Wawasee HS Shell entry problem with Cycle Analyst

[Pletch]

We had Wawasee High School's electric car out Sat for it's first test. The car had not been on the ground since last fall. The car ran fine without the Cycle Analyst attached. When the AC was hooked up, a slight press on the throttle got the car a start, but then quickly cut out. This would repeat each time. Removing the AC would allow the car to run normally. I suspect a problem with settings, but didn't think anyone of the class changed any of the limits. The battery was completely charged, and all seems normal. Monday when I can get to the car I thought I'd do a Full Reset on the AC and see if that changed anything. Any other areas that I should look into?

eZee20-B 20 inch (300rpm) motor
48v 10Ah LiMn eZee battery pack
thumb throttle
Cycle Analyst
Analogger

Regards,
Pletch

[itchynackers]

Yes, probably the settings. Go through each one ( I suspect either Rshunt value, or LVC).

[Pletch]

Yes, probably the settings. Go through each one ( I suspect either Rshunt value, or LVC).

Thanks for your advice. We're fairly new at AC settings. I assume that LVC is the "low Voltage " setting. Do you have any thoughts about what a Rshunt value or LVC setting would normally be? One of my steps probably should be to talk with Grin's tech folks to see what settings would be typical. To my knowledge students have not changed the settings from Grin's original settings. If students made changes, we may need to simply return to Grin's default settings.

Thanks again for your help. As soon as we solve this, I will report back what changes were made.

Regards,
Pletch
for Wawasee High School

[amberwolf]

If the Analogger was attached and running, go thru the data and see if the pack voltage dipped enough to trigger the CA's LVC (assuming you have the CA setup to cut throttle upon LVC).

You could have a bad cell or connection in or from the pack causing a voltage drop under load.

If the pack just sat around totally unused, then if it has a BMS in it it could easily drain one or more cell groups in the pack if left connected to the cells for months.

It would be even worse if the pack was left connected to the controller/CA/etc. for all that time, as it would have drained it down to BMS LVC, and then the BMS would have continued to drain whichever cell groups power the BMS, possibly to zero.

That would leave you with at the least an unbalanced pack after a first charge, requiring etiher manual balancing or leaving it on the charger for potentially weeks while the BMS balances things out. At worse, it could have damaged cells causing higher Ri in them and probably lower capacity.

[Pletch]

If the Analogger was attached and running, go thru the data and see if the pack voltage dipped enough to trigger the CA's LVC (assuming you have the CA setup to cut throttle upon LVC).

You could have a bad cell or connection in or from the pack causing a voltage drop under load.

If the pack just sat around totally unused, then if it has a BMS in it it could easily drain one or more cell groups in the pack if left connected to the cells for months.

It would be even worse if the pack was left connected to the controller/CA/etc. for all that time, as it would have drained it down to BMS LVC, and then the BMS would have continued to drain whichever cell groups power the BMS, possibly to zero.

That would leave you with at the least an unbalanced pack after a first charge, requiring etiher manual balancing or leaving it on the charger for potentially weeks while the BMS balances things out. At worse, it could have damaged cells causing higher Ri in them and probably lower capacity.

Thanks for your input. It's causing me more worry though. The Li battery was stored over the winter with nothing attached to it. It was back on the charger in late January. We charged it in early Match as we finished up the body. I hope that the battery is OK. You used a couple of terms that I don't understand: BMS and BMS LVC. Can you fill me in with definitions?

Regards,
Pletch
Wawasee High School

[itchynackers]

He's refering to a Battery Management System, if you have one hooked to the battery. Many BMS's are crappy, and can slowly drain a battery if left unchecked (over winter). If you don't have one, we'll rule that out as a possible cause. LVC is the Low Voltage Cutoff setting, where a controller, or Cycle Analyst will cut amps if as the voltage approaches the LVC number. Your Rshunt number is based on the shunt(s) inside the controller, and it will vary from controller to controller. If you tell us the controller type, we may be able to get you close on the value, otherwise you could figure it out by trial and error. I do it this way:
Let charger completely charge battery.
Reset the trip usage stats on your CA.
Run your vehicle, discharging battery about half way (guesstimate).
Be sure to record the watt-hours used, and amp-hours used.
Let charger completely charge battery.
Record the wh or ah that the charger puts into battery.
If the CA values don't closely match the charger values, then you need to adjust your Rshunt value.
For example, if CA says 2.048ah used, and the charger says 2.276 ah used, then multiply your Rshunt value by (2.048/2.276), so if you are at an Rshunt of .800mohm, the multiply it by 0.9, for a new Rshunt value of 0.720mohm.

Hope this helps.

[Hillhater]

Guys, ..unlikely a battery/bms problem , since from the OP ..

...The car ran fine without the Cycle Analyst attached. When the AC was hooked up, a slight press on the throttle got the car a start, but then quickly cut out. This would repeat each time. Removing the AC would allow the car to run normally.

..so i would focus on those CA setting rather than checking the battery condition or BMS.

[Pletch]

Thanks for all your replies. The battery has no BMS. The charger is the one that grin sells with the 48v 10ah LiMn battery sold as an option for the eZee kit. It is listed as a 3amp one place and 4amp in another. In the Q&A, they say the eZee controllers use a RShunt running 1.3-1.6 mOhm.

It is pictured at the following link:
http://www.ebikes.ca/store/photos/B4810LiM-EZ_Kit.jpg
I appreciate your help with terms. We're trying to learn fast.
Regards,
Pletch
Wawasee High School

[amberwolf]

@Hillhater: You're probably right, but I wanted to be sure they checked the battery too, as I am not certain they completely know exactly what they've got (especially after the subsequent replies).


@Pletch: I think that your battery *does* have a BMS, unless it has been removed or disconnected for some reason. Based on your original post plus your link to the picture, it should have a BMS that allows a max of 35A discharge.

48v 10Ah LiMn eZee battery pack

The battery has no BMS. The charger is the one that grin sells with the 48v 10ah LiMn battery sold as an option for the eZee kit. It is listed as a 3amp one place and 4amp in another. In the Q&A, they say the eZee controllers use a RShunt running 1.3-1.6 mOhm.

It is pictured at the following link:
http://www.ebikes.ca/store/photos/B4810LiM-EZ_Kit.jpg

When I check Grin's site, that p/n (for the battery) shows this description:
"B4810LiM-EZ 48V 10Ah LiMn battery with Samsung cells, 35A Max BMS. No charger"

So it should have a BMS in there, as it comes from Grin Tech. Apparently the BMS itself doesn't think there's anything wrong with the battery, so there shouldn't be, but it's possible for a BMS to be designed so that it cannot detect a dead cell, only one that crosses from above the LVC threshold to below it. I don't know why anyone would do that, but it could be done and it migth be a cheaper way of doing things, and cheaper is often "better" for manufacturers regardless of consequences. I have no idea how the EZ BMS is designed. Other than opening up the pack to physically check, you'd have to ask Grin Tech if there actually is a BMS and how it works if so.

The easy way to see if the CA settings are causing the problem is to disable throttle control from the CA, so it does not disable or modify the throttle, but leave the CA hooked up so you can still get min/max voltage and current readings. Ensure the CA Rshunt setting is set to match the controller's mOhm value. If the controller is not marked with it's exact value anywhere, you'll have to test it using a constant-current supply and a good meter to read the voltage off of it, and then use Ohm's law to calculate it's exact value. (the complete procedure is in Methods' Calibrated CA thread in the Items-For-Sale-New section).

Then retest with the CA hooked up, and see what happens from there. That way you can read the max current pulled from the battery on throttle usage, and can also see the voltage drop under load.

[Pletch]

We continue to sort out the car, and are getting close. We have been able to eliminate battery and BMS. We believe the problem we had with the motor cutting out is connected to the speedomoter reading and the mph limiter. We input the wheel size, entering 1515 mm for a 20 x1.75" tire as the book suggested That gave us mph reading that were much too high. The mph limiter would then shut us down. We tried entering the wheel size in inches, but that gave a mph that was far too low. I was able to talk with Grin Tech today and he confirmed that the problem had to be the numbers from the magnetic pickup. We will address that tomorrow am.

At any rate, today the car performed well on the school's 1/4 mile track. We must average 15mph at Shell, and our driver ran a mile in 3 min 50 seconds. Our technique is to accelerate to 20 mph and coast down to 10 mph and repeat. We took our shift points from a phone's gps. We tried 23 mph as the high and 10 mph for the low, but covered the mile with too much time to spare. We want to run as close to the 15 mph minimum as we can. We will continue to refine our driver technique in the next week.

We do feel that any problems we had can be traced to faulty speed readings and not other electronic, motor, or battery problems. I want to thank all on the forum who helped out. Having a source like you fellows is of great value. My complements to Grin Technology; they were very helpful today as well.
Regards,
Pletch

[amberwolf]

Do you get better efficiency with pulse-and-glide? On a regular ebike, without an aero shell, I get better efficiency with constant operation, because it takes more power to accelerate than to hold speed, due to higher motor currents at acceleration. But I am riding heavy bikes with poor aero.

[Pletch]

On the electric car, we're unsure which method is best. Our experience with the gas and diesel cars is that run and coast is more economical. We do work very hard to coast very well. On the 5/8 mi banked oval at O'Reily Raceway track in Indianapolis, we burn the gas engine coming out of turn 4 and coast all the way around, burning out of turn 4 again. Typically a 6-7 second burn will do this.

Tomorrow I hope to test both methods. We'll reset the CA, restart the Analogger, and run a mile both ways. Those results will tell us if we coast well enough to off set the energy coast of the acceleration. One thing that can easily change our result is that we have not run on the track with the streamlined top installed. We are much more slippery through the air with the top. Our coast should be better with the top. When the top is finished, we'll want to retest. You can see why track time is so important to us right now.

Regards,
Pletch

[Philistine]

If it is a CA DP, if the Rshunt value was incorrectly entered, wouldn't the maxamps limit cut in strangely like that and cut the throttle. Regardless, it is essential that the Rshunt value be correctly entered for the CA to have any purpose anyway (if it is a CADP).

[Pletch]

If it is a CA DP, if the Rshunt value was incorrectly entered, wouldn't the maxamps limit cut in strangely like that and cut the throttle. Regardless, it is essential that the Rshunt value be correctly entered for the CA to have any purpose anyway (if it is a CADP).

The Rshunt was one of the original concerns that the guys on the forum mentioned. When I got back to school, I found that the Rshunt value (1.73 mOlms) was listed on the controller. When I went through the setup on our CA-DPS, I found that the same value had been entered by Grin. When I talked to Grin's tech guy last night, he confirmed that.

Thanks for your help. I hope to iron out tha last of our setup stuff this morning.

Regards,
Pletch

[itchynackers]

It is doubtful you will get more efficient with pulse and glide. I tested this last summer and it didn't work (with electric motors). You should test to confirm. If you want to average 15mph, then you should set your max amps and max mph in the CA to be close to 15mph. Also, to be very accurate, you need to air up all your tires to whichever pressure you will run in competition (high), and then accuratly measure the circumference of the tire with the speed pick up. Many on this site do it like this: Put a wet paint mark on your tire. Then with the car fully loaded (with driver), push the car for at least one rotation. Then measure the distance between paint marks on the ground. Enter that value (in millimeters) into the CA.

[Pletch]

Today was a good day for the electric car. Before school a student and I reinstalled the magnetic pickup now have an accurate speed reading. The earlier install was skewed to miss a disk brake, but we're good now. We ran 4 one mile trials - two with run and coast and two with a steady speed. Neither held an advantage today. The lowest amp/hr went to run and coast, but a later comparison went the other way.

There are two variables that will have an influence on what we do. The high school track is rubberized, and coasting is far worse than hard asphalt. We'll run better later on a hard surface. The second is that our streamlined top was'nt ready today. We expect that the top will cut air resistance and extend our coast. Our past experience with other cars allow us to predict improvements when dealing with these variables.

If weather permits, we'll be on the track tomorrow. If it rains, we'll work inside.
Regards,
Pletch

[itchynackers]

Are you using a cruise control, or limiting the amps with the CA? I'm assuming this is an efficiency contest. Are you only able to use a certain number of watt hours? Please keep us posted with your progress.

[Pletch]

We've been busy with minor details like body, mirrors, safety equipment, and many other things. We hope to have the car out soon to confirm energy use with the top on. We expect to coast better with the top on.

There is much to do. The cars are loaded a week from today for the trip to Houston. The diesel car and gas car are ready except for minor adjustments. With track time, the electric car should be ready late in the week. I should have numbers by then.

Regards,
Pletch

[Pletch]

The Shell Ecomarathon is over, and Wawasee High School did well over all. We won the diesel class the second year with 1288 mpg. Last year we won with576 mpg. The closest car to us had 703 mph.

The gas car was seventh with 933. This sounds good, but the gas class was won with 2100 mpg. We should be capable of 1200 with our present engine.

The electric plug in class was where we competed with our eZee hub motor. We placed second with 399 km/ kwhr. The winner was 674.

The competition was held in front of the George R Brown Convention Center in Houston - a .6 mile course on city streets. We ran 10 laps for a 6 mile course. We next compete in Indianapolis in April. we have plans for a number of improvements.
Regards,
Larry Pletcher
wawasee High School.

[amberwolf]

How did it test out with pulse/glide vs continuous motor use?

[Pletch]

We're finally home from Houston will unload the truck this afternoon. We had others taking pictures, but I wanted to share a couple of the cars. The first pic below is a team photo:


The car on the right is the eZee car.


Gas car on the track.


Diesel car on track.


eZee car practicing

Amberwolf, with our slippery top, the edge goes to run and coast. However the difference was slight - maybe the better run was caused by wind changes that were constantly changing. The other electric cars at Houston used the same technique. Also we coast extreeeemly well. Ceramic bearings lubed with very thin, watery high tech lube. They need constant monitoring. They don't have to last 1000 miles - just one run at a time. We can run up to 20 mph and coast the whole .6 mile lap. The ability to coast at Houston is HUGE.

Regards,
Pletch