Tips from Carl "the Fixer"
czrl


disclosure/disclaimer:
Carl has been known to do a little buying and selling and fixin' up of RC Cars
and is a great rescource for our club. The legal staff here at zoomersrccarclub.com tells us that we need to tell you that neither Carl, the Zoomers RC Club, nor the web master at zoomersrccarclub.com can be held liable for how these tips are applied. (Unless, of course, they work out really well.)

send your questions for"The Fixer" to: butley1@gmail.com

 

Now for something new, Batteries and Chargers

 

There is some confusion over types and capacity of batteries and chargers maybe I can simnimh battplify this slightly.

NIMH or nickel-metal hydride batteries (the batteries that come with most RTR cars and trucks) are rechargeable and can be recharged many times. A NiMH cell is  1.2 nominal  volts and around 1.4 volts fully charged . Most rc cars use a certain number of cells combined to produce a given voltage. The capacity of these is rated in MAH ( milliamp hours.)   A thousand mah battery, will, in theory, put out 1 amp constantly for 1 hour. The lowest mah rating you want is 2200mah but 5000+ is best (make sure batt. will fit your battery tray.

The nimh battery starts at full capacity but the mah output and voltage starts dropping as soon as you start using it so as you drive your vehicle the the output drops quite a bit over time giving you much less performance as running time increases. This drop in performance continues until battery will no longer power your vehicle and the battery is discharged. Discharging a NiMH battery does NOT damage the battery as severely as  it will on a lipo battery but that is it’s only real advantage other than lower cost.

 

The LiPo (lithium polymer) batt. is a different animal. It has many advantages over the NiMh battery and with careful use is a great battery to use in rc applications.lipo

The nominal voltage per cell in a lipo batt. is 3.7 volts per cell and 4.2 volts when fully charged. You will notice that lipo batteries. are identified as 2c,3c,4c etc. this denotes the number of cells in the battery pack. Multiply the number of cells by 3.7 and you have the voltage of the pack. Lipo packs are rated in mah just like nimh packs are BUT there is a big difference in performance. The Lipo battery puts out close to full power all during use. One major difference is that you must NOT not fully discharge a lipo battery.  Fully discharging a lipo will ruin the battery pack and can cause overheating of the pack with a fire as a result. ONLY use lipo’s in an rc designed for and set for lipo use. Rc vehicles made for lipo use have a built in voltage detection circuit that will shut off the vehicle at a certain minimum battery voltage to prevent battery destruction and torching your vehicle.

The lipo battery is also smaller and lighter for a given capacity. For our track 2 and 3s batteries are the highest voltage needed and 3000-10000 mah capacity is all we need and 5000-6600 is fine for our applications.

There is one more specification on lipo packs that we can use. That is the C rating. In our case C stands for capacity. In simple terms this number is the maximum safe continuous discharge rate of a battery pack. Well in theory this would mean that a 10c battery of 5000mah rating could safely put out 50 amps continuous until it reaches lipo shutoff voltage. Remember I said in theory because when the manufacturers figured out a way to fudge the tests, some of the cheap batteries are about half the c rating that they are marked. For our use in our 10th scale vehicles 20-30c real rating is fine with 30 being a great average. It will do no good to spend lots of money on a 60-100c battery when our vehicles only use 30c. to operate. 100c will not last longer than 50c on our cars but 5000mah batteries will keep your car running much longer than 2200mah batteries. This is my opinion, but I would say that 5000-7000 mah 20-40 c packs are great for our track.

Some reliable battery pack makers are as follows:

     Traxxas

     Turnigy ( The nano-tech are great.)

     Gens Ace

     Zippy (These seem to be great for the lower price packs.)

     Venom

 

There are many more and I know I left out most of them but the above ones are packs I have used with great success. I have gotten most of my batteries from hobbyking.com but just make sure you order from the usa warehouse. They carry turnigy and zippy packs and I have had no complaints with hobbyking and prices are great.

 

Now to chargers. First, forget the ones that come with the vehicles. They are junk. They work but almost all work ONLY on NiMh batt. and the charge rate is so low that it can take all night to charge your battery.

venom

When you do get a better charger, make sure it will charge NiMh,Lipo, and the newer LiFe batteries that may catch on soon. Buy a charger that has an amp output to match your batteries Mah rating. Example if your battery is a 5000mah you want 5amp,6000mah you want 6amp charger. 6 amp rating will charge all lipos because you can adjust the charging rate from almost zero up to the max of 6amp, but a 10000mah battery will take about twice as long to charge as a 5000mah...4hrs. vs about 2.

All the better chargers have adjustable charge rates to match your battery. This brings us to charging your batteries. ALWAYS charge outdoors in a safety charging bag or box. ALWAYS charge at the mah rate of the battery, not higher. You should always be present when charging any of your batteries.

Lipo batteries require balance charging about every 5th to 10th time they are used. They have a special plug that you plug into the charger (make sure your charger has this capability). The purpose of balance charging is to equalize the charge in all cells of a lipo battery. This extends battery life and increases power output since all cells are equal power.

Hope this info helps take a little of the confusion out of rc batteries and chargers. This is just a general discussion on the subject, S0, as always, read and follow the instructions that come with batteries and chargers for the manufacturer's specific instructions and have "Fun N the Sun."

.

My next post might be about motors and esc’s.   Any comments, good, bad or indifferent are appreciated. At least up to a point!

 

Carl, "The Fixer"

 

 

 


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8/22/2014
Traxxas has a new velineon system out but almost all their current cars on the shelf and at dealers have no new motors or only new esc's installed. Nobody should buy new VXL cars for awhile. Traxxas is trying to get rid of old stock from their shelf.
The new systems have a letter R after motor number and esc number. The new motors are now 4 pole motors. You can tell the new motors by a bigger end cap and much stiffer braided wire covers and the new esc,s have large capacitors at one end of the esc
the old VXL motors are 2 pole and have less torque and run hotter than the new ones BUT will NOT work right with the old esc's. The new esc will work with the old motor
Both the motor and esc must be purchased for the system to work correctly. I ordered 5 new velineon systems in and the price was good at 159.00
(see note below) for the motor and esc and noticed that 2 were old system 3 were new. I tried new R series and wow what a difference. Longer battery life, ran cooler, and better performance. I sent back the old ones and will have the new systems. AGAIN anyone buying Traxxas VXL cars should make sure they have new system for much better performance.


Note: Here are pix of the new system the motor pn: 3351R the esc is 3355R I sold what I had but can get more but price is going up with demand 169.95 is the latest for the pair. I really like the new system

escmotor

 

*****

 One of the track rules is that a charging bag for Lipo batteries is necessary at the track. I think better yet is one of those century fireproof safes, $20.00 plus at Walmart. I can charge the batteries in the safe with the lid down. It also makes a great safe way to store the lipos when not in use. [editors note: Bruce also drilled some vent holes in the lid to avoid excessive pressure building up in case of a fire.]

safe

 

charging


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