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View Full Version : What 7.2v battery pack do you use?



Matt Battle
08-16-2006, 09:39 PM
Hi everybody,

I am looking to use a 7.2v battery pack to run the BOE and was wondering what brand/company do you guys use/like for your projects/RC? I know the mAh I am looking for will be around 1900-2000. That will be an increase of 700 to 800 from the generic battery I am using now. Also what do you recommend between NiCd and NiMH? Thanks guys and girls.

Regards,
Matt

Robert Kubichek
08-16-2006, 09:50 PM
Matt Battle said...
Hi everybody,

I am looking to use a 7.2v battery pack to run the BOE and was wondering what brand/company do you guys use/like for your projects/RC? I know the mAh I am looking for will be around 1900-2000. That will be an increase of 700 to 800 from the generic battery I am using now. Also what do you recommend between NiCd and NiMH? Thanks guys and girls.

Regards,
Matt


I would look at a NiMH for greater power to weight ratio, and the fact that you do not have battery memory issues like you do with NiCd...
The NiMH packs used for RC hobbies are a good place to start, AND there are several online sites that make custom packs for a very reasonable price.

Bob http://forums.parallax.com/images/smilies/scool.gif

studysession
08-16-2006, 11:03 PM
I am considering hooking up my 7.4v 3700 Mah LiPo pack. Not sure if anyone else here is using LiPo or not. Light weight and longer runtimes in my RC cars and trucks. I use them in a electric Hyper 7 PBS 1/8 scale buggy that I converted from nitro to electric.

..

KB3JJG
08-16-2006, 11:10 PM
Radio Shack sells a 3300 MaH NiMh pack for 24.99 cat no 23-319 these are great packs for the $$$, they also have a 2000 MaH NiMH pack and charger combo for 24.99, cat no 23-322.

You might also check your local stores for clearance pricing on their old 3000mah pack, I picked a bunch of these up cheap not so long ago!

dandreae
08-17-2006, 01:28 AM
Tower Hobbies has a wide variety of batteries to choose from that are reasonably priced.

www.towerhobbies.com (http://www.towerhobbies.com)

Make sure to click to the third page of batteries that are listed.

Dave

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Tech Support
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Post Edited (Dave Andreae (Parallax)) : 8/16/2006 6:31:59 PM GMT

Matt Battle
08-17-2006, 04:06 AM
I see that everybody is talking about 3000mAh or higher batteries. I guess everybody hates to recharge on a daily basis also. Dave, I was planning on buy the battery from towerhobbies. They seem to have a good selection at a great price. It’s just crazy how I seen the price go from 10-15 bucks for ones around 2000mAh to 30-40 bucks to ones over 3000mAh. I might have to froogle to find some great sales.

Matt

bulkhead
08-17-2006, 10:13 AM
What are you running on your BOE? If you need a battery to deliver lots of current (30+ amps continuous) then spending the extra money ($30+) for brand name cells (such as GP) or for "matched" low internal resistance battery packs is worth it. This is often the case with high performance RC cars.

However, if you are just looking for better runtimes on your BOE, you can stick with lower performance batteries. The $25 GP 3300mah 7.2 pack at radioshack is a great deal. I probably wouldn't go any lower (in price or mah) than that. You may also want to consider www.cheapbatterypacks.com/main.asp?sid=602686&pgid=superlisting&type=car&manufacturer=4&model=23 (http://www.cheapbatterypacks.com/main.asp?sid=602686&pgid=superlisting&type=car&manufacturer=4&model=23), the elite 4300mah 7.2volt pack is $36 without the upgrade (again, the upgrade will only help if you need it). They can also custom make a pack to fit your needs.

Lipo's offer better power to weight ratio than Nimh's, which is why they are growing popular with RC, but the performance gain probably isn't noticeable or worth it for your BOE. They also pose more of a fire hazard risk than Nimh's (just look at dell).

Keep in mind with any of these batteries you should use a quality peak charger to properly charge these Nimh batteries. Overcharging can damage these batteries more severely than they could Nicd's. I would suggest this charger: www2.towerhobbies.com/cgi-bin/wti0001p?&I=LXCLD5&P=ML (http://www2.towerhobbies.com/cgi-bin/wti0001p?&I=LXCLD5&P=ML) since it displays all the charge info, and costs only about $20 more than the least expensive peak charger out there.

Matt Battle
08-17-2006, 10:46 AM
bulkhead said...
What are you running on your BOE? If you need a battery to deliver lots of current (30+ amps continuous) then spending the extra money ($30+) for brand name cells (such as GP) or for "matched" low internal resistance battery packs is worth it. This is often the case with high performance RC cars.

However, if you are just looking for better runtimes on your BOE, you can stick with lower performance batteries. The $25 GP 3300mah 7.2 pack at radioshack is a great deal. I probably wouldn't go any lower (in price or mah) than that. You may also want to consider www.cheapbatterypacks.com/main.asp?sid=602686&pgid=superlisting&type=car&manufacturer=4&model=23 (http://www.cheapbatterypacks.com/main.asp?sid=602686&pgid=superlisting&type=car&manufacturer=4&model=23), the elite 4300mah 7.2volt pack is $36 without the upgrade (again, the upgrade will only help if you need it). They can also custom make a pack to fit your needs.

Lipo's offer better power to weight ratio than Nimh's, which is why they are growing popular with RC, but the performance gain probably isn't noticeable or worth it for your BOE. They also pose more of a fire hazard risk than Nimh's (just look at dell).

Keep in mind with any of these batteries you should use a quality peak charger to properly charge these Nimh batteries. Overcharging can damage these batteries more severely than they could Nicd's. I would suggest this charger: www2.towerhobbies.com/cgi-bin/wti0001p?&I=LXCLD5&P=ML (http://www2.towerhobbies.com/cgi-bin/wti0001p?&I=LXCLD5&P=ML) since it displays all the charge info, and costs only about $20 more than the least expensive peak charger out there.


Bulkhead,

Thank you for questions and suggestions. My BOE is going to be mounted on a 1:10 scale RC car chassis. At the moment I am in the midst of redesigning an ESC to be powered through the 3-pin servo connector and also have a servo to control steering. That will be my platform that I will be using for the next couple of months to a year to test out numerous things; i.e. wireless communication, camera, sensors, and maybe a GPS. So I am trying to figure if one 7.2v battery that is around 3000-4000mAh will be enough to power all of this or maybe 2 2000-3000mAh battery. One for the platform and one for everything else.

Regards,
Matt

bulkhead
08-17-2006, 10:56 AM
Ok, sounds like you might need more power than the average BOE. What kind of motor will you be running? (ie # of turns). Since you are using it to carry around equipment, you should adjust the gear ratio for more torque, and that way, you can get away with using a lower quality pack. The battery upgrades are really only worth it if you race RC cars, where you will drain your 3000+mah pack in 5 minutes or so. In your case, I would still go with the GP3300 or the 4300, depending on your budget and needs. One option is to get two GP3300's from radioshack, so you can alternate and never be without a pack. However, I still wouldn't go lower than 3300 mah. Nimh sub-c packs typically start at about 3000mah anyways.

Matt Battle
08-17-2006, 11:12 AM
It is a 540 motor that came stock with the R/C car. I don't know if that tells you how many turns it is? So your saying that one 33000mAh is going to be enough? I going to have to do the math and see how long that will last. I might go with having two power sources on the platform just to make sure it can move around and do stuff for awhile before it needs a charge.


-Matt

bulkhead
08-17-2006, 11:32 AM
Well typically, the 540 motors that come with them aren't very fast. On average, you can get about 20 minutes of driving time with those. For your application, I am assuming you wont be driving around at top speed for 20 minutes, or doing any hard accelerating or corning, for that matter. A single 3300 pack should be plenty. Keep in mind the more weight (batteries) you add, the more power it will consume also. It may be better to simply alternate two packs, unless you absolutely need it to run non stop for over an hour or so.

iamscottym
08-17-2006, 11:49 AM
Just to clarify, bulkhead- dell's batteries are lithium ion, not lithium polymer. No one used polymer, aside from hobbyists..they're too dangerous(for the average consumer).

I second the 3300's...unless you can get your hands on liions (I use 3.6V 1100mAh liions to make packs...they're lighter)...though I used to use the 3300's from RS...they're a very good deal. The 4300's arent worth it in my opinion; almost double the price for an extra 1Ah? no thanks, Ill just buy a second pack and swap out when one dies.

Just out of curiousity- what car are you using?

Matt Battle
08-17-2006, 12:19 PM
bulkhead said...
Well typically, the 540 motors that come with them aren't very fast. On average, you can get about 20 minutes of driving time with those. For your application, I am assuming you wont be driving around at top speed for 20 minutes, or doing any hard accelerating or corning, for that matter. A single 3300 pack should be plenty. Keep in mind the more weight (batteries) you add, the more power it will consume also. It may be better to simply alternate two packs, unless you absolutely need it to run non stop for over an hour or so.


I was thinking of upgrading the motor down the road once the weight began to add up. I hope I can get more then 20 minutes of run time out of this. I don’t plan on driving the platform around at top speed. I still haven’t figured out what speed I want it to move yet. So I might be looking at 35-40 minutes per charge. If not then I might have to figure out some other type of power source.


iamscottym said...
Just to clarify, bulkhead- dell's batteries are lithium ion, not lithium polymer. No one used polymer, aside from hobbyists..they're too dangerous(for the average consumer).

I second the 3300's...unless you can get your hands on liions (I use 3.6V 1100mAh liions to make packs...they're lighter)...though I used to use the 3300's from RS...they're a very good deal. The 4300's arent worth it in my opinion; almost double the price for an extra 1Ah? no thanks, Ill just buy a second pack and swap out when one dies.

Just out of curiousity- what car are you using?


Then the 3300’s seem to be the pack I will be buying. Here is a link (http://cgi.ebay.com/ws/eBayISAPI.dll?ViewItem&ih=004&item=140014119081&rd=1&sspagename=STRK%3AMEWA%3AIT&rd=1) to the same car that I bought.

-Matt

studysession
08-17-2006, 09:44 PM
No offense, I will be very surprised if you get 20 min off a single 6 cell pack. Grant it I use motors that draw more load off the packs but I usually don't get over 10 or 12 minutes off 1/10 scale RC's.

Matt Battle
08-17-2006, 09:53 PM
studysession said...
No offense, I will be very surprised if you get 20 min off a single 6 cell pack. Grant it I use motors that draw more load off the packs but I usually don't get over 10 or 12 minutes off 1/10 scale RC's.


hmmm. I do not like the sound of that. I don't want to be following this thing around replacing its batteries every 10 minutes. Does anybody have any suggestions or ideas to fix this problem. I might have to start a new thread on this.

-Matt

studysession
08-17-2006, 10:02 PM
What I did is get two very high priced LiPo packs. Each 7.4v and 3700mah. Then ran in parallel. But your looking around $150 for that. That gives me over 30 minutes of runtime.

bulkhead
08-18-2006, 01:45 AM
Matt Battle said...

studysession said...
No offense, I will be very surprised if you get 20 min off a single 6 cell pack. Grant it I use motors that draw more load off the packs but I usually don't get over 10 or 12 minutes off 1/10 scale RC's.


hmmm. I do not like the sound of that. I don't want to be following this thing around replacing its batteries every 10 minutes. Does anybody have any suggestions or ideas to fix this problem. I might have to start a new thread on this.

-Matt


Again, given your application I would say it shouldn't be uncommon for you to get 3 or 4 times the runtime of a regularly driven RC car. Given the nature of the project, I doubt you will run it faster than 5mph or so. Most RC cars go at least 25mph, at that speed the battery is drained much faster than at 5mph, given road friction and air resitance (which increases exponentially). Also, many RC cars are driven offroad, which adds even more of a load to the motor, not an issue for you.

If you really want to be scientific about it, hook up a multimeter to your car when you get it and measure the current peak when you accelerate from a stop to a walking pace (or whatever you think will be your top speed). Take the peak current reading, and as your worst case scenario, calculate your runtimes with a 3.3Ah pack as if that peak current reading were the continuous current draw.

Steve Andrues
09-25-2006, 12:44 PM
I'll disagree with bulkhead. There is nothing from GP batteries that I would use in my outhouse. They build a good battery, but they do not build a great battery. If you want something that you would want to run for a long time, consider SAFT batteries. I use them in some of my aircraft applications, and have never had a problem (in the last 15 years). After 35 years in aviation I have tested more batteries than i would like to think about. The bottom line is that they work like you expect them to. There are several distributors in the Bay Area. Try Ni-Cad Syatems in Hayward.