From: Bdale Garbee Date: Thu, 27 Apr 2023 18:33:38 +0000 (-0600) Subject: add an FAQ section with one answer for now X-Git-Url: https://git.gag.com/?p=web%2Faltusmetrum;a=commitdiff_plain;h=c4d4688179dcec6376a32309ea6869e30ed9c488 add an FAQ section with one answer for now --- diff --git a/FAQ.mdwn b/FAQ.mdwn new file mode 100644 index 0000000..df8333e --- /dev/null +++ b/FAQ.mdwn @@ -0,0 +1,7 @@ +[[!meta title="FAQs"]] + +# Frequently Asked Questions + +[[!inline pages="./FAQs/* and !*/Discussion and !*.ihx and !*.sh and !*.html + and !*.bz2 and !*.zip and !*.exe and !*.dmg" show="10" rss="no" raw="yes" ]] + diff --git a/FAQs/pyro_current.mdwn b/FAQs/pyro_current.mdwn new file mode 100644 index 0000000..02777a1 --- /dev/null +++ b/FAQs/pyro_current.mdwn @@ -0,0 +1,35 @@ +# What's the maximum current a pyro channel can handle? + +Older Altus Metrum products used Vishay Si7232DN FETs as switches. They are +rated for 25A continuous, 40A pulsed. Newer products use Taiwan Semiconductor +TSM200N03D FETs which are rated for 20A continuous, 80A pulsed. In pyro use, +we're closer to the pulsed rating than continuous. However... + +Please note that Ohms law applies. Whatever your battery voltage is and +whatever your e-match or other device's resistance are will limit the +actual deliverable current. With a single-cell LiPo battery, the fully +charged voltage is 4.2 volts, and a feature of LiPo batteries is that +they have very low source resistance, so we can mostly ignore it. A +typical e-match has 1.0-1.7 ohms depending on the wire length. The FET +on resistance is less than 20 milliOhms, so we can basically ignore +that, too. Only the resistance through wiring and the match matters. +So, by Ohms law, E = IR, I = E/R or 4.2/1, meaning the most current you +can deliver to the pyro element is 4.2 A. + +A typical commercial e-match fires in about 13 microseconds under these +conditions, which is why we think 50 milliseconds is .. a very long time! + +You'd think moving to a 9V alkaline would allow you to deliver 9A, but +it doesn't really work that way. Unlike LiPo batteries, Alkaline cells +have a very high source resistance and their current producing ability +is nowhere near linear. + +If you're using a programmable pyro channel on Altus Metrum products that +include that capability (TeleMega, EasyMega, EasyTimer) to do something like +turn on other electronics, there is an additional consideration. The screw +terminal strips we use can handle large peak currents, but are only rated +for a maximum of 6A continuous current per screw. This means the best plan +if you need to switch something power hungry is to include a high-current +FET switch in your electronics, and use our FET to switch just enough current +to control it. + diff --git a/index.mdwn b/index.mdwn index 19fd061..ea8f912 100644 --- a/index.mdwn +++ b/index.mdwn @@ -35,6 +35,8 @@ Bdale's online store has a form you can use to # [Latest News](News) # +# [Frequently Asked Questions (FAQs)](FAQ) # + # Where to Buy the Hardware # Altus Metrum products are available directly from