VCCA Home Forums TECHNICAL - GENERAL Electrical - 6 volt fitting a 12volt cooling fan to a 6 volt system

Hi there,
I have bought a 12 inch Davis Craig 12 volt cooling fan for my radiator, and managed to fit it through the small aperture at the bottom of the grill.

I discovered that all their fans (12volt) can be run on a 6 volt system, but they run at half speed.

The relay that is supplied is 12 volt and needs at least 8 volts to trigger the switch. I am fitting it up with a simple on/off switch.
An extensive search of Australian company's drew a blank for sourcing a 6 volt 5 prong relay.

I turned to google and ebay had a selection available from the good old USA, as usual....
I have one on order and will see how it all works in a couple of weeks time when it arrives.

I write this post for the benefit of others who may wish to go this way with extra cooling for those 100 deg + days in the summer. It took me many phone calls and a day of time to discover that the 12 volt relay actually wont work with the 6 volt system, so now you may save some time with the above information?


Another thing I learnt is that if the headlights are wired via a relay, the brightness will be enhanced by 60% ? It also lengthens the life of the switch as well....it says....
Can anyone explain this phenomenon

The End

Peter

Hi Peter, I used to live in Australia from 1985 to 1990 -- Castle Hill NSW, a northwest suburb of Sydney, a bit north of Paramatta.

I will provide an answer about the headlight relay. I have done two of my cars this way. I am not sure about the 60% increase, could be true if your dash switch, dimmer switch and wiring is in bad condition. I do it differently than most articles suggest. What they suggest is mounting a relay on the firewall, power it direct from the battery (With a fuse in line) then on to the dimmer switch and thus to the headlights. I have found that the dimmer switch is a major cause of voltage drop, so here is how I do it.

I purchase TWO relays, and mount them on the firewall (or other convenient location) and power both of them with a #12 wire direct from the battery terminal on the starter. The reason you don't need two wires is that only one relay will require a load at a time, so a single wire is more than adequate. I put an inline fuse in that wire to protect the circuit, and I locate that fuse CLOSE to the starter so as to protect the wire in case of a short. I locate the wire running from the dimmer switch (I think in Australia you call it the DIPPING SWITCH) to the high beam and low beam side of the head lights. I trigger one of the relays with the high beam wire and the other relay with the low beam wire. Therefore, the only load the light switch and the dimmer switch see is a fraction of an amp to trigger the relay. Thus, these two switches will last almost indefinitely, because the only load left is the relay and the tail lights, which is minimal. Attach the other end of the wire you cut going to the head lights, and attach the high beam wire to the LOAD side of the High Beam relay, and likewise attach the other wire to the LOAD side of the low beam relay. You now have a direct path from the battery terminal to the headlights, bypassing the volatage drop through two switches. The shorter the wire path is, the more voltage you will have at the headlighs. To impove the situation even more, run a new heavier wire from the relay to the two headlights, thus reducing the voltage drop even more.

What I do to test this theory out is BEFORE MKING ANY CHANGES, I start the engine and set it on fast idle. I turn on the head lights high beam, then at a point very close to the headlights I stick a needle into the insulation making contact with the wire inside. I use a volt meter and record the reading. On the last vehicle, I was getting 4.2 volts at the headlights. Do the same thing with the low beam. After making the changes with the relays in place, I again started the engine and set the engine speed at the same place as before. Checked the voltage at the headlights and found that instead of 4.2 volts, I now had 5.9 volts, or a 40.4% increase in voltage to the light globes (Light bulbs for you Yanks). That could very easily account for at least a 40% increase in light output, if not even more.

Ron

Hello again Peter, One downside to how I have described this is that I by-pass the amp meter, so you won't see the drain on the battery on the amp meter on the dash panel. It is possible that you could actually be draining the battery with the headlights even though the amp meter shows a charge.

Ron

Actually using a relay isn't odd at all. The output and input of the relay are high current input directly from the battery with heavy wire has only the resistance of the wire from the battery and almost zero resistance internally in the relay and very little to the headlamp filaments. The switching coil of the relay requires a small amount of current which is good because it is the regular headlight current from the headlight switch. The relay allows direct current from the battery to the headlamps. This is important noticeable in the six volt system since the wattage required to power the headlamps needs two times the current of that of a 12 volt system.

hi there Ron,
my brother lived at baulkham hills and I used to drive through Castle hill most weekends (40 yrs ago), so i know just where you are coming from.
Thanks for the info on relays, I did not realise how important they are in automotive construction.
They are expensive at $18 plus postage the same again, so I will have a go at the headlights later.
cheers

Peter

just an update for you,
I fitted the new 6 volt relay and the 12 volt fan now works perfectly, but at half the speed of the 12 volt setup.

I have wired it in so that even with the ignition turned off, it will still run and cool the radiator when stationary, via the simple on/off switch. It makes quiet a noise so I will never forget to turn it off....I hope

Peter

Peter
Most "after market" parts shops can get a automatic thermal switch that will turn the fan on and off at predetermined temps, some are user temperature adjustable.
Tony

hi there,
thanks Tony for the info, there was a mention of that in the instructions for the Davis Craig fan. It looked too complicated for me to try and fit, so I went for the simple switch....

Peter