# Building a very simple capacitor bridge-rectifier power supply

#### AnalogKid

##### Well-Known Member
Here's an important question that I can't figure out.
What king of amperage can I expect to see after the 115 vac 15 amp current runs through a 370v 80uF Run Capacitor, then converts to vdc through a 500v rated Bridge Rectifier?
None.

A capacitor has an impedance that varies with the frequency of the signal going through it. At 60 Hz, an 80 uF capacitor has an impedance of 33 ohms. For simplicity's sake, lets replace the capacitor in your with a 33 ohm resistor as run the numbers.

Using Ohm's law, the voltage developed across a 33 ohm resistor with 15 A going through it is 495 V. This means that to get 15 A through the resistor, the voltage source must be 495 V. And that's just for the resistor. If you want 300 V across the batteries in series with the resistor, then the total is 795 V for the circuit.

Also, a bridge rectifier cannot "convert" a low input voltage to a high output voltage.

The circuit in post #8 is a half-wave voltage doubler. The peak output voltage is approx 2.8 times the input RMS voltage, so for 115 Vac in that is approx. 325 Vpp (volts peak to peak). Note that as soon as you draw any current, that peak voltage will have a lot of 60 Hz ripple; the effective value of the DC output voltage will decrease. With only 80 uF capacitors, it will take less than 0.5 A of output current to have the ripple approach 50% of the peak value. I'm running these numbers in my head, so they might be off a bit. But you get the idea.

ak

#### rjenkinsgb

##### Well-Known Member
What king of amperage can I expect to see after the 115 vac 15 amp current runs through a 370v 80uF Run Capacitor, then converts to vdc through a 500v rated Bridge Rectifier?
Whatever the mains supply can provide!

Things will catch fire or explode without a deliberate current limiting system or component.

Also, as already stated, you CANNOT connect a non-isolated system to the vehicle. That would be lethal and also have a good chance of damaging the vehicle electronics.

The power source you use must be isolated from the mains and current limited.

#### bruceberquist

##### New Member
I know that this has been done with capacitor and bridge Rectifier.
That is why I am attempting it.
However, with the result I got it seems that I must be missing something.

As long as the current is less than 7 amps it will not damage the battery.

But I need to step up the voltage from 115 to at least 450 or 500 in order to have 300DC after it passes through the rectifier.

In regard to isolation from the main, I am having a hard time seeing/understanding the issue. Seems to me that the battery chargers and power supplies I have used are not isolated???

But given a need for isolation, and since capacitors store a charge, can I just switch off the 115 main source supply once the capacitors are charged, then send the capacitor charge out through the rectifier to charge the battery. (Then repeat as needed after discharge)?

Also, can I charge 4 capacitors to 115v individually, then send their combined charges at 460v to the rectifier to create near 300vdc output?

Or will the 4 capacitors combined only still send 115v?

It has worked for somebody before. What am I missing to make it work for me?

By the way. I really appreciate the input and technical explanations.

Successful or not, I have learned a lot.

#### Pommie

##### Well-Known Member
You haven't listened to anyone. Bye.

Mike.

#### bruceberquist

##### New Member
I have listened but have not gotten the "clue" probably because the answer came in some kind of tech language that just raised more questions for me.

Please speak to me in simpleton English descriptive language. Like I'm a child.

What would make my charger design "isolated"?

I go early don't understand.

And the "doubler" is super simple, which I want, but would provide far too much current and amperage to the point of being damaging or dangerous.

Also, I am not trained in understanding what component is what In a drawing if it is not labelled as such.

It like talking to an IT computer pro who doesn't understand that his client doesn't understand IT code language, but still prides himself in continuing to talk in code.

I have been listening. And I am grateful for what has been shared, and for what from that I have learned.

Still, I feel my search does not seem to be directed much better, and I am left with more questions as I try to understand what I am told.

I'm an educator and one thing I have learned is that there are experts who can not teach, there are good teachers, there are experts who are great teachers, and there are teachers who need more expertise.

#### Pommie

##### Well-Known Member
What would make my charger design "isolated"?
You don't have a design, you have something that is nonsense and dangerous.

Mike.

#### bruceberquist

##### New Member
I am opened to starting over from scratch.

What components would I need to create a safe 300vdc charger from either a 115vac source or from a 12vdc or 24vdc source?

If you know what is nonsense and dangerous, you should also know what is operable and safe.

Guide me in the right direction so I can learn.

#### rjenkinsgb

##### Well-Known Member
First, an isolating transformer.
Examples; there are many available in different power ratings:

A 500VA would provide up to near 2A at 250V output.
A 1500VA near 6A.

The transformer needs fusing before and after, and following by an appropriate high current & high voltage bridge rectifier, smoothing capacitors and a current limiting device of some sort, appropriate to the current the transformer can safely supply. That could be as simple as a suitably rated filament lamp.

The second transformer above can also be configured to provide 230V out for 115V in, so a normal bridge rectifier rather than a voltage doubler.

#### bruceberquist

##### New Member
Wow! That's the kind of response I have been looking for. Clear and easy to understand. THANK YOU!

Now all I have to do is spend a little time doing some research, planning, and some shopping.

#### AnalogKid

##### Well-Known Member
You say that there are commercially available devices to do what you want, but they cost too much.

1. How much do they cost?

2. What is your budget for this project?

ak

#### AnalogKid

##### Well-Known Member
I'm getting more and more nervous about helping with this thread. You have neither the training nor the experience necessary for this task, which is dangerous enough to make an experienced designer pause. That is not a put-down, merely a fact. A multi-hundred watt, high voltage, off-line power supply is not a beginner, or even an intermediate-level project. It is clear that you do not know the functions of even the most basic electrical components, or even that they exist.

Other forum sites are much more restrictive about projects like this one, with good reason. Me, I just don't want to be sued by your relatives. Hate to do it, but I recommend that this thread be closed.

ak

#### bruceberquist

##### New Member
I can understand the liability concerns.
I also think that you judge wrongly based on you known superiority of the language and engineering of electronics.
Though I am far from being an engineer or designer I have many years of work experience in the installation of high voltage assemblies in both the Hybrid and EV field and also in major and military airline assembly and manufacturing, working from static sensitive to high voltage.

I have all full knowledge of safety precautions and procedures, and I own all of the proper equipment.

I am quite intelligent but I am also not "design" "component" smart, and am willing to be first to admit it.

I am an eternal student and I take processing what I learn very seriously.

What I needed here was somebody who was willing to step away from their pride and prowess in engineering and design lingo.
Somebody to speak to me on a simple layman's plain English level, so that I could actually learn and be safe, as somebody finally did on this thread.

Don't worry, I don't jump in all mad scientist into the actual connection and operation of anything I build till I do a full re-evaluation, safety check, and ask for expert advice

#### bruceberquist

##### New Member
As I did on this thread.

I get your concern, but you never "got" me.
I am NOT a dangerous fool.

#### bruceberquist

##### New Member
You say that there are commercially available devices to do what you want, but they cost too much.

1. How much do they cost?

2. What is your budget for this project?

ak

The commercially available systems start at around $700 and go much higher. I had found some second hand at around$550.

I'm my retired guy budget my maximum range of affordability is about $120. So I have to live my life now in a DIY and low budget fashion. The old hybrid car that I have now could very well be the last car I will ever afford to own, so I intend to gather the tools, methods and procedures to keep it alive for a very long time. I came on this site to honestly learn and get expert advice so I can accomplish these things correctly and safely. I would actually be that dangerous fool you think I am if I didn't come to this site. #### AnalogKid ##### Well-Known Member Most Helpful Member I'm not going to clip the sentences from your posts. Here is the short form. That chip on your shoulder is getting bigger and bigger as your frustration increases. What you don't see accurately is our frustration with you. The question you are asking is WAY about your experience base, and you have not adjusted your pre-conceived opinion of what it would take to do this job. Note - there is nothing wrong with pre-conceived opinions. *all* projects start with some. The problem is that yours have not changed despite several corrections by us. Example: bridge rectifier. No one here has called you a "fool", or said that *you* are dangerous. Your project, very. Experience with some dangerous components and systems does not mean you are safe to deal with all components and systems. And by definition, you cannot see that about yourself. That is why we keep bringing it up. Example: isolation transformer. a) it appears that you didn't know such a thing existed, a critical flaw when dealing with off-line power; b) the secondary of an isolation transformer still can kill you, as in dead-before-you-hit-the-floor. Re-read this thread. No one is flaunting their "superiority" or "prowess" with any kind of "pride". You came here for expert advice, and then balked when the experts told you your base idea was wrong. There is way more to electrical engineering than just about anyone outside of the field suspects. The real math behind capacitors and transformers involves integral and differential calculus with complex numbers in the exponents. A relatively small capacitor in an AC power circuit will not do what you want it to do, and the explanation gets very thick very fast. There is no "simple layman's plain English" for it. ak Last edited: #### rjenkinsgb ##### Well-Known Member Most Helpful Member I'm my retired guy budget my maximum range of affordability is about$120.
Just an isolation transformer is going to take the majority of that, before you get to any of the other vital parts.
(And note you cannot use an "autotransformer"; they are cheaper for a given power rating but do not provide isolation).

You then need a suitable enclosure to house the transformer and other parts, either all metal or all platistic & strong enough for heavy parts to be attached.

I believe you need to re-think your budget for this.

I've no objection in principle to helping you with this, as long as the parts and assembly are all to a suitable quality and safe standard - no open lashups or Heath Robinson type rigs. Everything must be good quality, properly mounted, enclosed and fused etc. etc.

From a quick bit of research, the battery may need to be totally disconnected from the vehicle for even trickle charging at a fraction of an amp, as it apparently needs the battery fan system operating to prevent heat and possibly gas buildup within the battery.

#### Les Jones

##### Well-Known Member
I would guess that a commercial unit would use switch mode technology so the isolation would be provided by a much cheaper transformer running at a few hundred Khz rather than a large (Expensive .) transformer running at mains frequency. Unless you can get a surplus mains transformer at a good price I think a commercial unit could work out cheaper.

Les.

#### bruceberquist

##### New Member
I think that apologies are due on my part. My frustration in trying to understand what was shared with me, and with the flood of more questions that entered my mind, I mishandled and expressed in ways that the folks here who were trying to be helpful didn't deserve.
I am sorry.

I am putting this idea on the backburner for a while.
And when it comes to maintenance and balancing the SOC on my HV Battery assembly, I am just going to do it in the tedious and time consuming manor that I am already familiar with, that does not require specialized equipment/tools that I came here with the concept of creating.

Thank you to everybody who tried to be helpful, and thank to for the lesson.

Bruce

#### bruceberquist

##### New Member
I think that apologies are due on my part. My frustration in trying to understand what was shared with me, and with the flood of more questions that entered my mind, I mishandled and expressed in ways that the folks here who were trying to be helpful didn't deserve.
I am sorry.

I am putting this idea on the backburner for a while.
And when it comes to maintenance and balancing the SOC on my HV Battery assembly, I am just going to do it in the tedious and time consuming manor that I am already familiar with, that does not require specialized equipment/tools that I came here with the concept of creating.

Thank you to everybody who tried to be helpful, and thank to for the lesson.

Bruce

Replies
5
Views
2K
Replies
16
Views
11K
Replies
18
Views
3K
Replies
5
Views
2K
Replies
2
Views
3K