Start a car with IMR cells?

Hi,
sorry if this is in the wrong place , but I was here thinking , and there is probably a easy answer , if it is possible to use a cluster of 18650 IMR cells to start a car?

I was reading the post below and I see each cell is able to do safe at least 15AMPs. But the problem is that my understandings in eletronics is not the best so...

Imagine a car that uses a 50amp battery , how many , if possible , 18650 IMR cells will it be needed to do the same work?
And if it is able to start the car , can it be used after that ? Be charged with the car charger etc?

Once again , sorry if its in the wrong place or this is a really stupid idea

Regards,

Art said:

Hi,
sorry if this is in the wrong place , but I was here thinking , and there is probably a easy answer , if it is possible to use a cluster of 18650 IMR cells to start a car?

I was reading the post below and I see each cell is able to do safe at least 15AMPs. But the problem is that my understandings in eletronics is not the best so...

Imagine a car that uses a 50amp battery , how many , if possible , 18650 IMR cells will it be needed to do the same work?
And if it is able to start the car , can it be used after that ? Be charged with the car charger etc?

Once again , sorry if its in the wrong place or this is a really stupid idea

Regards,

Click to expand...

Starting a typical car takes 500-1000 amps at 12 volts nominal, sagging to not less than 7V. If you put four cells in series that would get you 15V nominal at the same current, say 15A. Now multiply by 50 cells to get 750 amps. That's a total of 200 cells. All safety issues aside, it seems impractical. Better to carry a purpose-built spare starter battery in the trunk.

I've never seen it done with IMR's but there's a company making LiFePO4 dropin replacement packs for cars. Their name escapes me at the moment

The current battery im using to start my track car is only 40ah 330AMP cracking power and it starts fine , my idea would be to get something able to do enough power to start the car. It only needs 2 to 4 seconds.
If I use series of 4 packs of 18650 and imagine that in the best case it would do 30amps 3 pack of 4 cells would have more less 100amps... lets imagine it is enough to start the car what problems could I have with the cell pack?
Risk of explosion on start? Will it be able to charge with the engine alternator? Or would it have too much power?

I know this seems stupid , there are a lot of specific car battery packs , race ones with 5kg having 600amps cranking power , but this is something that is on my mind for a long time and I will probably end up testing it so help would be nice so I dont kill my self or the car

You could easily build a pack powerful enough to crank the engine and not destroy itself in the process, but without some sort of charge controller I doubt they would take kindly to being charged from the alternator.

I think at a minimum you'd need a 4S 10P pack.

flashflood said:

Starting a typical car takes 500-1000 amps at 12 volts nominal, sagging to not less than 7V..

Click to expand...

It my experience, those numbers are pretty extreme. Maybe more common in larger diesel engine, perhaps. I'd say in the average passenger car, 70A-500A, varying with engine size, displacement, age and technology. Common among residential car shops are 200A capable jump boxes. As for voltage, there are several motors that will "operate" below 9.6V, but the current draw at that point tends to be ridiculously high to be effective.

-DF

I did a quick search on Amazon and found the battery in the link below. Looks to have the specs you are after:

http://www.amazon.com/dp/B005730960/?tag=cpf0b6-20

Good luck!!

People on youtube start their cars with 4 A123 cells. (Obviously they don't leave them connected once car has started)

A few years ago CPF'er _mdocod_ posted a video here where he jump-starts his dead car after charging it for 2 minutes or so. He used a relatively small number of A123's IIRC.

I think it would be pretty cool to keep a Mag D hotwire in your car and to be able to connect it as needed to cars for jump-starts.

As DF mentioned above, 200 Amps and a little more is about what the typical starter motor draws for stock gasoline engined cars. This goes back to my 1980's and 1990's mechanic days and reflects starters in V-8's. In today's 4's and 6's, its significantly less than 200 Amps. The initial "strike" will be somewhat more but only for a micro second.

I believe the big hazard in using Li batteries to start a car is the maximum safe discharge current on most of the Li re-chargeable batteries is a small multiple of capacity. I.E. it isn't safe to draw more than about 6-9 amps from a 3ah Li battery. By contrast most Lead Acid cells and NiCd's are capable of provididing a much larger mutlipe. This allow a 50Ah battery to delivery 500 amps for few seconds to start a car. DC resistance of most starter motors is a tiny fraction of 1 ohm, however the current draw falls very rapidly as the motor spins up due to the generation of 'back emf'. The faster the starter motor turns, the less current it draws. Maximum current draw on a DC motor is at zero rpm.

Today's car starters draw a lot less curent than was typical 20 years ago because the typical engine displacement has fallen quite dramatically. It takes a whole lot less energy to turn over a 2 liter 4 cylinder engine than it took to turn over a 5.7 lliter V8. Things like electronic ignition and fuel injection has made most engines start within a second or two.

However there is nothing that prevents you from charging the car battery at 6-9 amps for a few minutes to get enough charge to be able to start the engine. As I pointed out, most engines today start very quickly compared to 20-30 years ago, so you don't need a lot of amp hours in the battery to be able to start the engine these days.

mattheww50 said:

I believe the big hazard in using Li batteries to start a car is the maximum safe discharge current on most of the Li re-chargeable batteries is a small multiple of capacity. I.E. it isn't safe to draw more than about 6-9 amps from a 3ah Li battery.

Click to expand...

You're thinking of LiCo chemistry. OP is speaking of IMR LiMn chemistry. Both mammals, but different animals...

-DF

Art said:

Imagine a car that uses a 50amp battery , how many , if possible , 18650 IMR cells will it be needed to do the same work?
And if it is able to start the car , can it be used after that ? Be charged with the car charger etc?

,

Click to expand...

i don't see why it can't be done, with enough cells, and proper chaging, it sure can be done, tesla roadster runs on almost thousand 18650.

mvyrmnd said:

I've never seen it done with IMR's but there's a company making LiFePO4 dropin replacement packs for cars. Their name escapes me at the moment

Click to expand...

Shorai and Turn Tech are probably the two most common. There are some others too. My limited experience is they are aimed more towards small motorcycles and rzrs, ranges, atvs etc.

I've actually seen it done with a lipo. If I remember, it was 4s ~3000mah battery rated at 40c.

Locked rotor current for a '94 Honda Civic starter motor is 400 A and the applied voltage at this point is 4V. Steady state current might be 200A.

BTW, you can use one of the motor cables as a shunt if you know the wire length and diameter, and therefore the resistance per foot.
E.g., 3' of awg #2 copper will have a 117 mV across it for 250A through it.

If I recall correctly CPF member Mdocod used a pack of Emoli cells to start a car. Pretty sure he made a vid several years back.


EDIT: Here ya go.

http://www.youtube.com/watch?v=PCtE0lP1lcE

flashflood said:

Starting a typical car takes 500-1000 amps at 12 volts nominal, sagging to not less than 7V. If you put four cells in series that would get you 15V nominal at the same current, say 15A. Now multiply by 50 cells to get 750 amps. That's a total of 200 cells. All safety issues aside, it seems impractical. Better to carry a purpose-built spare starter battery in the trunk.

Click to expand...

Naw, it doesn't take anywhere near 500-1000A to jumpstart a normal car. Take a look at this video on youtube: http://www.youtube.com/watch?v=qcvmvrmTMMk

Jumpstarted a car with a dead battery with 4x A123 26650's. Those cells can handle pulses of 100C, but not anywhere near 500-1000A.