hello
I have a two speed fan controller on my power amp. (hot&cold speeds via two heatsink thermals A+B.)
One of the caps (channel A heatsink) has many Megaohms resistance, compared to the other channel B that has only 293ohms.
I believe A cap has failed as the fan (A) also does not want to spin very fast at all when cold.
I attach the schematic below that seems to show the two thermals are linked to both fans.
But from my experiment they seem to be independent thermals. (test: i shorted one thermal A and only one fan(A) went full speed;
i did the same, shorting thermal B and again only fan (B) went full speed. My amp may be older?
I wonder what type of 1uf 400vdc cap should I buy as a replacement? is there a specific material or type?
Thanks for your help. : )
I have a two speed fan controller on my power amp. (hot&cold speeds via two heatsink thermals A+B.)
One of the caps (channel A heatsink) has many Megaohms resistance, compared to the other channel B that has only 293ohms.
I believe A cap has failed as the fan (A) also does not want to spin very fast at all when cold.
I attach the schematic below that seems to show the two thermals are linked to both fans.
But from my experiment they seem to be independent thermals. (test: i shorted one thermal A and only one fan(A) went full speed;
i did the same, shorting thermal B and again only fan (B) went full speed. My amp may be older?
I wonder what type of 1uf 400vdc cap should I buy as a replacement? is there a specific material or type?
Thanks for your help. : )
An externally hosted image should be here but it was not working when we last tested it.
The high resistance cap is good, a cap[ should in theory have infinite resistance.
When you measure the B cap, is that while it is in circuit? If so, you are really measuring the cap in parallel with the switch. So it points to a switch that is bad, having a few 100 ohms resistance.
Not spinning very fast when cold is what you want, right. You want it to spin fast when warm.
You can remove the caps, it would still work. The caps are there top prevent the switch contacts to burn in but a few cycles will not harm.
There is a good chance that what you see is how it should be. Switch A goes on at a certain temp, the slow fan starts. Switch B goes on at higher temp, fan B also starts, now you have two fans. Sounds like a design.
Why do you think anything is wrong?
Jan
When you measure the B cap, is that while it is in circuit? If so, you are really measuring the cap in parallel with the switch. So it points to a switch that is bad, having a few 100 ohms resistance.
Not spinning very fast when cold is what you want, right. You want it to spin fast when warm.
You can remove the caps, it would still work. The caps are there top prevent the switch contacts to burn in but a few cycles will not harm.
There is a good chance that what you see is how it should be. Switch A goes on at a certain temp, the slow fan starts. Switch B goes on at higher temp, fan B also starts, now you have two fans. Sounds like a design.
Why do you think anything is wrong?
Jan
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Your diagram shows the two fans in parallel and yet you mention that they operate independently when the switches are shorted out. So the diagram has to be wrong.
Could the caps reactance be used as a 'watt-less' dropper for the low speed? Would 1uF pass enough current... it might. Perhaps the fan is partially seized and not spinning o the low current available, whereas on the higher speed it does.
Could the caps reactance be used as a 'watt-less' dropper for the low speed? Would 1uF pass enough current... it might. Perhaps the fan is partially seized and not spinning o the low current available, whereas on the higher speed it does.
Hi
The thermal switches when cold are open ( no circuit). So the capacitor gives current to each fan.
They seem to be independent systems as mentioned.
Because when i short the thermal on (A), (A) fan speeds up full. B remains slow.
when i short thermal (B) (B) speeds up full A remains slow.
however, When in a cold state, and the Cap is providing the current not the thermal. Fan A's slow speed is slower than B.
so I measure the caps with my multi meter and find they are not the same, one is in the megohm region and the other a couple hundred ohms.
So I determine one cap is bad.
hi yes they definitely are independent.
i bought new fans. and they do spin, so are not seized.
but as mentioned the capacitors are needed for the slow speeds. one cap is in the megaohm region and the other only 290ohms
so surly the one cap is bad on the side which i am having issues? ( i have another brand of fan here that wont even spin on the low setting , all the same specs)
it must be the cap.
i would like slightly less resistance than 293ohms so they spin just a bit quicker on slow.
I wonder why they are caps and not resistors?
thanks for your help.
As I said, the cap is there to protect the switch contacts. What you describe is fully normal. If you think it's the cap, remove them and there will be no change. Cold, one fan, hot, two fans.
You still haven't told us what 'issues' you have.
Jan
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hi Jan you were right about the ohms. When i measured one side, the fan must have been disconnected.
so now they are both in the megaohm region now. equal it seems. ( but they are independent circuits. I triple checked)
I have 4 types of 80mm fans here. The ones i really want to use with the ball bearings do not even spin when the thermal is cold. As there is not enough power, but are really great when the thermal is hot ( or i short across the thermal with a wire)!
Q: Can i change the caps for another value so my new fans can have enough power in the cold state? (when the thermal has not engaged)? (btw, they are the same as the old ones at 115v but do not like the lower power state)
Thanks for your help
so now they are both in the megaohm region now. equal it seems. ( but they are independent circuits. I triple checked)
I have 4 types of 80mm fans here. The ones i really want to use with the ball bearings do not even spin when the thermal is cold. As there is not enough power, but are really great when the thermal is hot ( or i short across the thermal with a wire)!
Q: Can i change the caps for another value so my new fans can have enough power in the cold state? (when the thermal has not engaged)? (btw, they are the same as the old ones at 115v but do not like the lower power state)
Thanks for your help
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Assuming the two fans are original and have the same part number then all you have to do is swap the wiring over and see if the fault stays with the fan or whether it moves to the other one.
Increasing the value of the cap will increase the arcing that occurs when the contacts close. You can mitigate that a little by adding a series resistance to the switch... buts trial and error and depends on the fan characteristics. You may or may not get the result you want.
Increasing the value of the cap will increase the arcing that occurs when the contacts close. You can mitigate that a little by adding a series resistance to the switch... buts trial and error and depends on the fan characteristics. You may or may not get the result you want.
So lets get the issue clear, to prevent going off on all kinds of tangents: there is no problem with the original circuit but you want, for some reason, to use other fans. These new fans do not run in the cold situation.
One thing you could check is whether there is a series resistance somewhere in the feed circuit to the fans that limits the voltage to them. That could be the case, for instance to limit max fan noise the amp produces.
Apparently the new fans need more voltage to run, so in this scenario this series R should be made lower in value.
There is also the possibility that those caps do double duty as 'series R' in the cold situation. That can be checked by increasing them in value and see whether the fan eventually does start up in the cold situation. A quick test would be to increase the cap to say 10uF.
BTW, I can understand that as a diy-er you want to play with stuff, but these things can lead to unexpected effects so are you sure you want to mess with this?
Jan
One thing you could check is whether there is a series resistance somewhere in the feed circuit to the fans that limits the voltage to them. That could be the case, for instance to limit max fan noise the amp produces.
Apparently the new fans need more voltage to run, so in this scenario this series R should be made lower in value.
There is also the possibility that those caps do double duty as 'series R' in the cold situation. That can be checked by increasing them in value and see whether the fan eventually does start up in the cold situation. A quick test would be to increase the cap to say 10uF.
BTW, I can understand that as a diy-er you want to play with stuff, but these things can lead to unexpected effects so are you sure you want to mess with this?
Jan
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