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Posts posted by flippityflop

  1. are there any advantages/disadvantages to using an auto-ranging DMM such as this?


    i would expect that they are not as responsive as regular DMMs... but then again if you need to measure rapidly changing signals, you might as use other means or equipments, like say a low bandwidth oscilloscope would do. also, the hobby electronics i'm into have signals that are pretty constant, except on audio applications...

    i've also gathered (not  sure about this) that auto-ranging DMMs don't get overvolt-ed or overcurrent-ed, unless the very maximum limit is reached; unlike regular DMMs, where there is a possibility of overvolt-ing or overcurrent-ing IN EACH RANGE... can anybody confirm this??

    so are there any disadvantages??

    i'm asking as i was going to buy an auto-ranging DMM. but arrived at the store closed so i went to another store, and bought a non-ranging one... now i have buyer's regret and i'm trying to rationalize why i settled for a non-ranging one.

  2. so i got this multimeter (the only one i have now), which i purchased about 8 years ago or so. i think WAS pretty good quality back then.

    throughout the years, every now and then, i would mismatch the probes to the multimeter function (volts, current, resistance). sometimes, i would first be measuring voltage, then current afterwards (properly switching the selector to the correct function), but leaving the red probe at voltage/resistance socket. ok... this could be harmless.

    but sometimes i would accidentally leave the red probe on the Amps socket when i would be measuring the voltage or resistance (with voltage being in the range of 16-32V)

    when i use it, *almost* everything seems to work fine. all the readings of the functions are consistent to each other (ohm's law). i have reliable power supplies and when i read the voltage using the multimeter, it confirms it. though it is about 3-5% higher than what it used to read before. i'm fine with that... but when i use the resistance function at ranges 200kΩ and up, even if no probes are attached, it shows a constant resistance of 36.6KΩ; going all for the 200kΩ, 2MΩ and 20MΩ ranges.

    i thought there could be just a shorted/busted resistor somewhere but visual inspection suggest it doesn't.

    do i need to replace my multimeter?

  3. i left this capacitor (http://www.digikey.ca/product-search/en?vendor=0&keywords=382LX123M100N082) outside and it rained. it was in an upside down position (as shown in the picture). it was like that as i soldered big gauge wires to it, as i sometimes use it to rectify high currents.

    there was very little white tarnish/oxides around the boundaries where the rubber and metal can meet. looks a bit of the metal oxidized due to the 1.5V difference. they happen to trace a path from the negative to positive.

    i took it back in as soon as i got out of bed. tested it with 1.5VAC again then +40VAC... seems to rectify just fine.

    as a precaution, i peeled off some of the plastic cover and then super glued the metal/rubber boundaries and then applied plasti-dip on it (pic attached).

    i measured with my LC meter and it was registering 11mF. labeled as 12mF... 8% deviation, and the specs say 20%, so good.

    but i'm still worried about internal shorting... how do i detect this?


  4. alright, i've set out almost exactly a year ago to build the 0-30V power supply in the project section (or at least a slightly modified version of it). well, a year afterwards i'm finally getting on with it (took me long enough, but i was preoccupied with other things).

    anyways, i'm building it in modular units so i can mix match and borrow sections for other projects. i'm assembling the dead easy rectifier unit (the diode bridge, capacitor and a small LC filter -- the filter just for kicks).
    as for the diode bridge i have 3 of these:

    i've always meant to use them in parallel, so to increase the current rating. i`ve tried 2 together in parallel, months ago and what it did was to overheat very quickly, so i unplugged it immediately. thankfully neither of the bridges burnt out. then that was the only time i decided to read up a bit and found out that a slight difference in voltage drop causes significant difference in heating and with NTC, ends to a slippery slope of over-currenting.

    but i happen to see this:

    would this work to increase the current rating as simply the sum of each bridge??

  5. i'm trying to find more uses for my current arc welder which has the specs of
    mode 1: 25V @ 50A and
    mode 2: 23V @ 70A
    (i forgot the cycles for each, but it's less than 60 secs or so)

    so i figure i'd modify it to also function as a mini spot welder... i'm targeting about 1.5-3V @ 750A max

    since my welder already ramps down the AC to above voltages, i figure it that there are other taps in the transformer that might go down pretty close to 3V.... well i opened the thing for the first time (and confirming my hunch that it's just one big transformer, as implied by it's low price 4 years ago), and found no other taps.

    so i'm thinking maybe buy another large transformer core, say one taken from a microwave oven, rewind it's coil (and having the secondary a much thicker gauge), then connect it to my old welder; bringing 23 or 25V down to 1.5V.
    but... i could've just connected the microwave oven transformer to the mains in the first place... like some diy-ers have done and blogged online.

    so which is better, connecting the microwave salvaged transformer to the welder transformer first (2 stage) or directly to the mains??

    would the other handle higher currents than the other configuration?

  6. i've got a 6V lead acid battery that i ripped off a portable CFL. i tried charging it with the old circuitry that it came with, but it won't get past the ~4V mark.

    then i tried charging it from a wall wart of 12V  with a max current of 1A. it was exceeding 1.5A when charging the lead battery, so i used some a voltage divider from some spare high wattage resistor that i got to lower the charging to around 7V @ 800-900mA. it got the lead acid battery to 4.83V. but after that it plateaus, no matter if i leave it charging for extended periods of time.

    i've never heard of lead acid batteries having memory effect, so i'm assuming that the battery is not in perfect condition. i have a welder that can supply 25VAC (@ 50A max, neither a constant voltage or current sourcew) which i can rectify and filter with a large capacitor... do you think using this 25VDC would bring it up to 6V that it originally were??

    i'm not gonna leave it for too long at that though, i'll keep a eye on it.

  7. Here's the service manual.  Everything can be fixed, the question is how hard is it to get the parts and is it worth it.

    yeah, already have a copy of that manual before i went here. i first checked the PSU and it SEEMS like it's in good condition. when i measure the output (if you  could cross reference it with the manual, pg 124), from ground (CP52), CP51 is 42.7V and CP53 is 41.7V. i'm not completely sure if CP53 is ok, as i don't know even what's "PSC" is supposed to be. but these are the measurements. no burning components.

    then i unscrewed the main board, inspected it (visually seems ok), then plugged it all back in (with the aforementioned FFC that got disconnected when i first disassembled, then connected the PSU. when i press the power button, there is very momentary LED lightup in the adjacent button used for checking ink levels, then never powers up. there's also a bit of a click in the PSU.

    the mainboard  has 2 power transistors. TO3034 and TO3043. (http://obrazki.elektroda.pl/2304073300_1362587659.jpg  <-- yey, seems like i'm not the only one that had problems with this printer, it's in russian, though). of the two the TO3034 (the one with a green stripe in the pic), is that one that's overheating and apparently where the faint smell was coming from. also noted that its soldered leads seems to have remelted, as it is silvery (unlike the leads of the TO3043) and the flux remelted too.

    i would be happy to hear if the problem was only with either the said 2 power transistors or the PSU. since, i think that only needs minor replacements.

    in case it was the power transistors, is there a possibility the ICs in the mainboard are fried too?? please tell me that the power transistors were shielding the rest of the mainboard so it's the one taking the damage.

  8. ---- PROLOGUE ----
    so i purchased a second hand Epson R280 for direct to PCB etch resist printing. it needs no modification at all, as you can simply put the pcb on the CD printing tray. eezy peezy... well, it's color balance is always off, but other than that i have no complaints.

    well, i was doing some adjustments. i had the copper clad piece taped down and the tape gets caught in the ink head and there were smudges. didn`t worry about it  since it`s happened before. so, to make sure that smudges have been cleared out, i tried printing on paper sheets. on the 3rd or so print, the paper wasn't loading properly. it was crumpling. i thought it was probably a small piece of paper or tape that got caught in the gantry or whatever. when i tried to print again, to make sure, it won't respond at all. so i did a more thorough check and saw a bottle cap in the paper loading tray.... (fcK!). with all the mess in my room, that wasn't at all that unlikely to happen.

    then i inspected the loading tray more carefully and somewhat figured that for the last time it loaded a piece of paper, the bottle cap got caught on the rollers and dislodged the rollers.
    ---- PROLOGUE ----

    now, this is the part that i shouldn`t have done... i disassembled it and figuring there wasn't going to be a problem, plugged in the power and turned it on. there slight buzz from the circuitry and then it suddenly turned off, followed by a faint smell. not a burnt smell, you know the smell when you open a new electronic gadget?? that sort. it won`t turn on again after that.

    then i checked and then saw that one FFC (Flexible flat cable) were not in the socket when i turned it on. i was careless (i was worked up by the fact that i might have wrecked this one permanently). it probably got pulled out when i was disassembling it.
    perhaps that fried the main board? then again, the FFC leads to the print head, so a disconnection there is unlikely to cause major damages. or would it??

    maybe i probably should`ve just re-lodged the rollers using pliers, without having to open the whole thing...

    what do you guys think? can this be fixed??

  9. The ballast makes 500V to 600V when the starter opens to start the light.

    i ripped an electronic ballast from a portable desk lamp that was going to be thrown away. i posted a question in yahoo answers where i mentioned measuring a voltage that goes up to thousand of volts (most likely AC, since it registers for both DC and AC, but goes higher than what my multimeter can take) ... it's most likely because i used an incompatible DC power supply.

    see, the old portable lamp had a wall wart providing 9V @ 1A. i have long burned that out in my electrochemical experiments... so when i tested the said ballast from the portable lamp with the 9W that i got from ebay, i used another wall wart which is 16V (from an old printer). that's probably why the voltage almost doubled (i was hoping it'll be pretty much the same). right now, i can't test any other DC supply (i haven't got to building my 0-30V variable power supply) and all wall warts i got here and there were all burned out from electrochemical experiments a long time ago. the only reason the 16V wall wart from a printer is still kicking is that it shuts off whenever it exceeds current ratings (well, it was from an HP printer)

  10. The photo on the ballast shows two CFL bulbs with 4-wires each. But your OLD CFL bulbs have only 2-wires each.

    i don't think you read through the listing page description:

    Lamp Configurations

           (2/1)  CFQ/M13W/G24q
           (2/1)  CFQ/M13/GX24q
           (2/1)  CFS16W/GR10q (2D)
           (2/1)  CFS10W/GR10q (2D) 4-pin lamp
           (2/1)  CFT9W/2G7
           (2)     CFT7W/2G7

    - it lists CFT9W and 2G7 together. google'd it and found CFT9W are  2-pins, while 2G7 are 4 pins. maybe it can accommodate (2/2) same types or two CFT9W and one 2G7 (2/1), so it has a total of 8 wires??

  11. you mean to say i should've gotten these ??:
    http://www.ebay.com/itm/321293131731  (36W)

    about $~28 total (price + shipping) -- hardly inexpensive. i wasn't just buying any CFL (which are around $~7 or so), these are UV lamps.

    well, the four 9W "old" UV CFLs that i bought were practically just a dollar each ($~6 total) and i thought finding the appropriate ballast was just easy peezy.

  12. i`m thinking of buying this ballast

    to power 2 of my 2pin 9W UV CFLs:

    it says it can drive two 9W CFLs at the same time.... but i wanna push it and probably drive more (maybe 4 in total??)... can it be cheaply done? maybe a separate starter for each new lamp added and then have them parallel for each output.

    i have a feeling the answer would be no, hey, i still gotta ask.

  13. so i got these 4 CFLs:

    they are 2 pin and i don`t wanna buy a ballast for each and i think we have a few busted screw-on CFL () in a box in our garage.

    so i thought i could just rip off the electronic ballast off the busted screw-on CFLs and then connect the 2 pin lamps there. just so happens, as i`ve read more into screw-on CFLs and what i saw as i opened one of them, is that they have 4 connectors that connect to the raw fluorescent tube itself... wired that way because integrated to it`s ballast is also a starter.

    i`ve read that the 2 pin CFLs that i got from ebay have their own starter, but a separate ballast (external of the lamp), that`s why they`re only 2 pin.

    so i was wondering how can i connect the 4-connector electronic ballast (with it`s own starter) taken from a screw-on, to a 2 pin lamp that i got from ebay??

    another option is ripping open the 2 pin lamp i got from ebay and then removing it`s starter and then connecting the 4-connector electronic ballast of a screw-on.

    but i haven`t actually opened a lamp to know if i can safely rip off the starter and end up with 4 connectors from it.

  14. so for the past 5 years i've been putting up with my lousy PC speakers that i bought from a thrift store. i've always wanted to replace them, both for reasons of better music listening and that it doesn't match with my overall black PC.

    i also want a long term device so i've always had my eye on high end speakers. the problem is, the good ones come in hundreds of dollars. so to save money and since i've always wanted to design my own sound system, i'm think i'm gonna build myself one step by step.

    i don't need a surround sound, quadraphonic must the most i'm gonna be stretching with the system (probably). but i'm gonna at least be having stereophonic speakers (with tweeters and mid range speaker in one enclosure) and a single sub-woofer. 40W is probably good enough for me and they should be able to plug in to S/PDIF, HDMI and 3.5mm (for portability... or maybe just use external adapters, i don't know...). since the 2 PAIR of tweeters and mid range speakers are gonna be sharing the same input, at least, i was thinking of having an active crossover inside the enclosure that separates the high frequency (2,000-20,000 Hz) and the mid-range frequency (300-5000 Hz), with very, very, very little loss of quality, then feed them to 2 pairs of amplifiers (high range and mid-range) to more accurately cover the range. the subwoofer would be in a bigger and separate enclosure, also able to take S/PDIF, HDMI and 3.5mm, but filter in only the 40-1000Hz range).

    i've never done anything like this steeped in audio electronics. so with "step-by-step" i meant that i just want, for now, to assemble the tweeters drivers and the amplifiers for it. i'll put the assembly in a small temporary enclosure, road test it for a few weeks. when i'm satisfied with it AND if i have the time, i'll assemble the mid-range speaker, it's amplifier and also the crossover that separates the high and mid frequencies. then the enclosure for the whole thing (i'll handle picking the correct enclosure design... gonna be hanging around diy audio forums for a while, then on to some carpentry). then i'll get on to assembling the sub-woofer after that.

    i'm doing this because it's something i can do incrementally and modify if on the way i change my specs. also, i'm not too big on dishing out big bucks then do the whole thing in one go.

    how does it sound?? realistic?? sound like i'm one of those "just-consumer" guys that think they know audio engineering (i admit i don't) and can build something cheaper for almost the same specs??

  15. so i bought this cheap portable device and it worked ok for the first week. then i started noticing it would get discharged more and more quickly, until it doesn't even power up. i reckoned that it was a battery problem. so i wanna replace it. i don't have any more spare li-po battery, but what i do have are a couple of AA-sized lithium ion batteries (3.7V). i want to solder an AA-battery holder, so i can simply swap the lithium ion batteries whenever they get discharged.

    my question is, if i where to leave the AA-batteries in and plug in the recharging cord, which is USB, rated 5V, would it also charge up the AA lithium ions, just like it charges the old li-po??

    assuming it does, can i charge (in parallel) more than 1 AA lithium ions?? i'm not sure about the current rating of the power charger for the portable device, so i might have to watch out for that...

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