advice on wattage of these smd resistors?

Discussion in 'General Electronics Chat' started by sdowney717, Aug 9, 2013.

  1. sdowney717

    Thread Starter Member

    Jul 18, 2012
    385
    13
    Are part of circuit for an inverter using IRf 3205
    They are 10 ohms each marked 100 on their tops.
    The inverter circuit shorted and fried mosfets and also these resistors are out of spec.

    ALSO, was thinking for me it would be easier to replace using standard resistors. Thoughts?

    [​IMG]
     
  2. Papabravo

    Expert

    Feb 24, 2006
    10,135
    1,786
    Surface mount resistors are usually either 1/8 Watt or 1/10 watt.

    A 10 Ohm resistor will dissipate 1/10 watt at 100 mA

    I don't think it is likely that the resistors are "out of spec" or were the root cause of the problem. More likely is a misunderstanding of the requirements of the active devices and the effects of parasitic elements.
     
  3. sdowney717

    Thread Starter Member

    Jul 18, 2012
    385
    13
    I removed the Mosfets and these 10 ohm resistors are reading from 10 to 30 ohms and one reads open.
    And the heat cooked these resistors so that when cleaned off, they numbers came off.
    I had a dueling short between the 3000 watt inverter and a 6500 watt gen. Was rather depressing.
    I had turned on my AC and the inverter was on and the gen was on and they are connected by a 4 pole DT relay
    So the inverter could not power the AC and clicked off the relay allowing the gen to power the AC and the high current arced inside the relay which momentarily connected both powers sources together.

    http://www.westfloridacomponents.com/surface-mount-resistor-sizes.html
    http://www.hobby-hour.com/electronics/smdcalc.php

    They measure about 1.5mm wide and 3.5 mm long and seem to be about 1/4 watt when going by those 2 sites.
     
  4. sdowney717

    Thread Starter Member

    Jul 18, 2012
    385
    13
    I thought I would be ok since the inverter detects overloads and automatically shuts down.
    But I was wrong.

    Would a circuit breaker on both hot and neutral solve any future problem?
    Since breakers can slow trip , that might not help either?
    I should have shut the inverter off, power on the gen , then turn on the AC.

    Or if Inverter is on, somehow must automatically prevent gen from being started.
     
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