Very Simple Solar Charge Controller Questions - Page 1
Forum section: electronics / beginners

author: EpicIntelGamer
author_rank: Regular Contributor
timestamp: November 24, 2013, 04:48:03 am
content: Hello!Lately I've been messing around with two tiny 5V solar panels hooked up in series that are never in direct sunlight so even at the best times they only produce about 5 or so Ma, at 10V.I've just been putting that straight into a 7.2V 3300MaH NICD battery pack. I know that the voltage sounds a bit high but with the battery connected its not at all.I was considering buying some small SLA's and using them with some bigger solar panels (maybe 10watt, but still not in direct sunlight) and I wanted to build a charge controller.I always try to do it in the simplest way and I was thinking, why not just have a P channel mosfet in series with the battery and solar panels and have a potentiometer on the gate of it set to whatever voltage I want the charge controller to stop charging. Or even have an N channel mosfet with a potientiometer on the gate that will enable the n channel mosfet and dump some power into a dummy load.I understand there is no current regulation but I can pretty much guarantee that the current will never exceed float charge levels, but if you have any good ideas on how to current limit, let me know.Now, are these ideas too good to be true? For some reason nobody else seems to use them, so why not, am I missing something?

author: EpicIntelGamer
author_rank: Regular Contributor
timestamp: November 24, 2013, 04:49:45 pm
content: Quote from: EpicIntelGamer on November 24, 2013, 04:48:03 amAny help?

author: EpicIntelGamer
author_rank: Regular Contributor
timestamp: November 24, 2013, 06:05:56 pm
content: 50 Views in over 12 hours and I haven't got a single person to answer this simple question..............I'm sorry if I sound impatient but, I could've had this entire thing built by now and batteries on order but no, I have to wait for someone who will answer my question first.

author: Lightages
author_rank: Unknown
timestamp: November 24, 2013, 06:25:06 pm
content: Well.....People don't always have a quick answer with such little information. You are asking for opinions on very vague ideas. There are many schematics on the internet for solar chargers, cheap solar chargers to buy, and for many different types of batteries.QuoteNot very much information to help you with. Be more specific and you will get "some" help. You certainly won't get any by being demanding.

author: EpicIntelGamer
author_rank: Regular Contributor
timestamp: November 24, 2013, 06:31:42 pm
content: Sorry, I didn't think I was lacking info.I want to build the most simple controller man has thought of, to cut off the panels from charging a 12V sla battery when the panel's voltage exceeds the SLA's charging voltage. I plan to have a P channel mosfet in between the panels and the battery, with a potentiometer connecting the panels to the gate of the mosfet, I can then adjust the potientiometer to apply enough voltage to cause the P channel to stop allowing the solar panels to charge the battery.So for example, everything is connected as I just explained, the panels are outputting 13V through the mosfet into the SLA, this is because with the potientiometer on the gate pin the potientiometer has reduced the 13V from the solar panels to so little that it doesn't trigger the gate of the p channel. However, when the panels raise to 14V, there is enough voltage through the potiometer to trigger the gate and make the p channel disconnect the panels from the battery.I would regulate the maximum current to float or trickle charge levels using resistors, unless there is an easier way.

author: Avotronics
author_rank: Regular Contributor
timestamp: November 24, 2013, 06:35:53 pm
content: QuoteYou do realise how big a twat you sound? I'd be surprised if anyone helps you.Sent from my Nexus 4 using Tapatalk

author: EpicIntelGamer
author_rank: Regular Contributor
timestamp: November 24, 2013, 06:39:10 pm
content: Well I'm not lying, I could've done what I said by now but instead I must wait. I don't want to order everything and then have overlooked something, and that is why I am asking here before building everything. I just don't want to wait here forever.Not sure why that has you so fussed?I enjoy building things, not fussing over details, so I'd prefer to have the "fussing over details" stage be as quick as possible so I can build and have fun and I don't see why it takes so long to answer a question about a design I thought up in 10minutes.And I'm not sure if maybe I should report you considering you seem like a spammer based on what you've said here and also your signature which seems to look negatively at electronics hobbyists.

author: EpicIntelGamer
author_rank: Regular Contributor
timestamp: November 24, 2013, 06:47:17 pm
content: I guess the biggest problem I can foresee with this design is the possibility that the amount of time that the voltage is at a point that the mosfet is just teetering between triggered and not triggered and thus possibly generating too much heat.Other than that this seems like a good design.I appreciate any advice, and I'm sorry if I sound rude.

author: Kevin.D
author_rank: Frequent Contributor
timestamp: November 24, 2013, 06:53:14 pm
content: Ok , so Why not show us a circuit diagram of your idea instead of using words to describe your idea.?

author: EpicIntelGamer
author_rank: Regular Contributor
timestamp: November 24, 2013, 06:59:34 pm
content: Quote from: Kevin.D on November 24, 2013, 06:53:14 pmI know this diagram looks terrible but I'm not so good with Eagle yet and I think this will help get my idea across even with how crude it is.I left out some components that are implied, like the fuse and diodes....

author: EpicIntelGamer
author_rank: Regular Contributor
timestamp: November 25, 2013, 01:04:07 am
content: Bump

author: IanB
author_rank: Super Contributor
timestamp: November 25, 2013, 02:04:27 am
content: I don't think anyone will really be very eager to help you with your "feed me" attitude.If you want a working solar charge controller without fuss, you can buy one ready made.If you want to learn about electronics, then "fussing over the details" is the whole point of it. You don't seem to want to do any work, yet you want everyone else to do work for you.Why not buy the parts, try building the design you are thinking of, and then see exactly how it works compared to your expectations? That's the only way to learn, is to experiment...and from your experiments to improve your knowledge.

author: HackedFridgeMagnet
author_rank: Super Contributor
timestamp: November 25, 2013, 02:56:18 am
content: Yeah have a look around for more conventional circuits.Or try it in LTSpice and see how you go.LTSpice isn't bad for quick schematics too.

author: EpicIntelGamer
author_rank: Regular Contributor
timestamp: November 25, 2013, 03:36:49 am
content: Quote from: IanB on November 25, 2013, 02:04:27 amSurely I'm not the only one around who gets disgruntled when in, whats it now, almost 24 hours, nobody has yet to answer a simple question of "will this work or not". All of the people on here, all of the views on this topic, all of the Replies on this topic, and none answer my question. Surely you can see why I'm frustrated. And actually if you knew me, you'd retract the "feed me" statement. I'm only ever this rude and impatient on this forum, it just has a bad reputation with me so far from past grievances with people here, but I figured with this solar panel question, maybe it'd give this forum a chance to redeem itself. Also you should know that I, by my knowledge alone, design and build unique vacuum tube amplifiers, so I am not a "feed me" kind of person and I DO take offense to that. You say I don't want to do any work, but its the opposite, I want to get to work instead of waiting for answers, but in this case this is an issue of safety, its not really the thing I want to test out and see if it works because if it doesn't than I could ruin batteries etc.I'm not interested in buying one for a few reasons, some being that I don't think I can supply enough Ma to even make the charge controller work. At the sunniest part of the day my panels alone can barely power the 12Ma draw of an Arduino, however I may buy more.And not really, I already know quite a bit about electronics, more than I'd have you believe (I design and build Vacuum Tube Audio Amplifiers as well as make and repair other electronics) and I've learned it all by actually avoiding the fussing, I like to build the thing and then work out the bugs, not vice versa.Normally I'd go build it, and then work out the bugs like both you and I said, but I don't have a P channel on hand so I figured I'd have to wait at least a few days to get one, so why not ask here first. Once again I agree, I learn best by experimenting, it's what got me this far with electronics and vacuum tubes.PS: I've attached a picture of my current work in progress tube amp endeavor, notice it's a Mono tube amp with a 12AU7A preamp stage and a 6CU6 Power Tube, you cannot find a schematic using those two tubes, I've designed it myself.

author: EpicIntelGamer
author_rank: Regular Contributor
timestamp: November 25, 2013, 03:40:14 am
content: Quote from: HackedFridgeMagnet on November 25, 2013, 02:56:18 amHello!I'm not sure I'd like to look at other circuits. I rarely did that with vacuum tubes as I love to grab some tubes and throw something unique together, something original, not just a circit from a cookie cutter schematic found everywhere online. Also most of the charge controller schematics online complicate things with (as far as I know) unneeded devices like op-amps and 555timers, which not only complicate things like I said, but also increase the power I need just to power the charge controller.I was introduced to LTSpice a bit ago when my interest in vacuum tube amplifier design took off but I never really learned to use LTSpice, maybe now I will try again.Thank you for your reply.PS: Hehe, I see you've spotted the wayward electron!

author: HackedFridgeMagnet
author_rank: Super Contributor
timestamp: November 25, 2013, 04:30:35 am
content: I should have been a bit more explicit.The pot attached to the gate will do nothing a DC.Unless of course it is attached to the ground as well in which case it needs to be drawn.If you only want protection against over charging there must be a ton of circuits. As you said the small solar panel will current limit itself.firstactually second one I googledhttp://www.electroschematics.com/6888/solar-battery-charger-circuit/The advantage of this one is it uses some sort of controllable feedback.ps. On you schematic it really needs polarity to even make any sense.Good luck, LT Spice is good, just bear in mind its limitations.

author: IanB
author_rank: Super Contributor
timestamp: November 25, 2013, 06:36:43 am
content: Quote from: EpicIntelGamer on November 24, 2013, 06:47:17 pmQuote from: EpicIntelGamer on November 25, 2013, 03:36:49 amYou may be aware the a MOSFET is something like a solid state analog of a vacuum tube. You are supposing that a MOSFET can be "triggered" or switched on and off when the gate voltage reaches a certain level. But does a vacuum tube behave that way? Does a vacuum tube suddenly "trigger" on and off when the grid voltage reaches a certain value?

author: EpicIntelGamer
author_rank: Regular Contributor
timestamp: November 25, 2013, 11:43:19 am
content: Quote from: IanB on November 25, 2013, 06:36:43 amNope, a tube's output is proportional to its input. I see what your trying to say, but perhaps I can use this to my advantage? Let me explain.Suppose I had that circuit built up, I previously though that the gate would suddenly trigger when the voltage exceeded charging voltage for the battery, now I know it will slowly trigger as it gets around that voltage, but maybe this is a good thing. Maybe it will slowly disconnect the load as the supply increases? This may work to my advantage.I'm going to do some experimenting with this idea later today.

author: Harvs
author_rank: Super Contributor
timestamp: November 25, 2013, 12:41:43 pm
content: Have a look at an IV characteristic for a solar panel. Your short circuit current is directly proportional to the irradiance falling on the panel, then it drops off as the PN junction of the solar cell becomes forward biased.So, what this means is unless you pick a panel that has a Isc higher than the maximum rated charge current of the battery, you don't want to provide any current limiting, that will only waste power. Solar cells aren't voltage devices, they're current, so it's not like loading a battery.However, you do need to provide reverse polarity protection (e.g. a shockley diode). There is a relatively high parallel resistance intrinsic to a PV cell that will cause slow discharge at night.Now the cheapest, most common approach to regulating battery charge for solar cells that don't use DC-DC converters, is a simple shunt regulator. As you generally want to control the battery charge voltage to a fairly tight level, a simple MOSFET and 20c opamp with a voltage divider to set the maximum voltage level is all that's needed. Just have the MOSFET short out the solar panel when the battery voltage is above the set level. The opamp should provide you with effectively an on/off situation due to the high gain, and therefore you should end up with minimal power dissipated in the MOSFET. You'll probably need to add some hysteresis in the switching action. In case you were wondering, a solar cell is happy to sit in short circuit condition all day long, its effectively in the same situation when open circuited (where the intrinsic PN junction limits the output voltage.)

author: Harvs
author_rank: Super Contributor
timestamp: November 25, 2013, 12:47:51 pm
content: Quote from: HackedFridgeMagnet on November 25, 2013, 04:30:35 amI'm not a fan of that circuit. Wasting 2-3V by using the LM317 is an unnecessary. Shunt type regulators don't waste any of the available cell voltage and are as good as you'll get efficiency wise without using a switching converter. Also, you don't now need any significant heat sinking. Shunt type PV battery charge regulators have been used for a long time now and for good reason.

author: EpicIntelGamer
author_rank: Regular Contributor
timestamp: November 25, 2013, 07:50:16 pm
content: Quote from: Harvs on November 25, 2013, 12:41:43 pmMy only concern as to current limiting was that if I had a panel capable of 1A of current in direct sunlight, and on some freak day the sun hit it directly, AND 1A of current was too much for the type of charging I want to do, then I wanted to have a limit.I realize that solar panels are constant current, I also realize I need a diode to block power from going to the panels, I just omitted that from my diagram for simplicity.I'm very interested in this shunt regulator circuit your talking about. I think I'll look into that some more because if I'm right I'd be able to do quite a lot more than just short the panel with that mosfet. For example, maybe I can use that mosfet to engage a dummy load if voltage is too high, so I could still charge the battery and the excess power is turned to heat. I think I'll do some research into this shunt regulator you suggested.I also agree that although that liked charger circuit is very simple and I have all of the parts on hand, I just cannot afford to have 3V on top of my charging voltage. I also cannot say I have enough Ma to even feed an lm317.I have 2x 5V 150Ma panels wired in series which gives me (at best) 10V at maybe 10Ma. Believe it or not that amount of current does charge a 7.2V 1800mah NICD battery. Now there is a possibility of me buying some nice big 12V 10watt panels or something if I see that it is worth it running these panels where I'm running them (not in direct sunlight).Thank you very much for your suggestion, it really set me in the right direction!