Sip>
I've worked in the UK and know about this. Phil hasn't and might not.
Slow blow doesn't mean that they they can't get damaged by repeated spikes.
You can say what you like - I'm infinitely more worried about Phil's claim that I've got it wrong, which isn't all that worried. You merely are the dimmest of dim jerks.
Nonsense. I've never even heard of a mains fuse being damaged by spikes in the supply line. Fuses shrug off that kind of thing indefinitely. Then to go further and claim that a surge in current in the 13V supply to a 4W amp IC can damage the mains fuse over time is quite frankly ludicrous.
If I'm the dimmest dim jerks but correct in dismissing your claim, then that doesn't say much for your level of expertise in this area.
Googling 'F2887103' (- in the Yaesu FT-763R transceiver) gives you all the info you'll ever want about R30, in this 30yr old device.
RL
A piece of gear that has a 12 volt internal power supply and some loads should not have giant current surges; the supply should ramp up at some sensible rate and current limit.
We do expect huge surges, visible sparks, when a live external DC supply, a battery or a wall wart, is plugged into our box. That's worth thinking about.
Warts can also be the wrong voltage - they all look alike - or even, rarely, the wrong polarity.
indefinitely.
And you've never heard that climate change is real and CO2 levels really are rising. You should have done but you've worked out how to close your ears to information you don't want to hear.
This is coming from the guy who prefers to believe crap CO2 level measurements from the 1890's to Charles Keeling's serious CO2 monitoring that started in 1958. Stuff has got to be frankly ludicrous before you'll even begin to take it seriously. Fuses do fail for no obvious reason from time to time and cumulative damage from spike loads is as good an explanation as any.
Big if. You really are the dimmest of dim jerks and you really are unlikely to be correct in this particular instance. You certainly don't make a habit of getting stuff right.
My search returns variations of three webpages: a 2016 ad for an audio board for sale, an Austrialian ham who replaced his audio board because R30 failed open, and a Yaesu FT-736R Operating Manual. Info about the purpose of R30 is wanted. But my search returns no pertinent info. A lack of disclosure about design details doesn't surprise me. Given a vendor's typical reluctance to share such specifics.
Danke,
Same here. That suggestion was a waste of time.
I've no idea what the main inrush limiter is in the transceiver. Regardless, the resistor will limit inrush current to the cap at turn on (assuming of course that the cap is discharged at that time). And that repetitive inrush current stresses the resistor. There may well be other circuitry to handle inrush to the transceiver, but the fact remains that the discharged 2200uf will try to draw enormous current through R30 from the 13.8 supply. If we assume worst case no other limiting, 14V input, R30 exactly 1 ohm and no other resistance, R30 will limit current to 14 AMPs max, reducing exponentially with time until the cap is ~fully charged in 11 ms. (Or until R30 fails). You know all that, but other readers may not.
Actually ~.2 J not ~.4 J. Even so, the R lasted ~35 years in spite of being under sized. And it _is_ too small based on what the schematic shows. Apparently that is a known failure point in the FT 736.
Ed
Maybe not in general, but I've got you this time, Bill. You made a stoopid observation and now you're trying to cover your tracks by diverting the subject into climate change. That won't wash. You've been exposed as a bullshitter once again.
On 2023-08-14 16:43, ehsjr wrote:> On 8/13/2023 6:31 PM, Phil Hobbs wrote: >> ehsjr snipped-for-privacy@verizon.net wrote: >>> On 8/13/2023 12:58 PM, Cursitor Doom wrote: >>>> On Sun, 13 Aug 2023 12:51:09 -0400, legg snipped-for-privacy@nospam.magma.ca> wrote: >>>>
Right you are, 1/2 CV**2. My bad.
Because it's not actually seeing that big an inrush.
It's unlikely that a 1/4 W film resistor is going to survive having even
200 mJ dumped into it in a couple of milliseconds. For instance, the graph on P. 5 of this datasheetCheers
Phil Hobbs
--------------------------------------
** Overcurrent pulse failure of R30 requires the 13.8V DC supply to appear very suddenly - as with "hot plugging" a battery or external DC supply to the DC socket on the back of the radio. Also hot plugging that audio PCB onto the internal DC rail would do the same. Normal mains on-off cycling would not be likely to do such damage as it takes a short time for the internal DC rails to rise to full voltage. Maybe helps explain the reported 35 year delay....... Phil
Of course pulse-withstanding resistors exist. They’re commonly used with large caps to get the right ESR to stabilize a voltage regulator, for instance. (*)
But that piddly axial thing at R30 ain’t one of them.
Cheers
Phil Hobbs
(*) Putting the resistor in series with the cap preserves the load regulation, and to survive an output short it has to be a pulse-rated type.
Except that it wasn't a stupid observation, and we'd got onto your credibility which is essentially zero because of your enthusiasm for to touting attention-getting nonsense. Your enthusiasm for climate change denial is the obvious example. but your enthusiasm for telling us about the globalist conspiracy and George Soros isn't far behind.
Back in your box.
Not as big a waste of time as discussing repair methods with CD on SED.
RL
On 2023-08-15 10:11, Don Y wrote:> On 8/14/2023 7:45 AM, Phil Hobbs wrote: >>> The boards don't have to be particularly sturdy as >>> they will be supported completely by their undersides. >>>
Dirt cheap, solder mask and silk screen optional, PTH also optional. We built some breakout boards for prototyping.
(Small rectangular pads on a grid of 0.5 x 0.65 mm are super useful too.)
Cheers
Phil Hobbs
You are right, of course. We don't know how much R30 actually "sees" - wire/trace inductance and resistance, power supply "ramp-up" time, other factors(?) that limit the current are not known.
It's the repetitive surges over time (~35 years in this case) that probably killed R30, not how much current 1 ohm limits in a single event (to paraphrase the question).
It does beg the question (the answer is, "you'd have to the designer") "why those values for the low pass filter?"
Maybe they had a boatload of 1 ohm 1/4w R's on hand. I dunno.
Ed
Yep. I'm sure that axial TH resistors exist but we rather use SMT cuz when you get one wrong, almost always guarranteed to get all of them wrong :)
We specify all resistors 100 Ohms and below (usually) to have a decent pulse rating like, 50 watts per ms for gate drive etc.
Even the so called zero Ohm resistors are specified to be 20 milliohms which break a lot. I try to design those out if I know I won't be using a real part there in the future because of the unreliable nature.
boB
I saw a data sheet for a zero ohm resistor that specified the value to be ±10%.
I'd like to see them do the calculations on that one!
After kicking this around in a FT-736R forum someone mentioned how R30 looks like a decouple. And it seems on the money, to me.
A quick glance at the UPC2002H datasheet App Notes
does not reveal any hints as to the purpose of R30.
Regardless, Figure 7 in AD's MT-101 TUTORIAL Decoupling Techniques
shows a small series resistance close to an IC power line as a way to reduce Q. The tutorial goes on to say:
However, a decoupling network composed of a 100 μF capacitor and a 1 μH inductor resonates at 16 kHz. Left unchecked, this can present a resonance problem if this frequency appears on the power line. The effect can be minimized by lowering the Q of the circuit. This is most easily done by inserting a small resistance (~10 Ω) in the power line close to the IC, as shown in the right case. The resistance should be kept as low as possible to minimize the IR drop across the resistor. An alternative to a resistor is a small ferrite bead which appears primarily resistive at the resonant frequency.
Long story short, decoupling seems to be the purpose of R30.
Danke,
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