Recent Posts

1

Beginners / Re: AC brushed motor, caps & inductors

« Last post by MarkT on Today at 07:51:52 am »

Many of the sewing forums advice is ‘just remove them, they were for the days of analogue TV & AM radio’.

Ignore that dumb advice - you might need to replace old caps that are failing, EMI suppression is more important today than ever, and excess arcing will destroy the motor over time as well as play havoc with EMI.

High frequency stuff coming off brushes usually only needs 1nF to 10nF Y2-class ceramic capacitor (*) to ground on each brush connection, but first ensure the motor body itself is securely earthed (+) and you have a 3-pin plug - essential anyway to prevent it being a death-trap.  Adding a ferrite to the motor lead next to the motor is another good mitigation measure for EMI.

(+) internal windings in motors can and do become detached, then shorting to the metal work of the motor, so all mains universal brushed motors needed to be properly earthed unless galvanically isolated from the rest of the machine.
(*) for instance: https://cpc.farnell.com/vishay/wko102mcpcj0kr/capacitor-class-y-1-0nf-400v/dp/CA05844

2

Test Equipment / Re: Ipm6300 Power Quality Analyzer - does anyone have one?

« Last post by Bakaman on Today at 07:49:45 am »

The device itself apparently detects transients as fast as 40us, which would seem to indicate that it is detecting fast peak transients like my Fluke 289.
I can set a threshold (5-99%) which vary by that amount from a particular rms voltage, and displays a time stamp and an H, L, or 0 for each event, and its duration in terms of supply frequency cycle counts.  Not much use in itself other than indicating that there was a swell, dip, or outage at that time - how big wast it? was it a peak voltage of 375v, or 575v?  Anyway, hopefully the device has also recorded more info with a number of samples for each event that I can save and view or analyse on a pc.
I know that I'm expecting a lot from a small cheap device, it might not do what I want which is OK.  There is no info in any help files, nor explanations in any manuals.
I just want to know if anyone has had better success in obtaining transient info out of this than I have.
Thanks.

3

Beginners / Re: how can I measure AC voltage of bridge diode on PCB of CRT TV?

« Last post by wasedadoc on Today at 07:49:03 am »

Your final paragraph is correct.

4

Projects, Designs, and Technical Stuff / Re: Searching for Decoder/Demultiplexer with Tri-State outputs

« Last post by Roehrenonkel on Today at 07:40:43 am »

Hi rfdes,

would the 74x538 work?

5

Beginners / Re: Beginner questions about resistors

« Last post by MarkT on Today at 07:37:07 am »

For 5, yes resistors overheat, but its a bit more subtle than that.  For instance in pulsed operation you can exceed the continuous power rating for a short time, since the average power over a few seconds is what determines the temperature reached (for smaller resistors that time is shorter, for larger, longer).  And in practice the maximum power rating will come with notes in the datasheet about the conditions in which that can be achieved (ambient temperature, adequate convection etc).

In practice you'd not normally run a resistor more than about 50% of its power rating without good reason as high temperatures lower reliability in the resistor and nearby components.

The factor by which you can exceed the rated power in short pulses depends on the resistor construction - metal thin-film resistors have a lower factor than carbon composition for instance - this data may not always be given in datasheets either.

And one factor worth noting is that resistors have a rated voltage too - this is to do with discharge across the surface of the device, smaller resistors have smaller voltage ratings.  You'd never use an 0402 surface mount resistor for 250V for instance, even if it was many megaohms.

6

Repair / Re: JBC SL-2300

« Last post by lionelkjh on Today at 07:33:32 am »

Good morning; if anyone has this model; could you give me detailed photos of the card??? Thanks in advance

7

Projects, Designs, and Technical Stuff / Re: A naive question about automotive CANbus sniffing and spoofing

« Last post by darkspr1te on Today at 07:29:08 am »

I dislike touch screens in cars, i like to be able to reach out and feel the button.
My quirks aside sniffing the subaru info-tainment bus is quite easy and has been done before , open pilot has a lot of the can codes too.
I had to do the same to make my JDM rav4 compatible with my android radios canbox, so a arduino and canbus adapter allowed me to sniff the bus, figure out the codes for ac controls and add that to the canbox adapter.
I have seen you can buy these adapters for subaru so chance are you can swap your OEM info system out for a Android model .




darkspr1te

8

Projects, Designs, and Technical Stuff / Re: Brinking Light pattern for maximum attention distance at night

« Last post by Wilson__ on Today at 07:28:45 am »

Is it better to use two colour flash or use single colour LED that has the highest mcd output? 

Different colour LED has different light output at same current.

9

Projects, Designs, and Technical Stuff / Re: I made a 50 ohm load with BNC connector, Is this correct?

« Last post by daisizhou on Today at 07:28:23 am »

Good idea, I've updated it

10

Projects, Designs, and Technical Stuff / Re: I made a 50 ohm load with BNC connector, Is this correct?

« Last post by daisizhou on Today at 07:27:31 am »

Usually I use 300Khz-750Khz。