Recent posts
#31
General Radio Discussions / Li-Ion battery thermal runway ...
Last post by DU2XXR - Nov 12, 2023, 03:19 AMhttps://splash247.com/how-one-handheld-radio-ripped-a-ships-bridge-apart
QuoteThe National Transportation Safety Board (NTSB) in the US has issued its report into the blaze on the bridge (pictured) of the crude tanker S-Trust 12 months ago. Investigators determined that the probable cause of the fire was the thermal runaway of one of the cells in a lithium-ion battery for a UHF handheld radio.
The S-Trust carried 20 ultra-high frequency (UHF) handheld radios for the crew to use to communicate during vessel operations. The two radios assigned to the bridge were a Motorola DP4400e radio (pictured), which used a lithium-ion battery, and a Motorola GP328 radio, which used a nickel-metal hydride battery.
Investigators found the remains of three batteries – one nickel-metal hydride and two lithium-ion – on the communications table. The single nickel-metal hydride battery was intact; one of the lithium-ion batteries was found intact in the remains of the chargers. Investigators only found components of the second lithium-ion battery.
Lithium-ion battery cell explosions are typically caused by a thermal runaway. An initial orange flash and puff of smoke caught on video feed at the time of the accident (see below) was likely the result of one of the missing lithium-ion cells exploding due to a thermal runaway.
#32
General Radio Discussions / Repeater etiquette
Last post by DU2XXR - Nov 11, 2023, 09:50 PM #33
General Radio Discussions / Handling the traffic net
Last post by DU2XXR - Nov 07, 2023, 12:28 AMI handled my club's 2 meter net call tonight after several years of hiatus, and in an impromptu manner (since the original NCS had technical difficulties). Some things I did differently:
I think this is one good way of elevating our nets into actual traffic nets, so that clubs and groups can effectively direct and manage traffic. Thoughts?
- Called only club members during the first half+ of the net and prioritized those with traffic to share with the rest of the club (announcements, messages). Reiterated the traffic to ensure it was understood and to ensure the listeners also understood it. All messages were duly logged for public to see (on the dx1arm.com website).
- Acknowledged non-club members who stated their callsign, but advised them that NCS will call on them for their turn after the members' traffic exchange.
- Called for priority or urgent traffic at any time of the net and not only during the start (because emergencies can happen anytime).
- After the members' traffic exchange, for the remaining 15 minutes or so, NCS then called each non club member for their turn to share traffic if any, and logged these as well (or the lack of traffic). Also called for additional checkins. Expressly thanked those who waited for their turn to share their traffic.
- Instead of late checkins, only called for priority traffic toward the end of the net (~3 minutes before closing).
- Ended the net on time, because there was no purpose of "late checkin" unless there is priority traffic to be shared. It is understood that everyone listening to the net is a part of the net.
I think this is one good way of elevating our nets into actual traffic nets, so that clubs and groups can effectively direct and manage traffic. Thoughts?
#34
General Radio Discussions / Re: GENERAL AMNESTY FOR UNREGI...
Last post by DU2XXR - Nov 02, 2023, 06:13 PMForm attached.
#35
General Radio Discussions / FREQUENCY BAND ALLOCATION AND ...
Last post by DU2XXR - Nov 02, 2023, 01:29 PM #36
General Radio Discussions / Ham Radio Operators’ Ionospher...
Last post by DU2XXR - Nov 01, 2023, 04:03 AMhttps://hackaday.com/2023/10/31/ham-radio-operators-ionospheric-science-during-the-solar-eclipse/
QuoteThe Earth's ionosphere is the ionized upper part of the atmosphere, and it's also the most dynamic as it swells and ebbs depending on whether it's exposed to the Sun or not. It's the ionosphere that enables radio frequency communications to reach beyond the horizon, its thickness and composition also affects the range and quality of these transmissions. Using this knowledge, a group of ham radio operators used the October 14 solar eclipse to crowdsource an experiment, as part of the Ham Science Citizen Investigation (HamSCI) community.
A solar eclipse is an interesting consideration with ionospheric RF transmissions, as it essentially creates a temporary period of night time, which is when the ionosphere is the least dense, and thus weakening these transmissions and their total range. As with previous solar eclipses, they turned it into a kind of game, where each ham operator attempts to contact as many others as possible within the least amount of time. Using the collected data points on who was able to talk to whom on the globe, the event's effect on RF transmissions could be plotted over time. For the August 21, 2017 solar eclipse, the results were published in a 2018 paper by N. A. Frissell et al. in Geophysical Research Letters.
One points which they wished to examine during the 2023 solar eclipse were the plasma bubbles that form near the Earth's magnetic equator, in regions like Brazil. These plasma bubbles cause a lot of interference, which in the preliminary data can be seen as a clear Doppler shift of the signal due to the diffusion of the ionosphere as the eclipse's effect took hold. For the next lunar eclipse in April 2024 another experiment is scheduled, which will give even more ham radio operators the chance to sign up and contribute to ionospheric science.
#37
General Radio Discussions / HX-4S-F30A LiFePO4 balancer po...
Last post by DV1YKL - Oct 20, 2023, 01:05 PMWhile building a 4s LiFePO4 pack, I noticed a potential design flaw while trying to characterize the BMS behavior. As it turns out, there seems to be a design flaw in the BMS circuit.
There have been documented issues with the BMS for li-ion/lipo chemistries where the HY2213 balance chip's release voltage (4.19V) is still too high for the DW01 charger chip's overcharge release voltage at 4.05V.
For the LiFePO4's case, it seems as if the manufacturer swapped the DW01 chip with the FM2112 chip for a more appropriate overcharge voltage of 3.75V and release at 3.6V, but failed to replace the HY2213 balance chip. Once one of the cells reaches 3.75V, the charger stops. But, since the balancer still activates at 4.2V and releases at 4.19V, the cell never gets balanced back down to the overcharge release voltage.
As a result, one cell gets charged to 4.2V and the rest stays unbalanced.
Quote1. When any cell is full, the BMS stops the chargerfrom stackexchange
2. While the charger is off, the BMS removes some charge from the cell with the highest voltage
3. After that voltage drops sufficiently, the BMS restarts the charger
There have been documented issues with the BMS for li-ion/lipo chemistries where the HY2213 balance chip's release voltage (4.19V) is still too high for the DW01 charger chip's overcharge release voltage at 4.05V.
For the LiFePO4's case, it seems as if the manufacturer swapped the DW01 chip with the FM2112 chip for a more appropriate overcharge voltage of 3.75V and release at 3.6V, but failed to replace the HY2213 balance chip. Once one of the cells reaches 3.75V, the charger stops. But, since the balancer still activates at 4.2V and releases at 4.19V, the cell never gets balanced back down to the overcharge release voltage.
As a result, one cell gets charged to 4.2V and the rest stays unbalanced.
#38
APRS, Winlink & Packet Radio / APRS to NTS
Last post by DU2XXR - Oct 17, 2023, 09:58 PMhttps://nts2.arrl.org/ntsgte-an-aprs-nts-gateway/
NTSGTE: an APRS-NTS Gateway
You can now use an APRS to send a radiogram through the NTS gateway. NTSGTE is an APRS information service that receives radiograms and forwards them on to the Digital Traffic Network. Radiograms are then relayed on as usual. This service can be useful in situations where you need to send a radiogram but are unable to check in to a traditional NTS net.
NTSGTE: an APRS-NTS Gateway
You can now use an APRS to send a radiogram through the NTS gateway. NTSGTE is an APRS information service that receives radiograms and forwards them on to the Digital Traffic Network. Radiograms are then relayed on as usual. This service can be useful in situations where you need to send a radiogram but are unable to check in to a traditional NTS net.
#39
General Radio Discussions / Eclipses do odd things to radi...
Last post by DU2XXR - Oct 07, 2023, 11:42 AMQuoteDuring the American solar eclipses of October 2023 and April 2024, hundreds of radio amateurs will take to the airwaves. Their goal is to help scientists investigate what happens to radio signals when the Moon blocks the Sun.
https://www.bbc.com/future/article/20231005-eclipses-do-odd-things-to-radio-waves-to-learn-more-an-army-of-american-amateurs-will-broadcast-during-the-next-ones
#40