# Suspiciously slow



## schmidtbag (Aug 7, 2019)

I've been working on converting a 1977 VW Rabbit with a 4-speed manual transmission for the past 3 years. Here are the specs:

AC-20, since at 96V it has a little less HP than the original 1.6L engine the car came with.
I'm using 4x Tesla Model S batteries in series, which gets to about 94v fully charged.
Curtis 1238E

I'm well aware these batteries do not continuously provide the ~650A this motor needs in order to achieve 108lbs/ft of torque. According to the motor controller, it has drawn a max around 430A, which already seems off. The battery output is rated for 1000A for 10 seconds, so I wouldn't think they're the problem, and the motor controller is rated for 650A. According to the BMS, the batteries are in good condition, so even if I were to get 500A for 10 seconds, I should still be able to accelerate faster than I do now.

Is there anything that might be limiting the power?


----------



## remy_martian (Feb 4, 2019)

At 140 ftlb on the axle, in 1st gear at 40 ftlb, your acceleration will be the equivalent of your girlfriend pushing it with all her weight. So, no, it's not even going to squeak the tires.

You need to get the torque up. What's the motor rpm at 50mph and what's its rated rpm?


----------



## brian_ (Feb 7, 2017)

schmidtbag said:


> I've been working on converting a 1977 VW Rabbit with a 4-speed manual transmission...
> 
> 1st gear has a ratio of 3.45, so even at 40lbs/ft, I imagine that would be enough torque to make the wheels slip (most of the weight is now in the rear).


If I found the right specs, first is 3.46:1, and the final drive ratio is 3.89:1. That would make the torque to wheels 13.5 times the motor torque, or 538 lb-ft. The stock tire size is 155/80R13, for a radius of a bit under 289 mm (11.4"). With that radius, 538 lb-ft (729 Nm) of torque would produce a tractive force at the road surface of 566 pounds or 2519 newtons (force = torque / radius)... equally split between the two front tires. I doubt that most of the weight is in the rear, even with the battery back there, so that force will be much less than the weight on the tires and with any reasonable tires they won't slip.


----------



## schmidtbag (Aug 7, 2019)

remy_martian said:


> At 140 ftlb on the axle, in 1st gear at 40 ftlb, your acceleration will be the equivalent of your girlfriend pushing it with all her weight. So, no, it's not even going to squeak the tires.
> 
> You need to get the torque up. What's the motor rpm at 50mph and what's its rated rpm?


Ah right, I guess it makes sense when you put it that way hah. Perhaps I am close to the 2/3 power then. In either case, if the 1000A for 10 seconds is true, I should be getting a higher peak amperage, right? Even if I got half the amperage for 10 seconds, I should still get more.

I don't have exact numbers but the motor RPM should be around 3000RPM in 4th gear at 50MPH. The motor really starts to lose power at around 5000RPM. I haven't pushed the motor that fast yet.



brian_ said:


> If I found the right specs, first is 3.46:1, and the final drive ratio is 3.89:1. That would make the torque to wheels 13.5 times the motor torque, or 538 lb-ft. The stock tire size is 155/80R13, for a radius of a bit under 289 mm (11.4"). With that radius, 538 lb-ft (729 Nm) of torque would produce a tractive force at the road surface of 566 pounds or 2519 newtons (force = torque / radius)... equally split between the two front tires. I doubt that most of the weight is in the rear, even with the battery back there, so that force will be much less than the weight on the tires and with any reasonable tires they won't slip.


4th gear is 0.97:1.
The front is pretty light. The motor, controller, transmission, DC-DC converter, washer fluid, and some fuses are all you'll find up there. The "engine" bay is pretty empty. When the car gets moving, you can steer the wheel with your pinky (obviously, no power steering).


----------



## brian_ (Feb 7, 2017)

schmidtbag said:


> 4th gear is 0.97:1.


Okay... but I thought you were talking about the lack of ability to spin the tires in _first _gear; obviously it won't be able to spin the tires in fourth gear, with only about one-quarter as much torque to the tires for the same motor torque.

Perhaps you don't understand what "final drive ratio" is? It's not the top gear ratio. In the transaxle power flows from the input shaft to the next shaft through one of the gear sets (ratios 3.46:1 in 1st, 1.94:1 in 2nd, 1.29:1 in 3rd, and 0.97:1 in 4th). That next shaft has a small gear it that drive the large gear around the differential; this final stage of reduction gearing is called the "final drive". The final drive ratio is 3.89:1. As a result, the ratio between motor speed and axle speed is the product of multiplying one of the four gear ratios (or the reverse ratio) by the final drive ratio, or 3.46 x 3.89 = 13.5 in first gear.

I got those gear ratios from Transmission Ratios; see "4 speed to '80 (Rabbit)" line of the table.



schmidtbag said:


> The front is pretty light. The motor, controller, transmission, DC-DC converter, washer fluid, and some fuses are all you'll find up there. The "engine" bay is pretty empty. When the car gets moving, you can steer the wheel with your pinky (obviously, no power steering).


No, it's not. The stock Rabbit has perhaps 60% of its roughly 2000 pound weight on the front tires, and the majority of that is not the engine. Even replacing the engine with the electric motor, there is still half a ton of car on the front tires. Try running over your toes with a front tire, and let us know if it's really light. 

My first car didn't have power steering, it was a stock front-engine front-wheel-drive Toyota which was about the same weight as a Rabbit, and one-finger driving wasn't difficult... but the front tires (same size as the Rabbit) were still being squashed by over half a ton between them.

Because the car is front wheel drive, when acceleration shifts load from the front tires to the rear tires, load on the driven tires is reduced and thus traction is reduced; however, there isn't enough drive force available here to make the front end actually light - this isn't a drag racer lifting the front tires as a thousand horsepower churn the sticky slicks in the back.


----------



## brian_ (Feb 7, 2017)

schmidtbag said:


> I don't have exact numbers but the motor RPM should be around 3000RPM in 4th gear at 50MPH. The motor really starts to lose power at around 5000RPM. I haven't pushed the motor that fast yet.
> 
> 
> 4th gear is 0.97:1.


This confirms the gearing: 3000 RPM divided by 0.97 and by 3.89 is 795 RPM. That speed with the stock tires (877 revolutions per mile according to published specs) gives 0.907 miles per minute, or 54 MPH. So the final drive ratio is at least close to 3.89:1, and you can use these 1st through 4th gear ratios and final drive ratios with the tire size to calculate motor speeds in any gear at any speed.


----------



## brian_ (Feb 7, 2017)

schmidtbag said:


> The motor really starts to lose power at around 5000RPM.


Yes, with about 96 volts from the battery, power drops off rapidly past 5000 RPM, as the HPEVS performance chart from the HPEVS AC-20 page shows:









For best short-term performance you would want to shift to keep the motor speed as close to 5000 RPM as possible; you won't reach that motor speed until 25 MPH in first gear (and 45 MPH in second).


----------



## schmidtbag (Aug 7, 2019)

brian_ said:


> Okay... but I thought you were talking about the lack of ability to spin the tires in _first _gear; obviously it won't be able to spin the tires in fourth gear, with only about one-quarter as much torque to the tires for the same motor torque.


Well yeah I know, but you said final gear (which I assumed meant 4th, but apparently not), so I wanted to clarify it's 0.97 and not 3.89. At this point, I don't even necessarily care about spinning the tires in 1st gear, but would like to be able to tap into more of the power these batteries supposedly have. Even if I were to get half the amperage for half the duration, I should still get better results. 


> Perhaps you don't understand what "final drive ratio" is? In the transaxle power flows from the input shaft to the next shaft through one of the gear sets (ratios 3.46:1 in 1st, 1.94:1 in 2nd, 1.29:1 in 3rd, and 0.97:1 in 4th). That next shaft has a small gear it that drive the large gear around the differential; this final stage of reduction gearing is called the "final drive". The final drive ratio is 3.89:1. As a result, the ratio between motor speed and axle speed is the product of multiplying one of the four gear ratios (or the reverse ratio) by the final drive ratio, or 3.46 x 3.89 = 13.5 in first gear.


Gotcha. Thanks for the clarification.


> No, it's not. The stock Rabbit has perhaps 60% of its roughly 2000 pound weight on the front tires, and the majority of that is not the engine. Even replacing the engine with the electric motor, there is still half a ton of car on the front tires. Try running over your toes with a front tire, and let us know if it's really light.


I replaced the suspension, where the front and rear springs appear to be the same (same thickness, same number of winds). The rear sagged significantly more than the front. Thankfully, these, coilovers are adjustable, but the rears are about as high as they can go. I can grab the tire and turn it relatively easily while the car is still on the ground. While I'm not saying the front is light, I think this is enough evidence to suggest it is lighter than the rear. Perhaps not by a lot.
In any case, I acknowledge it isn't light enough to make a difference.


> Because the car is front wheel drive, any acceleration shifts load from the driven tires to the rear tires, reducing the load on the front tires and thus reducing traction; however, there isn't enough drive force available here to make the front end actually light - this isn't a drag racer lifting the front tires as a thousand horsepower churn the sticky slicks in the back.


Well yeah, but I would have assumed the immediate torque in 1st gear would be enough to chirp the tires, as opposed to an acceleration rate akin to grandma driving and realizing her laxatives have kicked in on her way to church: slow, but not annoyingly slow.


----------



## brian_ (Feb 7, 2017)

schmidtbag said:


> Well yeah, but I would have assumed the immediate torque in 1st gear would be enough to chirp the tires, as opposed to an acceleration rate akin to grandma driving and realizing her laxatives have kicked in on her way to church: slow, but not annoyingly slow.



I could chirp the tires in my old car (I used it in autoslalom competition so it did get pushed hard), but that was with a rated torque about the same as the AC-20 with 650 amps... at half of that, the drive would be quite "relaxed".

Keep in mind that torque is roughly proportional to motor current, but battery current is not motor current. The controller divides the voltage from the input (from the DC link to the battery) to the output (as 3-phase AC to the motor), while multiplying the current by almost the same ratio (of course considering the RMS value of the total current in the three phases). That's why the HPEVS graphs show current rising up to the "knee" (around 4500 RPM in the 96 V / 650 A chart); with increasing speed the _battery_ current is rising while the battery voltage stays constant, but the _motor_ current is constant (limited by the controller) while the motor voltage increases as it must with speed. It would be nice if both the performance chart and operating information from the controller showed the RMS value of motor current, because looking at DC link (battery) current by itself doesn't tell you what is going on at the motor.

Below the knee in the curve, the DC link current is limited by the motor (controller output) current; above the power peak, the DC link current is limited by the battery voltage available to drive the motor. This means that peak DC link (battery) current is only observed near the knee, as the curve shows; observe the motor under any other condition, and battery current will be lower.


----------



## schmidtbag (Aug 7, 2019)

brian_ said:


> Keep in mind that torque is roughly proportional to motor current, but battery current is not motor current. The controller divides the voltage from the input (from the DC link to the battery) to the output (as 3-phase AC to the motor), while multiplying the current by almost the same ratio (of course considering the RMS value of the total current in the three phases). That's why the HPEVS graphs show current rising up to the "knee" (around 4500 RPM in the 96 V / 650 A chart); with increasing speed the _battery_ current is rising while the battery voltage stays constant, but the _motor_ current is constant (limited by the controller) while the motor voltage increases as it must with speed. It would be nice if both the performance chart and operating information from the controller showed the RMS value of motor current, because looking at DC link (battery) current by itself doesn't tell you what is going on at the motor.


Understood, and I agree that the motor current in the chart isn't quite enough. But here's the main reason I posted:
The battery can provide 1000A for 10 seconds and 225A continuously. 10 seconds is enough to get me to in-town cruising speed, and I assume 225A ought to be sufficient to maintain cruising speed on a flat road. Since the motor controller is limited to 650A, that buys me more time for acceleration. The problem is, the motor controller reports max power draw nowhere close to 650A. It's as though something is limiting how much power it can use.

The motor controller has a pin for economy mode. It isn't clear whether it's engaged or disengaged when 12v is applied, but when toggling it, there wasn't any significant change. I'm not sure if there's something else I'm supposed to do.
On that note, the motor controller's clutch/shift switch doesn't seem to do anything either (regen brake always seems to be on). These are the only two 12v functions that don't seem to do anything; all other functions work. But, my current priority is the lacking power.


----------



## brian_ (Feb 7, 2017)

schmidtbag said:


> The problem is, the motor controller reports max power draw nowhere close to 650A.


That makes sense, but nowhere close to 650 A (from the battery)... at what motor speed?


----------



## schmidtbag (Aug 7, 2019)

brian_ said:


> That makes sense, but nowhere close to 650 A (from the battery)... at what motor speed?


I'm referring to the max amperage reported by the motor controller, which from what I recall was around 430A. I assume this is the amperage it outputs to the motor. The motor reached around 4000RPM during that test (I don't recall that it logs max RPM). So, I should have got much closer to 500A, based on what those charts said.

But also... shouldn't the stall current be much higher? I've done a bit of work with much smaller motors (ones that weigh less than 1kg) and the stall current was often the highest value.


----------



## BAstereo (Dec 28, 2018)

schmidtbag said:


> The motor controller has a pin for economy mode. It isn't clear whether it's engaged or disengaged when 12v is applied, but when toggling it, there wasn't any significant change. I'm not sure if there's something else I'm supposed to do.
> On that note, the motor controller's clutch/shift switch doesn't seem to do anything either (regen brake always seems to be on). These are the only two 12v functions that don't seem to do anything; all other functions work. But, my current priority is the lacking power.


I'm not super familiar with the 1238e, but on the 1238, there is no connection to the 12 volt system. The Curtis 1238 only knows your traction pack voltage, so all inputs/outputs must be referenced (grounded) to your traction battery, not 12v battery.


----------



## schmidtbag (Aug 7, 2019)

BAstereo said:


> I'm not super familiar with the 1238e, but on the 1238, there is no connection to the 12 volt system. The Curtis 1238 only knows your traction pack voltage, so all inputs/outputs must be referenced (grounded) to your traction battery, not 12v battery.


My controller not only has a connection to the 12v system but provides a low-amperage 12v output (and 5v, for that matter). The 12v is working for several other functions.


----------



## BAstereo (Dec 28, 2018)

Is your traction battery negative is connected to your 12v battery negative?

If your are using the 12v, 5v, and IO ground outputs from the controller, those are referenced to your traction battery negative. 
Switching them and returning that signal to the controller then you're probably doing it right.


----------



## schmidtbag (Aug 7, 2019)

BAstereo said:


> Is your traction battery negative is connected to your 12v battery negative?
> 
> If your are using the 12v, 5v, and IO ground outputs from the controller, those are referenced to your traction battery negative.
> Switching them and returning that signal to the controller then you're probably doing it right.


No, my DC-DC converter is isolated so there no continuity to the traction battery or anything 12v.
The 5v, 12v, and ground pins provided by the motor controller have no continuity to the traction battery either; they are also isolated. All I/O pins for the controller are only using the voltage and ground sources that the controller provides.
Both ends of the traction battery are only connected to a contactor, a fuse, the motor controller, and the DC-DC converter. The BMS reads 100% isolation.


----------



## BAstereo (Dec 28, 2018)

Ok, sounds like you've got a good handle on the situation. I was just grasping at threads when you mentioned the 12v and motor controller input.
On the 1238, I believe IO ground isn't isolated.

Is your motor an induction motor? If so the stall current I've seen from Curtis is low. It seems like they limit below even 650 amps AC at 0 rpm.


----------



## schmidtbag (Aug 7, 2019)

BAstereo said:


> Ok, sounds like you've got a good handle on the situation. I was just grasping at threads when you mentioned the 12v and motor controller input.
> On the 1238, I believe IO ground isn't isolated.


Haha yup, the IO ground on my controller is also isolated. Though, it wouldn't since I don't have it connected with the rest of the 12v system.


> Is your motor an induction motor? If so the stall current I've seen from Curtis is low. It seems like they limit below even 650 amps AC at 0 rpm.


Yes, it is an induction motor. That is definitely useful to know that they limit the stall current. So, I guess that means the only way for me to reach 650A is if I reach 5000RPMs under load. I haven't tried pushing it that hard.


----------



## BAstereo (Dec 28, 2018)

BAstereo said:


> Ok, sounds like you've got a good handle on the situation. I was just grasping at threads when you mentioned the 12v and motor controller input.
> On the 1238, I believe IO ground isn't isolated* from traction negative*. *It is isolated from 12v negative.*
> 
> Is your motor an induction motor? If so the stall current I've seen from Curtis is low. It seems like they limit below even 650 amps AC at 0 rpm.


Just clarifying myself here...


----------



## wstein25 (11 mo ago)

schmidtbag said:


> I've been working on converting a 1977 VW Rabbit with a 4-speed manual transmission for the past 3 years. Here are the specs:
> 
> AC-20, since at 96V it has a little less HP than the original 1.6L engine the car came with.
> I'm using 4x Tesla Model S batteries in series, which gets to about 94v fully charged.
> ...


The first thing that came to mind if you are really seeing current limiting is perhaps your wiring - the conductors from battery to motor controller are undersized, or the connectors are inadequate. Have you tried measuring the battery voltage at the battery terminals and simultaneously at the controller, while under full load, that is accelerating from zero at full throttle? If you have even a tenth of an ohm in the cable and connectors, 1000 amp would cause a 100 volt drop.


----------



## schmidtbag (Aug 7, 2019)

wstein25 said:


> The first thing that came to mind if you are really seeing current limiting is perhaps your wiring - the conductors from battery to motor controller are undersized, or the connectors are inadequate. Have you tried measuring the battery voltage at the battery terminals and simultaneously at the controller, while under full load, that is accelerating from zero at full throttle? If you have even a tenth of an ohm in the cable and connectors, 1000 amp would cause a 100 volt drop.


I would be surprised if they are undersized. I'm using 00 gauge wire, which I figure is overkill for the amount of power this motor demands. I'm using less than 12ft total of wire (for both positive and negative). The only things that are likely to add any resistance are the fuse and contactor, since neither of those appear to have copper terminals. While it might be a stupid idea to remove the fuse, I should maybe try to measure how many ohms it is.


----------



## remy_martian (Feb 4, 2019)

Direct to input shaft of transmission or is there a clutch there?


----------



## schmidtbag (Aug 7, 2019)

remy_martian said:


> Direct to input shaft of transmission or is there a clutch there?


Direct to input shaft.


----------



## remy_martian (Feb 4, 2019)

...and you are certain it's spinning 4000 and not 8000 rpm?


----------



## schmidtbag (Aug 7, 2019)

remy_martian said:


> ...and you are certain it's spinning 4000 and not 8000 rpm?


I don't think this motor can even get to 8000 under its own power with the wheels on the ground. I've never pushed it much further than 6000 with the wheels off the ground.


----------



## remy_martian (Feb 4, 2019)

Need to measure voltage at the motor is all I can think of...other than adding one more Tesla module and crossing your fingers. 

The voltage test eliminates the crossing your fingers part for what I suspect is inevitable.


----------



## wstein25 (11 mo ago)

schmidtbag said:


> I would be surprised if they are undersized. I'm using 00 gauge wire, which I figure is overkill for the amount of power this motor demands. I'm using less than 12ft total of wire (for both positive and negative). The only things that are likely to add any resistance are the fuse and contactor, since neither of those appear to have copper terminals. While it might be a stupid idea to remove the fuse, I should maybe try to measure how many ohms it is.


Ok - I just looked it up. 00 coper cable at RT is 0.079 ohms per thousand feet. If you push 1000 amps thru 10 feet of cable you would have a 0.79 volt drop. I doubt your fuse is of any consequence. In fact you could tell easily if you had a bad connection or other "ohmic" device as they would get very hot to the touch.


----------



## DMPstar (Mar 2, 2016)

Do you have any idea what the parameter settings are in your Curtis? There are a lot of things that could be set too low causing your limited power. Was it a motor /controller package from one vendor?



schmidtbag said:


> I don't think this motor can even get to 8000 under its own power with the wheels on the ground. I've never pushed it much further than 6000 with the wheels off the ground.


You may get to 8000 in first or second, but I haven't played with AC20 motors.
With wheels off the ground and full throttle how long does it take to spin up to 6k?
Got an ac-35 and 1238 on the bench (and a Rabbit keeping close watch) and in torque mode with all settings set pretty hot and it will hit 0-6000 in less than a second.


----------



## schmidtbag (Aug 7, 2019)

DMPstar said:


> Do you have any idea what the parameter settings are in your Curtis? There are a lot of things that could be set too low causing your limited power. Was it a motor /controller package from one vendor?


I don't. It was packaged and pre-programmed by a vendor.


> You may get to 8000 in first or second, but I haven't played with AC20 motors.
> With wheels off the ground and full throttle how long does it take to spin up to 6k?
> Got an ac-35 and 1238 on the bench (and a Rabbit keeping close watch) and in torque mode with all settings set pretty hot and it will hit 0-6000 in less than a second.


Yeah off the ground it can get to 6000 almost instantly. I didn't count how long but there's no struggle.

I have found that lately, the car is getting a lot more peppy. I didn't change anything, but it accelerates much better. Still not enough to chirp the tires but enough to be mildly fun. Do these controllers self-calibrate?


----------



## remy_martian (Feb 4, 2019)

Were outdoor temperatures any different?


----------



## schmidtbag (Aug 7, 2019)

Not really. About 50-60F each day tested.
All temperatures looked good. Hottest component was the motor, at around 44C max.


----------



## remy_martian (Feb 4, 2019)

I was looking to see what the difference in battery temperatures might be. 

For instance, warmer environmental temperatures or peppy was immediately driven after taken off the charger.


----------



## DMPstar (Mar 2, 2016)

schmidtbag said:


> Do these controllers self-calibrate?


No, they won't change their calibration or settings without user input, but as Remy is onto temperature cubacks and battery voltage range will change performance. 
Are there any current limit feedback inputs from the BMS to the Curtis?
Would be nice to get a hold of a handheld or pc programmer to see what you are working with.


----------



## schmidtbag (Aug 7, 2019)

DMPstar said:


> No, they won't change their calibration or settings without user input, but as Remy is onto temperature cubacks and battery voltage range will change performance.
> Are there any current limit feedback inputs from the BMS to the Curtis?
> Would be nice to get a hold of a handheld or pc programmer to see what you are working with.


Good to know. I don't recall the BMS being configured to limit current; no idea if the motor controller is set up that way.

I am beginning to wonder if the temperature is part of the problem though. It was still about 55F today, but I found after about a half hour of driving that if I floored it, the voltage would drop below 70V, and the motor controller seemed to cut the power entirely (including to the BMS) for less than a second. If I pull over, the voltage would creep back up to about 87v. The hottest battery was at 15C, coldest was I think 12C.
I would think this is warm enough, but maybe the batteries are just too cold to deliver the power? Because I am finding that the performance at times is improving.


----------



## remy_martian (Feb 4, 2019)

Lithium batteries need to be hard-run at above 65F (18C).

You're running them way too cold to get spec sheet output, as I suspected.

Take your shirt off. The two things on your chest are "too cold for lithium battery high current operation" indicators.


----------



## schmidtbag (Aug 7, 2019)

remy_martian said:


> Lithium batteries need to be hard-run at above 65F (18C).
> 
> You're running them way too cold to get spec sheet output, as I suspected.
> 
> Take your shirt off. The two things on your chest are "too cold for lithium battery high current operation" indicators.


Good to know - thanks, this might just be my issue all along. I look forward to when it gets a little warmer.


----------



## remy_martian (Feb 4, 2019)

Where are the batteries in the vehicle?


----------



## schmidtbag (Aug 7, 2019)

remy_martian said:


> Where are the batteries in the vehicle?


Mounted on the bottom. One is where the gas tank used to be, the rest are where the spare tire used to be. They get plenty of airflow (there is no intention on driving this car in wet conditions and it will not be a daily driver).


----------



## remy_martian (Feb 4, 2019)

I was thinking you could put a 300W halogen lamp under the car (for the heat...don't point the light at the car), or a small space heater, and drape it so it warms the batteries up, supervised, for a couple of hours, then test drive it. Just don't set anything ablaze experimenting this way.


----------



## schmidtbag (Aug 7, 2019)

remy_martian said:


> I was thinking you could put a 300W halogen lamp under the car (for the heat...don't point the light at the car) and drape it so it warms the batteries up, supervised, for a couple of hours, then test drive it. Just don't set anything ablaze experimenting this way.


Haha spring is around the corner - I can wait. More work needs to be done to the car anyway, so there's no rush.


----------



## DMPstar (Mar 2, 2016)

My experience with 96v 1238 Curtis only ever went as low as 96v nominal battery voltage (30s lifepo4). In most cases nominal was 102.4 (32s). Dropping below 70v to me is a major red flag that you are probably spending most of your time in undervoltage cutback range.
What vendor did you buy from and can they provide the controller parameter file for us to analyze?


----------



## schmidtbag (Aug 7, 2019)

DMPstar said:


> My experience with 96v 1238 Curtis only ever went as low as 96v nominal battery voltage (30s lifepo4). In most cases nominal was 102.4 (32s). Dropping below 70v to me is a major red flag that you are probably spending most of your time in undervoltage cutback range.
> What vendor did you buy from and can they provide the controller parameter file for us to analyze?


I don't believe the motor controller is the problem. More likely that the batteries are, because the BMS reports the realtime voltage dropping into the 70s. For what it's worth, the BMS is not connected to the Curtis.
If it is a problem with the batteries, that's real bad news because I can't return them at this point. It is worth pointing out it dips into the 70s after about 15 minutes of driving after charging.

Though speaking of charging, that could be part of my problem. I haven't yet been able to fully charge the cells (I set the max charge to 94v). I can get them to about 91v until there's a load balance issue with two neighboring cells (one is too high, the other is too low). I know voltage isn't a good indicator of how much charge you have left but I would think 91 is "high enough" to not have the system start choking after 10 miles.


----------



## DMPstar (Mar 2, 2016)

Charged surface voltage quickly dips down under any load as you have noticed. After 10 miles I would expect you to be hanging out in the low 80V range or less. Still not high enough for the controller to be truly happy. No, I dont think your controller is the issue, I think having the correct voltage available to it likely is. Can you add another battery module in series?


----------



## schmidtbag (Aug 7, 2019)

DMPstar said:


> Charged surface voltage quickly dips down under any load as you have noticed. After 10 miles I would expect you to be hanging out in the low 80V range or less. Still not high enough for the controller to be truly happy. No, I dont think your controller is the issue, I think having the correct voltage available to it likely is. Can you add another battery module in series?


There is currently no physical room (let alone funds) to add another battery. The controller and charger are both configured for 96v too, so that would be further complications to figure out.
I would first like to get the batteries charged to at least 94v and for the ambient temperature to rise before I start looking into alternative solutions. I was hoping for a minimum of 60 miles, so it's rather discouraging if I'm already seeing issues at 10.
It's just annoying, because it still drives just fine when it dips to 70v. Sure, it's not accelerating quickly, but it does accelerate, so I would imagine there are still enough amps left over. When I stop, the voltage did creep back to around 87v, which isn't far off from what I started with.


----------



## DMPstar (Mar 2, 2016)

Here is a shot of some stock HPEVS parameters for 96v 1238. If you are indeed hitting 70v or less you will be in cutback. Looks like there is still some room to drop these values without hitting bottom limit if you can get a hold of a programmer. Cheapest option from what I see...
Luckily these controllers were designed to work with the wide V range of lead acid so should be able to account for your range.


----------



## remy_martian (Feb 4, 2019)

This may sound dumb, but you could try bypassing (disconnect & bypass, don't short it out, lol) that weak cell that reveals itself at charging and see what happens to the driving experience...


----------



## DMPstar (Mar 2, 2016)

Note that the values I am referring to are the "undervoltage cutback range" and "User undervoltage"

Edit: Ignore the "volts per cell" stuff, that is all lead acid related as far as I can tell.


----------



## DMPstar (Mar 2, 2016)

remy_martian said:


> This may sound dumb, but you could try bypassing (disconnect & bypass, don't short it out, lol) that weak cell that reveals itself at charging and see what happens to the driving experience...


Yeah drop the batt Voltage a bit lower and see if the issue comes up quicker. Pretty easy way to determine if cutbacks are present. 
...unless you meant for another purpose? Doesnt sound like he has BMS feedback to the controller.


----------



## schmidtbag (Aug 7, 2019)

remy_martian said:


> This may sound dumb, but you could try bypassing (disconnect & bypass, don't short it out, lol) that weak cell that reveals itself at charging and see what happens to the driving experience...


I considered that, assuming the BMS will cooperate with that. In the meantime, any further insight on why the BMS is getting the readings they are? I assume it's no coincidence that the highest cell and lowest cell are right next to each other. I'm using a ZEVA V3, if that makes a difference.


DMPstar said:


> Doesnt sound like he has BMS feedback to the controller.


That's right, I don't. Would doing so yield any noteworthy benefit?


----------



## remy_martian (Feb 4, 2019)

DMPstar said:


> Yeah drop the batt Voltage a bit lower and see if the issue comes up quicker. Pretty easy way to determine if cutbacks are present.
> ...unless you meant for another purpose? Doesnt sound like he has BMS feedback to the controller.


Dual purpose. It could be the high internal resistance cell limiting performance of the pack. The second is simulating lower voltage with high SoC.


----------



## DMPstar (Mar 2, 2016)

Can you show some shots of your BMS values that you are describing? Highest and lowest cells beside each other etc, other nearby cell voltages? If I see 2 side-by-side cells with a large Delta it sometimes is caused by a bad cell tap wire.
Sounds like a separate issue, but should be investigated.


----------



## DMPstar (Mar 2, 2016)

remy_martian said:


> Dual purpose. It could be the high internal resistance cell limiting performance of the pack. The second is simulating lower voltage with high SoC.


Re: Lower voltage with higher SOC - No feedback of current limits back to Curtis. 
Weak cell or not, until it becomes reverse polarized due to drive current the pack voltage shouldn't dip too much due to it. Overall low operating voltage of the battery seems to be what's happening.


----------



## remy_martian (Feb 4, 2019)

I'm talking about current limiting, not voltage sag.


----------



## DMPstar (Mar 2, 2016)

remy_martian said:


> I'm talking about current limiting, not voltage sag.


I suppose I have not worked with Tesla modules, but would expect the battery to be capable of higher discharge currents than what the rated safe discharge specs are, and higher than what this setup can draw. Pulling more current than what the battery can provide in my experience will dip the cell voltages low enough to have the BMS throw a low cell voltage fault or disable discharge, which I'm not sure the OP has encountered. As you know the actual current limit of a battery and voltage sag go hand-in-hand.


----------



## schmidtbag (Aug 7, 2019)

DMPstar said:


> Pulling more current than what the battery can provide in my experience will dip the cell voltages low enough to have the BMS throw a low cell voltage fault or disable discharge, which I'm not sure the OP has encountered.


I haven't experienced that, because the BMS is powered by the DC-DC converter, which is powered _after_ the contactor operated by the Curtis. So, once it dips below 70V, it seems the Curtis very briefly turns off the contactor, thereby turning off the BMS along with it.
I don't know if this is the best way to go about hooking up the DC-DC converter, I just did it that way so it doesn't unnecessarily draw more power than needed.

Also, I'll try getting pictures of the BMS cell data later.


----------



## DMPstar (Mar 2, 2016)

schmidtbag said:


> I haven't experienced that, because the BMS is powered by the DC-DC converter, which is powered _after_ the contactor operated by the Curtis. So, once it dips below 70V, it seems the Curtis very briefly turns off the contactor, thereby turning off the BMS along with it.
> I don't know if this is the best way to go about hooking up the DC-DC converter, I just did it that way so it doesn't unnecessarily draw more power than needed.
> 
> Also, I'll try getting pictures of the BMS cell data later.


I would strongly suggest NOT having any other loads between Curtis's main contactor and the B+ lug of the controller. This can affect the controller's precharge timing and has the implications you have mentioned. You have no 12V battery to hold the system up without DC-DC as it sounds. Might be worth considering. It opens up your ability to wire the car's HV stuff properly. DC-DC draw on the pack when not in use can be rectified by the 12V battery approach as well.


----------



## schmidtbag (Aug 7, 2019)

The 2 cells within the red square are the ones that have issues. The car hasn't been charged for a few hours so the values have somewhat stabilized.
The 2nd image shows the individual cell values for BMS module 0; the values for module 1 are fine.
While charging, the BMS is constantly discharging M0 C7.


















DMPstar said:


> I would strongly suggest NOT having any other loads between Curtis's main contactor and the B+ lug of the controller. This can affect the controller's precharge timing and has the implications you have mentioned. You have no 12V battery to hold the system up without DC-DC as it sounds. Might be worth considering. It opens up your ability to wire the car's HV stuff properly. DC-DC draw on the pack when not in use can be rectified by the 12V battery approach as well.


Considering the BMS does not retain the SoC when it loses power, I have heavily considered a 12v battery.


----------



## DMPstar (Mar 2, 2016)

schmidtbag said:


> Considering the BMS does not retain the SoC when it loses power, I have heavily considered a 12v battery.


As you said, spring is around the corner, so get on that soon! Doesn't need to be big to help stiffen your 12V system for high startup loads of wipers, etc. Really helps to keep the system more logical.

Pics look like normal readings, just a lower cell with a bit of imbalance from the rest. Does your BMS have cell balancing?


----------



## DMPstar (Mar 2, 2016)

Sorry I now see what you said about the BMS discharging the high cell. Yes it balances.


----------



## schmidtbag (Aug 7, 2019)

So, there isn't anything suspicious about how C7 charges faster than C8? The pictures are the cell values after it had time to "settle". The voltage difference is a bit higher during charging.


----------



## DMPstar (Mar 2, 2016)

Yes imbalance will show itself most at top SOC due to the lithium Voltage:SOC curves.
Are you able to have your BMS in charge mode and let it sit balancing for an extended period of time without regular re-enabling of the charger? You should be able to balance out that high cell and eventually it should recalculate its balance algorithm to start bringing the rest down to that low one (if it is like BMS units I have used).
You could ignore the high cell for now and try to bring the low one up with manual charging via the (disconnected) tap wires using a wall wart 4 or 5V regulated supply. I suspect it has a self discharge rate higher than the other cells and will continue to cause you problems if frequent BMS balancing is not used.


----------



## schmidtbag (Aug 7, 2019)

I am able to have the BMS in charge mode without it actually charging, but what you see in that photo is where it normally stops load balancing. From what I can tell, the BMS only balances the highest cells that are over 0.05v higher than the lowest cell. Only one other cell (M1 C6 if I remember correctly) _occasionally_ gets high enough to also be load balanced; the rest never do, but the load balancing does keep up with it. The BMS does _not_ keep up with M0 C7. Eventually, it (and only that one cell) gains enough voltage that it shuts off the charger. That's why I'm suspicious, because it's weird to me that one cell is charging faster than the rest, and the cell neighboring it happens to be charging slower than the rest.

I'm a little skeptical of independently charging C8, in the event it isn't actually lower than the rest.


----------



## DMPstar (Mar 2, 2016)

Can you confirm the voltages with a meter and inspect the tap connections at the battery?
Is there any control on your BMS for changing the balance settings?


----------



## schmidtbag (Aug 7, 2019)

I have a while back checked the voltages with a multimeter and they seemed to match what the BMS was reading. However, the wires are super skinny and I don't know how clean of a connection I have with them. I don't recall measuring the tap connections at the battery, but that would be worth investigating to see if they're any different. I might not be able to do that for a few days though.

EDIT:
The BMS can change the balance settings, though there aren't many options.


----------



## burhan ahmad (2 mo ago)

im also face this problem can anyone tell


----------



## burhan ahmad (2 mo ago)

schmidtbag said:


> Haha spring is around the corner - I can wait. More work needs to be done to the car anyway, so there's no rush.


yes you are right


----------

