CurtPalme.com Home Theater Forum

[CZ Eddie]

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This Marantz VP4001 has three fans. They all look the same and all three are 12V .19A. Though the 3rd is rated for
slightly higher CFM than the others.

The goal was to replace two with NEXUS fans rated for the same CFM, but lower db. I did install swap out those two fans
and the projector started up fine. But after just a minute, it shuts down.
So far, I have managed to have just one fan swapped out for over a year now without any problems. But I'd like to
revisit this issue.

What would make the projector shut down, with just a simple fan swap? Maybe it doesn't like the higher amp rating of the
new fans? If so, what value resistor would I need to lower it from .33 to .19?

New fan on the left, original on the right.

[Curt Palme]

You've got SOME NERVE coming here asking advice on a digital...

You put the resistor in series with one of the leads of the fan. Keep in mind though that some fans have internal circuitry so as you lower the voltage, the fan will either work or come to a dead stop, and won't change speeds as you lower the voltage on the fan. Also make sure that the fan starts at the lower voltage if it does work for you.

I'd put say a 500 ohm or 1K 2 watt wirewound pot in series with the lead so you can tweak the fan's voltage. Once you know what setting works, measure it and buy the closet fixed resistor value.

[Curt Palme]

You've got SOME NERVE coming here asking advice on a digital...

You put the resistor in series with one of the leads of the fan. Keep in mind though that some fans have internal circuitry so as you lower the voltage, the fan will either work or come to a dead stop, and won't change speeds as you lower the voltage on the fan. Also make sure that the fan starts at the lower voltage if it does work for you.

I'd put say a 500 ohm or 1K 2 watt wirewound pot in series with the lead so you can tweak the fan's voltage. Once you know what setting works, measure it and buy the closet fixed resistor value.

[CZ Eddie]

Thanks, Curt. Sounds like nice advice.

But I have one of those mega-packs of resistors and no access to a wound pot without ordering it. Hopefully someone will come up with a suggestion. If not, then I may consider ordering one of those thingies you sugggested.

[Ben851]

Surely there's a radioshack around you? They should have one...

[macgyver655]

Oh man. Why are you doing this to me Curt? I read this post when it was first posted and didnt respond because I wanted to see the comments made. I didn't expect you to make this false comment. Curt, please reread the original post and edit yours so I can keep my mouth shut....

[CZ Eddie]

eh..?

[CIR Engineering]

I think a 1k variable resistor is a little on the high side...

If you have the RS pack of resistors, I'd first try something around 10 ohms on the + side of the fan in series. If that works, you could try a 15 ohm or even a 20 ohm resistor.

Be sure to take temperature readings before and after you slow down the fans.

craigr

[macgyver655]

Are you guys reading the same thread that I am?

[VideoGrabber]

27.

[Nashou66]

CZ, it might be something else besides the fans causing it to shut down. I know you say its only with a fan swap but maybe something else?


However the resistance of each motor you show is About 36 ohms for one and about 63 ohms for the other if using ohms law where Ohms=Voltage/Amperes .

Mac has me curious though. I need to learn !

Nashou

[macgyver655]

Alright, here's the deal. The original fan is marked 12v, .19 amp. That means that the fan needs at least .19 amps to run. You can send it .2, .3, .5, 1.0, 5.0, 10 or whatever amps, but it needs at least .19 amps. Now the fan you want to replace it with needs at least .33 amps, almost double the original. Now if when you install this fan the projector shuts down then that means its drawing more amps then the power supply has left after that circuit supplies everything else in the projector on that line.

So, the power supply of that circuit does not have enough power to run the higher drawing fans. And no resistors or pots or what ever is going to make that power supply put out more amps.

And adding resistors to reduce the voltage is going to cause the fan to draw even more amps then at the rated voltage.

This is also why when you try running 2 fans it shuts off even faster.

The only way to run those fans in there is to maybe pull power from a different circuit but you may run into the same problem again. The supply must not have much reserve left over and that is by design.

[VideoGrabber]

> And adding resistors to reduce the voltage is going to cause the fan to draw even more amps then at the rated voltage. <

Adding resistors doesn't reduce the voltage. The supply is still putting out 12V. It will, however, reduce the voltage across the fan, due to the resistive divider. In this case, to 6.8V, with a 27 ohm, 1W resistor. Which it may or may not be able to start at. That's a separate issue, and a separate spec on a specific fan.

The key point though is that inserting a resistor in series with the motor windings INCREASES the series resistance of the circuit, and REDUCES the current draw (from 330 mA to 190 mA), which is what the OP asked about. It's not going to "draw even more amps". Resistance and current are in an inverse relationship.

[VideoGrabber]

Oh, and the most important point of all is if when replacing a 2.4W fan with a 4W fan (greater load), by reducing its voltage from 12V to less than 7V (and thus dropping its RPM output), will the CFM of air it then moves still be adequate to cool that part of your PJ effectively?

The rest is pretty much irrelevant.

[macgyver655]

[macgyver655]

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.

[macgyver655]

And also, any electric device that is fed less voltage then it was designed to operate at will attempt to draw more current to make up the difference.

The issue of adding resistors to the fans to slow them down for quietness only applies when the power supply puts out enough current to begin with. In this case it is starving the power supply.

[macgyver655]

But you know what....throw a resistor in there and see what happens. You might just fool it enough to stop shutting down. Then I'll just be waiting for the thread saying "my projector just smoked up and now it wont turn on, what do I do".

[CZ Eddie]

Great advice in here!

The projector has almost 2300 hours on it and the bulb should have been replaced long ago. This model of projector has a reputation for shutting itself down prior to overheating. This requires you to remove the system cover and press a push-pin inside the chassis to reset it.
I figure if I'm going to push the boundries of this projector, then now is the time to do it. Before I buy it a new bulb.
The long term plans are to relegate it to bedroom duty.

I don't want to lose it, but I'm daring enough to try the resistor mod and see what happens.
As long as I don't lose the auto-fan function. Because it does ramp up the fan RPM's once in a blue moon when I let the room get above 78 degrees. Which isn't often. But will be a good warning sign if I hear the fans spin up in RPM's!

[betel]

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.

[VideoGrabber]

Nashou66 wrote:
> Mac has me curious though. I need to learn ! <

Naah. You know too much already, Nash.