# lithium for jr dragster



## jr dragster (Oct 11, 2010)

Where going to put lithium in the first electric jr dragster in CANADA, over the winter.We are running agms 6x12=72,where starting the race with 78 volts at the end of the run we have 75 volts left in the pack, we
can make two runs with them till the 1/8 mile times drop off.Do you guys have any suggestions for us?? 72 volts would like to pull 450 amps if possible.Need to keep the weight< under 80 pounds> price under <2,500> may go to 3,000.And need to charge in 10 to 15 minutes. must have bms . Any suggestions ???????????


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## jr dragster (Oct 11, 2010)

Found 72 volt kit at elite power solutions, gbs 40 ah 3.1 kw with bms and charger for $2,424.00 . 88.2 pounds it says on the site.Any one try one of these ??


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## major (Apr 4, 2008)

jr dragster said:


> Found 72 volt kit at elite power solutions, gbs 40 ah 3.1 kw with bms and charger for $2,424.00 . 88.2 pounds it says on the site.Any one try one of these ??


Hey jr dr,

Be careful. 450 A is over 11C rate on a 40 Ah cell. Some types of cells will support that high rate, others will not. I've not used GBS, but do not think they would be a good choice for high rate discharge.

I'm not sure where the number 3.1 kw comes from. Are you mixing power and energy? But from your post #1, you should be looking for 30 kW.

Regards,

major


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## Guest (Sep 18, 2011)

This is for a Jr Dragster. Doubtful you can stuff in a 30kw pack. He is talking pack size. My MG pack size was a nominal 12Kw pack. 120 volts of 100 AH cells. I'd go with at least 100 AH size cells because of the power factor needs or go with the smaller LiPO pouch size cells that will need a BMS and will allow high discharge and should recharge up in no time flat if you have a fast charger. 


Ultra-Power Lithium Polymer Cell
P68100120F-50C
Capacity: 6AH
Nominal Voltage: 3.7V 

$29.99 each

20 cells = 72 volts = $600
Need 20 AH pack
4 packs will equal a 24 AH pack for $2400 

At 50C and 4 cells in parallel that would give you 1200 amps. More than enough for your needs. 

Bottom balance them and don't charge them to full. Be careful of thermal issues. Maybe hook up a thermal cut off switch or a few of them around the pack. Bottom balancing will be a must at the track. No matter what lithium cell you decide to go with.


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## major (Apr 4, 2008)

gottdi said:


> This is for a Jr Dragster. Doubtful you can stuff in a 30kw pack. He is talking pack size. My MG pack size was a nominal 12Kw pack. 120 volts of 100 AH cells.


gottdi,

Do you know the difference between power (kW) and energy (kWh)?

Back in post #1 he says he wants 450A from a 72V pack. That is ballpark 30 kW (~40 hp) electrical from the battery. That is power. Obviously for a jr dragster which runs 1/8th mile races, large amounts of energy (kWh) are not required.

Regards,

major


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## Guest (Sep 18, 2011)

I know what he said. I took it as pack size not power. 30kw of power should be pretty easy to get with lithiums. Many of the cells can do quite high C rates. Being a race car I suspect that longevity is not as big an issue as is power out. I think 86.4kw is more than enough with what I proposed. That will still keep the cells well within the abilities of the cells and the cells will still live a good long life even with hard driving. If all you need is 30kw or 40kw of power then it would work just fine. 

My proposal is just one option.

Pete


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## jr dragster (Oct 11, 2010)

The car weights 350 pounds with the agms (they weight 78 pounds) i have to keep the weight under 400 pounds so i need to find the best possible battery pack with the weight . The best run with the agms with a 12 /28 gear ratio was 11.40 at 59 mph , changed to a 13 front gear and slowed the car down to a 11.75 , so the agms will not pull a higher gear, the agms are 18 ah ubs. That should give a base line.I checked into headways they seam like a lot of messing around (yaberts tread).So im up against weight and size .the thundersky 40ah says that they have a max discharge rating burst of 20c,(can you still get them ?)Calb 40 ah max discharge burst of 12c.the gbs cells say max 10c pulsed?. How accurate are these numbers ? I dont think i can fit anything bigger than a 40ah the weight is going to be to much with anything bigger , the only option for the weight is the headways ,will look see if i can get a ready made pack from them,the price may dictate what i have to use also. thanks


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## major (Apr 4, 2008)

gottdi said:


> 30kw of energy


30kw is a quantity of power, not energy. Things around here would be a lot clearer if people used the proper units


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## major (Apr 4, 2008)

jr dragster said:


> The car weights 350 pounds with the agms (they weight 78 pounds) i have to keep the weight under 400 pounds so i need to find the best possible battery pack with the weight . The best run with the agms with a 12 /28 gear ratio was 11.40 at 59 mph , changed to a 13 front gear and slowed the car down to a 11.75 , so the agms will not pull a higher gear, the agms are 18 ah ubs. That should give a base line.I checked into headways they seam like a lot of messing around (yaberts tread).So im up against weight and size .the thundersky 40ah says that they have a max discharge rating burst of 20c,(can you still get them ?)Calb 40 ah max discharge burst of 12c.the gbs cells say max 10c pulsed?. How accurate are these numbers ? I dont think i can fit anything bigger than a 40ah the weight is going to be to much with anything bigger , the only option for the weight is the headways ,will look see if i can get a ready made pack from them,the price may dictate what i have to use also. thanks


Hi jr dr,

Yes, I think you get my point about C rate. I really don't see why you need to carry 40 Ah cells down the track. You'll be quicker with less battery mass. I would look into the Lithium Poly type cells, such as gottdi suggested. I doubt you'll find a readymade pack with BMS and charger, and with LiPoly you have to be careful especially about charging. So the Headways might be a reasonable alternative.

Regards,

major


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## EVfun (Mar 14, 2010)

I think there is a bit of overkill going on here. A Jr. Dragster is kinda a half scale version of a top fuel dragster for kids to race. It is limited to 400 pounds* and a 96 volt pack (104 volts peak off charge.) Performance is limited to 7.90 seconds at 85 mph in the 1/8th mile. 

I think this would be a good place to use Headway cells. Perhaps 60, 38120P cells in a 2p30s arrangement using the factory cell holders and possibly even the factory cells connectors. The pack would cost about $1200.

* minimum weight 225#, with frame upgrades the weight can exceed 400#


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## Guest (Sep 18, 2011)

major said:


> 30kw is a quantity of power, not energy. Things around here would be a lot clearer if people used the proper units


Edited to reflect the proper term.


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## Guest (Sep 18, 2011)

Just have to remember that there are many who are not EE's and it is not usually at the tip of our tongue to say exactly what we should say. I am an X-Ray/CT Technologist not an EE. I will try to do better because it is important and I don't like to give bad or misleading information. Just gotta remember to slow down and engage the brain first.


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## Guest (Sep 18, 2011)

So rather than 4 packs of my suggestion you could get away with 2 for a 12AH pack. You will still have a lot more usable energy than with your tiny lead batteries. Much higher C rating and what ever your controller will dish out the cells will handle. $1200 then build a container and get a miniBMS attached. Balance your cells at the bottom. You will be draining your cells fast and you will be running them down. Be sure they all reach the low point at the same time. Weight should not be an issue.


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## jr dragster (Oct 11, 2010)

Got some prices for headway what does 4p24s mean ? does it mean 4 packs of 24 cells ?? They have a new cell out that looks good,38120hp it says 20c rate? So i was thinking 48 cells 2 strings of 24 ,be about $1200.00 40a charger 600-700. bms ?? can you get a bms for 500?


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## madmike8 (Jun 16, 2011)

4p24s - That would be 4 in parallel and 24 in series.


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## mora (Nov 11, 2009)

Are you still willing to pull 450A? If you go with those Headways you might want to paraller 3. 24S3P pack will weight about 53lbs and will happily put out 480A (160A * 3). If they sag to 2.5V at 480A you'll have 28.8kW. Cost will jump to 1600$ though. And that's without bms and charger. Doh. You can get miniBMS for under 500$. Probably charger too.


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## electrabishi (Mar 11, 2008)

mora said:


> Are you still willing to pull 450A? If you go with those Headways you might want to paraller 3. 24S3P pack will weight about 53lbs and will happily put out 480A (160A * 3). If they sag to 2.5V at 480A you'll have 28.8kW. Cost will jump to 1600$ though. And that's without bms and charger. Doh. You can get miniBMS for under 500$. Probably charger too.


I don't know if you can still get the original 38120-P cells, but in my testing of them I could pull 450 amps for 12 to 14 seconds without significant temperature rise (Maybe +20*F on the first pull and only +15*F on a subsequent pull).

If you can get these cells and you only need 450 amps from them, then go to the edge and buy 22 cells for 72V and just run a single string. These things weigh 0.66 lbs each. So your 1P22S pack would weigh 14.52 lbs. That is significantly better than 76 lbs of lead.

I looked at putting prismatics in our Junior. But it turns out that to get the discharge rate high enough I would have had to go with as much weight as the 84 lb lead pack. Now, while increasing the range by 5 fold for the car, the same weight and the same power would still give us the same times. For drag racing you need to carry only the amount of energy you need to make the run and get back to the pits.

For our Junior we are running a 1000 amp controller. So I figured we'd go with 2P22S. We would use about 66% of the energy capacity in the cells on a single run. We could not make multiple passes without charging, but then again we wouldn't be carrying around extra poundage. That would be like filling your 25 gallon gas tank to race your gas street car at the track, when you only need 5. 20 extra gallons weighs 120 lbs. Extra Amp-hours in you pack means extra pounds.

If you are concerned about running the 38120-P cells at 450 amps then buy 2 strings. Either run with both of them, OR, buy the second string for spares and when one pops then replace it with a spare. If you run both of them you might get to the point where you would like to shave that extra 14.5 lbs.

Mike


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## mora (Nov 11, 2009)

Isn't voltage sagging horribly low when pulling 450A from 10A cell (45C)? Even for short periods of time? Of course low weight is better. I just though that you couldn't get any decent power out of pack if voltage sagged too low.


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## electrabishi (Mar 11, 2008)

mora said:


> Isn't voltage sagging horribly low when pulling 450A from 10A cell (45C)? Even for short periods of time? Of course low weight is better. I just though that you couldn't get any decent power out of pack if voltage sagged too low.


In power testing cells you will get your maximum power transfer when the cell voltage is 1/2 OCV. For these Headways that would be 1.6V.

For the majority of my testing on these cells all I had was a 500 amp load tester. On one brief occasion I was able to borrow an 800 amp tester.

Now presuming all the mechanical bits of the cell are capable of taking the currents you will be putting through them the cell will deliver maximum power when the current is high enough to pull the fully charge cell to half voltage.

The problem with small load testers is that you cannot possibly pull enough current to do this. Especially with new lithium batteries. They will produce copious amounts of current with very little sag. If you were able to measure the current that dropped the cell to half voltage the number would be obscene.

So back to the testing..... what you want to do if you are not looking for max possible current, but rather how long a cell will deliver a certain current, is to fix that current at something like 400 amps and measure how ling it continues before reaching either 1/2 OCV or the manufacturer recommended cutoff. The manufacturer recommended cutoff is usually more conservative and the number I use. For the Headway's it is 2.0V. Thats the "Don't go below this value!!" number.

When I would do 450 amp pulls from the 38120-P cells the typical cell voltage I would see at 15 seconds was 2.2V. There was usually 1 cell in the packs of four that would hit 2.0V but a couple that were 2.2V and maybe 1 that stayed as high as 2.5V for the duration.

But regardless, if all of them stayed above 2.0V delivering 450 amps for 15 seconds, then I am comfortable using them in either the race car for 11-12 second runs, or the Junior for 8-10 second runs.

Mike


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## electrabishi (Mar 11, 2008)

mora said:


> Isn't voltage sagging horribly low when pulling 450A from 10A cell (45C)? Even for short periods of time? Of course low weight is better. I just though that you couldn't get any decent power out of pack if voltage sagged too low.


Oh I missed an important thing in your statement. On the Headway 10AH cells, yes the sag would be terribly low. In fact the Thundersky cells are better Power Density than the 38120-S cells.

However the 38120-P cells have significantly more power denisty and slightly less energy density. As you can tell, they are in the same size package but the -P cells are only 8AH.

Manufacturer specs 20C for 30 seconds, but I have verified 50C for up to 15 seconds. And yes I did do 160 amp runs (which is 20C) and timed them out well past 30 seconds. IN fact I believe (if I can find my notes) I was seeing 160 amps for nearly 2 minutes before voltage would drop to 2.0V (thats about where the knee is in the energy curve). At that point the cell was 66% depleted. OCV would then jump back up to around 3.0V.


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## major (Apr 4, 2008)

electrabishi said:


> But regardless, if all of them stayed above 2.0V delivering 450 amps for 15 seconds, then I am comfortable using them in either the race car for 11-12 second runs, or the Junior for 8-10 second runs.


But less sag is better because it yields more power at your current limit at base speed. So it is a tradeoff between more power and additional mass for the parallel cells with regards to ET  And this is not that easy to figure out. That maximum power point will occur when the controller just comes out of current limit, or at base speed. This will be quite a ways down the track. During the first part of the run, in current limit, below maximum power, sag is pretty much irrelevant. It is the current producing torque fighting the mass. So greater sag with less mass means a quicker launch. And if you're racing for ET, gettin' goin' faster sooner means a lot


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## electrabishi (Mar 11, 2008)

major said:


> But less sag is better because it yields more power at your current limit at base speed. So it is a tradeoff between more power and additional mass for the parallel cells with regards to ET  And this is not that easy to figure out. That maximum power point will occur when the controller just comes out of current limit, or at base speed. This will be quite a ways down the track. During the first part of the run, in current limit, below maximum power, sag is pretty much irrelevant. It is the current producing torque fighting the mass. So greater sag with less mass means a quicker launch. And if you're racing for ET, gettin' goin' faster sooner means a lot


Certainly a battery that can do 450 amps with no sag will put out more power than a battery that drops to 1/2 OCV and 450 amps. But to do that you would have to parallel a significant number of strings to meet that requirement. And so like you said, you would be adding weight to get more power.

But the other part you said was controller current limit. If you have a high enough pack voltage (or your RPM is low enough), your controller will be able to provide full motor loop current and still not reach the battery current limit. I have found that if I can keep the motor in current limit the battery current draw looks like a triangle. It ramps steadily to near the battery current limit, then when the motor and pack voltage are the same (100% duty cycle) then the battery current starts ramping down. Increasing the pack capacity will slow that ramp down. So you have to look at how much you'll gain by adding some number of pounds to get some number of amps increase on the top end.

Its a tough game to play ;-)

However for Junior dragsters its not about ET. Its about consistency. If you are trying to get to the sanctioning limits 7.9 seconds at not greater than 85 mph, that is entirely possible. But its not necessary. The electric will be way more consistent that the gas Junior ;-)

Mike


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## jr dragster (Oct 11, 2010)

Have you done any test on the new 38120hp cells ?? From what you are saying i was thinking run one string of 24 cells , and have another string charging and switch them out after each run then i wont be a panic to get one string charged bettween rounds, would have 25 minutes to charge if not more.We you take the cells down how quick can you charge them back up? the weight savings will take off 1/2 second .You are bang on the electric running cosistent we ran 11.40 ,11.43, 11.44 , 11.43 .11.44 , 11.43 all in the same day only lost out on last race on the tree, shes getting better at the tree. And if the one string was not enough i could build the battery box to take 2 strings and run 2. I like the weight savings of 1 string.


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## electrabishi (Mar 11, 2008)

jr dragster said:


> Have you done any test on the new 38120hp cells ?? From what you are saying i was thinking run one string of 24 cells , and have another string charging and switch them out after each run then i wont be a panic to get one string charged bettween rounds, would have 25 minutes to charge if not more.We you take the cells down how quick can you charge them back up? the weight savings will take off 1/2 second .You are bang on the electric running cosistent we ran 11.40 ,11.43, 11.44 , 11.43 .11.44 , 11.43 all in the same day only lost out on last race on the tree, shes getting better at the tree. And if the one string was not enough i could build the battery box to take 2 strings and run 2. I like the weight savings of 1 string.


I haven't tried the -hp cells. I did not know they existed but I'll try to find some to play with. Frodus on this list can tell us where to get them.

When I was doing my testing I only had a 10 amp bulk charger (12V 4 cells per string). I know the headways will take a charger faster than that. I don't think they would flinch at a 20 amp charge rate.

When running the lead powered Junior (72V XE-16's) we first charged with a cheap schumacher 10 am charger and a run would take ~30 minutes to recharge from. Occasionally I'd steal my PFC-20 from the truck and that would giver her 15 minute charge times. So if you can hit them with 20 amps you should be able to make the turn around in plenty of time.

We never had the time constraint on our Juniors, the track was never in a hurry to turn them around quick and the kids sometimes would sit in their cars staged for over an hour. :-(

Mike


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## jr dragster (Oct 11, 2010)

If we put one string of 24 cells in and switch after each run with the other pack ,do we need a bms ?? and if so where is best place to buy? I think i will get the cells from headway in the us, and the charger from there also,It may be cheaper to get from china but the jim at headway has to eat too.Do i need to make up something to mount the cells together or just buy the ones from headway? Or just get them to make the packs up?thanks for your help and ideas so far .


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## electrabishi (Mar 11, 2008)

jr dragster said:


> If we put one string of 24 cells in and switch after each run with the other pack ,do we need a bms ?? and if so where is best place to buy? I think i will get the cells from headway in the us, and the charger from there also,It may be cheaper to get from china but the jim at headway has to eat too.Do i need to make up something to mount the cells together or just buy the ones from headway? Or just get them to make the packs up?thanks for your help and ideas so far .


Get your batteries from Manzanita Micro http://www.manzanitamicro.com/products?page=shop.browse&category_id=29

The 38120P cells are $19 each or $456 for a 24-pack.
If you were to get the BMS (Three 8-cell boards at $320 each) the BMS would be $960 or twice what the cells are worth. But I know the BMS works. Everything I know about the Headway BMS is that they don't work very well, and even then only for low current chargers.

Now you could certainly find a BMS that would perform a basic function but that would even likely approach the cost of the cells themselves.

I used to be a proponent of spending the money to absolutely have a BMS. But the cost of the cells (for the Junior application anyway) is far less than the BMS by 2X. 

I think when I finally get the lithium for the Junior I'm going to just buy a whole second set of cells to use for spares. I am considering just charging to about 90% and running without the BMS. You could get away with this for 5 or 6 runs a day. And then using 2 or 3 smaller 3-amp individual chargers to peak each individual cell up independently back at home. Doing this and having a whole bunch of spare cells will likely last as long as having the expensive BMS. 

You'll likely smoke a few cells but they should be quick to change out.

Here is another thought I had. If you are going to swap batteries out and you only have a single string of cells, you could build a jig that held all the cells in place in compression. It would not take that long to pull out 24 cells from such a jig. Then you could put them into a charging jig that parallel's them all up for charging. In parallel they will always be balanced. But you would need a charger that would do 3.8V at like (20 amps X 24 cells) or ~500 amps. That might be hard to find.... but then again it might not. Its only a 2KW charger. Just a thought that I'm going to look into.

But I am tending to thing that for racing a Junior, skip the BMS and buy the extra cells. You'll need to get a $50 load tester so you could quickly determine when your cells are going bad. Or you could run them until they pop. But it might be better to check them often.

Mike


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## madmike8 (Jun 16, 2011)

If you could use those 3 cell holders and string the 24 cells together in 8 cell lengths. Put that in a PVC pipe with positive on one end and negative on the the other it would like your changing out a BIG AA battery between rounds!


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## jr dragster (Oct 11, 2010)

has anyone ordered headways straight from china? Im thinking or getting them from there .38120hp 8ah cells 55 cells make 2 strings of 24 and some for spares.Trying to figure out how to make pack up so i can charge pack at the track with 72 volt charger ,then take apart and charge each cell at home with single cell charger. no bms ? any ideas ? what is better for me top or bottom balance?


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## Yabert (Feb 7, 2010)

Hi

I think you can complete a balanced charge at home with the relatively cheap RC charger : http://epbuddy.com/index.php?main_page=index&cPath=17_1


They can balanced 8S or 10S string at time with a multitude of setting. 
I have does this to charge my 26s motorcycle battery pack and that worked perfectly. 

You will need to charge your pack in three step, but for 200-250$ (including the power supply), you can't find a cheaper/better way to charge and balance your cells.


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## tropes (Jul 24, 2011)

jr dragster said:


> has anyone ordered headways straight from china? Im thinking or getting them from there .38120hp 8ah cells 55 cells make 2 strings of 24 and some for spares.Trying to figure out how to make pack up so i can charge pack at the track with 72 volt charger ,then take apart and charge each cell at home with single cell charger. no bms ? any ideas ? what is better for me top or bottom balance?


As a newcomer to EV conversions I must say thanks to all who contribute to this thread. I have decided to go with LiIPo but sorting out which is the best option (power versus capacity), remains a puzzle. Since I am starting with an old K91 motor I must go with 72 volts but the configuration remains in question. I also own a Schumacher SE-1072 Multi-Battery Charger so I am hoping to use it. 
BTW, what motor are you using and would that determine the battery you use?
Tropes


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## jr dragster (Oct 11, 2010)

were using mars 1003 mabye not the best one to use but that was what would fit , with out to much work.When looking for batteries you need something with a high c-rate like 20 and up.Some only have a c-rate of 3 or 4 .


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## ken6881 (Oct 7, 2011)

Why not use lipo cells for under $400 you could have a 74v 15ah 20c continuous pack(300a capable would that be enough)?


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## tropes (Jul 24, 2011)

jr dragster said:


> were using mars 1003 mabye not the best one to use but that was what would fit , with out to much work.When looking for batteries you need something with a high c-rate like 20 and up.Some only have a c-rate of 3 or 4 .


Having used the Mars 1003 for the first year, you would have some idea as to the best motor for this application. Without any experience I purchased the K91-4003. It probably comes down to a motor/battery combination with weight and space being factors. What motor would you choose if you were starting over? As far as battery charge rate, my understanding is that any battery with a charge rate greater than 40 would probably not last as long as a battery with a C-rate of 20.


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## ken6881 (Oct 7, 2011)

C rate does not mean charge rate it is how many amps a batter can deliver compared to it's capacity. 15ah times 20c = 300 amps it can put out. Usually charge rates are less than discharge rates


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## jr dragster (Oct 11, 2010)

Was looking around on the net found these what do you guys think thunder power tp 5000-10spp65l 37 volts they claim 350 amps, max of 650, do you think they would work. very light weight, very expesive, $449.each ,what are your thoughts. thanks


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## Guest (Dec 13, 2011)

jr dragster said:


> Was looking around on the net found these what do you guys think thunder power tp 5000-10spp65l 37 volts they claim 350 amps, max of 650, do you think they would work. very light weight, very expesive, $449.each ,what are your thoughts. thanks


Looking at the specs, 5AH seems a bit shy of what you may want. You could burn through that 5AH real fast on the strip. One other mentioned a larger AH pack and a 20C discharge rate for bursts down the track seem more in line with what you should be looking at doing. Price is cheaper too. 

Pete


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## Yabert (Feb 7, 2010)

Hi Jr

I have always be interested by those high power Lipo cells for realy short burst of high power (relatively) and I think they can be good for your 10 sec application.

From long time now, I'm interested by those cells: http://www.hobbyking.com/hobbyking/...sAndProducts.asp?idCategory=378&LiPoConfig=10

Theorically, you can discharge those cells in less than a minute and two battery in serie can give you 15-20 Kw of power. Not bad for 7-8 lbs of battery! I think you can try for only 300-400$.
But please take extremely care of the dangerosity of those cells. Putting those one in an insulated metal box is probably a good secure idea.

Oh! and don't forget to charge with balancer charger...


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## ken6881 (Oct 7, 2011)

I have ran turnigy cells for rc use and would say that i am very happy with the quality and the price cheapest way to buy 20c 5000mah cells is actually to buy the 7.4v 2s pack just fyi if your interested in buying alot of them


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## jr dragster (Oct 11, 2010)

Yabert said:


> Hi Jr
> 
> I have always be interested by those high power Lipo cells for realy short burst of high power (relatively) and I think they can be good for your 10 sec application.
> 
> ...


DO these cells CATCH FIRE EASY?? I need something safe, or as safe as batteries can be .


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## ken6881 (Oct 7, 2011)

jr dragster said:


> DO these cells CATCH FIRE EASY?? I need something safe, or as safe as batteries can be .


as long as you dont over charge them, or stick a nail in one, or short one out you will be fine.


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## jr dragster (Oct 11, 2010)

ken6881 said:


> as long as you dont over charge them, or stick a nail in one, or short one out you will be fine.


 how about high discharge?


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## ken6881 (Oct 7, 2011)

jr dragster said:


> how about high discharge?



worst i have seen one do at high discharge is get puffy but never fire


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## jr dragster (Oct 11, 2010)

ive looked at some lipo batteries at hobbyking a few questions , wont the small 12 gauge wires melt when i hook them up and pull 450 amps from them? i was looking at the 7.4 volt 6.6 or the 18.5 5 amp. 10 or 4 the price is so close if this will work i was thinking of making two packs and switch out after each run. there both 65-130c .the chargers are around 200 and are balance capable, they will do 10 cells so will need 2.Im stuck between the lipo and the headway the price is so close, will the chargers form hk work on the headways?


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## major (Apr 4, 2008)

jr dragster said:


> wont the small 12 gauge wires melt when i hook them up and pull 450 amps from them?


Hi jr dr,

With these high C rate cells or batteries, the leads (wires) should be appropriate for the task, or so one would hope. The lead wire will heat due to the resistance of the wire. The ultimate temperature is a function of the loss (watts due to I²R) and the time the current flows through the wire. The magnitude of that current determines the length of time it is available from the cell. So the higher the current, the shorter the time. At the very high C rates, time is very short. 60C is at most 1 minute. Because the watts loss (heating) is a squared function of current, they will get hotter at 60C for one minute than at 6C for 10 minutes. The battery manufacturer's engineer should have taken this into account and properly sized the leads such that the discharge at any C rate will not last long enough to raise the lead temperature above the wire's rating. You can expect those leads to get hot.

Also, at very high current application, often times batteries are paralleled meaning those leads (wires) only carry a portion of the total current. 

Even though a cell or battery comes with a high C rating, you may be better off using it at well under that maximum. You suffer greater voltage drop due to internal cell resistance and put more stress on the cells at those very high C rates. Remember that the maximum power delivered by the battery or cell comes at half voltage. Look at the voltage profile for the duration of the run and see if it is better to carry more parallel cells and suffer the additional mass versus the higher voltage you will obtain.

Regards,

major

ps....You mention building 2 packs so you can switch out instead of charging between passes. If you do that, it gives a great opportunity to test the theory I put forth in the last paragraph. Leave space or provisions to run both packs in parallel with each other in the jr. Take a pass using one pack. Recharge. Take a pass with 2 packs connected in parallel. Who's quicker?


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## jr dragster (Oct 11, 2010)

I got an email from headway they will not have any 38120hp cells for about two months. They have the 38120p cells in stock .
here is what im going to order 
50 headway 38120p cells
100 2 hole conectors
50 2 peice holders.
Sound good?? Im going to build two packs of 24 cells each try running one pack and changing packs between races or will try with 2 and see which one works better.
Charger ?? headway has a 15a charger, should i get a higher amp charger 30 or 40 ? for quicker charging .Would like to charge pack in 15 minutes max.Any thing we should look for in a charger? I was going to buy a r/c charger/ balancer, to balance the pack at home.Thanks again for all your help on this site, without your help this never would have got done.GIVE YOURSELF A PAT ON THE BACK.


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## frodus (Apr 12, 2008)

get more bussbar, you're gonna want to double up for that high of amperage.

get a dependable charger.... that's just my opinion.


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## jr dragster (Oct 11, 2010)

Ordered batteries from china today ,hope they show up. Went with A123 20ah pouch cells


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## Yabert (Feb 7, 2010)

Good choice! how do you think build the 72v pack?

A bit more information about the price and quality after receiving will be nice...


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## jr dragster (Oct 11, 2010)

Yabert said:


> Good choice! how do you think build the 72v pack?
> 
> A bit more information about the price and quality after receiving will be nice...


I was thinking of building 12 packs or 4 cells each run 6 at a time, then if one goes bad i can just change out one pack? was hoping to run 1 pack and change out after each run ? not 100% sure will see when the batteries get here . Price was good for small order i think?? pm if you want to know .


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## rwaudio (May 22, 2008)

jr dragster said:


> Ordered batteries from china today ,hope they show up. Went with A123 20ah pouch cells


Good choice, I think you will be happy with the cells.
Have you decided on an assembly method for the cells?


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## jr dragster (Oct 11, 2010)

rwaudio said:


> Good choice, I think you will be happy with the cells.
> Have you decided on an assembly method for the cells?


YA was going to get you to put them together for me .LOL 
Was looking around at what everyone else was doing but will have to wait till i get cells to be sure what will work and fit in car.


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## rwaudio (May 22, 2008)

jr dragster said:


> YA was going to get you to put them together for me .LOL
> Was looking around at what everyone else was doing but will have to wait till i get cells to be sure what will work and fit in car.


I'm revising my assembly method slightly to remove some aluminium blocks. Ideally your connections should be tab to tab without a block in between. Use the blocks or other method for clamping only.

I was getting higher than expected voltage drop in places due to the number of series connections to make the pack, each connection has a small resistance but they all add up.


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## jr dragster (Oct 11, 2010)

Ive been looking on the here and the net cant really find anything on top balacing any one have a good site to go read up on it?


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## jr dragster (Oct 11, 2010)

Found some stuff to read up on .will the cells balance themself in packs of 4 ??


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## Yabert (Feb 7, 2010)

jr dragster said:


> .will the cells balance themself in packs of 4 ??


No! 
When you try to charge 2 cells in series or 4, 24, 100 cells in series, if one cell is fully charge before the other(s) (and continous to charge), this one can be damage.

I started to search a way to build a 24v pack (A123 AMP20) for a mower and I think use this design to build pack. Each cell tab directly in contact with the next one (best conductivity).
If that can help you!


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## jr dragster (Oct 11, 2010)

Yabert said:


> No!
> When you try to charge 2 cells in series or 4, 24, 100 cells in series, if one cell is fully charge before the other(s) (and continous to charge), this one can be damage.
> 
> I started to search a way to build a 24v pack (A123 AMP20) for a mower and I think use this design to build pack. Each cell tab directly in contact with the next one (best conductivity).
> If that can help you!


what did you make the white piece from? are the bolts just scewed into it or did you put nuts on the other side? I was looking and i like this design,do you have some more pics? thanks Batteries should be here monday


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## jr dragster (Oct 11, 2010)

The batteries are here the batteries are here.Time to get to work and get them built and in the car .Will keep you posted on plans


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## tropes (Jul 24, 2011)

Controller and battery finally here. i'll start building some brackets and cutting some cable. hope to have the wiring in place next week.


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## major (Apr 4, 2008)

tropes said:


> Controller and battery finally here. i'll start building some brackets and cutting some cable. hope to have the wiring in place next week.


Looks great. I recommend some type of cell monitoring so you don't over charge and can see if a cell gets out of wack. Those cells have stayed in balance nicely for me. I have had to equalize a cell about twice on the batteries we use on the karts. The race bike has a full blown BMS which balances every charge. 

Nice motor and reducer system


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## tropes (Jul 24, 2011)

major said:


> Looks great. I recommend some type of cell monitoring so you don't over charge and can see if a cell gets out of wack. Those cells have stayed in balance nicely for me. I have had to equalize a cell about twice on the batteries we use on the karts. The race bike has a full blown BMS which balances every charge.
> 
> Nice motor and reducer system


I realize a BMS would balance each cell. The battery has the monitoring and display wire harness for one 4 channel and two 8 channel Rudman control boards. The cells have been checked and balanced so initially I will use my old Shumacher 72 volt charger.

tropes


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## major (Apr 4, 2008)

tropes said:


> The cells have been checked and balanced so initially I will use my old Shumacher 72 volt charger.


I think the usual lead-acid charge profile will take those too high. Be careful and don't go over 4.2 volts on the cells. You can simply use a DVM on a single cell and watch it as you charge. Since they are balanced you're probably in good shape for the season, but worth a check now and then.


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## Arlo (Dec 27, 2009)

I use these http://www.hobbyking.com/hobbyking/...l_Voltage_Monitor_2_6S_Lipo_New_Version_.html to bulk charge. I only run lipo. And I only bulk charge. I pull 20-30 C out of cheep HK lipo all the time! I use these http://www.hobbyking.com/hobbyking/store/__10328__Hobby_King_Battery_Medic_System_6S.html to balance every few months on my bike I ride and charge daily! 

These pacs http://www.hobbyking.com/hobbyking/...y_nano_tech_5000mah_6S_65_130C_Lipo_Pack.htmlare some of the Highest C I have seen for a good price and they have proven to be safe if used properly. 3 basic rules never over 4.2v on any cell never below 2.7v on any cell and never puncture or open!


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## tropes (Jul 24, 2011)

A quick way to check cell balance: measure voltage from #1 cell to #10 cell, then measure from #10 to #20. the readings will be the same if the cells are balanced. 








Tropes


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## tropes (Jul 24, 2011)

major said:


> I think the usual lead-acid charge profile will take those too high. Be careful and don't go over 4.2 volts on the cells.QUOTE]
> 
> I don't know what the charge profile is but I did use the Shumacher and the voltage reading went from 72V to 79.3V in 35 minutes using my multimeter.
> Tropes


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## tropes (Jul 24, 2011)

The 

Shumacher doing it's thing. 20 minutes from 78V to 79.3V.

Tropes


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## tropes (Jul 24, 2011)

Finally got some testing runs in.


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## jr dragster (Oct 11, 2010)

what did he run ?how was the charging ? and most important did he have fun??


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## tropes (Jul 24, 2011)

jr dragster said:


> what did he run ?how was the charging ? and most important did he have fun??


Yes, most important he had fun. Didn't have a chance to charge the battery after going around pylons for half an hour but we managed to get in seven runs plus driving back (no tow vehicle) before we ran down the battery. Managed a couple of 10 sec. runs but mostly 11"s which was okay considering the lack of traction. No M.P.H. but I'm guessing 60. Would be nice to have 2 electrics at the same meet.

Tropes


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## tropes (Jul 24, 2011)

Finally ready to race. we will be in Saskatoon on Sunday. Hope to see Jr Dragster there too.


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