What cheap solar charge controller should I use?

[lotsofsparks]

I have a folding 160W panel that I will use for camping eventually but over the next 6 months it will be in the back yard to charge a 4S lifeo4 battery. I hooked up the panel direct (just for load testing purposes) to battery when it's at it's lowest terminal voltage (10.4 Volts). I was getting 3 Amps at a voltage of 12.5V from the panel and current dropped off and sometimes even stopped when clouds passed over head. it was only trickling in for the first 4 or 5 Amp hours because of the steep charge curve the battery has when discharge down to 10.4V and I wouldn't expect it to be able to provide the voltage needed to deliver the remaining 284AH It would need to charge it up to max. I've looked over the specifications of many affordable charge controllers and none are programmable that accept low input voltages. I'm very tempted to just hook up an adjustable buck/boost converter and be done with it at this point but I'm afraid it would be able to regulate the voltage ripple might over charge the battery if the JK BMS doesn't stop it. I really need a make and model recommendation I hear that these controllers exist but I just can't find them. Any suggestions would be appreciated.

 

[Mattb4]

Specifications of the 160w panel? If your battery is 300ah (guess from your mention of 284ah) than at 12vDC nominal it can develop at most about 3600wh. To recharge at your panel specs of 160w (more likely much less) takes 22.5 hours of full sun. It really is impractical. You would want enough solar panels to recharge your battery in about a days worth of sun production which would be 3600wh/6h=600w with no other loading during this time.

 

[lotsofsparks]

I Have 4 eve LF280K (280 Ah) cells connected in Series with a JK BMS. I capacity tested them at 288 Ah and they were very closely matched in capacity. It's only drawing 1.5 amps 24 hours a day and 5 amps for 8 hours a day Approximately. it takes me 4 days to run it down from full to empty at home without a panel or any form of charging. It's for camping mainly but I want to use it everyday because I have it. I have grid power to use it I need it. I will make a bigger system later with a 16s battery bank. I plan to load it depending on how much charge i get each day. when I go camping it will be plenty. It came with a lead acid charger which I intended to replace. It's a 160W mono crystalline panel with an open circuit voltage of 18.5 volts i think. If the voltage under load of the charger is only 12.5 V it won't charge my battery which requires 14.4V - 14.6V.

 

[rhino]

What is your definition of affordable?

 

[lotsofsparks]

I live australia so it would need to be available to me for $66 USD but half of that would be better.

 

[Mattb4]

I Have 4 eve LF280K (280 Ah) cells connected in Series with a JK BMS. I capacity tested them at 288 Ah and they were very closely matched in capacity. It's only drawing 1.5 amps 24 hours a day and 5 amps for 8 hours a day Approximately. it takes me 4 days to run it down from full to empty at home without a panel or any form of charging. It's for camping mainly but I want to use it everyday because I have it. I have grid power to use it I need it. I will make a bigger system later with a 16s battery bank. I plan to load it depending on how much charge i get each day. when I go camping it will be plenty. It came with a lead acid charger which I intended to replace. It's a 160W mono crystalline panel with an open circuit voltage of 18.5 volts i think. If the voltage under load of the charger is only 12.5 V it won't charge my battery which requires 14.4V - 14.6V.

Your battery charges as long as the panel is providing any voltage above batteries internal voltage. Batteries internal voltage is related to its state of charge. You might see this as only 12.5vDC when both are connected.. As the battery charges back up the voltage you see will rise up towards the panels Voc. However that is bad for the battery. So you add in a SCC (solar charge controller) to provide proper charging. There are 2 main types of SCC. A PWM and a MPPT. The PWM is not a whole lot different than directly hooking the panel to the battery though it does prevent over charge. A MPPT use a search algorithm to maximize solar production maintaining panel voltage at the best point.

For such a small panel there are tons of inexpensive charge controllers however you will want one that handles lithium batteries.

 

[lotsofsparks]

@Mattb4 I see a lot of SCC say input batt + 2v so 14.4 + 2 = 16.4 so wouldn't I need a SCC with a lower input voltage spec?
doesn't the bms effectively stop overcharge if programmed correctly?
Does charging at a higher voltage effect the battery if the C rate is less than 1?
Is the input voltage Spec of the SCC really the open circuit voltage of the panel (without a load)?

 

[Mattb4]

Look for the SCC spec for Voc and minimum voltage. Yes you need higher voltage than battery fully charge voltage. The panel supplies the voltage. See Voc and Vmp.
The BMS is there to protect the battery, it is not there to control the charge during normal operation.

Good source for understanding batteries is https://batteryuniversity.com/

 

[MisterSandals]

see a lot of SCC say input batt + 2v so 14.4 + 2 = 16.4 so wouldn't I need a SCC with a lower input voltage spec?

No, SCCs specify that the solar voltage needs to be 2V (most are 5V) over battery voltage to start charging.
The solar voltage just needs to be below the SCCs max input voltage to charge (and battery +2V).

 

[Tomthumb62]

doesn't the bms effectively stop overcharge if programmed correctly?

The BMS is not intended to stop charging, except as a last ditch effort to protect the battery. It should be called a Battery Protection System (BPS) instead of Battery Management System (BMS). The charger should be the one stopping the charging.

If your cells are not perfectly balanced (most of us don’t have perfectly balanced cells), and you try to charge to 14.4v, the BMS might stop the charging before the charger reaches 14.4v. Usually because one or more cells triggers the BMS charge protection. If ever one cell triggers it, the whole battery pack stops receiving a charge.

There are ways to improve this, but it’s slow and tedious. But the simplest way is to buy an active balancer and wire it up to your battery pack and it will balance your cells for you much quicker.

 

[mikefitz]

none are programmable that accept low input voltages.

When you connected the panel directly you 'pulled down' the panel volts to battery volts. The maximum power voltage of the panel will be around 17 to 18 volts, thus ideal for a solar controler.
The graph shows a typical solar output.

the voltage under load of the charger is only 12.5 V it won't charge my battery which requires 14.4V - 14.6V.

As discussed used above once you connect the panel to a MPPT controller, the controler will takein power at the maximum power volts, around 18 volts and convert to a suitable charge voltage . A ideal charge voltage is 14.2 volts, 14.6 is too high.
The charge voltage, absorbtion or boost voltage is a 'target voltage'. As the battery charges its voltage will slowly increase eventually reaching the target level. The graph shows the typical cell volts over a charge cycle, x4 for battery volts.

For your 160 watt panel I suggest a Victron Smart Solar controller, 75 15,

Amazon.com.au : victron smartsolar 75/15

Mike