"_TO4E50 Turbo
From: Ed Anderson <eanderson@carolina.rr.com>
To: Rotary
motors in aircraft <flyrotary@lancaironline.net>
Sent:
Monday, August 22, 2011 8:37 PM
Subject: [FlyRotary] Re: One Battery
- Two Battery was [FlyRotary] Re: Batteries
Yes, Kelly, back a few years ago, I did look into them. The models
I looked at had some strange characteristics that I didn't fully understand (and
didn't take the time to), so I passed. Besides in my case 3 volts would
taken me a bit closer to the airport before the relay let loose, but would have
done nothing to provide a solution for my problem - head up and locked
{:>).
I'm still waiting for the 16X before I start anything major new on
my aircraft - hope won't have to wait too much longer.
Ed
Sent: Monday, August 22, 2011 8:48 PM
Subject: [FlyRotary] One Battery - Two Battery was [FlyRotary] Re:
Batteries
Ed,
Have you ever considered "Solid State Relays" for
contactors..........The DC versions will operate
at down to 3 volts and draw a lot less amperage than the
electro mechanical
versions...........
Kelly Troyer
"DYKE DELTA JD2" (Eventually)
"13B ROTARY"_
Engine
"RWS"_RD1C/EC2/EM2
"MISTRAL"_Backplate/Oil
Manifold
"TURBONETICS"_TO4E50 Turbo
From: Ed Anderson <eanderson@carolina.rr.com>
To: Rotary
motors in aircraft <flyrotary@lancaironline.net>
Sent:
Monday, August 22, 2011 4:12 PM
Subject: [FlyRotary] Re: One Battery
- Two Battery was [FlyRotary] Re: Batteries
Yes, I have also found my GPS can get confused -
especially in the inner city (where you need it the most). So can my brain
when tired and/or under pressure - the old brain can do some not so funny
things.
I left out one important fact about why the switch in the wrong
position caused the engine out landing.
When I had designed that switch in to disengage the battery from
the alternator (in case of an over voltage condition), the switch not only
removed the battery from the alternator line - but also all my critical systems
(fuel, ignition) which were "smartly" tied to my battery bus. So even
though the alternator was putting out plenty of power - even if the battery had
been stone, cold dead, it could have powered all of those power hungry
devices. But having all of that on the battery bus and the battery bus
disconnected from alternator - that pulled that battery down even
quicker.
So the fact that it last 45 minutes including cranking drain for
engine start says a lot about the Odyssey PC 680.
Sent: Monday, August 22, 2011 2:44 PM
Subject: [FlyRotary] Re: One Battery - Two Battery was [FlyRotary]
Re: Batteries
Ed,
Thanks. I remembered you discussing it, but now it makes
sense why you didn't see the low voltage warning from the
battery.
I know that 'fixation' issue, all to well. On business
I'm always running between meetings in new cities, and got to the point where I
really loved (& blindly trusted) my Garmin
GPS. Well in Phoenix there was an
"W.Shangri-La Rd"
vs "E. Shangri-La Rd". Van full of hungry people
wanting dinner, and I kept following the GPS... despite a passenger
in the back telling me I was taking the wrong route. I just figured the
GPS was smarter as it rcd traffic information, and
would get us there faster! Had I thought to look at a map, or listened the
my passenger, but with a load of people, 5pm traffic, and overload after a day
in the sun.... my brain wasn't working. Live and learn!
Tom
From: Ed Anderson <eanderson@carolina.rr.com>
To: Rotary
motors in aircraft <flyrotary@lancaironline.net>
Sent:
Monday, August 22, 2011 12:27 PM
Subject: [FlyRotary] One Battery -
Two Battery was [FlyRotary] Re: Batteries
Actually, Tom, in that particular incident - a second battery
would have only enabled me to fly too far away from the only safe airport
to make a return and dead stick into. IF I had realized the root
cause (a switch accidently put in the wrong position) then one
battery would have worked just as well as two {:>).
Having said that, I certainly would not try to get anyone to change
their mind about using two batteries. . Some folks would not feel
comfortable even with two batteries - but, would add a second alternator,
etc. So, you have to think through your scenarios, the risk involved
and your personal risk tolerance. Yes, Bob now has several good electrical
designs - for just about any kind of power system you could come up with.
Back in 1992, I had never heard of Aeroelectric or
Bob.
But, since my previous engine out almost 5 years previous had been
fuel related and the engine was sputtering in a similar manner - my diagnostic
side of the brain got locked in to searching for a fuel problem
(again) - but even switching tanks did no good - because, this time the "fuel
problem" was a decreasing electrical power. This incident clearly pointed
out the need for an emergency check list that involved checking both fuel AND
electrical systems. Coming up with one in your head with the engine
sputtering is not recommended {:>)
Contributing factors were two early design decisions that on
hindsight revealed shortcomings.
One was an electrical system design that permitted my voltmeter to
keep showing me the 13.8 volts being generated by the alternator while the
battery voltage was steadly decreasing. Yes, I had a
low-voltage light right in front of my eyes - but, it was wired into the
alternator powered circuit - so never showed low voltage because the alternator
voltage was fine - up to the point the relay released.
Now, had it occurred to me I might
have an electrical problem - and switched the volt meter to the battery (instead
of alternator) AND had thought to observe it, I would have seen the battery
voltage decreasing and that MIGHT have got me looking for an electrical problem
rather than a fuel problem. But, when you get your head locked into one
focus - and you truly have mental blinders on, NOT GOOD!
The second design deficiency was that the relay holding the
alternator On-Line was provided current solely by the battery - so guess
what happened when the battery juice got too low to hold the alternator
on-line? Right "CLACK!!!!!" followed immediately by all lights,
radios, LEDS, panel going dark. It gets even lonelier when
the lights go out. Had I two batteries - all of this would have happened
further from my emergency airport in Salem, Al.
No, I have not added the second battery back in after the incident
- because in my particular case, the incident had nothing to do with one
battery vs two battery - it was a case of a mis-positioned
switch which the pilot never recognized was the cause - until later on the
ground, cleaning off the seat cushion. The corrective action was to put a
switch guard over that particular switch so it could NOT be
accidently toggled incorrectly AND rewire my relay so that a
dead battery would no longer prevent my system from using the power of a
perfectly good alternator.
But, this is just my perspective - provided for anyone to glean
what they wish from it - if that is two batteries, two alternators or what have
you, then as always in this hobby, that is up to individual
choice.
Just don't make the same dumb mistakes I made, we know how
those turned out - advance the state of the art and make NEW mistakes
{:>)
Oh, yes, the switch I accidently activated (I think I
probably hit it with my foot getting out of the aircraft at the previous
refueling stop) was one that enabled me to detach my battery from the
alternator. The thought at design time was that if my alternator ran-away
with high voltage, I could isolate the battery from the alternator thereby
preventing the battery from overheating/boiling and get to an emergency landing
on battery power alone. Seemed like a good idea at the time.
Ed
Sent: Monday, August 22, 2011 12:35 PM
Subject: [FlyRotary] Re: Batteries
Joe,
Which Bob Knuckles system? Z19?
I realize Ed is happy with one battery, but I like two
batteries. The THUNK of relays all popping open and the
realization of "I turned off the alternator, and voltage dropped
way too low.... followed with LAND NOW!" would have convinced Ed to
have put the second battery back in! It sure got my attention on why two
batteries is a good thing!(Great Story, but I'll let Ed tell
it!)
So two batteries, and a BIG RED LIGHT with "low voltage" will go on
my panel.
I did the spread sheet with 17AH batteries and
flying time. Add in Night, and no place to easily land.... two
batties seem like a good trade off. My biggest
shock was the FORD style contactor needed 1Amp draw to
remain closed. Shutting down non essential, but leaving
contactors, PDF, ECU and coils.... System
draw is around 15 Amps. 17AH implies you'd have an hour, but at
15Amp draw... more like 30-40 minutes, hence two batteries as 1
hour flying time makes finding a landing strip a little easier.
Tom
www.innovention-tech.com
www.innovention-tech.com
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