# Finally finished my build, but it seems "sluggish"?



## SCEV (Apr 10, 2012)

It's been a while since I've posted on here...my 6 month EV project turned into about a 2.5 year project when life got in the way (and I probably got a little lazy).

So about a year ago, I got my 60 CALB CA100 cells bottom balanced and charged them up to about 60% SOC. The cells sat like that for about a year until I finally finished the car this past weekend. After a couple test drives up and down the street, I did my first "complete" charge up to 210V (3.5V/cell). Since it was my first charge, I was out there with a voltmeter watching all the cells just to make sure none of them got out of control. There were two cells (54 and 57) that acted like the rest up until around 3.45V...while the rest of the cells continued to climb, these two started falling. By the time the charge finished they were down to just under 3.4V. There were another two cells that got all the way up to 3.69V by the time the charge terminated, but I'm not too worried about those...I think they would be fine if the other two hadn't dropped. 

Okay, enough back story...my problem is when I floor it, I'm expecting to get 1000A from the battery pack (10C), which the CALB CA series should be capable of for short bursts <5s. I'm using a Soliton1, so shouldn't be any problem there either (I've attached a screen shot of my settings, definitely let me know if anything jumps out). However, when I floor it, the batteries put out close to 1000A for just a fraction of a second and then the current starts to drop. It seems if I floor it from a stop they never get close to 1000A, but from 20mph they get there but then drop off very quick. Attached is a logger.txt file from a test run this afternoon. You can see around time 315420 I floor it, the battery current gets close to 1000A but then starts to fall even though I'm still requesting 1000A. Any idea what could cause this? Any suggestions on what to test?

I'm hoping this isn't it, but I just measured all the cells after they rested for about 20-30 mins. Cells 54 and 57 mentioned above are 3.285V and 3.282V respectively, while all other cells are 3.29xV. Could these two cells be bad and limiting the entire pack?

Thanks,
Scott


----------



## Duncan (Dec 8, 2008)

Hi SCEV

Your pack is sagging to about 130v at 1000amp - sounds like a lot to me

As your motor revs rise the motor produces back EMF and the controller has to increase the PWM to maintain current

About 1800rpm the controller goes to 100% - it can't go any higher - then as the revs continue to rise the current drops -
by 2000rpm you are down to 900amps
by 3000rpm you are down to 500amps - and your battery has recovered to 153v
by 3400rpm you are down to 400apms - and your battery has recovered to 158v

If you want to have more power higher up the rev range you need more volts!
(So do I)


----------



## SCEV (Apr 10, 2012)

Wow, do you think my entire problem is just back EMF? 

Also, does sagging from a resting 197V down to 130V at 1000A seem like too much sag for these batteries?

If there is an underperforming battery in the series string, would that effect the overall pack performance?

Scott


----------



## Duncan (Dec 8, 2008)

Hi Scott

I don't think a single cell (or two) would make that much difference,
My Headways (four strings of 40 off 16Ah) only seem to sag about 15v at nearly 1000amps
I hope somebody with CALB's can pipe up with some information

I have similar issues with power dropping off - but worse as I start with 130v! 

I vaguely remember somebody talking about sagging down to half! voltage


----------



## dladd (Jun 1, 2011)

So I don't know how to read these logs that well, but I don't see battery current in there. Is that correct?

Anyway, yeah sagging to 130v from 193v is a LOT, even for CALB cells I think. That's 2.17vpc. But it is 10c, so I could see that. Your motor current is sitting pretty at almost 1000a for a while, I can only assume the battery current eventually reaches 1000a as well before the motor current tapers.

personally I limit my sag to ~2.6vpc which with my somewhat unbalanced and not great condition 130ah blue CALB cells works out to around 500a when the weather is nice. But like I said my cells are not in great shape.


----------



## Duncan (Dec 8, 2008)

Ok so the CALB 130Ah go from ~ 3.2v - 2.6v at 500amps
So we would expect 2.0v at 1000amps - 2 x 60 = 120v
That was for 130Ah
So 100Ah would be worse??

Sounds about right for the numbers on your log

_but I don't see battery current in there. Is that correct?_
Yes
But if you look at PWM and motor current you can calculate battery current
The easy calculation is that at 100% PWM - Battery Current = Motor Current

This surprised me when I encountered it
Back EMF (or more correctly EMF) is proportional to;
Motor rpm AND motor current

So when I went to twice the current and a lower voltage it bit me hard


----------



## piotrsko (Dec 9, 2007)

Fwiw: stupid Chinese 1000 amp shunt I bought is 3 ohms!!!!!!
My battery cables to motor are about .02 ohms @ 20 ft. Doing the math 3.04 ohms X 1000 amps is: not a lot of voltage getting to motor. Removing shunt and I still have a 40 volt drop. I actually hit the low battery limit in the Sol1. 

My Kostov isn't really happy at 120 volts, so my summer project is new motor to battery cables, 4/00 instead of 1/00. Possibly re do the volt pack to 350v also.

Performance went way up when I yanked the shunt.


----------



## major (Apr 4, 2008)

piotrsko said:


> Fwiw: stupid Chinese 1000 amp shunt I bought is 3 ohms!!!!!!


Wait a minute! 3Ω * 1000A = 3000 Volts.  Let's see a pic of that shunt 

Also, it would have a power loss of 3 Megawatts  Cool


----------



## Hollie Maea (Dec 9, 2009)

major said:


> Wait a minute! 3Ω * 1000A = 3000 Volts.  Let's see a pic of that shunt
> 
> Also, it would have a power loss of 3 Megawatts  Cool


Also I would like to see a picture of the 3000 volt battery pack driving it.


----------



## piotrsko (Dec 9, 2007)

where did I say I was pushing 1000 amps through that shunt? As you so graciously point out, it may be physically impossible.

I'm using it for illustration of unsuspected ohmic losses caused by high currents to a person with a skill level that I have no knowledge of.

What else didn't you like? Perhaps the cheap Chinese shunt is 3 ohms measured using a harbor freight dvm? Sorry, my Simpson is broken, My o'scope and the heathkit VTVM have issues with low mu and weak filaments.


----------



## arklan (Dec 10, 2012)

the numbers youv mentioned seem weird to me
my only ev experience is my car with 48 100ah sinopolys but shouldnt be too different to calbs i dont think

to get my car to use the 500amps at the top of the gauge i need to be in 4th gear and floor it
third gear and it gets to about 380-400amps
im pretty sure its because my car is so light it just doesnt need that many amps
it will chirp the wheels on take off

so yeah my 2c is that maybe ur car is so light that its not using the full amps because your motor isnt being taxed enough
i dont know what kind of car you have though


----------



## kennybobby (Aug 10, 2012)

SCEV said:


> Wow, do you think my entire problem is just back EMF?
> 
> Also, does sagging from a resting 197V down to 130V at 1000A seem like too much sag for these batteries?
> 
> ...


Did you weigh your car now that it has been converted to get final weight?

i replaced a 944 tranny in an ICE car with one out of a 951 and found it to be sluggish due to the gear ratios. It had a higher top end but less pull down low. The weight and the gearing might be related to your performance.


----------



## Rob A (Feb 7, 2010)

Mine seemed sluggish also, its a 64 Ranchero with a Soliton1 and direct drive.
I adjusted the slew rate to 20000 and it made a big difference and I have my max battery current limited to 700 amps. It looks like your slew rate is set to 1000.


----------



## mizlplix (May 1, 2011)

Just as a side note: My 38 cell pack of CALB 130AH cells sags a lot too.

Even with a full charge and the pack at 130 volts, The first "hold it to the floor" acceleration will start the BMS squealing (A cell went below 3 volts) after 4 seconds. The amps on my hand held reads 625. I use the squealer as a driving aide to keep my foot in check....HeH...

Yes, I have checked the cells several times and can not find one weaker than the rest. I performed this accel test with the battery box lids removed, at night and it was not just one cell with a red light. It must have been at least half the pack.

I understand that this is not a "scientific" test, but it does get the message across.

BTW: I can get a comfortable 58 miles to a charge. (1,900# car) When driven sanely.

Miz


----------



## dtbaker (Jan 5, 2008)

whats the temp.... ? you get a lot more sag below 60 deg F. Worse if you have a couple unbalanced or weak cells.

the other thing is you really have to go thru all the limit settings. I found with the Zilla that the defaults really clamped down on performance until I found the right balance and set the low voltage and things like that to ALLOW significant sag under heavy load before clamping down amps.


----------

