0
\$\begingroup\$

I'm developing a wearable electronics product that runs on batteries. I would like to use a USB power pack like this as the battery, but I need to make sure it's not a fire hazard because it's going to be part of a clothing item. The power pack says it's UL listed, but I don't know how to find out what exactly that guarantees. Does anyone have any suggestions? Given the recent hoverboard incidents I'm inclined to be very cautious with Li-ion batteries.

\$\endgroup\$
8
  • \$\begingroup\$ No such thing as 100% certainty that it is not a fire or explosion hazard. Even if the battery is, can you guarantee your wiring in your clothing is... \$\endgroup\$
    – Trevor_G
    Mar 17, 2017 at 0:27
  • \$\begingroup\$ Ok yes there's never 100% certainty, but I need to make sure it's very unlikely. \$\endgroup\$
    – user135797
    Mar 17, 2017 at 0:30
  • \$\begingroup\$ I'm having a hard time finding the true manufacturer of those. They seem to be OEM as promo items. \$\endgroup\$
    – Trevor_G
    Mar 17, 2017 at 0:33
  • \$\begingroup\$ That's part of the problem. They're referred to all over as "Jolt chargers" but beyond that I've turned up nothing. I haven't been able to verify if the UL listing is real either. \$\endgroup\$
    – user135797
    Mar 17, 2017 at 0:35
  • \$\begingroup\$ Looks a lot like this company powerbank86.com/certificates-of-power-bank-charger.html \$\endgroup\$
    – Trevor_G
    Mar 17, 2017 at 0:37

1 Answer 1

5
\$\begingroup\$

Manufacturer is:

TWINTECH INDUSTRY INC
16420 MANNING WAY
CERRITOS, CA 90703 USA

UL File Number: MH60879
Model: 2706UL RetroFIT 1500P

This unit was certified UL 2054 compliant

UL 2054 checks or tests the following:

  • Components
  • Casing and Enclosure
  • Electrolyte
  • External battery pack connectors
  • Printed wiring boards
  • Lithium Ion Systems Only
  • Temperature Measurements
  • Short-Circuit Test
  • Abnormal Charging Test
  • Abusive Overcharge Test
  • Forced-Discharge Test
  • Limited Power Source Test
  • Battery Pack Component Temperature Test
  • Battery Pack Surface Temperature Test
  • Crush Test
  • Impact Test
  • Shock Test
  • Vibration Test
  • 2N Steady Force Test
  • Mold Stress Relief Test
  • Drop Impact Test
  • Projectile Test
  • Heating Test
  • Temperature Cycling Test



All Li-ion batteries and battery packs are governed by IEC 62133 and UN 38.3.

Some of the safeguards required for Battery Pack manufacturers:

  • Built-in PTC (positive temperature coefficient) protects against current surges.
  • CID (circuit interrupt device) opens the circuit at a cell pressure of 1,000kPa (145psi).
  • Safety vent releases gases on excessive pressure buildup at 3,000kPa (450psi).
  • Separator inhibits ion-flow by melting process when exceeding a certain temperature threshold.



LINK IEC 62133 Slide Presentation PDF

The sellers must provide a certification of compliance which will have statements like:

The cell used is a UL recognized component according to UL1642.
The battery is certified according to IEC 62133 edition 2 and UN 38.3




The UN 38.3 test includes:

T1 – Altitude Simulation: Low pressure simulating unpressurized cargo hold at 15,000 meters.
T2 – Thermal Test: Temperature extremes by keeping batteries for 6h at -40°C and +75°C.
T3 – Vibration: Test simulates vibration during transportation at 7Hz to 200Hz for up to 3 hours.
T4 – Shock: Test simulates vibration during transportation at given G-forces relating to battery size.
T5 – External Short Circuit: With fusing, apply a short circuit at 50°C. Case cannot exceed +170°C.
T6 – Impact: >20mm cylindrical cell tested for impact; all <20mm cell types tested for crushing.
T7 – Overcharge: Charge at twice the recommended current for 24 hours (secondary batteries only)
T8 – Forced Discharge: Same as T7, forced discharge with primary and secondary cells.


Reputable battery manufacturers do not supply Li-ion cells to uncertified battery assemblers.

I assume your concerns are liability. You need to do your due diligence to ensure you are buying safe products from a reputable supplier. To do otherwise would be negligent and significantly increase vulnerability. It's not cheap or easy for someone to sue you so if you do your job right you should be okay. Buy only from a reputable manufacturer and document your due diligence.


You may be better off with NiCd

Depends on if the capacity required is available in small enough pack.
May improve efficiency, 1.2v/cell gives you more input options. 2.4/3.6/4.8

  • Safest most rugged
  • Can withstand charge abuse
  • Ultra-fast charging
  • Long shelf life
  • Economical, lowest cost per cycle
  • Wide range of size and performance
  • 1.2v/cell can get 4.8v pack
  • No transportation regulations

NiMH

Differences compared to NiCd

Cons

  • More delicate than NiCd

  • Longer charge time

  • Less over charge tolerance

  • Less life cycles 300-500 vs. NiCd 1000

  • 50% higher self discharge 30% vs 20%

  • Slightly higher internal resistance

Pros

  • Improved memory

  • Higher capacity

  • Higher specific energy 60-120 vs 45-80

  • Less maintenance

  • Available in AA and AAA cells

\$\endgroup\$
9
  • \$\begingroup\$ Thanks, that clears things up a lot. A followup question: How safe is safe? Is there a common metric used in the industry, i.e. "expect 1 in 10,000 units to fail"? Or is the fact that something meets IEC standards all I have to go on? \$\endgroup\$
    – user135797
    Mar 17, 2017 at 1:43
  • \$\begingroup\$ @Matt24 I think the number is like 1 in 200,000 fail. They are safe, you just have to cover yourself and make sure you are buying reputable batteries. Here is a link to a site with lots of info: batteryuniversity.com/learn/article/safety_concerns_with_li_ion \$\endgroup\$ Mar 17, 2017 at 2:53
  • \$\begingroup\$ @Matt24 So you think you can power the device? That 5V Vin was a tough problem. It is much easier to use 3.3 or 3.6 and put the LEDs in series. That circuit I posted a couple of days ago was not easy to come up with. \$\endgroup\$ Mar 17, 2017 at 3:02
  • \$\begingroup\$ Still working on it. My current prototype uses 3.6V NiMH batteries, which work fine, but they're expensive and I have to include a special charger with them which is also expensive. The ease of recharging via USB will go a long way towards making the product desirable, but there are a lot of tradeoffs to consider. Safety of the design is priority #1 so I'll end up using NiMH if I can't be reasonably certain LiIon is safe. \$\endgroup\$
    – user135797
    Mar 17, 2017 at 15:49
  • \$\begingroup\$ @Matt24 You may want to consider NiCd, see my updated answer. \$\endgroup\$ Mar 17, 2017 at 17:03

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service and acknowledge you have read our privacy policy.

Not the answer you're looking for? Browse other questions tagged or ask your own question.