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Old 18-07-2015, 12:42   #1
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Are all brushless fans ignition protected?

Before I blow myself up (again) I thought I would ask this question. I have and enclosed box for my house bank with a 3" flexible hose leading to the outside for ventilation. I would like to add a small computer fan at the base of the hose/top of the box to help draw fumes out of the box. I know, I know; I'm supposed to put the fan down low and 'blow' the fumes out to reduce fire hazard, but it would be very difficult to completely seal the box and I don't want to blow H2 gas into the boat.

My question is, are brushless 12v computer fans considered 'ignition protected'?
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Old 19-07-2015, 09:39   #2
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Re: Are all brushless fans ignition protected?

"Nearly" always.
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Old 19-07-2015, 10:54   #3
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Re: Are all brushless fans ignition protected?

Ignition protection is often done on alternators by placing metal screening (like window screening) over the sparky areas, so that any flame front which is ignited, has to pass the screen and in doing so it is cooled down by the metal so much that it stops. At least that's what they've told me. So one extra step would be to just make a pouch of metal window screening (and I'd expect copper or stainless to last longer on a boat, if you can get it) and make sure the fan is installed in that.
But also, why not put the fan in another piece of ducting, and use it to bring in fresh air, even "cabin" air, pushing that through the battery box? That would be your best insurance against spark ignitions, keeping the fan upstream of any hydrogen generated.
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Old 19-07-2015, 19:18   #4
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Re: Are all brushless fans ignition protected?

Actually I prefer sucking out the humidity, heat and hydrogen, that way any crevices in the battery box allow fresh air IN instead of pushing hydrogen OUT into your cabin if using a pressure system.
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Old 19-07-2015, 19:48   #5
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Re: Are all brushless fans ignition protected?

You won't have an open spark if you don't have brushes. The permanent magnets in brushless motors do away with the brushes.
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Old 20-07-2015, 09:29   #6
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Re: Are all brushless fans ignition protected?

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You won't have an open spark if you don't have brushes. The permanent magnets in brushless motors do away with the brushes.
Nitpick: Both brushless and brushed motors have permanent magnets, IIRC. It's just a question of where the permanent magnets are. On brushed motors, the permanent magnets are on the case and the electromagnets are on the shaft (hence the need from brushes to deliver power). On brushless motors, the permanent magnets are on the shaft, and the electromagnets are on the case, and require a special speed controller in order to turn the different coils on and off at the right times.
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Old 20-07-2015, 10:51   #7
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Re: Are all brushless fans ignition protected?

Brushes always derive sparking as contact is not complete and the commutating circuit has gaps which are bridged. Brushless motors are much less likely to derive sparks and thus ignition of combustible gas, liquid or materials than brushed motors. But is not uncommon for the contact leads to a brushless motor to derive a spark because the leads may not be in full contact or the current may bridge to an alternate path.

To be on the safe side a NEMA 7 rated motor should be used in potentially explosive environments.

An appropriate first step is to mitigate the formation of explosive / combustible material on board a boat / ship. Ask yourself where is the hazard being derived. Are you using flood cells which gas? A recommendation is to use maintenance free cells to avoid the formation of H2 then one does not have to be significantly concerned about spark ignition. As always, the best advice is treat the source of the problem and not the after issue or symptom.

Happy sailing.
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Old 20-07-2015, 12:16   #8
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Re: Are all brushless fans ignition protected?

I believe the formation of hydrogen gas is actually pretty low, and assuming your vent hose is at the top of the compartment and running uphill, you won't get any gas to accumulate even without a fan?
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Old 20-07-2015, 12:37   #9
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Re: Are all brushless fans ignition protected?

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I believe the formation of hydrogen gas is actually pretty low, and assuming your vent hose is at the top of the compartment and running uphill, you won't get any gas to accumulate even without a fan?
Yeah, I'm thinking a brushless motor is fine. As mentioned once you have the ducting you shouldn't have accumulation even without a fan if the duct runs up hill.
Add to that that "ignition protected" often just means sealed you should be good to go JMHO.
The starter on my gas engine boat is the same as an auto starter except, there is a plastic plate separating the drive end of the starter from the electrical end.
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Old 20-07-2015, 13:57   #10
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Re: Are all brushless fans ignition protected?

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Originally Posted by Montanan View Post
Brushes always derive sparking as contact is not complete and the commutating circuit has gaps which are bridged. Brushless motors are much less likely to derive sparks and thus ignition of combustible gas, liquid or materials than brushed motors. But is not uncommon for the contact leads to a brushless motor to derive a spark because the leads may not be in full contact or the current may bridge to an alternate path.

To be on the safe side a NEMA 7 rated motor should be used in potentially explosive environments.

An appropriate first step is to mitigate the formation of explosive / combustible material on board a boat / ship. Ask yourself where is the hazard being derived. Are you using flood cells which gas? A recommendation is to use maintenance free cells to avoid the formation of H2 then one does not have to be significantly concerned about spark ignition. As always, the best advice is treat the source of the problem and not the after issue or symptom.

Happy sailing.
I agree with this view completely but you are looking forward to the venting of this box, if you place the fan as close as possible to the duct "discharge" even if you have a flash the fan should keep the brief flame front on the discharge side of the fan. You may also buy DC "intrinsic barriers" like they use in petrochemical plants for instrumentation if you wish no sparks.
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Old 20-07-2015, 14:53   #11
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Re: Are all brushless fans ignition protected?

Just purchase a ventilation fan designed for the engine compartment on a boat.
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Old 20-07-2015, 15:40   #12
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Re: Are all brushless fans ignition protected?

I use a computer fan, mounted in a duct, outside of the battery box, and penetrating at the bottom. Then, at the top, opposite side of the battery box I duct the gases out to a vent through the underwing draining wet locker. in addition, all of the cells on my 6ix volt L-16 batteries use Hydrocaps. The heat of the charging batteries warms a platinum screen in the Hydrocap, combining atmospheric oxygen via the platinum catalyst, and most of the hydrogen is returned to the electrolyte as water. I have to add about a tablespoon of top up water every six months. In the pictures I haven't connected the vent hose, and the box cover is removed. Straps secure the cover to the bilge floor.
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Old 20-07-2015, 16:14   #13
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Re: Are all brushless fans ignition protected?

Hydrogen is the lightest known element, an uphill path is all it needs.
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Old 20-07-2015, 20:31   #14
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Re: Are all brushless fans ignition protected?

Mike Reed is a bright guy and probably knows a fair bit about hydrogen. I suspect he understands the implications of "lighter than air", hence his concerns.
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Old 20-07-2015, 20:48   #15
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Re: Are all brushless fans ignition protected?

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Mike Reed is a bright guy and probably knows a fair bit about hydrogen. I suspect he understands the implications of "lighter than air", hence his concerns.
I tend to go with the idea that it was the fabric cover that caught on fire. It was the nitrate dope they used that burned so brightly.
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