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Discussion Starter · #1 ·
Hello all,

I've followed this forum on and off for a while, and now I can say I have a project of my own!

I am an Electrical Engineer (with a Mechanical & Aerospace Engineering education) at a company that builds commercial EV conversions. Before this company, I worked at a place that built custom lithium battery packs and sold EV parts to the DIYers. I've been helping people build their conversions for a while, so it is exciting that I finally have something to work on myself.

I was recently gifted a 15 year old EV conversion that has been broken down, parked on the street, for maybe 4 years. It is a 1996 Subaru Outback that was originally converted to Lead Acid then later upgraded with Lithium.
Some specs:
  • Warp 9 powered by a Curtis 1231c (that I am currently having issues with)
    • Mated to the original 5-speed manual, keeping the AWD.
  • 144V, 180Ah LFP pack with a Lithiumate Lite BMS
  • Zivan NG3 charger & Zivan NG1 configured as a DC-DC.
  • A custom HV heater... that I am not going to test out.
My first goal is just to get it road worthy again, then I can enjoy driving it around town while planning & saving up for some upgrades.

So far I have replaced the 12V battery, and reduced the pack from 42S to 41S due to some very dead cells that were preventing the BMS from being happy. With just that I am able to now cruise around the neighborhood but with very little torque. The Curtis controller seems to be at half power with it maxing out at 250A to the motor. I think I have checked everything I can and am a bit stumped on how to get more power out of it. The batteries appear okay-ish for now. Having a dumb charger is a little problematic when you are trying to balance old cells.

Anyways, I'm glad to be here. If you have any experience with the Curtis or the Lithiumate I would appreciate any tips or help.
 

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Hello & welcome 馃

I'd start off by taking a "deep dive" into examining the batt pack (all the way down to the cellular level)
...while sitting
...& also, while under load (if possible)

An old/weak batt pack may let you "putt around"
...but, sometimes can't release (or don't have available) the "power" (or umph) you're expecting
...or that your motor "needs" to perform
 

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Discussion Starter · #3 ·
A cellular inspection is certainly in order. Unfortunately the way the pack is constructed I can not easily see about 1/3 of it without disassembling the other 2/3rd that is on top. I also don鈥檛 have a garage and winter is fast approaching so a pack tear down will have to wait for warmer days.

However with my putting around I鈥檝e seen plenty more current draw from the battery at the higher speeds than I ever see when taking off from a standstill. From what I understand of the Curtis DC controller, it is essentially converting the higher pack voltage to a lower voltage with high current. Then as you increase RPMs the voltage increases until you reach pack voltage, which at that point you would then be matching battery current to motor current.

Hello & welcome 馃

I'd start off by taking a "deep dive" into examining the batt pack (all the way down to the cellular level)
...while sitting
...& also, while under load (if possible)

An old/weak batt pack may let you "putt around"
...but, sometimes can't release (or don't have available) the "power" (or umph) you're expecting
...or that your motor "needs" to perform
 

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I am an Electrical Engineer (with a Mechanical & Aerospace Engineering education) at a company that builds commercial EV conversions. Before this company, I worked at a place that built custom lithium battery packs and sold EV parts to the DIYers. I've been helping people build their conversions for a while, so it is exciting that I finally have something to work on myself.
I'm not questioning you
...but, if this is true, you should know more about this EV stuff than most of us. ;)
...& you would also know that "if" your car has a Lithiumate BMS then, you should have access to the voltage reading of "all" of the cells in your pack (whether you can actually see them or not)

However with my putting around I鈥檝e seen plenty more current draw from the battery at the higher speeds than I ever see when taking off from a standstill. From what I understand of the Curtis DC controller, it is essentially converting the higher pack voltage to a lower voltage with high current. Then as you increase RPMs the voltage increases until you reach pack voltage, which at that point you would then be matching battery current to motor current.
IMO it sounds like you're experiencing a "MASSIVE" voltage drop on "take off from a standstill"
...& then, that "voltage drop" lessens as you get going


Here is an example, of a massive voltage drop on take off & then, leveling out (while still under load):
In this kart the batt pack starts off at ~64V (~1:10)
...& on take off the voltage "drops" all the way down to ~55V (~1:28)
...& then, the voltage slowly "raises" back up to ~61V (~2:07)
 

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When you say you're seeing 250A to the motor, are you measuring average current, or instantaneous peak ? The controller's "500A" spec may refer to peak current, not RMS. So, if your controller is operating at 50% duty cycle (which seems likely at modest speeds or modest throttle) then you may see only 250A average.

Does your BMS provide a "Max Discharge Current" signal to the controller? If so, one or more bad cells (or poor interconnections) could cause the current to be limited. If not, monitor the pack voltage as you accelerate to see if you're experiencing voltage sag. You may have more bad cells. If you found one very dead cell, chances are good you will find more.

Different tack (ie: not for everyone) Even 500A on Warp9 in high gear will yield underwhelming acceleration. I would try a lower gear. ~140V should be high enough to run the Warp9 up to at least 4000RPM in a low(ish) gear. Can you start in 1or 2 and then shift gears? If you have a clutch, use it. Shifting without a clutch takes some practice, and you will put some wear on the synchromeshes as you learn the technique. (and maybe even after you learn it)

Another tack: use a low gear and enjoy the car until you can budget the time and money to replace the curtis with a zilla. (and renew the battery)
 

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Discussion Starter · #7 ·
I'm not questioning you
...but, if this is true, you should know more about this EV stuff than most of us. ;)
...& you would also know that "if" your car has a Lithiumate BMS then, you should have access to the voltage reading of "all" of the cells in your pack (whether you can actually see them or not)



IMO it sounds like you're experiencing a "MASSIVE" voltage drop on "take off from a standstill"
...& then, that "voltage drop" lessens as you get going


Here is an example, of a massive voltage drop on take off & then, leveling out (while still under load):
In this kart the batt pack starts off at ~64V (~1:10)
...& on take off the voltage "drops" all the way down to ~55V (~1:28)
...& then, the voltage slowly "raises" back up to ~61V (~2:07)
I may have the book smarts, but I do not have the street smarts and experience that some of you in this forum do.

I do have access to the BMS and all of it's data. I have been recording a log every time I've gone for a drive. During discharge all of the cells looks pretty good. Fairly well balanced, and no single cell is sagging more than the others. Charging is a different story though. There is some weird behaviour with a group of cells that are, you guessed it, the ones I can't visually see.

I have been suspecting a voltage drop too. I will need to make some longer voltmeter leads so I can read voltages from various places while driving. There is a voltmeter gauge on the dash, but I have not tracked down where it is reading from yet.
Could it be the motor brushes?
 

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Discussion Starter · #8 ·
When you say you're seeing 250A to the motor, are you measuring average current, or instantaneous peak ? The controller's "500A" spec may refer to peak current, not RMS. So, if your controller is operating at 50% duty cycle (which seems likely at modest speeds or modest throttle) then you may see only 250A average.

Does your BMS provide a "Max Discharge Current" signal to the controller? If so, one or more bad cells (or poor interconnections) could cause the current to be limited. If not, monitor the pack voltage as you accelerate to see if you're experiencing voltage sag. You may have more bad cells. If you found one very dead cell, chances are good you will find more.

Different tack (ie: not for everyone) Even 500A on Warp9 in high gear will yield underwhelming acceleration. I would try a lower gear. ~140V should be high enough to run the Warp9 up to at least 4000RPM in a low(ish) gear. Can you start in 1or 2 and then shift gears? If you have a clutch, use it. Shifting without a clutch takes some practice, and you will put some wear on the synchromeshes as you learn the technique. (and maybe even after you learn it)

Another tack: use a low gear and enjoy the car until you can budget the time and money to replace the curtis with a zilla. (and renew the battery)
I'm getting that measurement from a shunt that is wired to a gauge in the dash. When I have it floored (which is all the time because it has no power) the gauge stays at ~250A. This BMS has a throttle reduce output which I have felt function before. With troubleshooting I have disconnected that so it is no longer influencing the throttle input. I have been recording and monitoring the BMS while driving. There are no faults or current limits. There is of course a voltage sag but it has not pulled any of the cells into the red.

This is underwhelmingly underwhelming. I keep being told that it could drive around in 3rd all day, but at the moment I have to take off in 1st. Even then in 1st the acceleration is incredibly slow and I have to get a little running start to go up my driveway (a very mild incline). The Curtis 1231C has a couple of adjustment pots for Current limit and Acceleration Rate. I have already tried giving those a few turns and nothing seems to have changed. I don't know if it requires something like a 100 turns, but I did several and no difference.

There is no clutch, is there a name for that technique?

There is definitely something wrong with the power. The car is easy to roll around in Neutral and also coasts well, so I think I can rule out a drivetrain issue?
I am good friends with the guy that converted this vehicle and the level of power it has now is not safe to drive on public streets.
 

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broken down,
Please elaborate?

I am good friends with the guy that converted this vehicle and the level of power it has now is not safe to drive on public streets.
What kind of "level of power" did it have before?
What kind of acceleration did it have before?
What was the previous top speed?

What is different now?
...it's just been sitting for a while? (~4 years)
...& why did he "park" it?
 

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There is no clutch, is there a name for that technique?

This is a good explanation

Tip: Practice on your friend's car, first. 馃お
 

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Discussion Starter · #12 ·
Please elaborate?


What kind of "level of power" did it have before?
What kind of acceleration did it have before?
What was the previous top speed?

What is different now?
...it's just been sitting for a while? (~4 years)
...& why did he "park" it?
I was told something kept killing the 12V. Could have also been because of the bad cells in the pack that were preventing the BMS from staying happy.

From the guy that converted it, "it could break loose the tires in 1st" and "you could drive around in 3rd all day and not worry about shifting". Now... I have to get a run at going up the driveway in 1st or it won't make it.

The previous owner has been out of town and I have only been talking with the guy that did the conversion. So at the moment I don't really know a lot about the vehicles' life and what lead up to it being parked and forgotten. Yea so there's a lot of mystery. What I'd do for a simple schematic. Ha.
 

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I'd try & do more research before spending any money
...but, if you plan on getting it going, to use regularly, I seriously think about getting a fresh battery pack.

Here is an example of a "weak" battery pack compared to a new pack.

This kart was designed to "pop wheelies"
When I took it for a test ride it "zipped" right along
...but, couldn't even think about "popping a wheelie"

Then, I installed a brand-new battery pack
...& it went !ARRIBA!
 

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Interesting post. I am getting into this hobby also and learning about all the car systems after being into ebikes for a while. Just a thought for u. Could the voltage range parameters of the Curtis controller be causing a limp/safety mode?
U stated the car was originally designed lead acid batteries and that u also changed the number of cells in series after a battery change? Could be the expected voltage settings in the curtis controller be different than the settings currently being received from the current battery pack? thus causing a curtis programmed safety mechanism to kick in?
I have a curtis controller on my little Vantagey-ev and I am just starting to learn about the various curtis system settings and its programming capability.
 

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I have modded my Zivan NG3 to use an Arduino as the CPU.

Basicly makes you able to control the charge curves, voltages, currents, beepy noises and led colours yourself.

Most important was to get a clean CC/CV with a set cutoff amperage, so it doesn't overcharge the pack.

Only did the first testing last week, voltage part works OK, havent been able to test the current part (shouldn't do anything weird, just no idea how the settings & analog readings correlate to real current. So have it set very LOW for now, until everything is tested, mostly due to lack of having a battery / current sink to test it on)


Passive circuit component Circuit component Computer Hardware programmer Electrical wiring


Maybe it can help you out. Msg me on discord if you are interested >> itsPointless#6048


Also my 2c on the 250A limit. I think it's a combination of you being a cell short & a tough voltage sink when giving it some beans.
The controller current limits if voltage is going down.


I'd also look at corrosion inside the motor at the brush contacts. 250A @ 144V is still roughly 36kW. I think that should really make it move easily.

So either you're running way below 144V or you're losing power somewhere else.

Note too that LFPs aren't especially designed for high currents. Can imagine the old owner set it to 250 to not blow them up.
 
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