Renogy 12V 200Ah drop-in LiFePO4 battery

[Jon57]

8 minutes ago, MtB said:

 

Because automotive alternators are not rated to run continuously at full rated output. They overheat....

Now that would be a good place to put the hot box for them with a composting toilet as well. 👍

[rusty69]

29 minutes ago, MtB said:

 

Because automotive alternators are not rated to run continuously at full rated output. They overheat....

True. I wasn't specifically referring to charging from an alternator though.

[MtB]

15 minutes ago, rusty69 said:

True. I wasn't specifically referring to charging from an alternator though.

 

Well taking your question literally, 

 

"Why not charge at the maximum voltage Lithiums will accept then?"

 

I'd say there is no such voltage from a practical point of view.

 

If you try to raise the charge voltage higher than the voltage it settles at when you connect a charge source, the current will rocket away into the thousands or tens of thousands of Amps. Leading to fuses blowing or the magic smoke escaping.

 

 

According to that nice Mr Ohm and his law anyway.

 

I = V/R, dunnit. 

Edited January 9, 2023 by MtB

[rusty69]

9 minutes ago, MtB said:

 

Well taking your question literally, 

 

"Why not charge at the maximum voltage Lithiums will accept then?"

 

I'd say there is no such voltage from a practical point of view.

 

If you try to raise the charge voltage higher than the voltage it settles at when you connect a charge source, the current will rocket away into the thousands or tens of thousands of Amps. Leading to fuses blowing or the magic smoke escaping.

 

 

 

I seriously doubt that.Won't it be limited by the current limit of the supply?

 

ETA. I'm not suggesting it be done in practice, btw as its a stupid idea. The battery voltage will eventually be pushed too high.

Edited January 9, 2023 by rusty69

[MtB]

5 minutes ago, rusty69 said:

 

I seriously doubt that.Won't it be limited by the current limit of the supply?

 

Yes it will, and Ohm's Law tells us when that happens, the voltage will be clamped down to whatever voltage it takes to deliver that current. Which is not what you asked! If you succeed in raising the cell terminal voltage to say 4.000V on a LiFePO4 cell you will get a truly massive current. For a while at least.

 

 

 

Edited January 9, 2023 by MtB
speeling

[rusty69]

1 minute ago, MtB said:

 

Yes it will, and Ohm's Law tells us when that happens, the voltage will be clamped down to whatever voltage it takes to deliver that current. Which is not what you asked! If you succeed in raising the cell terminal voltage to say 4.000V on a LiFePO4 cell you will get a truly massive current. 

 

 

 

Fairy nuff. The point I was trying to make though (badly) is that they can be charged with a higher voltage as long as they are not left to their own devices.

[MtB]

1 minute ago, rusty69 said:

Fairy nuff. The point I was trying to make though (badly) is that they can be charged with a higher voltage as long as they are not left to their own devices.

 

How are you measuring this 'higher voltage'? 

 

Voltmeter probles directly on the terminals on the LiFePO4 battery? Or a gauge/display somewhere else on the system?

 

[rusty69]

4 minutes ago, MtB said:

 

How are you measuring this 'higher voltage'? 

 

Voltmeter probles directly on the terminals on the LiFePO4 battery? Or a gauge/display somewhere else on the system?

 

Well, if done with a bench power supply, directly on the terminals before connecting it to the battery.

 

Here, this bloke explains it:

 

 

[nicknorman]

1 hour ago, rusty69 said:

Fairy nuff. The point I was trying to make though (badly) is that they can be charged with a higher voltage as long as they are not left to their own devices.

basic rules for charging Li is constant current until the cell voltage reaches 3.65, then constant voltage. The choice of the current in the constant current bit is limited either by the maximum output of the charging device, or the battery limit. The battery limit can be due to the cell chemistry - typically 1C max, 1/2C better for long life. Or the battery BMS FETs which might limit the max current to less.