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  #1  
Old 10-19-2008, 09:25 PM
Hondacrzy Hondacrzy is offline
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Default Battery amps or motor amps???

So if I am only running one amp meter, do I want the motor amps or battery amps? Which one is most useful and which one is most common? I did read some are using two amp meters but is it necessary or just a want on their part.
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  #2  
Old 10-20-2008, 01:10 AM
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Default Re: Battery amps or motor amps???

I personally purchased two shunts, and 1 meter. A switch will allow me to switch between the two locations. For the extra cost of a shunt, it's a win win to me.

I can see both sides of the argument, motor amps won't tell you if something else is going south on you, and battery amps aren't going to accurately tell you what's happening with your motor. So, why not do both?
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Old 10-20-2008, 01:57 AM
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Default Re: Battery amps or motor amps???

This is the way to go. Two shunts, two fuses, one switch and one meter. Isolated from auto ground. Keep in mind that these are shunted off the main power pack and you must have them fused. It is nice to have a simple setup that allows for monitoring both with one gauge.


Pete : )

Quote:
Originally Posted by gmijackso View Post
I personally purchased two shunts, and 1 meter. A switch will allow me to switch between the two locations. For the extra cost of a shunt, it's a win win to me.

I can see both sides of the argument, motor amps won't tell you if something else is going south on you, and battery amps aren't going to accurately tell you what's happening with your motor. So, why not do both?
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Old 10-20-2008, 02:11 AM
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Default Re: Battery amps or motor amps???

Motor mounted will give you some kind of coarse torque meter which might be fun but probably not entirely useful in every days life. It might be a good thing to have if you ever encounter problems (like a controller that misbehaves) though. Battery pack mounted will give you an estimate of your "eco driving", making it possible for you to see what gear that pulls the least energy out of the pack.

So without having an EV (but pretty experienced in the field of general short circuits ) I'd say the pack current is most useful as long as things work as intended.
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Old 10-20-2008, 10:21 AM
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Default Re: Battery amps or motor amps???

I find battery amps is most useful and meaningful. A lot of Motor amps is just hystereses maintaining current flow between pulses although it is the reason for the higher efficiency and higher torque output and smooth performance of modern PWM controllers, don't forget to keep wiring from motor to controller as SHORT as possible, so if you put the motor in the back, put the controller there too, or both in the front.. Of course the shunt goes in the battery wiring, after the contactor, then a one amp or less 250 volt rated fuse and holder go in each of the two wires from the shunt to the indicator, mount the fuses (2) as close to the shunt as possible. And connect to the indicator with 250 v. or better wires. I like to connect my pack charger to the junction of the shunt and the contactor, so the meter shows charging current too.
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  #6  
Old 10-20-2008, 05:00 PM
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Default Re: Battery amps or motor amps???

What is the ball park differences you see on motor amps verses battery amps??? Is it 1/2 60% again just a ball park idea.

Brian
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Old 10-20-2008, 10:34 PM
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Default Re: Battery amps or motor amps???

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Originally Posted by rctous View Post
What is the ball park differences you see on motor amps verses battery amps??? Is it 1/2 60% again just a ball park idea.

Brian
I don't have mine up and running but theoretically the relationship between battery amps and motor amps should vary depending on what speed you are running the motor at, right? Power equals volts times amps. Theoretically, power at the battery and the motor should be the same (ignoring losses in the controller and accessories). However, if the car controllers are like most DC drives, the motor voltage will vary with speed. So if you have full voltage at the batteries but say only half the voltage at the motor (and you ignored controller heat loss) you'd see twice as many amps at the motor as you would at the battery.

Someone who has real life experience should really chime but theoretically that should hold true.
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Old 10-26-2008, 09:58 PM
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Default Re: Battery amps or motor amps???

Quote:
Originally Posted by Engineering Manager View Post
I like to connect my pack charger to the junction of the shunt and the contactor, so the meter shows charging current too.
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E.M.

Can you expound on this? My shunt is in series from pack positive to contactor then controller. My charger is connected at pack negative and at the shunt input (pack positive). How would I monitor charging current?
Would I simply connect the charger to the output of the shunt?

Thanks.

Z.D.
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  #9  
Old 10-27-2008, 03:49 AM
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Default Re: Battery amps or motor amps???

Zendaddy - See attached picture.

In general: there should be a microswitch in the charger inlet port that interrupts power to the battery pack contactor coil whenever a plug is inserted into it (or some other means of preventing said contactor from being energized while the charger is plugged in).

Battery Amps: the average amps drawn from the pack times the pack voltage gives you the kw consumed - i.e., the EV equivalent of the gas gauge. Battery amps = motor amps * PWM duty cycle, more or less.

Motor Amps: practically irrelevant to the driver; critically important to the controller.

Hope this helps.
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  #10  
Old 10-28-2008, 09:35 AM
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Default Re: Battery amps or motor amps???

When I think about monitoring charging and discharging amps using same meter 2 things come to mind, charging current is opposite direction than discharging and generally 10 times less amount. So the needle on the meter will be moving to the left of 0 mark and will only move a small fraction on a typical 0-400 Amp meter if charging current is only 15-20 Amps. Of course I am assuming small analog 0-400 ammeter that I have, results may vary with digital meters, etc.
In my scenario this doesn't look very practical.
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