# AH , max amps and parallel ?'s



## clintster7 (Jun 29, 2010)

I have a few questions about parallel and its effect on the hot crank amp ratings 
here is a battery info just for example ..


BATTERY PERFORMANCE
Category Motorcycle / Powersports
Ahr (amp hours) @ 10 hr. rate 7Ahr
Pulse Discharge (HCA)
310 cranking amps for 5 seconds
250 cranking amps for 10 seconds
225 cranking amps for 20 seconds
200 cranking amps for 30 seconds
HCA @ 80°F (27°C) 200A
CA @ 32°F (0°C) 150A
CCA 100 A
Reserve Capacity @ 25 A 9 min.
Cycle Life (Deep cycle capability) 400 @ 100% DOD (depth of discharge)
500 @ 80% DOD
Temperature Range -40°F (-40°C) to 140°F (54°C)
Resistance at 1 kHz @ 77°F 27m Ohms
Short circuit current 455A
Terminals Female threaded for M6 stainless bolt
Max. installation torque 50 in-lb.


now one of my questions is theoretically could I run the full 350 amps through a electric motor for 5 seconds . 

If 2 of the batteries are put in parallel would the hot crank amps double or would only the AH rating double ?


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## major (Apr 4, 2008)

clintster7 said:


> I have a few questions about parallel and its effect on the hot crank amp ratings
> here is a battery info just for example ..
> 
> 
> ...


If the motor and external resistance was 0.007 ohm and there was no rotation, yes.



> If 2 of the batteries are put in parallel would the hot crank amps double or would only the AH rating double?


The current for the pair of batteries is twice that of a single battery and the charge (Ahr) for a pair batteries is twice. The current and charge for each battery remains the same. But to draw twice the current from the pair of batteries in parallel, the load resistance would have to halve.

And the charge (7 Ahr) is specified at the 10 hr rate, so if this is a Pb-Acid battery, expect about one fifth of that at high current, or like about 1 to 2 Ah.


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## clintster7 (Jun 29, 2010)

..so the answer is "yes"? 
if I had 2 batteries with 200 (HCA) put in parallel it would give me 400 (HCA) not just double the AH


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## clintster7 (Jun 29, 2010)

in the example above it has this
"short circuit current 455A" 
what exactly does that mean ? And how would the short circuit come about or cause it


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## major (Apr 4, 2008)

clintster7 said:


> in the example above it has this
> "short circuit current 455A"
> what exactly does that mean ? And how would the short circuit come about or cause it


clint,

Maybe you should read up on electricity fundamentals. 

Short circuit means a zero resistance path. So, for a short circuit current on a battery, take a large gauge wire or like a copper bar and connect it to the positive and negative terminals of the battery. The battery then will be _short circuited_. Obviously this is something you do not want to do on purpose. The only thing which will result from this is internal heat in the battery.

The battery in your example has an internal resistance of 0.027 ohms. So at 12 volts, a short circuit (meaning zero resistance connected to the terminals), will have only the internal resistance. 12V ÷ 0.027Ω = 444A. Close enough to the 455A specified.

About the only thing useful from the short circuit current figure is that you can divide it in half to get the current at which peak power will occur. So, 444 ÷ 2 = 222A. And that will also be at one half of the battery terminal voltage. So 6V * 222A = 1332W. 1.332kW is the peak power for this battery.

The power curve (versus current) is a parabola with zero power at zero current (open circuit) and zero power at short circuit current and peak power at half way in between. For engine cranking applications, operation at current beyond peak power can be of value. But in a power conversion application, it makes no sense to operate the battery at a current above one half of the short circuit value.

So for the example battery, you would never want to go above 222A. And in fact, due to the nature of the parabola, the closer you get to the peak, the less power per amp you get. I would think it would not be beneficial to run this battery above 150, maybe 175A max. That would give you 1273W. Or about 1.7 hp/battery before any losses in the motor and control circuit. Figuring efficiencies of the power conversion and transmission, I'd estimate each battery could put about 1 to 1.2hp to the wheels.

Regards,

major


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## clintster7 (Jun 29, 2010)

ok I would never want to short circet the battery that's what I thought but what I'm asking is would the battery short circuit wit 2 batteries in parallel say 300 and 300 amps each ..thats 300 total amps that's above the short circuit rating ..


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## major (Apr 4, 2008)

clintster7 said:


> ok I would never want to short circet the battery that's what I thought but what I'm asking is would the battery short circuit wit 2 batteries in parallel say 300 and 300 amps each ..thats 300 total amps that's above the short circuit rating ..


clint,

Your question doesn't make sense.

Using the example, with one battery, if you connect a load of 0.013Ω, then the battery will deliver 300A to that load. If you have 2 of those batteries in parallel and connect a load of 0.0065Ω, then the load will see 600A, but each battery will deliver 300A.

If you short circuit one battery, the short across the terminals will conduct 444A. If you connect 2 batteries in parallel and short circuit the pair, then the short will carry 888A and each battery will deliver 444A.

major


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## clintster7 (Jun 29, 2010)

it just clicked in my head what you are saying .. The amp load is split and the amp from one batterie does not go through the other at all ..right


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## clintster7 (Jun 29, 2010)

clintster7 said:


> ok I would never want to short circet the battery that's what I thought but what I'm asking is would the battery short circuit wit 2 batteries in parallel say 300 and 300 amps each ..thats 300 total amps that's above the short circuit rating ..


sorry i did this post while doing other stuff .. I used my phone .. I know it dont make sense and I now understand what u are telling me now but just for clarification on this .. it should of said 

"I would never want to short circuit a battery ( that's what I thought) But what I'm asking is would the battery short circuit with two batteries in parallel say 300 and 300 amps each ..thats *600* total amps. 600 amps is above the short circuit rating .."

Sorry I just now got to a computer with a keyboard 

thanks that was a big help .. here is a page I found and saw the diagram of four batteries in parallel with the one in the middle busted .. I reread it and now understand 
http://www.batteryuniversity.com/partone-24.htm

thanks again


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## clintster7 (Jun 29, 2010)

It has been a while and I re read this thread . I think i missed the mark on this one . 

let me try agian .

To short circuit a battery is not something you would want to do mainly 
because that would mean the electric motor is not turning at all once the motor is moving the less amps that can flow " related to load of course " 

but theoretically for a split second a motor could pull the max available amps from a given battery . The max available amps a battery can give in this example is relative to the battery temp . 

For a internal short in this battery to occur the internal temp of the battery will have to be very high .. rather it be due to an external short {post to post} heating up the battery or a combo of heatsoak and an external short . 

*Am I correct to say that internal short would not happen on a cold day and I put a copper wire across the post for say 2 seconds " that would represent an external short" but would not give the battery an internal short due to the internal temp but it would be the start of the internal temp rising ?*


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