Search results

Search Forums New Posts
  1. duke37

    Lead-Acid BATTERY-Negative tab rotten& Chapped. Whyy ???

    Some batteries have lead alloy plates for strength. Batteries for static use have pure lead plates. In the latter case, the gunge can only be lead sulphate.
  2. duke37

    Need help with a PSU schematic

    I would think that C9 and C10 are OK. Are they not feeding as voltage doublers? The normal voltage doubler is half wave, this would be full wave. I know because I have a gold star !
  3. duke37

    question about RC range

    A big antenna will beat a little antenna but it must be designed, tuned and matched to the transmitter correctly. Do you have the equipment to do this? If you change the power supply, make sure that the polarity is correct, otherwise by, by tx/rx.
  4. duke37

    Variable current limited Power Supply

    Here is a sugestion to reduce the possible current limit. The voltage at the base of Q2 is raised by the emitter/base voltage of Q5. This means that Q2 will turn on as soon as Q5 base is raised a little. I have put a led in the collector of Q2 but thinking about it, this may inhibit the...
  5. duke37

    Variable current limited Power Supply

    A pnp transistor emitter follower between the sense potentiometer and Q2 could raise the base voltage by 0.7V so getting down towards zero current would be possible I need to hoe the garden but could post a sketch if you want.
  6. duke37

    Variable current limited Power Supply

    Good point Chris. It looks as if a redesign is necessary.
  7. duke37

    How does gain apply in diff op amp?

    The gain is -2 rather than +2 since it is an inverting amplifier. I missed point 6 because of the complicated post before and after it with many irrelevant decimal points. The + input (1.5V) is the reference point. The - input voltage is 0.5V more than this so the output voltage will be 1V...
  8. duke37

    Variable current limited Power Supply

    Q1, Q3 and Q4 may have some leakage and there are no emitter/base resistors to help shut them down. Q2 needs to be turned on to shut the output triple down, therefore there must be at least 0.7V across R1. I = V/R = 0.7/0.5 = 1.4A
  9. duke37

    How does gain apply in diff op amp?

    We were here only a short time ago, look up the previous thread. The gain is -2, offset by 1.5V. The + and - input will be at 1.5V. Ri drops 0.5V. The same current goes through another resistor of double the value so will drop 1V. 2V - 0.5V - 1V = 0.5V
  10. duke37

    Lead-Acid BATTERY-Negative tab rotten& Chapped. Whyy ???

    The potentials are the same, charging or discharging. An interesting case of differential corrosion is season cracking (stress corrosion cracking) which caused great problems when brass bullets were stored in stables in India and the ammonia attacked the grain boundaries and the bullets...
  11. duke37

    Historic Item repair

    I do not have the CV transistor equivalents, possibly oc45, OC81D and two OC81. You will not get much audio power out of this, about the same as a small transistor battery radio. The suppressor circuit should have its switch closed. Measure the voltages on the transistors to start and...
  12. duke37

    Historic Item repair

    The first thing to do is to get a circuit diagram (schematic) to know what the components do. It appears to be a transistorised amplifier from the 1950s The most likely faulty components are the capacitors. These can be disemboweled and filled with newer, smaller capacitors.
  13. duke37

    What is this capacitor?

    The capacitor marked 105 should be 1uF. I do not see how you get 1.9uf on either unless the capacitor is leaking and upsets the meter reading. What are the dark marks on the big one?
  14. duke37

    Alarm reset timer

    I've had another thought, that is the second this week. With a LDR in the circuit, perhaps the detector is intended to be inhibitied in daylight. The LDR will be low resistance in daylight and it could be tried with the LDR shorted. If this works to stop the alarm on switch on, then Kris's...
  15. duke37

    Lead-Acid BATTERY-Negative tab rotten& Chapped. Whyy ???

    1. The weld material will be different to the base material. (Stress, grain size etc.) It seems to be more susceptible to galvanic corrosion. 2. The battery changes its plates from lead sulphate to lead and lead oxide when charged. If the battery is not kept charged, the lead sulphate becomes...
  16. duke37

    Alarm reset timer

    I had a look for time delay relays and the ones I saw were horribly expensive. As to Kris's suggestion that the alarm would be delayed, this could be obviated by pulling in the relay with a time delay after the power comes on and running it continuously. The modification that Kris suggests...
  17. duke37

    Lead-Acid BATTERY-Negative tab rotten& Chapped. Whyy ???

    The white gunge will be lead suphate, possibly formed if the battery has not been kept charged. Lead and lead sulphate are poisonous as is sulphuric acid. Take the battery to a recycling centre where it can be disposed of safely.
  18. duke37

    solution to soft start an ac induction motor

    I have used a resistor, shorted out with a relay after about a second. The resistor needs to be a few ohms and many watts. The timing can be done with a rectifier, resistor and capacitor. I do not see how this will work with a direction switch, perhaps a current transformer could be used...
  19. duke37

    Inverting input greater than non-inverting input = positive voltage?

    Look at it another way. The 324 if operating correctly will have 1.5V on both inputs and will take no input current. With 2V input there will be 0.5V dropped across the 10k resistor. The same current goes through another 10k resistor so you get another 0.5V drop and an output of 1V. The...
  20. duke37

    3W IR LED isn't very bright?

    Insults never did anyone any good, why do you do it? The article *steve* pointed to was not typed by someone else, it was typed by *steve*. The current should be determined by the power supply and the resulting voltage will be determined by the led. This is the opposite of what normally...
Top