Richard,
6 seconds is probably too long to hold the soldering iron on the joint. If your
meter is reading .2 ohms, you'll be alright. If you aren't getting a good joint
in a very short period of time, your soldering iron's power might be too low.
That's Power (wattage), not temp. I use a 50W Weller soldering station for most
electronic work and it's takes less than a second for a good joint. When you go
to soldering school, the instructors are very good at dissecting bad joints.
They often use X-ray and can tell right away if you have double struck a joint.
Ken
On Jan 19, 2017, at 11:57 AM, R Dierking wrote:
Unfortunately, I don’t have a very good ohm meter. However, I checked the
resistance before I started the test. But, not before soldering the
terminals! But, it seemed OK; 0.2 ohm over what I measured alligator clip to
clip (meter baseline). I was going to do this again at the conclusion of
testing. Now, just checking the voltage occasionally and again, seems to be
not changing.
So, since I don’t have many switches, I’ll check the resistance, then solder
the next one at 6 seconds hold time.
It takes practice soldering terminals. I’ve been able to reduce how long
things take with practice, but when you start out I think there’s a tendency
to overheat stuff.
Yes, I too would like to see at least photos of a failure. Students are
usually very good at dissecting failures.
Richard Dierking
From: Vern Knowles
Sent: Thursday, January 19, 2017 11:29 AM
To: roc-chat@xxxxxxxxxxxxx
Subject: [roc-chat] Re: Switch Warning - Schurter 110-220
I suggest the first test would be to just find out if this is even a problem.
(Later on, the test could be changed to determine what is an acceptable
soldering dwell time for reliable operation.) For now, I would just try
abusing a switch with something like 5-8 seconds soldering time on all four
terminals. The switch can be inspected before and after soldering to verify
the contacts have been “degraded.” Then do your cycle testing to see if the
switch still works reliably. Then inspect again at the end of the test.
One thing you might want to consider for your test is to measure the
resistance of the switch contacts with an ohm meter. This would be a more
sensitive test than a light bulb circuit. It is difficult to measure low
resistances accurately but if the contacts are degrading due to cycling or
soldering, then the resistance will start to climb. If it becomes
measurable then it is probably a problem.
Here is another thought. These switches have two small floating
spring-loaded mechanisms inside them to press the contacts together. If one
of those mechanisms gets bound-up or jammed then the switch will likely fail
to conduct. Therefore, it might be worth thinking about what would cause
that. In a rocketry environment, that might be fiberglass or carbon fiber
dust that finds its way into the switch. These switches are not sealed. It
might be interesting to dunk a switch into a bath of fiberglass dust and then
see how well it works.
It would be really valuable to autopsy an actual failure. Anyone have one?
Or is all the data we have so far just anecdotal hearsay?
Vern Knowles
From: R Dierking [mailto:applerocketry@xxxxxxxxxxx] ;
Sent: Thursday, January 19, 2017 11:29 AM
To: Vern Knowles; roc-chat@xxxxxxxxxxxxx
Subject: RE: [roc-chat] Re: Switch Warning - Schurter 110-220
Thank you Vern. I bought 3 switches and was wondering what I was going to do
with the 2nd switch. Switch #1 is at 150 cycles with no signs of trouble
btw. I’m keeping Switch #3 as the control and will be disassembling that one
too. Thanks for the tip on disassembly!
I soldered the current test switch (#1) using my simple 25 watt soldering
iron, but I have a more sophisticated Weller soldering station with temp
control and readout. After I get to the end of checking switch #1, I can
start cycling a switch where the terminals have been subjected to
high/prolonged soldering temperature. What do you think this should be?
There are specifications for solderability and resistance to soldering heat
in the manufacturer’s documentation. However, the sheet is for the PCB
mounted switch. Not being a ‘sparky guy’ I honestly didn’t pay much
attention to this. Given in the spec sheet:
Resistance to soldering heat: 260 C/5 sec acc. to IEC 60068-2-20, Test Tb,
method 1A
Richard Dierking
From: Vern Knowles
Sent: Thursday, January 19, 2017 9:56 AM
To: roc-chat@xxxxxxxxxxxxx
Subject: [roc-chat] Re: Switch Warning - Schurter 110-220
I have used many Schurter switches over the years and not had any issues.
I am wondering if maybe the problems some people have had with them is
related to soldering. I just did a quick test and discovered that the
surface finish on the internal switch contacts does change visibly if a
terminal is heated to soldering temperature for more than a few seconds.
With the soldering iron I used, a couple seconds is okay but at about 4-5
seconds there was enough heat conducted into the switch to change the contact
surface finish. I have no proof the change in surface finish is detrimental
to the operation of the switch but frankly, under the microscope, it does
look somewhat “degraded”. The finish is not as nice and smooth. It would
not surprise me if the number of reliable switching cycles is significantly
reduced by this but I have not tested it. (By the way, the switch is very
easy to take apart for inspection. Just squeeze together the two plastic
posts sticking out the bottom. It is also very easy to re-assemble. Just
push it back together.)
It would be easy for someone to do some testing to see if this is a problem.
(hint, hint!).
Vern Knowles
www.multitronix.com
From: roc-chat-bounce@xxxxxxxxxxxxx [mailto:roc-chat-bounce@xxxxxxxxxxxxx] On ;
Behalf Of R Dierking
Sent: Wednesday, January 18, 2017 7:35 PM
To: kurtgug@xxxxxxxxx; roc-chat@xxxxxxxxxxxxx
Subject: [roc-chat] Re: Switch Warning - Schurter 110-220
I think the 3D printed switch arrangement that Mike brought to the meeting is
better. So are the screw-type Aerocon switches, and the one that holds the
PCB switch that someone posted. I’m doing this mostly for people that have
the 110-220 switches already in their rockets. Also, of course, I’m looking
for a reassurance for the switches I’m using in my L3 project.
I’ll definitely take the test switch apart after the testing concludes. I’m
not sure what number of cycles to stop, but I’m thinking about dropping the
test box on the garage floor every 100 cycles after 500. Really give the
switch a shock to see what happens.
I’ll be taking one of the new switches apart too. I want to see if I can pot
one of the Aerocon PCB switches inside the 110-220 switch case. So, retrofit
with no re-wiring.
From: kurtgug@xxxxxxxxx
Sent: Wednesday, January 18, 2017 5:27 PM
To: roc-chat@xxxxxxxxxxxxx
Subject: [roc-chat] Re: Switch Warning - Schurter 110-220
Hey Richard. Great work you are doing there. You should also dissect the
switch at the end of the testing to see if you can see any wear and tear on
the housing or the contacts.
I'm also interested in making a switch like what Kramer came up with, a micro
switch and screw. That could also be a viable solution.
Kurt
Sent from my iPad
On Jan 18, 2017, at 2:37 PM, R Dierking <applerocketry@xxxxxxxxxxx> wrote:
After the group of posts on this switch and other types used to arm
electronics, I wanted to run a simple test. Maybe to provide some
reassurance to people that already have this switch installed for their
project. On the other hand, there’s no way I can guarantee a favorable
result.
There were a couple of concerns voiced during the last thread for the 110-220
selector switch. One was the lifetime specified in the manufacturer’s
documentation: 300 operating cycles (without load). The other was reports
of failures including high resistance, unreliable connection, and switches
actually cracking during use.
I believe that at least some failures could be attributed to installing what
is intended to be a flat panel mounted switch on curved airframe tube. I’m
thinking that some switches are being over-tightened creating stress on the
rotatory selector.
Please see the attached photos.
Installation:
The hole for these switches is not ½”, but it is close. The manufacturer’s
dimensions for installation are metric. If you just drill a ½” hole, the
hole will probably be too large to use the small protrusion that should be
used to prevent the switch from rotating. Please see the arrow on the first
photo. The switch doesn’t have to be tightened much at all on the mounting
panel. Unfortunately, I’ve never seen any documentation on installation when
you buy them. Anyway, you should drill a smaller hole, and gradually
increase the size until the treads just clear. Also, the notch needs to be
filed for the small projection to prevent rotation.
Durability:
To test the lifetime, I installed a new switch that powers a small light bulb
(9 volt battery for power) and also has posts to check the voltage. I’m
keeping track of how many times I cycle this switch on-off. I’m occasionally
operating the switch 10 times when I go out into the garage. I observe the
light for intermittent connection, occasionally tap the test box, and jog the
selector. So far, I’m at 80 cycles. Again, looking for any problems. I’m
keeping the box on my clothes dryer because it vibrates when operating, and
even the temperature varies. This morning it was 45 F in my garage, and
after operating the dryer for a couple loads of laundry, the test box was 80
F.
So, we’ll see how many cycles I get from this switch. Please keep in mind
that this simple test is not designed to check mean time between failure
(MTBF) because those tests are a lot more involved.
Questions and comments are appreciated.
Richard Dierking
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