please help with recommendation for drag car

[El Luchador]

hi guys,

im new here, and 100.00% of the stuff here is above my head.

ive been researching NIGHT and DAY for 2 weeks now and I found some good information here and thought maybe you all can help.

I come from drag racing where runs are 5-6 secs long and i noticed some people switching to lithium batteries. i can save about 50 lbs switching to lithium. and if i go this route i can do it inexpensively. I havent found a cheaper way to knock 50lbs out of my car.

i looked at lifepo4 with a123 cells but i dont want to solder
so i looked at headway and calb lifepo4 but they are quite heavy

finally i found lipoly cells which i believe would do what i need and would come in at less than 5lbs.i need to start the car a few times in the lanes, and make a 5-7 second pass. the only electric items are efi box, 4 dis coils, o2 sensor, and all engine sensors. the car has no alternator, lights,horn, radio,gauges, electric water pump, electric fans etc, none of that. just the efi box, sensors, and 4 coils.

the starter draws a max of 250 amps, and settles to about 175, and the electronics draw maybe 25 amps.

i settled on 2x 8000mah 5s1p packs, 25-50c discharge because i calculated 16 amp hours, up to 800 cranking amps, and still leaving plenty of juice for a few starts and my pass. i will charge the battery between rounds.


OK, here are my questions

1. Can I please get some recommendations on a decent charger that will balance charge a 5s lipoly pack, or maybe even 2 packs at once, and not be too slow? if i can get full charge in 30-45 minutes that is plenty for me.
i would also like one that prevents overcharge.

2. do i need a LVC? how does it attach to the pack? very confused on this. will it allow the allow the packs to deliver 250+ amps?
could i get a recommendation on one , if needed?

3. i will have the packs in a removable container and charge outside of the car. im worried about fires. should i try to have them in a fire safe enclosure/material while in the car?

4. how does one go about calculating how many AH will be used up during a pass?

5. anything else i need to know?

thanks all, and i greatly appreciate any help that i do get.

 

[Lebowski]

ICharger 1010B+, charging of a regular car battery ?

 

[zombiess]

5-6 seconds I'm going to guess eighth mile.

I looked at doing this same thing for my own car at one point. My biggest concern is protecting the batteries from engine heat because my battery was stock, you most likely have a battery box in the trunk at your times. I was a heavy street car still with AC which I often used in our long hot staging lines making 6.0 to 6.5 1/8th times and decided I was to lazy to put forth the effort of battery games.

Another alternative to lipo are the dyna batt dry cell batteries which are light and would help keep the complication down. Just wanted to toss that out there.

I agree with the icharger, love them. In your situation you will have to do some experimenting to verify capacity needed. Two 8ah packs paralleled will handle your amp load on starting and I think averaging your amps drawn between starts 3 seconds plus another 10 to move the car plus your staging and burn out which is 1 to 3 mins then your pass.

Always plan for the worst case! Especially if you got one of the guys who tries to burn you down at the tree.

I will try to crunch some numbers for you later.

 

[El Luchador]

ICharger 1010B+, charging of a regular car battery ?

hi, thanks for the recommendation.

i have a generator i take to the track so it will be 120v

is it this one?
http://www.hobbyking.com/hobbyking/store/__6609__iCharger_1010Bplus_300W_10s_Balance_Charger.html

this one can charge two batteries at once for a few dollars more. how would it compare?

http://www.hobbyking.com/hobbyking/store/__20613__Turnigy_MEGA_400Wx2_Battery_Charger_Discharger_800W_.html

 

[El Luchador]

5-6 seconds I'm going to guess eighth mile.

I looked at doing this same thing for my own car at one point. My biggest concern is protecting the batteries from engine heat because my battery was stock, you most likely have a battery box in the trunk at your times. I was a heavy street car still with AC which I often used in our long hot staging lines making 6.0 to 6.5 1/8th times and decided I was to lazy to put forth the effort of battery games.

Another alternative to lipo are the dyna batt dry cell batteries which are light and would help keep the complication down. Just wanted to toss that out there.

I agree with the icharger, love them. In your situation you will have to do some experimenting to verify capacity needed. Two 8ah packs paralleled will handle your amp load on starting and I think averaging your amps drawn between starts 3 seconds plus another 10 to move the car plus your staging and burn out which is 1 to 3 mins then your pass.

Always plan for the worst case! Especially if you got one of the guys who tries to burn you down at the tree.

I will try to crunch some numbers for you later.

thanks for the reply. im glad to know that it could work. thanks for the offer to crunch numbers.

i race eighth mile as you thought. ive been on a weight reduction kick and you would be surprised how much weight can be taken out of a car. a lb here, a lb there, adds up REALLY quickly. ive already taken more than 70 lbs out of the car, if i only count what i didnt spend money on. if i count what i spent money on, its a lot more.

i look forward to your calculations.

 

[Lebowski]

Yep, that's the charger i meant... but if you're running two packs in parallel and basically have 21V all around the car, you can parallel the packs on cell level and you only need one charger that can handle a 5 cell pack. An iCharger 106 for instance. For protection you could use a cell monitor/ beeper thingy, also sold by Hobbyking.
Note that this sort of charger runs of a low voltage, like 9 to 18V, dependent on the model. Coming from 120V AC, you'll need either a power supply, or you feed the charger from a 12V car battery...

 

[El Luchador]

Yep, that's the charger i meant... but if you're running two packs in parallel and basically have 21V all around the car, you can parallel the packs on cell level and you only need one charger that can handle a 5 cell pack. An iCharger 106 for instance. For protection you could use a cell monitor/ beeper thingy, also sold by Hobbyking.
Note that this sort of charger runs of a low voltage, like 9 to 18V, dependent on the model. Coming from 120V AC, you'll need either a power supply, or you feed the charger from a 12V car battery...

wait, I thought 5s running voltage was around 18v??? am I wrong? I may need to switch down to 4s.

btw, I did not know about the charger voltage. THANKS for that information. ill plan for a power supply as well

 

[agniusm]

So this is just a starter battery you are looking for? I have these kits for 20AH A123 cells to make car battery. No soldering required. I have it in my car, testing for 5 months now, all good.
Here is the link on my battery build and someone from LA Porsche Club: http://endless-sphere.com/forums/viewtopic.php?f=14&t=38545&hilit=a123+battery+kit&start=600
I was cranking my Toyota diesel at 450A, then i went for some more and was cranking an old Russian tractor T-40 (didn't measured current but should of been much higher):

with success.

 

[El Luchador]

im looking at all my options, and your kit may be a good way to go.

i sent you a pm asking a few more details. thanks

 

[Punx0r]

5S will be 5 x 4.2V = 21.0V when fully charged

 

[agniusm]

Yes, he needs 4S LiFePO4, very sweet at 14.6V. My cars alternator charges at 14.4V which leaves .1V per cell play. I had mine for half a year now and it needs balanced as cells drifted, 3.38V lowest, 3.5V highest, A123 20AH. I don't mind balancing twice a year. Still need to check the capacity as it was charging at -18C.

 

[El Luchador]

thanks for the info punxor and agnuism,

ill go 4s in that case.

ag, i looked at your setup. i like the 20ah spec and fact it is lifepo4, but i think i want to start with lipo first. i may graduate to that setup later

 

[999zip999]

What BMS will you use ?

 

[El Luchador]

What BMS will you use ?

bms?

what is that?

i mean, i have an idea, but then again i dont really know what the bms is ,or where it goes, so maybe you could enlighten me.

 

[999zip999]

Battery Management System. It's for the hvc - lvc and balancing of the cells in your pack for safety Plus ?

 

[El Luchador]

Battery Management System. It's for the hvc - lvc and balancing of the cells in your pack for safety Plus ?

thanks. does it go with the battery, or is it part of the charger?

any links to one that would work?

 

[zombiess]

Here are the numbers I just crunched for you. As long as I didn't mess up my math it look slike you need 1.18 A/Hr capacity per pass.

 

[fechter]

The BMS is like a voltmeter on each cell that hopefully prevents you from over draining the cells.
Since you don't really want to mess with a big circuit that can handle the full cranking power, you can use some kind of voltage monitor that sets off an alarm if a cell gets too low. There are many inexpensive low voltage alarms that will work for 4s packs. Search eBay for "lipo voltage alarm". If the alarm goes off, you need to stop the discharge before the cells get damaged. The balance charger takes care of things during charge.

 

[El Luchador]

Here are the numbers I just crunched for you. As long as I didn't mess up my math it look slike you need 1.18 A/Hr capacity per pass.

Hi, THANKS A BUNCH FOR THAT!

now, im probably gonna be laughed at for missing something obvious, but should total amp seconds be 5000+3000+4250?

 

[El Luchador]

The BMS is like a voltmeter on each cell that hopefully prevents you from over draining the cells.
Since you don't really want to mess with a big circuit that can handle the full cranking power, you can use some kind of voltage monitor that sets off an alarm if a cell gets too low. There are many inexpensive low voltage alarms that will work for 4s packs. Search eBay for "lipo voltage alarm". If the alarm goes off, you need to stop the discharge before the cells get damaged. The balance charger takes care of things during charge.

thanks buddy. I'll get a couple.

 

[zombiess]

have to look at the spreadsheet I used. Had to edit my post because I had a math error when I double checked my work. That's what I get for waking up early.

1 pass:
5 starts 250A for 5 seconds
5 moves 25A for 10 seconds
1 pass 25A for 120 seconds

Starting = 250 Amps/Sec for 5 sec done 5 times
Moving = 25A Amps/Sec for 10 seconds done 4 times
Pass = 25A/Sec for 120 sec done 1 time

Total run time = 5s * 5 + 10s * 4 + 120s * 1 = 185 seconds run time

250A * 5 + 25A * 10 + 25A * 120 = 4500A over 185 seconds = average of 24.32 A/Sec

24.32 A/Sec = 0.006755556 A/Hr

0.006755556 * 185 seconds = 1.25 A/Hr pulled from the pack per pass.

Pack is 16 Aamp/Hr (two 8 A/Hr packs in parallel), only 12 of that is usable so 12 A/Hr / 1.25 A/Hr = 9.6 passes before pack is dead.

I hope I got my math correct here if someone would care double check it.

 

[El Luchador]

thanks again Zombiess.

that makes sense to me.

so here is a follow up question.

my initial plan was to use 1x 8ah battery in the lanes, then switch it out right before my burnout , and use a fresh battery for the burnout, stage, and pass. it looks like I'll be using little enough juice that I can do this.

would this be easier on the batteries than having two batteries in parallel for the whole run from staging lanes to finish?


also, could you clarify something for me : say a pack is 8ah *30c. if you use 2 in parallel, do you get 16ah * 30c, or 16ah * 60c?

thanks

 

[liveforphysics]

Never underestimate the draw of a serious electric fuel system. I don't know how much power you're making, but in the import world, each bosch 044 fuel pump means another 25-30amps or so when it's at full flow rate, and some cars are running at least 3 of them. The fuel system in some cars is enough to cause ignition system brown-outs as your alternator and a tiny lead acid battery can't hold the voltage up for long with ~30-100amps on it for say 10 seconds just for fuel system needs every time you go to move forward a space in the staging lines (unless you're in a class where your car is towed/pushed the whole staging process).

 

[El Luchador]

Never underestimate the draw of a serious electric fuel system. I don't know how much power you're making, but in the import world, each bosch 044 fuel pump means another 25-30amps or so when it's at full flow rate, and some cars are running at least 3 of them. The fuel system in some cars is enough to cause ignition system brown-outs as your alternator and a tiny lead acid battery can't hold the voltage up for long with ~30-100amps on it for say 10 seconds just for fuel system needs every time you go to move forward a space in the staging lines (unless you're in a class where your car is towed/pushed the whole staging process).

Hi,
thanks for bringing that up. It is an extrememly valid point. However I eliminated the noisy low flow pumps last year when I switched to a belt driven fuel pump.

it flows over 12 gallons a minute, or about 4680lbs/hour !!!,
ZERO amp draw, its dead quiet, you can turn it up to 150 psi if your injectors can handle it without bursting,it flows less at low rpms(heats the fuel less) AND it maintains its flow rate as you increase pressure, unlike an electric which flows less and less as you increase pressure.

I'll never run an electric fuel pump again.

 

[El Luchador]

have to look at the spreadsheet I used. Had to edit my post because I had a math error when I double checked my work. That's what I get for waking up early.

1 pass:
5 starts 250A for 5 seconds
5 moves 25A for 10 seconds
1 pass 25A for 120 seconds

Starting = 250 Amps/Sec for 5 sec done 5 times
Moving = 25A Amps/Sec for 10 seconds done 4 times
Pass = 25A/Sec for 120 sec done 1 time

Total run time = 5s * 5 + 10s * 4 + 120s * 1 = 185 seconds run time

250A * 5 + 25A * 10 + 25A * 120 = 4500A over 185 seconds = average of 24.32 A/Sec

24.32 A/Sec = 0.006755556 A/Hr

0.006755556 * 185 seconds = 1.25 A/Hr pulled from the pack per pass.

Pack is 16 Aamp/Hr (two 8 A/Hr packs in parallel), only 12 of that is usable so 12 A/Hr / 1.25 A/Hr = 9.6 passes before pack is dead.

I hope I got my math correct here if someone would care double check it.

hi,

I got slightly different numbers.

250 amps for 5 seconds at 5 starts each
250 amps * 25 secs total

250 * 25/3600
250 * 0.00694

=1.74 AH

I didnt do the driving and moving as they are miniscule, but either way it seems like one 8000mah pack should be plenty for one pass.

question - why do you say only 12 of 16 amp hours are usable. is this a general guideline?

thanks