Low speed on electric fan

[trunt]

I had a thought that may or may not come through but it was interesting experimenting

Some say that the mechanical fan needs to stay because it provides some airflow around the engine, my thought was why can't an electric fan do that? If I run it at a slow speed until its needed it would provide at least some some constant flow. the relays to achieve this were not difficult to work out, I wanted the Davis Craig fan controller to give full speed weather ignition was off or on but the low speed to come on only when ignition is on, until the controller asked for full speed.

I dug my fan out and despite a specification of 17A found it was running at 22A (300W) and its a bit of a beast! The resistor I had was 0.3 ohm. When I ran it with the resistor it calmed it down to what I would usually consider "normal" which I felt was still a bit too much. Also, as beefy as the resistor looked after about a minute it started smoking!! -- To the online calculators --(I used to be able to do this manually back when I was a boy!) and in theory this would mean about 14A @ 8.5v at the fan(122W) and when I actually measured it thats what I saw. So far so good.

I played with the calculators a bit and decided to try a 0.5 ohm resistor rated 100W which would drop the fan down to 12A @85W (75W on the resistor) I found a great resistor from an electronic supplier with chassis mounted heat sink and spade connectors,$12 so ordered it

Terry

[barkerwilliams]

I thought that the mechanical fan is replaced by an electric fan because for much of the time driving at a "reasonable" speed the airflow through the radiator provides sufficient cooling. A mechanical, or electric fan always running causes engine load which absorbs HP or more likely for our car usage increases fuel consumption.

The Stag however has very poor airflows at the front causing the airflow to avoid the radiator and slip around the cowl or simply build up in front of the radiator, hence the design of the Supergill radiator which permits better throughflow.

But all in all with radiators slowly furring up, dead insects jamming in the radiator etc your design might turn out to be a real advantage. It might be nice to be able to turn it off prior to starting or on a really cold day to assist the engine getting to temperature quickly.

Let us know how you get on.

Alan

[trunt]

It might be nice to be able to turn it off prior to starting or on a really cold day to assist the engine getting to temperature quickly.

Let us know how you get on.

Alan

Will do

All I'm looking for is some airflow at idle to keep the engine bay temps down. On the cold day I'm thinking the mechanical fan is not switched off, the thermostat (or in my case the EWP) deals with that.

Keep in mind I'm in The USA.. 40 degree days are becoming a yearly event, and in mid summer 32 and humid is pretty much the norm. I also have installed the TR6 Spoiler so giving it every chance! Hey I could even go with a vane switch to switch it off at speed. I have seen shrouds that have flaps that open at speed giving more ram airflow, at standstil they close allowing the fan to draw all its air through the radiator, simple but effective.

If going full electric I would love to go with a puller fan, anyone managed that?

Terry

[DJT]

I thought that the mechanical fan is replaced by an electric fan because for much of the time driving at a "reasonable" speed the airflow through the radiator provides sufficient cooling. A mechanical, or electric fan always running causes engine load which absorbs HP or more likely for our car usage increases fuel consumption.

The Stag however has very poor airflows at the front causing the airflow to avoid the radiator and slip around the cowl or simply build up in front of the radiator, hence the design of the Supergill radiator which permits better throughflow.

But all in all with radiators slowly furring up, dead insects jamming in the radiator etc your design might turn out to be a real advantage. It might be nice to be able to turn it off prior to starting or on a really cold day to assist the engine getting to temperature quickly.

Let us know how you get on.

Alan

In my experience, the standard Stag radiator is perfectly adequate as is the OE fan as long as the viscous coupling is in good nick. In over 100,000 miles, the backup Kenlowe hung in front of the radiator has rarely been needed. Never in the past 40,000 miles. Temp gauge needle sits just below vertical whatever the speed or outside temp, with an 88 degree thermostat.

[trunt]

In my experience, the standard Stag radiator is perfectly adequate as is the OE fan as long as the viscous coupling is in good nick. In over 100,000 miles, the backup Kenlowe hung in front of the radiator has rarely been needed. Never in the past 40,000 miles. Temp gauge needle sits just below vertical whatever the speed or outside temp, with an 88 degree thermostat.

Understood and agreed but as I said it gets hot here, I’m just covering my bases, I have the standard radiator, mechanical fan and a good viscous coupling but I also like the thought of an electric fan and water pump running after switch off which the Davis Craig controller can provide to reduce heat soak. Once I have a electric fan on there for that I am just investigating options.

Others say the electric fan alone does the job, the usual argument against it is the engine bay temps, hence my thought process.


Terry

[Hughesy]

I run my Stag regularly in 40 degree heat on an electric fan only in Perth Australia. No viscous. I also monitor under bonnet temperatures with an sensor above the vee at the bonnet catch with the digital display in the cabin. Not surprisingly the maximum under bonnet temperature occurs when sitting at traffic lights or in slow moving traffic. In these instances the electric fan is on and providing maximum air circulation through the radiator and around the engine bay in the same way that a viscous fan does, only better as it is running at maximum speed whereas the viscous is being driven by an idling engine at a maximum of 700-800 rpm Once moving the under bonnet temperature quickly drops (over 20C drop) and the electric fan cuts out once it hits the thermostat control setting around a water temp of 90C. So in my experience the viscous doesn't do the best job of cooling the engine bay at idle and is then using engine power and additional fuel at speed when it is not required. I also note that all modern cars only run electric fans. Cheers Craig

[trunt]

That’s great info Craig, thanks!

Terry

[wilf]

I can echo what DJT said, in that after fitting a new viscous coupling last year, the (additional) leccy fan has become pretty much redundant, and I suspect only Stag paranoia makes me keep it. This even during the "hot" days of last summer ( I recognise that "hot" for us would be considered "chilly" in other parts of the world).
With the new coupling, and a flushed radiator and block, I am becoming used to a cooling system that works as it should.

Terry - I think your idea of an electric fan running on low speed is a good one, although I think there may be better ways ( thinking electronic here) to achieve that than a crude ( and very hot ) dropper resistor.

[mole42]

I have been thinking about the electric-only option but I would use an electronic (PWM) speed control, probably with two temperature sensors - one for the coolant and one for the engine bay.

However, I have just replaced the Torquatrol and fan with new, so I want to see what improvement that makes before I go modifying again.

Richard

[trunt]

I can echo what DJT said, in that after fitting a new viscous coupling last year, the (additional) leccy fan has become pretty much redundant, and I suspect only Stag paranoia makes me keep it. This even during the "hot" days of last summer ( I recognise that "hot" for us would be considered "chilly" in other parts of the world).
With the new coupling, and a flushed radiator and block, I am becoming used to a cooling system that works as it should.

Terry - I think your idea of an electric fan running on low speed is a good one, although I think there may be better ways ( thinking electronic here) to achieve that than a crude ( and very hot ) dropper resistor.

Crude?? I'll have you know this is the pinnacle of 70's technology

[mjheathcote]

Just remember that any two speed fan using a resistor is still using the same full speed current, just that the current is split between what the fan consumes in motor rotation, and what the resistor consumes in heat.
This is why many newer cars have two fans.
I know it is difficult to package two fans however on the Stag radiator, they would be both small.
You are also putting a lot of constant load on the alternator, especially if you have an electric water pump too.
Under bonnet temperatures are more probamatic these days with the increase in ethanol in our petrol causing fuel vapourisation, so getting a good air flow underbonnet is more important than ever.

[Hughesy]

For those who are interested in running in hot ambient temperatures, I also have fitted an air extraction system from the top of vee area into the mud guard. The system consists of a 12v extraction fan and 100mm flexible hose connected electrically to come on with the radiator fan. See photo.. What I have found from my under bonnet temperature measurements is that most of the heat is generated from the exhaust manifolds. They generate the rapid temperature rise when stationary. Somewhat surprisingly the addition of the extraction system does not result in a lower maximum under bonnet temperature when stationary as what quickly becomes obvious is that the exhaust manifolds get very hot and tit would take a huge volume of extraction to make any difference. What the extraction system does do though is increase the rate at which the under bonnet temperature drops once underway. It increases the cooling rate by about 2. I have been using this system for over 3 years now so it is well tested.

Just to clarify for UK cooler weather conditions I believe the standard system is just fine and I don't think there is really any issue with the cooling system or with under bonnet temperatures in a well sorted car!

[trunt]

Just remember that any two speed fan using a resistor is still using the same full speed current, just that the current is split between what the fan consumes in motor rotation, and what the resistor consumes in heat.

No, thats not the case, the series resistor adds more resistance to the circuit and that lowers the total current flow through both, so in my case with the 0.5 ohm resistor on the 0.6 ohm fan the current drops from 22A (300W) at the fan down to 14 amps and the total power drops to around 160W total (85W on fan, 75W on resistor) you can also think of it as a voltage divider, the 0.5 ohm resistor is dropping about 6v off the normal 13v fan voltage.

OK on the alternator, I am fitting an uprated one and this is about the same load as the lights I guess, but at night? I am still to see what this can achieve, maybe in the end I can go up to 1 ohm and it will suffice? maybe its a bust!

Terry

[marshman]

Why not do as Richard (mole42) suggested and use a PWM controller? Such as this (or similar - I didn't spend much time searching):

https://www.ebay.co.uk/sch/i.html?_from=R40&_trksid=m570.l1313&_nkw=323585726803&_sacat=0

PWM so it is much more efficient and pretty much infinitely controllable, virtually no wasted power and relatively cheap. I know this one is cheap Chinese electronics but it could be OK to experiment with then change it for a "quality" model if and when it fails, (I have two mains versions controlling our house ventilation system and they have been happily running continuously for 5 years, cost less than £5 each) Also if you mated it to the correct resistance slope temperature sensor you could get it to automatically increase the fan speed as the temperature increases, or just use as a simple speed controller where you can manually set the slow speed suit.

Just a thought

Roger

[trunt]

Yup Roger, I was looking at them last night,

Surprised me how cheap they are and it would give a better way to experiment with it but in the end it would need to be more rugged. . One thought was weather you can ground one of the outputs? probably not, so then you are into double pole relays or ways of switching it to full speed electrically. (short out the potentiometer with a relay contact?)

My basic thoughts were that if the "puller" engine fan is there you really need a shroud and basically, I dont have one! they are pretty rare and cost $200+ when they do come up. I really like the insurance of the electric fan and its ability to run on a little after engine switch off. Without the engine fan and therefore no shroud the radiator opens up a bit for free airflow at speed helping(?) the "electric pusher fan blocks airflow" issue. The only issue then was engine bay temperatures.

The basic premise could be promising, I dont even have the engine in the car yet it was just something that occurred to me to wire in as I was assembling the relay box for the fan

Got us all thinking though!