Circuit simulation app that can simulate charging/discharging AA batteries - Page 1
Forum section: electronics / beginners

author: Txm-L
author_rank: Newbie
timestamp: June 28, 2023, 01:03:05 am
content: I am making a NiMH battery charger and I want to test out my design before building it. My problem is that all the circuit simulation/designer applications I found treat batteries only as power sources instead of allowing for charge/discharge. Some (like CircuitLab) allow me to add NiMH batteries but not charge them, others (like Tinkercad) only offer standard 1.5v AA disposable batteries. Is there an application I can use to allow me to test a battery charger design?

author: Jwillis
author_rank: Super Contributor
timestamp: June 28, 2023, 01:25:41 am
content: I've never used a battery simulator let alone this one . I'm not even sure if it's free.https://elektroautomatik.com/shop/en/service/downloads/ea-battery-simulator/I think this one is only for Lithium batteries only .https://ebikes.ca/tools/charge-simulator.html?ver=72&bat=cust_c26_s8_p5_l30I just use an an electronic load with data logging to test battery packs . Not sure if any of these will work for you. Be interesting to try. Let me know.

author: Txm-L
author_rank: Newbie
timestamp: June 28, 2023, 01:53:13 am
content: Thank you for the reply!After reading up on these it looks like they are solely for testing batteries and their power curves independently of the circuit that’s providing the power. I am looking to test a circuit design I made and see if it would properly trickle charge some AA NiMH batteries. Perhaps, instead of looking for a program where you can design a circuit and have the batteries be part of it, I can substitute where the batteries would go for some other component. I’m only trying to check the voltage and amps going through where the batteries go. Is there a component (like a resistor or a capacitor, or something else) that can have the same effect on the circuit as a charging battery would? And if so, what would that be?

author: Jwillis
author_rank: Super Contributor
timestamp: June 28, 2023, 04:11:47 am
content: I don't know. A capacitor I guess. A battery is essentially a capacitor. But with a AA battery, your looking at several thousand Farads.Maybe 5000 to 6000 Farads. But unlike a capacitor a battery won't instantly discharge when shorted. With that many Farads your looking at a possible simulated explosive situation unless theirs a series resistor to slow the discharge significantly. Not to mention the inrush current when charging.Personally I bench test circuits instead of simulation. Not that I have to much against Sims, I just have more fun bench testing.

author: MrAl
author_rank: Super Contributor
timestamp: June 28, 2023, 06:23:23 am
content: Quote from: Txm-L on June 28, 2023, 01:03:05 amHi,There are battery models but to test a charger circuit you can use a capacitor with a small series resistance.The capacitor value depends on the ampere-hour rating of the battery and the voltage range from min to max voltage.The defining equality is:dv/dt=i/Cwheredv is the change in voltage,dt is the change in time,i is the current,C is the capacitance.Since we want to know what the capacitance is for a given ampere hour, we can first convert this into an ampere hour form.Multiplying both sides by 'dt' and by 'C' we get:C*dv=i*dtand now we have it in a form where the right side is in ampere seconds. To convert to ampere hours, we just multiply that side by 3600:C*dv=AHr*3600What we have now is a form where we can use the ampere hour rating of the battery and the span in voltage from min to max to calculate the value of C. Since a regular AA NiMH battery has a voltage span of about 0.9v to about 1.6v when fully charged, 'dv' comes out to:dv=1.6-0.9which is of course 0.7, so replacing that we get:C*0.7=AHr*3600Many NiMH batteries of the AA size are around 2000mAHr, which is 2AHr, so we replace AHr with 2 and get:C*0.7=2*3600or:C*0.7=7200Now to solve for C we just divide both sides by 0.7 and we come out with:C=10285.714 Faradsand rounding up we get:C=10286 FaradsBut even 10000 Farads would be close enough for a simulation.The series resistance should match that of the actual battery, but it is good to simulate with more than one value for that resistance.Start with maybe 0.02 Ohms and go up to maybe 0.50 Ohms to see the difference in how the battery charges and how long it takes. This is good to see how the battery charge process changes as it ages.