Battery cable size

Battery cable size

Author
Discussion

paulathome

Original Poster:

686 posts

217 months

Wednesday 28th January 2015
quotequote all
Morning all,
Can anyone tell me the size of the battery cable from the battery to the starter motor and also the cable size from the alternator to the starter motor please via the 100amp fuse. Also an approximate length of each.
I'm not near the garage at the moment but need to get the cable ordered for the weekend.

Thanks in advance for your help.
Paul.

Colin RedGriff

2,525 posts

256 months

Wednesday 28th January 2015
quotequote all
I ordered 3m of red and had plenty. The original cable is generally regarded as under specced. I used modern 50mm Hi Flex cable

I found it impossible to feed the cable starting from the footwell and in the end routed it in to the footwell from underneath the car. When you remove the old cable make sure you attach a strong draw wire to allow you to pull the new wire in

This post may help

http://www.pistonheads.com/gassing/topic.asp?h=0&a...

ChimpOnGas

9,637 posts

178 months

Wednesday 28th January 2015
quotequote all
The original cable is 35mm² and is a good 7ft long!

Given the weedy gauge and considerable length it was just about adequate when new. After 15-20 years draped over the bell housing trapped between the cylinder heads & the bulkhead getting cooked by the engine & exhaust manifolds it will certainly be corroded & very crispy by now.

And that means it's gone from adequate.... to very high resistance indeed.

Replace the old crispy high resistance 35mm² cable with good quality marine grade & tinned 50mm² cable in red, finally run an additional earth cable from one of the starter motor mounting bolts (or the engine block) directly back to the negative terminal of the battery. Use the same 50mm² gauge cable but in black for this heavy duty earth return.

Assuming your battery is in good health and your battery terminals are tight your slow starter that you thought was on it's last legs will now spin the engine over like you never thought possible.

Threading those 50mm² cables through the bulkhead grommet can be challenging but the difference your new live & earth cables will make will absolutely astound you the first time you turn the key.

Do the above, bypass the immobiliser on the starter solenoid circuit (or have a new security system fitted) then fit a relay on that circuit to protect your ignition switch contacts and deliver a full helping of amps direct to the starter solenoid, and your TVR will start better than you ever imagined and be more reliable than you ever thought your TVR would be.

A few simple steps to a Chimaera that cranks like a jet and never ever gives you the so called hot start problem again.

If you really want to go to town a full sized high performance battery like the Odyssey PC1500 is a good addition, as is a new good quality starter motor if yours is genuinely showing signs of age, A full de-cat (especially the pre-cats) will massively help reduce the effects of radiant heat the exhaust manifold inflicts on the poor old starter and will considerably extend it's life.

Finally keep your battery on a proper regulated charger (with float charging mode) to maintain it in perfect health and if you haven't got access to mains power use the BatteryBrain device to disconnect the battery remotely when you leave the car for any length of time.

SILICONEKID345HP

14,997 posts

230 months

Wednesday 28th January 2015
quotequote all
ChimpOnGas said:
The original cable is 35mm² and is a good 7ft long!

Given the weedy gauge and considerable length it was just about adequate when new. After 15-20 years draped over the bell housing trapped between the cylinder heads & the bulkhead getting cooked by the engine & exhaust manifolds it will certainly be corroded & very crispy by now.

And that means it's gone from adequate.... to very high resistance indeed.

Replace the old crispy high resistance 35mm² cable with good quality marine grade & tinned 50mm² cable in red, finally run an additional earth cable from one of the starter motor mounting bolts (or the engine block) directly back to the negative terminal of the battery. Use the same 50mm² gauge cable but in black for this heavy duty earth return.

Assuming your battery is in good health and your battery terminals are tight your slow starter that you thought was on it's last legs will now spin the engine over like you never thought possible.

Threading those 50mm² cables through the bulkhead grommet can be challenging but the difference your new live & earth cables will make will absolutely astound you the first time you turn the key.

Do the above, bypass the immobiliser on the starter solenoid circuit (or have a new security system fitted) then fit a relay on that circuit to protect your ignition switch contacts and deliver a full helping of amps direct to the starter solenoid, and your TVR will start better than you ever imagined and be more reliable than you ever thought your TVR would be.

A few simple steps to a Chimaera that cranks like a jet and never ever gives you the so called hot start problem again.

If you really want to go to town a full sized high performance battery like the Odyssey PC1500 is a good addition, as is a new good quality starter motor if yours is genuinely showing signs of age, A full de-cat (especially the pre-cats) will massively help reduce the effects of radiant heat the exhaust manifold inflicts on the poor old starter and will considerably extend it's life.

Finally keep your battery on a proper regulated charger (with float charging mode) to maintain it in perfect health and if you haven't got access to mains power use the BatteryBrain device to disconnect the battery remotely when you leave the car for any length of time.
Is it important to upgrade the alternator live and replace the fuse and fuse holder ?It looks a bit weedy .

ChimpOnGas

9,637 posts

178 months

Thursday 29th January 2015
quotequote all
SILICONEKID345HP said:
Is it important to upgrade the alternator live and replace the fuse and fuse holder ?It looks a bit weedy .
The best thing you can do with the fuse is replace the mechanically weak strip fuse as it can crack with vibration, the original strip fuse looks like this:



Replace it with a much more robust Midi fuse like this:



The maximum output of the alternator is 100amps so use a 100amp fuse, a 100amp fuse is actually designed to fail quite a margin above 100amps so dont be tempted to fit a fuse of a higher amp rating.

A midi fuse is better by design as the weak point is encapsulated with plastic, it still functions in the same way as the original fuse used by TVR it's just it wont crack through vibration fatigue like a strip fuse can.

Here's a direct comparison between the two types (midi fuse on the left and original crack prone strip fuse on the right)



The fuse holder itself is fine, you only need to replace it of it's in poor condition, make sure it snaps closed as it should so the fuse is protected from moisture. The positioning of the fuse holder is quite exposed so its well worth making sure it seals properly and use some petroleum jelly when fitting your new physically stronger 100amp midi fuse.

Saying all that midi/strip fuse holders are cheap and replacing it is an easy enough job:



The cable from the alternator seems adequate to me so I haven't felt the need to upgrade it with a heavier gauge run.

I did however replace the short 6" lead to the fuse holder when I upgraded the battery/starter cable and fitted a direct earth return, all of which was completed using proper marine grade tinned 50mm² cable which is a significant upgrade on the weedy 35mm² cable I pulled out. My original cable was also corroded internally and crispy after years of being cooked by radiant heat.



Since doing all this the car cranks significantly faster and stronger, which was absolutely no surprise looking at the dreadful state of the thin gauge crispy stuff I ripped out.

The switch to a midi fuse and the cable/earth return upgrade is definitely well worth doing, but personally I dont think there's any real benefit to be had in upgrading the brown alternator cable unless yours is in a poor state of health.

Here's my new heavier gauge 50mm² starter/battery cable next to the old tired 35mm² one before fitting:


SILICONEKID345HP

14,997 posts

230 months

Thursday 29th January 2015
quotequote all
I don`t fancy running a second ground all the way back to the battery in the boot .Would it still do the same job if i ran a new ground from the engine block to the ground point below ? I have already beefed up the engine the chassis ground .


Linking to this point would ground it back to the battery .


ChimpOnGas

9,637 posts

178 months

Thursday 29th January 2015
quotequote all
SILICONEKID345HP said:
Would it still do the same job if i ran a new ground from the engine block to the ground point below? I have already beefed up the engine the chassis ground.
No


SILICONEKID345HP said:
Linking to this point would ground it back to the battery .

You are correct, however I recommend you go away & compare the resistance of the chassis with a good quality fresh run of 50mm² cable.


SILICONEKID345HP said:
I don`t fancy running a second ground all the way back to the battery in the boot.
Well you shouldn't have stuck the battery way back there in the boot then should you, it's miles from everything that needs power.

Remember, the longer your live & earth cables the higher the resistance, putting the battery in the boot is an excellent way to increase that resistance.

TVR put the battery up front in the passenger footwell for weight distribution, then put the fuse box there too so it's as close as possible to the battery.

I still profess the footwell is by far the best place for the battery, and a proper full sized battery at that. The only disadvantage is restricted leg room for passengers.

If this is a problem for you, you married a woman who's too tall tongue out

SILICONEKID345HP

14,997 posts

230 months

Thursday 29th January 2015
quotequote all
ChimpOnGas said:
Well you shouldn't have stuck the battery way back there in the boot then should you, it's miles from everything that needs power.

Remember, the longer your live & earth cables the higher the resistance, putting the battery in the boot is an excellent way to increase that resistance.

TVR put the battery up front in the passenger footwell for weight distribution, then put the fuse box there too so it's as close as possible to the battery.

I still profess the footwell is by far the best place for the battery, and a proper full sized battery at that. The only disadvantage is restricted leg room for passengers.

If this is a problem for you, you married a woman who's too tall tongue out
If i connect it to that point it does go straight back to the battery .. The cable comes from the battery to that chassis point so they will be joined as one cable .

ChimpOnGas

9,637 posts

178 months

Thursday 29th January 2015
quotequote all
SILICONEKID345HP said:
If i connect it to that point it does go straight back to the battery .. The cable comes from the battery to that chassis point so they will be joined as one cable .
It seems you're answering your own questions Daz.

If you're happy with a great long mass of daisy chained cables go for it.