Yeah, I use my meter to indicate major problems. Mostly, continuity or not. I
heard (again no evidence seen yet), that there have been failures due to power
losses from excessive resistance through the switch. So, I thought I might be
able to identify a problem by occasionally checking voltage.
Now, I think Vern has identified the most likely cause of this problem. The
switches are ‘cooked’ prior to even being used.
Richard
From: Allen Farrington<mailto:allen.farrington@xxxxxx>
Sent: Thursday, January 19, 2017 12:12 PM
To: roc-chat@xxxxxxxxxxxxx<mailto:roc-chat@xxxxxxxxxxxxx>
Cc: Vern Knowles<mailto:knowles.vern@xxxxxxxxx>
Subject: [roc-chat] Re: Switch Warning - Schurter 110-220
Richard, with a regular ohm meter, even a professional one, you can't
accurately measure the resistance of a switch like that. You are measuring the
resistance of your leads, mostly.
You'll need a four-lead ohm-meter to do what you're thinking of. Not a standard
item.
Allen
Sent from my iPad
On Jan 19, 2017, at 11:57 AM, R Dierking
<applerocketry@xxxxxxxxxxx<mailto:applerocketry@xxxxxxxxxxx>> 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<mailto:knowles.vern@xxxxxxxxx>
Sent: Thursday, January 19, 2017 11:29 AM
To: roc-chat@xxxxxxxxxxxxx<mailto: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<mailto: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<mailto:knowles.vern@xxxxxxxxx>
Sent: Thursday, January 19, 2017 9:56 AM
To: roc-chat@xxxxxxxxxxxxx<mailto: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<http://www.multitronix.com>
From: roc-chat-bounce@xxxxxxxxxxxxx<mailto: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<mailto:kurtgug@xxxxxxxxx>;
roc-chat@xxxxxxxxxxxxx<mailto: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<mailto:kurtgug@xxxxxxxxx>
Sent: Wednesday, January 18, 2017 5:27 PM
To: roc-chat@xxxxxxxxxxxxx<mailto: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<mailto: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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