Fast Charging

[srfnmnk]

I have this battery charger.

One of the options is fast charging. Regularly we want to charge the battery in one hour by setting the input amperage = to the mah (i.e. 1000mah = 1 amp). When fast chargin I am guessing we want to select fast charge and select 5 amps. My understanding is that the charger will slow the charge down as the battery approaches is capacity, is this right? Is it hard on the battery to speed charge it all the time?

 

[srfnmnk]

bump, anyone know?

 

[nerdnic]

Be careful to not charge your battery at a higher c than the manufacture rates it at. Most lipos can do 2c charge rate, but double check.

I would not suggest fast charging. It's very easy to get cells out of balance which can lead to fires. Balance charging is really the best and safest way to charge and you should balance charge every charge.

To speed up charging many chargers have an option to reduce the time the balance portion of the charge takes. Check your charger settings for 'waste time charge/discharge' and set it to the lowest. Once a cell hits 4.2 the charger will back off for the amount of time to see if voltage drops, and then it will try again. It will keep doing this until all cells hold 4.2 after power is removed.

Hope this helps!

Edit:
I believe fast charging just pumps power until your pack reaches full voltage and then it it's stop. It won't check to make sure the battery holds that voltage and it won't take each cell into consideration. So if you set it for 3s it will just pump until total pack voltage equals a 3s pack. This can be an issue if one cell is lower than the rest you risk another cell being over charged.

 

[ExperimentalRC]

What charger do you have? Read the manual about the fast charging setting. On my venom pro 2 charger the fast charge rate settings just mean that it won't fully change the battery but will be much faster. It also says this method is not recommended on a daily basis.

 

[stay-fun]

Check the manual of your charger. On the iCharger line, the regular "balance charge" mode charges at the set current, while balancing at the same time. When reaching 4.2V per cell, charge current is reduced to keep constant voltage. When 10% of the set charge current is reached, charging will be terminated.

The fast charge option does the same (double check if it's balancing!), but stops chatting already when 20% of the set charge rate is reached.

Example: you're charging at 1A (=1000mA). Regular balance charge will terminate charging at 0.1A (100mA). Fast charge will already terminate at 0.2A. So there is slightly less charge put into the pack, but charge time is reduced significantly.

Even if your charger isn't balancing, do connect the balancer, because most chargers do monitor individual cell voltage when available, even when balance charge is not selected. This will prevent overcharging and fire!

 

[srfnmnk]

I went back and looked at the charge rates and am planning to charge at 80% of max charge rate. I also plan to simply use balance charge to do this instead of "fast charge". I think this is the best way to do it. If anyone thinks not, please object.

 

[stay-fun]

Objection!

Charge at 1C max whenever possible. Unless you want to fly in a short period of time. Charging faster than 1C is hard on any battery. Yes it can be done, but reduces battery life.

 

[TheWW1FlyingAce]

Most modern batteries support charging at least at 2C, and many state 5C. Tests have shown little to no effect on battery longevity or reliability when charging at rates faster than 1C as long as the battery is rated for it. There are some caveats, however:

- Once you go past 3C or so the decrease in charge time for a faster charge hits a point of diminishing returns, since charging at a faster rate only affects the constant current portion of the charge. Above 3C or so the time spent in the constant voltage portion of the charge overshadows the amount of time spent in the constant current portion. I.e. 2C is a lot faster than 1C, 3C is noticeably faster than 2C, 4C is not much faster than 3C.
- Chargers with low balancing bypass current and/or which don't start balancing until the constant voltage portion of the charge may struggle to balance batteries at higher charge rates. Higher end chargers, such as the FMA Powerlabs or iChargers balance throughout the whole charge and have higher balancing bypass currents so they are more suited to fast charging.

Fast charging does have one advantage which might actually extend the life of a battery. Storing batteries fully charged definitely reduces their lifespan. Being able to quickly charge the batteries on the morning of the day you're going to go flying (while you load up the car) instead of the night before may actually improve the health of the battery.

As far as safety goes, it is possible that a bad battery that is close to failure might catch fire during a fast charge when it might have survived a slow charge. This needs to be balanced with the fact that with a faster charge you're more likely to keep an eye on the charge process.

 

[stay-fun]

David has said in one of the Q&A videos that it does matter how fast you charge. I'd be interested in those tests (not an attack on your statement, I'm really interested in this stuff)

- I agree on your diminishing returns
- My iCharger even has a 'fast charge' setting, but that basically meants it stops charging when it reaches 20% of the set charge rate, instead of the normal 10%. And it does not balance in that mode. (it does monitor the individual cell voltages to prevent overcharge, though).

On a side note: I have found that it's not always beneficial to have the balancer active in CC mode. I have a fairly new pack, and 2 of the 3 cells have a higher internal resistance than the 3rd cell. In CC charge mode, the voltage on cells 1 and 2 is higher due to the higher IR, and the balancer makes sure the 'low' cell (cell 3) is charged more than the others. Later on, in CV mode, it notices that cells 1 and 2 have less charge than cell 3, and it has to do the opposite... This had led to very long charge times.
In the beginning I didn't balance charge, but just charge with the balance lead plugged in (so at least it was monitored), and the charge was way faster and when fully charged all cells had similar voltage.
Now I've set my iCharger to only balance in CV mode, problem solved.

I agree on charging in the morning, for me it's fast enough at 1C though.
If a battery catches fire while being used within it specs... Time for a new pack... It's probably puffed anyway.

 

[TheWW1FlyingAce]

I'm going off a lot of discussions in the Batteries forum of RC Groups. The majority consensus now is that if there is an effect, it's negligible, specially if you're charging well below the battery's rating - i.e. charging a 5C-rated battery at 2-3C. Charging at the full rating might be more of a problem, but given the diminishing returns there's no real reason to.

On the Powerlab, the Fast Charge setting stops at 10%, but balances throughout the whole charge. The Accurate Charge setting stops at 5%.

The fact that the charge stops at a percentage of the set charge current adds another wrinkle to the issue: it is well known that charging the pack to a slightly lower rest voltage (i.e. 4.18V/cell instead of 4.20V/cell) has a positive effect on the longevity of the pack. Setting the stop point to 10% instead of 5% has this effect. But setting a higher charge rate also has the same effect. If I charge at 1A and end at 10% I'd end at 100mA, but if I charge at 2A and end at 10% I'd end at 200mA, i.e. the same ending current as if I'd charged at 1A and ended at 20%. So it's possible that increasing the charge rate might actually improve the battery's life due to a lower charge ending current.

 

[TTMR]

Stay fun, I think the charge rate really depends on the pack. My eflite 1s batteries say to charge at 3c. There was once a time where even a half c was the max the packs could handle.