4gauge wire is way overkill for an electric fan. Shit, 8 gauge is probably
larger than he really needs to use, and I highly doubt his "in-rush" would
be anywhere close to 120 amps. If that was the case, it would kill the
truck when the fan turned on since the alternator in most daks isn't even
that large. His relay choice and wire sizing is just fine and will work
great for him. The only thing I still suggest is to go to a smaller circuit
breaker. I'd say a 6amp break will be plenty large to keep it from tripping
all the time and will still be small enough to protect the rest of his
components. If anything, go a little smaller on the breaker.
brian cropp
-----Original Message-----
From: owner-dakota-truck@bent.twistedbits.net
[mailto:owner-dakota-truck@bent.twistedbits.net] On Behalf Of Phillip Batson
Sent: Sunday, June 21, 2009 9:33 AM
To: dakota-truck@dakota-truck.net
Subject: Re: DML: Taurus Fan Update
You may call me crazy, but I have a healthy respect when it comes to
electricity. If others have done the same mod in the past without issue,
then I'll defer to them.
If *I* were doing this, however, I would err on the side of safety. If your
in-rush can be up to 3 times the normal amp draw, you're looking at a
possible 120amps. Granted, it will be at that draw for a very short time,
but I would feel a lot safer have 5awg or 4awg wiring, and then a 120+amp
relay. Then you could adjust your breaker size accordingly. Then I wouldn't
have to worry about wires melting or the relay wearing out prematurely.
----- Original Message ----
From: Matt Beazer <teseract@moparhowto.com>
To: dakota-truck-moderator@bent.twistedbits.net
Sent: Saturday, June 20, 2009 2:48:15 PM
Subject: Re: DML: Taurus Fan Update
Yeah, I figured on the inrush current, which is one reason why I went for
the 80 amp breaker, now I'm told that was a mistake. I based my wiring
choice on other people's info (10 gauge gets hot, 8 doesn't) and on this
site's chart listing for chassis wiring:
http://www.powerstream.com/Wire_Size.htm
For chassis wiring, it shows 73 amps being the max, 24 for "power
transmission" (which I assume means house wiring, etc). The stock wiring
looks to be 8 gauge as well.
Most people use 14awg fuse links rather than a fuse or breaker and I HATE
HATE HATE fuse links (bad previous experience). They use them because
they're "slow to blow" so they don't pop under the startup current spike.
All I want is something resettable that won't pop under the fraction of a
second of current inrush. I was hoping having a higher rated thermal
breaker would reduce the risk of resetting under the inrush current and
still keep a loose wire from doing any accidental welding on the frame. ;)
I bought the diodes since an article said you needed one for when the fan
was free-wheeling in air coming in the grill, turning the fan into a
generator, since the reverse current would reduce the life of the relay.
If I don't need to splice it in I'm happy with that.
As for the fan measurements, I've not test-fitted it yet. I'm not
concerned if there's a couple inches of gap around it, the shroud will
still be effective for cooling the majority of the radiator, and the
shroud is way bigger than that of the typical shroud on say, a black
magic fan which is little more than a ring of plastic around the blades.
3rd gen Dakota owners don't have 100% coverage and they find it cools
better than the stock fan setup.
MattB
On Sat, 20 Jun 2009 14:17:49 -0400, Dan Kramarsky wrote:
> Matt,
>
> BTW, your choice of the 75-amp relay was actually a good one and NOT
> overkill for 2 reasons:
>
> 1.. When you start up a DC motor there is something called 'in-rush'
> current. This current is sometimes 2.5 to 3 times the motor's
> 'continuously-on' rated current.
>
> 2. The relay's contacts will have a longer life when you use a slightly
> larger relay than the DC Load requires.
>
>
>
> Also, I would be careful in selection of the protection devices like
> the circuit breaker or fuse. These items should be very close to the
> rating of _wire_ you are using. In other words, makes sure you
> understand what is current carrying capacity of the wire. Then use
> circuit protection devices (i.e. breaker) that would allow only 100 to
> 110% of the capacity of the wire to ever be reached. For 8 gauge wire,
> that's roughly 40 Amps
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