I have a power amp with an AC fan (about 10cm square) which runs continuously and makes a noticeable amount of noise. I'd like to change it to a temperature controlled fan but I think most are DC (and/or PWM controlled). Can anyone point me in the right direction?
Depending on voltage there are many to choose from.
Axial Fans | Cooling Axial Flow Fans | RS Components
I would fit a bipolar thermal switch at say 60℃ to turn the fan on when it heats up.
Axial Fans | Cooling Axial Flow Fans | RS Components
I would fit a bipolar thermal switch at say 60℃ to turn the fan on when it heats up.
Thanks for the reply, I had thought of this but I read that oil may damage the plastic around the bearing. Also, I don't have a handy 12VDC supply in the amp.
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Now that would be a good idea if I can find one to switch 115VaC it could just go in series with the existing fan. I had been thinking of a new fan but the existing one is OK, it just moves a lot of air continuously and that causes the noise.
You can also use a solid state relay to drive the fan. A NTCR driven off a dc supply attached to the heatsink can drive the input terminals. Say a 10k, salvaged from a PCAT power supply. DC supply can come from the input stage of the amp.
Cheaper than a solid state relay is a triac, on the neutral side of the AC source. These require 50 ma DC to drive the gate, so you need an additional NFET to drive the triac. The NTCR goes series the fet gate, with a 10-20 k resistor to analog ground. Fet source goes to the triac gate, drain to the DC power supply. Doesn't work on flying analog ground amps like PV-1.3k. Analog ground has to be roughly the same voltage as the AC neutral/safety ground. How you getting 115 VAC in UK, the safety ground to one hot?
Cheaper than a solid state relay is a triac, on the neutral side of the AC source. These require 50 ma DC to drive the gate, so you need an additional NFET to drive the triac. The NTCR goes series the fet gate, with a 10-20 k resistor to analog ground. Fet source goes to the triac gate, drain to the DC power supply. Doesn't work on flying analog ground amps like PV-1.3k. Analog ground has to be roughly the same voltage as the AC neutral/safety ground. How you getting 115 VAC in UK, the safety ground to one hot?
Yes, of course, typical heat sink thermostats are mains voltage rated.
Only difference is you will need a NO (normally open) type .
Then you can keep your current AC fan, which also will be more powerful than the average DC PC fan.
WHEN it turns on, I bet ambient noise/mussic will be looud enough to mask fan noise.
Only difference is you will need a NO (normally open) type .
Then you can keep your current AC fan, which also will be more powerful than the average DC PC fan.
WHEN it turns on, I bet ambient noise/mussic will be looud enough to mask fan noise.
Good DC fans are actually ac squirrel cage motors, there is a circuit to give AC from DC inside.
More reliable than brush type motors.
Ordinary grease or oil works, you can use a synthetic type if you want to stop worrying about plastics damage.
Find a mains powered fan, it would be 120 or 110 mm square, 38 mm thick.
Choose the ball bearing type, highest air flow and lowest noise figure.
The German company Papst is famous, there are others like Rexnord in India and Commonwealth in Taiwan.
Even the bush types are good.
Run a pair of wires from the mains switch to the replacement fan, that is all.
More reliable than brush type motors.
Ordinary grease or oil works, you can use a synthetic type if you want to stop worrying about plastics damage.
Find a mains powered fan, it would be 120 or 110 mm square, 38 mm thick.
Choose the ball bearing type, highest air flow and lowest noise figure.
The German company Papst is famous, there are others like Rexnord in India and Commonwealth in Taiwan.
Even the bush types are good.
Run a pair of wires from the mains switch to the replacement fan, that is all.
To lube the fan, peel off the sticker in the centre, there is a rubber stopper in the centre, take it off.
Add oil, moving the spindle in the axial direction, this is for plain bush bearings, ball bearings won't do this.
Add about two match heads grease. Currently I use front axle grease, it has a high temperature and high life rating.
Put the stopper back, clean excess oil with cotton or cloth soaked in alcohol or volatile paint thinner. This will allow the sticker to stick back in place.
Put the sticker back, usually I peel it enough to reveal the stopper.
Fix fan back in place.
Done...
Add oil, moving the spindle in the axial direction, this is for plain bush bearings, ball bearings won't do this.
Add about two match heads grease. Currently I use front axle grease, it has a high temperature and high life rating.
Put the stopper back, clean excess oil with cotton or cloth soaked in alcohol or volatile paint thinner. This will allow the sticker to stick back in place.
Put the sticker back, usually I peel it enough to reveal the stopper.
Fix fan back in place.
Done...
Thanks for the idea. In the meantime I found a device KSD-01F Thermal Switch which looks as though it might do the job and
needs no supply. Plus I could mount it on the heatsink by a blthole in the device? What do you think?
needs no supply. Plus I could mount it on the heatsink by a blthole in the device? What do you think?
I think the noise is more to do with the movement of air than the bearing but I will take a look, thanks.
FWIW this is the AC fan used in Fender BXR300 Bass amplifiers.
Remember that contrary to Home Hi Fi amps, Musical Instruiment amps get *regularly* played full power,for hours on end, they NEED powerful reliable cooling.
They use an AC mains powered fan, a 10W series wirewound resistor is chosen so it noiselessly works when cold, just "moving air around", light duty, but a heatsink mounted Normally Open switch shorts the resistor above your chosen temperature, often around 70C (uncomfortable to finger touch threshold).
Not too clear copy, but circuit is SIMPLE anyway.
Remember that contrary to Home Hi Fi amps, Musical Instruiment amps get *regularly* played full power,for hours on end, they NEED powerful reliable cooling.
They use an AC mains powered fan, a 10W series wirewound resistor is chosen so it noiselessly works when cold, just "moving air around", light duty, but a heatsink mounted Normally Open switch shorts the resistor above your chosen temperature, often around 70C (uncomfortable to finger touch threshold).
Not too clear copy, but circuit is SIMPLE anyway.
Attachments
The newest fan speed controllers here use capacitors in series wiith the fan motor to control the speed, different capacitors are used through a switch like the one that switched resistance in the old cieling fan speed controllers.
Do this - put a capacitor in series with the fan - if you feel that a slower fan will reduce the noise. But the air flow also will go down.
You can put a thermostat like above, too. That means it will go to full speed when the heat sink reaches a particular temperature.
Do this - put a capacitor in series with the fan - if you feel that a slower fan will reduce the noise. But the air flow also will go down.
You can put a thermostat like above, too. That means it will go to full speed when the heat sink reaches a particular temperature.
Good idea! I might try a mod to the existing wiring and see how the temperature goes before putting a switch in. It would reduce the temperature increase rate so might mean the fan switches on less often.
Am I correct in thinking that this circuit has three modes, one being Off when neither thermal switch is operated, then a low speed using the resistor when the first switch operates, followed by a higher speed when the second thermal switch shorts the resistor?
Was noticing these thermostats. They have both make and break options. Available and not very expensive.
https://www.mouser.com/datasheet/2/212/1/KEM_SE0202_OHD-1104231.pdf
https://www.mouser.com/datasheet/2/212/1/KEM_SE0202_OHD-1104231.pdf
The circuit in post 13 has TS2 that shorts the 1k resistor series the fan when it is hot. That speeds the fan up.
TS1 is series both the fan and the transformer primary. It is normally closed and shows 246 deg. So when the application point (probably the heat sink) hits that temperature the power to both the transformer and fan shut off. The transformer drives the amp circuits.
TS1 is series both the fan and the transformer primary. It is normally closed and shows 246 deg. So when the application point (probably the heat sink) hits that temperature the power to both the transformer and fan shut off. The transformer drives the amp circuits.
Or use a changeover type themostat.
Most can be set for cut in temperature with knob and a setting screw,
When it cuts off, the bypass gets byepassed, giving mains to the fan, and when it cuts in, current goes through the step down device
For reducing voltage, try a 0.1 or 0.22 400 v non polar capacitor
Most can be set for cut in temperature with knob and a setting screw,
When it cuts off, the bypass gets byepassed, giving mains to the fan, and when it cuts in, current goes through the step down device
For reducing voltage, try a 0.1 or 0.22 400 v non polar capacitor
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