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  1. duke37

    Battery charger gismo

    My brother has given me a very unenthusiastic battery charger to look at. I have evicted the spiders and brushed out the chaff. There is no name or model, it is labelled 6 Amp and has a 6V/12V switch. It does not have an ammeter but has 6 leds. The main charging circuit has a bridge rectifier...
  2. duke37

    Is there a chance to get blind or serious physical damage while prototyping ?

    One hazzard which has not been mentioned is when snipping component legs. I always put my thumb over the leg to stop it flying. It also has the advantage that I do not have to grovel to find them.
  3. duke37

    Is there a chance to get blind or serious physical damage while prototyping ?

    Diconnecting a soldered wire from a tag strip can flick a blob of solder. I had a burn close to my eye, this taught me a lesson and I always wear glasses when soldering. These days they will be reading glasses.
  4. duke37

    I can't explain this by myself...

    I am somewhat at a loss here. The components will fail either from excess current or voltage. The rectifiers are unlikely to have excess current so that leaves excess voltage. In order to limit the voltage on fet switch off, there must be close coupling between the drain connections. It looks...
  5. duke37

    I can't explain this by myself...

    Comments The battery is connected the wrong way round. Diodes VD1 and VD2 do nothing. I assume these are just drawing errors. Is the frequency high enough to stop the transformer going into saturation? Is the primary bifilar wound? Is the frequency low enough to keep the dissipation in the...
  6. duke37

    Replacing paper capacitors

    There has been much discussion on this topic on vintage-radio.net/forum/ Paper capacitors would be replaced by polyester or polypropylene capacitors, just make sure the voltage rating is adequate. New capacitors will have different preferred values from the old ones. Just chose the nearest one...
  7. duke37

    Why put MOSFET's on negative side vs positive of motor

    You can use a P channel mosfet to switch the positive supply but the input is reversed, 0V gives no current for n channel but full current for p channel. Also, your positive line can be up to 60V which is more than what the base/ source of the P channel can stand so extra components would be...
  8. duke37

    Can someone help me figure out what i'm looking for?

    Nein
  9. duke37

    T Type Thermocouple for delta T measurement

    You are correct that you do not need and should not have any cold junction compensation. To get temperature just take voltage (µV) and divide by 39. To get an idea of accuracy, measure the resistance of the thermocouple and find a resistor somewhere near. Pass a known current through it and...
  10. duke37

    simple fm receiver

    A two transistor bistable circuit looks to have each transistor in saturated mode but they always work. This circuit is similar but I think it should run with two oscillating frequencies. The first controlled by L and C and the second one controlling squegging using the output capacitor as the...
  11. duke37

    T Type Thermocouple for delta T measurement

    What do you mean by delta T. Do you wish to measure the temperature difference between two position or the temperature change at one position. To measure the temperature difference of two positions, put a junction in each position and balance one voltage against the other. To measure a...
  12. duke37

    3 phase stray voltage

    You need to get it sorted by a competant electrician. I know of a case in Shropshire where most earthed devices were at 80V. It stopped the sheep shearing. The neutral and earth were bonded correctly in a PME (phase multiple earth) system but here there was only one earth. The problem was a...
  13. duke37

    adding a start capacitor to a circuit

    Kris The problem is that you need the torque to start. My brother has an air compressor that was fed by a long cable. It would turn until the piston started to compress the air and then stall, it was moved to the other side of the road so that the cable was much shorter. The thermistor would...
  14. duke37

    adding a start capacitor to a circuit

    An induction moter takes 6 or 8 times its full load current to start. There is not much you can do about this particularly if the load has peaks in the torque requirement. I have used a start resistor to limit current on an organ blower motor but here the torque was negligible at low speeds. It...
  15. duke37

    simple fm receiver

    As I said in #6, the BF255 is not as agile as the BF199 by a factor of 2 0r 3. You could try tuning the circuit to a lower frequency to see if it will work or get super fast transistors. The antenna loading will be critical. Circuits such as this which need to be set up optimally are not the...
  16. duke37

    Evaluating a cap. power supply in LTSpice

    The positive half cycle starts at 0V and peaks at 14.4V Edit 14.14V The led needs a voltage of say 2.5V to turn it on so the current starts when the input is 2.5V and peaks when the input is 14.4V. At the peak there is 11.6V to drop across the resistor. If 330 ohm is used, the peak current will...
  17. duke37

    Evaluating a cap. power supply in LTSpice

    You can replace D1 with another led. Make sure it is connected the right way round and each led will protect the other. Two for the price of one!
  18. duke37

    simple fm receiver

    My eyes are dim and I cannot see if the diagram needs a 5V or 3V supply. I think it is 3V which matches your battery so should be OK. I do not have the BF255 connections to hand, look these up and check if you have them correct. Too short an antenna will give low sensitivity. Too long an...
  19. duke37

    Digital programmable CDI ignition for 2-stroke engines

    You can not decide on components until you have the circuit, then you will need to make a test to see if it works as expected and then modify as required. If you are going to use capacitor discharge ignition, then you could read "Power Supply Handbook" by John Fielding ISBN 1-905086-0 EAN...
  20. duke37

    Norslo relay Help! Replacement

    Dan "Why not say so?" They printed 24V- (dash). The convention is = for DC. They could also have printed DC. Why not? 24V relays are very common, I have a box full here, some new, some second hand. They mostlly have the continental base. Perhaps one would be suitable.
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