Continue to Site

Welcome to our site!

Electro Tech is an online community (with over 170,000 members) who enjoy talking about and building electronic circuits, projects and gadgets. To participate you need to register. Registration is free. Click here to register now.

  • Welcome to our site! Electro Tech is an online community (with over 170,000 members) who enjoy talking about and building electronic circuits, projects and gadgets. To participate you need to register. Registration is free. Click here to register now.

Simple DC Charger (Help!)

Status
Not open for further replies.

tkc100

Member
I need some help with a simple charging circuit.
I attempting to use a many parts as I have on hand and there by keep the expense of this project to a minimum.
See the attached flow chart of what I am trying to accomplish.

The portion of the flow chart I need assistance with is the charger (Red)
Attached is a simple circuit diagram I think will work for the charger. I already have the transformer, two SCRs, maybe the capacitor, heat sink, and a case to mount it all in.

What do you all think?

My concerns and what I need help with are as follows:
1) I need an output voltage of at least 14.5 volts
a) I’m not sure how much will be lost over the SCRs
b) The actual output of the transformer is 16.4 VAC
c) Here are the specification on the SCR
USA 245040 R
245040 Specifications
Renard Manufacturing Co
Silicon Rectifiers SCR
Military/High-Rel : N
I(O) Max.(A) Output Current : 50
@Temp (?C) (Test Condition) : 150#
V(RRM)(V) Rep.Pk.Rev. Voltage : 400
I(FSM) Max.(A) Pk.Fwd.Sur.Cur. : 400
V(FM) Max.(V) Forward Voltage : 1.18
@I(FM) (A) (Test Condition) : 79
@Temp. (?C) (Test Condition) : 25
I(RM) Max.(A) Reverse Current : 1.0m
@V(R) (V)(Test Condition) : 400
I(RM) Max.(A) Pk. Rev. Current :
@Temp. (?C) (Test Condition) :
Maximum Operating Temp (?C) : 175
Description : Cathode to case
2) I am assuming the capacitor serves a smoothing function but I have no idea what its value should be.
a) I salvaged a 10 mfd 660 VAC out of a 12 volt converter will it work?
Any assistance and or suggestion you all might have will be greatly appreciated.
Thanks!
 

Attachments

  • Flow chart of circurt.jpg
    Flow chart of circurt.jpg
    58.4 KB · Views: 148
  • Charging Circurt Diagram.jpg
    Charging Circurt Diagram.jpg
    87.2 KB · Views: 163
You left out a crucial piece of information:

What kind of battery/batteries do you plan on charging?

I'm sure you can see how it would be nice for us to know this.

Looking at your circuit diagram, there's a basic misunderstanding on your part. The diodes in the bridge rectifier (the four arranged in a diamond pattern) aren't SCRs; they're just silicon diodes. Big difference (SCRs are silicon controlled rectifiers, used for other purposes entirely.)

Your circuit will charge a battery--assuming, that is, that it doesn't overcharge it, or make it explode. It lacks any kind of regulation or charge controlling.

It's important to know what kind of battery (lead-acid, NiMH, lithium, etc.) you're charging, as they all have different "appetites" when it comes to how much electricity to pump into them, at what rate and what timing.
 
Last edited:
Caronzit
Thank for getting back to me so quickly.
I am not really too concerned with the inability of this circuit to regulate itself. If you take a quick look at the flow chart in my previous post you will see a charge controller between this charger configuration and the batteries. The charge controller, very precisely controls and monitors the actual voltage seen by the batteries. The only requirement of this charging circuit is to output 14.5 to 55 volts DC at about 50 amps.

As far as the SCR go, I’m not an electrical engineer just a tinker forever involved in one project or another. I am so grateful for individuals such as your self that take the time to help. The components, (I have been corrected also for calling them diodes) in question can be seen in the attachment the only identification on them was USA 245040 R. I thought I was being pretty tick when I was able to find a reference to them on the internet. They came out of a 50amp RV power converter. Since this is not what I need can you tell me what I should be looking for?
What about the circuit, do you think it will meet my requirements?
Finally what about the capacitor, do I need it, and if so got any idea as to the value?
 

Attachments

  • Diode (Medium).JPG
    Diode (Medium).JPG
    45.3 KB · Views: 142
  • Heat Sink Mounting (Medium).JPG
    Heat Sink Mounting (Medium).JPG
    74.9 KB · Views: 142
So basically all you need is a power supply for a battery charger, which will use something called a "Xantrex charge controller", correct?

Really, the battery charger is all of this stuff taken together. All you're asking about is the power supply part.

All you need for the power supply are rectifier diodes. As I explained above, these are not SCRs. The exact part you need will depend on how much current the power supply will deliver. Diodes are rated both by voltage (maximum forward and reverse voltages) and forward current, so you'll need to let us know how much current you expect this thing to draw. (If you can find it, the data sheet for the charger controller should tell you this.)

Rectifier diodes are really really cheap, so I wouldn't sweat that part of it. Chances are you can use something in the 1N400X family.

Whether or not you need the filter capacitor depends on the charge controller. I'd assume you do need one, since the controller is an electronic circuit which probably wouldn't be too happy with a lot of ripple, so figure on putting at least 1000-2200µF of electrolytic capacitance where you show it. Electrolytics are also cheap, so no big deal there. (Make sure it's rated conseratively; get a 50 volt cap and you won't have to worry about it blowing up.) And yes, the capacitor smooths out the pulsating DC.
 
Last edited:
OK
The power supply needs 4 “rectifier diodes” rated for at least 16.4 Volts at 50 amps.
The transformer I have has an open circuit voltage of 16.4 and is supposed to deliver 50 amps although I can’t swear to that.
Can you recommend a “rectifier diode? It would be great if in mounted on the existing heat sink pictured in my last post. I know I will have to modify the heat sink into two separate plates but once again I am trying to make use of the parts I have. If the diodes press into the heat sink two will need to have a cathode case and two will need a anode case I think.
The Xantrex charge controller is used in alternative energy designs. (Solar, Hydro, Wind and or a combination of these) It is a rather expensive piece of equipment and this project would not be feasible except for the fact I already have the controller. It is rated for up to 55 volts DC at 60 amps continuous duty. Further more it’s a three stage PWM charge controller.
Will there be a voltage drop over the “rectifier diodes” and if so how much. I can’t lose very much without having to shop for another transformer.
I have a 10 mfd 660 VAC out of a 12 volt converter will it work?
 
Why do you think you need 50 amps? That is a hell of a lot of current. Are you planning on charging an entire pallet of batteries at one time?

If you really do need that much current, then this bridge rectifier from Digi-Key should do the job. (No need to buy 4 separate diodes: a bridge rectifier has them conveniently put in one package.) This one just handles 50 amps (it was the highest-current one that was actually in stock I could find), and will set you back $3.75. You can mount this on any metal surface to dissipate heat (or use a heat sink).

All diodes have a voltage drop. Silicon diodes have, on average, a 0.7 volt drop. Since a bridge rectifier has 2 diodes in series on each side, there's a total of a 1.4V drop.

I told you that you might need somwhere in the neighborhood of 1000-2200µF of capacitance. You tell me if 10µF will work or not.
 
A transformer rated at 16.4 volts and 50 amps is one which outputs 16.4 volts A.C it's peak voltage will be 16.4 x 1.414 volts ( 23 volts ) so the diode voltage drop of 2 x 0.7 volts should not be a problem. However a capacitor has several properties and one is the ripple current it can handle. I have some capacitors rated as "high ripple current" and it states on them the are good for 7 amps so you can see this is way down on the 50 amps you say you need. A standard electrolytic capacitor cannot handle anything like 50 amps and will almost certainly overheat and probably explode. Your 10 mfd capacitor will be useless in this circuit. What is it specifically you are trying to charge/ Are you sure it requires 50 amps? If so you are talking about a large bank of heavy duty batteries.
 
Thank you all for you comments!

I know just enough to be dangerous.

I have done some more research and here is what I found.

The controller when bulk charging is wide open to sending all of the current available up to the limit of the controller, in this case, 60amps. The power supply will essentially see no controller while bulk charging. Herein lies the problem, most power supplies when connected to a battery will want to send a near infinite amount of current as the low internal resistance of a discharged battery will seem like a dead short to the power supply.

So here is where I'm at.

I need to deliver ≈ 25 amps of charging current to the posts of my Lead acid battery bank. This will of course decline as the battery's counter voltage increases. After some considerable head scratching this will be adequate

The actual voltage at the battery post will vary dependent on the SOC and the controller in series with the power supply.

The C-60 charge controller can work with 15.3 volts to 55 volts (delivering three stages of charging voltages) at up to 60 amps.

Here I do have a concern. The C-60 is a PWM controller (It pluses the charging current, truns it off and on) A DC regulator (C-60 controller) needs not to be over voltage or overshoot input voltage maximum when the charge controller goes into PWM mode the transformer may have some pretty good inductive kick.

Please see attached the schematic has been modified some what
I calculate the capacitor's value at 13000µf

I am still stuck on how to limit the final output to 25 amps
a 25 amp bi-metal breaker on the output would be a simple an inexpensive solution but I have some concerns as to its actual performance. In practice I seldom discharge the battery bank below 50% so there is only a brief period of time when full charging current is required but even with a 50% discharged battery bank it will bulk charge briefly. I other words the battery would be fully open to the power supply. During that period of time the charging current will exceed the safe charging limits (of both the batteries and the transformer) if not controlled. A bi-metal breaker only has so many cycles in its lifetime and I afraid it would have a short life in this configuration.

What about placing a resistor in series with the secondary winding to limit current output. I don't understand how this works or what values I would be looking for. Care to comment of this.

So this is what I thought was a simple project. Is there any hope? Is anyone willing to take it on or am I looking at something that can't be feasibly done?

Once again thank you all for your selfless assistance!!
 

Attachments

  • Charging Circurt Diagram.jpg
    Charging Circurt Diagram.jpg
    86.2 KB · Views: 138
Status
Not open for further replies.

Latest threads

New Articles From Microcontroller Tips

Back
Top