# ramping up amps



## rwaudio (May 22, 2008)

dtbaker said:


> My dependable, cheap, old-fashioned Curtis 1221 controller seems to ramp up to (not even quite all the way up to) its rated max quite slowly. If I am in second gear and 'floor' it, I can watch the amps climb up to about 360 or so fairly gradually.....
> 
> Do different controllers 'ramp up' to maximum faster than others, or is this a function of the motor speed being able to suck up more amps at higher rpm?
> 
> what I am wondering is if a 'high performance' controller like Zilla or Soliton would offer quicker acceleration, even with the same max amp limit by vitue of a faster 'ramp up' of what it feeds the motor?


The biggest question is are you monitoring battery amps or motor amps?
If it's motor amps the Soliton family will "ramp up" at whatever rate you set in the software, so for the Soliton1 a 1000A/S rate would get you to full current in 1 second. The default (500A/S) would get you there in 2 seconds. 

If you are monitoring battery amps, it's going to climb gradually no matter what controller you are using because it's also related to RPM and load.


----------



## dtbaker (Jan 5, 2008)

rwaudio said:


> The biggest question is are you monitoring battery amps or motor amps?
> If it's motor amps the Soliton family will "ramp up" at whatever rate you set in the software, so for the Soliton1 a 1000A/S rate would get you to full current in 1 second. The default (500A/S) would get you there in 2 seconds.
> 
> If you are monitoring battery amps, it's going to climb gradually no matter what controller you are using because it's also related to RPM and load.


well... I guess I really don't know. the shunt is between my most neg battery cable and controller, so I guess that is battery amps. right?

if so, than a higher performance controller with a faster ramp setting would not really change performance since the amps used from the battery pack wouldn't really be available any faster (all else being equal), right?


----------



## rwaudio (May 22, 2008)

dtbaker said:


> well... I guess I really don't know. the shunt is between my most neg battery cable and controller, so I guess that is battery amps. right?
> 
> if so, than a higher performance controller with a faster ramp setting would not really change performance since the amps used from the battery pack wouldn't really be available any faster (all else being equal), right?


You are correct, you are measuring battery amps, so unless the ramp settings that Curtis uses are very conservative then a Soliton Jr. for example wouldn't change performance that much everything else being equal, unless you are exceeding the continuous current capability of the controller. 

If it's possible in your setup, you could move the shunt to the motor loop, even just to test, then you can watch how quickly the current ramps to full.


----------



## dtbaker (Jan 5, 2008)

rwaudio said:


> You are correct, you are measuring battery amps, so unless the ramp settings that Curtis uses are very conservative then a Soliton Jr. for example wouldn't change performance that much everything else being equal, unless you are exceeding the continuous current capability of the controller.
> 
> If it's possible in your setup, you could move the shunt to the motor loop, even just to test, then you can watch how quickly the current ramps to full.



I might be able to move the shunt to check out of curiosity... or maybe I can find this info in the Curtis manual somewhere. I would bet it isn't TOO slow, so is probably just limited by how many amps the motor CAN suck up at low rpm.


----------



## EV-propulsion.com (Jun 1, 2009)

I believe the 1221 has an acceleration rate adjustment like the 1231. have you tried that? it may make a little difference. There is a curtis manual available at www.curtisinst.com if you don't have one that explains it. Also, use an insulated screwdriver for adjustments.
Mike
www.EV-propulsion.com


----------



## dtbaker (Jan 5, 2008)

EV-propulsion.com said:


> I believe the 1221 has an acceleration rate adjustment like the 1231. have you tried that? it may make a little difference. There is a curtis manual available at www.curtisinst.com if you don't have one that explains it. Also, use and insulated screwdriver for adjustments.
> Mike
> www.EV-propulsion.com


I did finds the manual, at
http://curtisinstruments.com/index.cfm?fuseaction=cProducts.DownloadPDF&file=12092.pdf

and on page 25 it does say there is a pot screw under the cover bolt that changes the accelerate rate. I hesitate to screw with it without knowing any more about it, or what the 'default' is. I am tempted to try giving it a twist just to see if it makes any difference.....


----------



## EVfun (Mar 14, 2010)

Those are delicate little trim pots so don't go "cranking." That said, I turned the throttle ramp rate and current limit pots up to max. Just be gentle, it takes no more force than having the shaft of a small screwdriver between your thumb and index finger. 

If you are taking off in second gear I would guess it's the slowly increasing motor rpm that is limiting the ramp rate. I recommend taking off in first gear with an old Curtis 1221, they don't monitor the temperature of the freewheel diodes. If they heat up to quick the controller can die.

If you where using a Zilla or Soliton the current would ramp up faster with the same 400 amp battery current limit because the motor current could be higher. With the extra torque the vehicle would accelerate more quickly. If you had the controller set up with a 400 battery amp / 600 motor amp limit you would have 50% more torque at lower rpms. You would hit 400 battery amps at about 2/3 the motor rpm you do now and the current would hang at 400 amps up to the point where it starts declining again with the Curtis. In short, you would have the same peak power but with a broader flatter peak and more low end torque.


----------



## dtbaker (Jan 5, 2008)

EVfun said:


> Those are delicate little trim pots so don't go "cranking." That said, I turned the throttle ramp rate and current limit pots up to max. Just be gentle, ... you would have the same peak power but with a broader flatter peak and more low end torque.


ok, I may be inspired to try this at some point... perhaps make an attempt at some timed test on a specific stretch of road. I want to go make a few runs with the controller unchanged to compare with some times I took with a 96v lead pack versus the upgraded 120v Li pack.... sure FEELS different!

I am not too worried about overheat from extended pulls since I do not do any constant highway miles, just suburban with stop/go.

When I don't have anyone behind me I often just leave it in 2nd gear, but if I need to get off the line with traffic, I do use first.... and now I can keep up with all but the muscle cars.


----------



## Qer (May 7, 2008)

Ok, if I were you I wouldn't touch anything on the controller without first measuring the motor current, because the battery current doesn't tell you jack.

Typically back-EMF will be proportional to RPM so if we ignore the losses in the motor your motor Voltage will "accelerate" in sync with the car (and the losses will show as a motor offset decided by Imotor * Ri). This means that a motor that's still will have the voltage of:

Umotor = Imotor * Ri

which is pretty damn close to a short circuit. This is important to keep in mind!

So what will happen when you floor it is that the controller will pump out maximum current at zero Volt (or rather 400*Ri Volt which, if I'd guess, would be somewhere around 10-15 Volt total with cable losses etc). Let's say you have a perfect pack of 100 Volt that never sag (I wanna keep it simple) and a motor Voltage that's 10 Volt @ 400 Ampere and 0 RPM you get:

Umotor = Ubattery * D

where D is the duration of the PWM (between 0 and 1, 0 is completely off, 1 is completely on). That gives:

D = Umotor / Ubattery = 10/100 = 0.1

Now, the difference between motor and battery current looks similar (but the opposite), ie:

Ibattery = Imotor * D = 400 * 0.1 = 40 Ampere.

So your motor current is 400 Ampere but battery current is only 40 Ampere since the only thing you feed is the internal losses of the motor (and the efficiency of the motor is 0%) but as the motor start to gain speed the motor voltage increases so at 50 Volt over the motor (back-EMF + I*Ri) and 400 Ampere motor current D is 0.5 and your battery current is 200 Ampere.

When back-EMF + I*Ri hit pack voltage D becomes 1 and motor and battery current becomes equal (which is when you read 360 Amp on your gauge) any increase in speed (and thus back-EMF) will start to decrease the current (and since D is 1 motor and battery current are still equal) and you will see the current starting to drop.

This is the same for all DC-controllers (AC-controllers behave similar, but more complex) and as long as you measure battery current rather than motor current the "ramp" you see is actually just the effect of a perfectly working controller and the laws of physics. Ie, completely pointless for the information you're looking for.

Will a Jr accelerate faster? Hell yes, but not because you can set the ramp but simply because it can dish out 50% higher motor current. Just like EVfun said.

Oh, and the motor can't "suck Amps". The controller force feed the motor a certain voltage that turns into current which result in a certain amount of torque/power that the motor has to convert into mechanical movement. Or simply die trying.


----------



## EVfun (Mar 14, 2010)

Qer said:


> Ok, if I were you I wouldn't touch anything on the controller without first measuring the motor current, because the battery current doesn't tell you jack.


The pots in question are designed to be user adjustable. One is the current limit, up to the controller max of 400 amps. The other is throttle ramp rate and it feels like an RC network working against the pot. Even maxed out the Curtis won't ramp up all that fast. That's a good thing (in this case) because the B model (1221b) has a hard time limiting current fast enough near stall.


----------



## Qer (May 7, 2008)

EVfun said:


> That's a good thing (in this case) because the B model (1221b) has a hard time limiting current fast enough near stall.


I can see why from our experiments on the dyno, it doesn't take much pulse width for the current to suddenly leap up, it's much easier and smoother to handle the current as soon as the motor start to spin at a reasonable speed. I'm not surprised that Curtis implemented the 1.5 kHz mode (aka squealing) on the 1231...


----------



## dtbaker (Jan 5, 2008)

I favor durability and dependability over max performance in this case which was why I picked the curtis 1221c in the first place. I probably won't mess with the pots at all, I just want to know more about it and the pros/cons. 

I have not been able to find what the factory default is supposed to be set to, and I don't see how to measure what the change would be be if I gave the ramp rate a turn, so I hesitate to mess with it!


----------



## honn1002 (Nov 26, 2008)

dtbaker said:


> I favor durability and dependability over max performance in this case which was why I picked the curtis 1221c in the first place. I probably won't mess with the pots at all, I just want to know more about it and the pros/cons.
> 
> I have not been able to find what the factory default is supposed to be set to, and I don't see how to measure what the change would be be if I gave the ramp rate a turn, so I hesitate to mess with it!


The accel pot and current limit pot are user adjustable. The factory default setting for accel pot is linear (medium throttle response). Take a flash light and look at the last pot to the right. The pot has an arrow indicating clock at 1:30 which is default setting. You can adjust it clockwise to max 4:00 and get instant throttle response. You'll feel the difference when you step on the throttle pedal.


----------

