# Too many amps?



## ZachR (Nov 26, 2007)

Hi all,

I'm Zach. I've been lurking on this list for a while, but this is my first post. I am building an ev from the ground up. The body and chassis are based on a Lamborghini Diablo Kit-car. I've been blogging about the build at http://www.electricdiablo.com

Currently, the chassis is drivable (I haven't mounted the body on it yet). So, it's basically a big go-cart. I've driven it around our parking lot many times. As it stands, it tops out at about 30mph. Everything seems to be running smoothly. Aerodynamically the bare chassis is probably quite poor. When the body is on it should have a drag coef of .32. 

For the drive system I have a Warp11 motor attached to an Audi 5000 5 speed transmission. I built the custom flywheel and adapter. The clutch is installed, but I haven't run the clutch lines yet, so I get to experience clutch-less shifting. However, I have a hard time feeling the difference is taking off from first vs forth gear. The tires are not exactly what you would call "low" rolling resistance. They are 18x9 rims on the front, 18x10s on the back (I know I am probably loosing efficiency there, but they look so good). On top of that, I have steering, suspension, and brakes. 

For electronics, I have a Zilla 2k wired up to 72v of lead acids. This is just the temporary setup for testing. Lithium is in my future. 

Here's the issue: on level ground, from a dead stop, if I floor it, I see about 500amps for a few seconds as it gets up to 30mph, then it pulls about 350 amps to keep it there. My gut tells me that 350amps is a bit high. (My gut could easily be wrong as this is my first electric car). Does 25.2KW sound reasonable to keep this car running at 30mph?

Thanks for your help,

Zach


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## Mastiff (Jan 11, 2008)

Most motors get more efficient at higher voltages, it could be that your motor is pulling a bit more amps than usual because of this.

The other reason is you could just have the transmission in too high of a gear.

An electric motor will pull more AMPS based on how much load is on it, reduce the load and it can pull less amps and use more RPMs using the voltage more efficiently.

Try watching your Amperage in 2nd gear then 3rd gear and 4th and try to maintain 30MPH each time(if you can) and watch your amperage draw.

I'm not a huge expert on this but experimenting is the best way to learn anything.


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## wakinyantanka (Apr 8, 2008)

First let me say 
kudos on the craftsmanship, nice work.
Second, I can't thank you enough for the picture of the zilla internals. I can't afford the one I need so I'm building my own, not to mention I like doing things myself.


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## Coley (Jul 26, 2007)

What does your car weigh, as driven in the test stage?

Mine is a boxy 1690lbs and at 40 mph on flat ground, 72 volt system, in 4th gear, I am pulling only 100 amps.

Possibly wheel alignment hasn't had the final adjustment?


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## Dennis (Feb 25, 2008)

> For electronics, I have a Zilla 2k wired up to 72v of lead acids. This is just the temporary setup for testing. Lithium is in my future.
> 
> Here's the issue: on level ground, from a dead stop, if I floor it, I see about 500amps for a few seconds as it gets up to 30mph, then it pulls about 350 amps to keep it there. My gut tells me that 350amps is a bit high. (My gut could easily be wrong as this is my first electric car). Does 25.2KW sound reasonable to keep this car running at 30mph?
> 
> ...



At 72 volts that seems about right, horespower wise and current wise if you look up the performance specs of your motor here: http://www.go-ev.com/images/003_20_WarP_11_Graph.jpg. It's probably putting out 90 Ft*Lbs at 350 amps and 160 Ft*Lbs at 500 amps limit if you set it to that setting of your controller. It will not hurt a Warp11 motor as that is within the high efficiency range of the motor to not cause any severe heating. It just so happens that they test with 72 volts, non controller (they did not use a constant torque type controller as evident by the torque curve, just a regular 72V power supply with maybe a max current start up limit)...

Btw, does your warp11 use the GE rugged style type brush holder or is it that crappy sheet metal spring type that barely puts pressure on the brushes?


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## the gas wizard (Apr 19, 2008)

i work in a dyno tuning shop here in australia and as a rule of thumb, you need about 12kw's to keep a large family car doing 100km/h on a flat road with no wind, once upto speed .........just a thought


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## CPLTECH (Sep 14, 2007)

Always heard that EV DC motors need 3-4000 RPM to keep the motor cool. Check max for your unit.
That many RPMs on the trans is hard to move reg lube around. Try RedLine MTL syn lube.
I like the clutch for faster shifting. Takes a long time for motor to slow down, but that is probably due to flywheel mass.
Depending on your gearbox ratios, I run 1st up to ~20, 2nd up to ~40, 3rd up to???, 4&5 never, on my 9” ADC motor.


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## major (Apr 4, 2008)

Hi Zach,

Yeah, sounds like too many amps to me. Can you give us more data? Actual voltage at the motor? Motor RRM? Did you try motoring with the wheels up? Careful not to overspeed the motor. See what the amp draw is with wheels spinning in air. Could be you have a bind in the driveline somewhere, or driving with the brakes on. Does the car coast down smoothly?

Regards,

major


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## ZachR (Nov 26, 2007)

Hi everyone,

Thanks for the replies. I'll be working on the car tomorrow morning and it sounds like I should run some "wheels up" tests to verify my drive line is smooth. I'll also do some data collection to verify RPM, current, voltage of both batteries and motor. I can capture the zilla DAQ info and generate all kind of graphs. I might even toss in a few more batteries just to get the voltage up a little to see if that makes a difference. Stay tuned...

Zach


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## Hi Torque Electric (Dec 23, 2007)

Hey Dennis

To my knowlege, all Warps run with the thicker brass holders (kind of like to think I had a hand in that 8^) but it isn't because they didn't put enough pressure on the brush (actually those springs weren't the issue) but if over heated the sheet metal would warp (no pun intended) grabbing the brush, which prevented it from making good contact with the comm which in turn would cause it to arc bad until it lost contatct all together.

Zach, with just 72 volts the amps will be higher than if run at a higher voltage. The other issue you're facing is probably due to the motor being brush advanced for a higher voltage as is probably set at 12.5 degrees which isn't needed for 72 volts. If Li are far away I'd advise moving the comm plate to the neutral timing holes where eff and torque will be better, although you'll loose some top end speed.

Hope this helps.
Jim Husted
Hi-Torque Electric


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## aeroscott (Jan 5, 2008)

Coley said:


> What does your car weigh, as driven in the test stage?
> 
> Mine is a boxy 1690lbs and at 40 mph on flat ground, 72 volt system, in 4th gear, I am pulling only 100 amps.
> 
> Possibly wheel alignment hasn't had the final adjustment?


 thats 2880 watt hours / 40 mph = 72 watts/ mile do I have this right ? with 3 meters of this new nano solar panel you could run down the road on solar alone. met a U C Davis grad student at a ev meeting last night working on this pannel same tech applies to batteries . these nanos pick up infra red and convert it . if that works in a battery wow .sorry for the drift


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## MrCrabs (Mar 7, 2008)

aeroscott said:


> thats 2880 watt hours / 40 mph = 72 watts/ mile do I have this right ?


wouldn't 72 v * 100 amp = 7200 watts?
7200 watts * 1 hr / 40 miles = 180 watt hrs / mile

Coley, what kind of car is this? under 1700 lbs sounds pretty light to me...


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## ZachR (Nov 26, 2007)

Here is the data I collected last weekend. For the tests, I started in first gear and went through each up to fifth. Next time I run this test I will make sure to get to the same RPM in each gear. For the wheels down test, I was driving around a very large parking lot. I would estimate I hit a top speed between 35 and 40mph. For completeness, here are my gear ratios:
1st - 3.6
2nd - 2.13
3rd - 1.36
4th - .97
5th - .73

Final 4.11

I'm still trying to get my head wrapped around the data. Any help with this is appreciated...


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## major (Apr 4, 2008)

Hi ZachR,

Nice data, although a little tough to interrupt due to scales and offsets. But from what I can see, using 
http://www.go-ev.com/images/003_20_WarP_11_Graph.jpg 
which is the motor, I think, it makes sense. There are a couple of points (or short stretches) in the wheels up data where the system is in equilibrium. These show about 2000 watts. So there is not excessive driveline drag, maybe a little high.

With the wheels on the road, there are also a few areas of equilibrium where you can make sense out of it. And these match the motor curve pretty well.

The main thing here is you are powering a heavy vehicle (I think) with a low voltage. Yeah, the power for the speeds looks somewhat high, but hard telling if you are driving straight or turning. Anyway, you don't say what batteries you use. And there is a significant droop at running currents. Maybe close to 60 volts at 300 amps and 50+ at 500 amps.

I suggest you try for higher motor RPM. This is done by leaving it in a lower gear. As the RPM come up, you will lose torque, or acceleration. This can be offset by increasing battery voltage. I think you should be trying to cruise at 3000 RPM. Maybe higher. You might want to check with the motor vendor about safe RPM limit.

Regards,

major


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## dataman19 (Oct 7, 2009)

Major,
So what I get from your posts is that you want to keep RPM high?
..
Does this mostly apply to a DC Motor? Or is it the same with AC Drive?
..
Just asking..
..
dataman19


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