Building a very simple capacitor bridge-rectifier power supply

[bruceberquist]

Okay. I found other similar posts, but in them I haven't found the kind of answers I need.

I am building a very simple low amperage 300vdc power supply using a 115vac source, to a switch, to a 370vac 80uf single Run Capacitor, to a 500v bridge-rectifier, to 300+vdc output cord and connectors to service a 300vdc battery pack assembly.

I do not require additional accessories such as output regulators or auto shut of switches, since this is only going to be operated in a gaged/monitored environment, so I don't need such input and advice, unless it relates to solving my following issue.

Here's my issue that I hope somebody can help me with, and I can be educated from.

When powered up, the capacitor is receiving the full 115vac source. however, the capacitor output is reading initially 108vac that draws down to 70vac in about 2 minutes.
The DC output of the bridge-rectifier is reading at about 60% of that in dcv.

The Capacitor is not collecting the 300+vac that I was expecting it would, from the 115v source.

I have tested both the capacitor and rectifier for faults and shorts. There are none. The components are good.

BTW; these readings are being done with out any connection to the battery pack assembly on the output end.

Question; Am I missing something in my simple design?

Is there a needed component for allowing the capacitor to collect the full 370v voltage from from the 115vac source I am feeding it?

Any constructive answers and collaborative troubleshooting assistance will be greatly appreciated.

 

[JimB]

Your description is very confusing.

It would be helpful if you could show a schematic diagram of your circuit.

JimB

 

[AnalogKid]

Question; Am I missing something in my simple design?

Yes, a schematic.

It is i.m.p.o.s.s.i.b.l.e to evaluate your circuit without a schematic. To paraphrase Rear Admiral Joshua Painter,

"Engineers don't take a dump, son, without a schematic."

Also, a description of the load, its impedance and frequency characteristics, the peak load current, etc.

At 60 Hz, an 80 uF capacitor has an impedance of 33 ohms. How does this figure into your circuit design calculations?

Why do you think a 115 Vac source will yield over 300 V in your circuit?

ak

 

[augustinetez]

When powered up, the capacitor is receiving the full 115vac source. however, the capacitor output is reading initially 108vac that draws down to 70vac in about 2 minutes.
The DC output of the bridge-rectifier is reading at about 60% of that in dcv.

Correct - you will only get 0.637 x 115VAC = 73.255V DC max out of the bridge rectifier - the cap is basically doing nothing more than limiting the current and dropping the voltage in to the rectifier, further reducing the DC out.

In fact, with the components you are using, there is very little chance of you getting 300V DC direct from the mains (115V AC).

 

[augustinetez]

You need a circuit like this to give you the voltage you want - adjust the value of the capacitors (both the same value) to get close to your DC voltage and you may need to add a series resistor to drop it a little further depending on exactly what is required for your application.

 

[bruceberquist]

I just came to learn that the capacitor is only going to store as must voltage as I supply it (115vac).

So other than using other methods that I am not aware of, other than spending big money for a commercial power supply, I theorize that the only way to get over 300vac out of 115v through capacitation would be to charge 3 (or 4) capacitors to 115v each, then switch the 3 (or 4) capacitors together to send approx 345vac to 460vac. Works in theory but I have yet to find out if it works in real life.

Since I am going to use the output to charge a battery pack assembly I believe I am going to need a much larger uF in order to collect enough electrons to fulfill the needed service to the battery pack.

I believe I am speaking in pretty simple language, and am only dealing with a simple handful of facts;
*115vac source
*370vac 80uF capacitor (but now going to 3 or probably 4 of them, considering the volt loss in the rectifier)
*Basic 500v bridge rectifier
*Need for for 300+vdc output

I am truly a layman and do not speak and only slightly understand electrical engineering terms.

So speak to me though I am a simpleton, who is somebody who really enjoys DIY approaches to designing tools for his needs, and believes that he is experimenting and learning on a good concept.

Thank you for the helpful responses so far.

 

[augustinetez]

We need more information:

What type of batteries is the battery bank made from?

What is the 300v battery bank used for? This can have an impact on the charging circuit needed.

Charge current (amps) needed for the battery bank?

Does the charging voltage/current need to be specially controlled to prevent damage to the batteries?

One other thing - converting the mains and using it directly to charge the battery bank is potentially very dangerous.

Learning and experimenting with high voltages is not a good idea without at least some knowledge.

 

[Pommie]

deleted.

Mike.

 

[bruceberquist]

Thank you for your input. It is all very helpful.
The doubler set up does look very simple to accomplish and might be a good candidate for what I am trying to do, as long as it does not exceed 7 amps. Actually, I would prefer to keep this down to 1.5 or 2 amps (or even less) to prevent overheating the cells in the 300v battery pack assembly.

Though I do not speak the "tech" language well, I assure you that I do have actual pro working experience in handling high voltage, know precautions very well, and have the correct protective equipment.

This charger is being designed for very occasional maintenance and balancing of a Gen 1 Toyota Prius Hybrid NiMH battery assembly made up of 38 x 7.8v cells/modules.

Though the cars hybrid charging system does charge at a much higher amperage, I only need in the range of .65a to 2.5a to properly maintain this assembly. In the maintenance and balancing process, which entails charging and discharging, I do not require or desire the fast charge that the car's hybrid system does. A low amperage charge is best.

As long as the amperage is low and the process is well metered and monitored, as it will always be, there is no need for other equipment or accessories with which to protect the battery.

Here is a drawing of my upgraded idea for accomplishing the 300vdc charging current.

Wish I didn't need the 4 switch bank but I'm under the impression that in order for the capacitors to fully charge to a good 115v individually that I am going to have to prevent them from discharging into each other while they charging.

If I am wrong about that, it would be great. I'd love to avoid the complexities of putting those switches in.

 

[Pommie]

Deleted

Mike.

 

[bruceberquist]

I'm sorry. I thought that the bridge Rectifier took care of the final conversion to DC?

Should I be running the rectifier first?

Easy to change, but I guess this is definitely a learning experience for me.

 

[Pommie]

Deleted.

Mike.

 

[bruceberquist]

Thank you. I will give it a try tomorrow. I think I still have everything to assemble it that way.
I'll let you all know.
Thanks again.

 

[Pommie]

Deleted.

Mike.

 

[rjenkinsgb]

DO NOT CONNECT THAT VOLTAGE DOUBLER TO YOUR BATTERIES. There is nothing to limit the current and many amps may flow and damage the batteries.

Agreed! Though with a high current rated EV battery, it's more likely to make the bridge rec explode or the wiring catch fire...

Also, if that is run directly from AC mains, and connected to the vehicle battery while it is in place, the whole vehicle may become "live" at a lethal DC voltage.

Disconnecting the main battery plug alone is not adequate as there is also monitoring electronics connected to various points within the battery unit. An un-isolated supply may destroy part of the vehicle system.

Use an isolation transformer to feed the psu, and an appropriate high power filament lamp as a current regulator between the DC out out from the power supply and the battery to regulate the current.

 

[Pommie]

Deleted.

Mike.

 

[rjenkinsgb]

Edit, I'm assuming now that the US mains supply has the neutral earthed - neutral being the star point and live being one of the phases.

The commonest domestic US wiring system, as far as I am aware, uses a single phase 230V or 220V supply that has the sub transformer centre tap as neutral, and the centre tap is also grounded.

So two separate 115V supplies alternated in the fusebox / distribution panel, with loads to neutral distributed between them.
But, with the option of using both lives to run higher power 230V appliances, via different design power outlet sockets.

 

[AnalogKid]

What is the charging regulator / circuit / device that will be between the 301 Vdc output in post #9 and the battery array?

ak

 

[bruceberquist]

As long as the amperage is below 7 amps there is no need for anything between the 301vdc output and the battery.

Though the battery rests at a nominal charge of 285v it commonly charges to 327v in regular operation.

So 301v is not an issue. In fact as much as 45 amps is not an issue, except that in maintenance, with out the battery cooling fan in operation, it is best to run low amperage in order to reduce risk of overheating cells.

 

[bruceberquist]

I am trying to build a very affordable tool for maintaining the hybrid battery on my car with out having to disassemble or remove the HV Battery assembly.

There are grid chargers on the market to do this and they are priced way beyond my retirement spending budget.

I can maintain and balance the assembly by way of servicing each of the cells individually. Simply using a regular car battery charger.
Which is what I have done.
VERY TIME CONSUMING!

If this plan to build an inexpensive high voltage charger is going to become a fiasco, which I strongly believe it shouldn't be, then I will just stick to the old labor intensive method.

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?