Portable Electronic Glass Stength Tester

Make it realistic. Use a pump pellet gun.

Actually UL1703 uses a 6.78 joule impact ;)

Cheers

Find a low friction ramp, and a method of supporting it perpendicular to the panel. Roll a large steel bearing down the ramp. The energy transferred will be controlled by the distance the ball is started up the ramp, and the angle of the ramp. Some math will be required. This is similar to the Charpy and Izod impact tests. No electronics required.

Sounds like a job for an air canon. Mythbusters did something like that when testing the resistance of a Cessna 150 wind screen to impacts by frozen chickens. A scaled down version should work. Presumably, the hail stones will hit terminal velocity (about 200 mph) depending on its wind resistance, which will probably destroy any solar panel. Safety might be a problem.

However, if you're "only" interested in launching hail stones at the solar panel: "This type of glass is designed to withstand a direct vertical impact of hail up to 1 inch in diameter, traveling at 50 miles per hour."

With the 1" hailstone and 50 mph. volume = 4/3 * Pi * r^2 = 1.33 * 3.14 * 0.5^2 = 1.04 in^3 which has a mass of: 1.04 * 0.036127 lbs/in^3 = 0.038 lbs = 0.0172 kg 50 mph = 22.4 meters/sec At 50 mph, the energy delivered is: Energy = 0.5 * mass * velocity^2 = 0.5 * 0.0172 * 22.4^2 = 4.3 joules That can be done with a solenoid gun or an air or spring power launcher.

You are going to want to monitor the position of the plunger in real time. It's easy enough to determine the mass of the plungers, and if you know it' s velocity as it approaches impact, it's easy enough to make sure that prov ides precisely 6.78 joule of impact energy.

If you can measure how much the glass is displaced by the impact, you get a n extra bit of information about the strength of the surface you are testin g.

A bar-code etched into the side of the projectile and a pair of optical sen sors looking at the bar code through a stationary grid pattern (one grid in quadrature with the other) would do the job. The LED illuminating the bar code would use up a bit of current, but it would only be active around impa ct time.

I'd go for a magnetic actuator, but for serious economy of power, use a spr ing operated plunger, that the operator has to pull back against the spring , and rely on the magnet only to adjust the impact energy during the period after the catch has been released. Organising the electronics so that they can come on and spring into full active life in the interval between the c atch being released and the plunger hitting the glass might be challenging, but it would maximise battery life.

A swinging weight on a pendulum - a Charpy Impact Tester - is repeatable and often used, but not small...

Or perhaps a pre-set calibrated automatic centre punch...

Cheers

It turns out that my proposal is essentially an instrumented automatic centre punch ...

punch ...

The highly portable non-instrumented variety can be used to test the strength of the temperered glass used in car windows, as some who have parked their cars in the wrong place have discovered.

Best regards, Spehro Pefhany

Charpy/Izod tester was my first thought- it's complicated a bit by the variable panel orientation wrt gravity, and the usual machines are large.

What about manually increasing compression on a spring (the pressure could be measured with an electronic gauge) to the desired value, then releasing the hammer mass with a manually operated pawl?

If necessary you could correct for the force of gravity on the hammer mass with a tri-axis accelerometer, or manually with a table of settings for the approximate angle.

Best regards, Spehro Pefhany

A can see a few problems with accuracy and calibration. I really don't know what degree of accuracy is required. The spring might vary a few percent with age, temperature, orientation, position of the moon, etc. The ramp is a little better, but changes in altitude (density of air) might have an effect if testing a solar panel on top of Mt Everest. Impact velocity could be easily measured with two photocells and a start/stop timer as the ball rolls down the ramp. Adjust the spring tension until the desired velocity is achieved. A bubble inclinometer should be sufficient for measuring tilt and adjusting the travel distance of the ball to compensate for the tilt. The specs should say something about the impactor contact area. Solar panel glass is tempered, which means that it's under tension on the surface. Break the tension with a sharp point, and the entire panel will shatter into tiny pieces of glass, even if the glass is glued to the solar cells. (I know because I've done it). I suspect the inclined ramp and ball idea may need to be modified into a pendulum or "rail car" style impactor to control the contact area.

Yep. Available off the shelf for the purpose: Just beat on the glass until it breaks. Then record the energy required. This could be fun.

For only 50 mph (~22m/s) he could just drop ice cubes from a ~25m building. (v^2 = 2gh).

I guess that's not very portable :^)

George H.

Thanks for sall the mechanical suggestions. We ruled these out due to inherent variables and aging of parts.

Can anyone tell me how to build a solenoid operated plunger that will have the necessary force? Or at least a viable starting point with regard to circuit design.

Mark "Hailstorm" Harris

You may get some ideas from these articles:

IEC 61215 (crystaline panels) 10.17 is the hail impact test. IEC 61646 (thin film panels) IEC 62108 (CPV Modules)

"Simulated Hail Damage and Impact Resistance Test Procedures For Roof Coverings and Membranes"

"Construction of a Hail Gun for Solar PV Module Testing" JPL at its best. PVC air cannon firing 1" ice balls.

"Effect of Hail Impact on Thermally Tempered Glass Substrates Used for Processing CdTe PV Modules"

I really like this video, which uses frozen paint ball pellets to compare impact strength of tempered glass and acrylic skylights:

"Photovoltaic Solar Panel Resistance to Simulated Hail. Low-Cost Solar Array Project."

No fun. I was hoping for an ice ball cannon.

From IEC 61215 10.17 1st edition(1993)

- Test apparatus as described in section 10.17 with a velocity repeatability of +/- 5%.

- Instrument for velocity measurement with an accuracy of +/- 2%, no more than 1 m from module impact surface

- Weighing instrument with an accuracy of +/- 2%

- Freezer and container for production and storage of ice balls

- Apparatus to verify ice ball diameter to within +/- 5% of requirement and mass within +/- 5% of requirement.

This looks more like a piece of laboratory equipment, instead of a field tester. Which are you designing?

No, but I have a suggestion. The mass of the impactor isn't going to change between shots. The velocity will. So, the problem is how to get a controlled and accurate velocity. Measure the velocity of the ice ball with two photocells. Setup a non-destructive target, like a block of wood. Fire the ice ball and measure the velocity. Adjust the launcher pressure, position, tension, whatever to obtain the desired velocity. Once the velocity is set, subsequent shots should retain the same impact energy as the test shot, within variations of ice ball shape, mass, surface smoothness, etc.

For building the electronics, it's just a period counter, with start and stop inputs. The ice ball breaks a light beam to start the counter and breaks a 2nd beam to stop the counter. The speed is the distance traveled divided by the time it took to travel the distance.

If you want to get fancy and expensive, I guess you could provide feedback to propulsion device. For example, an air cannon could have its pressure controlled by the velocity calculation. After firing a few shots in rapid succession[1], the ice ball velocity should converge on the target value.

I see a major problem in casting or delivering ice balls to the test site. A portable freezer might work, but does tend to be rather clumsy. It might be possible to use plastic or porous clay balls in place of ice. The specific gravity should be about the same, and with sufficient porosity, simulate the brisance of ice shattering on impact. However, this may be breaking new glass, errr... ground, as all I could find under simulated hailstones were those made from ice.

Various commercial ice ball makers:

Lots of good ideas here:

Beware of those that take "hail to the chief" quite literally.

They're all mechanical to some degree.

It remains to be seen whether the friction and other temperature etc. related variations in a solenoid plunger would be any better than an electronically calibrated spring force.

Regardless of how you drive them, solenoids provide a very nonlinear force with plunger position.. so they're actually not very well suited to your application. The more efficent ones (with a closed magnetic circuit when they're actuated) are much worse. Some of the temperature related variation could be eliminated with a constant current type drive, but I doubt that's your biggest problem with that approach.

Maybe you could fling a mass around with a motor. Or pump up a relatively large reservoir with air to a calibrated pressure and use an air cylinder. Or if cost is not a concern and you're stuck on the solenoid-ish idea, consider a linear motor*.

BTW, (baseball) pitching machines use two methods that I've seen- the portable ones use a rotating urethane wheel set to a calibrated RPM. The "Iron Mike" style uses a spring that is deflected by a motor-driven cam which releases under set tension to pitch the ball at up to ~90mph.

• eg. from the makers of the Retro Encabulator:-
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  Uses semi-boloid slots?

A 'voice coil actuator' would be better than a solenoid. I know little of these but Google has lotsa hits...

Cheers

I think I'd try some spring loaded gizmo first. I was thinking about the ice cube on the end of a string idea, but unless y ou've got a long string it's hard to see how you'd get the panel inserted.. . You could release the string at some point, but that strikes me as scarie r than the ice-ball air cannon.

I've got it, set the panel on the side of the road, get your car up to 50 m ph with the ice ball held out the window. Trigger some release mechanism a t the right point so the ice-ball drops and impacts the panel. Slightly more portable than than dropping ice cubes from buildings. :^)

George H.

The OP mentioned something about an accuracy problem. Citing my last rant:

From IEC 61215 10.17 1st edition(1993)

- Test apparatus as described in section 10.17 with a velocity repeatability of +/- 5%.

- Instrument for velocity measurement with an accuracy of +/- 2%, no more than 1 m from module impact surface

- Weighing instrument with an accuracy of +/- 2%

- Freezer and container for production and storage of ice balls

- Apparatus to verify ice ball diameter to within +/- 5% of requirement and mass within +/- 5% of requirement.

Yeah, but I like your idea. However, not one string but two as in a traditional sling: It worked on Goliath, so a mere tempered glass window should not be a major challenge. I prefer 2 or 3 overhead spins because I can use a longer length rope, and it helps seat the projectile in the pouch, but vertical spins with shorter ropes should also work. To indicate the desired velocity, a teapot whistle, or electronic equivalent, is attached to the end, which signals the when to let go. Some practice and calibration will be required. In the event of collateral damage, a good insurance policy might also be useful. I suppose all this could be automated, in the Mythbuster style, that takes the fun out destructive testing. If accuracy is a problem, then several small hailstones could be simultaneously launched. At least one might hit the target panel.

Ummm... the panels are usually mounted on a rooftop. Unless there's an adjacent building, that is 25 meter higher, the drop test method isn't going to work.

However, you gave me yet another marginal idea. At 50 mph (22.4 meters/sec), liquid water and ice will transfer about the same amount of energy to the glass. No need to use a frozen ice ball proxy, when a small water balloon filled with non-frozen water will suffice. This was demonstrated by Mythbusters in the chicken cannon, and by me in college when I used a sling to launch water balloons. This was deemed a major escalation in inter-dormitory warfare and was immediately suppressed by the administration after I sent a fairly small water balloon through a non-tempered window (at about 30 meters range).

The ice, or the building? ;-)

That has a moving coil. Inland Motor (now part of Danaher Motion) used to m ake a linear motor in which the moving part was a steel rod into which had been cut a helical groove.

The groove was then back-filled with non-magnetic chrome, You did have to p revent the rod from rotating, but the groove was enough for a Sawyer type l inear synchronous motor to grab onto.

The flat linear motor in your URL could be topologically transformed into s omething similar by stacking Neodynium-Iron disk magnets (of alternating po larity) into a rod, but keeping them stacked would be tricky, and grinding them into a uniform circular rod would be worse.

Soft iron aka steel isn't a nice material for fast-stepping synchronous mot ors - the rapidly changing magnetic fields turn into current circulating wi thin the metal, which doesn't do anything except warm the rod.