General transformer question

[Cazzo]

yOOOO -----( i have made my direct questions in Bold and underlined)

so yeah, i made this little circuit, idk what its called, it uses a TIP 31C transistor, an LED, a transformer and a resistor. i connect the battery and the transformer hum's. if i bring the high voltage side of the transformer (is that the primary winding???) the wires produce a bright blue arc to each other and it makes a screatch sound.

it measures on multimeter of around 200V AC. i beleive the little circuit i built takes the battery DC and makes AC with the transistor.

so i see 200V AC. what i did was connect a bridge rectifier at the transformers output leads to get a DC voltage, that has been boosted by the transformer. it says 84v AC. i understand that by rectifying it, i have taken away half the voltage, because i removed the other sine wave cycle. you know what i mean

So by now, ive got 84V DC to play with. i thought if i connected a little 9V motor it will spin like crazy because its got 84V running through it, when its rated for 9. So i connect it, and nothing happens????

----Why do i have 84V DC that does nothing but run an LED??? I know its got to do with current
but i thought my transformer would boost the Voltage, that the motor could use to go
crazy??

I know how to measure how much current a certain load will draw. you connect the multimeter between the wires like a switch. but how do i measure the max amount of current my supply will give??

^^ i beleive my motor wont run because the transformer is not providing enough current.

-----How do i figure the current the transformer is providing when the little circuit is
connected to it??

Im screwing around with a transformer to learn how they work. i thought i connect a battery and it will step up the voltage, which it has but why wont this high volts be of use to my motor.

and how do i step up the current??

another thing about current, how do i find the max current my battery will supply???

A few questions there but they sound simple enough for a pro

Please help me understand this thanks

 

[Boncuk]

Hi Cazzo,

it looks like you have connected the secondary winding of your transformer to mains.

That would explain why the transformer hums and puts out a voltage too high.

84V are definitely too much for a motor rated 9V and it also too much for an LED with a forward voltage of 1.8 to 3.5V (depending on the make).

If you happen to possess a multimeter go these steps:

- Disconnect the transformer terminals completely from mains and any load.
- Use two wires (normally leaving the transformer side by side) and measure the resistance
- The winding with the higher resistance (KOhm range) MUST be connected to mains, since it is the primary winding.
- For varification measure the other two wires. Their resistance should be in the Ohm range.

Boncuk

 

[Cazzo]

Nooo i did not connect it to mains

The side of the transformer with 3 little wires is connected to a little transistor circuit, and the other 2 thick high voltage wires are just not connected to anything. if i bring them close, the arc a big spark. if i connect them to a speaker, it hums with high pitch.

would u be able to answer my bold questions to help me understand?

 

[audioguru]

A hum sound has a low pitch like 50Hz or 60Hz from the mains. A squeal or whistle sound has a high pitch.

You forgot to say which battery you used. If it is a little 9V battery then when it powers the transistor oscillator and the transformer steps up the voltage then the small amount of current from the battery is stepped down by the transformer because the transformer output power must not be more than the battery power (9V x 100mA= 0.9W). The transformer produces 200V so its output current is only 0.9W/200V= 4.5mA or less.

 

[Cazzo]

Thanks audioguru

Where did the 100mA in your equation come from? and what do i use Watts for ??

So with your equation, my transformer puts out 4.5mA which is nothing. what can i do with the transformer so it puts out low volts and high current???? do i turn it around??

i heard that i had to rewind the transformer so that there is less turns, with thick guage wire on the secondary.

with that in mind. how do i figure out what sort of battery or power supply i need to get a certain amount of current out from the transformer??

i have a drill battery that says it has a 12V 1.2 A NiCad battery. if i connect it to a transformer, it will not work cause its DC. how can i make my drill battery AC for the transformer to use those 1.2A and give me higher current???

Thanks

 

[Reloadron]

Hi Cazzo

You also have this thread going which seems to be connected. It would be nice if you could post some drawings of what you have and exactly what you are trying to do?

Also, something to note is when we look at transformers, discounting inefficiencies there is a ratio. For example if I start with 12 VDC and I want 220 VAC there is a trade off. Let's say you want 220 VAC at 10 amps. That is 2,200 watts. That same power in watts at 12 VDC works out to 2,200 / 12 = 220 amps so you would need a very large deep discharge battery.


Ron

 

[audioguru]

Batteries are not rated in AMPs. They are rated in amp-hours. Frequently their amp-hour rating is how long the battery will last when its current is 1/10th its amp-hour rating.

A little Energizer 9V alkaline battery is rated at 625mAh when its current is only 25mA. The 625 number cheats because it is when the battery voltage has dropped to only 4.8V.
A graph on Energizer's datasheet shows that it can power a 100mA load for only 4 hours or a 300mA load for 1 hour when its voltage has dropped to a reasonable 6V.