Charging rates and times

[helimadness]

Hi All.
So I have a PL6 charger that has served me well for a couple of years and I really like it. Unfortunately I only have a 500w power supply so only using half its capacity. I am finding I end up with more and more lipos to charge before I go flying and Charging is becoming a chore.
So I have a Goblin 700 with 3 sets 12s (2 x 6s) Sticks around 5000 - 5300 mah, plus a 2s 1800 flight pack.
Trex 500 with 5 x 6s 2600 mah
A hex with 4s 4400 mah
a wing, Bixler, a few 3s 900mah for my FPV kit. etc etc
Sorry for the long story but.... end up going to the field with sometimes 20 odd lipos. Charging them all up to go takes a while.

So am I better to charge the night before at say 1c which is about the max my PSU is good for on the 12s packs. (I do a lot of parallel charging) Or get a bigger PSU and charge at 3c the morning I am going to fly.

I know this is splitting hairs but been debating it in my head so thought I would put it out there.
I know Lipos don't like being left fully charged so its a trade off between faster charging or leaving charged for longer time. Im sure there are many people out there with more experience than me that can shed some experienced comments.

I try and look after my lipos well. After flying I always put them back storage charge ready for the next weekend. This helps reduce the charge time next time and has looked after them well. Some of my 500 lipos are coming up 3 years old with 100's of cycles and there capacity and IR is very very close to some of the new ones I have.


Cheers

[trillian]

I don't think having them charged overnight or even a couple days is hard on them (from what I have read). The important thing is that when they're fully charged they are kept somewhere without big temperature fluctuations, I have been told that's what will shorten their lifespan, but just being charged for a little while isn't that traumatic.

I always charge the day before I fly and this way I'm not worried about charging fast so I generally charge at 1C or 1.5C and I have LiPos that are three years old and still going.

[bigbladelittleblade]

Sell half of your batteries and invest in a bigger power supply (1000w) and a suitcase generator (kipor) for on site charging. I only charge when I go to the field and by the time I'm ready to fly I have a least 4 packs charged and ready to go, 4 packs charged in under 20 mins, you can't beat it!

[fraggle42]

I've been working with large LifePO4 packs and talking to the manufacturers for a little while now and have found out a few tricks to enhance their lifetime.

Nearly all LiPo / LifePO4 don't like being discharged too much, or charged too much. For optimal lifespan, keep charge level between 20% ~ 25% and max 95%. Keeping between that has shown to double or even treble the number of cycles a battery can withstand.

If you keep within that they're happy to hold the charge for any length of time you like.

Charging over 95% capacity and the amount of power you're putting into the battery that is converted into heat goes up and up and up, IIRC a test showed that the last 5% of charging generated over 80% of the heat in the battery (and wasted over 60% of the power).

Of course the applications I'm working with (solar power storage systems) a typical battery is 24V 200Ah 5KW, ~ 50Kg, and increasing the battery size to compensate for the fact you're using 75% of it's total capacity is easy to do, the extra size and weight isn't a problem and the cost saving is a big benefit.

RC helis wouldn't like carrying a bigger capacity battery much

Sorry, not all that relevant to your question, but (assuming the battery construction is similar) if your charger can be told to charge to 95% and stop you can do that and safely store the battery for a few days with no danger and over a couple of days the self discharge won't matter.

[helijohn]

So am I better to charge the night before at say 1c which is about the max my PSU is good for on the 12s packs. (I do a lot of parallel charging) Or get a bigger PSU and charge at 3c the morning I am going to fly.

Without reading the other replies first my thinking, as a relative newcomer to electric, is to charge the night before and then give a small charge "top up" in the morning. I personally like to always balance charge and also personally like about 1C charge rate but can go to 2C if needed (so far never).

Having said that a big PSU will never be a mistake. I also like the flexibility of several chargers on the go at once. I cann do this as I only do 5 big packs and sometimes a few smaller ones (for my 500 and 450s) but I like to have one charger per battery.

[woodsta888]

In the for sale section MAJ has a 24v meanwell 1500W pSU for considerably less than half RRP in it's own case. Steal.

[Made2Fade]

Can i suggest you do not 'top up' your batteries... You'll find that they will loose their capacity far quicker doing that.
Store them at 3.8v per cell and keep them in temperatures between 5 - 27 degrees C. The closer to 5 the better 3.8v i think is around 40% of their fully charged state.
And make sure you let the packs come down to ambient temperature before you put them on charge again. Dont fly the packs, pull them out and whack them straight on your charger which is plugged into your suitcase generator on the field. Youll damage them if you do!
So im not sure a generator is actually a good thing unless your waiting for the lipos to cool first (more time consuming and kind of defeating part of the object).
I personally aim to have 5 assembled packs for each of my helis, on trays ready to go. I charge them at 1C the day before i go flying. Occasionally i will charge at 2C if im in a bit more of a hurry. I parallel charge also but it is good practice to charge the packs individually every so often. 2C is proved not to damage your packs. Obviously charging higher than that regularly will damage them (it basically means you are slowly killing the packs capacity alot quicker - meaning they'll not last as long).

[helijohn]

Can i suggest you do not 'top up' your batteries... You'll find that they will loose their capacity far quicker doing that.

Ah now that's interesting as I put out a question a few months ago about what people thought about nipping out for 10 mins while the batteries are on charge in the morning fully expecting the response would be no. Several said switch off for the ten minutes then switch on again on returning. But here's the crack, some said why not charge the night before then just top up in the morning. Go figure.

[SaneAdam]

I personally aim to have 5 assembled packs for each of my helis, on trays ready to go. I charge them at 1C the day before i go flying. Occasionally i will charge at 2C if im in a bit more of a hurry..

Thats the way i do it too. All on trays ready to go. Always balanced charged at 1c night before flying. I generally fly 3 days a week so i never end up storage charging. My packs come down at 25%, then usually get charged later in the eve, with a view to flying again in the next 2 or 3 days.

[helimadness]

Hi All
Thanks for the great comments. Always learn good things here :-) Good to hear fraggle42 results on similar batteries.

A generator is not really practical for me. I live in an apartment and have no where to store a petrol powered motor. Hence all my helis are electric.

I am also living in China so the PSU on the fore sale board is not really an option. I have found a 1200w 0-30v adjustable supply for about 55 quid so silly not to go for it. I sometimes have a couple of weeks between flying so like to put the packs back in storage. Also makes charging quicker next time. I figure a lipo is less volatile in storage. I guess fully charged they are the most dangerous which is another reason I dont like leaving them charged. Really need to get better storage for them as well.

For sure if parallel charging its good to do them individually from time to time as parallel charging can mask problems. I had a lipo with a dud balance port pin. Parallel charging it didnt show up as its parallel partner was giving a good signal. It wasn't until I charged it on its own the error showed. Why it wasn't a problem if that cell had good out of whack the charger wouldn't know and it could potentially get over charged.

Cheers

[Made2Fade]

Ah now that's interesting as I put out a question a few months ago about what people thought about nipping out for 10 mins while the batteries are on charge in the morning fully expecting the response would be no. Several said switch off for the ten minutes then switch on again on returning. But here's the crack, some said why not charge the night before then just top up in the morning. Go figure.

I wouldnt consider it bad advice exactly but what i am saying is if you do that then dont expect your batteries to last as long. Think of it like this...
Lets say for arguments sake that we have a particular battery, and that said battery could be charged 500 times before it needed to be retired. If you 'top them up' then effectively your giving the battery 2 charges instead of a needed 1 charge. So instead of getting 500 flights you get 250. Your basically halfing the batteries life. Now of course those figures wont be correct and we couldnt possibly predict exact numbers for any battery because theres too many variables to consider. But the point being, without doubt the life of the cells will be less.
If your using turnigy batteries then who cares... If your using high end packs then maybe you'd want to look after them a tad better. I use turnigy in my fixed wing models... They are retired and replaced as soon as they show signs of loss in power. They are so cheap to buy that its not so expensive to do that.

[trillian]

Think of it like this... Lets say for arguments sake that we have a particular battery, and that said battery could be charged 500 times before it needed to be retired. If you 'top them up' then effectively your giving the battery 2 charges instead of a needed 1 charge. So instead of getting 500 flights you get 250. Your basically halfing the batteries life. Now of course those figures wont be correct and we couldnt possibly predict exact numbers for any battery because theres too many variables to consider. But the point being, without doubt the life of the cells will be less.
If your using turnigy batteries then who cares... If your using high end packs then maybe you'd want to look after them a tad better. I use turnigy in my fixed wing models... They are retired and replaced as soon as they show signs of loss in power. They are so cheap to buy that its not so expensive to do that.

So is there a difference between charging continuously vs stopping the charge and then re-starting? So for example if you fully charge them in one session you might go from 3.8 volts per cell to 4.2. What is the difference if you charged from 3.8 to 4.0 and stopped for a while to run some errands, come back and resume the charge from 4.0 to 4.2 volts?

[helijohn]

What is the difference if you charged from 3.8 to 4.0 and stopped for a while to run some errands, come back and resume the charge from 4.0 to 4.2 volts?

I was told the charger just sees what needs doing and gets on with it. I had to do this once or twice.

As for halving the number of charges I don't get that. A few minutes top up surely is not like a charge from 20% to 100%.

[trillian]

I was told the charger just sees what needs doing and gets on with it. I had to do this once or twice.

As for halving the number of charges I don't get that. A few minutes top up surely is not like a charge from 20% to 100%.

What I'm wondering is if there's more wear or trauma to the battery based on each time you start a charging session, would two 10 minute charging sessions cause more wear / shorten its lifespan vs one single 20 minute charge to acheive the same state of charge. I'd really like to know what variation of charging approach gives the longest lifespan. Is it charge rate? Limiting the max voltage to a bit under 4.2 volts? Does it make any difference if you have to split a charging session vs completing the charge in one session? etc.

I haven't charged at the field in ages so I'm always charging at home and the packs are cool and I rarely charge over 2C, usually 1 or 1.5C.

[helijohn]

I haven't charged at the field in ages so I'm always charging at home and the packs are cool and I rarely charge over 2C, usually 1 or 1.5C.

I charge in the morning now and then - early at 6am - and if I run out of time as long as the volts show 4.1* then I take 'em.