Circuit to simulate a battery - Page 1
Forum section: electronics / projects

author: krish2487
author_rank: Frequent Contributor
timestamp: February 16, 2014, 08:12:01 pm
content: Hello folks,I have a rather peculiar problem.I work on custom power supplies, specifically battery chargers. Almost always, it happens that the battery also powers a small DC-DC converter.AC/DC Battery charger --> Battery --> DC-DC Converter.While working a design a while ago, I came across the need for such a device.I wanted to seek from other members who may have worked in similar areas and have more knowledge than me.What I am looking at is designing a test jig for such Power supplies. I will need to test the charger and later the DC-DC converter.Here is the problem. To test the battery charger I need a current sink where-as to test a DC-DC converter I need a current source.Is there a circuit that can simulate a battery i.e a current sink and a source.From what i understand I would to get a dual quadrant power supply i.e a power supply that can sink current.Anyone who has worked on such a circuit before and can share it here with us?The closest I have come to addressing this issue is this link :http://www.accelinstruments.com/Applications/TS200/Battery-Simulator-AppNote.html(Figure 2 )But it has two independant connectors for sourcing and sinking current. I would prefer one connector which can both sink and source current.I know, you have solutions from agilent and delta elektronika that do what I asked for, but it is out of curiosity and as a hobbyist, for my purposes at home, on my test bench I cannot justify the cost of either. Hence I am looking at a DIY solution.So please help guys...

author: PChi
author_rank: Frequent Contributor
timestamp: February 16, 2014, 09:52:13 pm
content: How many volts and how many amps?It may be possible to use an audio power amplifier Integrated Circuit to make a 2 or even 4 quadrant power supply. There are some snags, they are usually only designed to be stable with a fair amount of gain and might not be stable when connected to large capacitors.Other manufacturers of power supplies that can source and sink are Kiethly and Kikusui.

author: dannyf
author_rank: Super Contributor
timestamp: February 16, 2014, 09:58:43 pm
content: It depends on what elements of a battery you are trying to simulate.in terms of sinking and sourcing current, most amps can do that - go to a local hi-fi or pro audio shop and get yourself a power amp and call it a day.

author: jeroen79
author_rank: Frequent Contributor
timestamp: February 17, 2014, 03:31:58 am
content: QuoteWhat do you mean by that?A battery has two poles so a battery simulator should have two connectors, right?The circuit infigure 2is capable of both sourcing and sinking current.You would need to add something to control the direction of the current based on the voltage between the positive and negative connectors.In figure 2 an opamp is doing this.*edit*If you mean the terminals marked + and -, I don't think that one is for sinking and the other for sourcing.The + is the voltage output in fig 2 and would sink or source and the - is the ground in fig 2.

author: krish2487
author_rank: Frequent Contributor
timestamp: February 17, 2014, 04:24:25 am
content: @PchiUsually about 12V and rarely 24V and about a couple of amps. Sub 100 watts always.Can you suggest any app note or such which I can use. The closest that springs to mind for the single chip solution is the LM3886.Though running it at 50 watts would be pushing it.@dannyfI am not sure I understand your question. I am not trying to simulate Internal resistance, charge-discharge characteristics etc.I am merely trying to simulate the ability to sink and source current through the same terminal.@jeroen79Maybe it is time I gave it another look with a rested set of eyes.It does sink and source current. I misread the Voltage input and Voltage output as two independant terminals for sink/source seperately.

author: codeboy2k
author_rank: Super Contributor
timestamp: February 17, 2014, 05:40:59 am
content: Quote from: krish2487 on February 17, 2014, 04:24:25 amIf you take a look at the circuit posted as fig2 above by jeroen79 (I'll link it again:figure 2) you will agree that the schematic is a typical push-pull stage , and this is exactly what is used on the output of an audio power amplifier to drive a speaker.Danny is suggesting you use the output stage of such an audio amplifier. The larger ones have 8-10 BJTs on massive heatsinks and can sink and source 35V up to 40V or more, across 4 ohms.. that's up to 10A and 400W (!) For many audio amps the schematics are available online and you can tap into the output stage to force a DC level out the back. You can hook up some feedback if you want regulation.I once got an old Yahama receiver off craigslist for $20.00 and re-purposed the output stage as a power supplyHere's a photo just after I took it apart...(click for a bigger view)

author: ConKbot
author_rank: Super Contributor
timestamp: February 17, 2014, 01:06:47 pm
content: Quote from: krish2487 on February 16, 2014, 08:12:01 pmUnless I'm missing something, that has only one connection for sourcing and sinking, the 'input' is an analog modulation input so you can use another instrument to control to output voltage. (step changes, or just to simulate a charging curve)Also, you can do this simply with a DC power supply and a DC load with the outputs hooked together. Set the power supply to your desired battery voltage, and set the DC load to constant V mode, a couple dozen millivolts above the output of the power supply. When your circuit tries to charge the battery, the 'battery' voltage rises a few mV, but not enough to trip OVP on the power supply and the load starts sinking current.But yes, if you're trying to do it on the cheap, a class AB amplifier could do it if you can modify it to be DC coupled. I'd add extra fans on the heatsink just because on a cheap amp the the heat sinking was probably questionable for audio duty, let along constant duty that it operating at DC will provide.

author: krish2487
author_rank: Frequent Contributor
timestamp: February 17, 2014, 01:46:56 pm
content: @codeboy2KOne more reason why lack of sleep and focussed working dont go hand in hand.Had another look after resting my eyes and seems like a good way to go about.You just have to love the yamaha construction.single sided construction and TONS of jumpers. :-)@ConkbotYou are right. My sleep-deprived eyes did see but my brain did not register.Nice tip about the power supply + DC Load. I ll try thesame first seeing as how I have a hobbyist made DC load and a bench PSU.Thank you!!Again, Thank you all who have responded in kind!!!If I am able to righ some sensible stuff up, I ll be sure to put it here for scrutiny.Maybe it may come in handy to others later!!!

author: PChi
author_rank: Frequent Contributor
timestamp: February 19, 2014, 08:24:04 pm
content: Sorry for the slow response but things have been a little crazy here with roads being blocked by flooding.Your requirements for 24 V and a couple of amps was more than I was expecting. The only app note that I have found is Linear Technology Application Note 112, Developments in Battery Stack Voltage Measurement. Units that I have used from Agilent and Keithely had current limits that could be set. From memory I think that was true for sourcing and for sinking current. So they can simulate behaviour of the battery better than an audio amplifier.

author: dexters_lab
author_rank: Unknown
timestamp: February 19, 2014, 09:48:28 pm
content: the agilent 6632 psu can source and sink, there are a few app notes about it on the agilent website which might prove helpfulhttp://cp.literature.agilent.com/litweb/pdf/5990-3262EN.pdf