Cooling fans- interesting viewing.

[Dez]

Just saw this-



It's a semi-scientific test, but not testing a compatible size electric fan is a glaring omission in my eyes. Interesting to see just how big the parisitic losses are though.

[VW]

Dammit, now I need a new fan too.

[Dez]

Yeah, my thoughts too.

I would surmise that European engines with smaller fans would loose a lot less as an outright figure, as they have less mass to spin up and less force acting upon the smaller blades, but conversely they have a lot less HP to loose to start with, so as a percentage of available power it could well be an even worse number than the 8% or so that they lost.

[adam73bgt]

I've been keeping up with the engine masters series and saw that ep today as well, I was surprised by the levels of losses seen as well

They did briefly mention about electric fans in the video, but as you say it would have been nice to run one as well to see what the results would have been

Might have been nice to do another baseline, no fan run at the end as well just to show that the engine itself was still making the power it was at the start, but I imagine it would be.

[VW]

Yeah, I thought a final no fan run would have been good.
I see their point about not bothering with an alternater run as you'd be fitting one anyway.
Engine wont care if the electric system has a fan on it or not.

[bortaf]

May 1, 2017 18:33:49 GMT VW said:

Yeah, I thought a final no fan run would have been good.
I see their point about not bothering with an alternater run as you'd be fitting one anyway.
Engine wont care if the electric system has a fan on it or not.

It will do when it's on, any electrical load on the alt will transfer to the engine, it's why your engine slows when you turn on the lights, shame they missed a lecy fan out, it would have just made a more complete episode, enjoyed it as usuall though, i'd love to see a UK tuner trying this on YT, can you imagine a sseries from dave walker

[VW]

I thought the charging system made the same charging power no matter what the draw on the system and excess was just dumped to earth.

I admit ive no real idea why I thought that, and have never actually looked at it.

[Dez]

I think the electrical system will care.

Anecdotal I know, but my mx5 had a slightly loose belt last week, didn't manifest itself in normal daytime driving but if you put the Lights or blower fan on it did.

I'm a bit rusty on such things, but I think it's an application of ohms law, where although the voltage stays fairly constant, to keep it so with an increased current demand would also increase the resistance, requiring more horsepower to overcome it.

I think the question is what HP draw will an extra 30-40 amps load on the alt take? I've not done the maths but a quick Google finds a few people who have, and the answer seems to be 1-2HP, so far less than a mechanical fan.

[slater]

The thing is your fan will never be running when you are looking for full power. The fan only runs when your stationary (or you have it setup wrong)

[fad]

Electric fan absolutely puts a greater load on your alternator and therefore engine.

So, a quick electronics lesson. Voltage and current - lots of folk don't seem to understand this.

Bin the idea of engines and alternators for now, lets look at a power supply that says "12v, 4A" on it.

Voltage is voltage, that number is whatever is says on the tin (massively over simplifying this), so that power supply is kicking out 12v. If you put that onto something that needs 5v, then bang. If you put it on something that needs 24v, then nothing happens (again, over simplifications for those who do know their electronics and electrical, but bare with me). If you put it on something that needs 12v, it works.

Now, over to the current. Your 12v thingy-that-now-works says on it that it needs 2 amps to run. But your power supply says 4amps on it. It doesn't mean that it is going to ram 4 amps into it and it will go "Bang" like if you put too much voltage in. It doesn't work that way. The "2 amps" you see on your load tells you how much current it will consume. If your power supply cannot output enough current, then it won't run properly. That consumption is governed entirely by the impedance (resistance) of your load (Ohms Law). The greater the impedance, the greater the resistance, the lower the current that it consumes. (Yes yes all the smart arses who know a bit more are about to correct me and point out dynamic resistances, dynamic loads, and all sorts of things, but we are talking in simplest terms here). It doesn't just dump "spare" power to earth, it simply means that it is capable of producing more when needed. When you increase that load, the power supply will draw more current from the mains end, and pump it out (but of course it will draw much less current at a much higher voltage and put out a higher current and a lower voltage, and convert from AC to DC - I can explain deeper here if anyone is interested how that conversion works).

Ohms law:

Voltage = Current x Resistance (Impedance)

This will apply to BOTH ends of the power supply, input and output (as the power supply is also a "load").

So, this tells you when voltage is fixed (as per your power supply), then the resistance (impedance) will decide your current. This is also one of the reasons things go bang when your voltage is incorrect.

(for those interested, power calculations are the same when we are talking basic terms and not being smarty pants muddying the waters with RMS values, AC supplies, and all the rest of it - power = current x voltage)


So, lets translate this to your car. Your alternator is running, putting out 14v (to make maths easier). We are assuming your earths and everything are good. So, we shall pluck a figure out of the air, say it needs 12A. Your alternator can produce 90A before it craps out. Then you switch on your fan, which needs another 2A, meaning your alternator has to put out 14A in total. Where does that extra amperage come from? It's not always pumping out 90A (things would get VERY hot if it were!). It simply means that it CAN put out 90A. Well, because the alternators "input" power is converted from mechanical energy to electrical from the engine, the extra power comes from the engine. If you were pedaling the alternator yourself, and someone switched on the fan, would would notice a distinct change in the resistance of your pedals. If you are REALLY bored, this is actually easily testable. Get a small DC motor (the kind you find in battery operated kids toys). Wrap a bit of cotton or string around the shaft and pull. It will spin nice and easy... Now put a small light bulb over the terminals of the motor and repeat. It's suddenly harder to spin. The electrical load on an alternator directly translates as greater mechanical resistance to being spun.

The reason for this... You are having to push more electrons around. Electrons don't like being pushed (another over simplification but it will do for now). More electrons for the fan, means more pushing, means more mechanical resistance. Bigger fan, more air pushed, more power required, more load on the alternator. In short, you would be robbing Peter to pay Paul if you used an electrical fan rather than mechanical, and you would have in there the inefficiencies and parasitic losses in converting the mechanical energy into electrical and then back to mechanical (the fan motor, the alternator, they all need power to run and will waste energy). You would probably see WORSE performance with an equivalent sized electrical fan assuming it was running constantly. However, as already pointed out,were this "real world" and not dyno testing... Then you would find that your power would be GREATER as the fan would shut off when you had sufficient airflow over the radiator. That said, a mechanical fan would actually see no air resistance and therefore present no load to the engine at speed either once the air volume coming in exceeded what the fan could push.

If you wanted your fan to not affect the draw on the alternator, you would connect it to a separate battery that was not connected to the alternator in any way.

[VW]

fad
Thanks for the explination. I knew a reasonably amount of that but not how the extra load on the alternater translated into more resistance at the pulley.

[fad]

May 2, 2017 10:39:15 GMT VW said:

fad
Thanks for the explination. I knew a reasonably amount of that but not how the extra load on the alternater translated into more resistance at the pulley.

Folk not fully understanding the nature of voltage and current is actually really common, even in my field I find some very bright people who have not quite understood a fundamental that then leads to unnecessary work, poor designs etc. It's not really an obvious one, we are so used to going by numbers on boxes that we forget to think about what they mean. Hope it helps, anyway (And I REALLY hope it wasn't patronising!! That's REALLY not how I meant it!)

[steveo3002]

all you need to care about is the elec fan wouldnt be running much when out and about , and who cares if its sapping 5hp when sat in traffic

[gib]

There are some fundamentals that have been missed in the experiment and the explanations above. But the results as pure results were interesting and surprising ( I guessed at a few HP max certainly no more 10).

As for the laymen's explanation you negate the fact that draw is from the battery / alternator circuit the time for which is not linear. I.E you can put the power in the battery on over run or in fact at any time and then use this at any time. This is why the theory of electric superchargers is sound but the practicality is only just starting to come to fruition. Also its on demand rather than based on a few factors which are related to but not necessarily directly linked i.e engine bay temp / water temp / rpm.

This is why power cuts for alternators are great for max power.

Why they didn't hook up a Anemometer (windy meter) I don't get as ultimately you want max airflow for minimum hp. But inversely this is direct drive so there is not a lot you can do.

Good video as it even gives you the cue to fast forward over the advert, sponsor bit

[fad]

^See, smarty pants coming out of the woodwork LOL You are of course right (and the basis of kers technology and many hybrid vehicles is around that principle). But the trouble is when you include the battery, you end up with none-linear consumption, you need to consider state of charge of the battery, size and type of the battery and the inherent characteristics of it, and all sorts of other bits and bobs that muddy the waters and really don't help with the basic explanation. Laymen don't need to know all that. I also negated the dynamic impedance of the fan motor, rather assuming it to be of a fixed impedance, lumped the parasitic losses into the load, stepped around the fact that indeed the consumption from the battery would not be regular (though touched on that later when I talked about the fan going off when not required), ignored the fact that the alternator would not actually be supplying an extra 2 amps in reality, ignored temperature of conductors, assumed perfect connections for ground, ignored ripples etc. We could go on all afternoon playing "who knows more about vehicle electrics", though I appreciate where you are going with the bits I missed.

I wanted to convey the basics of voltage and current and the understanding of the two and where it comes from so folk would understand a little more of what is often considered a "dark art", not to patronise those who already have a sound knowledge of such things.

[VW]

He also suggested in the vid that the power the fan uses would probably be the same no matter what the hp output of the motor.

Cant be as clear cut as that otherwise even with their smaller fans old british cars would be screwed. I spent £1500 getting my sidevalve from 25hp to 45hp (ish). Are they suggesting I could have just took the fan off

[welshpug]

I doubt your 45 bhp engine would have anything like the behemoths of fans they run on a big block!

[VW]

Indeed, sidevalve had a 4 blade fan something like 10-12 inch I believe, long time ago.

I guess I was being a little flippant.

[fad]

Lots of VW racers take the fan belt off their air cooled when racing. Mine removes it's own fan belt when I am asking the engine to scream past 7000rpm...

[paul99]

My area of work, so interesting viewing. What most won't know is that power consumption will rise with the square of speed, so little surprise at the high powers at high RPM. The trouble with engine driven fans is that to be effective at low revs, they will be over performing at high revs. Surprised at the disdain of the presenters for electric fans (which will be optimised for their intended rpm, and being independent, will run at that speed) and of course be switched off completely when not needed. I'm guessing that's why most mainstream car makers use electric.