LiPo Charger - Rates & Cutoffs?

[djmcnz]

Hi,

I've got the common Intellect 4200 2S 30c saddle packs and currently balance charge at 4.2A. The packs don't get above room temp.

Am thinking of the following settings:

Balance Charge: 4.2A (1C)
Fast Balance Charge: 6.3A (1.5C)

It seems that good quality packs can now charge at 2C. Anybody have experience with this? Thoughts on my fast charge setting?

I've set the charger safety cutoffs to:

4.3v/8.6v
4500mah
40c degrees

Are the v and mah cutoffs okay?

What should I discharge the packs to 3.2v at (assuming I need to)? The full 10 amps of the charger? They're reported as 30c cells.

Thanks in anticipation!

[bigred5765]

you don't need to discharge them,don't treat them like nimh, charge run them and leave them with a charge in them, go manufactures web site for full lipo details

[_sleigh_]

Would say the voltage cut off is a little high. I'd say 4.2v per cell is better/safer.

[djmcnz]

Originally Posted by bigred5765

...go manufactures web site for full lipo details

Drew a blank...

Originally Posted by _sleigh_

Would say the voltage cut off is a little high. I'd say 4.2v per cell is better/safer.

I just wondered if I'd trip the safety before the cells were properly balanced at 4.2v if I set it there?

I realise there's the "try and see" approach but I will only resort to that if I can't draw on the experience of you all... (yep, have searched and learned a lot, these are my outstanding q's).

[Col]

Because you're not discharging your lipo's (see BigRed's post), they should never be flat (see Sleigh's post). Therefore you will never need to charge at more than 1C.
The only purpose it could serve is to reduce the lifespan on your lipo's.

[djmcnz]

Thanks all... I hope I'm not coming across as a noob as that was not my intention (although I am new to LiPo's, I have lots of RC battery experience).

Whilst I respect all of the comments I think it's important to point out to those that may stumble across this thread that:

It's no longer accepted science that LiPo's can be charged at 1C max. There's anecdotal evidence of 3S being charged at 3C and 2S being charged at 2C many times and without incident. And if there is no temperature change at 1C then it's a reasonable conclusion that the chemistry of the battery can tolerate a higher charge rate.

There's no evidence that I can find that charging batteries at a safe charge above 1C will shorten their life. Equally, there seems to be no firm evidence that charging them at less than 1C will lengthen their life.

The risk aversion that led many to settle on 1C seems more related to generation 1 LiPo's from circa 2006/7... although of course I am no final authority on this.

I will do a 1.5C charge in a safe bag and report back on temps, times and balance.

With respect to discharging, I accept that this wouldn't be common practice but again, should I need to (e.g. disposal), what rate should I use?

Having said this, if somebody cares to disagree in the interests of useful information for all then please go ahead...

[mark christopher]

you dont need to discharge lipo, if your in the uk you should follow the brca guidelines of 1c charge and cutoff of 8.4 volts. Batteries are checked at meetings, going more can be a risk to others,
1c is enough but trakpowers new dark serries have can be charged at a higher c

[bigred5765]

you can charge them at slightly higher c ratings, but what is your reason for doing this,there not like nimh were you would gain more punch, a lipo is different and they don't charge with any heat unlike nimh,the only gain is slightly shorter charge times,and shorter life span of the cell,4.2 volt per cell or 8.4 v per 2s pack is the safe limit,

[djmcnz]

Hi again.

@ bigred5765: Just time, just precious time...

----
So, I've done a quick test after running two packs down. The results below are by no means conclusive because of the sample size but it's actual data at least.

Pack 1 - New, Fully Charged, Run Down in Vehicle
Charge: 3.21/3.23v (measured with a multimeter)
Charged at: 4.2A (1C)
Time taken: 60:52
Temp @ end: Room temp (<25 degrees C)
Charge @ end: 4.20/4.20v

Pack 2 - New, Fully Charged, Run Down in Vehicle
Charge: 3.22/3.22v (mulitmeter)
Charged at: 6.3A (1.5C)
Time taken: 39:24
Temp @ end: Room temp (<25C)
Charge @ end: 4.20/4.20v

Findings:

• LVC on the ESC works just fine
• Balancer on the charger works just fine
• Charging at 1.5C makes a considerable difference to charge time (-33%)
• Charging at 1.5C has no measurable effect on cell temps

As a result I will continue to charge pack #2 at 1.5C and pack #1 at 1C to see how many cycles I can get before noticeable difference in battery charge capacity, run capacity, temps etc.

From this rather simple exercise I am happy that the risk of properly charging these packs at greater than 1C is not terminal or particularly dangerous. Indeed with no appreciable temp differences between the two methods it would actually be incorrect to claim these cells have a 1C safe charging limit.