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.
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?
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.
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E39 (1997 - 2003) >
Another battery question...
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?
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.
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):
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E39 (1997 - 2003) >
Another battery question...
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.
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.
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:
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E39 (1997 - 2003) >
Another battery question...
This thread is only about how many amps it takes to crank our cars.
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.
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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