XRAY - Model racing cars

Hi,

I started using my car (T2'007) in April/May 2010 and since a few weeks I'm more comfortable on the race track meaning the car goes faster and faster, but now the car is much less autonomous (normal since it consumes more energy).

But I would like to compare with others like you, e.g. I use 2S LiPo 5000mAh and the car was able to drive during 15 minutes. Now that the car goes faster the run can last up to 10 minutes but it happens sometime that the car even stops on the car because of being out of power. And it's really a battery issue because more than 4500mAh is used when charging the battery.

Hence my question, can you please tell what king of battery you have and how long a run usually last with you?

Thank you.

Gratulation to your progress. Runtime depends mainly on the kind of motor you use. On big tracks you sometimes can only run maybe 6 minutes with a 4.0T motor.

But as races usually go over 5 minutes, there is no problem.

Which motor do you use?

I use a 7.5 motor and the track is .

I can use the small ring or the big one, but I started to use the big ring and I wonder if I will kill the batteries by doing that, but the engine, controller and battery are not that hot (engine is around 75°C) at the end of the run.

It is better not to discharge the batteries completely each run. So you could set a timer (maybe on your transmitter) to 6 minutes.

If you are using 40C or 50C batteries there will be no problem. It is more likely to kill a motor than a battery.

We treat our batteries harder, when we are using 4.5T Motors (which we use on that big tracks). So there should be no problem. I had races where the temperatures increased to over 100°C, but that should be the absolute limit, as this reduces your motors life significantly.

In fact I just wanted to know what is a realistic time, because the timer was set to 15 minutes and that was far too much when you go fast. I will decrease to 6 minutes then, to be on the safe side.

Re motor temperature, I noticed the manual said the max is 100°C, I bough an infrared thermometer to check that.

Then I will have to either buy more batteries or raise the current charge to be able to stay at the track for a longer time. But raise the current charge is not that good for batteries, I use to charge with a very low curent like 500mA, it takes several hours but I don't want to damage my batteries.

Thank you for the tips

I have 2 battery packs, and use them 3 to 6 times a day (at the racetrack). I charge at 6A. This should not be a problem.

I understand I can charge 1C, 2C or 3C, etc... depending on battery specification but how long is the battery life time when you use suche a high current?

I guess your charger also balance voltage between battery elements?

I'll invest in a charger that has the balance feature then, my charger is an old one and hasn't balancing, I check balance manually with a voltmeter.

My batteries are IP 5000mAh 25c+.

I'm not sure with these batteries, but since they are 25c+ (older generation) I think 1C charge is the recommended charge current.

If the batteries keep in balance you may not need a new charger.

Another tip, if you're not aware, you should store the batteries with 50-60% (around 7.8 volt) charge, never keep them fully charged over a long period. This will reduce the capacity of the batteries over time. I've heard if you plan not to use the batteries for more than 10 days this should be done.

Thanks again for advices.

Some chargers have a "storage loading" functionnality, i.e. it won't charge the battery fully.

Can I ask where you buy your batteries?

Mamac, don't worry too much about Lipos , they are much more forgiving than NiMhs. Just do what it says on the can. I have some 4900s which I have had for 2 years now. They get charged at 1c all the time (their maximum). They get balanced charged on Saturday night and fast charged on race day - you can run for several months without balance charging with no ill effect. They are not my main batteries now but get used for practice and my youngest son uses them when he races. If you have a balance charger you might as well balance charge them regulalrly but it is not necessary on a regular basis.

I'm using Polyquest 2S1P 5050mAh LiPos 35C constant discharge rate. I don't know if there's a difference in performance between 1P and 2P packs but I only buy 1P packs as a 2P pack has 4 cells and the more cells the bigger the risk that one will become damaged.

I also noticed a difference in runtime from 10min to 25min out of my older 4000mAh 2S LiPo by just programing the ESC different. 6.5T BL star wound and Genius 90 V2 from GM Racing.