How big of an A123 cell would it take to start a car? - RC-Monster Forums

hyperasus · **How big of an A123 cell would it take to start a car? -** 01.05.2009, 02:27 PM

I can't help but wonder how large of an A123 pack it would take to start a car. A 4cell A123 pack would put out 13.2volts.

sleebus.jones · 01.05.2009, 02:45 PM

In this case, it's the amps, not the volts. Probably a 4S10P would do it.

BrianG · 01.05.2009, 02:45 PM

Depends on engine size, temperature, etc. Car batteries are typically rated from 400-900 cold cranking amps (CCA). To get 900A from a 30C burst A123 cell, you'd need a 4s12p pack. But to keep voltage drop down, I'd use at least a 4s20p.

hyperasus · 01.06.2009, 05:05 PM

Wow. Thats alot more then I would have thought it would take. Oh well. Was a fun thought.

pb4ugo · 01.06.2009, 07:04 PM

How would the A123 batteries stay in a charged state? The alternator doesn't put out cc/cv, so I'm wondering.

_paralyzed_ · 01.06.2009, 10:10 PM

Quote:

Originally Posted by pb4ugo

How would the A123 batteries stay in a charged state? The alternator doesn't put out cc/cv, so I'm wondering.

not important with a123s. alot of people charge 3s packs with a wire directly attached to a car battery. the length of the cord determines current and a timed (15 min) charge gets it to proper votage.

MetalMan · 01.07.2009, 12:05 AM

Quote:

Originally Posted by _paralyzed_

not important with a123s. alot of people charge 3s packs with a wire directly attached to a car battery. the length of the cord determines current and a timed (15 min) charge gets it to proper votage.

That wire acts as a resistor, hence why it needs to be the proper length. However, the voltage an alternator puts out is typically low-to-mid 14v. This is too high for A123s and the wire won't decrease the end voltage.

sikeston34m · 01.07.2009, 12:21 AM

IIRC, the recommended charge voltage is 3.6 volts per cell on A123. 4X this is 14.4 volts.

I remember charging 4S2P A123 with an automotive type charger at 10 amps. It could even be cranked up to a 20 amp charge rate. The cells didn't seem to mind.

After the charge cycle completed, the voltage would settle back some, but with good results.

I'm not sure what the deadband or upper and lower voltages of most automotive type regulators is. But the charge termination voltage of the charger I used was 14.5 volts. In other words, the alternator does satisfy when the voltage comes up to 14+, and doesn't kick back in until voltage gets back down around 13.0 volts or so.

I've often thought about building an A123 pack like this. The longevity of it could be really good.

4S10p could produce a 700 CCA setup. This would yeild a 23AH Battery.

In thinking about this, a good Deep Cycle Battery averages 100ah.

The downside to all of this. It would require 40 cells. Gets expensive really quick.

I'm tempted to build a smaller version for testing on my 4 wheeler maybe.

lutach · 01.07.2009, 12:32 AM

Here you go guys:

www.tekbattery.com

The video:

http://www.youtube.com/watch?v=lyYBh...eature=related

_paralyzed_ · 01.07.2009, 12:41 AM

Quote:

Originally Posted by MetalMan

That wire acts as a resistor, hence why it needs to be the proper length. However, the voltage an alternator puts out is typically low-to-mid 14v. This is too high for A123s and the wire won't decrease the end voltage.

oh, the length sets the charge rate and the voltage is the voltage. Got it. My point was cc/cv wasn't necassary. Thanks MetalMan!

_paralyzed_ · 01.07.2009, 12:47 AM

Quote:

Originally Posted by _paralyzed_

oh, the length sets the charge rate and the voltage is the voltage. Got it. My point was cc/cv wasn't necassary. Thanks MetalMan!

necessary. Sorry guys. I realy hate mispelld wirds.

MetalMan · 01.07.2009, 02:42 PM

Quote:

Originally Posted by _paralyzed_

oh, the length sets the charge rate and the voltage is the voltage. Got it. My point was cc/cv wasn't necassary. Thanks MetalMan!

Well my point wasn't totally correct, I was comparing the voltage of 3s A123 to the output voltage of the alternator. But sike is right, the alternator output would be perfect for 4s A123. I just didn't consider it cuz the trick using the car battery to charge 3s A123 only works for 3s

.

What's_nitro? · 01.07.2009, 12:31 AM

THIS big!

What's_nitro? · 01.07.2009, 12:37 AM

That poor starter...

bruce750i · 01.07.2009, 04:17 PM

I remember having one of those wire chargers, it would heat up and cut through anything plastic it was laying on.
I had a 12v lead acid battery blow up in one of our work vans this year. It went Boom after a one hour trip of 15 to 16 volts charging it the whole time. Funny tho the battery still started the van one more time to go get another one. We changed the alternator only to have the same problem. After doing some reading the voltage was being controlled by some CPU. I guess thats where they get the voltage cut-off.