12v Circuit Question

Thread Starter

NoobCircuits17

Joined Jan 10, 2021
15
Hi everyone,

So i've been working on a circuit thats powered by solar and I have attach my schematic below. Okay so im pretty much new to the circuits an I have a background in wiring so I understand the basics. Lets jump into what i have,
Parts List

* DC12V 10W Solar Panel W/ USB Port Car Chargers For 12V-Battery Accessories Tool
* W1209 12V -50-110°C Digital Thermostat Temperature Control Switch Sensor + Case
* 4S 40A BMS 12v - 16v Heatsink Kit Li-ion Lithium Battery Charger Balance
* 18650 Battery Charging 4 BAY Cell Holder PCB Solder With Wire Lead
* 4x 18650 Battery 3.7v 3300mAh
* 120mm Fan 12v 1.6amp


Okay so with the parts above I sketched my circuit on a piece of notepad paper below. Now the problem I am having is after connecting all the components everything is operational up too the 12v relay on the W1209. When the parameter is met the relay wont engage. After taking a look at each component I found that the output voltage on the BMS was only 4 volts not 12v as I anticipated. Alright so I figured that i could throw on a DC to DC converter. Below is the part i bought,

* DZS Elec XL6009 DC - DC Booster Converter Module 3V - 32V to 5V-35v 4A Adjustable Step-up Voltage Regulator 5v 9v 12v 24v Power Supply Module

Last but not lease the second attach picture is the updated schematic with the booster converter. Last problem the highest output voltage I was able to get was 5v not enough to engage the relay still. Im at a loss now so any input would be great thanks for reading.
 

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dl324

Joined Mar 30, 2015
12,256
Welcome to AAC!

What is the coil resistance of the relay? What is the current requirement of the fan?

It would be helpful if you labeled the inputs and outputs for the 3.7V to 12V converter because the normal convention is inputs on the right and outputs on the left. Why aren't you using the batteries to provide power to the fan?

Do you want the fan to be on all the time? Or only when the solar panel is generating voltage? The way you have it wired, the relay isn't needed.

Function would be clearer if you mirrored the converter, relay, and fan so you could show the connections to the input of the converter less ambiguously. It took me awhile to notice the squiggly lines you had on the output of the solar panel.
 

sghioto

Joined Dec 31, 2017
1,865
After taking a look at each component I found that the output voltage on the BMS was only 4 volts not 12v
Actually the W1209 should connect to the 8.4 volt terminal on the BMS. Input voltage range for the W1209 says 6 to 12 volts do not exceed 12 volts.
Don't need a boost converter, double check your wiring on the battery pack.
 
Last edited:

bassbindevil

Joined Jan 23, 2014
147
The "BMS" is really just for protection against catastrophic overcharging, short-circuits, or over-discharging; it doesn't have the brains to limit charging current or recognize when to stop charging. (Some provide cell balancing; looks like yours does, since there's two sets of 6-legged chips.) It's best to have a charge controller between the solar panel and the battery pack, to limit the charging current, and stop charging once the battery is full. Although, a little 10W panel won't make enough current to be a problem, and probably won't be able to fully charge the battery if you have a load like that fan.
I would include a little voltmeter or battery tester with a switch to check the battery status; those are very cheap from ebay.
Don't connect loads directly to the battery terminals, since that bypasses the protection, and will unbalance the cells. If you need to supply a lower voltage to loads, use a step-down converter.
If you're only getting 4V output from the pack, check the voltage on each individual cell. Try charging the pack with a real charger (something like an iMax B6 "hobby charger"), or charge them individually. It's better to charge the pack as a whole; the BMS could be damaged if cells are added or removed in the wrong order.
 

bassbindevil

Joined Jan 23, 2014
147
The load should be connected to the "common port to load and charger" terminals on the BMS, not directly to the cells. Connecting directly across the full pack won't unbalance it, but you won't get the benefits of over-current and over-discharge protection.
 

Thread Starter

NoobCircuits17

Joined Jan 10, 2021
15
Welcome to AAC!

What is the coil resistance of the relay? What is the current requirement of the fan?

It would be helpful if you labeled the inputs and outputs for the 3.7V to 12V converter because the normal convention is inputs on the right and outputs on the left. Why aren't you using the batteries to provide power to the fan?

Do you want the fan to be on all the time? Or only when the solar panel is generating voltage? The way you have it wired, the relay isn't needed.

Function would be clearer if you mirrored the converter, relay, and fan so you could show the connections to the input of the converter less ambiguously. It took me awhile to notice the squiggly lines you had on the output of the solar panel.
Great questions I’ll try to answer all of them. Sorry for the wiring sketch so the fan needs 12v has a 1.6amp draw I’m not sure of the coils resistance at the moment. As for the batteries I’m not sure how I would set that up. The idea behind this build is to vent when the temperature reaches a certain parameter by exhausting the heated air with the fan and shut off to the desired temp. Building a green house to cool and heat mechanical by itself is what I’m looking for. So for the battery setup I’m really not sure exactly how I should be hooking them up but I want to charge them while suppling power to the fan when it’s needed. Hope this helps with some of your questions. Thank you for response.
 

sghioto

Joined Dec 31, 2017
1,865
The load should be connected to the "common port to load and charger" terminals on the BMS, not directly to the cells.
After further review I agree with that statement.
Connect the input of the XL6009 to those terminals and adjust the output to 12 volts to power the W1209.
 

Thread Starter

NoobCircuits17

Joined Jan 10, 2021
15
The diagram is correct. The question is do you need the BMS. I don't fully understand the BMS operation. It says it charges and discharges the batteries so how does that work if you have a load connected?
From my understanding is that you have to charge lipo batteries per cell to keep a balanced charge for each cell. With that said to keep them balanced means extending the life correct ? If there’s a better more reliable solution I’m all for it. Second I don’t fully understand the bms operation either since I know you can't charge and discharge at the same time. Good question!
 

Thread Starter

NoobCircuits17

Joined Jan 10, 2021
15
After further review I agree with that statement.
Connect the input of the XL6009 to those terminals and adjust the output to 12 volts to power the W1209.
Question I have so I don’t need the individual red wires coming from the bms to each cell? Do I still connect the solar panel and load to the common port to load and charger ? Why I ask is because I ran the load from the load terminal of the bms but only getting the 4v output as described above. Once I connected the step up it was only giving me a max output of 5v if that. Not sure I’ll try to redo the wiring in the diagram and go from there. Thank you for your response (sghioto)
 

Thread Starter

NoobCircuits17

Joined Jan 10, 2021
15
Here’s a couple of pictures I took of the test batteries and my new batteries both charged to 3.7v and the wiring I did it’s ugly for now but cleaned up in the future lol
 

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