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Solar Controller OK ???
#1
Hello All
I have just setup a small DIY solar system with the following: 24v 300 watt panel, 20A CPY - 2420 MPPT solar charger, BMS and battery Bank on 7SP1 of 18650s.  No load yet.

Now the system charge the battery to about 45% full and it seems to have stopped charging.
I test the amp flow with the whole system connected and its on producing 0.02Amps, however when i remove the Charger i have upto 1.5 amps.  Now to me that say the controller is stuffed, however i have read that a MPPT controller wont run small panels. Only new to Solar i am unsure if that is correct and is the actual control not working.

Second question do i need a charger in such a small system, how safe is it to run it just thru the BMS until i can get a better charger.
Thanks
Andy
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#2
You should always have some sort of controller. Otherwise you need diodes to keep the battery from discharging back into the panel at night.

It would help if we knew which charge controller you have.
Proceed with caution. Knowledge is Power! Literally! Cool 
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#3
(01-16-2019, 02:22 AM)Korishan Wrote: You should always have some sort of controller. Otherwise you need diodes to keep the battery from discharging back into the panel at night.

It would help if we knew which charge controller you have.

https://www.ebay.com.au/itm/20A-MPPT-Sol...2749.l2649
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#4
Well, firstly, that's probably a PWM charger, even though it "says" MPPT.

I'd open it up and see if anything got toasted. This would also confirm if it's PWM or MPPT
Proceed with caution. Knowledge is Power! Literally! Cool 
Knowledge is Power; Absolute Knowledge is Absolutely Shocking!
Certified 18650 Cell Reclamation Technician

Please come join in general chit-chat and randomness at Discord Chat (channels: general, 3d-printing, linux&coding, 18650, humor, ...)
(this chat is not directly affiliated with SecondLifeStorage; VALID email req'd)
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#5
For 49 dollars it is definitely not mppt also it is very small for mppt. On the specs for the controller, it stops charging at 14.7 volts x2 = 29.4 volts for 24 volt systems. Your 7s 18650 fully charges at 4.2 x 7 = 29.4 volts. What I see happening is the closer it gets to the max voltage it reducing the amp output. The controller thinks the battery is full and might be going into float mode. 

Your 300 watt panel is actually a 36 volt panel and wouldnt be considered small, anything over 160 watts is usually 36 volts. With a true mppt you should get something like 15 amps of charge current. With pwm controller you max out at about 8 amps of charge current. But if your 300 watt panel is a 24 volt ( actually 21 volt) panel then that could be your problem, that will never fully charge a 7s battery, it will never reach a high enough voltage. Double check the back of your panel, it should say what the max voltage is.

I use to have a 120 watt panel and it max out at 21 volts, my 240 watt panel maxes out at 36 volts. I don't think there is anything wrong with your charge controller.

I notice you said you get 1.5 amps from your panel, thats what a 30 watt panel will put out. If you have a 30 watt panel (instead of 300 watt) then you do have a 21 volt panel and it won't fully charge your 7s battery. But if you connect 2x 30 watt panels in series, that will charge a 7s battery. One 21 volt panel will only charge 12 volt systems. Mppt will work with small (21 volt) solar systems but it won't give you any benefits over pwm, mppt requires the larger 36 volt panels to increase your amp output.

This is a picture of my solar system, I use the ecoworthy 20 amp mppt (true mppt), notice how I got a overvoltage relay to disconnect the solar panel when the voltage gets too high. I don't rely on the BMS to stop the charging. The bms can always fail, thats why you need something that can monitor the battery voltage just in case.
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#6
Here is the panel i have at the moment, i hope its 300 watts otherwise i be contacting the seller. Is there anyway to test the panel. I thought they are good panel for the price.

https://www.ebay.com.au/itm/300W-Solar-P...ctupt=true

I am starting to think that the charger maybe in float mode, last time i checked it was charging at 1 amp. maybe i need more panels to really test the charger.

I really was hoping not to have any problems like this as i want to upgrade now i have a decent source of batteries. I will looking at a better solar charger even for this small system.
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#7
(01-16-2019, 05:40 AM)AndyMc1970 Wrote: I really was hoping not to have any problems 

The only problem is that you purchased a charger without paying attention to its max charging voltage - if you discharge the pack you'll likely see the charging current rise, hopefully to somewhere close to the chargers max rating.
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#8
Put the panel in full sun at right angles to the sun light with nothing else connected.
Measure the open circuit volts on the wires with your meter (Voc).
Then set the meter to 10A or 20A current & measure the current from the panels wires (Isc)
Tell us the numbers you get.
This will tell what the panel really is - ebay is full of poor deals....

If you do open the controller, MPPT controllers have some sort of coil, PWM types don't. Post a pic if you're not sure. Unlikely a $50 one would be MPPT.
Running off solar, DIY & electronics fan :-)
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#9
Solar Panel - First of all you have to see what kind of '24V' panel do you have? Is it a 60 cell or 72 cell panel? Seeing it's 300W it's most likely a 72 cell. The reason is that under load these panels don't produce the voltage you get when you hook it up to a multimeter directly. When you measure the panels directly you will get what's labeled Voc (Voltage Open Circuit) on the sticker on the back. Under load it's labeled as Vmp. So going back to 60 vs 72 cell. A 60 cell might measure at 36V with the volt meter, but be under 29V with load, which means it's probably underpowered for a 7S configuration (4.2V*7=29.4V). A 72 cell has a Voc of around 42V and a Vmp of around 35V. So a 72 cell is more suitable since the max panel voltage must be greater than battery voltage.

Controller - Now some others have said that it's a PWM. In some cases some MPPT charge controllers may be able to buck the voltage from a lower voltage panel like a 60 cell, but a PWM will not be able to do this. But more to the point, a charge controller is supposed to limit the energy into battery once a certain voltage is set. So let's say if your set voltage is at 28V, then as it reaches 28V the current will start to drop. So if you're not seeing the voltage, it's possible that the set target voltage has been reached and it's on float mode. What is this voltage point set to on the controller? Most cheapass PWMs are usually set for Lead Acid batteries which has a high Bulk Voltage, then drops way down for the Floating Voltage. Not suitable for a lithium setup.
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#10
Your solar panel has an open circuit voltage of 29.76V and a Vmp around 24V and your pack max charge is 29.4V.

If the panel does not have full sun (cloudy guessing from the low A when the controller is removed) the Vmp will be lower.

The controller is PWM so will not step up or down (boost/buck) the voltage to charge your pack if the output is not high enough. The controller needs a voltage of around 1V to overcome the internal diode losses so guessing the Vmp of the panel was just less than 1V above your pack voltage. This is why connecting / disconnecting the controller showed up the current difference.

Either way, because the panel is Voc of 29.76V the panel will not work well with the pack and likely never get to 100% charge, even if left connected for a week aas the current decreases the closer to Voc you get.
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