Search results

Search Forums New Posts
  1. duke37

    Milwaukee sawzall repair

    You do not say where you are but, in the UK, it is necessary to bond all metal pipes, water and gas to an earth connection. Do you have different rules for the plumbing in you area? Any leakage should trip the supply. I say get it fixed. 'Accidents' are usually the result of several...
  2. duke37

    Milwaukee sawzall repair

    Any portable tool should be supplied through an earth leakage circuit breaker and more than 30mA leakage should trip the supply. You have two faults. 1. A supply which does not trip when there is a leakage. Get a professional elecritrician to check and approve it. 2. A tool which leaks...
  3. duke37

    Rail Gun

    The energy in a capacitor is C * V^2/2. 3 * 400 *400 * 22000E-6 /2 = 5280J N * 250 *250 * 400E-6 /2 = 5280J N = 5280 *2 /250/250/ 400E-6 = 422.4 say 420 This is all rather simplistic and the efficacy of the capacitors will depend on the resistances and inductances of the circuit.
  4. duke37

    Subwoofer: wacky volume = replace variable resistor?

    There is a diference between silicon and silicone. Silicon is a hard semiconductor, used as hard cubes in aluminium pistons as the rubbing component. Silicone is a compound often where silicon has replaced carbon. The spray you refer to seems to be a replacement to oil or wax to act as a...
  5. duke37

    Subwoofer: wacky volume = replace variable resistor?

    Never heard of white silicon. There are various makes of switch cleaner but I do not know the best. Servisol is often recommended. The squirt can I have came from a general shop selling all kinds of things. Some cleaners consist of a solvent and some also contain a small amount of lubricant...
  6. duke37

    Subwoofer: wacky volume = replace variable resistor?

    The volume control VR201 is a variable resistor which will give full volume if the wiper gets disconnected. You can try washing it with switch cleaner, operating the control a few times. You will need to get the cleaner on to the rubbing track. If this does not affect things, get a new control...
  7. duke37

    What is this component?

    You could draw out the circuit diagram to determine the purpose of the thermistor and its appropriate voltage rating. It looks as if it may be part of the power input circuit.
  8. duke37

    RF amp problems

    Your input circuit must be tuned to the received frequency. It should have a larger capacitance, say 50pF and an inductance to suit. This will be a more realistic L/C ratio. Any loading by the scope probe will give severe detuning. To drive a transistor, the drive must be taken from a tap on...
  9. duke37

    1993 Milwaukee Super Sawzall Cat No. 6527 carbon brush replacement

    I know nothing about your saw so what I say is generic only. It looks as if Pin9 holds the handle end on. The saw is povided with three wires, two will be power and the third earth (ground). If the earth is connected, then you should not get a tingle. Make sure your power supply is up to...
  10. duke37

    What is this component?

    It looks as if it could be a themistor. Board is labelled TH102.
  11. duke37

    Solenoid Back EMF

    I can think of two places which are lossy. 1. The contacts will always spark when opened. The rate of opening will control the time that the arc will last. 2. If the solenoid has an iron core, then there will be eddy current losses. Being within a factor of two for the voltage seems to...
  12. duke37

    Wall warts

    An open circuit primary is a common fault and could be due to a thermal fuse failing. I have never been able to repair these. The transformer is very small so the primary winding resistance will be quite high and the correct range on your meter must be used or you may get erroneous results...
  13. duke37

    Solenoid Back EMF

    Quote I have 0V connected all the time and tab the power on and then release to produce the EMF spike, my scope is connected across this clip to 0V, probe is x10 12pF. I see negative spike first and then a series of +/- ringing. Quote It seems to me that you have a switch of one sort or...
  14. duke37

    Solenoid Back EMF

    If the switching is not instataeous then there will be energy lost in the switch and the voltage will be lower than calculated. If the capacitor is faulty in a car ignition, then there will be a large spark at the contacts and it is doubtful if there would be enough volts to get a spark at the...
  15. duke37

    Solenoid Back EMF

    I agree with the numbers but it is only necessary to equate the two energies, giving V = I * SQR(L/C) A car ignition has a 'condenser' across the switch which allows the points to open before the voltage has risen to a very high level. The coil gives about 300V on the primary and has a...
  16. duke37

    Solenoid Back EMF

    The energy in an inductance is I * I * L /2 The energy in a capacitor is V * V * C/2 If the solenoid is abruptly switched off, the energy is transferred from the inductance to the capacitance. Thus the theoretical voltage can be calculated. In practise the turn off will not be abrupt...
  17. duke37

    Multimeter accuracy -- 3d, 5d, 10d?

    My interpretation is that at 200V AC, it should read 200.0 It could read 1.2% high or low, i.e. 197.6 to 202.4 Add or subtract 10 digits gives 195.6 to 203.4 Check it on any critical range with your posh meter.
  18. duke37

    US - UK Step down transformer

    The juicer and blender have motors i8nside whch will have fans to stir up the air and aid cooling. A transformer is normally naturally cooled so will need a much bigger surface area for the same power. I have a multiway US socket strip which you are welcome to if this helps. The plugs can...
  19. duke37

    US - UK Step down transformer

    Yes, you have messed up but at least, you have not blown up the devices and then asked me to mend them ! The Maplin transformer is nowhere near big enough for the job. You will need to get a 500W transformer and it should be in a suitable case with appropriate plugs and sockets. You may be...
View older results
Top