SparkFun Forums

[JoseyEire]

Hi, I added a 0.07ohm resistor to increase the charging current to the battery on my sparkfun sunny buddy.

According to the formula, charge current = 0.1/(R1||R_SEN) = 0.1/(0.22||0.07) = 0.1/(0.0531) = 1.88A

During testing on my work bench with a power supply input of 19v and current limited to 1.2A I see the board is drawing 0.4A from the power supply.

At the above level however the inductor, 683C, becomes too hot to touch with my finger.

Is this a concern or normal behavior?

What do you suggest?

Thanks,

Paul

[jremington]

What is the load resistance and charge current?

I'm not sure that using a current limited power supply is a good idea. It might interfere with the switching behavior of the LT3652.

[JoseyEire]

Thanks for your reply.

The load is just a 3.7V, 7800mAh Li-Ion battery. I don't know it's resistance, how would I measure that?

Also, can you tell me how I could measure the charge current easily?

Thanks,

Paul

[jremington]

Use a multimeter in series with the battery to measure the charge current.

[JoseyEire]

Hi again,
it's quite awkward using a multimeter that way so I'm making a special cable up.

In the meantime I've deployed the sunny buddy to my project box and connected it to the solar panel. It charges the battery and connected load, raspberry pi, until sun down. Then the load discharges the battery over night until it runs out and the load thus powers down.

But the next morning the sunny buddy does not recharge the battery, even in good sunlight. I can see FAULT & CHG both are low i.e. "ON".

Then I disconnect the load, battery and solar panel and measure the battery voltage to be 3v.

I reconnect everything and the sunny buddy starts to charge the load and battery, I see FAULT at 4V "OFF" and CHG "ON".

Can someone explain what might be happening here?

I've assumed that the sunny buddy would automatically charge the battery once there is sufficient sunlight but it seems something is causing the FAULT "ON" state.

Thank you,

Paul

[jremington]

If your battery has a "protection PCB" built in, that circuit may be shutting down to prevent overdischarge.

If so, there is probably some trick you need to do to force the protection circuit to reset.

[JoseyEire]

Thanks again,
ok that makes sense. By simply disconnecting and reconnecting the solar panel this seems to reset the battery charging and off we go again.

As the battery protection circuitry may be complex for the likes of me to figure out quickly can I ask the following:

1. Is this normal behavior for batteries that connect to the sunny buddy board?

2. Could I use lipo batteries without the protection circuitry or does that bring other problems?

3. Would sparkfun batteries work better?

Thanks,

Paul

[jremington]

Could I use lipo batteries without the protection circuitry or does that bring other problems?

Other problems. If you discharge a Li-based battery below about 2.8 V, it will be completely destroyed. If you do not use the "protection circuit" you have to design and implement your own.

For most projects that require rechargeable batteries, NiMH and lead acid batteries are much, much safer as they tolerate a great deal of abuse and don't explode or catch fire (although you must always have fuses for short circuit protection).

[theropod]

Could I use lipo batteries without the protection circuitry or does that bring other problems?

Other problems. If you discharge a Li-based battery below about 2.8 V, it will be completely destroyed. If you do not use the "protection circuit" you have to design and implement your own.

For most projects that require rechargeable batteries, NiMH and lead acid batteries are much, much safer as they tolerate a great deal of abuse and don't explode or catch fire (although you must always have fuses for short circuit protection).

Lead acid batteries can and do explode. If plates direct short while under charge an arc can be created inside a hydrogen bubble and an explosion can happen. My 65 Mustang was having battery issues and with the engine running the folks that sold me my battery put it under load. The resulting boom sent acid and battery guts everywhere. Luckily the tech was wearing his PPE, and the shop had cleanup protocols in place.

RS

[jremington]

OK, lead acid and NiMH batteries can explode under extremely rare circumstances, mostly if not protected by the required fuse.

In contrast, lithium based batteries catch fire or explode quite frequently and are not at all safe for beginners in electronics.

[JoseyEire]

If your battery has a "protection PCB" built in, that circuit may be shutting down to prevent overdischarge.

If so, there is probably some trick you need to do to force the protection circuit to reset.

Yes I believe this is what's happening, the battery is stuck in some sort of low voltage disconnect sleep mode.

Do you know of a trick that would overcome this?

Would a Sparkfun LiPo battery be better to use?

Thanks,

Paul

[jremington]

You should ask Sparkfun Technical Support how their battery PCBs work (if used). I haven't used their batteries.