Mover fans - how fast is good enough?

I'm swapping out cooling fans on some of our movers this week. I'd like to use silent fans where possible, since we use these fixtures for theatrical applications, but I'm concerned about getting enough air flow to keep lamps cooled properly.

When I called tech support at one manufacturer, the guy told me he thought a quiet fan moving 5.5 CFM would be about as good as the factory-installed 8CFM fan. He said as long as we were getting air moving across the lamp, there would be diminishing returns going to faster and faster fans.

I was really surprised at this response. It's great news if I can use quiet fans, but I'm scratching my head. It somehow just feels too good to be true. Can anyone confirm this - or contradict it with some good old-fashioned science?

In my experience, heat is your ultimate enemy. More air = less heat. With less air, you fixture will run hotter. Your lamps will fail faster, your electronics will fail faster, and your glass is more likely to break. First generation Mac Vipers had a problem with their filters being too good. Once they filled up (after about 9 months) users started reporting as much as 50% faster lamp failure. No matter what that technician said, I'd be terrified to cool something less, and would always err on the side of cooling more.

Part of it depends on your environment. When they're designing the lights they have to plan for everything, from cool theaters, to outdoor summer festivals. If your lights are only used in temperature controlled environments then you could probably get away with fans that are moving a little less air.

I don't think I've ever run across a mover with head room as far as cooling is concerned. The fans that will be just enough to cool the unit are the cheapest to acquire and it's a competitive market so pennies in the BOM can matter. It's certainly possible that you could find equal CFM fans that have better bearings or something that will allow them to run cooler, but I wouldn't reduce airflow.

FWIW, I've been doing IT long enough that I remember PCs that had dust filters on their fan intakes.

It was *never* a good idea; a clogged filter was *always* the first point of failure.

Clean stuff regularly and don't worry about filters, was my approach.

Now, there are enough moving parts in a moving light that that approach might not be as serviceable there, but...

sotonfan said:

I'm swapping out cooling fans on some of our movers this week. I'd like to use silent fans where possible, since we use these fixtures for theatrical applications, but I'm concerned about getting enough air flow to keep lamps cooled properly.

When I called tech support at one manufacturer, the guy told me he thought a quiet fan moving 5.5 CFM would be about as good as the factory-installed 8CFM fan. He said as long as we were getting air moving across the lamp, there would be diminishing returns going to faster and faster fans.
I was really surprised at this response. It's great news if I can use quiet fans, but I'm scratching my head. It somehow just feels too good to be true. Can anyone confirm this - or contradict it with some good old-fashioned science?

Click to expand...

Yeah, you should be surprised at that response, mainly because it is completely wrong. Porkchop (Brett) up above has the best answer so far. The fixtures are designed to cool the lamps properly. If they overcool the lamp, the lamp will explode, taking out color wheels, lenses, etc. If the lamp is undercooled, it will have a reduced life and divitrification of the quartz will happen early, reducing the output. Cooling on a moving light is essential to their operation and isn't something you should ever mess with. Even the Fixture manufacturers themselves make this mistake on occasion...

<<First generation Mac Vipers had a problem with their filters being too good. Once they filled up (after about 9 months) users started reporting as much as 50% faster lamp failure.>>

Not true actually. What happened was they launched the fixture with perfect cooling. No lamp failures at all. Honestly, it was the best launch ever in terms of quality and no complaints from the market. Then they got many requests to reduce the noise so the fixtures could be used in theatres, on broadway, etc., so they released a patch that slowed down the fan speed-- and suddenly the lamps started failing left and right. Once we got them to increase the fan speed again in a future firmware patch, the cooling was good again and the lamps no longer failed. It's not rocket science. Don't mess with the fans!

Are these LED or conventionals?

And am I reading right that the mfgr tech actually told you that it's OK to replace the fan with an inferior one?

So do we make some popcorn and watch for the lamp and other mechano-electrical failures or start a friendly office pool for the date when failures begin?

@porkchop is spot on. Every product is designed to meet a target price point and your can bet your next paycheque that the least-expensive components that meet the performance objectives were used. This doesn't mean the components are inferior, only that they meet the required specification for the least cost.

If there is another fan that is a drop-in replacement with lower SPL, the same CFM and otherwise will work, it will cost more and that is why the OEM didn't use it. I'd be extremely leery of using any fan that doesn't deliver the same air flow within the fixture.

"I see a bad moon a-rising
I see trouble on the way
I see earthquakes and lightnin'
I see bad times today"
- Credence Clearwater Revival

TimMc said:

So do we make some popcorn and watch for the lamp and other mechano-electrical failures or start a friendly office pool for the date when failures begin?

@porkchop is spot on. Every product is designed to meet a target price point and your can bet your next paycheque that the least-expensive components that meet the performance objectives were used. This doesn't mean the components are inferior, only that they meet the required specification for the least cost.

If there is another fan that is a drop-in replacement with lower SPL, the same CFM and otherwise will work, it will cost more and that is why the OEM didn't use it. I'd be extremely leery of using any fan that doesn't deliver the same air flow within the fixture.

"I see a bad moon a-rising
I see trouble on the way
I see earthquakes and lightnin'
I see bad times today"
- Credence Clearwater Revival

Click to expand...

Popcorn. The answer is always popcorn.

From all the work I've done with computers and servers, I've learned a lot about fans, so I'll give some insight here.
Right now I'm under the assumption that you know what voltage fan you need, and that you know what size fan as well; if you could share that info, that'd help greatly.

If you're looking for a 40mm fan, and you can get away with ~5.5CFM, Noctua makes some 40mm fans that come in 12 and 5 volt varieties. If you need absolute silence, Noctua might be the way to go, as the A4x20's come in just under 15 dB/a.

If you can't get away with 5.5CFM, then Delta makes the AUB0412HDYFM, a 40x40x20mm fan that operates on 12v, and moves 8.01CFM at 22 dB/a- you might be able to find a 5v variant. Having worked with servers and enterprise networking equipment, I'll say that Delta is a great fan manufacture; so much so that I have a TFC1212DE in my main desktop (look at the specs for it, you won't be disappointed).

Another company worth checking is San Ace, I have a server with several of their fans mixed in with two Nidecs, and they were quieter than the spare Delta I had bought for it, but I haven't looked too much at them.

Again, since I don't know what size and voltage fan you need, it's hard to give specifics, so I just went with a basic assumption of 40mm fans (partly due to the fact that we're talking <10CFM here).