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I'm starting to experiment with small solar panel and wind turbines to get my head round what's involved in getting from sun/wind to stored electricity.

I have a 12V version of the opamp and transistor current source part of this schematic on a breadboard and plugged into a cheap, generic solar panel charge controller charging a 12V battery and as far as I can tell it's basically working as expected.

I would like to increase the battery and input voltages to 24V - but I need to have a better idea of how this circuit is working and what the component limitations are before I do that.

Right now my technical knowledge stops just after "If it's not too hot to touch it's working."

Given this very basic schematic - which doesn't include the charge controller and attempts a basic lead-acid battery - I'd appreciate any advice on what parts of this I should be measuring to check against data sheets or where it could be improved or any potential issues - both in the sim and on the breadboard.

Thank you!

Current Source v0.3

Edit: Updated the schematic to try and include the solar panel charge controller

formerlolz
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  • C1 and C2 block DC current from entering or leaving your batteries. Perhaps you meant to wire those in parallel with the batteries? – evildemonic Apr 05 '23 at 14:15
  • Where does the 30 V come from? It seems this is what is charging your batteries, not the solar panel or wind turbine? – evildemonic Apr 05 '23 at 14:21
  • @evildemonic (V4, C1, R5) and (V5, C2, R6) are meant to be 2x 12V batteries in series. I have just copied this from something I saw trying to emulate a battery without really understanding it - idea being a 'high capacitance, low series resistance source'. I'd be up for advice on improving that. – formerlolz Apr 05 '23 at 14:33
  • @evildemonic "Where does the 30 V come from?" Yes - that's not clear here is it. Currently running everything off 1x 12V battery. Idea is to run 2x 12V batteries in series for 24V then run a voltage doubler off that (via something to take it from 48V down to 30V) to power the input summing / current source part of this. Thanks. – formerlolz Apr 05 '23 at 14:35
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    You can model a battery as a (very) large capacitor with a series resistance and get pretty close to true behavior, however, you also have actual batteries shown in the circuit. Do one or the other. – evildemonic Apr 05 '23 at 14:35
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    That would be batteries charging the batteries? Sorry, I'm having a hard time following you. Do you intend to have the solar/wind charge the batteries? Or have the batteries take over when solar/wind isn't present? – evildemonic Apr 05 '23 at 14:37
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    If you are trying to charge the batteries via wind/solar, where you have +30V marked (on the collector of Q1) should be coming from the solar panels or wind turbines. This is the current that will be going to your batteries. – evildemonic Apr 05 '23 at 14:39
  • @evildemonic Updated the schematic to try and make the intended signal flow clearer. The intention is to have solar/wind > current source > charge controller > batteries - but the batteries also power the opamp/transistor circuit (hopefully drawing less power than they use!). Thanks - appreciated. – formerlolz Apr 05 '23 at 15:22
  • Your schematic doesn't make sense. There is no path from your renewable sources to actually charge the batteries. All you have is a loop where the +30V charges the batteries...which generate the +30V...and repeat. Which means the batteries will just start on whatever initial charge they have until they die out. I also don't understand what is supposed to be your current source circuit. It looks more to me like an emitter follower inside a feedback loop; usually a trick done to keep the opamp well above the lower rail of saturation while the actual output can swing close to the rail. – Ste Kulov Apr 06 '23 at 05:29
  • @SteKulov My understanding is the solar/wind input voltages are summed through the LM324 wired in a single-supply, non-inverting, summing config - which also has a transistor current booster Q1 on the output/feedback loop as a current source. The current output from that booster comes via the Q1 emitter. That is connected to the batteries being charged via a diode for reverse voltage protection. That also runs the 'voltage doubler' which - in this schematic - turns 24V into 30V - and that 30V is VCC for the LM324 and Q1. – formerlolz Apr 06 '23 at 09:06
  • @SteKulov Breadboard version appears to be working as expected so far but I'm only just starting to test it with anything but the lightest Current Load. Be great to know if any of the above assumptions were completely off! Thanks. – formerlolz Apr 06 '23 at 09:07
  • First circuit in this link is what I've based the voltage summer/current source on: https://www.renesas.com/us/en/document/apn/r13an0008-boosting-op-amp-output-current – formerlolz Apr 06 '23 at 09:26
  • I think the problem you're having is you're trying to go from block diagram to circuit blocks, but then the circuits blocks you're choosing to fill in your block diagram with don't exactly represent what you want to do. For example, you want to combine the power from each renewable source into a single output. You chose an opamp summer circuit, which sums whatever voltages are present at each source and then produces a copy of that number at the output. Its output power for this copy is sourced by the opamp's supply rail and further by the power connection at the NPN's collector. – Ste Kulov Apr 07 '23 at 01:52
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    In other words, the power from your renewables is not making it through the opamp. I think a better starting point would be to simply "diode-OR" your two renewables into the battery node. Whichever one is at a higher voltage (in each instant) will win and transfer its power to the battery, so if you want both at the same time you need some more complicated circuitry to achieve that. – Ste Kulov Apr 07 '23 at 01:56
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    I found some other questions on this site which pertain to the same thing you're trying to do. Maybe the information can help you: https://electronics.stackexchange.com/questions/524680/ https://electronics.stackexchange.com/questions/158799/ https://electronics.stackexchange.com/questions/207830/ – Ste Kulov Apr 07 '23 at 20:53
  • @SteKulov haven't had a chance to check those links properly yet but I just wanted to say thanks for taking the time to add them. Much appreciated. – formerlolz Apr 18 '23 at 10:42

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