Date: Mon, 21 Jan 2008 23:22:16 -0800
Reply-To: Scott Daniel - Shazam <scottdaniel@TURBOVANS.COM>
Sender: Vanagon Mailing List <vanagon@gerry.vanagon.com>
From: Scott Daniel - Shazam <scottdaniel@TURBOVANS.COM>
Subject: Re: Electrical questions. Radiator fan circuit from 85 Vanagon
into 81 air cooled Westy.
In-Reply-To: <c4e7c5f90801212149t617b333dvaa065e43360e23a9@mail.gmail.com>
Content-Type: text/plain; charset="us-ascii"
Hi, neil,
Well, no it's not correct to say 'the relay takes the load of the switch."
Though you might have said those words but meant this :
The relay, is a switch actually, a switch that is flipped , ie. the larger
load carrying contacts in it are joined ( one contact hinges against a tiny
spring pressure ) , when a very small electromagnet is energized.
The dash switch or control switch completes the circuit to energize the
little electromagnet.
So the dash switch energized the magnet, the magnet pulls the two larger
contacts together, and the larger load of the rad fan or whatever flows
through those big contacts being held together by the little energized
electromagnet.
It can either supply power to the little electromagnet, the other side of it
being grounded.......that will complete the circuit to energize the little
magnet, which pulls the two larger load-carring contacts together.,
OR the switch could be in the ground side of the electromagnet circuit.
Lots of relay are that way, almost most of them have the ''control signal'
in the ground side if the electromagnet circuit. In that case the other
side of the electromagnet goes to battery voltage, or 'ignition on' voltage.
, and closing the dash switch, ( control signal I'm calling it ) completes
the circuit through the electromagnet, the two main contacts are closed and
the load consuming device gets it's power.
An example of the switch being in the ground side of the electromagnet
circuit is the fuel pump relay, the ECU supplies ground to energize the
electromagnet in the relay. The other side of that electromagnet would be
connected to batt powr or ign. pwr., The ecu supplies ground, the main
electrmagne pulls the contacts close,d power is routed through them to the
fuel pump.)
Make sense now ?
There are endless ways to make logic arrangements with relays. Supposing
you only want to complete the circuit through the electromagnet portion of
the relay only when two conditions are met. Say you only want fog lights to
work only if low beams are on. So you send your 12 volts low beam signal to
one side of the electromagnet, and on the other side you put your switch,
which supplies ground when you flip it. Thus, fog lights only work IF low
beams are on and IF the switch is flipped on the dash.
I find these rather fascinating, the possibilities. There are double
relays, there are ones that flip from one state to another each time it's
energized - a hi/low beam relay would be like that, thpse don't go from
on to off, bur from A to B ie. - join these 4 wires ) or B - undo those,
and join these 4 wires )
And some of hem are not actually energized in either state, but only when
hit with a signal to make them flip to the other state. Once they make A
contact say, it stays that way until it's hit with the 'control signal'
again. A hi beam relay can be like this, sits on low, until it gets a
singal from the stalk, that flips to to high, and it just stays there
conducting until it gets another control hit, then it flips to low. And no
signal is needed to keep it in either state - neat huh ? - the
possibilities or endless. I worked on aircraft system - radar, infrared,
weapons, radio etc........and would have to deal with pages for relay, like
30 in one system, often intertwined. Great fun.
And really............honest, having the switch carry the actually load of
the current consumer in any circuit is low tech and crude. And old
fashioned. Only in low current circuits to you want the current of the
load consuming device going through the switch.
There are other advantages and purposes too, but the primary one is to
isolate the switch function from the load carrying function, both in amount
of current carried and distance. Ignition key sends a signal on a medium
sized wire way back there to the rear of the van and remotely triggers a
good size electromagnet ( the starter solenoid ) which carries a much bigger
current through fat wires and completes the circuit ( of a short distance )
from the battery to the starter.
Isolates the load portion from the switching function.
Scott
www.turbovans.com
What engine is going in this ?
It's an air cooled 85 being made into a watercooled 'sort of 85' ?
.....which trans and which engine. If you say it's a 4 speed, say if it's a
DK from the air cooled or if the 091 from the 85, plz
-----Original Message-----
From: neil N [mailto:musomuso@gmail.com]
Sent: Monday, January 21, 2008 9:50 PM
To: Scott Daniel - Shazam
Subject: Re: Electrical questions. Radiator fan circuit from 85 Vanagon into
81 air cooled Westy.
Thanks for the great explanation Scott.
I don't know why, but my thinking got skewed into thinking that relays
reduced load on wiring so manufacturers could reduce wire gauge and
cost. But of course the relay is there to take the load of the switch.
Like duh! Thanks :)
Yah totally wanted to have an indicator light that would show if the
rad fan was on, but then maybe I worry too much! If the fan fails to
go on when it should, the temp gauge will let me know.
I'll stick with stock. If I decide I really need the indicator light
and/or an override switch, I'll re-read what you wrote here.
Thanks!
Neil.
On 1/21/08, Scott Daniel - Shazam <scottdaniel@turbovans.com> wrote:
> Hi, Neil
> The 85 vanagon rad fan circuit is *perfect*.
> I have never seen that relay fail in hundreds of vanagons, don't give
that
> a thought.
> And you could bypass it in an emergency if you had too.
> You want a two speed system, you don't need or want the high speed unless
> it's really needed.
> The stock system with a 3 pin single sender is perfect.
> Putting a switch on yourself is ok, and mark, I think he meant a separate
> indicator light, not one as part of the switch circuitry, but your warning
> is really good.
>
> What you want to do neil if you want a manual control in addition to the
> sender system ( just leave the stock system like it is ! ) .....you make
the
> switch trigger the relay, just like the sender does. If you want an
> indicator light to tell you the fan is on ( either manual or sender
> triggered ) do not take the light signal from the switch, get it from the
> rad fan ..........so that you know that voltage has actually gotten to the
> rad fan.
> Why anyone would wire an indicator light for a device in parallel with the
> device, rather than from the device itself is just beyond me. - we don't
> want to know the switch is flipped, we want to know that power has gotten
to
> the device - duh !
> But car engineers can't seem to grasp this it seems. ( they sure didn't
get
> it for diesel vanagon glow plugs, the light doesn't' tell you there's
power
> at the glow plugs, just that the relay for the glow plug has told the
light
> to be on. An example of how 'german engineering think' is only for when
> things are 'right' .........no sense about providing extra 'real' info
etc.
>
>
> Sometimes when you want to energize a device ( like this relay for the rad
> fan ) it's necessary to put a diode in he circuit to not get a signal
where
> you don't want it.
> For example, and I know you are not trying to do this, but on a Enough
16
> I had long ago, I wanted to use the 4 way flasher light as a rad fan
> indicator light, but still wanted it to work with 4 way flashers too, so a
> diode was needed on one branch of that light circuit, so that when the rad
> fan went off, it wouldn't also feed into the 4 way flasher circuit.
>
> But leave it alone from the relay downstream to the fan.
> It's perfect.
> The only thing downstream of the relay that you'd want to do is pick up
rad
> fan voltage for the indicator light, which you could just pick up at the
> output of the relay probably just fine.
> Relays are great devices.
> their biggest advantage and main purpose almost is so that the device load
> doesn't' go through the switching device. Imaging how big the ignition
> switch would have to be if it had to carry full starter current.
> Like when you upgrade headlights, you have the light switch energize
relays,
> which take almost no current to energize, and the actual headlight high
> current goes through the relays, which are designed for that load, and the
> plastic light switch isn't very much.
> Relays be good in many situations. Just keep that part stock - on the rad
> fan. . I would check the push-on ground connections right in that same
area
> very carefully ......above the fuse box, left. They get weak after a
while.
> I change them to screw and eye usually, about 8 grounds or so there.
> Scott
> www.turbovans.com
>
> -----Original Message-----
> From: Vanagon Mailing List [mailto:vanagon@gerry.vanagon.com] On Behalf Of
> neil N
> Sent: Monday, January 21, 2008 7:04 PM
> To: vanagon@GERRY.VANAGON.COM
> Subject: Electrical questions. Radiator fan circuit from 85 Vanagon into
81
> air cooled Westy.
>
> Hi all.
>
> If I'm reading this correctly, P 97.66 in Bentley shows a relay that
> when energized by "Rad Fan Thermo Sw II", energizes the higher speed
> of the Rad fan.
>
> Is the relay there to handle the higher current? Or am I totally
> misunderstanding the purpose of the relay?
>
> And when I install the cooling systems' electrical components into my
> air cooled Westy, (Jetta Gas engine conversion) could I eliminate the
> Rad Fan Relay?
>
> Could I also wire the circuit so when either "Rad Fan Thermo Switch" I
> or II is activated ONLY the high speed portion of the fan is
> energized?
>
> Are these bad ideas? I was going for simplicity and more reliability.
> (no relay to fail)
>
> FWIW, I will wire the fan circuit with an "override" switch and LED.
>
>
> Many TIA,
>
> Neil.
>
> --
> Neil Nicholson. 1981 Air Cooled Westfalia - "Jaco"
> http://web.mac.com/tubaneil
>
> Engine swap beginings: http://tubaneil.googlepages.com/
>
>
--
Neil Nicholson. 1981 Air Cooled Westfalia - "Jaco"
http://web.mac.com/tubaneil
Engine swap beginings: http://tubaneil.googlepages.com/
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