Convert ac to dc

[Ben Gustave]

This high voltage is due to the fact that the circuit is unloaded. When you
hook up the pump the voltage will drop, according to the current draw of the
pump(and the capacitance of the cap). Chances are you don't have a big (10+
watt, 25 ohm) resistor to load the supply while you test for voltage (if you
do have something like that, run the numbers through P=E^2/R to see if it's
too small). If you hook the resistor up and test the voltage, you'll see
what I'm talking about. If you do, be careful, because the resistor will get
hot if it's powered for a while.

OT: I absolutely hate how much $$ I can waste at Radioshack (The Source,
here, actually) during a project....absolutely despise that place.

-ben

 

[Homer J Simpson]

OT: I absolutely hate how much $$ I can waste at Radioshack (The Source,
here, actually) during a project....absolutely despise that place.

It is what it is. Do you really want to pay S&H for a $1 battery holder?

 

[Victor MacQuarrie]

Hello John......Disconnected the cap. and now I have a steady 13.3
volts. Hopfully the problem is solved.... I'll let you know.

Vic.....

Hello again........ Reconnected the cap. and connected the
pump...13.39 volts and it seems to run fine except the transformer
gets to hot to touch......?????

Vic.......

 

[Jamie]

Hello again........ Reconnected the cap. and connected the
pump...13.39 volts and it seems to run fine except the transformer
gets to hot to touch......?????

Vic.......

you need a higher amp transformer.

 

[redbelly]

Hello again........ Reconnected the cap. and connected the
pump...13.39 volts and it seems to run fine except the transformer
gets to hot to touch......?????

Vic.......

How much current does the pump draw? What is the max current the
transformer is rated for?

Mark

 

[jasen]

Hello again........ Reconnected the cap. and connected the
pump...13.39 volts and it seems to run fine except the transformer
gets to hot to touch......?????

is it OK without the capacitor?

The capacitor causes inefficient usage of the transformer which
makes it get hotter that without.

If you need the capacitor you'll need to get a bigger transformer.

Bye.
Jasen

 

[Victor MacQuarrie]

Hello, I have a power transformer that converts 110 v ac to 12 .6 v
ac. What is easiest way to change 12.6 v ac to 12.6 v dc to run a 12 v
fish pond pump continuously. Thx..........Vic

 

[Victor MacQuarrie]

Was this measurement taken with the pump operating?
because if it wasn't it's not telling you anything useful.

If you want less voltage, using a smaller cap may do it.

A little, or even a large amount of, ripple is unlikely to damage a motor.
This sort of equipment is designed to withstand vibrations: a thyristor
speed control gives worse ripple than a full-wave rectifier.

Bye.
Jasen

I disconnected the cap. and took a reading with pump running,.
The output is 10.98 volts at 1.9 amps. The trans is rated for 3 amps
ac, and the pump rated for 2.5 amps dc. It all seems to be working so
far.
Thanks for all the input........Vic

 

[Victor MacQuarrie]

I don't know what happened to my last post but it seems the original
reposted itself.
I will try again....I disconnected the cap. and took a reading with
pump running.
10.98 volts at 1.9 amps dc at pump end. The trans is rated for 3 amp
ac and the pump 2.5 amps dc. It seems to work fine so far no excess
heat.
Thanks again guys......Vic

 

[cdd]

Hello John......Disconnected the cap. and now I have a steady 13.3
volts. Hopfully the problem is solved.... I'll let you know.

Vic.....

I would still put a capacitor in cicuit-if you think the higher
voltage is a problem
put a smaller cap on it -but even then I would stay around 3000uf-
when the motor
runs I cannot see how you've ended up with such a high voltage-is the
transformer
rated for 220v on the primary -giving a slightly higher output on the
secondary side
of the transformer-you are measuring the output of the secondary in
RMS AC volts
or is it the peak voltage?

 

[redbelly]

I would still put a capacitor in cicuit-if you think the higher
voltage is a problem
put a smaller cap on it -but even then I would stay around 3000uf-
when the motor
runs I cannot see how you've ended up with such a high voltage-is the
transformer
rated for 220v on the primary -giving a slightly higher output on the
secondary side
of the transformer-you are measuring the output of the secondary in
RMS AC volts
or is it the peak voltage?

His value of 12.6 V must have been RMS AC, otherwise he could not have
gotten 18.9 V DC with the rectifier & cap. (Which means his actual
transformer output is more like 13 or 14 V AC).

At any rate, it seems things are working well for him, which is a
victory for s.e.b. Using a 3300 uF cap caused his transformer to get
pretty hot.

Mark

 

[Victor MacQuarrie]

His value of 12.6 V must have been RMS AC, otherwise he could not have
gotten 18.9 V DC with the rectifier & cap. (Which means his actual
transformer output is more like 13 or 14 V AC).

At any rate, it seems things are working well for him, which is a
victory for s.e.b. Using a 3300 uF cap caused his transformer to get
pretty hot.

Mark

The unit has been running continously now for 5 days with no cap in
the circuit. The trans does warm up but not to the point you can't
touch it. Voltage varies 10.9 to 11.9 at 1.9 amps.
I'll let you guys know how long it lasts ;-).......
..........Vic

 

[cdd]

The unit has been running continously now for 5 days with no cap in
the circuit. The trans does warm up but not to the point you can't
touch it. Voltage varies 10.9 to 11.9 at 1.9 amps.
I'll let you guys know how long it lasts ;-).......
.........Vic- Hide quoted text -

- Show quoted text -

It's geat it's going but could someone shed some light one what effect
the capactor
is having on the output of this transformer-why does the transformer
run with increased
heat?

 

[John Popelish]

It's geat it's going but could someone shed some light one what effect
the capactor
is having on the output of this transformer-why does the transformer
run with increased
heat?

The capacitor concentrates the current into pulses around
the peaks of the rectified wave, and slightly fills in the
valleys with its charge. This increases the RMS current
through the transformer, heating its resistance more. It
also slightly raises the average voltage (because of those
filled in valleys), making the motor draw more current,
which heats the transformer even worse. The motor obviously
does not require filtered DC voltage, but runs just fine on
the rectified voltage wave, smoothing the current some, with
its own inductance.

How's that?