DavR Posted April 25, 2017 Posted April 25, 2017 (edited) Here's one for some a little more electrically minded than me.... I've got an amplifier with a knackered fan in it, bearings have gone, so I ordered a new fan. As far as I can tell, it's identical to the existing one - 24V DC, two pin connection. But, having swapped them over, this new fan periodically shuts off. Pretty sure this isn't a function of the amplifier, it never shut the fan off with the old part, the fan runs constantly. It seems to behave differently whether or not I've got the case open - from cold with the case open, it seems to run ok. With the case closed it shuts off after about 15 seconds. Have I bought the wrong type of fan? Seems unlikely, a fan's a fan right? Apply current and it spins. Is the fan cutting out due to air resistance or overheating? A fan that cuts out when it gets hot is surely fundamentally flawed. Or, have I just been sold a duff one and I should send it back? Edited April 25, 2017 by DavR
3s-gtech Posted April 25, 2017 Posted April 25, 2017 Does it shut off after 15 seconds then never come back on until it's power cycled? Or does it periodically spin up? 1
DavR Posted April 25, 2017 Author Posted April 25, 2017 (edited) Not until it's power cycled as fan as I can tell. Although I admit I haven't left it running for more than a minutes afterwards, in case it overheats. Edited April 25, 2017 by DavR
Dos_Box Posted April 25, 2017 Posted April 25, 2017 Does the new fan allow the amp to overheat? Just thinking the old one may have been controlled by a theromstat but was perhaps broken meaning it always stayed on. Admittedly the controller would have been on the amp and not the fan. 1
DavR Posted April 25, 2017 Author Posted April 25, 2017 It's a thought, but seems unlikely that an 80mm case fan would have that sort of intelligence on board. There's nothing suggesting thermostat control on the amp itself, especially as the fan tends to shut down as the unit heats up, ie, when you'd need it most. The warmer it gets, or the more restricted the airflow, the less time it will run for. Increasingly leaning towards this one being a dud tbh!
robyholmes Posted April 25, 2017 Posted April 25, 2017 Can you put a multimeter across the 24v supply the fan and make sure that's constant? 1
pcstru Posted April 25, 2017 Posted April 25, 2017 Increasingly leaning towards this one being a dud tbh! Seems a little odd that it would spin at all if it was dud. I have noticed some fans respond differently to PWM control (where they switch the power off and on again very fast to control the speed) - with some refusing to operate below 80/90% duty cycle while others will happily go down to 30%. If you have an oscilloscope handy (yea - shirt pocket stuff!) might be worth looking at the signal to the fan to see if it is straight DC or being pulsed. 1
DavR Posted April 25, 2017 Author Posted April 25, 2017 Can you put a multimeter across the 24v supply the fan and make sure that's constant? Constant, yes, but a constant @ 33v! That's probably not ideal is it....
robyholmes Posted April 25, 2017 Posted April 25, 2017 Constant, yes, but a constant @ 33v! That's probably not ideal is it.... Don't suppose you have another one to test it against? Seems very odd to be that high.
Dos_Box Posted April 25, 2017 Posted April 25, 2017 What make/model amp is it? We may be able to dig deeper if we can take a better look at the details.
DavR Posted April 25, 2017 Author Posted April 25, 2017 It's an IMG Stage Line STA-700 - https://www.monacor.com/en-gb/img/products/audio/pa-amplifiers/analogue-pa-amplifiers/sta-700/
bald_pig Posted April 25, 2017 Posted April 25, 2017 Constant, yes, but a constant @ 33v! That's probably not ideal is it.... That sounds like peak voltage for 24vac to me?
DavR Posted April 25, 2017 Author Posted April 25, 2017 Meter was reading it as 33v DC... I see your point though! If that voltage issue were such a big problem though, I'd have thought both the old and the new would be struggling because of it.
bald_pig Posted April 25, 2017 Posted April 25, 2017 True. If it's a problem when the unit is closed up, it could be an earthing problem? Just seen that it's an all-metal unit. 1
DavR Posted April 26, 2017 Author Posted April 26, 2017 True. If it's a problem when the unit is closed up, it could be an earthing problem? Just seen that it's an all-metal unit. If it were reliably just contacting the lid then maybe, but I can reproduce it with the lid off. My theory at the moment is it's the airflow restriction that causes it, either the fan speeding up and conking out, or just struggling against the restriction.
difinity Posted April 26, 2017 Posted April 26, 2017 Can you measure the resistance of the old and new fan ? Fans have different wattage ratings, voltage is applied, they draw the required current. Photos of the stickers on the fans might help identify the difference. Was the 33v you measured with or without the load of the fan ? Your amp has thermal protection. It will turn off to protect itself it gets too hot. You don't need to worry when testing. 1
DavR Posted April 26, 2017 Author Posted April 26, 2017 (edited) I've put the old fan back in and returned the amp to use for the moment. Here are the two fans though, neither have much in the way of identifying marks! Old on the left, new on the right. 33v was without the load of the fan, with the load of the fan also it was ~29v. No spikes or dips when the fan stops, the reading just returned to 33v afterwards. Edited April 26, 2017 by DavR
DavR Posted April 27, 2017 Author Posted April 27, 2017 Well, I bit the bullet on this one in the end. Made a few phone calls, tracked down the manufacturer, then a reseller, and have bought official spares. Three times the price (£26 + p&p for an 80mm fan!) but at least this one should be certified to work with the amp. Moral of the story? Not all fans are created equal.... or something!
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