Hey guys, if you have been following HC's section on ECF much you might notice some commotion of the "spring defect" of their new APV's after a quick glance, a few measurements with my verniers here is a couple tidbits of information you would like to know to fully understand what is going on here.
DISCLAIMER: I am not an engineer, my professional field is IT but I have an interest of both mechanical and electrical engineering, I should be considered very much a NOOB when it comes to these things, all I am doing is reporting my findings and assumptions. None of this is supported by a deep understanding of engineering. Sorry this is a little confusing it is hard to explain without diagrams.
TLDR: Flattop batteries are too short, use button tops or one a protected battery which has a diameter of < 18.5 mm
OK so is there really a problem with these battery springs? Short answer: No. Long Answer: No. It's not a "defect" problem, more of a "lack of recommendation/information" problem.
Most HC consumers who bought this device, who have never used an APV or did not have their own batteries, would have more then likely paired it with the flat top Joyetech battery HC sells as well (This assumption is based on the fact that HC recommends this battery on the APV's product page, along with being sold out with the APV's). Flat top 18650 DO work in this battery BUT it doesn't seem to provide enough length to compress the spring to a point where the amount of force is sufficient to sustain a connection during any sort of movement of the device.
The Joyetech battery has these dimensions
Listed vs Actual
Diameter: 18 mm vs 18.16 mm
Length: 65 mm vs 65 mm
Spring Measurements:
Diameter of spring wire: .52 mm
Outer diameter of spring (Since the spring is not uniform this is the measurement of the middle coil): 7.3 mm
Free length of spring: 8.63 mm
Number of active coils: 4
Other Measurements:
Negative end of the battery to the edge of the APV housing (While the battery was inside): 4.74 mm
Top edge of end cap to top tip of battery spring: 1.78 mm
Inner diameter of the APV battery compartment: 18.5 mm
Thread Depth on APV for end cap: 3.52
What does this all mean?
Basically the spring has to travel (from the end of the APV without the cap) 4.74 mm. Since we are unable measure the depth of the device with the end cap attached I used the depth of thread for the end cap (3.52) combined with the 1.78 mm of the spring protruding from the tip of the end cap resulting in 5.3 mm. 5.3 mm represents the distance the amount of "reach" the spring has from the end of the APV without the end cap. (You cant just measure the length of the spring since screwing on the end cap increases the overall length of the APV). We can take this figure and subtract it from the depth of the battery compartment and get 0.56 (5.3-4.74 = 0.56).
So we can see here that my current setup (the APV with the Joyetech 18650 battery) only has a spring length compression of 0.56 mm! Using Compression Spring Calculator we can see a rough value of what the force applied might be (since we do not know the material, I assumed it to be the lowest steel) most of these figures are only baseline figures to work from. One figure which would be similar across the usual materials is the max travel length of the spring (5.510 mm). 5.510 is the value recommended as the maximum compression distance before causing fatigue on the spring itself.
How to "fix" this?
Use a button top battery
Such as:: New! Panasonic CGR18650CH With Top Button, 2250mAh IMR High Drain 18650 Battery Cell-Made in Japan
Which has a length of 66.9mm creating a compression length of ~2.46mm
or a protected battery such as: 3400mAh Protected Panasonic 18650 battery cell by Orbtronic
Diameter (mm): 18.5 mm (+/- 0.03) You have to be careful however as it may be a very tight fit if the dimensions are not exact
Height (mm): 68.9 mm
Personally I would go for the protected battery since it would give you an extra 3.9mm of compression making a total of ~4.4 mm.
So its not really a defect, its just that it doesn't seem that this APV was designed to be used in conjunction with flat tops.
I apologize if this post is poorly written, I quickly threw it together before having to run some errands but I hope this clears up somethings on the whole "spring issue"
DISCLAIMER: I am not an engineer, my professional field is IT but I have an interest of both mechanical and electrical engineering, I should be considered very much a NOOB when it comes to these things, all I am doing is reporting my findings and assumptions. None of this is supported by a deep understanding of engineering. Sorry this is a little confusing it is hard to explain without diagrams.
TLDR: Flattop batteries are too short, use button tops or one a protected battery which has a diameter of < 18.5 mm
OK so is there really a problem with these battery springs? Short answer: No. Long Answer: No. It's not a "defect" problem, more of a "lack of recommendation/information" problem.
Most HC consumers who bought this device, who have never used an APV or did not have their own batteries, would have more then likely paired it with the flat top Joyetech battery HC sells as well (This assumption is based on the fact that HC recommends this battery on the APV's product page, along with being sold out with the APV's). Flat top 18650 DO work in this battery BUT it doesn't seem to provide enough length to compress the spring to a point where the amount of force is sufficient to sustain a connection during any sort of movement of the device.
The Joyetech battery has these dimensions
Listed vs Actual
Diameter: 18 mm vs 18.16 mm
Length: 65 mm vs 65 mm
Spring Measurements:
Diameter of spring wire: .52 mm
Outer diameter of spring (Since the spring is not uniform this is the measurement of the middle coil): 7.3 mm
Free length of spring: 8.63 mm
Number of active coils: 4
Other Measurements:
Negative end of the battery to the edge of the APV housing (While the battery was inside): 4.74 mm
Top edge of end cap to top tip of battery spring: 1.78 mm
Inner diameter of the APV battery compartment: 18.5 mm
Thread Depth on APV for end cap: 3.52
What does this all mean?
Basically the spring has to travel (from the end of the APV without the cap) 4.74 mm. Since we are unable measure the depth of the device with the end cap attached I used the depth of thread for the end cap (3.52) combined with the 1.78 mm of the spring protruding from the tip of the end cap resulting in 5.3 mm. 5.3 mm represents the distance the amount of "reach" the spring has from the end of the APV without the end cap. (You cant just measure the length of the spring since screwing on the end cap increases the overall length of the APV). We can take this figure and subtract it from the depth of the battery compartment and get 0.56 (5.3-4.74 = 0.56).
So we can see here that my current setup (the APV with the Joyetech 18650 battery) only has a spring length compression of 0.56 mm! Using Compression Spring Calculator we can see a rough value of what the force applied might be (since we do not know the material, I assumed it to be the lowest steel) most of these figures are only baseline figures to work from. One figure which would be similar across the usual materials is the max travel length of the spring (5.510 mm). 5.510 is the value recommended as the maximum compression distance before causing fatigue on the spring itself.
How to "fix" this?
Use a button top battery
Such as:: New! Panasonic CGR18650CH With Top Button, 2250mAh IMR High Drain 18650 Battery Cell-Made in Japan
Which has a length of 66.9mm creating a compression length of ~2.46mm
or a protected battery such as: 3400mAh Protected Panasonic 18650 battery cell by Orbtronic
Diameter (mm): 18.5 mm (+/- 0.03) You have to be careful however as it may be a very tight fit if the dimensions are not exact
Height (mm): 68.9 mm
Personally I would go for the protected battery since it would give you an extra 3.9mm of compression making a total of ~4.4 mm.
So its not really a defect, its just that it doesn't seem that this APV was designed to be used in conjunction with flat tops.
I apologize if this post is poorly written, I quickly threw it together before having to run some errands but I hope this clears up somethings on the whole "spring issue"
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