My DC fan doesnt spin fully... only stutters

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Old 07-12-17, 03:46 PM
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My DC fan doesnt spin fully... only stutters

Hello All.

I have a DC 24v Fan, which at full load uses around 7Amps.

I brought a DC 24v 13A PSU Driver, which when i first tested the fan powered it just fine.

After a week or so went by, I reconnected the driver again, and now the fan doesnt spin even 2% of what it did before.

What happens is the fan just about rotates(not very fast spin at all) for half a second then stops for 5 seconds then makes a weak half a second rotation again.

Around 2 seconds after I unplug the PSU Driver or dissconnect it from the fan, the fan spits out one last weak rotation attempt for a bit longer than half a second.

What could be the problem here?

Is it the PSU or the fan?
 
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Old 07-12-17, 04:02 PM
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With the fan connected to the power supply and running..... you need to check what voltage the power supply is putting out.
 
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Old 07-12-17, 05:33 PM
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Well, the fan doesnt run technically, but do you mean check the voltage whilst the fan is doing its half second weak rotate and 5 seconds of nothing?
 
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Old 07-12-17, 06:53 PM
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Yes. Check the power supply not connected and then again with the fan connected.
 
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Old 07-13-17, 05:35 AM
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Is your power supply trying to control the speed of the fan? If there is no temperature input the power supply may think the fan doesn't need to run or it may be running it at a slow speed. 7 amps is pretty high draw for a computer fan so the power supply might be sending out the current needed to slowly turn a smaller fan.
 
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Old 07-16-17, 02:59 PM
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@PJmax

Ok, tested the voltage.

I purchased another of the PSU, and am having the same issues with it as the first.
Without the fan connected, the voltage on the PSU reads 24.0V - on both PSU - which is just perfect.

When connecting the fan, and then testing the Voltage, the reading shows 0.2V, then every 5 seconds or so when the fan kicks, the Voltage jumps to around 1.0V.
Lastly when unplugging the PSU, the fan has one big last kick AFTER it is unplugged, the voltage of that kick goes up to 2.0V.

Putting the Voltage test aside, I kept touching the fan wires to the PSU over and over, and maybe one out of 20 times the fan seemed to spin at full 24V and stay on until I removed the wires...
It seemed that if I left the PSU on for a while w/o any load, and then touched the fan wires on the terminals after 40 seconds, I am more likely to get the fan to spin at 24V correctly. but if I keep touching the fan wire to the terminal it never seems to work...

What could the voltage test indicate? And what could the scenario I posted below that indicate?

Fan or PSU?

Also one last question, I attempted to use this PWM http://www.ebay.co.uk/itm/152558432200
with the PSU's and Fan, is there anyway this could damage the PSU's?

I am also wondering whether to get a higher amperage PSU? 24V 20Amp, currently I have 24V 15A
 
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Old 07-16-17, 03:57 PM
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Those switching type power supplies are protected from dead shorts. Your DC motor is appearing as a dead short to that supply. Those power supplies don't all act the same way but they are all protected from short circuits.

You will need a linear power supply to run that fan. A linear supply has a full size transformer to convert the voltage.

ebay/uk/24vdc+linear+power+supply.
 
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Old 07-16-17, 04:48 PM
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@PJmax.

Am I right in saying the fan shouldn't appear as a dead short?

Does this mean perhaps the fan has a fault somewhere?

I looked at those linear PSU's, there seem to be not so many, and they are expensive.

I can get this fan replaced, if the "dead short" issue goes away, then wouldn't either of those 2 24v 15A PSU I already bought be ok to use?
 
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Old 07-16-17, 04:51 PM
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Also will those linear PSU allow the voltage to be adjusted?

The Manufactuer Spal of the Fan told me its perfectly normal to adjust the Voltage to adjust the speed, and that that is what most vehicles do when cooling the rad.
 
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Old 07-16-17, 07:14 PM
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I have dealt with electric fan issues in cars. Most I've worked on the fans are on or off..... no variable control. Also.... they were 12vdc and higher current.

I'm fairly certain those types of fans use brush type motors which present a large load when first starting.

Some of those linear power supplies do have variable output.
 
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Old 07-17-17, 01:24 AM
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If this fan does produce a larger load when starting, wouldnt perhaps a larger Amp PSU work?

Like 24V 20A instead of my 24V 15A? It might explain why sometimes the fan works and sometimes doesnt, perhaps the time it worked the inrush surge wasnt as high for w/e reason.
 
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Old 07-19-17, 04:14 PM
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@PJmax Hey dude some good news, the 20A PSU I brought worked, the fan spins always now.

If I used a thermistor, could I use a 10A PSU to power this 7A Fan?
 
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Old 07-19-17, 07:41 PM
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If I used a thermistor, could I use a 10A PSU to power this 7A Fan?
It is very possible. They are sometimes used in motors to reduce the inrush current.
It's going to be experimental what size to use but it won't hurt anything to try.

Good news on the power supply.
 
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