Battery cable size

[chinkamon]

Hi all 

Looking at putting the battery back in the boot.

Currently using a 50ah 450A battery in the front.

Standard 1500 precrossflow original starter etc

Wondered what size should I buy taking into account voltage drop etc 

Tried looking online but it fizzed my brain 😂

 

[katana]

The rule is - Bigger is definitely better when spec'ing battery cable! For back to front i'd say min. 35mm sq - 50mm sq better - 70mm sq if you can afford it!

[Miniliteman]

My 2 cents: I've seen many battery-in-boot conversions where the owner had starting issues even with the very big cables that katana suggested. The key here is that you use quality connections for the cable and a proper crimping tool, not just "crimped-in-a-vice". My car has a similar sized battery in the boot (and a high compression BD under the bonnet) with (just) twin 16 sqmm cables to the battery-cut-off switch on the dash. As your original starter uses alot of amps I would suggest you use twin 25 sqmm cables with properly crimped connectors. The advantage of twin cables is that they are easier to bend / twist to get from the boot to the front of the car than one very big cable.

[chinkamon]

32 minutes ago, katana said:

i'd say min. 35mm sq - 50mm sq better - 70mm sq if you can afford it!

Thank you very much 

21 minutes ago, Miniliteman said:

I've seen many battery-in-boot conversions where the owner had starting issues even with the very big cables that katana suggested.

 

The key here is that you use quality connections for the cable and a proper crimping tool,

 

My car has a similar sized battery in the boot (and a high compression BD under the bonnet) with (just) twin 16 sqmm cables to the battery-cut-off switch on the dash.

 

As your original starter uses alot of amps I would suggest you use twin 25 sqmm cables with properly crimped connectors. 

This is why I'm asking as had issues when I first had the car running an decided to move the battery to the boot.

 

By proper crimping tool, is the one you smash with a hammer any good or not

Are you running twin cables just from the boot to the cut off on the dash? 

 

Twin 25sqmm you think would be enough then?

[Miniliteman]

30 minutes ago, chinkamon said:

By proper crimping tool, is the one you smash with a hammer any good or not

Are you running twin cables just from the boot to the cut off on the dash? 

Twin 25sqmm you think would be enough then?

A hammer is a hammer, not a crimping tool ... see photo of proper crimping tool.

I have twin 16 sqmm cables from battery-in-boot to cut-off switch on dash. From that switch I have one 16 sqmm cable to the starter and one 16 sqmm cable to the alternator. For your spec twin 25 sqmm cables will be plenty enough.

[Miniliteman]

[chinkamon]

13 minutes ago, Miniliteman said:

Sorry I thought I attached a photo to my post I saw ones like this, 

Ok so proper handle type is best,

 

Since my father's business shut down in retirement all access to this kind of thing has disappeared 

[DT36]

https://www.carbuilder.com/uk/search?q=Battery+cable

 

[Miniliteman]

4 minutes ago, DT36 said:

https://www.carbuilder.com/uk/search?q=Battery+cable

 

Never use things like these:

https://www.carbuilder.com/uk/quick-release-battery-terminals

https://www.carbuilder.com/uk/brass-screw-on-battery-terminals

[Brenda1978]

Expect a voltage drop of 1v to 2v. I got ahalfords battery with 860ccA and it does the job. 

[chinkamon]

1 hour ago, DT36 said:

https://www.carbuilder.com/uk/search?q=Battery+cable

 

Yea I been going through their website whilst asking the questions👌

58 minutes ago, Miniliteman said:

Never use things like these:

https://www.carbuilder.com/uk/quick-release-battery-terminals

https://www.carbuilder.com/uk/brass-screw-on-battery-terminals

I looked at them and couldn't work out from the photos how they work, I couldn't just them as I'm sure with my luck one bump in the road and it'd come off haha

[katana]

13 hours ago, Brenda1978 said:

Expect a voltage drop of 1v to 2v. 

If I was seeing that much drop, I'd seriously be upgrading the cable! Max. 0.5v is acceptable!

With a 2v drop, you'll be cranking with 10v so a 1.4kv starter that usually draws 116A will be drawing 140A - it all stacks up!

[Miniliteman]

21 minutes ago, katana said:

If I was seeing that much drop, I'd seriously be upgrading the cable! Max. 0.5v is acceptable!

With a 2v drop, you'll be cranking with 10v so a 1.4kv starter that usually draws 116A will be drawing 140A - it all stacks up!

You mean 1.4kW I guess. And it doesn't work that way. A starter doesn't draw more amps if the voltage is less. It will draw less amps.

[katana]

7 hours ago, Miniliteman said:

You mean 1.4kW I guess. And it doesn't work that way. A starter doesn't draw more amps if the voltage is less. It will draw less amps.

Which will then mean its not being a 1.4Kw starter - either way equally bad!

[Miniliteman]

Would you be surprised if I tell you that a 1.4 kW starter draws less current at the same voltage than a std 0.7 BHP (= 0.5 kW) starter?

[katana]

16 hours ago, Miniliteman said:

Would you be surprised if I tell you that a 1.4 kW starter draws less current at the same voltage than a std 0.7 BHP (= 0.5 kW) starter?

I would, unless you've managed to re-arrange a principle law of physics, that is, Power measured in watts = volts x Amps. Your knowledge of electrickery is certainly greater than mine but that was always a fundamental rule I was taught? So please explain unless its something in the construction between the two that produces the difference, in which case its not an apples vs apples comparison. Introducing other factors such as electrical / mechanical efficiencies / drag / magnetic flux / quality of materials etc. can skew the result - dontcha think? 😉

[Miniliteman]

The newer type of reduction geared starters are "permament magnet" DC motors. So indeed you cannot compare the two just by using Watt = Voltage x Current.