Lipo help please.

[gixxer1000rider]

Hi all.

i am returning to this hobby after 20+ years away and have a newbie question regarding lipos.

i have have just built a 1/10th buggy with club racing in mind and have purchased a pair of Team Orion 7.4v 90c 5500mah saddles. now, i have never used lipos before and am struggling to understand my charger and the batteries themselves.

i have bought a Core AC50 charger : specs below.

Universal Digital Charger, Discharger and Cycler, 12v & 110-240v.

The CORE RC Universal Digital Charger UAC-50 is a multifunction balance and rapid charger/discharger controlled by a high performance microprocessor and specialized operating software.
Multi voltage input of 110-240v AC or 12v DC with compatibility with all types of batteries including Lipo,(1s-6s) Li-lon, NiMH, NiCd,(1-15cells) Pb and LiFE. Fast charging up to 6 amps, discharging, balancing, cycling and much more....you won't need any other charger!!!
Specification;

• AC Input 110V-240V
• DC Input 11V-18V
• Max Charging Power: 50Watts
• Max Discharging Power: 5Watts
• Charge current range: 0.1-6A
• Discharge current range: 0.1-1A
• Nicd/NiMH Battery Cell Count: 1-15Cell
• LiPo/Li-Fe/Lilon Cell Count: 1-6Cell
• Pb Battery Voltage: 2-20V
• Temperature sensor available
• Balance: 2-6Cells
• Case: Plastic with gunmeatal chrome.
• Display: 16*2 character blue backlit display
• Dimension: 135mm X 112mm X 61mm
• Multiple leads included for all applications
• UK 3 Pin plug lead for 240v
  
  

what settings do i need for these lipo's? 2s balance charge obviously, but what Amp? and for how long?

also, this may be a stupid question but how do i know when they are charged?

and do they have to be discharged for storage?

sorry for all the questions but lipo's are all new to me.

thanks for your help in advance.

[peetbee]

2s balance charge at 5.5 amps would be safe.
The charger will stop charging when the cells are full.
It seems to be that for storage you don't want then to be flat or fully charged these days. Personally I leave them after the last run as that's approx half charged (I'd have to read the instructions for discharging my cells if I didn't finish my last heat!)

This has worked well for my lipos, but check what orion say themselves regarding storage just to be on the safe side.

[gixxer1000rider]

Thanks Peetbee, so simply set the charge at 5.5A and it will stop on its own when fully charged.

simple enough, thanks again.

[trax de max]

don't you have to set the capacity too. in the menu

[mark christopher]

if its this charger http://www.racing-cars.com/pp/Manufa..._RC/CR161.html

then it also has a storage mode.

[blue_pinky]

So Lipo's....you've had the right advice so far, but if you want to understand a little more about it...hopefully the following will help. I'm not a 'professional expert', but this has been my understanding of all the info I've found out.

Typically you charge at 1C, your battery will have a charge rate in terms of C printed on it somewhere. Some of the newest ones say you can charge at higher rates. This is new, and a bit of an unknown IMO, but will probably be the norm in time to come. Faster charge rates in theory reduce the life of the cells, so I tend to stick to 1C as I can peak between races at that rate anyway. Apart from anything else, currently few chargers can give you charging rates higher then 1C anyway!!!

C = Capacity...so if you have a 5500mah battery, then you'd ideally charge at 5500mA = 5.5A

Lipo's must always be charged in Lipo mode (CC-CV mode, constant current-constant voltage), whereby it will charge at full constant current to begin with, ie the 1C rate until the voltage gets to a certain (virtually fully charged) point, then it will automatically start to slowly vary (drop) the current so that the voltage stays constant and peaks at a fraction under 8.4v in theory. That's all automatic though so no need to worry about it, just helps to understand what it's doing and what the numbers all mean.

Never use Ni-MH mode on a lipo...this will invariably lead to damage of the lipo and potentially a fire! Essentailly the currrent/voltage drop that you used to see on a Ni-MH cell to see it was charged never comes (if my memory serves me correctly!), so it will just keep pumping current in! This is bad!

Also, in use, lipo's don't have the same peak behaviour, where the cells are most punchy early on in a race and gradually drop off like Ni-MH's did....they just keep punching all the way until they dump. Always run with a voltage cut-off on you ESC...you should never let them actually dump as that also damages the cells and may cause a fire in the most extreme cases.

In the same vein, if you haven't peaked your cells, you won't see bad performance on your car either, so it's not a problem...you just get less run time...if you ever even get close to it, which is extremely unlikely in club racing environment.

Damage and fires are very uncommon, and lipos are really a lot easier to use than the old technologies...you just need to understand how it works

[gixxer1000rider]

Wow! Thanks for taking the time out to reply in such an easy manner to understand.

I am charging at the moment and was looking at the charger screen I was seeing 8.38V on my 7.4V battery and began to panic!

So, am I right in saying once the lipo's sit charging at 8.38-8.40V they are fully charged? And the charger is just keeping them balanced and topped up?

What is the usual charge time after a five minute run?

Thanks

[mpg200]

Originally Posted by gixxer1000rider

So, am I right in saying once the lipo's sit charging at 8.38-8.40V they are fully charged? And the charger is just keeping them balanced and topped up?

Thanks

Not quite, the charge will stop when the charge current in CV mode drops below a preset limit. not sure what this limit is though. when the battery first hits 4.2V per cell (8.4V for a 2 cell battery) it is only about 60 - 80% charged. the remainder of the charge is done in CV mode when the current is dropping. so when the charger sits at 8.4V its doing the last 30% ish of the charge and this is when most of the balancing is done.

[Appie53]

I ám confused by this, when fully charged and for some reason not used directly, can it stay like this for some day's, or is it not wise?
Thanks.

[blue_pinky]

It can...but there is some risk of damage...though only a low risk I'd say.

I had a pack that I used to charge up at the end of a club night ready for the next week.

It was fine for a long time, about a year, but with infrequent use, so the pack staying fully charged most of the time. I left them fully charged without using it for a few weeks/month's at a time and the once when I came back to use it again the cells had swollen up considerably....this was just before charging in lipo sacks was a requirement too, so it had also been left in the car the whole time as well. I suspect the compound effect of them not being used very often and only being stored charged was bad in the end.

These days I leave them after the last run, then charge on the day of use, had no probs since.

[Appie53]

OK, so some day's won't do any harm?