Battery location and cable upgrade?
Discussion
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s p a c e m a n said:
I just assumed because the fuse was underneath the starter motor. How much do we need to get from starter to boot, 4 meters red and 1 meter for earth? Those hydraulic crimps look good, I've got the old fashioned draper whack it with a hammer type somewhere but I might buy myself another Christmas present
I think your 1m will be a bit conservative.
Steve
I asked a similar question earlier this year and received some really good ideas from the PH community. Link below:
http://www.pistonheads.com/gassing/topic.asp?h=0&a...
http://www.pistonheads.com/gassing/topic.asp?h=0&a...
Twistygit said:
Is 50mm cable a bit overkill? I've just been looking and they say it's about 340amp cable
Don't ask me the technical description but my understanding is it is not about the amp rating more about volt drop on long cables.Stand to be both corrected and educated.
Steve
ETA a quick Google indicates start current at between 300 & 500amps.
Edited by Steve_D on Sunday 11th December 22:58
A useful guide for you, 50mm should be fine. No harm in going over the top slightly with cable sizes.
http://www.12voltplanet.co.uk/cable-sizing-selecti...
http://www.12voltplanet.co.uk/cable-sizing-selecti...
Its interesting to see this modification referred to as an upgrade, I appreciate putting the battery in the boot releases some passenger leg room, but people should also except it can only ever deliver worse performance regarding the starting of your engine and the length of time you can leave your TVR before the battery becomes so discharged you can't start the car. Resistance in a wire increases in direct proportion to it's length, if you put your battery in the boot you're going to end up with longer cables, and it's not like the cable on the standard setup is short in the first place.
Now add a smaller battery!
Consider a big healthy fully charged 072 sat in the footwell will deliver 650 cold cranking amps, whereas a little Odyssey PC925 in the same condition will only serve up 330 cold cranking amps, and these figures are at full charge so will become significantly worse as the battery discharges between starts. In this respect the bigger 072 gives you a lot more head space whereas the smaller PC925 only starts out as adequate when in its fully charged state. First you significantly increase resistance by using longer cables, then you half the system's cranking power by fitting the smaller PC925 battery, thats not really what I'd call an upgrade.
The reality is if you use heavier gauge cables even though your new 'to boot' cable is significantly longer you probably won't have any starting issues, especially as anything will be better than the awful string thin cable used by TVR. The more serious potential issue however is one of battery discharge, all cars suffer parasitic drains but TVRs are worse than most. Keep in mind a healthy 072 starter battery will typically give you 65 amp hours when in it's fully charged state whereas a PC925 will only give 28 amp hours, so if your TVR will just about start it's engine after 10 days of not being driven (typical of most Chimaeras), then after just 5 days of not using the car with the smaller PC925 battery fitted you'll be running the very real risk of being unable to start your car.
I understand for most people their TVR is just a toy kept tucked up in a garage on a float charger, so this big amp hours deficit may not be considered an issue, but for those without access to mains power a battery that becomes so discharged you can't start the car in just 5 days is not exactly a practical situation.
Those people can solve the discharged battery issue by disconnecting it, typically a completely disconnected 072 battery (fully charged when disconnected) will hold sufficient charge to still start the car as much as 4 months after it was disconnected. The problem for the TVR owner is the car will only lock with the battery connected and its impossible to disconnect a battery inside the car after you've locked it... unless you fit your disconnect switch somewhere on the outside of the car. So with most owners wanting to lock their car when they leave it they've either got to fit that disconnect switch on the outside (not ideal)... or find another solution.
The Battery Brain device is an excellent solution for this problem as it allows you to remotely disconnect your battery using an IR fob after you've locked the car, when you return to the car reconnect the battery using the Battery Brain IR fob and you can unlock the car as normal. It's not perfect because the Battery Brain device itself produces it's own parasitic drain, but its a very small one and the battery is still disconnected from all the heavier drains TVR gave us.
Using a Battery Brain can give you as much as 3 months layup on a 072 battery before things start to become critical and the likelihood of a failed start returns, but the truth is you can still half this time window if you're using the smaller PC925. Therefore people considering this upgrade must acknowledge fitting longer cables and a smaller battery will always add resistance, reduce cranking power, and shorten the time you can leave the car before you suffer a discharged battery.
I'm not saying it's a bad idea to put your battery in the boot, clearly there are some worthwhile advantages in doing so namely battery access and more leg room for your passenger. I'm just making people aware of the performance loss elements that the rules of physics dictate will always come with this upgrade. If you don't necessarily need that extra passenger legroom you're probably better off leaving the battery where it is and upgrading the cables.
Saying that having the battery in the boot makes it massively easier to remove, a little light PC925 mounted on top of the petrol tank means you can simply remove it and take it home to keep it on your float charger. This is perfect for people who don't have mains power where they keep their TVR, but it does still mean leaving the car fully locked will be tricky. People should consider both the positives and negatives to this upgrade and must base their decision to relocate the battery to the boot on their specific needs, use of the car, security considerations and access to mains power.
Now add a smaller battery!
Consider a big healthy fully charged 072 sat in the footwell will deliver 650 cold cranking amps, whereas a little Odyssey PC925 in the same condition will only serve up 330 cold cranking amps, and these figures are at full charge so will become significantly worse as the battery discharges between starts. In this respect the bigger 072 gives you a lot more head space whereas the smaller PC925 only starts out as adequate when in its fully charged state. First you significantly increase resistance by using longer cables, then you half the system's cranking power by fitting the smaller PC925 battery, thats not really what I'd call an upgrade.
The reality is if you use heavier gauge cables even though your new 'to boot' cable is significantly longer you probably won't have any starting issues, especially as anything will be better than the awful string thin cable used by TVR. The more serious potential issue however is one of battery discharge, all cars suffer parasitic drains but TVRs are worse than most. Keep in mind a healthy 072 starter battery will typically give you 65 amp hours when in it's fully charged state whereas a PC925 will only give 28 amp hours, so if your TVR will just about start it's engine after 10 days of not being driven (typical of most Chimaeras), then after just 5 days of not using the car with the smaller PC925 battery fitted you'll be running the very real risk of being unable to start your car.
I understand for most people their TVR is just a toy kept tucked up in a garage on a float charger, so this big amp hours deficit may not be considered an issue, but for those without access to mains power a battery that becomes so discharged you can't start the car in just 5 days is not exactly a practical situation.
Those people can solve the discharged battery issue by disconnecting it, typically a completely disconnected 072 battery (fully charged when disconnected) will hold sufficient charge to still start the car as much as 4 months after it was disconnected. The problem for the TVR owner is the car will only lock with the battery connected and its impossible to disconnect a battery inside the car after you've locked it... unless you fit your disconnect switch somewhere on the outside of the car. So with most owners wanting to lock their car when they leave it they've either got to fit that disconnect switch on the outside (not ideal)... or find another solution.
The Battery Brain device is an excellent solution for this problem as it allows you to remotely disconnect your battery using an IR fob after you've locked the car, when you return to the car reconnect the battery using the Battery Brain IR fob and you can unlock the car as normal. It's not perfect because the Battery Brain device itself produces it's own parasitic drain, but its a very small one and the battery is still disconnected from all the heavier drains TVR gave us.
Using a Battery Brain can give you as much as 3 months layup on a 072 battery before things start to become critical and the likelihood of a failed start returns, but the truth is you can still half this time window if you're using the smaller PC925. Therefore people considering this upgrade must acknowledge fitting longer cables and a smaller battery will always add resistance, reduce cranking power, and shorten the time you can leave the car before you suffer a discharged battery.
I'm not saying it's a bad idea to put your battery in the boot, clearly there are some worthwhile advantages in doing so namely battery access and more leg room for your passenger. I'm just making people aware of the performance loss elements that the rules of physics dictate will always come with this upgrade. If you don't necessarily need that extra passenger legroom you're probably better off leaving the battery where it is and upgrading the cables.
Saying that having the battery in the boot makes it massively easier to remove, a little light PC925 mounted on top of the petrol tank means you can simply remove it and take it home to keep it on your float charger. This is perfect for people who don't have mains power where they keep their TVR, but it does still mean leaving the car fully locked will be tricky. People should consider both the positives and negatives to this upgrade and must base their decision to relocate the battery to the boot on their specific needs, use of the car, security considerations and access to mains power.
^^Excellent bit of info sharing there Dave^^
I intend to do the battery to boot mod using my existing 072 battery in a purpose made battery box combined with somewhat heavier cable. I have concerns about fitting such a heavy component on top of the petrol tank as this is above the centre of gravity so will detract from the car's cornering performance. As I now use a Surrey Roof I'm most likely going to place it in the boot floor, probably passenger side.
As for cable, I'm tempted to go for 50mm# but this is definitely overkill and may be overly difficult to fit. Jury is still out on that one, 35mm# is adequate which may mean it's not quite good enough. Still looking for inspiration on this aspect
I intend to do the battery to boot mod using my existing 072 battery in a purpose made battery box combined with somewhat heavier cable. I have concerns about fitting such a heavy component on top of the petrol tank as this is above the centre of gravity so will detract from the car's cornering performance. As I now use a Surrey Roof I'm most likely going to place it in the boot floor, probably passenger side.
As for cable, I'm tempted to go for 50mm# but this is definitely overkill and may be overly difficult to fit. Jury is still out on that one, 35mm# is adequate which may mean it's not quite good enough. Still looking for inspiration on this aspect
Lloyds Special Developments, who installed my Canems, have advised me to replace the battery cable with 40mm2/539 strand/300amp cable. This is for the standard position battery but now changed to an Odyssey PC925. I shall fit the new cable into reflective sleeving between the battery and the starter motor.
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