Hillhater
100 TW
Hmm ? Isnt that less than 4-5 mins run time ?galderdi said:
Hard to believe you would burn 6-7 kWhr that quick ?
Do youhave any means of collecting data,.volts, amps etc during a run ?
Aussie EV Autocross Special
- Thread starter galderdi
- Start date
Hard to believe you would burn 6-7 kWhr that quick ?
Do youhave any means of collecting data,.volts, amps etc during a run ?
Yes, that is about 5 minutes of run time (including some movement between runs). I was expecting more too. But I couldn't even charge the pack before the event and it was sitting at 147V from the start. I beleive the nominal voltage should be 155.4v and the fully charged pack should be about 170v. So I went to the event knowing it would be short lived.
I don't currently have any way of gathering the data. I do have some devices, but I haven't had the chance to install them (My first device didn't work). However based on my experience with the lead acid batteries I roughly calculated the car to use about 0.5Kwh per run. I calculated this prior to the event last weekend but I think it still roughly holds true. That would mean I used about 2.5Kwh during the event. I am hoping 147v = about 3.9 Kwh (ie 2.5Kwh that I used plus 1.4Kwh or 20% unusable capacity). I am nervous about these figures because at 5.6Kwh of usable capacity and assuming my estimate of 0.5Kwh per run is accurate that only gives me a maximum of 11 runs per day. I was really hoping / aiming for more like 14 per day. But hopefully my estimates are just a little pessimistic.
I don't currently have any way of gathering the data. I do have some devices, but I haven't had the chance to install them (My first device didn't work). However based on my experience with the lead acid batteries I roughly calculated the car to use about 0.5Kwh per run. I calculated this prior to the event last weekend but I think it still roughly holds true. That would mean I used about 2.5Kwh during the event. I am hoping 147v = about 3.9 Kwh (ie 2.5Kwh that I used plus 1.4Kwh or 20% unusable capacity). I am nervous about these figures because at 5.6Kwh of usable capacity and assuming my estimate of 0.5Kwh per run is accurate that only gives me a maximum of 11 runs per day. I was really hoping / aiming for more like 14 per day. But hopefully my estimates are just a little pessimistic.
Oh, but before I left for the event I did hook up a temporary Ammeter. I went for a short burst of acceleration and saw about 200 amps peak. But there was not as much grip in that test (due to the surface) so I suspect on bitumen the current would be a touch higher as the motor struggles more to get the wheels moving.
kiwiev
100 kW
http://www.evwest.com/catalog/product_info.php?cPath=37&products_id=162
I really need to take the Sonic to a Motokhana looks like fun, wow you certainly accelerate fast to 30 kph
Grab one of these amp hour meters $69 usd on above link
Cheers Kiwi
I really need to take the Sonic to a Motokhana looks like fun, wow you certainly accelerate fast to 30 kph
Grab one of these amp hour meters $69 usd on above link
Cheers Kiwi
Yeah thanks. I think I only had it set on 8 too. In hindsight I think that was a mistake.
motorkhana are great fun but khanacross are even better.
I do have 2 meters simular to that. The first didn't work. I haven't had a chance to install tge second.
motorkhana are great fun but khanacross are even better.
I do have 2 meters simular to that. The first didn't work. I haven't had a chance to install tge second.
Also when I replace my flywheel with the modified one I didn't know it hadn't been balanced. At first it vibrated a little but I could live with it. But its been getting worse and at the end of the event I reved the motor in neutral with the cover open. It was trying to shake itself to bits. It has vibrated some play into my adaptor plate. So I need to open it up remove the flywheel, have it balanced, tighten the adaptor plate and re-assemble it all. Not a big deal but it is necessary before the next event.
oatnet
1 MW
galderdi said:
Hey those runs look like fun! It looks pretty quick, but more amps will will give you more torque and better times - that motor can take more than you are giving it.
I built a bank of (6) CellLogs (8 cells each) to give me a bar-graph display of each cell's voltage, meets my needs but YMMV.
https://endless-sphere.com/forums/viewtopic.php?f=1&t=64655#p1134867
-JD
Thanks, yeah once I have the gauge installed I will start tweaking the current limit on the controller. I assume that is the only thing hold the current back. I estimate the peak is about 250A at the moment. Another 75A would be great. Any more than that would start worrying me.
My biggest challenge at the moment is no so much the bms but more the need for the comms (can bus) to trigger the charger. I have still not been able to charge the battery.
My biggest challenge at the moment is no so much the bms but more the need for the comms (can bus) to trigger the charger. I have still not been able to charge the battery.
oatnet
1 MW
galderdi said:
Your 9" ADC an handle 500a-600a on the street. At 250a, you are getting about 48lb/ft; at 325a, 64lb/ft; and at 600a you'd see 140lb/ft. It could even do 1000a=240-260lb/ft- as long as run was less than 10 seconds. :lol:
On the street, in such a light vehicle RPMs come up fast, which generate back-EMF that quickly limits how many amps can get into the motor. OTOH your duty cycle spends a lot of time with low rpm acceleration, but are short runs with a chance to cool down between them. Does your controller have an input for the motor's temp sensor?
I'd think traction and drivetrain will be your limiting factor - but maybe that is what you meant anyhow. What is the model# of your controller? What #cells/chemistry is it programmed for?
-JD
Yeah absolutely. You are correct I still have plenty of untapped potential.
Step 1. will be to install the gauge so I can see what is going on.
I can't do an effective test at home so I am forced to tweak the current a little and then wait and see the results at the next event. The short term target would be around the 325A.
Step 2. I have a fairly extensive list of modifications based on the information from that past event:
a)Get charger working
b)ackerman angle adjustment
c)Soften front suspension
d)Raise steering rack
e)brake adjustment (more pressure required)
f)Lower front tyre pressure
g)Get Flywheel shaved and balanced
h)Install additional rear sway bar
i)Make Fibreglass copies of the battery covers
I expect all of these modifications combined to significantly improve the performance. But realisitically before the next event I will likely only get 1, 2a, 2c, 2e, 2f, 2g and 2i done.
Down the track once I get through this list and I am no longer fighting with the car (drivability) I would look at increasing the current to around 375A. I wouldn't go further than that without significant upgrades. But realistically I expect any more than 375A would be wasted through wheel spin anyway. I do have a set of wider front wheels with slicks, and I'll put them on once the car is getting more competitive. The real target is to have it as competitive as possible by the next Australian championship 3rd quarter 2017.
Step 1. will be to install the gauge so I can see what is going on.
I can't do an effective test at home so I am forced to tweak the current a little and then wait and see the results at the next event. The short term target would be around the 325A.
Step 2. I have a fairly extensive list of modifications based on the information from that past event:
a)Get charger working
b)ackerman angle adjustment
c)Soften front suspension
d)Raise steering rack
e)brake adjustment (more pressure required)
f)Lower front tyre pressure
g)Get Flywheel shaved and balanced
h)Install additional rear sway bar
i)Make Fibreglass copies of the battery covers
I expect all of these modifications combined to significantly improve the performance. But realisitically before the next event I will likely only get 1, 2a, 2c, 2e, 2f, 2g and 2i done.
Down the track once I get through this list and I am no longer fighting with the car (drivability) I would look at increasing the current to around 375A. I wouldn't go further than that without significant upgrades. But realistically I expect any more than 375A would be wasted through wheel spin anyway. I do have a set of wider front wheels with slicks, and I'll put them on once the car is getting more competitive. The real target is to have it as competitive as possible by the next Australian championship 3rd quarter 2017.
looking at the chart here : http://www.mpoweruk.com/soc.htm
147v equates to 3.5v per cell and indicates 75 - 85% discharge before I even started the event.
I did 5 runs on what seems to be about 10 -15% of my battery capacity. If these estimates are correct that would mean on a fully charged pack I could get 25-40 runs. But I think this is a little Optimistic. Unfortunately the voltage for most of the SOC is extremely flat which does not lend itself to this type of estimation. Hopefully the reality is some where between my other, pesimistic estimate (15 runs max) and this optimistic estimate (25 runs). I would be very happy if it lands at around 20. 30runs would be brilliant as it would allow me to have 2 drivers at an event, which was one of my primary goals.
147v equates to 3.5v per cell and indicates 75 - 85% discharge before I even started the event.
I did 5 runs on what seems to be about 10 -15% of my battery capacity. If these estimates are correct that would mean on a fully charged pack I could get 25-40 runs. But I think this is a little Optimistic. Unfortunately the voltage for most of the SOC is extremely flat which does not lend itself to this type of estimation. Hopefully the reality is some where between my other, pesimistic estimate (15 runs max) and this optimistic estimate (25 runs). I would be very happy if it lands at around 20. 30runs would be brilliant as it would allow me to have 2 drivers at an event, which was one of my primary goals.
Hillhater
100 TW
galderdi said:
but if after thse 5 runs your pack was finished... You must have used more than 15% ?,...or started with less than 75% ?Correct. It seems I had around 75% discharge leaving me with 25% charge of which I could only use about 10%. So if 10% gave me 5 runs then 85% could give me around 30 runs. But these are based on flimsy numbers. I have now managed to get the pack up to 150v but I think there is a ways to go yet.
I have also taken out my lightened flywheel and replaced it with the original. I'll now have it lightened further and more importantly it will be balanced. That was costly assumption.
I also got my old faithful 280zx going today....yay!
I have also taken out my lightened flywheel and replaced it with the original. I'll now have it lightened further and more importantly it will be balanced. That was costly assumption.
I also got my old faithful 280zx going today....yay!
As I mentioned I have the pack charging by using a charger from a Remote control car. It is slow but it is working. However I am now nervous about when to stop charging.
The voltage between 70% and 100% is very flat. So I can't use a certain voltage to determine when to stop. Plus they are second hand batteries so I don't know what their capacity is at the moment.
My research tells me to stop charging when the current drops to 3% or less of the current capacity. But it didn't specify how to calculate this.
Would it be 3% of the battery current rating?
If so is that based on the nominal current?
If the batteries can handle 300amps then 3% is 9 amps which is more than the charger can supply right from the beginning. So that would not be useful
Would it be 3% of the charger's capability?
The charger can handle 6amps then 3% would be 90mA. That doesn't seem right either.
Or do I just trust the charger to stop charging when the batteries are full? The problem here is the charger is designed to charge something like a 9ah battery. Mine are more like 45ah. The the charger tends to time out before it gets close to fully charging the batteries. So far I have been letting the charger charge until it times out and then restarting it again. But I have only been game to apply this approach up to 3.76v per cell.
My absolute maximum would be 4.047v per cell to give my total pack voltage of 170v. So I won't be exceeding that voltage regardless. I know the maximum capacity of Li-ion is around 4.2v when new. But what if the maximum for these second hand batteries has dropped below 4.04v and I keep pumping amps into it in an attempt to reach 4.047v, am I risking damage or a fire?
I will keep doing the research but if anyone already knows the answer I would appreciate you sharing.
The voltage between 70% and 100% is very flat. So I can't use a certain voltage to determine when to stop. Plus they are second hand batteries so I don't know what their capacity is at the moment.
My research tells me to stop charging when the current drops to 3% or less of the current capacity. But it didn't specify how to calculate this.
Would it be 3% of the battery current rating?
If so is that based on the nominal current?
If the batteries can handle 300amps then 3% is 9 amps which is more than the charger can supply right from the beginning. So that would not be useful
Would it be 3% of the charger's capability?
The charger can handle 6amps then 3% would be 90mA. That doesn't seem right either.
Or do I just trust the charger to stop charging when the batteries are full? The problem here is the charger is designed to charge something like a 9ah battery. Mine are more like 45ah. The the charger tends to time out before it gets close to fully charging the batteries. So far I have been letting the charger charge until it times out and then restarting it again. But I have only been game to apply this approach up to 3.76v per cell.
My absolute maximum would be 4.047v per cell to give my total pack voltage of 170v. So I won't be exceeding that voltage regardless. I know the maximum capacity of Li-ion is around 4.2v when new. But what if the maximum for these second hand batteries has dropped below 4.04v and I keep pumping amps into it in an attempt to reach 4.047v, am I risking damage or a fire?
I will keep doing the research but if anyone already knows the answer I would appreciate you sharing.
Hillhater
100 TW
Even old, well used , capacity depleted, lipo cells,..still charge to 4.2 volts, without problems. So dont worry about that voltage.
Infact , that last 0.1, 0.2 volts takes awhile to reach because the charger should be into its CV phase by then with very low current flow.
What RC charger and voltage setting are you using ?....It may be adjustable for peak charge voltage.
That 3% charge cut off is refering to 3% of the battery Ahr capacity rating.
So for your 45Ahr cells, that would be about 1.3 Amps.....but i am not sure that recommendation applies to all lipo chemistries.
Infact , that last 0.1, 0.2 volts takes awhile to reach because the charger should be into its CV phase by then with very low current flow.
What RC charger and voltage setting are you using ?....It may be adjustable for peak charge voltage.
That 3% charge cut off is refering to 3% of the battery Ahr capacity rating.
So for your 45Ahr cells, that would be about 1.3 Amps.....but i am not sure that recommendation applies to all lipo chemistries.
Thats great news.
Its a Hitech x4 80:
http://hitecrcd.com/files/X4-80Manual.pdf
I have set it to the Li- ion setting
The voltage does not seem to be editable. It is set at 3.6v nominal per cell.
However I am selecting the maximum number of cells (6) which then increases the nominal voltage to 21.6v
I have increased the maximum current to 6 amps, but as you say the charger has been gradually decreasing as the SOC increases. Most recently it was only achieving about 2.5 amps
I have been usng the fast charge option up till now. I will wire up the balance connections before I go through any more charge cycles.
Currently each cell is at 3.8v
At the end of the day I can't exceed 4.04v per cell because I would risk my controller shutting down. Then it wouldn't start again until I discharge some of the current. Thats not a scenario I want to risk so I am aiming for a maximum of 170v (5v under the theoretical controller cutoff).
Its a Hitech x4 80:
http://hitecrcd.com/files/X4-80Manual.pdf
I have set it to the Li- ion setting
The voltage does not seem to be editable. It is set at 3.6v nominal per cell.
However I am selecting the maximum number of cells (6) which then increases the nominal voltage to 21.6v
I have increased the maximum current to 6 amps, but as you say the charger has been gradually decreasing as the SOC increases. Most recently it was only achieving about 2.5 amps
I have been usng the fast charge option up till now. I will wire up the balance connections before I go through any more charge cycles.
Currently each cell is at 3.8v
At the end of the day I can't exceed 4.04v per cell because I would risk my controller shutting down. Then it wouldn't start again until I discharge some of the current. Thats not a scenario I want to risk so I am aiming for a maximum of 170v (5v under the theoretical controller cutoff).
oatnet
1 MW
The voltage will not be flat between 98% and 100% charge, it will rise sharply. Charge the cells to full voltage with the 4.1v Once all the cells in the pack are full, connect a 100w (or higher) lightbulb to your 150v DC pack, and drain it down to the voltage that won't trip your controller. There aren't many w/h at peak charge, so it should be pretty quick.
-JD
-JD
Thanks, thats a good option.
Also I was just reminded that our club is helping the Fiat car club with the Motorkhana component of their Nationals on Sunday. They are hoping to be finished their motorkhana by around 1pm so I am going to take my car in the hope I can get a few test runs in after they are done. At worse I can use it like a golf buggy to get between test areas. This means I only have Saturday to install the new gauge so I have some useful data from Sunday.
Also I was just reminded that our club is helping the Fiat car club with the Motorkhana component of their Nationals on Sunday. They are hoping to be finished their motorkhana by around 1pm so I am going to take my car in the hope I can get a few test runs in after they are done. At worse I can use it like a golf buggy to get between test areas. This means I only have Saturday to install the new gauge so I have some useful data from Sunday.
Hillhater
100 TW
oatnet said:
JD,..whilst i agree a full charge , then drain back to working voltage is a better idea, ...i think you may be confusing the discharge rate with the charge rate of lipo.
That top 0.2 volts drops rapidly on discharge ( constant current), But when charging, nearly all chargers will be heavily into CV mode for the last 0.2-0.3 volts, and only be pushing 0.5 amps or so. That last 0.2 volts of CHARGE, can take quite a while ! With galderdi using a small RC charger on such a big pack, its probably not worth the extra hours for him to bother going to 4.2v ....until he gets the big charger working .
A typical lipo charge curve...note the relative time between 4.0 and 4.2v,.....over half the total charge time
Obviously this varies between chargers and different lipo chemistries.
Also, just for interest, i dont know the "capacity profile". for galderdi's cells, but some lipo can have significant capacity in that top 4.0-4.2volt range.... See this example from Drkangles thread..
Hillhater
100 TW
Galerdi,
Your RC charger has logging ability. You should take the oportunity to download a charge profile from one or more cells , and analyse it to see exactly how much capacity those cells have above 4.0volts.
If there is significant capacity in that range, you may want to consider reducing the series number of cells in your pack so that you can run with a fully charged pack,... because it might just give you MORE available capacity (Ahrs), than your current set up running at 4.04v max ! :wink:
Your RC charger has logging ability. You should take the oportunity to download a charge profile from one or more cells , and analyse it to see exactly how much capacity those cells have above 4.0volts.
If there is significant capacity in that range, you may want to consider reducing the series number of cells in your pack so that you can run with a fully charged pack,... because it might just give you MORE available capacity (Ahrs), than your current set up running at 4.04v max ! :wink:
sketchism
100 W
commenting to follow the thread, im down on the gold coast not far from you, i'd be keen to come to an event and say hi
Hillhater said:
Will do. More data.....must have more data.
My knowledge and available information is growing very quickly.sketchism said:
Sure thing. Happy to catch up with anyone who is interested. I will be at Willowbank (back of the drag strip) on Sunday. I will be helping for most of the day (starting around 6.30 and finishing mid afternoon) I hope to get a few test runs (non competitive) after the Fiat guys finish. Likely to be around 2.30pm But it will be outside the scope of the competition so I will need to be very careful not to upset the officials etc.
Otherwise the next competitive outing will be at the same location on April 24 for a motorkhana or better yet May 22nd for an khanacross.
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