Zener and rgulator

using the 7805 should be fine to give you regulated 5V, i am using a similar setup to bring a 9V supply to 5V to supply the MCU.

using the 7805 should be fine to give you regulated 5V, i am using a similar setup to bring a 9V supply to 5V to supply the MCU.

But I still need to step it down, I am taking from 115vAC so 115 * 1.44pp = 165.6VDC the Lm7805 can only take 35v Dc at the input

What you are doing is unsafe. Use a transformer. Forget the zener.

--------- D1 | Xformer |--->|---+----------------Mosfet----+ | 12V | | | | | |---+ | PIC | --------- | | D2 | | | +--->|---+---7805---+ [Battery] | | | | | | | [C1] [C2] | [C3] | | | | | | | +----+--------+-----+----+------+

I'm assuming you're controlling a mosfet with the PIC - the above is a generalized schematic. I don't know what you have for C1, but make C2 a good sized electrolytic, like 100 uF. C3 is .1 uF D2 can be any 1N400x diode. D1 and the transformer depend upon how much current you intend to allow.

Ed

Hi ed, the idea was to make a charger using no transformer. If I use a buck boost converter to bring the voltage down, I need a timer, with no Pic chip activated, I dont have a timer. Is there a way to make the zener circuit safe ?

Ken

Don't plug it in.

what you need for safety is isolation from the mains.

For a while some people were promoting switched capacitor isolation It always seemed to me to be kind of scary and I've not seen any new stuff. so the only proatical way to do it is some sort of transformer.

I did see one guy who'd hooked a washing machine motor to an automotive altenator to charge his battery and run his radio equipment.

Bye. Jasen

Ok i will get a wall transformer to bring down the power.

Am i missing something here? Isnt modulation of a 150vdc source still just short pulses of 150vdc? How are you getting 13.8 vdc from a short pulse of 150vdc?? Arent you just reducing its duty cycle, not voltage? Seems like the life of the battery would be rather short because of this. Is this done commercially??

thanks -eric

If I was to respond with shouting (*BOLD CAPITOL LETTERS*) and a whole bunch of expletives about the thing being unsafe, would that make the point that it is unsafe? If so, pretend that I did that. It is unsafe.

Let's pretend we were discussing a safe circuit. With a proper PWM controlled circuit, you could take a higher source voltage and produce a lower output voltage - or you could take a lower source voltage a create a higher output voltage. _Many_ commercial power supplies these days use PWM to achieve the desired voltage. Unless one relies heavily on the work done by others, designing such a supply is not the province of newbies.

Ask yourself this: using a 24 volt DC source, a stopwatch, a switch and a resistor of your choice, how would you charge a 1 farad capacitor to approximately 15 volts? No voltmeter is allowed.

Ed

I cant agree more about it being unsafe, thats why i asked if it was done commercially this way and regarding the circuit in general, i feel stupid for not even thinking about the resistor. I was sleepy and caught up in the safety implications. Damn i suddenly feel stupid. Big "DUH " moment. I guess i was thinking the only thing between the primary power supply and the battery was a mosfet. If it was a BJT it would make sense but my brain was thinking FET.

thaks for the reality check :) -eric

I wanted to use PWM to charge my battery. I guess there will be too much current in the circuit and could damage the battery. It needs a better circuit i agree

You can use PWM if you want. But if you want to live long enough to learn how, restrict _all_ your electronics experimentation to low voltage, until you *know* what you are doing.

In the meantime, you can build simple battery charger circuits very easily. In doing that, you will learn about batteries. Then, when you learn PWM you'll know how to set it up to charge a battery. Hopefully by then, you'll also discover some of the excellent IC's that are made for that job.

Ed