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BQ24074 Charger Solar cell selection
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BQ24074 Charger Solar cell selection

by jeffsmit12 on Mon Apr 26, 2021 3:54 am

Hi,
My load consumes around 200mA at peak for just 3-4 times a day, I am thinking of using the BQ24074 with the Adafruit Small 6V 1W Solar Panel (https://www.adafruit.com/product/3809). Will it be sufficient for my application?

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Re: BQ24074 Charger Solar cell selection

by mikeysklar on Mon Apr 26, 2021 5:38 pm

How long is your load running during the 3-4x a day executions?

The 1W panel you have selected assuming your 200mA draw is short (minutes, not hours) and you have plenty of battery capacity. Keep in mind that significant shade or clouding could result in zero charge days.

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Re: BQ24074 Charger Solar cell selection

by jeffsmit12 on Tue Apr 27, 2021 2:15 am

In the worst case scenario, my load will run for maximum 1.5 hours daily total. So it would consume approx 300mAh per day maximum. I will be attaching a 6.6Ah 1s Li-Ion pack to the system. Ignoring cloudy days, I believe the 1W solar panel would be sufficient for me?
Also, what is the maximum current the BQ24074 solar charger can give to Load?

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Re: BQ24074 Charger Solar cell selection

by mikeysklar on Tue Apr 27, 2021 5:17 pm

The solar charge max charge current and load rate is 1.5A. Whether it is coming in or going out that is the limit.

Yes, 1W sounds sufficient with that size of battery bank.

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Re: BQ24074 Charger Solar cell selection

by jeffsmit12 on Wed Apr 28, 2021 7:29 am

Thanks.
1.) I read that the charger varies the charge current in order to keep the input voltage above 4.5V, is there also any minimum input current limit below which the charger cuts off and stop charging?
"EN1 and EN2 - Input current limit configuration" Not sure what exactly are EN1 and EN2 are used for?

2.) "Set for 1000mA max charge rate, can be adjusted to 500mA or 1.5A by soldering closed a jumper"
If I am using the 1W solar panel (current 180mA), so the max charge rate does not matter in my case right?

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Re: BQ24074 Charger Solar cell selection

by mikeysklar on Wed Apr 28, 2021 10:40 am

1) I believe that 5mA is the lowest current draw per cell (you have 12 on your 6v panel) so 60mA might be your bottom out current draw where you max could be as high as 38mA per cell. Take a look at the design notes.

https://learn.adafruit.com/adafruit-bq2 ... sign-notes

2) Yes, you can ignore max charge rate jumpers as current will be on the lower side.

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Re: BQ24074 Charger Solar cell selection

by jeffsmit12 on Thu Apr 29, 2021 1:26 pm

Ok, I also wanted to know which voltage regulator will be most ideal for the load?
I am using load at 5v, can you suggest any 5v boost converter that I could attach to the load port?

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Re: BQ24074 Charger Solar cell selection

by mikeysklar on Thu Apr 29, 2021 1:36 pm

Depending on the connection types of your load device you can select different boosters. This one is the most minimal and least expensive that can give you a solid 5V @ 1A off the LOAD port off the BQ24074 charger, but you have to make your own connections.

https://www.adafruit.com/product/4654

The PowerBoost is a better options if you want to use a straight 2-pin JST connector and have a USB-A port.

https://www.adafruit.com/product/2030

There are several variations on the powerboost connections like this one with a micro USB.

https://www.adafruit.com/product/2465

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Re: BQ24074 Charger Solar cell selection

by jeffsmit12 on Thu Apr 29, 2021 11:38 pm

Thanks a lot.
Do you also have JST cable that I can plug in the load port to connect to the booster?

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Re: BQ24074 Charger Solar cell selection

by mikeysklar on Fri Apr 30, 2021 12:37 pm

You will have to make your own JST 2-pin (F) <--> JST 2-pin (F) to connect load to booster. We can sell you ends with leads, but for whatever reason we don't sell one that has two female ends.

https://www.adafruit.com/product/261

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Re: BQ24074 Charger Solar cell selection

by jeffsmit12 on Fri Apr 30, 2021 1:56 pm

Ok.
https://www.adafruit.com/product/261 This will fit in the load port of the charger?

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Re: BQ24074 Charger Solar cell selection

by mikeysklar on Mon May 03, 2021 1:12 pm

Yep. That is why I linked to that product. The 2-pin JST connector (product id #261) has the correct JST connector for LOAD and our battery JST LIPOs.

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Re: BQ24074 Charger Solar cell selection

by jeffsmit12 on Fri May 14, 2021 11:07 am

Thanks. I have been testing it out, it works quite well!

I have one more load, it can take maximum of upto 4.2V input voltage. But the BQ24074 provides around 4.4V at load pin.
So, do you think connecting the load in parallel with the battery would make sense?

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Re: BQ24074 Charger Solar cell selection

by mikeysklar on Fri May 14, 2021 12:23 pm

What is the load source that can take up to 4.2v? You could use a diode for a voltage drop.

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Re: BQ24074 Charger Solar cell selection

by jeffsmit12 on Fri May 14, 2021 1:53 pm

I am designing my own load source. The issue with diode to drop the voltage would be when at night solar is not providing any power, so the Load pin will have voltage equal to battery. In this scenario i would be unnecessarily losing power due to diode.

So, do you think connecting load in parallel to the battery would be a nice idea?

I was also thinking of using 3.3V buck converter. https://www.adafruit.com/product/4920 - But it has an input voltage range of 3.4 to 5.5V. The issue in this would be when at night time the load has voltage equal to battery, and when the battery voltage goes below 3.4V, the buck converter would stop working.
Can you suggest any 3.3V buck converter that has input voltage range of 3 to 5V?

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