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1. 06:25 AM - Re: Solid State Master Relay (user9253)
2. 07:10 AM - Re: Re: Solid State Master Relay (Robert L. Nuckolls, III)
3. 04:35 PM - Re: Solid State Master Relay (Justin Jones)
4. 07:29 PM - Re: Solid State Master Relay (Robert L. Nuckolls, III)
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Subject: | Re: Solid State Master Relay |
The specs for the solid state relay state,
> Internal diode protection for inductive load
> switching
I am curious as to how this protection works. Any inductive induced current will
flow in the SAME direction as normal current.
Joe
--------
Joe Gores
Read this topic online here:
http://forums.matronics.com/viewtopic.php?p=434167#434167
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Subject: | Re: Solid State Master Relay |
At 08:24 2014-11-20, you wrote:
>
>The specs for the solid state relay state,
>
> > Internal diode protection for inductive load
> > switching
>
>I am curious as to how this protection works. Any inductive induced
>current will flow in the SAME direction as normal current.
http://aeroelectric.com/Pictures/Curves/Relay-Contactor_Performance/Cole-Hersee_without_Diode.gif
They're talking about limiting any potential effects
for having SWITCHED an inductive load to an OFF
state. Here they're speaking to protection of the
contactor as a switch and assuming that unlike
legacy practice for protecting battery master
and starter contactor switches, the installer
would use the device to manage an inductive
load that is not also surrounded with coil
suppression.
Bob . . .
Message 3
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Subject: | Re: Solid State Master Relay |
Apologies for not responding sooner. I am currently deployed.
The relay failures that I have experienced were on Cessna aircraft and
both were the factory installed part numbers. One was a rental aircraft
(172) and one was my own aircraft (182). The 182 relay failed after 500
hours of use. The failures can and do happen, although they are rare. I
have over 3,300 hours of flight time in everything from small aircraft
to C-130s. I have had numerous electrical emergencies on certified
aircraft and 3 of them were due to failed relays (not master relays).
The C-130 has a set of =9CK=9D relays that switch the AC
busses and they are notorious for giving crews issues. There has been
some talk of testing zero switching SSRs to see if some of the failure
rates can be reduced.
The cost is higher, but SSRs have rated cycles of 100,000 to 500,000
cycles. This outlasts legacy mechanical relays by far. They haven=99
t been proven for 50+ years, but if we don=99t start testing them,
they will never be proven. I don=99t expect to put 100,000 cycles
on my system, but if it works as advertised, I should never have to
replace the relay.
The relay heat sink has to be able to dissipate the heat that 300A of
continuous usage would generate. I can=99t think of a situation
where the battery would last long enough for heat to be an issue with
this relay. If it is, the aluminum heat sink should be able to handle
it. Living and operating the aircraft in Alaska will help with this as
well. I can weigh it when I get home, but I do remember thinking that
this is much lighter that I initially thought. I believe it is on par
with other 12V master relays.
I am building a Bushcaddy L164 for off airport operations in Alaska.
One reason I would like to use the SSR master relay is to experiment
with it and test it. I am interested to see if it is a viable option to
replace the legacy relays. If so, failed relays may become a thing of
the past.
The reason for the installation of the remotely operated battery
disconnect switch would be to stop a running battery in the unlikely
event that the relay sticks and starter contacts weld together. Skytec
has a webpage about this and has explained it. The gentleman in the
article installed a starter run-on light modification that simply lights
an LED when the starter is receiving power. This will tell you if the
starter relay has stuck closed. The gentleman in the article has
installed an Eaton starter relay. It should be noted that he has a 28V
system.
http://www.skytecair.com/Cessna_Solenoids.htm
<http://www.skytecair.com/Cessna_Solenoids.htm>
Justin
> On Nov 19, 2014, at 4:01 PM, Jeff Luckey <jluckey@pacbell.net> wrote:
>
> Justin,
>
> I'm curious about the decision process that lead to selecting the
solid-state relay. I see some down side:
>
> 1. Cost - that relay is 4 or 5 times the price of an equivalent
mechanical device
> 2. Power dissipation - That's a pretty hefty heat-sink. How much
power does it need to dissipate
> 3. I wonder if it is heavier that a mechanical - I didn't see a weight
spec.
> 4. "Proven technology" - How much track record is there for this
device? (I compare this against the standard Master relays with a 50+
year history.)
>
> This is the Master Relay I'm using (I like it because it's
lightweight, small, low coil current, & reasonable cost):
> http://tinyurl.com/nb72gal
<https://theelectricaldepot.com/index.php?main_page=product_info&cPath=
12_72&products_id=427&zenid=29d44d150400a94d7270facaa3468e89>
>
> Re wiring starter directly:
> That's what I'm doing in my RV-7. Battery to start-assist solenoid to
starter. BobN just made a post in the last couple of days re this topic
and I concur w/ his thoughts. Basically a hung start-assist solenoid is
such a rare event that I don't worry about it.
>
> A couple of questions:
> 1. Which airplane are you building?
> 2. Tell us about your master relay failures. What aircraft? which
relay/contactor?
>
>
> Please understand that my intent is not to be critical but rather to
understand how you reached your conclusions. (I might learn something.)
>
>
> -Jeff
>
>
>
> On Wednesday, November 19, 2014 2:16 PM, Justin Jones
<jmjones2000@mindspring.com> wrote:
>
>
> I purchased the following solid state master relay to use in my
project. It is designed to be used as an ambulance master relay.
>
> http://www.waytekwire.com/item/44407/300-AMP-SOLID-STATE-BATTERY/
<http://www.waytekwire.com/item/44407/300-AMP-SOLID-STATE-BATTERY/>
>
> I am wondering what the typical inrush and cranking amperage is to the
Skytec starters for the Lycoming IO-360. I am contemplating wiring the
starter from the battery, through the relay and to the starter rather
than connecting it thru the Battery Master Switch. It would seem that
limiting the high amounts of current that the starter draws would
prolong the already long life of these solid state devices. The maximum
rating for this relay is 500A for one second. Over the years, I have
experienced numerous master relay failures, and I am anxious to try this
out. The link to the data sheet is below.
>
> http://www.waytekwire.com/datasheet/44407.pdf
<http://www.waytekwire.com/datasheet/44407.pdf>
>
>
> One other option I considered is to wire the starter from the battery,
to a manual disconnect (such as one in the links below), then through
the starter relay, thence the starter. One could attach a push-pull
cable or rod to the armature of this switch, and easily disconnect the
battery from the starter while sitting in the cockpit in the unlikely
event of the starter contacts getting welded together, or the starter
relay fails closed. This switch should probably be located as close to
the battery as possible.
>
> http://www.jegs.com/i/Flaming+River/898/FR1006/10002/-1
<http://www.jegs.com/i/Flaming+River/898/FR1006/10002/-1>
> http://www.jegs.com/i/Flaming+River/898/FR1003-1/10002/-1
<http://www.jegs.com/i/Flaming+River/898/FR1003-1/10002/-1>
> http://www.jegs.com/i/Moroso/710/74105/10002/-1
<http://www.jegs.com/i/Moroso/710/74105/10002/-1>
> http://www.jegs.com/i/Unisteer/668/8070030/10002/-1
<http://www.jegs.com/i/Unisteer/668/8070030/10002/-1>
> http://www.jegs.com/i/Unisteer/668/8070040/10002/-1
<http://www.jegs.com/i/Unisteer/668/8070040/10002/-1>
>
>
>
> Thoughts are welcome
>
> Justin
>
>
>
>
>
>
>
<http://www.aeroelectric.com/>
<http://www.buildersbooks.com/>
<http://www.homebuilthelp.com/>
<http://www.mypilotstore.com/>
<http://www.matronics.com/contribution>
<http://www.matronics.com/Navigator?AeroElectric-List>
>
Message 4
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Subject: | Re: Solid State Master Relay |
At 18:33 2014-11-20, you wrote:
Apologies for not responding sooner. I am currently deployed.
The relay failures that I have experienced were
on Cessna aircraft and both were the factory
installed part numbers. One was a rental
aircraft (172) and one was my own aircraft
(182). The 182 relay failed after 500 hours of
use. The failures can and do happen, although
they are rare. I have over 3,300 hours of flight
time in everything from small aircraft to
C-130s. I have had numerous electrical
emergencies on certified aircraft and 3 of them
were due to failed relays (not master
relays). The C-130 has a set of =9CK=9D relays
that switch the AC busses and they are notorious
for giving crews issues. There has been some
talk of testing zero switching SSRs to see if
some of the failure rates can be reduced.
Certainly, alternative parts with higher
degrees of robustness can improve the
MTBF numbers in any system. But quite
often, it's less expensive, simpler and
lighter to design for failure tolerance.
For example, all of the Z-figures featuring
and Endurance Bus combined with well maintained
batteries can make the loss of the battery
relay no more than a maintenance event.
The cost is higher, but SSRs have rated cycles of
100,000 to 500,000 cycles. This outlasts legacy
mechanical relays by far. They haven=99t been
proven for 50+ years, but if we don=99t start
testing them, they will never be proven. I
don=99t expect to put 100,000 cycles on my
system, but if it works as advertised, I should
never have to replace the relay.
If that is the design goal, by all means.
Suggest you verify that it's not just a battery
isolation relay but truly capable of
bidirectional conduction (charge and discharge).
The relay heat sink has to be able to dissipate
the heat that 300A of continuous usage would
generate. I can=99t think of a situation where
the battery would last long enough for heat to be
an issue with this relay. If it is, the aluminum
heat sink should be able to handle it. Living
and operating the aircraft in Alaska will help
with this as well. I can weigh it when I get
home, but I do remember thinking that this is
much lighter that I initially thought. I believe
it is on par with other 12V master relays.
Good . . .
I am building a Bushcaddy L164 for off airport operations in Alaska.
Wheeled or floats?
One reason I would like to use the SSR master
relay is to experiment with it and test it. I am
interested to see if it is a viable option to
replace the legacy relays. If so, failed relays
may become a thing of the past.
It may well be. Suggest you use it in conjunction
with an architecture that includes a Plan-B that
tolerates loss of battery contactor . . . contactors
can fail to close for reasons other than failure
of contactor itself.
The reason for the installation of the remotely
operated battery disconnect switch would be to
stop a running battery in the unlikely event that
the relay sticks and starter contacts weld
together. Skytec has a webpage about this and
has explained it. The gentleman in the article
installed a starter run-on light modification
that simply lights an LED when the starter is
receiving power. This will tell you if the
starter relay has stuck closed. The gentleman in
the article has installed an Eaton starter
relay. It should be noted that he has a 28V system.
http://www.skytecair.com/Cessna_Solenoids.htm
Quoting from the article:
Why pick on Cessna? Can't this happen to any similarly configured aircraft?
This absolutely could (and occasionally does)
happen to any/all brands of aircraft. However,
we see this occur far more often with Cessna
aircraft because of the type (architecture) of
relay Cessna specified for use as a starter
contactor in production of their aircraft.
The RBM/Stancore/Cole-Hersee 'beer barrel' contactors have
often been cited for an elevated failure rate. But one mechanic
I talked with some years ago admitted that numbers of
Cessnas running through his shop were about as great as all
the other brands combined. He wasn't sure that Cessna was
experiencing a FAILURE RATE significantly higher than other brands.
A data point he offered was the fact that poorly
maintained batteries were the greatest threat to the
health of any contactor . . . with the 'beer barrel'
style being the most vulnerable. Tentative and or
chattering closures when a soggy battery is loaded
by the starter places all contactors a higher risk
for sticking.
Wrong Part - By Design?
Observing the parts manual for most Cessna
aircraft, you will note the same part number used
to describe both the starter contactor as well as
the master switch relay (master contactor).
Really? I'll have to check on that tomorrow. I've
got some work to do in the EMC lab at Cessna in the morning
I'll get into a computer and dig through some service manuals.
I recall writing about the DIFFERENCES
between intermittent duty and continuous duty
contactors for service as battery and starter
control . . . but don't recall the specific
models. I'll check the drawings.
For instance, one of our customers, Willie Zeiger
who flies a beautiful Cessna 185 out of Anchorage
Alaska, notes in a letter to the factory, "Both
relays are rated for continuous duty and are good
for both the master relay and starter relay."
However, the duty of each of these functions
(starter contactor vs. master relay) are quite
different and, as such, should (and in other
makes of aircraft DO) require different types of relays.
I cannot dispute anyone's observations for having
found a battery contactor installed in place of
a starter contactor but I'm skeptical that the
parts catalog calls it out. The difference between
them is well understood. Further, they're the same price
to the OEM. Any notion that such a condition exists
by design is suspect. I'll check.
Bob . . .
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