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E39 (1997 - 2003)
The BMW 5-Series (E39 chassis) was introduced in the United States as a 1997 model year car and lasted until the 2004 when the E60 chassis was released. The United States saw several variations including the 525i, 528i, 530i and 540i. -- View the E39 Wiki

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  #1  
Old 06-21-2015, 09:21 AM
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Pinpoint question: How many amps of current does it take to start an E39 (amp hours)?

EDIT: The answer seems to be about 117 amps (max) for a few seconds for the I6 and about 142 amps (max) for the V8.
~117 amps · ~5 seconds · 1 minute ÷ 60 seconds · 1 hour ÷ 60 minutes ~= 0.20 amp hours
~142 amps · ~5 seconds · 1 minute ÷ 60 seconds · 1 hour ÷ 60 minutes ~=
0.20 amp hours

How many amps does it take to start our bimmers anyway (both the I6 and the V8)?

This question came up as part of the diagnostic sequence for a user today who had complained that a brand-new 640CCA battery wouldn't start the car, so, he ordered another battery with 900 CCA to solve the problem.
> E39 (1997 - 2003) > Another battery question...
Quote:
Originally Posted by Dalva View Post
I had my battery changed and after driving around with the new one, (640CCA) with my A/C on, parked the car and right 5 mins. later the car wouldn't start. Battery dead, just some clicking noise...
Quote:
Originally Posted by bluebee View Post
Quote:
Originally Posted by Dalva View Post
I still don't understand why most of web selectors come up with a 640CCA batteries for 525i BMW?
While I have nothing against more CCAs, how many amp hours does it take to crank our bimmers anyway?

QSilver? JimLev? cn90? Fudman? acoste? 540iman? Flybot? MatWiz?
Any of you guys know how many amp hours it takes to start our bimmers?

As usual, I'll embarrass myself by positing a figure.

I'd guess, offhand, about 80 amps for about 5 seconds (summer temps).
Let's double that, for safety, and assume it's 160 amps for 10 seconds.
Heck. Let's double that (for winter perhaps), and say it's 320 amps for 20 seconds.

320 amps * 20 seconds * 1 minute/60 seconds * 1 hour/60 minutes = 1.8 amp hours
(Someone please check my math!)

The BMW spec for our batteries, according to QSilver7's graphic below, is 90amp hours.
That's 90 amps, for an hour, on a brand new battery!

So, while I have nothing against CCAs, I don't think that a 640CCA battery is your real problem.

DISCLAIMER: Someone who actually knows what it takes to crank a bimmer should correct where I err.
Quote:
OEM specs are Group 49, 720 CCA, vented
  • BMW 61.21.8.381.762
  • USA 729905-10
  • EN 12V 90Ah 720A
  • SAE 160 RC 720 CCA.
EDIT: This thread only pertains to cranking the E39 (summer & winter) on a NEW battery; that is, we're not talking WHY you want more CCAs to give you a RESERVE for when the battery gets old and decrepit.
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Last edited by bluebee; 06-22-2015 at 11:27 AM.
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  #2  
Old 06-21-2015, 10:37 AM
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Oh Bluebee.....
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  #3  
Old 06-21-2015, 11:23 AM
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Quote:
Originally Posted by Flybot View Post
Oh Bluebee.....
How would you tackle the problem?

A. I6 owner complains that a brand new 640CCA battery won't start the car.
B. I6 owner complains so much, in fact, apparently, that the shop returns their money, and, apparently, at the same time, provides a loaner battery so the owner can buy a larger CCA rated battery.
C. I'm trying to explain to the owner that CCAs aren't the problem.

I'm approaching the solution by explaining to the owner that the wattage it takes to start the car is so far below the capacity of even the smallest brand new fully charged battery, that the CCA's can't possibly be the problem.

But, I don't really KNOW what the wattage is, needed to start our cars.

Since the owner's car won't start, and since the owner blames the brand new fully charged battery's CCA rating, how would YOU approach the solution?
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Old 06-21-2015, 11:52 AM
HTK12 HTK12 is offline
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Quote:
Originally Posted by bluebee View Post
How would you tackle the problem?

A. I6 owner complains that a brand new 640CCA battery won't start the car.
B. I6 owner complains so much, in fact, apparently, that the shop returns their money, and, apparently, at the same time, provides a loaner battery so the owner can buy a larger CCA rated battery.
C. I'm trying to explain to the owner that CCAs aren't the problem.

I'm approaching the solution by explaining to the owner that the wattage it takes to start the car is so far below the capacity of even the smallest brand new fully charged battery, that the CCA's can't possibly be the problem.

But, I don't really KNOW what the wattage is, needed to start our cars.

Since the owner's car won't start, and since the owner blames the brand new fully charged battery's CCA rating, how would YOU approach the solution?
If the battery really is providing the full 640CCA it will start the I6 easily (the battery should be tested to see the output). If the battery is putting out the 640CCA and it won't start the car there us an issue is with the car. The 660CCA is enough to start even the E39 V8.
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  #5  
Old 06-21-2015, 03:04 PM
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Quote:
Originally Posted by HTK12 View Post
If the battery really is providing the full 640CCA it will start the I6 easily (the battery should be tested to see the output). If the battery is putting out the 640CCA and it won't start the car there us an issue is with the car. The 660CCA is enough to start even the E39 V8.
  • CCA is how much current the battery can source in a short burst
  • AH is the total current the battery can source until it is dead
Specifically, 640 CCA means the battery can deliver 640 amps at 0°F for thirty seconds without its voltage dropping lower than 7.2 volts.

Likewise, 90 amp hours means the battery can deliver 90 amps for one hour, or 10 amps for 9 hours, or 20 amps for 4˝ hours, or 180 amps for 1/2 hour, or 360 amps for fifteen minutes, or 10 amps for 9 hours, (or any reasonable combination where the math works out).

So, if it takes, say, 90 amps to start the bimmer, that new fully-charged battery can crank constantly for an entire hour before being worn out.

However, if the car takes, say, 640 amps to start, then that battery can only crank for about 30 seconds (at 0°F anyway) before it is depleted.

All I ask in this thread is what a typical amount of amps is for starting a car.

EDIT: RDL pointed out over here that 90AH@20Hr means the most accurate figure is actually 4.5 amps for 20 hours.

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Last edited by bluebee; 06-22-2015 at 11:20 AM.
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  #6  
Old 06-21-2015, 05:47 PM
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How many amps does it take to start an e39. Which e39, The amps required to start a 6 cylinder are less then the amps to start the v8. This is due to the difference in power requirements for a given starter. The amps will need to increase as the temp goes down. To find the answer to your question we need to know what the power requirement for your starter is.
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Old 06-21-2015, 07:39 PM
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Well BB, I cant give you a pinpoint answer. Howerver I will say this- The CCA number is simply a rating. Its a tool to be used for compairison. If you have a 800 CCA battery it wont crank a car any "better" than if it had a 400 CCA battery. The amp draw is the same if you were to swap out the batteries. The only difference being, if the car doesnt start and you end up cranking over and over. You could never use the CCA rating of say 800 CCA for 30 seconds in your car. Thats why its just a rating for compairison purposes. 800 amps would melt the ground cables. They arent rated for that. 00 gauge wire for instance is rated at about 280 amps max. Thats approx the gauge we have in the E39s.

I would simply tell said person that shes wasting her money, and something else is wrong with her car if it will not start after a new battery is installed. Cased closed. Next.
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Last edited by Flybot; 06-21-2015 at 07:41 PM.
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Old 06-21-2015, 08:51 PM
spoddye39 spoddye39 is offline
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IMO its unlikely to be the CCA rating.

I dont know how many amps are required to crank an engine but I'd say its a lot more than 90A - I'd say 200-250A feels more correct. To be clear I've never measured it, its more a feeling based on the size of the battery and wiring that the battery feeds.

You also cant extrapolate a peak current draw and the Amp Hour rating and expect to get a useful time value. The trouble is that as the current increases the losses in the system increase as a square of the current - everything gets pretty intense when you're cranking the engine. Then as other people have mentioned, the temperature of the battery has an effect on the battery capacity, and the temperature of the engine has an effect on the amount of current required to turn it.

The CCA rating is intended as an indicator of the quality of the battery internals - higher quality means better internal connections etc and therefore more capacity when cold.

If someone has a problem with a battery not cranking a car, I'd be looking at the cabling and interconnections - a small amount of resistance in any of these will mean the voltage sags when cranking. Since a E39 has the battery at the back there is quite a bit to check eg the battery terminals (the E39 has an explosive separator there too I think), the ground connection, the connection at the starter etc. Measure the voltage at all the various points while someone is cranking the engine. You could try unlocking the cluster and watching the voltage there while its cranking, might tell you something.

Spod

Last edited by spoddye39; 06-21-2015 at 08:52 PM.
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  #9  
Old 06-21-2015, 09:53 PM
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Quote:
Originally Posted by clark49660 View Post
How many amps does it take to start an e39. Which e39
Both. Either. Any.

I'm guessing about 80 to 90 amps for a few seconds.
But I don't know.
That's why I had asked.

Quote:
Originally Posted by clark49660 View Post
To find the answer to your question we need to know what the power requirement for your starter is.
That makes sense.

In fact, it might be as simple as asking what the start motor current draw is.
I'll start searching, but, if anyone has taken apart their starter, maybe they have a picture of a plate on the side.

Do starters have plates with amperage on them like electric motors do?

Quote:
Originally Posted by Flybot View Post
The CCA number is simply a rating.
I should never have brought up CCAs as this thread, really, has nothing to do with CCAs.

You and I and most of us know everything there is to know about CCAs, so, I will take the liberty of appending the CCA information to the thread where the poster (erroneously) thinks CCAs are his problem.
> E39 (1997 - 2003) > Another battery question...

Quote:
Originally Posted by Flybot View Post
If you have a 800 CCA battery it wont crank a car any "better" than if it had a 400 CCA battery.
I'm sorry I brought up CCAs, as this thread really has nothing to do with CCAs.

It was my fault for bringing up the topic of CCAs.
Let's try to concentrate on amps alone.

How many amps does the starter draw?

Quote:
Originally Posted by Flybot View Post
800 amps would melt the ground cables. They aren't rated for that. 00 gauge wire for instance is rated at about 280 amps max. Thats approx the gauge we have in the E39s.
Now we're getting somewhere!

Given the cables are rated for about 280 Amps maximum, that means the amps to crank our engines are probably far less than that.
For now, we'll assume 280 amps is our upper range.

Quote:
Originally Posted by spoddye39 View Post
IMO its unlikely to be the CCA rating.
I should have known better than to bring up CCAs as this thread is about the Amps it takes to crank our engines.

I will put all CCA information into the other thread, where the poster needs to better understand what a CCA is (I understand CCA completely):
> E39 (1997 - 2003) > Another battery question...

Quote:
Originally Posted by spoddye39 View Post
I dont know how many amps are required to crank an engine but I'd say its a lot more than 90A - I'd say 200-250A feels more correct.
Your guess is as good as mine, but, note Flybot says your number is just about at the current capacity of the wires.

So, I suspect 1/3 of that is a more accurate number.

I think clark49660 was on to something because the STARTER motor is the only major current draw, right?

So, all we need to know is how much the starter motor draws when cranking.

Quote:
Originally Posted by spoddye39 View Post
the temperature of the battery has an effect
Actually, the temperature of the battery is almost certainly nearly meaningless with respect to the question of how many amps the engine needs to start.

Of course, the temperature of the ENGINE matters (i.e., friction and stoichiometric ratio issues); but let's deal with the temperature of the engine changing engine friction and fuel ratios as a second-order issue.

Let's first find the current at ANY temperature.
Then we can worry about other temperatures.

Quote:
Originally Posted by spoddye39 View Post
The CCA rating is intended as an indicator of the quality of the battery internals
Again, my fault for bringing up CCA, which has nothing to do with the question.
I will put that CCA information in the thread that prompted this thread though:
> E39 (1997 - 2003) > Another battery question...
This thread is only about how many amps it takes to crank our cars.

Quote:
Originally Posted by spoddye39 View Post
If someone has a problem with a battery not cranking a car,
I will append any and all CCA information to that thread, but, for this thread, let's concentrate on amps.
> E39 (1997 - 2003) > Another battery question...

Here's my best guess at the answer to the question:
Q: How many amps does it take to start an E39 at STP?
A: 100 amps · 10 seconds · 1 minute÷60 seconds · 1 hour÷60 minutes = 0.3 amp hours
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Last edited by bluebee; 06-21-2015 at 10:52 PM.
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  #10  
Old 06-21-2015, 11:01 PM
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Searching for how many amps a starter motor takes, I find this which seems kind of high:
> 5 Series DIY > DIY - Starter Motor 6-Cylinder Engine (M52 Motor)
Quote:
Starter motors take about 300-400 amps when turning over the engine
This PDF also seems to echo pretty high numbers:
- Starting Systems Current Draw Tests

Those numbers above seem a bit high, because this 4-cylinder was tested at 100 amps under load:

This video shows a loaded known-good starter drawing 128 amps average (152 amps maximum):
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Last edited by bluebee; 06-22-2015 at 11:16 AM.
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  #11  
Old 06-21-2015, 11:09 PM
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Looking up in Realoem for my Bosch SR0448N starter motor, it's 1.4 kilowatts:
- 2002 BMW 525i Bosch 1.4KW Starter Motor, P/N 12412354709
I = P ÷ V
I = 1,400 Watts ÷ ~14 VDC
I ~= 100 Amps

If I use 12 Volts, we get:
I = P ÷ V
I = 1,400 Watts ÷ ~12 VDC
I ~= 117 Amps

Advanced Auto Parts lists the Bosch BOS-SR0448N as being 1.4KW and 117 amps:
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Last edited by bluebee; 06-22-2015 at 12:09 AM.
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  #12  
Old 06-22-2015, 12:26 AM
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Most engines need circa 100 A to start the engine. YMMV.
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Old 06-22-2015, 02:40 AM
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easiest way to do this is to put a amp clamp on the positive terminal and look for the highest number


but since i cant be in the trunk and in the drivers seat at the same time ...
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  #14  
Old 06-22-2015, 04:56 AM
HTK12 HTK12 is offline
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The 540 has 1.7kw starter. If we assume the battery voltage is 9V while cranking 1700W/9V=~190A. There are other things like ecu etc that need power, but still even a typical 45ah battery with ~400CCA should be able to start even the V8.
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Old 06-22-2015, 06:53 AM
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Bee, as you have likely now realized, there is no one answer. Kinda like "what is reality"? Depends.

Depends on temp., thickness of oil, condition of starter, et al. Question is without merit except as advice as to what would be "to spec." 1000 CCA, etc.

Like, how many coats of paint are needed to cover pink wall to become a blue wall? Too many variables and not really relevant except to say "get the most CCA you can afford"!
BMW has far larger drain under "normal conditions" than most cars. Follow their lead on this one. 800-1000 CCA good start, but also depends on where you live! Warmer states will buy you a lot.
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Old 06-22-2015, 11:06 AM
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Quote:
Originally Posted by edjack View Post
Most engines need circa 100 A to start the engine. YMMV.
I looked it up yesterday, for about an hour or so (watching videos and the like), and I agree that it's usually in the range of 100 to 150 amps for a working gasoline engine at STP.

While I saw numbers double and triple that, I don't believe them, as none that quoted such high numbers provided any proof. The ones that were measured were all under 150 amps.

Of course, we're assuming a working engine, as a damaged starter/engine might require far more current.
Quote:
Originally Posted by Burning2nd View Post
easiest way to do this is to put a amp clamp on the positive terminal and look for the highest number
That's pretty much what they did in the SnapOn video shown above.

Quote:
Originally Posted by HTK12 View Post
The 540 has 1.7kw starter. If we assume the battery voltage is 9V while cranking 1700W/9V=~190A. There are other things like ecu etc that need power, but still even a typical 45ah battery with ~400CCA should be able to start even the V8.
Thanks for that 1,700 watt nominal figure for the V8 starter motor.

That means the nominal current draw for the I6 is 117 amps (max) while that of the V8 is 142 amps (max) under normal starting conditions.
I'll update the OP so that folks can get the answer in the first sentence.
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Last edited by bluebee; 06-22-2015 at 11:17 AM.
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Old 06-22-2015, 11:12 AM
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Quote:
Originally Posted by 540iman View Post
Too many variables and not really relevant except to say "get the most CCA you can afford"!
Actually, Bill, I think it is quite relevant for us to know approximately how much current our starters draw under normal operation.

We could use the nominal numbers as a baseline test of our starters, for example. And, it helps us make tradeoff decisions when buying batteries and comparing specs.

In addition, it even has relevance to the Fudman thread on calculating how long you can go on a car where the alternator has died if starting is part of the equation.
- How far can you drive once the red light alternator warning shows up on the instrument cluster before the battery is dead (1)
Quote:
Originally Posted by 540iman View Post
BMW has far larger drain under "normal conditions" than most cars.
I know. I've measured mine...
- How to find which parasite is causing overnight battery drain parasitics (1)

See also:
- How to test a BMW battery & alternator (1) & how to find which parasite is causing overnight battery drain parasitics (1) & one user's attempt to locate, describe, and photograph all fuses and relays with a picture of every fuse & relay (1) & how to choose a good aftermarket battery (1) and a simple battery replacement DIY (1) & how not to replace your battery (1) & what is the most often recommended dead battery charger or drained battery tender (1) & how many amp hours does it take to start our bimmer (1) & how far can you drive and how long does a battery last and how many miles can you go once the red light alternator warning shows up on the instrument cluster before the battery is dead (1) & where is the proper place to hook jumpstarting cables (1) & the theory of turning on headlights of the dead or donor car before disconnecting jumper cables (1) & where are all the ground straps for grounding and how to tighten the ground wire for the charging system and where are the major battery brown wire connections (1) & what is the correct BMW battery reset procedure (1) & what is the battery disconnect 16-minute timeout sleep warning (1) & where to find the Battery Safety Terminal BST explosive charge emergency quick disconnect (1)
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Last edited by bluebee; 06-22-2015 at 11:15 AM.
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Old 06-22-2015, 11:49 AM
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Whatever, but what can one do with this information? Say, how long can you drive w/o alternator..... entirely depends on condition of battery more than whatever its rating was at time of purchase as well as what else is drawing current while driving. Amp draw at "room temperature" is fine, but what if you are not at room temp or you have DRL feature enabled, foot on brake pedal even! What do we do with this knowledge. Kinda like a child that just keeps saying "why" over and over. Answers are great if they are pertinent and reproducible.

Bad information is, in my opinion, worse than no information. *If* I know it takes 160 amps to start a 540, what do I do with that? If I suspect my battery can't supply, do we really think we won't try it!? Or, if I were to somehow know my battery had 200 amps available, but my car is a "hard starter" and does not catch always right away, will it still start? Who knows and really...who cares- or maybe better put- what are we going to do differently armed with the answers you seek? Seeking relevance or pertinence that will suffice in most all situations and no one answer, can answers all the many, real-life variables...that's all. By all means, carry-on!

Last edited by 540iman; 06-22-2015 at 11:52 AM.
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Old 06-22-2015, 03:56 PM
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Quote:
Originally Posted by 540iman View Post
but what can one do with this information?
I know how you feel.

I feel much the same when people incessantly ask about absolutely meaningless idiotic things such as staggered wheels, wheel spacers, coilovers, painted calipers, cellis retrofits, seat and steering wheel retrofits, debadging, M-style anything, or any of a million-other poser questions (usually by people trying to make a non-whatever "look" like a "whatever" car without it actually being one).

People care about different things.

The fact that it takes between 100 and 150 amps for a few seconds to start your car is not at all meaningful to you. I get that.

The initial problem I had was one of simple arithmetic.

I was trying to explain to someone that pretty much any battery (even a motorcycle battery, in all probability) had enough current capacity to start our cars.

I just didn't have the numbers to plug into the equation.

Now, I do. And it turns out the answer was surprisingly easy to attain and consistent across the I6 and V8 (both of which are 0.2 amp hours).
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  #20  
Old 06-23-2015, 04:30 PM
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540iman 540iman is offline
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Location: N.W. Indiana
 
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OK! Riddle me this.....how long will MY 540IA run (miles or time is fine) once the alternator quits putting out?

Depends and I don't mean the diapers in my future some day in the not too distant future! God, please take me first (or send me *somewhere*) whatever the case may be......

What can be said is that my car will likely run longer/farther than it would were I to have a 600 CCA battery installed at same time rather than what I actually have (1000CCA) and maintained just the same. For comparison purposes only. Any further inferences becomes "cloudy" in anyone's crystal ball.

Don't take this info too far.

And a resounding "YES" to all of us seeking different knowledge. World would be a boring place indeed otherwise! Cheers.

Last edited by 540iman; 06-23-2015 at 04:37 PM.
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  #21  
Old 06-23-2015, 05:06 PM
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bluebee bluebee is offline
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Location: San Jose, California
 
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Mein Auto: 02 BMW 525i M54 auto 130K
Quote:
Originally Posted by 540iman View Post
OK! Riddle me this.....
How about, instead, since the data is available, the question of whether I can start my car with a jump start from a motorcycle battery?

Let's say it's a BMW motorcycle with a brand new battery that happens to ride by and stop to help me.

PS: I know the answer, based solely on the information in this thread & the spec for the battery below.

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Last edited by bluebee; 06-23-2015 at 06:36 PM.
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  #22  
Old 06-23-2015, 06:12 PM
Burning2nd Burning2nd is offline
Under the lift arms
Location: Under the lift arms
 
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Mein Auto: E39 540, E36 328is, E83x3
This has turned in to needing to understand electricity thread...

yes you can start you car with a bike battery
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  #23  
Old 06-23-2015, 06:15 PM
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Flybot Flybot is online now
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I just want to know causes electromagetism to work?
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Old 06-23-2015, 07:45 PM
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bluebee bluebee is offline
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Originally Posted by Flybot View Post
I just want to know causes electromagetism to work?
Funny you should ask about special relatively because it has always amazed me that simple movement causes length contraction, which is what makes electromagnetism work.

That is, from the starter motor's frame of reference, due to the chemistry of the battery, the copper wire's positive charges are moving in the motor's copper wire relative to its electrons, so, in accordance with special relativity, the separation of the positive charges will be slightly contracted (because they are moving).

On the other hand, from the electron's perspective, they aren't moving; so, the electron spacing is not contracted.

The resulting higher density of the positive charges, relative to the negative charges in the wire, now makes the copper wire positively charged, which is the force that eventually turns the engine over.

In other words, a magnetic field is simply an electric field, viewed from a different frame of reference. They are one and the same (just as space and time are one and the same).

In other words, depending on your frame of reference, you see an electric field, or a magnetic field (but it's the same thing in both cases, just viewed differently).

So, to answer your question, what causes Faraday's electromagnetism to work is simply that the charges induced by the battery flow through starter wires (at 0.0000000001% the speed of light, which is the "Celerity" in E = m · C2) where the movement causes length contraction, which causes charge concentration, which reveals itself (in one frame of reference) as the electromagnetic force.
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  #25  
Old 06-23-2015, 08:19 PM
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Yep, Science!
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