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 Post subject: Re: electric fan
PostPosted: Fri Sep 18, 2020 8:45 pm 
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Location: Harrow Middlesex
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I've just found the problem with my electric fan - the 80 Watt motor one that I thought might be too small.
It still might be, but there's a bigger problem in that while it blows fine when it first comes on, after less than a minute is starts to slow down, and after 5 it's hardly blowing at all, which just sucks. I assume that's a problem with the motor, as the battery voltage is holding up reasonably well. So it's a good job I have a replacement 120 Watt one in the garage.
I hope I don't have to pull the rad to swap them over.

Graham
Graham

Ive made brackets to hold my fan to the radiator simular to yours,i can get my radiator out of the car with the fan still attached bit tight but do able

Dave


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 Post subject: Re: electric fan
PostPosted: Fri Sep 18, 2020 9:21 pm 
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Location: St Annes on Sea, Lancs.
It's only the bottom mountings that are through the rad, and the grills are on allen screws. So I may be able to cut the ties at the front or back and pull the fan up with the rad left in place - I hope. I'll look tomorrow and hope to have it done sunday.

Could have got started today, but I only discovered the problem in maccies car park after boiling over in the drive-thru. Let it cool while me and the lad ate, topped it up, and came home with no problems.

Realized it was hardly blowing when I switched off in the car park, but when I got home, it came on reversing into the drive, and was blowing well. So I left the fan blowing with the bonnet up, and could hear is slowing down. Checked the voltage and that wasn't dropping, so I deduce the fan's motor is buggered. I'll confirm all this before I pull it. If I do, I'll see whether I want to put a new motor on that fan or replace the whole caboodle.

Graham

_________________
The 16v Slant 4 engine is more fun than the 3.5 V8, because you mostly drive it on the upslope of the torque curve.

Factory 1977 TR7 Sprint FHC VVC 697S (Now all of, but still needs putting together)
B&Y 73 Dolomite Sprint UVB 274M (kids!)
1970 Maroon 13/60 Herald Convertable (wife's fun car).


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 Post subject: Re: electric fan
PostPosted: Fri Sep 18, 2020 10:53 pm 
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Surely the answer is to buy a quality fan.
I can highly recommend the Spal range. Not exactly cheap, but they just work as they should. So under £60 gets a quality bit of kit.

Also be aware, having tested teh current flow of a couple of cheaper fans, the power quoted was on start-up. So a 120Watt fan did indeed pull 10A, but within a second or two was down to about 5amps, so 60watt when running.

https://www.t7design.co.uk/catalog/prod ... tegory/33/

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Clive Senior
Brighton


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 Post subject: Re: electric fan
PostPosted: Sat Sep 19, 2020 1:55 pm 
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Location: St Annes on Sea, Lancs.
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Surely the answer is to buy a quality fan.
I can highly recommend the Spal range. Not exactly cheap, but they just work as they should. So under £60 gets a quality bit of kit.

Also be aware, having tested teh current flow of a couple of cheaper fans, the power quoted was on start-up. So a 120Watt fan did indeed pull 10A, but within a second or two was down to about 5amps, so 60watt when running.

https://www.t7design.co.uk/catalog/prod ... tegory/33/
Not sure it's a surprise that it draws more power while starting than steady state - some 120 Watt ones do mention 7 Amps draw, presumably as continuous current, from a 12-13 Volt supply.

My main concern about the budget fans is the waterproofing, which I worry won't really be the full IP68 level.

The problem I have is that if I knew what CFM value I need and what current/power that relates to, I'd be able to evaluate fans on specification and check what I get against that. As said, I want to do this with the smallest power fan that does the job, unless I can add speed control (and there are complications in that option). I certainly don't automatically believe that bigger is necessarily better anymore than I accept that "you get what you pay for" is a real axiom. But as I don't know what CFM/current/power that is, I can only really suck it and see. And while in that mode, I will do what I can to save costs and try to characterize what does the job.

All I can say, so far, is that a fan drawing 4 amps continuous with the transverse curve of the blades the right way round - low pitch against the rad - is a bit short of what's needed when stuck in traffic in high summer. However, it's not too much current draw with the engine idling with the lights, wipers, and demist fan all on.

As to the fan shown at that link, the one pictured is the wrong way round to go behind the Dolomite's radiator on both counts of the curvature's of the blades (and it's listed as a 24 Volt unit). Also, there's definitely room for a 12" fan rather than an 11". I know it's not a huge difference, a 30 cm vs 28 cm fan gives 17.5% more swept area, assuming the same 11 cm hub, but I think it's worth that extra. Also, if we're looking at quality not cost, is it being a brushed motor, rather than brushless, not a concern?

Graham

_________________
The 16v Slant 4 engine is more fun than the 3.5 V8, because you mostly drive it on the upslope of the torque curve.

Factory 1977 TR7 Sprint FHC VVC 697S (Now all of, but still needs putting together)
B&Y 73 Dolomite Sprint UVB 274M (kids!)
1970 Maroon 13/60 Herald Convertable (wife's fun car).


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 Post subject: Re: electric fan
PostPosted: Sun Sep 20, 2020 11:38 am 
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Well the replacement fan is in and running. It's an Aeroline 12" curved blade 120 Wat with the blades reversed to pull through the rad. I got it from Watford Classics. The picture on their eBay listing is wrong, but the one supplied fits perfectly on the back of the Dolomite rad.

Image

Starts at 10 Amps and drops to just under 8 after a second or so. So it's running power consumption is only about 100 Watts. That's twice what the supposedly 80 Watt fan it's replaced was using.

Yesterday when air temperature was about 19 C, it was cooling well enough at idle to turn off at about 90 C measured on the hot end of the rad, having turned on at 95. Those are measured with a £2 LCD thermometer with its sensor wedged in the fins. But they shouldn't be far off, as it boils over well above 100 on that gauge.

Worst points are that the power leads won't stay in the clips without and extra tie-wrap and it thrums a bit at full power. I guess that's less than perfect balance in the blades, and it feels like its being spun close to a resonant frequency. So, possibly, iffy design from a low cost fan. But I don't expect that thrumming will do worse than reduce it's life a bit.

_________________
The 16v Slant 4 engine is more fun than the 3.5 V8, because you mostly drive it on the upslope of the torque curve.

Factory 1977 TR7 Sprint FHC VVC 697S (Now all of, but still needs putting together)
B&Y 73 Dolomite Sprint UVB 274M (kids!)
1970 Maroon 13/60 Herald Convertable (wife's fun car).


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 Post subject: Re: electric fan
PostPosted: Sun Sep 20, 2020 12:04 pm 
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I decided that the N/S of the rad gets hottest quickest as that's where the hot water comes in from the engine, so it's the best place to put the fan anyway.
[Pedant Mode=On]
Actually it's the worst, consider a stationary car without a fan (I'm going to exaggerate here). As the air around the radiator heats toward the temp of the radiator the rate of heat transfer reduces. At the hot side there is a big temperature differential, lots of energy transfer before the air is heated and transfer stops. At the cool side the differential is less, less energy is removed from the rad before transfer in that area stops. There is a limit to the rate of energy transfer per unit area, you want to keep as much area as possible providing useful cooling. On the hot side blowing more air with more powerful fans is likely to reach the limit of the rate of thermal transfer, blowing more after that adds nothing. On the cool side you add a fan to prevent ambient air reaching radiator temperature, keep that side doing useful work.

But ignore me, stick the fan where it will fit. In practice the difference is probably negligible on a car. On a megawatt chiller on ethylene cracker it matters rather more. Picture in your mind a horizontally mounted radiator wearing a 4x4 grid of 2 meter diameter fans. The controller is programmed (that's my bit) to start the ones on the cool side start first if they are looking for efficiency. Sadly that's rare. More common is complex control aimed at wear levelling (and hence maintenance cost reduction). More even than that just turn the lot on, less control gear to go wrong and screw the environment.

At the end of the day so long as the return temperature is low enough to keep the thermostat from sitting fully open you're all good, the system isn't saturated.
[Pedant Mode=Off]

_________________
1978 Pageant Sprint - the rustomite, 1972 Spitfire IV - sprintfire project, 1968 Valencia GT6 II - little Blue, 1980 Vermillion 1500HL - resting. 1974 Sienna 1500TC, Mrs Weevils big brown.


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 Post subject: Re: electric fan
PostPosted: Sun Sep 20, 2020 1:08 pm 
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Quote:
Quote:
I decided that the N/S of the rad gets hottest quickest as that's where the hot water comes in from the engine, so it's the best place to put the fan anyway.
[Pedant Mode=On]
Actually it's the worst, consider a stationary car without a fan (I'm going to exaggerate here). As the air around the radiator heats toward the temp of the radiator the rate of heat transfer reduces. At the hot side there is a big temperature differential, lots of energy transfer before the air is heated and transfer stops. At the cool side the differential is less, less energy is removed from the rad before transfer in that area stops. There is a limit to the rate of energy transfer per unit area, you want to keep as much area as possible providing useful cooling. On the hot side blowing more air with more powerful fans is likely to reach the limit of the rate of thermal transfer, blowing more after that adds nothing. On the cool side you add a fan to prevent ambient air reaching radiator temperature, keep that side doing useful work.

But ignore me, stick the fan where it will fit. In practice the difference is probably negligible on a car. On a megawatt chiller on ethylene cracker it matters rather more. Picture in your mind a horizontally mounted radiator wearing a 4x4 grid of 2 meter diameter fans. The controller is programmed (that's my bit) to start the ones on the cool side start first if they are looking for efficiency. Sadly that's rare. More common is complex control aimed at wear levelling (and hence maintenance cost reduction). More even than that just turn the lot on, less control gear to go wrong and screw the environment.

At the end of the day so long as the return temperature is low enough to keep the thermostat from sitting fully open you're all good, the system isn't saturated.
[Pedant Mode=Off]
Interesting.
If I thought the effect on air flow when driving from the fan, which will windmill in the airflow, was very significant, I'd worry more about it's position. But in the worst case situation, which is when the airflow is only from the fan, having it on the hot side gives the highest heat loss for a given fan power.

In the other, less than worst case situations, when there's forced airflow from the cars movement, I think there'll be more than enough airflow, in most cases, that the loss from the fan's hub (11cm dia) and cage, and a bit drag from the windmilling blades, won't make much difference.

However, I admit, in those less than worst case situations, having it on the hot side causes the most effect on cooling from lost flow.

Graham

_________________
The 16v Slant 4 engine is more fun than the 3.5 V8, because you mostly drive it on the upslope of the torque curve.

Factory 1977 TR7 Sprint FHC VVC 697S (Now all of, but still needs putting together)
B&Y 73 Dolomite Sprint UVB 274M (kids!)
1970 Maroon 13/60 Herald Convertable (wife's fun car).


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 Post subject: Re: electric fan
PostPosted: Sun Sep 20, 2020 1:31 pm 
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Done some testing on the new 120 Watt (100W measured) fan to see what's what. It's only about 18 C air temp here today, so not exactly the worst case conditions. But it not much I can do about that.

At idle, coming on about 90 and going off at about 85, measured as said, the fan's on for a fairly constant 80 seconds about 5 mins apart. So on about 1/3rd of the time. I guess if I measure that ratio at some other air temperatures, I can estimate what air temperature it's on all the time. But to estimate at what temperature the fan can't stop it boiling at idle, I'd need to do this letting it rise to almost that temperature before the fan comes on, and I don't fancy that test much. Maybe I can get if from mark/space ratios for different on/off temps at one air temp, but it's more mucking about than I'm up for.

But on a 3rd at that low setting, even at only 18 air temp., seems very reasonable to me, and much more satisfying than the supposedly 80 Watt one ever was.

Voltage wise: With the dipped headlights and heater blower on, the battery voltage drops from 12.7 to 12.2 Volts in the 80 seconds. And drops and rises back fairly quickly, a few seconds from turn on or off.

I don't know what extra effect the wipers will have, as I won't run them on a dry screen and I ain't micturating about with a hose with the bonnet up.

Graham

_________________
The 16v Slant 4 engine is more fun than the 3.5 V8, because you mostly drive it on the upslope of the torque curve.

Factory 1977 TR7 Sprint FHC VVC 697S (Now all of, but still needs putting together)
B&Y 73 Dolomite Sprint UVB 274M (kids!)
1970 Maroon 13/60 Herald Convertable (wife's fun car).


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 Post subject: Re: electric fan
PostPosted: Sun Sep 20, 2020 4:27 pm 
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finished the mounting brackets for the fan and the radiator , i noticed on my fan theres a weight on one of the blades my fan is 220w

Dave


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 Post subject: Re: electric fan
PostPosted: Sun Sep 20, 2020 4:41 pm 
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Location: St Annes on Sea, Lancs.
I've seen fans with a clip on one blade. I assume it's to correct some imbalance in the moulding.

Graham

_________________
The 16v Slant 4 engine is more fun than the 3.5 V8, because you mostly drive it on the upslope of the torque curve.

Factory 1977 TR7 Sprint FHC VVC 697S (Now all of, but still needs putting together)
B&Y 73 Dolomite Sprint UVB 274M (kids!)
1970 Maroon 13/60 Herald Convertable (wife's fun car).


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 Post subject: Re: electric fan
PostPosted: Sun Sep 20, 2020 4:51 pm 
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Joined: Sun Sep 08, 2013 3:35 pm
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Location: St Annes on Sea, Lancs.
Quote:
my fan is 220w

Dave
Do you have a meter that can measure the current it draws? Be interesting to know if the 220 Watt figure is peak at startup, like 120 Watts is on mine.

Will you be testing what happens to battery voltage when all the other likely electrics are on at idle?

Graham

_________________
The 16v Slant 4 engine is more fun than the 3.5 V8, because you mostly drive it on the upslope of the torque curve.

Factory 1977 TR7 Sprint FHC VVC 697S (Now all of, but still needs putting together)
B&Y 73 Dolomite Sprint UVB 274M (kids!)
1970 Maroon 13/60 Herald Convertable (wife's fun car).


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 Post subject: Re: electric fan
PostPosted: Sun Sep 20, 2020 8:04 pm 
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Location: Harrow Middlesex
Quote:
Quote:
my fan is 220w

Dave
Do you have a meter that can measure the current it draws? Be interesting to know if the 220 Watt figure is peak at startup, like 120 Watts is on mine.

Will you be testing what happens to battery voltage when all the other likely electrics are on at idle?

Graham
Graham

Ill test it at the weekend


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 Post subject: Re: electric fan
PostPosted: Sat Sep 26, 2020 2:42 pm 
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I've just noticed that at least one of the ties that goes through the rad, and is sprung behind then fan, has given a bit. I've tested on an old one, and with a bit of head from the shrink gun, the long pin will bend over the plastic rove on the front of the rad and should then hold. So I'm going to have a go at that later.

Graham

_________________
The 16v Slant 4 engine is more fun than the 3.5 V8, because you mostly drive it on the upslope of the torque curve.

Factory 1977 TR7 Sprint FHC VVC 697S (Now all of, but still needs putting together)
B&Y 73 Dolomite Sprint UVB 274M (kids!)
1970 Maroon 13/60 Herald Convertable (wife's fun car).


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 Post subject: Re: electric fan
PostPosted: Sat Sep 26, 2020 6:50 pm 
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Location: Harrow Middlesex
Ive not used any tyes only the brackets i made

did get time to test the fan today


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