Please help...with making battery pack

[erevo1*16]

I have a simple question, and if you want to just answer yes or no, thats fine... I would love to learn if there is anybody that wants to take the time to teach.

Thanks in advance.


I am looking to make some battery packs to power my RC car. It is a Traxxas 1/16 scale E-Revo VXL if you want to get some specs on it, but I think what you need to know, I will have posted below.

The Factory battery packs are 6 Cell packs of 2/3A 1200mAh cells at 7.2V. There is room to run two packs in the car and the Electonic Speed Control can handle up to 14.4V if you run two packs in series.

The Packs I want to make would be 4 Cell packs of Double A (AA) 2500mAh at 4.8V and run them in series for 9.6V (space is an issue...)

What I am wondering though is: Will the (AA) cells be able to handle the current that the 2/3A cells can?????? or am I just going to fry the (AA's) after a few charges??

here are the specs that you may want to look at to answer...

Electronic Speed Control Specs:
Name: VXL-3M
Input Voltage: 6 to 12 cells NiMH, 2S to 3S LiPo
Case Size: 26.5mm W x 46.5mm D x 22mm H
Weight: 38 grams
Motors: Sensorless Brushless
Motor Limit: None
On Resistance: 0.0005 Ohms
PWM Frequency: 12,000Hz
Peak Current: 326A
Continuous Current: 52A
BEC Voltage: 6.0V DC
Motor / Battery Wiring: 16-Gauge Maxx® Cable
Transistor Type: MOSFET
Low Voltage Detection: 2-Stage indicators, switchable (on or off)
Thermal Protection: 2-Stage thermal shutdown
Single-button setup: Yes, Traxxas EZ-Set®
Battery Input Connector: Traxxas High-Current Connector
Motor Connector: TRX 3.5mm Bullet Connectors

Brushless Motor Specs:
Name: Velineon 380
Type: Sensorless Brushless
kV (RPM/Volt): 4000kV (8T)
Magnet Type: High Temp Sintered Neodymium
Connection Type: TRX 3.5mm Bullet
Wire Size: 16g Maxx Cable
Continuous Current: 25A
Max Current: 50A Burst
Max RPM: 50,000
Weight: 140g (4.94oz)

Here are the cells that I bought to make these packs...

https://www.all-battery.com/aa2500mahhighcapacitynimhrechargeablebattery10320.aspx


Thanks again.

 

[alec_t]

Those cells will be fine. Because you will be using 9.6V the current (and of course the maximum speed) will be less than if you were using 12V.

 

[Dragon Tamer]

Your AA batteries will need to be rechargeable, that bing said as long as they are NiMH batteries they should have no trouble keeping up with the battery that came with the car. The battery that came with the car will be "dead" first though, forcing the AA to pick up the slack for a while. Make sure the voltage doesn't drop below 1V per cell other wise they will not charge properly and this will severly shorten their life and lower their load potential.

The specs for the battery pack that came with the car implies that that they are NiCd batteris not NiMH.

Are you trying to increase the speed or increase the run time? (runtime will have the batteries in parallel, speed would be in series) If I'm not mistaken, the 2/3A specification is for charging speed.

 

[erevo116]

Man I hate trying to log in to some sites... I made another profile because I got locked out of erevo1*16... ugh...

Sorry if I left out a few items of detail…

The Factory packs are NiMh. Each pack is a 6 cell (7.2V) 2/3A size cells at just 1200mAh. The RC car can hold 2 packs… totaling 12 cells of 2/3A size. The Speed control can handle ANYTHING from 7.2V up to 14.4V (NiCd, NiMh, Lipo… ANYTHING)

The best pack that I can find with out going to Lipo is a 2/3A 1600mAh and they are about $22 each… the reason I am looking to do this project is saving$ on packs.

I do not know what kind of discharge rate the factory packs have… as in like what they do with Lipos and giving the pack a “C” rating to indicate the current that it can push or ‘have drawn from…’

The Cells that I found that I am wondering about are a AA size, and I am limited by the size of the battery tray to keep it to “stick packs” of 4 cells on each side of the car(left and right). They are a 2500mAh cell, so if I make 2 packs of 4 cells, and run them in series, I will have both more power on tap (9.6 vs. 7.2), and an extra 100mAh of juice in the packs… It seems like a logical step to me… There are a few Reasons I don’t want to run two stock batteries:

1: The 14.4V of power (from 2 packs in series) to this car is almost impossible to control.
2: The motor gets very hot (thermal shut down) if I am running it on any surface other than just smooth asphalt because of the extra drag in the system… I have heard the same remarks from some of the guys that use the 3s Lipo’s at just 11.1V
3: The 14.4V in series is still only 1200mAh…
4: In Parallel it is still only 2400mAh at 7.2V…
5: They factory packs are spendy, and the aftermarket set up from Duratrax are even more expensive($22) but at least they get 1600mAh.

so the next logical step for me is to think that this will work best with having 9.6V at 2500mAh… to me it looks like win-win-win-win-win… I got 24 cells shipped for $30 and all the wire leads and Tin/Flux is super cheap… I got all that I need and then form shipped from onlybatterypacks.com for 13$ (including shrink wrap.)

The electronic speed control can draw a peak current of 326A But it likes a constant 52A.

My real question, that I can not get a simple answer for is this:

Will the AA 2500mAh NiMh cells that I have linked here work in an application that is this ‘power hungry’???? I still get mixed reviews…


Link:
https://www.all-battery.com/aa2500mahhighcapacitynimhrechargeablebattery10320.aspx

Thank you in advance for the info, I truly do appreciate the help with this.

 

[Dragon Tamer]

Yes, your 2500mAh batteries have more power than the battery pack that came with the car. Beware though, having that difference in power means that when the original battery pack goes dead, the batteries you bought will have to pick up the slack and get drained even more. If you can, try to find some NiCd batteries that have the same power rating or, just replace all of the batteries with the new ones you have picked out.

If you do go for lithium technology, you have more power for less weight and this may improve your run time and performance. Just make sure that you read the directions for your lithium battery very carefully (they can explode or catch fire if charged or discharged improperly).

 

[erevo1*16]

@ Dragon Tamer-

I'm not looking for any Lipo, or NiCd... and I am not running different packs mixed together... I am looking to make "more" packs so that when I take my RC car out I can run for more than 10 minutes at a time. I have right now 8 packs of the 2/3A cells... Each pack is good for between 5 and 12 minutes of use depending on running condition and surfaces... (Grass/mud =5 minutes, baseball infeild or dry dirt= 8-10, and pavement is about 12minutes per pack.) the reason I started this thread was to try to figure out if the AA cells would be able to keep up with my motor or not???? I am not an electrical specialist by any means, but nobody can give me a straight answer to the simple question about constant current draw of the two cells...

I have these cells... does anybody know what the constant current for discharge would be compared to one another???? or doe anyone know how I can go find the answer??????

Cell one: 2/3A size 1200mAh at 1.2v NiMh

Cell two: AA size 2500mAh at 1.2v NiMh


Please....

 

[alec_t]

does anybody know what the constant current for discharge would be compared to one another?

Not sure what you mean.
If the bats are used in a car the current certainly won't be constant.
If you discharge the cells at a constant current of, for example, 1 Amp then Cell 1 will last 1.2 hours and Cell 2 will last 2.5 hours.

 

[erevo1*16]

Alec_t... I have done some homework on that, and I understand how one can make the equation to find out how long the batteries should last...

The motor that I am using can have a peak current draw of 326A... but a constant draw of 52A.

I think after doing some more homework I have found a way to aske the question that I am concerned about...

I see that this cell is listed as a "high discharge rate" of 30amps... **broken link removed**
but I can not find from any source what the "discharge rate" of the AA cells that I am look at are... if they only discharge at 2A... That wouldn't make much sense to put into a high draw application...

If I am way too worried and you guys don't think that this is a big deal at all I am fine with that... but I have noticed that some cells are labled as "high discharge rate" and others are listed as "low self discharge rate"---those make sense to me for something that wouldn't need much power... like the radio that I use to control my RC car.

Thanks.

 

[alec_t]

I can not find from any source what the "discharge rate" of the AA cells that I am look at are

Try emailing the manufacturer of the AA cells to find out their discharge current ratings (peak, average, time).

 

[Dragon Tamer]

@ Dragon Tamer-

I'm not looking for any Lipo, or NiCd... and I am not running different packs mixed together... I am looking to make "more" packs so that when I take my RC car out I can run for more than 10 minutes at a time. I have right now 8 packs of the 2/3A cells... Each pack is good for between 5 and 12 minutes of use depending on running condition and surfaces... (Grass/mud =5 minutes, baseball infeild or dry dirt= 8-10, and pavement is about 12minutes per pack.) the reason I started this thread was to try to figure out if the AA cells would be able to keep up with my motor or not???? I am not an electrical specialist by any means, but nobody can give me a straight answer to the simple question about constant current draw of the two cells...

I have these cells... does anybody know what the constant current for discharge would be compared to one another???? or doe anyone know how I can go find the answer??????

Cell one: 2/3A size 1200mAh at 1.2v NiMh

Cell two: AA size 2500mAh at 1.2v NiMh


Please....

I gave you a stright answer, you chose to make it complicated. You are not being clear as to how you intend to connect your batteries. You said you wanted to connect them so that the total voltage would be 9.6V, meaning you connected them in series and this would make your car faster but it would still only run for about 10 minutes. If you connected them in parallel you could run for 20 minutes (assuming both batteries are equal)

To connect the batteries in parallel you connect the positive and the negative leads of each battery back together. This will increase your run time but only if your batteries are equal voltage and current rating. This is why you need to look for more batteries, the home made pack must have an output voltage of 7.2V otherwise your batteries will be wasting power trying to charge each other.

The current is not quite as critical but you should try to keep them equal. The batteries that you are planing on buying have a higher power rating than the pack that came with your car, meaning they can run longer by themselves.

If you want to get into the discharge rates of the batteries, you are starting to make things more complicated than they have to be. Contact the manufacture and see what they have to say about the issue.

On the spot I can tell you that right now the battery pack that came with your car are rated for 1200mAh right? That means they can deliver 1200 milliamps for 1 hour. Take that value and divide it by your current draw at max power and you will get your theroetical run time in hours.

The batteries that you specified are ratted for 2500mAh so it can deliver 2500 milliamps for 1 hour, or 1200 milliamps for about 2 hours. The reason your car stops running is because your controller has a cut off point for the cells or that the car is drawing a lot more power from the cells than you may think. I'm inclined to think the later.

Does that answer your question now?

 

[erevo1*16]

Pre-post review- I just re-read this post, and I want to make sure that you know I do appreciate the help, after reading it, I thought that maybe some of it sounded a little "snippy or rude" that isn't what I want it to sound like... I am not trying at all to be a dick. I really do thank you for the help... don't read it as me being pissy, just kind of frustrated that I can not convey the questions the correct way to get them answered. (this is the first time in my life that I actually feel a bit dumb... I graduated w/3.85 and got some $ to go to college... ended up with a biology degree that I don't even use.... and the electronics was never a feild I studied at all.... Now car and home audio systems is something I can get on board with a bit more.... but this is V. Current, mAh... is all greek to me.)

I really appriciate the help, and I am sorry that I have had such a hard time trying to word my question... It is fairly difficult to do with out the foundation of formal education with the vocabulary of an expert... for that I appologize. (I am just a car sales man, and have never had any electronics training of any kind.)

I don't have the answer yet... but I have been sent to the MFG to find it from both of you... I didn't realize that there are sooooo many different types of batteries.... (not talking about physical size... more about power and current from the same sized cell...)


everything else that you said is information that I already know, and didn't ask about, and even said in a previous post that I was not planning to mix packs made of different cells... thats very basic stuff.... really don't want a cell going (-0.1) in any application that I am aware of.

As far as not being clear about how I plan to hook up my battery packs... I took this from my very first post. "The Factory battery packs are 6 Cell packs of 2/3A 1200mAh cells at 7.2V. There is room to run two packs in the car and the Electonic Speed Control can handle up to 14.4V if you run two packs in series.

The Packs I want to make would be 4 Cell packs of Double A (AA) 2500mAh at 4.8V***EDIT HERE (unless I am missing something; in order to have 4.8v out of a 4 cell AA pack of ANY kind... they need to be in series.) END EDIT**** and run them in series for 9.6V (space is an issue...)***Edit again... pretty sure that what i wrote is clear... END EDIT****

What I am wondering though is: Will the (AA) cells be able to handle the current that the 2/3A cells can?????? or am I just going to fry the (AA's) after a few charges??"

So like I edited in my quote, I guess the only way that I might not have been clear is if I am missing something about common battery cell for voltage not being 1.2v/cell????

I feel bad that you took all the time to type that response, but I didn't ask any of those questions about how to hook up a battery in series or parallel, I even started in the first line of my post that you quoted that "I am not running different packs mixed together..."

And you said something about my car stops running???? I have no idea what brought that up... I dont think I have ever said that my car "quits running..." (meaning I am stumped about why it no longer moves....) I said that packs only last so long blah blah blah... My speed control does have a low voltage cut off... but I have it disabled. I am not worried about going negative on my cells, and being that I am not running Lipos I am not really worried about going below 1.1V either. I don't think I said anything about my car not running, I might have missed it re reading the thread, but if I did say it quit running, it was 100% the case of a thermal shut down...and a thermal shutdown doesn't bother me one bit. (So long as I understand where the heat is coming from... like do I have it over geared for the size wheels that are on it... or do I have it running alot of start and stop really tight corninging where it is 90% of the time either accelorating or slowing down and not just running on a longer straight line... all kinds of reasons for a thermal shut down...

So, thank you for the info, I am sorry that I some how asked you to write a brief text book on the basics of batteries... It was not my intention to have the questions that you answered be asked... I am sorry if there was something that I missed saying or said that made you think that i needed those answers.

and thank you both for referring me to the MFG.


Best regards.