# Battery Cranking Amps rating in relation to peak motor Current draw?



## Catrell92 (7 mo ago)

Hey guys, just out of curiosity, how exactly does the Cranking Amps rating come into play as far as battery/motor selection when planning out an EV powertrain? 

Is the CA rating considered the overall "cap" as far as the peak current that the motor is allowed to draw/ What it can support current draw wise?

lets use this as an example.

*Motor/inverter: *
-AC35 Motor (676 Amps- Peak current draw @ peak TQ) 
-72 Volts 
-Curtis 72-96v 900A Inverter

*Battery:* 
XS Power D950 AGM Deep cycle battery
-605 CA
-2,100 Max Amps
-40 Ah
(Ran in a 6S-2P Configuration)
(two packs of (6) and both packs ran in parallel)


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## kennybobby (Aug 10, 2012)

The CA is a rating that it can pull 605 Amps for 30 seconds at 0 F with the battery voltage not dropping below 7.x Volts. That brief usage would use nearly 25% of the useful capacity out of the battery without damage. Do that 4 times and you are basically out of useful energy in your battery, so 2 minutes and its all over--kinda like havin sex...

It is not very useful for an EV. Likewise for the peak or Max Amps, it is for only a brief burst of less than a second or so depending upon their definition and testing.

You need to know the continuous current rating to know whether these would be suitable for your vehicle, but now days the use of lead acid batteries is a non-starter for most applications. i don't think your example motor/inverter would operate very long using lead acid, plus the weight penalty for such low performance battery technology.


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## Catrell92 (7 mo ago)

kennybobby said:


> The CA is a rating that it can pull 605 Amps for 30 seconds at 0 F with the battery voltage not dropping below 7.x Volts. That brief usage would use nearly 25% of the useful capacity out of the battery without damage. Do that 4 times and you are basically out of useful energy in your battery, so 2 minutes and its all over--kinda like havin sex...
> 
> It is not very useful for an EV. Likewise for the peak or Max Amps, it is for only a brief burst of less than a second or so depending upon their definition and testing.
> 
> You need to know the continuous current rating to know whether these would be suitable for your vehicle, but now days the use of lead acid batteries is a non-starter for most applications. i don't think your example motor/inverter would operate very long using lead acid, plus the weight penalty for such low performance battery technology.


Sorry I Should have elaborated a bit more. The vehicle would not be for road use at all. pretty much a low speed crawler (10-15 mph tops) its pretty heavy though


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## kennybobby (Aug 10, 2012)

What's the estimated weight, and the top speed you need to run? And what range do you want/need?

Does it use wheels and tires, or tank tracks? What is the gear ratio of the drivetrain from motor to tires?


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## remy_martian (Feb 4, 2019)

It looks like, with the way you sized the motor & controller, you're trying to pull 400A to 500A continuously. 

Your batteries will be dead in ~12 minutes.


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