How many amps to turn an engine over?

Iamzod

Iamzod

Iamzod

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Quick question, I have googled and come up with wildly different answers of 140 - 400amps so thought I'd try here.

How many amps will be required to start an engine?

2.9L 6cyl Petrol, only thing belt driven is the water & PAS pumps. 9.7:1 Compression.

I am looking for an automotive circuit breaker and want to make sure I get the correct rating.
 
There's loads of variables, not an easy answer to give (as you may guess by the range of answers).

I'd look at the specification of your starter motor and go from there if possible.
 
ndmrpwr said:
Maybe the specifics like make model and brand would help us google for you ;-)
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It's a Ford Capri but it's running a 24v Granada/Scorpio engine mated to a 2.8i flywheel & starter motor. The aircon & viscous fan are gone.

I did manage to find some starter specs but they state 1100w @ 12v which i work out at only 92amps, can't be right?
 
breadturbo said:
the old 2.9 essex starter in the xr4x4 was 1400w (ive one in the garage) not sure if its the same block as the 24v?
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That will have been a Cologne rather than an Essex i think. It's the same block but totally different heads, maybe a beefier starter as they came with things like air-con?

Still only works out at 117A though?
 
Iamzod said:
That will have been a Cologne rather than an Essex i think. It's the same block but totally different heads, maybe a beefier starter as they came with things like air-con?

Still only works out at 117A though?
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yep you are right, i've got a starter here from a 2013 2.0dci trafic too, that's 1700w, so the numbers look right with petrol needing less.
**edit, also one here from a 406 3.0 v6, 1400w.
 
Don't think it's quite that simple, you'll have a cold cranking amp value that would be required to start the engine - this will be at a really low voltage so amps will be high 300A+
 
SO that's the starter figured out, i'm guessing that a petrol fuel pump & the ECU & EFI gubbins isn't going to draw more than 50 amps?

So 200Amp breaker with a 250amp fuse as a backup sound reasonable?
 
Mirage said:
Don't think it's quite that simple, you'll have a cold cranking amp value that would be required to start the engine - this will be at a really low voltage so amps will be high 300A+
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Gah, spanner in the works!

Just to point out, the car won't be seeing the light of day outside of the summer months so it'll never get started in the sort of temperatures we have now.
 
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Mirage said:
Don't think it's quite that simple, you'll have a cold cranking amp value that would be required to start the engine - this will be at a really low voltage so amps will be high 300A+
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In the USA, they sell heavy duty batteries with "1000 cold cranking Amps" to turn over 6 litre V8s using 50 weight oil on sub-zero mornings.
 
Terminal_Boy said:
In the USA, they sell heavy duty batteries with "1000 cold cranking Amps" to turn over 6 litre V8s using 50 weight oil on sub-zero mornings.
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They sell over 1000 cold cranking amp battery's in the UK as well ;)

It was only last month I had to buy x2 of these YUASA 625SHD battery's for a machine at my work place
http://www.yuasa.co.uk/625shd.html

625SHD

Cargo Super Heavy Duty Batteries (SHD)

625SHD 12V 220Ah 1000A Yuasa Cargo Super Heavy Duty Battery

Capacity at 20-hour Rate (Ah): 220
Cold Cranking Performance (Amps) EN1: 1150


£298.95
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Put an amp clamp on the battery main and give it a good crank on a cold start, it's pretty much the only way to get a semi-relevant reading for your cars particualr circumstances at that time. But even then doing the same the next morning could wield a number 50a or more different.
 
The surge on initial crank could be very high. It's very unusual to have a fuse or similar in the starting cable.
 
nutcase_1uk said:
The surge on initial crank could be very high. It's very unusual to have a fuse or similar in the starting cable.
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This.

Initial surge will be very high Typical cranking amps (engine turning freely but not firing) in most cases is around 100 Amps (Somewhat more for diesels because they are harder work, )

Some cars do indeed have fusible links in the starter cables (Some Volvos do)

Attempting to start the car in gear will blow them due to the heavy draw on a stalled starter.

Do not do this on a Volvo! the links on the Volvo are part of the cable assembly and not available as a separate fuse. it all needs to be expensively replaced!
 
nutcase_1uk said:
The surge on initial crank could be very high. It's very unusual to have a fuse or similar in the starting cable.
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Battery is being moved to the boot about 12 feet from it's original location. Don't want a short causing a fire if the cable gets damaged somehow.
 
I did read something the other day about the CCA along with the outside temperature, with some temperature ranges needing 1.5-2x the CCA.

Although i think it's rare that we'll have temps that extreme over here :D:D
 
I know it's a smaller engine but when I moved the battery to the boot on my old Rover (2 litre 4 cylinder petrol), I used a 150 amp fuse.

The fuse never blew over the 4 or so years I had the battery in the boot, even after multiple prolonged attempts to start the car while tuning Megasquirt.
 
Just a thought, might not even work, but would it be possible to hook a transformer up and put a clamp meter on the cables, then crank the engine over and see what it takes?
 
agw_01 said:
I know it's a smaller engine but when I moved the battery to the boot on my old Rover (2 litre 4 cylinder petrol), I used a 150 amp fuse.

The fuse never blew over the 4 or so years I had the battery in the boot, even after multiple prolonged attempts to start the car while tuning Megasquirt.
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Same 150amps should do
 
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