I tried to build a flyback converter

[David lopez]

i tried connecting flyback converter to, i think it was 3 18650 lithium ion cells, and using a, i think it was a 3.5 ohm resistor. i got a reading of 3.5 amps
then i got a decreasing reading. then one of the 18650 lithium ion cells overloaded. it is now damaged. is there any way to pass 3.5 amps through flyback converter, without overloading the 18650 lithium ion cells? this a schematic of the circuit i used.

 

[essenmein]

Not certain, but I think you might be missing some parts, here is a basic flyback schematic:

 

[David lopez]

i forgot to include the diode in the schematic. sorry. i didn't include a capacitor. if i use nonrechargeable batteries, can i pass 3.5 amps through the flyback converter without overloading the batteries?

 

[essenmein]

You also don't have a switch, which is basically the most critical part, or a means of creating PWM. Based on your schematic you are connecting a transformer to a DC supply through a resistor. Transformers only work with AC.

Your question of "can i pass 3.5 amps through the flyback converter without overloading the batteries " depends entirely on the batteries.

 

[David lopez]

if i use c cells, can i pass 3.5 amps through the circuit, without overloading the batteries?

 

[essenmein]

The way I would approach that question is to look up the data sheet for the proposed battery, determine its maximum discharge rate and total capacity (Whr or Ahr) and use that information to calculate how long the batteries would last with my load. Then you can decide if they are appropriate.

 

[David lopez]

what if i connect the batteries in parallel, then can i pass 3.5 amps through the circuit, without overloading the batteries?

 

[essenmein]

What is the maximum discharge rate and capacity of the batteries?

 

[David lopez]

i connect 18650 lithium ion cells in parallel, so discharge rate is c.

 

[essenmein]

2.998e8 m/s?!

 

[David lopez]

i don't understand the response. sorry.

 

[eq1]

i connect 18650 lithium ion cells in parallel, so discharge rate is c.

Is that sentence correct? That’s more than 2.5x the number of cells in a Tesla Model S, which is not your everyday pack. And I doubt they’re all in parallel...

https://en.m.wikipedia.org/wiki/Tesla_Model_S#Battery

 

[essenmein]

i don't understand the response. sorry.

C is not a number like a constant, c depends on the battery, you need to go and get a number from a data sheet, that number will be like 12.34Whr or 23.45Ahr. C, the constant, is the speed of light, 2.998e8m/s.

What is your electronics knowledge? Like what else have you built?

Based on your answers so far you don't seem to understand enough about batteries to be able to specify one for a project, that's probably a good place start before trying to build a functioning flyback converter.

 

[essenmein]

Sorry, capacity will be a number like 12.34Whr or 23.45Ahr, c would be in Amps, or as a multiplier to get amps.

 

[anorlunda]

18650 is a battery size, like AA or AAA.

 

[eq1]

18650 is a battery size, like AA or AAA.

Got it. That makes a lot more sense. :)
https://en.wikipedia.org/wiki/List_of_battery_sizes#Lithium-ion_batteries_(rechargeable)

 

[David lopez]

what if i connect the batteries in parallel, and the maximum discharge rate of each is say 2.4 amps, can i pass 3.5 amps through the circuit, without overloading the batteries?

 

[hutchphd]

The C rating of the battery is a measure of its maximum discharge rate capability. A battery rated C=1 can discharge its entire capacity in 1 hr. A battery rated C=60 can discharge its entire capacity in one minute. It is a parameter characterizing all various sizes of similarly constructed batteries. FYI

 

[anorlunda]

what if i connect the batteries in parallel, and the maximum discharge rate of each is say 2.4 amps, can i pass 3.5 amps through the circuit, without overloading the batteries?

It helps to look up the real number rather than just ask questions. I searched "18650 specifications" and quickly found the following.

Specifications:

• Model: INR18650HG2
• Capacity: 3000mAh
• Released: 2014
• Product Classification: Cylindrical rechargeable lithium ion battery
• Intended use (application): Power Tools
• Max. Constant Current 20 A (20000 mA)
• Cycle Life @ 10A: 300 cycles at 10 A
• Cycle Life @ 20A: 200 cycles at 20 A
• Initial AC impedance: less (or equal) than 20 mΩ
• Dimensions: Diameter Max 18.5mm, Height Max 65.2mm
• Weight: Max 47g
• Operating temperature (battery cell surface temp.): -20 ~ 75 ℃
• Lower limit (cutoff) discharge voltage under load: 2.5V

And yes, you can connect them in parallel to provide twice as much current. But there are caveats. The batteries in parallel much be closely matched.

 

[David lopez]

so if i connect them in parallel i can get twice as much current, without overloading the batteries?

 

[Tom.G]

According to the Data Sheet posted by @anorlunda and your statement of measuring 3.5A, you did NOT overload the batteries, the batteries are rated at 20A.

 

[alan123hk]

i tried connecting flyback converter to, i think it was 3 18650 lithium ion cells, and using a, i think it was a 3.5 ohm resistor. i got a reading of 3.5 amps
then i got a decreasing reading. then one of the 18650 lithium ion cells overloaded. it is now damaged. is there any way to pass 3.5 amps through flyback converter, without overloading the 18650 lithium ion cells? this a schematic of the circuit i used.

I think, if necessary, there are theoretically two ways to get more than rated current of single battery from multiple batteries.

1. Batteries in parallel plus prevention measure for circulating current flow between them, as well as other protections, such as each battery has its own over-current protection...

2. Batteries in series plus stepping down converter to generate more current...

Since you already have a flyback converter installed in your circuit, you may consider the second method and include the function in the flyback converter.

I don't like using batteries in parallel because I personally think that this is not a good approach, especially for DIY projects.

Besides, please pay attention to battery and circuit safety issues. You may reference the relevant instructions, standards and regulations for more information.

 

[David lopez]

so you are suggesting i use a stepping down converter?

 

[alan123hk]

so you are suggesting i use a stepping down converter?

I am discussing the feasibility of one of these options. In theory, a DC-DC flyback converter with regulated output voltage can boost or step down a variety of input voltages

If there is no specific reason to fix the input voltage, as long as the input voltage of the flyback converter is still within the rated range, it should be possible to connect more batteries in series to the input and then reduce the input current. Note that I = P / V. For the same power, a higher voltage indicates a lower current.

So I'm talking about integrating the input current reduction function into the existing flyback converter, not necessary to change it to step-down converter, nor adding another step-down converter.

 

[David lopez]

but i am trying to pass a higher current through the circuit, not a lower one.

 

[davenn]

but i am trying to pass a higher current through the circuit, not a lower one.

Forget about high current, get a working circuit sorted out first
You haven't even listened to what you were told in post # 4

 

[David lopez]

may i ask if you are an engineer?

 

[anorlunda]

The original question has been adequately answered. Before things get too hot, I am closing this thread.