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Hi Kelly,
Like all technology Solid state relays have
advantages/disadvantages - I did a quick search to see if I could find
assessments of DC relays using DC switching. Here is what I found
which seem to sum up both. I have no experience in
using them.
Ed
Advantages over
mechanical relays
Most of the relative advantages of solid state and
electromechanical relays are common to all solid-state as against
electromechanical devices.
- SSRs are faster than electromechanical relays;
their switching time is dependent on the time needed to power the LED on and
off, of the order of microseconds to milliseconds
- Lower (if any) minimum output current (latching
current) required
- Increased lifetime, particularly if activated many
times, as there are no moving parts to wear
- Output resistance remains constant regardless of
amount of use
- Clean, bounceless operation
- Decreased electrical noise when switching
- No sparking, allowing use in explosive
environments where it is critical that no spark is generated during switching
- Totally silent operation
- Inherently smaller than a mechanical relay of
similar specification (if desired may have the same "casing" form factor for
interchangeability).
- Much less sensitive to storage and operating environment. For example much less sensitive to mechanical shock and vibration,
humidity.
Disadvantages
- Voltage/current characteristic of semiconductor rather than
mechanical contacts:
- When closed, higher resistance (generating heat), and increased
electrical noise
- When open, lower resistance, and reverse leakage current
(typically µA range)
- Voltage/current characteristic is not linear (not purely
resistive), distorting switched waveforms to some extent. An
electromechanical relay has the low ohmic (linear) resistance of the
associated mechanical switch when activated, and the exceedingly high
resistance of the air gap and insulating materials when open.
- DC load must observe polarity (- and + not interchangeable) to
avoid an undesirable "always conducting" state that does not depend on
switching input. Electromechanical relays do not depend on polarity.
- Possibility of spurious switching due to voltage transients (due
to much faster switching than mechanical relay)
- Isolated bias supply required for gate charge circuit
- Higher Transient Reverse Recovery time (Trr) due to the presence
of Body diode
Here is a note from one
manufacture on their relays
Transient Voltage Protection:
When operating a solid state relay in an
electrically noisy environment, large voltage
transients may damage the relay. To
protect against this occurrence, it is advisable to
install appropriate MOVs across the
respective supply and load terminals of the relay
output. The “5V” option is available for
customers who want the MOVs to be supplied
internally with the solid state
relay.
Short-Circuit Protection:
CII Continental recommends the use of an
appropriately sized I 2t fuse on the
supply
side of the relay to protect the SCR devices.
Although a semiconductor relay is
designed for virtually countless operation
cycles, it can be destroyed by an overvoltage
or a short circuit, unless protected adequately
by an I2t fuse. NOTE: Overload
protection should be provided by another slow
acting fuse in series with the short
circuit protection fuse. (An overload being an
over-current
Sent: Tuesday, August 23, 2011 11:12 AM
Subject: [FlyRotary] The Case for Solid state Relays
(SSR)
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
From:
Ed Anderson <eanderson@carolina.rr.com>
To: Rotary motors in aircraft
<flyrotary@lancaironline.net>
Sent: Monday, August 22, 2011 11:20
AM
Subject: [FlyRotary] Re:
Batteries
Joe, I started out using two Concord 25AH RGB each weighing 22 lbs for a total of over 44 lbs of
battery (some joked I could get home by using the start to crank the prop
{:>)) ! I then transition to two Odyssey PC-680 17AH batteries each
weighing 14 lbs for a total of 28 lbs. Then after 6 years of flying with
two batteries and never using the second one - except to help crank on a cold
morning, I removed one of them. Have now been flying for over 4-5 years
with one Odyssey 14lbs. I swap it out every two
years. Ed -------------------------------------------------- From:
< jskmberki@windstream.net> Sent:
Monday, August 22, 2011 11:59 AM To: "Rotary motors in aircraft" < flyrotary@lancaironline.net> Subject:
[FlyRotary] Batteries > What size an type of batteries are required
for the rotary? I am leaning toward using 2 batteries and use Bob Nuckols system. Thanks for any help. >
> Joe Berki> Limo EZ> > -- > Homepage: http://www.flyrotary.com/> Archive and UnSub: http://mail.lancaironline.net:81/lists/flyrotary/List.html
-- Homepage: http://www.flyrotary.com/Archive and UnSub: http://mail.lancaironline.net:81/lists/flyrotary/List.html
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