RC car battery question?
 

After looking for a couple days, I got my boy a used Traxxas Emaxx. Now, I need help understand batteries. The batteries that came with this thing only held a charge for about 5 minutes. Off to the hobby shop we go. Wow, these things aren't cheap. :( What the difference between a 2400 and a 4500mah battery? Is it run time or release of power? It came with 7 cells but the hobby shop tells me I only need a 6 cell battery. At one point, this guy was talking abut these new lipo things that will have a long run time but I needed to change a bunch of things. Where do you guys buy your batteries. I like to support my local shop, but if they are ten bucks more then the net, I will order on line. They range from 20 bucks to 60. Oh, It has two brushed Titan motors that require two packs. That much I do know, if that helps. I am thinking about buying 4 packs. That must last for an hour?

There are three main RC battery types. Nicad, Nimh and Lipo.

Nicads take a lot of abuse, the others don't.

Abused Nimh just die.

Abused Lipos tend to catch fire.

For what you're doing you should stick with cheap nicads or nimhs.

The higher the amp rating the longer the battery will last and the higher amp draw it will support. The 'amp draw' is commonly referred to the 'c' rating. So if you have a 1000 mah battery that is 1 'C' it will support whatever voltage it is drawn at 1000mahs. If it is 10C then it will support whatever voltage it is drawn at 10*1000mahs.

I have 2 7 cell, 2000mah Nimh batteries that have very little use on them that you can have. I'm near the beach at the end of the 105.

7 cells are higher voltage than 6 cells, the higher the voltage the higher your amp draw will be. The higher the amp draw - the shorter your run times will be unless you put high amp batteries in there to compensate.

What are the amp rating on the batteries you have?

RC Batteries
 

Mike did a great job explaining RC battery choices. The short run time you are seeing is mainly due to 2 motors, that thing must be geared down for pulling stumps.

Lipo's are great but they are expensive, you need a more expensive charger (balancing), a special fireproof charging bag and should stay in the general area in case of a problem. I try and buy my RC stuff locally but the best shop is a 70 mile round trip.

To learn more check out RCtech.net, it is bigger than Pelican in terms of free information. I buy and sell cars and parts there each year to save a few bucks.

Most importantly have fun with your boy sharing the hobby. A real bonus is that RC is a great way to teach kids about physics, machines and electricity. DP

I have an Emaxx as well. The twin motors really use a lot of batteries and I do not think I have ever seen more than about 15 minutes run time on batteries. But it is a lot of fun! Good advice from the other guys.

Thank you, Mike. That's very nice of you. I will take you up on the offer. Let me know when you have time. In return, I maybe able to help you with a solution on the steps going out into your backyard if you have already done so.

How do I find out how much these little motors are drawing at any one given time? Will it draw more current when they are climbing vs. going all out on the flats?

Jeff

What kind of betteries are you putting in there?

Hey Jeff, it'll be cool to talk to you about it.

Now, post a pic of the battery connectors between the speed control and the batteries. If you bring the car I can most likely test the draw for you on a meter I have (called a watt meter).

I'll be home most of the day and will send you a PM with my contact information.

The guy gave me several charges. They will charge Nimh batteries. The vehicle has what's call Dean or is it DIN connectors. I will most llikely come out after 2or 3 today. I will call you.

Jeff

It actually has been some time since I played with this. I only use NiCads. I had one set of 2000mAh and the rest were 1500mAh. Of course the 1500's ran down quicker.

If you have deans plugs on there then we are most likely good to go. Bring the whole shebang when you come by.

The Dean's plugs are good. I can't remember if all Dean's plugs have gold connectors/contacts, but if yours are gold, that's about at good as you can get on the connector issue.

The 7-packs are gonna give you a little bit more runtime and ooomph, so if you ever run across a decent price, get a coupla sets.

Another thing to keep in mind is that running through grass is gonna really suck the runtime down because it puts up a lot more resistance than you would think, so try not to run it in grass very often. It causes the motors to heat way up, too. It's like if you were running a mile in knee-deep water.

If I remember correctly we upgraded my son's 2000 mAh battery to a 4500 mAh battery in his Slash, his run time basically doubled and it was noticeably faster. 2000 is a pretty basic battery. The more voltage (cells) and the higher mAh means more run time and faster speeds. Do some research on your ESC to determine the maximum voltage it can handle. Good batteries make a big difference.

Great, now I have new rc truck fever...

I hope its not my fault. Hey, thanks again for the batteries. He had a ball with it today after lunch.

Jeff

Big +1 on the grass. Even if you had more battery life, or kept switching packs, motor heat is going to limit you on grass, although how much it affects it depends on the type of grass.

High performance RC's are going to put a fairly heavy load on batteries, and a heavy one like a E-maxx is going to increase it even more. Going to a brushless motor can do a lot for run times. Also, the higher the MAH rating of a battery, the longer life you can expect.

As for your question about what uses the most battery life, the stuff at lower RPM/higher torque is what uses it. The amp draw(and torque) decreases with RPM, so the truck packs a punch off the line, and peters out. "rock crawling", where the truck is very near stall current, will hit you the hardest unless you have some really high gear ratios. If you're cruising at lower speeds, run it in 1st gear for better battery life.

Excellent.

What was the run time?

about 10-15 minutes over dirt and and a bit of grass. Why is grass so hard on motors? Where's the resistance coming from for the huge draw of power?

The e-maxx is a great truck to bash around with. You can drive it off a cliff and it will still be going....Stay away from the lipo's if you just drive it in your backyard. They are great and extremely powerful batteries but you need to know what you're doing. As mentioned before, you need a LiPo balance charger, and a low voltage cut-off on your ESC (electric speed control) If you draw them to low it will kill the battery. I have seen them explode several times and it will destroy the car. (and your house if your a bit out of luck).

Try to find at least 4500 MH to get some running time out them. My e-maxx, with the upgraded Mamba Monster ESC/Motor will run 10/15 min on a 4500 MH or about 15/20 min on ther lipo's.

Try to stay away from the grass, it will suck your battery dry fast, and might kill the motors. (happened with Sam's Rustler). Climbing hills and dirt is where it's build for.. And, be careful on gravel......the emaxx will trow gravel like a shotgun.....

It's a great hobby. I started with the e maxx just to bash around and now we have a basement full of off road and on road cars. This is Sam's latest car:

https://lh6.googleusercontent.com/-U...0/IMG_1899.JPG

https://lh5.googleusercontent.com/-c...0/IMG_1900.JPG

https://lh6.googleusercontent.com/-TLqd_BtnFGg/Tsq4LdkqRYI/AAAAAAAAUk0/lBdb1_1KaJE/s640/IMG_1886.JPG

Like another user said, its like trying to run in knee deep water. The grass sticks up and adds a lot of resistance, so you're drawing a much higher load when running across it. The larger the diameter of your tires, the better it can deal with it. Monster trucks can handle grass better than the smaller cars, but it still makes for hotter motors and shorter run times.

What timing!! I just bought a Losi SCT 1/16 Stadium truck and the guy was trying to sell me lipo batteries. The battery that came with the car has a long run time, compared to the 6 cell batteries we used to run in 1/10 off road cars, of 4 minutes!!!