AA Cells versus SC Cells?

[Cildein]

I was looking at the space I have to mount my batteries and I got to thinking. Why not use AA cells? Their size allows me to put more of them in the emaxx axle/arm (where the shock is usually positioned) I am using and if I put two sets of five (6v) in parrallel (2300mah AA) I should get something close to 4600mah power! This would really work better then my 2 SC cells in series at 4.8vols (3200 mah). I am running a EVX with johnson motor.

If this would not work is there a slightly smaller than SC cell that I could use maybe?

[Davkin]

I use GP1100 2/3A cells in my TLT. I think the GP1100's are the only cells that small that will give you enough juice to handle a mild 540 or 550 motor. I'm running a 550 cordless drill motor in my TLT and the GP1100's handle it just fine, never even get warm and no noticble drop in performance from the SC's, but a much lower CG that is very noticible when crawling. The GP1100 is the only cell I'd try this with though, most small cells can't handle the current. You can get GP1100's at www.cheapbatterypacks.com If you are using a hotter motor such as a competition 27T or even an MM I'm don't I'd use them, but they should handle a lathe motor or similar just fine.

David

[Cildein]

Actually cheap packs has a 1650 AA cell that I am ordering that can handle up to 20 amps. I planned on doing two sets in parrallel which should be able to handle bursts in the 40 amps!

[DirkDigler]

There is more internal resistance in the smaller cells, therefore will burn up quicker than a SC

[Davkin]

Actually cheap packs has a 1650 AA cell that I am ordering that can handle up to 20 amps

A 20 amp cell may be pushing it. Maybe try only four or five cells, lower voltage=lower amps.

parrallel which should be able to handle bursts in the 40 amps!

It doesn't work that way. No matter how you wire them you only get the 20 amps of current handling, that's a limitation of the cell, the internal resistance as Digler puts it. Wiring in parallel only increases the capacity. No question a smaller cell, even the GP1100's will not last as many cycles under those kinds of loads, assuming they can deliver the current needed at all. I'm pretty darn confident in my GP1100's though. After heavy usage on six cells they hardly even get warm.

David

[Ace]

I ran 8 cell AA packs at our last comp in my clod w/ lathe motors.

Worked EXTREMELY well. The 8 cells made for about 10% more punch than my 6 cell 3000 nimh's. Run time was excellent (30-40 minutes of continous hard crawling).

I got 60 2250mAh "Powerizer" cells off ebay for $60 buy it now. So that makes the packs about $8 a piece! (+ a deans connector)

Would they work in a shafty running Magmayhems? Maybe dunno.

I do know they were just warm after running them in my clod...

I also know I won't be buying sub C's for a clod anytime soon!

[Cildein]

Here is the motor I am using and I forgot to mention I have it hooked up to a GD-600 with 2.5 gear.

http://www.allelectronics.com/cgi-bi...165&type=store

What I need to do is get an ampmeter and use it on my SC cells. See what the rating is under load and go from there.

[EeePee]

Look into 4/5A cells, less internal resistance than AA, or 2/3A cells, and about the same size as AAs.

[JohnRobHolmes]

subject- wiring two packs in parallel will increase the current handling

Originally Posted by Davkin

It doesn't work that way. No matter how you wire them you only get the 20 amps of current handling,.... Wiring in parallel only increases the capacity. ......
David

Actually, wiring packs in parallel DOES increase current handling of the cells. if he wired two packs in parallel he would have 40 amps of current burst available, and double the runtime. this is only necessary if the packs cant handle the current. check the battery temp when running the first few times and make sure they dont get past 150*F.

just run one pack at a time if the cells can take it. the extra weight just makes the motors work harder.

[Cildein]

Originally Posted by johnrobholmes

subject- wiring two packs in parallel will increase the current handling


Actually, wiring packs in parallel DOES increase current handling of the cells. if he wired two packs in parallel he would have 40 amps of current burst available, and double the runtime. this is only necessary if the packs cant handle the current. check the battery temp when running the first few times and make sure they dont get past 150*F.

just run one pack at a time if the cells can take it. the extra weight just makes the motors work harder.

What is funny about this subject is that i have asked at least 4 people who are electricians and they all had both yes and no anwsers. Cheapbatterypacks guys told me yes it would burst to 40 amps. I tried with one pack and hooked up my multimeter that goes to 20 amps. Well under strain it went over 20amps and the pack heated up a little (warmish). I will try tomorrow with both packs in parallel and see how it runs. Just by holding it in place I can see/feel the difference between the SC cells doing 30+ amps and the AA cells. However this is not totally fair because the SC where in 7.2v versus the AA in 6v. Need to make my parallel connector!

[Davkin]

Well, I'm no electrician but common sense tells me you might get some increase in current handling capacity but nowhere near double. Maybe if all the conditions were just perfect, but this is the real world. I don't see a motor pulling current off each pack equally.

David

[BultacoJim]

Originally Posted by johnrobholmes

subject- wiring two packs in parallel will increase the current handling


Actually, wiring packs in parallel DOES increase current handling of the cells. if he wired two packs in parallel he would have 40 amps of current burst available, and double the runtime. this is only necessary if the packs cant handle the current. check the battery temp when running the first few times and make sure they dont get past 150*F.

just run one pack at a time if the cells can take it. the extra weight just makes the motors work harder.

Guys,
He’s 100% right. He definitely knows about batteries.
He said “40 amps of current burst available”. Depending on the resistance of the load “electric motor(s)”, the current will be: Current = Voltage / Resistance. 40A = 7.2V / .180 ohms
This means if the total resistance of your motor(s), ESC, and the wiring drops to .180 ohms under full throttle or full stall conditions, then two 20 amp batteries connected in parallel can “potentially” deliver 40 amps of current.

But remember, your motors only draw the amount of current it needs (depending on its’ resistance), not the maximum available from the power source. You have either 15 or 20 amps available in the 120v outlets in your home. Just because you plug in your LED nite-light into an outlet, 15 amps of current is not flowing through the device.

Davekin mentioned “the real world”. He’s right, batteries are not made perfectly equal and all batteries have internal resistance, wires have resistance, and ESCs will also present (very small) resistance. But at least on paper, two batteries connected in parallel will supply equal current flows.

Here’s a site from Interstate Batteries: http://www.ibsa.com/www_2001/content...battconnec.asp

CCA means Cold Cranking Amps (or Maximum current available at 0 degrees F)
Notice how it doubles when you hook two car batteries up in parallel.
Ever have your car “jumped” on a cold day?


Here’s another site, which answers the question, Why put Batteries in parallel.

http://www.4physics.com/phy_demo/bat...nParallel.html