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Discussion Starter #1
I've recently been looking at blowers for use in an EV, for battery
boxes and for motor cooling. For battery boxes, I've found some long
crossflow fans that seem convenient to mount along the top edge and seem
to provide adequate airflow (I know they're not as good as centrifugal
blowers). They'll be blowing into the box creating positive pressure, so
they don't have to deal with acid mist.

But I've been wondering what actual CFM is recommended for this purpose,
and for motor cooling, assuming that the rest of the intake vents are
closed (to control where the air comes from, perhaps to filter it)...
I'd like to have some actual numbers to work with, instead of guessing
-- "that seems like enough air".

Also, I've been wondering about when it's appropriate to ventilate a
battery box. I have assumed that it's necessary when charging, but is it
also necessary during discharge? AC fans are easier to find, but if they
must operate during discharge as well, then they'll need to be DC.

Blowers seem to be left out of a lot of EVs I've seen, but I'd like to
get an idea of the "right way".


--
Christopher Robison
[email protected]
http://ohmbre.org <-- 1999 Isuzu Hombre + Z2K + Warp13!

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Discussion Starter #2
Hello Christopher,

I am using total all plastic box fan from Rotron that is use for my battery
box. It is duel voltage rating of 230 vac at 340 cfm at 3300 rpm, or you
can run it at half speed on 115 vac.

source of supply is www.surplussales.com

I do not ventilate my battery box with the fan running. I use 2 inch pvc
pipe fittings and 1/4 inch thick pvc flex hose to connect up the this type
of fan. I cut two square flanges with and attach a pvc pipe fitting to them
and bolt them to bolt side of this fan, which makes it a inline unit.

I run a inlet and outlet pipe below the EV and cut a 45 degree angle on the
outlet pipe pointing straight down with the 45 degree cut pointed to the
back. The inlet also has a 45 degree cut pointed to the front, so now we
have a ram air system when the vehicle is moving.

If I am doing equalization charging inside a building, I can connect up one
of those exhaust hoses on the outlet pipe and run it through a port in the
garage door, like they do for ICE in service stations.

I do use a larger Dayton Blower in my equipment enclosure to pressurize it,
that contains a PFC-50 charger, contactors, fuses, and circuit breakers.
The blower is rated at 165 cfm at 115 volts. Uses a 6 inch carb type air
cleaner on it for the inlet air. I use that 3-M bulk air filters that look
like scotch pads but is about 1 inch thick. I cut a piece of this in stuff
it into the inlet air for the battery boxes.

Roland





----- Original Message -----
From: "Christopher Robison" <[email protected]>
To: "Electric Vehicle Discussion List" <[email protected]>
Sent: Tuesday, October 30, 2007 5:40 PM
Subject: [EVDL] Blowers


> I've recently been looking at blowers for use in an EV, for battery
> boxes and for motor cooling. For battery boxes, I've found some long
> crossflow fans that seem convenient to mount along the top edge and seem
> to provide adequate airflow (I know they're not as good as centrifugal
> blowers). They'll be blowing into the box creating positive pressure, so
> they don't have to deal with acid mist.
>
> But I've been wondering what actual CFM is recommended for this purpose,
> and for motor cooling, assuming that the rest of the intake vents are
> closed (to control where the air comes from, perhaps to filter it)...
> I'd like to have some actual numbers to work with, instead of guessing
> -- "that seems like enough air".
>
> Also, I've been wondering about when it's appropriate to ventilate a
> battery box. I have assumed that it's necessary when charging, but is it
> also necessary during discharge? AC fans are easier to find, but if they
> must operate during discharge as well, then they'll need to be DC.
>
> Blowers seem to be left out of a lot of EVs I've seen, but I'd like to
> get an idea of the "right way".
>
>
> --
> Christopher Robison
> [email protected]
> http://ohmbre.org <-- 1999 Isuzu Hombre + Z2K + Warp13!
>
> _______________________________________________
> For subscription options, see
> http://lists.sjsu.edu/mailman/listinfo/ev
>

_______________________________________________
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Discussion Starter #3
Thanks for your input Roland; I have a few questions/comments for you or
anyone else:

Roland Wiench wrote:
> Hello Christopher,
>
> I am using total all plastic box fan from Rotron that is use for my
> battery
> box. It is duel voltage rating of 230 vac at 340 cfm at 3300 rpm, or you
> can run it at half speed on 115 vac.
>
> source of supply is www.surplussales.com

I'm looking for a continuing source of fans, instead of buying surplus.
Apparently "Rotron" applies to two different companies; Comair-Rotron
(http://www.comairrotron.com) who make one model of biscuit AC blower at
only 22CFM, and Ametek-Rotron who make larger blowers, but only sell to
military and aerospace (http://rotron.com).

Is 340cfm really necessary? This has me concerned, as the crossflow fans
I've chosen supply a maximum of 50cfm. Having to choose another fan at
this point will complicate the design (should have asked earlier).


>
> I do not ventilate my battery box with the fan running.

Do you mean, you don't ventilate the battery box with the "car" running?

> outlet pipe pointing straight down with the 45 degree cut pointed to the
> back. The inlet also has a 45 degree cut pointed to the front, so now we
> have a ram air system when the vehicle is moving.

This seems like a good idea. At any rate, it seems like you're
recommending airflow through the battery box during discharge. Is the
problem of outgassing just as high as when charging? Since the ducting
will be difficult to fit in the current design, I may have to use a DC
blower to provide airflow while driving.

> I do use a larger Dayton Blower in my equipment enclosure to pressurize
> it,
> that contains a PFC-50 charger, contactors, fuses, and circuit breakers.
> The blower is rated at 165 cfm at 115 volts. Uses a 6 inch carb type air
> cleaner on it for the inlet air. I use that 3-M bulk air filters that
> look
> like scotch pads but is about 1 inch thick. I cut a piece of this in
> stuff
> it into the inlet air for the battery boxes.

Early PFC chargers certainly needed very effective cooling; I'm hoping
more recent ones deal with heat a bit better, here in Austin.

--
Christopher Robison
[email protected]
http://ohmbre.org <-- 1999 Isuzu Hombre + Z2K + Warp13!

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Discussion Starter #5
storm connors wrote:
> I cut a 2" hole in the side of the battery box near the top and
> mounted a computer slot fan on the outside. Pulls the air out. Runs on
> 12v. If you have a dc/dc and you run the fan while charging, ac or dc
> would seem to make little difference. You don't produce much hydrogen
> until the last 20% of the charge cycle. Anyway, these fans can be
> found on Ebay real cheaply. Like number 280167663555. Watch the
> shipping charges and the CFM rating.

You've found this to be enough airflow for charge and discharge? Do you
run the fan during discharge? I don't see a CFM rating on the fan in this
eBay posting, but I get the idea that it's less than 320 :)


> Battery boxes should have exhaust fan, not pressurizing.

I specifically chose to use positive pressure, as I didn't want acid mist
gradually damaging the fan after a few years of operation. The air will
vent to underneath the car. How long has your installation been in place?
Maybe I'm overly paranoid ... (?)


--
Christopher Robison
[email protected]
http://ohmbre.org <-- 1999 Isuzu Hombre + Z2K + Warp13!

_______________________________________________
For subscription options, see
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Discussion Starter #6
If you need a fan or any other electronic components, try Jameco.com


storm connors wrote:

> I cut a 2" hole in the side of the battery box near the top and
> mounted a computer slot fan on the outside. Pulls the air out. Runs on
> 12v. If you have a dc/dc and you run the fan while charging, ac or dc
> would seem to make little difference. You don't produce much hydrogen
> until the last 20% of the charge cycle. Anyway, these fans can be
> found on Ebay real cheaply. Like number 280167663555. Watch the
> shipping charges and the CFM rating.
>
> Battery boxes should have exhaust fan, not pressurizing.
> On 10/30/07, Christopher Robison <[email protected]> wrote:
>> I've recently been looking at blowers for use in an EV, for battery
>> boxes and for motor cooling. For battery boxes, I've found some long
>> crossflow fans that seem convenient to mount along the top edge and
>> seem
>> to provide adequate airflow (I know they're not as good as
>> centrifugal
>> blowers). They'll be blowing into the box creating positive
>> pressure, so
>> they don't have to deal with acid mist.
>>
>> But I've been wondering what actual CFM is recommended for this
>> purpose,
>> and for motor cooling, assuming that the rest of the intake vents are
>> closed (to control where the air comes from, perhaps to filter it)...
>> I'd like to have some actual numbers to work with, instead of
>> guessing
>> -- "that seems like enough air".
>>
>> Also, I've been wondering about when it's appropriate to ventilate a
>> battery box. I have assumed that it's necessary when charging, but
>> is it
>> also necessary during discharge? AC fans are easier to find, but if
>> they
>> must operate during discharge as well, then they'll need to be DC.
>>
>> Blowers seem to be left out of a lot of EVs I've seen, but I'd like
>> to
>> get an idea of the "right way".
>>
>>
>> --
>> Christopher Robison
>> [email protected]
>> http://ohmbre.org <-- 1999 Isuzu Hombre + Z2K + Warp13!
>>
>> _______________________________________________
>> For subscription options, see
>> http://lists.sjsu.edu/mailman/listinfo/ev
>>
>
>
>
> --
> http://www.austinev.org/evalbum/1059
> http://stormselectric.blogspot.com/
> Storm
>
> _______________________________________________
> For subscription options, see
> http://lists.sjsu.edu/mailman/listinfo/ev
>

_______________________________________________
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Discussion Starter #7
----- Original Message -----
From: "Christopher Robison" <[email protected]>
To: "Electric Vehicle Discussion List" <[email protected]>
Sent: Wednesday, October 31, 2007 9:46 AM
Subject: Re: [EVDL] Blowers


> Thanks for your input Roland; I have a few questions/comments for you or
> anyone else:
>
>
Roland Wiench wrote:
> > Hello Christopher,
> >
> > I am using total all plastic box fan from Rotron that is use for my
> > battery
> > box. It is duel voltage rating of 230 vac at 340 cfm at 3300 rpm, or
> > you
> > can run it at half speed on 115 vac.
> >
> > source of supply is www.surplussales.com
>
> I'm looking for a continuing source of fans, instead of buying surplus.
> Apparently "Rotron" applies to two different companies; Comair-Rotron
> (http://www.comairrotron.com) who make one model of biscuit AC blower at
> only 22CFM, and Ametek-Rotron who make larger blowers, but only sell to
> military and aerospace (http://rotron.com).
>
> Is 340cfm really necessary? This has me concerned, as the crossflow fans
> I've chosen supply a maximum of 50cfm. Having to choose another fan at
> this point will complicate the design (should have asked earlier).
>
With this type of fan, use 115 volts and the cfm will be cut in half. It is
cut down even more when place in a duct work. I am running my unit at about
150 cfm with no problem.
> >
> > I do not ventilate my battery box with the fan running.
>
> Do you mean, you don't ventilate the battery box with the "car" running?
>

Yes, I mean with the car running.


> > outlet pipe pointing straight down with the 45 degree cut pointed to the
> > back. The inlet also has a 45 degree cut pointed to the front, so now
> > we
> > have a ram air system when the vehicle is moving.
>
> This seems like a good idea. At any rate, it seems like you're
> recommending airflow through the battery box during discharge. Is the
> problem of outgassing just as high as when charging? Since the ducting
> will be difficult to fit in the current design, I may have to use a DC
> blower to provide airflow while driving.

I do not have any gassing during discharge, it is use mostly to cool the
batteries when its hot out.
>
> > I do use a larger Dayton Blower in my equipment enclosure to pressurize
> > it,
> > that contains a PFC-50 charger, contactors, fuses, and circuit breakers.
> > The blower is rated at 165 cfm at 115 volts. Uses a 6 inch carb type
> > air
> > cleaner on it for the inlet air. I use that 3-M bulk air filters that
> > look
> > like scotch pads but is about 1 inch thick. I cut a piece of this in
> > stuff
> > it into the inlet air for the battery boxes.
>
> Early PFC chargers certainly needed very effective cooling; I'm hoping
> more recent ones deal with heat a bit better, here in Austin.
>
> --
> Christopher Robison
> [email protected]
> http://ohmbre.org <-- 1999 Isuzu Hombre + Z2K + Warp13!
>
> _______________________________________________
> For subscription options, see
> http://lists.sjsu.edu/mailman/listinfo/ev
>

_______________________________________________
For subscription options, see
http://lists.sjsu.edu/mailman/listinfo/ev
 

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Joined
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70 Posts
Discussion Starter #8
From: Christopher Robison
> I've recently been looking at blowers for use in an EV, for battery
> boxes and for motor cooling. For battery boxes, I've found some long
> crossflow fans that seem convenient to mount along the top edge and
> seem to provide adequate airflow... They'll be blowing into the box
> creating positive pressure...

Crossflow fans have very low flow into even small amounts of back pressure. They would not be a good choice if there are any restrictions at all.

> I've been wondering what actual CFM is recommended for this purpose
> and for motor cooling... I'd like to have some actual numbers to work
> with, instead of guessing -- "that seems like enough air".

Battery ventilation is largely a "what if..." issue. Gassing is quite low under normal circumstances; good batteries, and a charger that properly shuts off when complete.

But ventilation requirements go up significantly when something goes wrong. Old flooded batteries gas at least twice as much as new ones. Shorted cells lower the pack voltage, which can make the charger fail to turn off and blindly keep charging. The excess energy gets converted to heat and gas.

Sealed batteries are not immune from this. They too will gas when they have cell failures or just get old.

There is no way to predict just how bad the gassing could get, unless you can predict how many cells might fail, or how long the charger might run wild. This is what leads the standards rganizations to specify huge amounts of ventilation. For example NEC 625's ventilation requirements assumes that the entire output of the charger will be converted to gas and heat!

It makes more sense to have a battery management and charging system that a) detects bad cells, and b) refuses to charge when things have gone wrong. In this case, you *can* predict the maximum amount of gassing, and size your ventilation accordingly.

Motor cooling is far more straightforward. The motor's efficiency and power input are very predictable; so you know how much heat it is producing. You know the maximum allowable motor temperature, and the ambient air temperature. From this it is simple to figure out how many CFM of air must be pushed through the motor (or radiator) to cool it. For example, X CFM of air that rises Y deg.F as it goes through the motor carries away Z BTU's of heat.

> Also, I've been wondering about when it's appropriate to ventilate
> a battery box.

Any time when there is a noticeable air volume inside the battery box where gas could collect.


--
"Excellence does not require perfection." -- Henry James
--
Lee A. Hart, 814 8th Ave N, Sartell MN 56377, leeahart-at-earthlink.net

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Discussion Starter #9
I do not run the fans on discharge, but I could. One I have here is 42
cfm. I have had them installed for a couple years with no problem. I
adopted this scheme because I have 5 battery boxes. The largest has 4
batteries. 3 others have 2 batteries and one has just 1 battery. So 5
fans = 200 cfm. Of course the fans probably move nowhere near this
volume of air due to restrictions on the replacement air ingress. All
the parts exposed to fumes are plastic. Acid shouldn't bother them- at
least it hasn't yet.

On 10/31/07, Christopher Robison <[email protected]> wrote:
>
>
storm connors wrote:
> > I cut a 2" hole in the side of the battery box near the top and
> > mounted a computer slot fan on the outside. Pulls the air out. Runs on
> > 12v. If you have a dc/dc and you run the fan while charging, ac or dc
> > would seem to make little difference. You don't produce much hydrogen
> > until the last 20% of the charge cycle. Anyway, these fans can be
> > found on Ebay real cheaply. Like number 280167663555. Watch the
> > shipping charges and the CFM rating.
>
> You've found this to be enough airflow for charge and discharge? Do you
> run the fan during discharge? I don't see a CFM rating on the fan in this
> eBay posting, but I get the idea that it's less than 320 :)
>
>
> > Battery boxes should have exhaust fan, not pressurizing.
>
> I specifically chose to use positive pressure, as I didn't want acid mist
> gradually damaging the fan after a few years of operation. The air will
> vent to underneath the car. How long has your installation been in place?
> Maybe I'm overly paranoid ... (?)
>
>
> --
> Christopher Robison
> [email protected]
> http://ohmbre.org <-- 1999 Isuzu Hombre + Z2K + Warp13!
>
> _______________________________________________
> For subscription options, see
> http://lists.sjsu.edu/mailman/listinfo/ev
>


--
http://www.austinev.org/evalbum/1059
http://stormselectric.blogspot.com/
Storm

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