[lou-ace]

Reality check.
Ok guys, here’s the scenario. I’ve built the EV, (chassis 1994 Mazda b2300 truck, motor ADC 9” 4001, controller Curtis 1231c, pack 120v #20-6volt lead, crown GC 225 amp, new batts, 2-0 copper welding cable top mount connectors), I’ll start out in first gear and pull =500 amps than draw down to =100, 2nd gear the same to about 45 mph, 3rd will pull highway speeds of about 55-60 mph, on a flat grade, with some effort and continuous draw of 200-300 amps. This seems like A LOT of current. Now the front end does need a rebuild (which I’ve done and am now awaiting alignment at the shop), and I’m happy that none of the connections feel hot, nor does the controller heat up, nor does any of the wiring feel hot after a run at load, and the last run of 14 miles seemed to only use ¼ SOC, per hygrometry, still this still seems like A LOT of current. Does this seem like a normal current usage for this kind of build? I have no reference for the current usage for this vehicle and don’t know what kind of performance to expect and the math is squishy for performance estimation. Now it is winter and I’ve been testing the EV at 35-45 degrees f. hopefully my range performance will increase with warmer weather and some more optimization, and life on the lead pack. I’ve also put 30-50 wt oil in the trans (5speed manual) and rear end. Opinions??????????? Thanks again…… Lou-ace.

 

[Tesseract]

Reality check.
Ok guys, here’s the scenario. I’ve built th
...3rd will pull highway speeds of about 55-60 mph, on a flat grade, with some effort and continuous draw of 200-300 amps. This seems like A LOT of current. ...

What's the battery pack voltage sagging down to when drawing this much current? 120V x 250A is 30kW, which is a bit high for 55-60mph, even in an old pickup. But if your batteries are sagging down to 90V at this current then you are at a perfectly reasonable 22.5kW. Small, aerodynamic cars can get by with about 10-12kW at 60mph, but not an old, large pickup, especially if it has alignment issues, etc.

 

[peggus]

Nice looking conversion.

I believe your shunt is in the motor loop and not the battery loop. The battery current will start out low and increase as you accelerate, the motor current does the opposite, and exactly what you describe.

200-300motor amps is about what I'd expect.

Move the shunt to the battery side of the controller and you'll get more useful data for estimating your range.

 

[peggus]

Ah hah!

 

[Tesseract]

I believe your shunt is in the motor loop and not the battery loop. The battery current will start out low and increase as you accelerate, the motor current does the opposite, and exactly what you describe....

Good catch... I totally missed that but in retrospect it should have been totally obvious given the "starts out at 500A then drops down to 200-300A"...

Yeah, lou-ace, you are getting totally normal numbers for motor current. Battery current is what you need to be monitoring instead.

 

[Overlander23]

What's the battery pack voltage sagging down to when drawing this much current? 120V x 250A is 30kW, which is a bit high for 55-60mph, even in an old pickup.

Seeking clarification... if the vehicle is pulling 250 battery amps, but isn't necessarily spinning at its max rpm, is it using all 120V battery volts?

Even if you were drawing the full 120v from the battery pack @ 250A, wouldn't that be PWM delivered at a lower than 100% duty cycle? If so, would it be correct to say that, given his scenario (I'm assuming a constant speed, but not necessarily maxed throttle to maintain highway speeds), he's using 30kW (120V x 250A)?

Confused... Just trying to figure out the correlation between battery electrical usage under load vs motor usage as it pertains to the controller.

 

[Tesseract]

Seeking clarification... if the vehicle is pulling 250 battery amps, but isn't necessarily spinning at its max rpm, is it using all 120V battery volts?

Nope.

This only gets explained at least once a week, Jeff, but I'll go ahead and do it again for you...

In a modern PWM controller:

Battery Current = Motor Current / Duty Cycle
Motor Voltage = Battery Voltage * Duty Cycle
Power Out = Power In - Losses (which are usually 1-5%)

So..

Battery Voltage * Battery Current = Motor Voltage * Motor Current

Motor current will always be higher than or equal to battery current, so, motor voltage will always be less than or equal to battery voltage.

 

[EVfun]

In a modern PWM controller:

Battery Current = Motor Current / Duty Cycle
Motor Voltage = Battery Voltage * Duty Cycle
Power Out = Power In - Losses (which are usually 1-5%)

So..

Battery Voltage * Battery Current = Motor Voltage * Motor Current

Motor current will always be higher than or equal to battery current, so, motor voltage will always be less than or equal to battery voltage.

Very clearly and succinctly put. That should be a sticky around here.

 

[Tesseract]

Very clearly and succinctly put. That should be a sticky around here.

I've honed it with lots of practice

 

[lou-ace]

Ok! move the shunt, easy enough. Now Tesseract, voltage sags to around 104v @ 200-300 amps with full charge slightly less with some extra drain on the pack. Does this still work with the shunt on the motor side?I just got back from the alignment shop ( the front end was way out, fixed now), and noticed much better rolling and less sag and amp draw. the voltage now seems to sag to around 112 volts and draws more closely to 200 than 300 amps. It might be my imagination but it seems like this should make a huge difference to the range of the truck. I will move the shunt, do some runs and get back to ya all, with the new data,......... thanks again.

 

[peggus]

Good catch... I totally missed that but in retrospect it should have been totally obvious given the "starts out at 500A then drops down to 200-300A"...

Yeah Tess, how could you? I've completely lost all respect for you now!

 

[Tesseract]

Ok! move the shunt, easy enough. Now Tesseract, voltage sags to around 104v @ 200-300 amps with full charge slightly less with some extra drain on the pack. Does this still work with the shunt on the motor side?

No, lou-ace, you have to know battery current and battery voltage at the same time to calculate battery power. Battery voltage and motor current doesn't tell you anything (besides, well, battery voltage and motor current).

 

[Tesseract]

Yeah Tess, how could you? I've completely lost all respect for you now!

You mean you still had some?!?

 

[Woodsmith]

Hmmm, read this with interest and learnt a little more in the process.

So, if you had gauges showing battery voltage and current then you will know how much power you are using.
If you then also had a gauge showing motor current would that sort of indicate motor torque, ie how hard the motor is working and hence how efficently it is running at the time?

 

[major]

If you then also had a gauge showing motor current would that sort of indicate motor torque

Sure, for the series motor, torque is proportional to motor current.

ie how hard the motor is working

I guess you could say that, kinda, maybe, don't really want to get into definition of work and all that.

and hence how efficently it is running at the time?

Well here, no. Motor current alone will not tell you motor efficiency. You would need to know several other operational parameters.

However, from the motor current alone, you can make some gross assumptions about the operating condition. For example, if the vehicle speed and grade is such you are using 10 kW from the battery and your motor current is like 600 amps, you may have selected the wrong gear, running the motor too slow at too low a voltage and too high a current.

Battery current is needed to know your "fuel consumption". Motor current is needed to know if you are operating your motor within its ratings. Especially with self ventilated motors (those with shaft mounted fans), selecting a gear where the motor runs too slow and with too high a current can lead to motor overheating and even failures.

I think the best approach is to have both a battery ammeter and a motor ammeter, particularly if you encounter a lot of hills. A battery voltmeter is a must. And a motor tachometer so you can protect your motor from the other extreme, too low current and too high RPM

major

 

[ElectriCar]

Speaking of Tach's major, I'm looking at a standard automotive tach but am looking for a prox switch or something to drive it. Drawings are showing a signal input from the coil OR something else for electronic ignition. Any idea if that something else is low voltage?

I just hate to buy a tach and prox switch then find the tach doesn't respond to 12V pulses. Any ideas? I may start a new thread if I can't find a solution.

 

[jehan12413]

All tachs that I have used connect to low voltage (the primary side of the ign coil).

 

[ElectriCar]

I just ordered an Auto Meter gauge #3707. It's a small 8000RPM tach. Auto Meter also has a sensor for it so that took care of any questions I had. Entire package cost about $185 USD. This is the answer to a lot of peoples quest for a stand alone tach.

 

[Woodsmith]

Thanks major, thats a good answer and given I am having direct drive on the trike I guess it will help having a motor ammeter alongside the battery ammeter and voltmeter.

If you are using a tacho look for one that has a programmable shift light. You can use the shift light signal to interupt the controller throttle pot input to help reduce the chance of the motor spinning to death.

 

[Jimdear2]

I just ordered an Auto Meter gauge #3707. It's a small 8000RPM tach. Auto Meter also has a sensor for it so that took care of any questions I had. Entire package cost about $185 USD. This is the answer to a lot of peoples quest for a stand alone tach.

ElectriCar,

Do you have a link to that sensor, we have made up several different tachometer driver and runaway stopper circuits using aftermarket tachs with shift lights, home made pulse wheels and industrial prox switches. Some have required an additional driver board for the runaway system latching relay because some shift lights are LEDs instesd of bulbs.

Thanks,
Jim