Do manufacturers push their components too hard....

Discussion in 'General Electronics Chat' started by Flamin_D, Sep 29, 2010.

  1. Flamin_D

    Thread Starter New Member

    May 3, 2010
    18
    0
    Right people! I own a couple of GENI Mojo spinmaster 1 DJ lights with a controller circuit that controlls motors and the bulb.

    Long story short(ish), there is a relay on the board that controls the bulb. When the unit has reset motors to '0' after power-on, and it receives a signal from its internal mic, it flicks the relay to turn the bulb on and start the sequence. Now, the bulb is 24V 250W, therefore should draw 10.4A. The relay on the board is rated at 10A @ 28v. I was wondering why, because this seems to be pushing it verrry close to its limit, there's not a lot of headroom for even the slightest of surge.


    I was replacing the ceramic bulb holder on one of my units. The new bulb holder actually had thinner wires and was smaller than the original holder (i didn't know this upon purchase). With the new holder attached and the unit powered on, when the relay flicked to power on the bulb the relay immediately blew.
    This baffles me - i made 100% there were no shorts in the new holder or at the connections; also the new holder having thinner wires should mean LESS amps are drawn due to a higher resistance! Why would it blow?


    If you have any feedback or comments whatsoever, please let me know, im completely confused with this one. Ill replace the relay and try again but still no sense. (Or im missing something obvious)

    Board:

    [​IMG]

    Relay:
    [​IMG]

    Bulb + New and Old Holders
    [​IMG]
     
    Last edited: Sep 29, 2010
  2. maxpower097

    Well-Known Member

    Feb 20, 2009
    795
    388
    The relay was expecting the bulb to use more power, since it was smaller and didn't that extra power went into the relay making it go over it tolerance and go boom. ? This is my best uneducated guess.
     
  3. tom66

    Senior Member

    May 9, 2009
    2,613
    213
    A device, and the relay, will only draw the current according to the load.

    To the OP, manufacturers are often overrating components. For example, I have found 10V caps filtering a 12V supply line. In this situation they would only work for about 100-200 hours tops. Which explains why the PSU died after only a few months. In their case, it was probably $1 more to get a 12A relay, and they didn't want to pay this.
     
  4. GetDeviceInfo

    Senior Member

    Jun 7, 2009
    1,571
    230
    This may be practical lesson #1, fuse your loads. At the very least, if you don't have current limit, which you won't on a relay, meter your load for a rough estimate of it's draw.
     
  5. cjdelphi

    New Member

    Mar 26, 2009
    272
    2
    I came across a similar issue with an electric blanket which runs on 240volts, I never had the correct tools to actually get inside the plastic case so I decided to just break it open, I then measured the resistance and calculated it to be something like 1.03amp draw, but the fuse was rated for 1amp...

    The conclusion was simple, the Electric blanket is /designed/ to blow after X amount of hours, I can only assume that they specifically calculated to make their blanket last roughly 3 - 5 months, eg, the amount of time it's Winter for and the amount of time a person would use it.

    In short, they have it designed to blow each winter on purpose! to make the person buy another one for next year, I could have replaced the 1 amp fuse but I completely destroyed the plastic heat level control box thing and It was too unsafe to use again So we bought a new one, but I know for a fact that the new one has a lifespan of only 150 - 300 hours or so and i KNOW it's going to blow the fuse again.

    I guess it comes down to the fact the company wants people to buy a new one every few years and want the components to fail and they know they eventually will due to the fact some components are underrated.
     
  6. eblc1388

    Senior Member

    Nov 28, 2008
    1,542
    102
    There is no conspiracy theory here.

    It is perfectly reasonable to use a 1A fuse for a maximum 1A load.

    The fuse rating is for a continuous current rating such that when the current is the rated current, the fuse would take infinite amount of time to heat to the point of fusing.

    In fact, most fuse manufacturer won't provide data for fusing time for say 1.05x current that is very close to the stated rating.

    Even with 3x the current rating, some would still take about 10 seconds to blow.
     
  7. sceadwian

    New Member

    Jun 1, 2009
    499
    37
    Keep something in mind about relay's as well, the amperage rating is what they're rated to SWITCH not carry, the switching current handling of a relay will always be lower than the maximum current that it can actually carry. At 10.1 amps the relay isn't going to explode suddenly, at 125% of it's rated capacity it'll still probably work just fine though contact bounce during making of the connection will probably decrease the number of possible switching cycles you'll get out of it. As far as things like electrical transients relays are pretty much immune to them the only thing you have to worry about is ohmic heating over the long haul not peak loads except during switching.
     
  8. sceadwian

    New Member

    Jun 1, 2009
    499
    37
    One thing as well, you said.
    How did you make 100% sure? Even the most experianced person checking something over even if they've done it a million times can make mistakes they aren't aware, did you use a meter or what?
     
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