Solar panel 250 watt to 12vdc without PWM/battery?  - Page 1
Forum section: electronics / general

author: DougSpindler
author_rank: Super Contributor
timestamp: April 10, 2018, 02:53:17 pm
content: I was give an LG 255 watt solar panel to “play” with. Output voltage is 30 volts at 8.5 amps. I would like to use it to power a 12 volt waterfall pump during the day. (No need for a storage battery.) I was told I could use a PWM, but when it arrived I found I needed a 12v or 24v battery. (Would like to avoid the need for a battery.)Here’s my question... What’s the best way to get 12 volts from a solar panel without a battery?Does someone make a voltage regulator? (I found some 48 volt to 12 volt golf cart regulators, but they were less than half the wattage.)Could I make my own voltage regulator circuit? (Have’t found one that handles 10 amps.)Or should I just use the $20 PWM I already purchased and buy a small storage battery?Thanks

author: fourtytwo42
author_rank: Super Contributor
timestamp: April 10, 2018, 05:42:43 pm
content: Hi first question before you spend money have you tested the slar panel ? do you know it's good and capable of producing it's full output ?Second question, you dont say how many watts at 12V your pump consumes.If your panel has adiquite watts for your pump then a PWM converter will work fine without a battery HOWEVER if the panel is unable to supply the starting power required by the pump you may need some additional energy storage, this does not have to be a battery, it could be a large capacitor for example.

author: DougSpindler
author_rank: Super Contributor
timestamp: April 10, 2018, 05:48:29 pm
content: Thanks for your reply.I beleive the panel to be good. Is there a simple test I could perform?Pump is 1 maybe 2a at 12vdc so 12 or 24 watts or about one tenth of the total ideal output of the panel.Are you sure a PMW doesnt' need a battery? The one I have is 12 or 24 volt and voltage is autoselected.

author: fourtytwo42
author_rank: Super Contributor
timestamp: April 10, 2018, 05:57:41 pm
content: Simplest test almost foolproof is short circuit current in strong sunlite and compare with manufacturers spec.This leaves open the posobility of an open string being bypassed by the anti-shading diode, best way to check for that is test voltage across a 1 amp load (big resistor) and again check against spec.OK so the pump is tiny reletive to the pane so should work in most light levels.You dont say what this PWM gadget is you have purchased so I have no idea if it would work but a straight forward 12V regulated output switching converter would do the job although it needs to be designed for your panels Vmpp or have MPPT if you know what all that meansIf your gadget is designed for battery charging it may still work without one.

author: DougSpindler
author_rank: Super Contributor
timestamp: April 10, 2018, 07:37:44 pm
content: Quote from: fourtytwo42 on April 10, 2018, 05:57:41 pmSo are you saying in mid-day sun just short the leads of the solar panel together with a 10a ammeter in the circuit.Link below to the charge controller I purchased. CMG2420 I'm almost certain it won't power on without a battery.I tried connecting it to an old small 12v sealed lead acid battery (Type found in UPSs) wiht some LCD lights. Worked fine but the battery wasn't able to hold a charge. They I think the charge controller had a diffiuct time with the voltage and somehow confugered itself for 24 volt and burned out the LEDs and one cell in the battery.I would prefer not to mess with batteries until I know what I'm doing.Am I correct that the solar panel will produce a voltage/current in some ratio as the the position/iradisence of the sun upto (in ideal conditions) upto 30 volts and 8.5 amps. But say in mid morning the votage might be 15 volts with no load. If say 1 amp load is applied the voltage might drop to 10 volts. (Or something like that?I appreciate the assistance.https://www.banggood.com/CMG-2420-12V24V-20A-Solar-Charge-Controller-Panel-Battery-Regulator-Auto-Switch-Overload-Protection-p-1181760.html?utm_source=google&utm_medium=cpc_elc&utm_campaign=ds-diy-mbz-rm1&utm_content=mandy&gclid=CjwKCAjwwbHWBRBWEiwAMIV7Ezl4JMkMSG7kJLwGfsY73u5oRkhMx-aOkkOmtjJDvpFR9TsPFf92wBoCyroQAvD_BwE&cur_warehouse=CN

author: fourtytwo42
author_rank: Super Contributor
timestamp: April 11, 2018, 07:28:22 am
content: Quote from: DougSpindler on April 10, 2018, 07:37:44 pmYes exactly thatQuote from: DougSpindler on April 10, 2018, 07:37:44 pmAhh yes I see, it's very sophisticated and not suitable as a simple batteryless voltage converterI will look around and see what I can find.Quote from: DougSpindler on April 10, 2018, 07:37:44 pmYes but the voltage remains fairly constant, it is the current available that changes, of course if you try to take more current than is available the voltage falls. If you look at the enclosed Q-cells spec section 5 you can see the classic pv power curve.

author: fourtytwo42
author_rank: Super Contributor
timestamp: April 11, 2018, 07:35:16 am
content: Quote from: fourtytwo42 on April 11, 2018, 07:28:22 amHere is an example of the kind of thing you are looking forhttps://www.ebay.com/itm/DC-DC-17-40V-24v-TO-12v-6A-buck-voltage-Supply-Power-converter-for-CAR-solar-led/171308305155?hash=item27e2c54b03:g:SgUAAOxyaTxTVmwOBUT this has no real spec so its a bit of a chance, also you need to check VOC of your panel spec is below 40V.

author: DougSpindler
author_rank: Super Contributor
timestamp: April 11, 2018, 09:28:00 am
content: Quote from: fourtytwo42 on April 11, 2018, 07:28:22 amThank you much appreciated. Interesting how the voltage remains fairly constant. (Not what I would have thought.)

author: DougSpindler
author_rank: Super Contributor
timestamp: April 11, 2018, 09:54:13 am
content: The eBay item is for a 6a and pannel max is 8.5a. Am I correct in thinking I will never get the 8.5.a out unless I’m on the equator at noon?I’m at Lat 38. From what I understand when the sun comes up the pannel will start producing in relation to the iridescence. So depending on the time of year an angle of the panel in the morning it would produce 25v at .5 a. And as the sun rises the full 30v output with amperage increasing throughout the day to say a max of 6 amp out of the 8.5a it could deliver at midday sun? As the day progresses it tapers off. Bell shape curve for the amperage. Then late int he day the when the sun is low the voltage begins to fall off.From the solar modeling I have seen there’s for non-equator locations there are 3 days out of the year for 30 minutes when a fixed angle mounted panel will come close to max output.Does all of this sound about right?Again thank you for your assistance. Very helpful.

author: Seekonk
author_rank: Super Contributor
timestamp: April 11, 2018, 01:19:58 pm
content: A buck converter on its own can work till you try to draw more power than than the panel can produce. Then it totally drags the power down. What you want is a linear current booster. These for some reason cost $150 or more. You can modify any cheap unsealed buck converter with just a few extra parts to keep the panel at close to power point. As panel power drops, the pump will continue to run at 10, 8 or whatever it can provide. This is called a LINEAR CURRENT BOOSTER and there among the numerous morons are some circuits to build one. So if you have any electronic nous and know how to search, you will be set.

author: fourtytwo42
author_rank: Super Contributor
timestamp: April 11, 2018, 01:44:07 pm
content: Quote from: DougSpindler on April 11, 2018, 09:54:13 amNo you only need enough current for your pump, it doesnt matter what the panel rating is.Quote from: DougSpindler on April 11, 2018, 09:54:13 amNot really I am 52degrees lattitude and can acheive 1000W/m2 quite often especially in summer.Quote from: DougSpindler on April 11, 2018, 09:54:13 amyesSeekonk is partly right about the buck regulator but I am hoping it has an undervoltage lockout at 17V input as it says thats what it's minimum is, all things being equal the pump will try dragging an amp that corresponds to 17W that is less than 10% of your panels rating so I am hoping in reasonable light it will start ok, bit of an experiment I am afraid. Sadly everything I have seen seems to be "charge controller" related and you did say you wanted to avoid any batteries. The only other way is DIY as Seekonk suggestedYou might be better to beg or borrow an old car battery (used outside of course) as you have the charge controller already just to get you started, I note that product of yours doesnt include the words MPPT anywhere in its documentation so god knows what it actually does ?

author: DougSpindler
author_rank: Super Contributor
timestamp: April 11, 2018, 07:26:07 pm
content: Quote from: fourtytwo42 on April 11, 2018, 01:44:07 pmI had two old car batteries. I think they were too far gone. Since my controller worked on 12 or 24 volt I tried parallel and serial configurations.I ordered one of the buck regulators.I had a class where we had solar electricy production modeling software. One could pick the make model of solar panel, place it at any latitude and at any angle and see the "ideal" output at any day and time of the year. Was actually quite intereing. Then they had an option to add cloud cover,I wish I still had access to that program. For my latitude for a fixed panel mount at the ideal angle is how I leanred max pannel output only coccurs for 30 to 45 minutes 3 days out of the year.Can you give me some idea about panel output? If you where you are or I were to mount a panel horizontal vs Ideal angle for our latitude what % differece in output would be? Are we talking 5% or 50%?

author: Seekonk
author_rank: Super Contributor
timestamp: April 11, 2018, 08:03:38 pm
content: This is an idea what to expect during the day. Even a little wisp of a cloud can drop the power dramatically. Panels are linear and your eye is log. What you think is bright, the panel doesn't. Since you have extra panel power, consider putting the panel much flatter than the charts suggest. Since you are not storing energy in battery you don't care about getting peak power. Flatter will give you a longer running time.

author: fourtytwo42
author_rank: Super Contributor
timestamp: April 12, 2018, 08:23:03 am
content: Quote from: DougSpindler on April 11, 2018, 07:26:07 pmYou need a site like thishttp://re.jrc.ec.europa.eu/pvgis/apps4/pvest.phpbased in the USA, I am sure there are tons and they are free. Avoid the sites run by people selling or installing panels as they may be a bit too optomistic and commercially oriantated.

author: bicycleguy
author_rank: Frequent Contributor
timestamp: April 12, 2018, 09:28:22 pm
content: Quote from: DougSpindler on April 10, 2018, 02:53:17 pmThe best way how, the cheapest, simplest, most efficient?What is the current output of the golf cart regulator, you don't need 10 amps if the motor only draws 2.

author: DougSpindler
author_rank: Super Contributor
timestamp: April 13, 2018, 02:16:47 am
content: Quote from: Seekonk on April 11, 2018, 08:03:38 pmYup, that's what I was thinking. Thank you for confirming that for me.

author: DougSpindler
author_rank: Super Contributor
timestamp: April 13, 2018, 02:22:46 am
content: Quote from: bicycleguy on April 12, 2018, 09:28:22 pmThis would be perfect. Only problem is it looks it won't work in the US, only Europe.Yes maybe for now I only need 2a but I'm playing around. So there's nothing wrong with getting a bit more amperage.

author: Seekonk
author_rank: Super Contributor
timestamp: April 13, 2018, 01:17:08 pm
content: Solar is all about bad decisions. If you have storage point right at the sun. Almost flat gives about 50% but a longer period of time if panel power is in excess. Angle of incidence works E-W as well as elevation. If you had two panels I would face them E-W. Do you want to guarantee 2 hours each day or most pleasing effect most days."I am hoping it has an undervoltage lockout at 17V input" I thought this was a strange comment from someone like 42 and I don't want you to get the wrong idea. I don't think motor protection is an issue and by the time 17V is reached it is all over. At that point you get less than half the panels potential power. Current remains pretty much constant with light intensity and when the voltage drops the watts are lost. This is why a linear current booster is needed. Looks like you already bought the wrong buck converter. I would think someone on an electronics board would be interested in a little project with only a half dozen components. What you have will likely work good enough. Understanding what you actually need only comes with actually seeing how the project works.

author: fourtytwo42
author_rank: Super Contributor
timestamp: April 13, 2018, 06:31:41 pm
content: Quote from: Seekonk on April 13, 2018, 01:17:08 pmI agree it is not a good solution but something off the shelf that just might work but no gaurentees. The UVLO I was talking about related to the input voltage, nothing to do with motor protection but rather let the panel get up to a reasonable voltage before trying to draw current from it, so I was hoping the motor might start in a sort of hiccup mode given the buck converter has some energy storage. I discounted a linear for two reasons, one when the sun is up and the panel is at 30V for a 2 amp motor the regulator would dissipate 36Watts requiring a fair heatsink but more importantly there would be nothing to stop the panel being shunted at startup. This is quite an unusual panel application without a battery and something not really catered for by plug and play off the shelf electronics. If I had the problem I would stuff a PIC in it with a buck converter and solve most of the issues in softwarebut that solution is not available to the OP. Of course there may also be a simple linear solution that someone might like to send him as a DIY project. I don't wish to step on any toes so I intend to bow out of this thread having explained my rational

author: DougSpindler
author_rank: Super Contributor
timestamp: April 13, 2018, 06:47:04 pm
content: Quote from: fourtytwo42 on April 13, 2018, 06:31:41 pmPlease don't bow out you and everyone else has provided valuable information. Very much appreciated.Side note about which way to position panels for grid tied soalr.The ideal direction is west folowded by south with nothing to the east or north. Why? Our power company pays/credits us for excess electricity we "sell" to them. In the morning, east facing sun we are paid $0.12. Mid day when facing south would be ideal, $0.22 Then in early afternoon we are paid $0.47 or nearly 5 times what we get credited for sun in the same positional angle as in the morning.In the past we traded kHrs with the power company. Now I can give 1 kHwr to the power company in the afternoon and get alomst five back that evening. And there are days when the power companys is paying/charing $0.85 kWhr. On those days for every kWhw "sold" to the power company one can get 8 back in the evening.

author: Seekonk
author_rank: Super Contributor
timestamp: April 14, 2018, 01:44:49 pm
content: So how did we get from stand alone DC pump to grid tie? I give up.

author: DougSpindler
author_rank: Super Contributor
timestamp: April 15, 2018, 05:21:39 am
content: Quote from: Seekonk on April 14, 2018, 01:44:49 pmIt’s in the post..... Side note.

author: bicycleguy
author_rank: Frequent Contributor
timestamp: April 19, 2018, 06:18:55 pm
content: SCE only gives you around $.03/KWH even though they charge $.44/KWH.https://www.sce.com/wps/portal/home/regulatory/tariff-books/rates-pricing-choices/net-surplus-compensation/!ut/p/b1/jY_JDoIwGISfxQdo-rMEw7GKweK-RezFVALYiG3TVg8-vUi8usxtJt9kMpjhHDPJ76LmTijJm5dn0TGjCfHS0KdpP0uALJN-sltHXjjxWuDQAvBBBH71sz8GfDMbzmrMNHdnJGSlcO64EVWFTkpdLM4Nd6VF2ohCyBoVZyWKso1l6ZC9Gd3cLCrUVZfSdr_wHrNuNk5hNM4WQNPtKgAarGC-ISQAiN7Al1_6mj-mg5jWpNd7AvWX6O8!/dl4/d5/L2dBISEvZ0FBIS9nQSEh/Here is the official calculator that Go solar California makes you use to figure out incentives. Note that you must use one of the listed inverters and panels. I have checked some of the details and they have really done a good job. Hard to believe its a government operation.http://www.csi-epbb.com/default.aspx

author: mmagin
author_rank: Frequent Contributor
timestamp: April 19, 2018, 07:02:12 pm
content: If I just had a solar panel and a 12V pump and didn't want any storage, I'd probably build a shunt regulator out of junkbox parts. I'm pretty sure I could do it with a TL431, a big transistor and a heatsink. (Plus passives.)