A while back I was playing with a small boxer 115v ac fan rated at .15 A. I tried runing it from 115v AC through a capacitor. When I used a 1mf cap the fan didn't turn at all but it seemed to run at about 1/4 speed when I used a 1.5 mf cap. So I tried a 2.2 mf cap expecting it now to be about 1/2 speed but instead it seemed to run at full speed. Any ideas what was happening ?
Fan motors must run with specific capacitor values (usually. 2.2uF). Probably with 1-1.5 uF you had a start torque issue, so that the motor was out-of-phase and wasn't able to spin correctly (or spin slowly).
Boxer fans don't normally use capacitors (other AC motors do).
It seems like a way to make an AC fan run *slower*.
One time I did it, and the fan ran FASTER.
The fan is not a pure resistance. It has significant inductance. Some value of C will resonate with the L and INCREASE voltage on the motor.
(While some AC motors are frequency-locked, fan motors usually are not, and the fan-load will give a voltage sensitivity.)
Anyway a 10 Watt resistor is usually cheaper than a 110V-safe cap. Your fan is 115V/0.15A which is 766.666667 Ohms. Try with 500 ohms in series. Buy a bag of 100r 5W and series them until you get your happy speed.
It seems like a way to make an AC fan run *slower*.
One time I did it, and the fan ran FASTER.
The fan is not a pure resistance. It has significant inductance. Some value of C will resonate with the L and INCREASE voltage on the motor.
(While some AC motors are frequency-locked, fan motors usually are not, and the fan-load will give a voltage sensitivity.)
Anyway a 10 Watt resistor is usually cheaper than a 110V-safe cap. Your fan is 115V/0.15A which is 766.666667 Ohms. Try with 500 ohms in series. Buy a bag of 100r 5W and series them until you get your happy speed.
Running an AC motor abnormally like this is definitely not recommended - you could even start a fire if you don't know what you are doing. You don't even know what type of motor it is...
All this talk about series capacitors connected to the mains electricity reminds me of the large import to the UK after WW2 of very small US bakelite radios .
They were series driven via a "line cord " which incorporated a resistance wire to drop the voltage to 115V AC.
In due coarse this wire was cut back resulting in blown valve (tube ) heaters,away back then in a radio magazine the "cure " was to fit a series capacitor (condenser ) which did the job .
I tried this out as I repair old valve (tube ) radios (wirelesses ) and it worked as getting a new line cord was very difficult .
Fitting a dropping resistor in those miniature (at the time ) radios was either impossible or resulted in a large crack above it in the bakelite casing due to heat rendering its value the same as a table weight.
They were series driven via a "line cord " which incorporated a resistance wire to drop the voltage to 115V AC.
In due coarse this wire was cut back resulting in blown valve (tube ) heaters,away back then in a radio magazine the "cure " was to fit a series capacitor (condenser ) which did the job .
I tried this out as I repair old valve (tube ) radios (wirelesses ) and it worked as getting a new line cord was very difficult .
Fitting a dropping resistor in those miniature (at the time ) radios was either impossible or resulted in a large crack above it in the bakelite casing due to heat rendering its value the same as a table weight.
I was always wondering how a series capacitor to feed a 115 V AA5 radio from the 230 Vac line can be calculated. Due to the very asymmetric, DC laden load I was even suspecting that this could be impossible at all.
Best regards!
Best regards!
A capacitor might work, sort of, because a large part of the radio loas was resistive: filaments.
Completly different to a mostly reactive electric motor.
I was dubious myself at first but it worked, of course this type of radio is banned ,at least in the UK as has a mains connected chassis nowadays its all double insulation but even that is not all its supposed to be given the "buy ,em cheap--sell ,em dear" business fraternity .
A very simple circuit and comment on it is as follows-
Calculate Resistor and Capacitor in Transformerless Power Supplies
A very simple circuit and comment on it is as follows-
Calculate Resistor and Capacitor in Transformerless Power Supplies
Some caveats with this method, first about safety: a 400VDC rated cap isn't OK as a dropper: you need an X-rated cap (X1, X2 or X3, it doesn't really matter. X2 are most commonly available).
X caps and DC/non-safety caps are two different breeds of cats, and using a DC-rated cap for across-the-mains applications is dangerous (you risk a house fire).
Details can be found on the net.
About the calculation method: impedances and generalized (vectorial) ohm law are OK if you deal with purely linear loads, but as soon as you introduce something like a rectifier it is not anymore valid.
A simpler and more accurate method is the charge law: you know what charge (Q) will be transferred for each cycle (half-wave mode) or each half-cycle (full-wave): it is C*(2*Vpeak-Vout).
For a unit second, the current is going to be Q*F, F being 50Hz (half-wave) or 100Hz (full-wave) (or 60Hz or 120Hz in the US).
Thus, Iout = C*(2*Vpeak-Vout)*F.
Solving for C: C = Iout/(2*Vpeak-Vout)*F.
For example, if you need 3mA/50V from a half-wave rectifier in a 230V/50Hz system, the cap will be ~0.1µF.
When Vout is low, the impedance and charge methods will yield practically the same result, but at higher voltages, you need to use the charge method.
There are other sources of inaccuracies, like the forward drop of the diodes, the series limiting resistor, etc., but for mains applications they don't matter
I supplied this to give a basic understanding in SIMPLE form to a question directed towards me , you have given me typical EW answer ,the person asking didn't require such detail.
If you read my post you will see I said its use in old radios is banned .
Cheap imports of electronic test gear are sold with a CE label which is applied in China , two German production engineers were talking on a specialized website , one said to the other who was in China checking up on the production line and telling him to keep quiet about manufactured goods with their logo on it saying --made in Germany .
The CE label only covers a limited area and doesn't stop low grade and even dangerous products from being sold in the EU .
I had 4 choices of the "same" soldering station ranging from £26 (UK) to £56.
I took apart the cheap one it was very dangerous internally ,dumped it and bought the top end model --all the outer plastic casings were the same .
Isn't it time this was stopped ?
China has a policy of all exporters taking full responsibility for any failures not their own manufacturers in China --I read their internal export rules and will build to a price ,naturally this is used to supply cheap rubbish by sly western exporters to gain massive profit .
China does have quality equipment but the cheap stuff is no better than the old live mains chassis radios I repaired.
If you read my post you will see I said its use in old radios is banned .
Cheap imports of electronic test gear are sold with a CE label which is applied in China , two German production engineers were talking on a specialized website , one said to the other who was in China checking up on the production line and telling him to keep quiet about manufactured goods with their logo on it saying --made in Germany .
The CE label only covers a limited area and doesn't stop low grade and even dangerous products from being sold in the EU .
I had 4 choices of the "same" soldering station ranging from £26 (UK) to £56.
I took apart the cheap one it was very dangerous internally ,dumped it and bought the top end model --all the outer plastic casings were the same .
Isn't it time this was stopped ?
China has a policy of all exporters taking full responsibility for any failures not their own manufacturers in China --I read their internal export rules and will build to a price ,naturally this is used to supply cheap rubbish by sly western exporters to gain massive profit .
China does have quality equipment but the cheap stuff is no better than the old live mains chassis radios I repaired.
Your intentions are laudable, but the example is somewhat unfortunate, because of the wrong safety advice, and the questionable method of calculation.
Regarding simplicity, this method is also very convoluted, with many lines of formula's.
The charge method uses just basic elementary arithmetics.
I understand that you prefer to post a link rather than write down all the stuff by yourself, that is something I also do whenever possible because it avoids wasting time, but if the contents has issues, it should come with a health warning.
The discussion has drifted very far away from the original subject, for which there is no simple, direct and universal formula for a series cap, which is not recommended anyway.
Note that for feeding a mixed load (filaments + rectifier), none of the methods discussed here is directly applicable.
First of all the person asking me is happy with the very simple explanation not all posters here are "well up " in arithmetical explanations so I avoid it as much as I can .
On a well known UK help website (NGO) I was censured for being "too technical " as ordinary members of the public could not understand me.
As regards your last paragraph I take it you mean SS rectifiers which were never used in those types of radios at that time ,the circuits functioned very well including the usual half-wave tube rectifier.
I "diverted " from the main object of attention to make a moral and engineering point that even in 2020 bad engineering is still used when it comes to profit best practices are not used .
On a well known UK help website (NGO) I was censured for being "too technical " as ordinary members of the public could not understand me.
As regards your last paragraph I take it you mean SS rectifiers which were never used in those types of radios at that time ,the circuits functioned very well including the usual half-wave tube rectifier.
I "diverted " from the main object of attention to make a moral and engineering point that even in 2020 bad engineering is still used when it comes to profit best practices are not used .
I know they worked, but adapting their voltage using a capacitive dropper requires more complicated calculation methods than the ones we examined.
Trial and error is probably the simplest way to go.
A better method would be a transformer (not an autoformer) that also ensures mains isolation.
It might buzz a little though, due to the asymetrical current drain
Well ---yes your right and your technical logic is the same as mine.
I did just that on several old British tube radios , converted the series heaters to parallel operation and made several changes to the HT+,
plate as in USA tech talk.
You have forgotten one thing though I was talking about USA bakelite miniature radios no chance of squeezing even a small mains transformer in anywhere, no buyer is going to buy one with an external transformer .
By the way have you seen the price of good colored versions ?
I did just that on several old British tube radios , converted the series heaters to parallel operation and made several changes to the HT+,
plate as in USA tech talk.
You have forgotten one thing though I was talking about USA bakelite miniature radios no chance of squeezing even a small mains transformer in anywhere, no buyer is going to buy one with an external transformer .
By the way have you seen the price of good colored versions ?
OK, but that's irrational (from the buyers): we (in Belgium at least) have lived with imports from other countries, mains-voltage changes, etc. and transformers were quite normal.
US-made goods were rarely adapted to exports and were 117V nominal; converting a 117V set to work internally on 220, 230, or 240V is therefore tampering with a historical artefact,.
Anyway, who is still listening to AM radio nowadays? Are there even AM transmitters still on air? Probably Radio 4, and a few other legacy services sending kW's into almost nowhere, but extinction is close.
No, but I can easily figure out their value: some bakelite items have become dearer than coral or amber.
There is a way to convert internally a set to other voltages: there are compact sinewave inverters capable of voltage conversion and galvanic isolation, but I think it's kind of cheating (and useless practically)