Anyone with the right equipment up for some experimental testing?

[BiduleOhm]

Ah ok, I didn't understood that the first time I read the OP, that makes sense.

It's actually a very good question: do you lose any life if you charge at a higher voltage but not at a higher SoC? well, only one way to answer this question...

What would be nice for this kind of tests is very small cells you can buy for a few dollars only (like the 18650 NMC for example) as they can be destructive. It would also be easier to charge/discharge and measure because of the lower currents involved.

 

[Craig]

@Craig
Craig...just realised you are talking about a four cell battery pack. My testing was only on a single cell. I have now changed the type colour in the original post to ensure that idea's are based on single cell. Thanks

No I was referring to a single cell.

 

[Solarfun4jim]

No I was referring to a single cell.

oh ok, just when i re read it, i thought you were referring to a 12v pack. In theory a 3.2v 280Ah cell which can take a 1C charge rate @preferably 3.65v charge rate, even if reducing to the recommended 0.5C charge rate, would indicate that ideally if setting the power supply to 3.65v then adjusting the amperage up to 140A should be perfect. I would have thought that increasing the voltage up to a high of 4v instead of 3.65v would have made it easier??

 

[BiduleOhm]

I would have thought that increasing the voltage up to a high of 4v instead of 3.65v would have made it easier??

Yes, but it's also more risky for the cell. Unless a test proves it isn't and you can go higher than 3.65 V without endangering the cell of course.

 

[Solarfun4jim]

Yes, but it's also more risky for the cell. Unless a test proves it isn't and you can go higher than 3.65 V without endangering the cell of course.

Oh right Biduleohm....i was under the impression from what Will Prowse had said previously, that degradation of lifepo4 chemistry cells didnt happen till you exceeded 4.2v !
Thanks for correcting my interpretation.

 

[Solarfun4jim]

Yes, but it's also more risky for the cell. Unless a test proves it isn't and you can go higher than 3.65 V without endangering the cell of course.

How to charge Lithium Iron Phosphate lithium ion battery packs including packs with high current and High Capacity.

High capacity LiFePO4, Lithium Iron Phosphate batteries.

www.powerstream.com

1. Fast "forced" charging:
Because an overvoltage can be applied to the LiFePO4 battery without decomposing the electrolyte, it can be charged by only one step of CC to reach 95% SOC or be charged by CC+CV to get 100% SOC. This is similar to the way lead acid batteries are safely force charged. The minimum total charging time will be about two hours.
2. Large overcharge tolerance and safer performance
A LiCoO2 battery has a very narrow overcharge tolerance, about 0.1V over the 4.2V per cell charging voltage plateau, which also the upper limit of the charge voltage. Continuous charging over 4.3V would either damage the battery performance, such as cycle life, or result in fire or explosion.

 

[BiduleOhm]

It's not because a battery tolerate it that it doesn't shorten its life.

Then, I can be wrong, a practical test will answer definitely this question

 

[Solarfun4jim]

It's not because a battery tolerate it that it doesn't shorten its life.

Then, I can be wrong, a practical test will answer definitely this question

Oh...im not saying your wrong....just bouncing about idea's and opinions...all just a learning curve to me.

 

[BiduleOhm]

Don't worry, I'd love to be wrong on that one

 

[Will Prowse]

Oh right Biduleohm....i was under the impression from what Will Prowse had said previously, that degradation of lifepo4 chemistry cells didnt happen till you exceeded 4.2v !
Thanks for correcting my interpretation.

please NEVER charge LiFePO4 to 4.2V. goodness I need to be careful what I say on here. You will have gas creation and swelling before you hit 4.2V. But no thermal runaway yet.

And here is a source: A LiFePO4 battery can be safely overcharged to 4.2 volts per cell, but higher voltages will start to break down the organic electrolytes.

How to charge Lithium Iron Phosphate lithium ion battery packs including packs with high current and High Capacity.​

High capacity LiFePO4, Lithium Iron Phosphate batteries.
www.powerstream.com

Gas creation can happen at lower voltage but it takes awhile for it to occur. I've also seen it mentioned in papers on LiFePO4.

The iron phosphate crystal is pretty robust though and over charging can technically do very little damage if it is for a short time. Electrolyte instant degradation occurs at 4.2V, and long term degradation happens while holding the voltage above 3.65V. If temperature increases, this effect will worsen.

But yeah, you can overcharge them for a few minutes on accident and pull full capacity. I've done it a bunch. The electrolyte will degrade a tiny bit but that's all.

3.65V is MAX potential per LiFePO4 cell. My absorption recommendations are here: https://diysolarforum.com/threads/r...e-for-diy-lifepo4-batteries-sticky-post.5101/

 

[Sverige]

Crumbs! What a thread to be in “Beginner’s Corner”! I thought I was reading the danger zone for a minute!

 

[Hedges]

Thanks...will use your guidance. Easy enough to 'set it' at the battery terminals for accuracy.(when i eventually do this)
Accept that 4v is very high, but that was part of the experiment, to see how much the higher differential could drive the rate of charge....i suspect the benefits tail off around 3.65V and any higher will give no appreciable difference, but would like to see exactly what the difference actually is in reality. For solar charging with very low C rates, i thought it would be worth exploring.
Thanks again.

oh ps...the 4v trial was based on something Will Prowse stated, that the degradation of the electrolyte doesnt start till above 4.2V. So long as charge is terminated at 3.6v, didnt think any harm would befall the cell.

"Setting it" (power supply voltage) would be easy enough, but as current tapered off the voltage at battery terminal would rise too high.
Cell internal resistances quoted (0.25 milliohm) are low compared to wire and contact resistance.

If you get a power supply with remote sense, it can correct for IR drop to the cell terminal. Ideally it would be a separate contact directly on the terminals of the cell, not simply to ring terminal at end of wire.

RIGOL DP821 DC Power Supply 140W, 2 outputs 60V/1A, 8V/10A

RIGOL DP821 DC Power Supply, 2 outputs, 60V/1A || 8V/10A, with Remote Sense, total power up to 140WThe DP800 Series Power Supplies combine the ability to source, analyze, and coordinate over time in a powerful new package. The DP800 Series is a family of linear power supplies systems with 3 outputs

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I could probably devise something where a stud used for clamping ring terminal to battery terminal also served as sensing contact. Like oversized ring terminal, insulating sleeve around stud, insulating washer separating sense lead connection from current carrying connection (e.g. top-hat washer). If you are charging multiple cells in parallel, however, this would only sense cell terminals for one of them and other cells would have more or less contact resistance.

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MECI are Distributors of Quality Electro-Mechanical Interconnect Electronic Components and Manufacturers of Plastic PCB Hardware, such as Plastic Insulating Bushes and Transistor Mounting Pads.

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