Converter In-Rush Thermistors etc, UPDATE -4
UPDATE on 17 Nov, Update 2 on 22 Nov, Update 3 on 16 Jan 14, Update 4 on 19 Oct 14. --------------- In a recent thread there was mention of how you can wreck your gizmo (in my case a converter) ...
Forum Discussion
BFL13 wrote:DryCamper11 wrote:
.............. You then plug in the assumed inrush current into a formula for minimum R.
Choosing an R above the minimum is OK. Below the minimum, you risk failure at turn on.
DryCamper11 was going from vague memory there (18 Nov), but now I can tell what he was talking about, wrt those two lesson plans, etc.
This relates to my current puzzle over the meaning of "minimum."
He and Ken seem to contradict the lesson plans where with 5.7 calculated they went with a 5 and with 1.2 calculated, they went with a 1. Ken says with 3.4 to go higher and use the 5.
I looked at the lesson plan here:
http://dkc1.digikey.com/us/en/tod/Ametherm/Choosing_NTC_Thermistor_NoAudio/Choosing_NTC_Thermistor_NoAudio.html
They calculated 5.7 ohms minimum and went with a 5 ohm device. They don't say why they went with less than the calculated "minimum," but read the next page. They calculate 7.94 ohms and select 10 ohms.
AFAICT, the reason they went with 5 ohms in the first example is just that it was close enough to the "minimum" given the tolerances and limits on their assumed numbers used in the calculation. However, when they calculate 7.94 as a minimum, they go up to 10 ohms.
Getting this "minimum" definition clarified would tell me whether, with a 3.4 calculation I should use a 4 or 5 or whether I could use a 2. ( If going with Ken's low size amps where that 3.4 came from)
Can anybody help with that definition of "minimum" business? Thanks.
If you calculate a minimum of 3.4, then you should not use 2 ohms. You should use at least 3.4 ohms.
