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garyfritz
Joined: 08 Apr 2006
Posts: 12088
Location: Fort Collins, CO
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| Posted: Tue Jun 01, 2010 2:09 pm Post subject: |
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| macgyver655 wrote: | | The fan wants 12v, .33amps. And it is going to try and draw that much and apparently there is not that much available. By inserting anything in that power line is not going to change what that fan wants and is not going to increase what the fan gets. Its not that difficult to understand. |
Amps = Volts / Ohms. The voltage from the power supply is fixed, or should be. Increasing the resistance across the power supply (by adding a resistor in series with the fan) reduces the current going through the fan/resistor combination. It also divides the voltage. So the fan will see less current AND less voltage. Like Mac says, it's not gonna be happy.
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macgyver655
Joined: 22 Aug 2007
Posts: 8508
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| Posted: Tue Jun 01, 2010 3:07 pm Post subject: |
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| garyfritz wrote: | | macgyver655 wrote: | | The fan wants 12v, .33amps. And it is going to try and draw that much and apparently there is not that much available. By inserting anything in that power line is not going to change what that fan wants and is not going to increase what the fan gets. Its not that difficult to understand. |
Amps = Volts / Ohms. The voltage from the power supply is fixed, or should be. Increasing the resistance across the power supply (by adding a resistor in series with the fan) reduces the current going through the fan/resistor combination. It also divides the voltage. So the fan will see less current AND less voltage. Like Mac says, it's not gonna be happy. |
Your missing part of this equation here. This is a motor, not a basic circuit. A motor tries to draw what it needs. If you try restricting what it needs it will try harder. If you try restricting the voltage then it will try to draw more current.
Have you not ever had an almost dead battery in your car but you keep cranking it hoping it will start. Then the cables get hot and starts smoking and even melts the rubber if you keep trying. Its not voltage that causes that and the voltage is already lower then normal. Its the starter trying to draw more current in an attempt to do its job.
The amps, volts and ohms formulas are for basic design and merely limit the voltage/amperage output of a circuit. BUT, that doesn't mean when something happens in that circuit causing an over draw of the rated output of that circuit and then causing circuit damage.
What do you think causes regulator failures in electronic circuits? Its not normal running conditions. Its caused when there is an attempt by that circuit to draw more then the regulator is designed to output. To much current is drawn through the regulator and it starts getting real hot. And if the problem is not resolver the regulator will fail. The circuit was still drawing the same voltage because the voltage is set, so it tries to draw more current.
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macgyver655
Joined: 22 Aug 2007
Posts: 8508
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| Posted: Tue Jun 01, 2010 3:24 pm Post subject: |
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| garyfritz wrote: |
Amps = Volts / Ohms. The voltage from the power supply is fixed, or should be. Increasing the resistance across the power supply (by adding a resistor in series with the fan) reduces the current going through the fan/resistor combination. It also divides the voltage. So the fan will see less current AND less voltage. Like Mac says, it's not gonna be happy. |
Let me also add to this. Another thing you guys are missing. I'm not saying that adding a resistor is not going to lower the available current which it really shouldn't anyways. What I'm saying is reducing the voltage is going to cause the fan to want to draw more current(the formula has nothing to do with this) and by installing that resistor you have also lessened that available current.
YOU CAN'T CHANGE WHAT THAT FAN WANTS!!!!!!
And the more you change the supply to that fan in a lesser degree the more its going to attempt to get what it needs.
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ecrabb
Forum Moderator
Joined: 13 Mar 2006
Posts: 15909
Location: Utah
TV/Projector: JVC RS40, Epson 5010
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| Posted: Tue Jun 01, 2010 3:46 pm Post subject: |
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I agree with Mac. By inserting the resistor in series, you do decrease the fan speed, but in the process, you also increase torque which draws more current. This is especially true at power-on, as the fans will draw even more current at that point then they ever do spinning. As Mac already mentioned, the power supply probably can't supply enough current to start all three fans. If you could hand-spin all three fans before you fired the projector, the PSU might be able to drive them, but it obviously won't spin them up.
I'd question whether the new fans really are even quieter, anyway. I don't see anything about the design that would really make them any quieter than the OEM fans... Usually, they're quieter because they don't move as much air. Plus, you can't control the noise induced from turbulence in the actual projector. Personally, I wouldn't even bother with the fan mod... Especially given the PSU inadequacy, and I definitely wouldn't do it without taking some measurements on the exhaust air temp.
If you REALLY wanted to do the mod, just let the projector's PSU drive the coil in a micro relay and use an external PSU to drive the fans.
SC
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CIR Engineering
Joined: 25 Aug 2008
Posts: 4269
Location: Chicago USA & Berlin Germany
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| Posted: Wed Jun 02, 2010 12:05 am Post subject: |
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| betel wrote: | | If you lower the fan voltage, you are going to lower it's speed, thus lowering the CFM. Then you have a machine running too hot. What's the point of that? This stuff isn't magic. Moving air makes noise. No way around it. No way I would try to use different fans in my projector unless I absolutely understood what I was doing. However, If I were to try it, I would fit higher rated CFM fans (probably bigger too) and then lower the speed to equal the target CFM. |
I also think that you should stick with the stock fans. However, if you want to try and quiet things down just use a resistor on the + side of the fan. If the projector runs with the resistor you should certainly compare before and after temperatures with the stock verse modified config.
A lot of projectors are over cooled for the most stringent cases. If your environment is relatively normal (say less than 100 degrees F) you may be ok with less cooling. Usually higher temps mean a shorter life.
craigr
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CIR Engineering
Joined: 25 Aug 2008
Posts: 4269
Location: Chicago USA & Berlin Germany
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| Posted: Wed Jun 02, 2010 12:07 am Post subject: |
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| ecrabb wrote: |
...I'd question whether the new fans really are even quieter, anyway. I don't see anything about the design that would really make them any quieter than the OEM fans... Usually, they're quieter because they don't move as much air. Plus, you can't control the noise induced from turbulence in the actual projector. Personally, I wouldn't even bother with the fan mod... Especially given the PSU inadequacy, and I definitely wouldn't do it without taking some measurements on the exhaust air temp...
SC |
_________________
JETI 1501-HiRes 2nm Spectroradiometer
JETI 1211 Spectroradiometer
Photo Research PR-650 Spectroradiometer
Klein K10-A Colorimeter
Murideo Fresco SIX-G HDMI 2.x Multimedia Generator
Murideo Fresco SIX-A HDMI 2.x Analyzer
Light Illusion ColourSpace XPT Color Calibration Software
Light Illusion LightSpace XPT Pro Version 10.x Color Calibration Software
OMARDRIS JVC Software Patch to use K10-A and Jeti with JVC OEM AutoCal Software!
Sencore CR7000 CRT Tube Analyzer / Rejuvenater
Authorized Dealer for Lumagen & just about everything worth buying
www.CIR-Engineering.com - craigr@cir-engineering.com
Phone: 865-405-6892
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richardc
Joined: 13 Feb 2008
Posts: 32
Location: Australia
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| Posted: Wed Jun 02, 2010 10:26 am Post subject: |
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Hi Guys
Are the two fans running at the same RPM.
Maybe the the new fan is running slower, the tacho (third wire )detects rotation movement if fan stops projector shuts down,
or maybe the projector is smart enough to detect a fan is startig to fail.
Just a thought.
Richard
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CIR Engineering
Joined: 25 Aug 2008
Posts: 4269
Location: Chicago USA & Berlin Germany
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| Posted: Wed Jun 02, 2010 2:10 pm Post subject: |
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A lot of the time the sense circuit on aftermarket fans uses a different current signal than the stock fans. I learned that the hard way when a SilenX fan failed in my G90 and the projector did not shut down (PA board burned up). The opposite can also happen where the fan is running, but the projector thinks it is stopped.
craigr
_________________
JETI 1501-HiRes 2nm Spectroradiometer
JETI 1211 Spectroradiometer
Photo Research PR-650 Spectroradiometer
Klein K10-A Colorimeter
Murideo Fresco SIX-G HDMI 2.x Multimedia Generator
Murideo Fresco SIX-A HDMI 2.x Analyzer
Light Illusion ColourSpace XPT Color Calibration Software
Light Illusion LightSpace XPT Pro Version 10.x Color Calibration Software
OMARDRIS JVC Software Patch to use K10-A and Jeti with JVC OEM AutoCal Software!
Sencore CR7000 CRT Tube Analyzer / Rejuvenater
Authorized Dealer for Lumagen & just about everything worth buying
www.CIR-Engineering.com - craigr@cir-engineering.com
Phone: 865-405-6892
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