Aussie EV Autocross Special

[kiwiev]

Hey mate your controller is a Curtis? And does it have the hour glass readout with plug on the back?

If so I have a Curtis hand held OEM programmer, this can allow you to change your upper voltage limit a wee bit


Cheers Kiwi

 

[galderdi]

Yes its curtis. But its an old model. No plugs or outputs. It only has the accelerator input dc input and motor outputs. But thanks for thinking of me.

 

[Hillhater]

I just did a quick and dirty test charge on a 5 Ahr, 5S, lipo pack that happened to be on my bench.
I settled it at 4.0 volts per cell (+-0.02v) ...then monitored and measured the charge until it reached 4.2v/cell
That 0.2v took 58,43" mins and the cells charged another 1.135 Ahr more than what they had at 4.0v.
Now thes are old cells ..6+ yrs and much used, so i seriously doubt they still hold 5 Ahr, but assuming they are close to that, the extra charge above 4.0v represents 22%+ of the total cell capacity...most likely more !
Im not suggesting these are the same as your Volt cells ( hard to find a real charge curve for those ?) , but several other lipo charge curves indicate similar capacity at the top of the voltage range.
So, you could be missing out on a lot of battery capacity (IE 20%. = 1.6kWhrs ?) , by not charging past 4.0 volts .!
You really should do a similar charge test.
How difficult is it to take 4 cell modules out of the pack ?

 

[oatnet]

How difficult is it to take 4 cell modules out of the pack ?

Destructive, they are not packaged like the Leaf cells.

Please be aware that "LiPo" is a blanket term (click here) that refers to lithium cells that are manufactured in a pouch format, encompassing thousands and thousands of varieties of chemistries and manufacturers with distinct and disparate discharge curves. Although they both fit under the umbrella term of "LiPo", there are no conclusions to be drawn by comparing your Lithium Cobalt technology from 6 years ago to the Volt's NMC chemistry, let alone other random unspecified "LiPo" curves. If you are looking for the discharge curve of a volt pack, check the link I posted earlier in this thread.

And regarding your earlier post, no I was not "confusing the discharge rate with the charge rate", nor did I recommend charging to 4.2v. :lol: I guess galderdi could follow your recommendation to not use his pack until he has a bulk charger, but he specifically asked for recommendations on which of the 6s charger's settings to use so he did not have to wait. I shared the 4.1v "LiIon" setting I'd choose from the options in the manual, and a technique I used on 153v, 164v, 175v, and 179v large-format EV packs where I faced the same pack v > controller v problem.

-JD

 

[Hillhater]

JD, no argument here, we are both trying to help Galderdi get more from his pack.
You by offering ways to charge to his voltage limit, and me by suggesting ways to get more capacity from the same pack whilst not exeeding the same voltage limit.
I know that my lipo charge capacity test is unlikely to simulate a volt cell, (and said so), and i am amazed that there does not seem to be a charge curve for those cells posted anywhere obvious ? (Despite them being over 6 year old tech also )
But , most all lipo capacity maps show there is useful capacity above 4.0v for those that want to maximise there run time between charges.
Even the discharge curve you linked to showed there was 6Ahr available above 4 volts ?...(13% of capacity)

 

[galderdi]

Thanks everyone. I am really pleased with the help and information I am being offered. It really does make a difference. I am amazed at the amount of information I have picked up in a relatively short time. (I only started building this car 12 months ago).

Anyway I have some good news and some not so good news.
First the not so good news. Yesterday I started to install my new gauge. I wrongly assumed the shunt would sit on the +ve side of the load. By the time I learned my mistake I was too far into the installation to reverse the mistake (I didn't have enough terminals to redo the fitting on the -ve side). But I thought I should be able to rig it to work on the positive side. WRONG!!!! POP, FIZZ, smoke, no more gauge.

So I still went to the Fiat event and helped them run their motorkhana. It was a great day and there was a fair amount of interest in the Batt mobile. I had a few drives in my car for various reasons, and afterwards I got the chance to have a practice in the Batt mobile. It was a marked improvement over all my previous tests but it still wasn't quite as good as I was expecting. Other than my acceleration etc from the camera I don't have a lot of data to work with. The launch is great, although I am still thinking it was better before, so I think that part is down to the increased flywheel (I'm having the light one balanced). But that doesn't account for the reduced acceleration each time I go up a gear.

Eg
Acceleration in 1st 9 out of 10
Acceleration in 2nd 7 out of 10
Acceleration in 3rd 4 out of 10
Acceleration in 4th 2 out of 10
Didn't get to try 5th

I have ordered a replacement gauge for the one I blew up. I will install it properly before the next competition day, April 25. Then I will be able to analyse further to work out where the weakness is. Although that event is a motorkhana so I won't get to see the higher gears. (Just first and reverse). And the performance in 1st today was great. But I might be able to sneak a faster run in when nobody is watching.

I just checked the voltage. It is down to 149v. I started with about 165v. I don't know how that equates as amp hours, kwh or % of capacity. I figure I did the equivalent during the day of about 10-14 motokhana runs. So I am fairly confident I will get around 20 (maybe more) motokhana runs out of a fully charged pack (170v)

I also think I need to perform a test to understand where the controller voltage limit actually kicks in. At some point (when I have some spare time) I will continue to charge the batteries (within their limits) above the 170v and keep checking if the controller still operates. When it eventually stops I will know the limit. Then I will discharge a little to bring it back under that limit.

Here are some of the (non competitive) tests from today:

[youtube]3-M9Uj1brPU[/youtube]
[youtube]_jZJoGj78Sw[/youtube]

 

[Hillhater]

You should always do the straps up on your crash helmet ! :wink: :lol:

 

[galderdi]

You should always do the straps up on your crash helmet ! :wink: :lol:

Ba hahahaha. Yeah that helmet is useless the visor didn't even keep all the stones and grit off my face

 

[dingoEsride]

You should always do the straps up on your crash helmet ! :wink: :lol:

Ba hahahaha. Yeah that helmet is useless the visor didn't even keep all the stones and grit off my face

Ha Ha hoon on the loose, good job on getting it all together and having fun, thanks to Telstra F&%$ up I can watch u tube clips today

 

[oatnet]

Hey gald - that looks like a blast, thanks for posting the video, I really like the overlay too. I'm telling you man, dial up the amps and it will be better than you expected. I'm pretty sure you said you had cooling on the batteries, so the batts can handle it, the controller can handle it, the motor can handle it; assuming your drivetrain can handle it, it's all good. Since I don't think your motor is cooled, I'd check it after a few runs at each new power level, to get a sense of the thermal load.

Oh, wait, did you say you have not run-in the brushes? Maybe wait on that advice I just gave... What does the patina look like on your commutator, can you post a few pictures? The brushes need to be worn down/shaped to maximize their contact area with the commutator, and a good patina on the commutator helps transfer watts better. Don't remove the brushes though, it shortens their life. Lift the rear wheels, and run it in first gear on a directly-connected 12v battery for a few days - you'll have to swap out batteries a few times - and you will be good to go. Blow at the carbon dust afterwards, so you don't risk a flashover.

So 149v/42cells = 3.54v/ cell, which is equivalent to 340.57v on the 96-cell pack tested for the EREV discharge curve, which correlates to taking 35ah from a fully discharged pack. Since your pack wasn't fully charged, 165v /42 cells = 3.93v/cell, which is equivalent to 377v on the same discharge curve, where about 10ah would have been pulled. I would speculate that you pulled 35ah-10ah=25ah from the pack out of a potential 42ah usable in the pack (or 47ah if you discharge past the "knee" in the discharge curve, as many do but I do not). This assessment is pretty crude because there is a lot of extrapolation going on against a random discharge curve under load, but that is the best I can do with the data you have so far, hope it helps.

Also keep in mind that AH is not a good gauge of power consumption, because it does not consider the volt side of the equation (volt*amps=watts), so you are getting far more watts at the start of the discharge when volts are high, far less when the pack is depleted and voltage is low. At the same number of watts needed to maintain a given speed, AH will go by much faster at the end of the discharge, so when you have used 1/2 the ah you have actually used up 2/3 of the pack's capacity. Watt hours (WH) are a more effective method of measuring discharge. I use a CycleAnalyst V3 for my "gas gauge"/coulomb counter, so I always have a sense of how many WH I've taken from the pack, and how many I have left.

I'd be really interested to see the sag under a given discharge - like at a 100a load, how much does the voltage drop from resting voltage - but I don't think you can capture that yet.

Even the discharge curve you linked to showed there was 6Ahr available above 4 volts ?...(13% of capacity)

So on the discharge curve on page 2 of the link I supplied earlier ( http://avt.inl.gov/pdf/EREV/batteryvolt3929.pdf ), the curve starts at 4.11v/cell in a 96 cell pack, which fits the charge setting I recommended. Not sure where the 4.0v figure came into the discussion, but the if the Curtis cutoff is at 170v, that translates to 4.047v, which is 388.47v on the pack's discharge curve. By my eye, that is 2 or 3ah from fully charged; suboptimal, but between a fixed 170v cutoff and difficult-to-alter pack, the point is moot.

Even if it were possible, removing 4 cells from the pack as you recommended would decrease 9.5% of the pack's capacity, I'd prefer leaving 5% on the table by not charging to the peak rating. In addition, while peak charging is useful for occasional top balancing it ages the cell, so usually I don't fully charge my cells to extend the life of my packs.

JD, no argument here, ... But , most all lipo capacity maps show there is useful capacity above 4.0v ...

Again, I would caution against making assertions about "LiPo" - a123/thunder sky/CALB LiFePO4 are also "LiPo", but their peak charge is 3.65v, so I assure you that their discharge curves (not capacity maps) do not show any useful capacity above 4.0v.

-JD

 

[kiwiev]

The video looks awesome mate 8)

The hole shot looks impressive are using the clutch?

The DC torque looks great

Cheers Kiwi

 

[galderdi]

Thanks guys, some great advice there. My previous statement about the current being adequate was based on my previous experience of the acceleration. It feels like it is a it less than that at the moment for some reason. So yes more current would be nice but I am not sure why they would have dropped. I am hesitant to make changes until I have the working gauge so I can see what is going on.

for the motorkhana I don't use the clutch. But for khanacross I do use it to change through the gears (not for the launch)

Oatnet, your estimates on my useage seems to align with mine. I think the pack size will work well for my events although I had hoped to have enough for two drivers... thatmight be pushing it.

the cutoff on the controller is between 175 and 180v. The 170v was just me giving myself a buffer because of the uncertainty,. But once I test it fully and know the cutoff I can charge closer to that limit. Hopefully that means something like 174v

 

[oatnet]

the cutoff on the controller is between 175 and 180v. The 170v was just me giving myself a buffer because of the uncertainty,. But once I test it fully and know the cutoff I can charge closer to that limit. Hopefully that means something like 174v

Oh, that is awesome mate, even if these turned out to be 4.2v cells that would be 176.4v peak, you could charge them all the way up for balancing and still be under the limit. Once you step on the throttle, both sag and decay of the peak charge will drop voltage fast, so as long as your starting voltage is under the limit feel safe and certain.

Still, I'd keep it to 4.1v/cell till you know more about them. I use a CBA-IV from west mountain radio to get discharge curves from single cells. The CBA doesn't do a lot of watts so it took a while to do a test on 60ah a123, but if you care enough to try there it is.

-JD

 

[galderdi]

Hey I almost forgot this test from yesterday morning. I had to do it at 6am to make sure nobody else was there yet. It handles pretty good. I had my rock hard motorkhana tyres on the back so it was want to let go in the rear. With proper tyres on the back it should go well. Still need to do an ackerman angle modification and soften the front a smidge. The brakes are a bit of a problem but I'll keep trying stuff until its good. As you can see I drove over something on the last lap. I wasn't expecting the bang and wasn't sure if I had broken something.

[youtube]7UPyA56Ku0g[/youtube]

 

[kiwiev]

Do you get small stones and grit off your wheels in your face with out mud guards, mine was bloody deadly

Coool video mate 8)

Cheers Kiwi

 

[galderdi]

Do you get small stones and grit off your wheels in your face with out mud guards, mine was bloody deadly

Coool video mate 8)

Cheers Kiwi

Absolutely. Particularly with those track tyres. They are so sticky I should hire the car out to clean the streets. But its usually not an issue because I am forced to wear a helmet.
Most of it skims up between the dash and the front extension of the roll cage. I have been tempted to put a bit of clear plastic in that gap, but its probably not worth the trouble and I have so many higher priority items to work on.

 

[kiwiev]

Hey mate
Do you have any hard data on the C ratings of these cells I thought volt packs were high voltage low current, this could be the reason its not accelerating as hard and as Hillhater states a big voltage sag.

The Sonic sags from 154 volts to 113 volts with a 1100 amp suck and the packs rated at 1600amps for 10 seconds the curtis controller captures low voltage and max amps, btw this varies with temperature and when I hill climb the second run always seams to pull stronger
Cheers Kiwi

 

[galderdi]

Yeah, I am not certain about the C rating but I thought/was told ot would be enough. I am fairly sure you are right. But for the moment it will have to do. It will be good enough to have some fun. I will stick with it while I am in the development phase. Then I will decide on the next option. Either double up with another set to increase the current or a replacement set with a higher c rating. Its a shame they weren't a symetrical pack or I could halve the voltage and increase the current. I was assured these batteries would be suitable. This is another reason I am not happy with the vendor. I will never do business with him again.

 

[kiwiev]

Yeah, I am not certain about the C rating but I thought/was told ot would be enough. I am fairly sure you are right. But for the moment it will have to do. It will be good enough to have some fun. I will stick with it while I am in the development phase. Then I will decide on the next option. Either double up with another set to increase the current or a replacement set with a higher c rating. Its a shame they weren't a symetrical pack or I could halve the voltage and increase the current. I was assured these batteries would be suitable. This is another reason I am not happy with the vendor. I will never do business with him again.

Im waiting on a price for the Kokam cells 3.7 volt 53 Ah and 424Amps for 30 seconds and only 45Kg and 265 Amps continuous.

Maybe a good option down the track, it is weird how batteries change the feel of your car day to day. A week with out driving it always makes it feel faster.

Cheers Kiwi

 

[galderdi]

Awesome, let me know how that turns out.

 

[galderdi]

By the way my next event is a motorkhana this sunday. This will be the first time with the batteries fully charged. I'll let you know how it turns out. Plus I think I have found my brake problem. The connector bar was bending under pressure. So I have now re-inforced it. That reminds me I should take a photo of the latest modification.

 

[galderdi]

QMC Round 3 didn't go to plan. I broke a weld on my brakes on the second test. I had welded the brakes while assembled because I couldn't figure a way to disassemble them first. I will have to modify the peddle box so the peddle can be removed. Then weld it properly and re-assemble it. Hopefully it won't weaken the peddle box significantly.

I am also thinking of halving my battery pack and running the two halves in parallel to increase my current. This would result in 60 - 72V depending on the state of charge. I know this will decrease my speed but will significantly increase my acceleration. I figure I can use the gears to compensate for the speed.

Here are the videos:

[youtube]UM3Yi4ka99M[/youtube]
[youtube]Q-bJ_m4NFVs[/youtube]

 

[jbalgley]

Subscribing.

 

[galderdi]

I had a delivery yesterday. It was a USB<>CAN BUS adaptor. Hopefully now I will be able to get my big charger working. The plan is to use the big charger to get 90% of the charge into the batteries. Then I'll use the little charger to balange charge the remaining 10% 6 cells at a time.

This weekend is a long weekend here. So I plan to make the ackerman angle adjustment.
Next weekend I need to repair the brakes. I will dissasmble the peddle box, weld the two peddles and then re-assemble the box.
The following weekend I will swap back in my lightened and now balanced flywheel.

Then I will be as prepared as possible for the next event (Khanacross on May 22)

 

[kiwiev]

Hey Greg still waiting on pricing for the Kokam as you guess you cant go direct.

Can you post pics of your steering mod please.

Cheers Kiwi