Battery location and cable upgrade?
Discussion
ChimpOnGas said:
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.
fNow 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.
k it, it's staying in the footwell 
Happy days 
Thanks Dave.Twistygit said:
So using. That table 35mm is more than sufficient, I'll probably just get some of that
So what figures did you use in the calculator to come up with 35 being OK?I used 300amp and 4m cable length.
Which brings me back to the question I asked Google....what amps does a starter draw?
General figures were anywhere between 300 and 500.
Steve
I'm running about 40kg more weight in my boot than a standard Chimaera carries. This is a worse case scenario using a standard Chimaera with a full petrol tank as a base line and comparing it with 'Ol Gasbag' at the point I have a full fill of 14 gallons of LPG on board and 5 gallons of reserve petrol too. With the right suspension setup I found some extra weight over the rear axle in a Chimaera actually delivers handling and traction improvements, so people really shouldn't worry about sticking their 20kg full sized 072 battery in the boot.
I should point out my maximum additional 40kg is all very centralised, whereas space constraints dictate you really need to put a big 072 battery in one or other of the two boot corners. With this in mind and with most of us diving our cars solo a lot of the time, I'd recommend putting it in the N/S boot corner as a nod towards keeping balance neutral. Personally I'd be tempted to fit two Odyssey PC925 batteries well insulated and wired in parallel on top of the petrol tank, wiring two 12v batteries in parallel still gives you 12v but it doubles the CCA and amp hour rating bring the neat and compact paired arrangement in line with a single 072.
An Odyssey PC925 is roughly 130mm deep when mounted on its side making it a perfect fit on top of the petrol tank which offers a shelf that's at least 200mm deep, the tank is a full meter wide so with two PC925s together only taking up 330mm they will easily sit side by side placed in a very centralised way. A PC925 on its side is 180mm tall and the space between the top of the tank and the boot lid when its closed is a good 200mm so the boot will shut easily too.
Weight wise two PC925s will be getting on for 24kg, but that's only 4kgs more than an average 072 and it'll be nicely centralised weight too, my petrol tank effectively sits in this position because my LPG tanks are now where the original 12.5 gallon petrol tank once sat. My smaller high mounted petrol tank usually has 3 gallons in it which weighs about 10kg and say another 3kg for the ally tank itself so I have 13kgs where the two PC925s would be sitting, it is weight carried high but the truth is in my experience you just won't notice it.
Fitting batteries on top of the petrol tank is perfectly safe as far as I'm concerned but their terminals do need to be well insulated and the batteries themselves very well secured as you wouldn't want live batteries flying about inside the boot space in the event of an accident. The trick to making my LPG conversion work without losing luggage space was to make use of the wasted space above the original petrol tank, making the best use of the available space when fitting a battery or batteries in the boot is really no different.
Two Odyssey PC925 batteries (well insulated and secured) wired in parallel and fitted centrally on top of the petrol tank has to be the ultimate solution, this location is by far the best use of what is essentially just wasted boot space, having two PC925s wired in parallel also delivers the cranking power and amp hours of one big on 072 in the passenger footwell. Just make sure you use the heaviest gauge cable you can get away with without making installation too much of a pain, remember the thicker it gets the harder it will be to rout easily as even a small increase in gauge can make for a very inflexible cable.
Don't underestimate this, thick cable can become really difficult to rout
Here's how I used that wasted boot space to good effect...
And yes my roof panel still fits nicely in the boot with plenty of space left over for luggage
I should point out my maximum additional 40kg is all very centralised, whereas space constraints dictate you really need to put a big 072 battery in one or other of the two boot corners. With this in mind and with most of us diving our cars solo a lot of the time, I'd recommend putting it in the N/S boot corner as a nod towards keeping balance neutral. Personally I'd be tempted to fit two Odyssey PC925 batteries well insulated and wired in parallel on top of the petrol tank, wiring two 12v batteries in parallel still gives you 12v but it doubles the CCA and amp hour rating bring the neat and compact paired arrangement in line with a single 072.
An Odyssey PC925 is roughly 130mm deep when mounted on its side making it a perfect fit on top of the petrol tank which offers a shelf that's at least 200mm deep, the tank is a full meter wide so with two PC925s together only taking up 330mm they will easily sit side by side placed in a very centralised way. A PC925 on its side is 180mm tall and the space between the top of the tank and the boot lid when its closed is a good 200mm so the boot will shut easily too.
Weight wise two PC925s will be getting on for 24kg, but that's only 4kgs more than an average 072 and it'll be nicely centralised weight too, my petrol tank effectively sits in this position because my LPG tanks are now where the original 12.5 gallon petrol tank once sat. My smaller high mounted petrol tank usually has 3 gallons in it which weighs about 10kg and say another 3kg for the ally tank itself so I have 13kgs where the two PC925s would be sitting, it is weight carried high but the truth is in my experience you just won't notice it.
Fitting batteries on top of the petrol tank is perfectly safe as far as I'm concerned but their terminals do need to be well insulated and the batteries themselves very well secured as you wouldn't want live batteries flying about inside the boot space in the event of an accident. The trick to making my LPG conversion work without losing luggage space was to make use of the wasted space above the original petrol tank, making the best use of the available space when fitting a battery or batteries in the boot is really no different.
Two Odyssey PC925 batteries (well insulated and secured) wired in parallel and fitted centrally on top of the petrol tank has to be the ultimate solution, this location is by far the best use of what is essentially just wasted boot space, having two PC925s wired in parallel also delivers the cranking power and amp hours of one big on 072 in the passenger footwell. Just make sure you use the heaviest gauge cable you can get away with without making installation too much of a pain, remember the thicker it gets the harder it will be to rout easily as even a small increase in gauge can make for a very inflexible cable.
Don't underestimate this, thick cable can become really difficult to rout
Here's how I used that wasted boot space to good effect...
And yes my roof panel still fits nicely in the boot with plenty of space left over for luggage
ChimpOnGas said:
Two Odyssey PC925 batteries (well insulated and secured) wired in parallel and fitted centrally on top of the petrol tank has to be the ultimate solution, this location is by far the best use of what is essentially just wasted boot space, having two PC925s wired in parallel also delivers the cranking power and amp hours of one big on 072 in the passenger footwell....
I don't dispute what you're saying, but if your existing 072 battery is in rude health, then Phillpots boot solution is about £250 cheaper.Steve_D said:
So what figures did you use in the calculator to come up with 35 being OK?
I used 300amp and 4m cable length.
Which brings me back to the question I asked Google....what amps does a starter draw?
General figures were anywhere between 300 and 500.
Steve
I think the high torque starters are 1.4Kw (1400 Watts) so full load current would be something in the region of 116 Amps.I used 300amp and 4m cable length.
Which brings me back to the question I asked Google....what amps does a starter draw?
General figures were anywhere between 300 and 500.
Steve
Cold cranking could be 4 or 5 times this figure, maybe more for a second or two.
sparkythecat said:
ChimpOnGas said:
Two Odyssey PC925 batteries (well insulated and secured) wired in parallel and fitted centrally on top of the petrol tank has to be the ultimate solution, this location is by far the best use of what is essentially just wasted boot space, having two PC925s wired in parallel also delivers the cranking power and amp hours of one big on 072 in the passenger footwell....
I don't dispute what you're saying, but if your existing 072 battery is in rude health, then Phillpots boot solution is about £250 cheaper.I do wonder how easy it is for Phillpot to put his roof panel in there though?
Personally I never felt the need to relocate my battery in the boot, as everyone knows I've got other madness going on in there, 4.5 years ago I went with 850 CCA Odyssey PC1500 and just stuck it in my passenger foot well... and it's still there today.
http://www.pistonheads.com/gassing/topic.asp?t=111...
The plan is to get 12 years out of it so it's got to last another 7.5 years yet, when I park the car in the garage I hook it up via a tail lead I fitted that comes right trough the car hidden under the carpet and long enough to extend 4ft out of the boot, I fitted 50amp Anderson connectors so I can connect it up safely to my AGM friendly Ring RSCPR50 charger in seconds. But not before I've locked the car and disconnected the battery using my Battery Brain, effectively I'm direct float charging a completely disconnected Odyssey PC1500 via its handy second set of front mounted terminals.
The car is typically either running and so charging the battery at 13.6v - 13.8v via the alternator, or sat disconnected on my Ring RSCPR50 charger at a 13.7v float charge. The only time the battery ever has to do any real work is when I use the TVR as a sub station at Le Mans, I always seem to end up flood lighting the tents with my headlights at night, charging everyone's phones and being the camp sound system for 3 days... but the PC1500 seems to relish these punishing duties as it's never once complained.
Amazingly the PC1500 just fits in the original TVR battery box too
At 4.5 years in so far, here's to the 12 year battery.... I wonder if it'll make it
sparkythecat said:
Do tell us more, please.
a flat level plywood base was created, lots of cardboard templates to get all the curves to fit boot well. This was bolted in place, on a bed of Sikaflex. The bolts are far enough under the curve of the rear wing to not be visible (unless you lay on the floor). A 1" ratchet strap was fed through a slot the wooden plinth and used to secure the battery. A 6mm plywood box was made to cover everything, and that covered in "exhibition carpet".The boot was quite a mess when I bought the car, looked like some kind of mega amp/sound system had been removed, the tank and filler neck covers were also re-made.
No "work in progress" pics of the Chimaera but these are my S3, similar principle............
Edited by phillpot on Monday 12th December 20:58
Belle427 said:
Steve_D said:
So what figures did you use in the calculator to come up with 35 being OK?
I used 300amp and 4m cable length.
Which brings me back to the question I asked Google....what amps does a starter draw?
General figures were anywhere between 300 and 500.
Steve
I think the high torque starters are 1.4Kw (1400 Watts) so full load current would be something in the region of 116 Amps.I used 300amp and 4m cable length.
Which brings me back to the question I asked Google....what amps does a starter draw?
General figures were anywhere between 300 and 500.
Steve
Cold cranking could be 4 or 5 times this figure, maybe more for a second or two.
People should know the little Odyssey PC925 is only rated a 330 CCA so it's a good 270 CCA & almost 50% off the mark! A PC925 will give you a burst of 900 amps for a few seconds making it fine most of the time, especially in the summer months, but a PC925 will likely struggle to crank a Rover V8 on a very cold morning when your engine oil is thick and the specific gravity of your battery electrolyte will have risen dramatically.
These two cold start conditions conspire together to make starting a engine in cold conditions much harder on a lead acid battery, it's also why you typically discover your battery is failing (or of insufficient capacity) on a frosty morning.
The lesson we should all pay attention to here is you simply can't beat a big battery with the right amount of cold cranking amps to do the job! Saying that if you only really use your TVR in the summer months and the battery is typically kept on a float charger you'll be absolutely fine with the little PC925.
It really does depend on how you use your Chimaera and how you're able to maintain your battery. Personally I want a good quality full sized battery that I know will start the engine no matter what, but I like to use my TVR all year round and sometimes that involves leaving the car outside and overnight in freezing conditions.
Steve_D said:
Twistygit said:
So using. That table 35mm is more than sufficient, I'll probably just get some of that
So what figures did you use in the calculator to come up with 35 being OK?I used 300amp and 4m cable length.
Which brings me back to the question I asked Google....what amps does a starter draw?
General figures were anywhere between 300 and 500.
Steve
Twistygit said:
Steve_D said:
Twistygit said:
So using. That table 35mm is more than sufficient, I'll probably just get some of that
So what figures did you use in the calculator to come up with 35 being OK?I used 300amp and 4m cable length.
Which brings me back to the question I asked Google....what amps does a starter draw?
General figures were anywhere between 300 and 500.
Steve
Steve
This type are fairly heavy duty. Most electrical wholesalers keep them in stock as they are widely used in industrial control panels etc.
http://www.12voltplanet.co.uk/copper-tube-terminal...
http://www.12voltplanet.co.uk/copper-tube-terminal...
Twistygit said:
With this talk of upgrading cable, are terminals created equal or are there better quality available? If there is does anyone know where to get them from as I only come up with poor looking ones,
You want popper tinned brass terminals.This guy sells the good stuff and a big selection too, unfortunately it looks like he's on holiday as his site is temporarily down until next Tuesday...
http://kojaycat.co.uk/epages/950000457.sf/en_GB/?O...
Or here if you can't wait...
http://www.polevolt.co.uk/acatalog/Battery_Termina...
I contacted D&C Trim, who were happy to supply a passenger side mat in the original colour at driver's side length. It fits well in the new longer space. Proper leg room too, at last.
I can't recall the price but it didn't break the bank. Questions to answer are colour of carpet, (obvs) colour of edging and colour of stitching. The last question caught me out, so check first.
I can't recall the price but it didn't break the bank. Questions to answer are colour of carpet, (obvs) colour of edging and colour of stitching. The last question caught me out, so check first.
I think you are guessing wrong - mine fits fine.
I have just spaghetti junction, ECU and the fuse box left there now.
I am planning on fixing some timber strips to the floor and walls to support it, with some sort of quick release catches each side, so that it stays put until access is required. I will be consulting with Erin (Mrs Dawes) as to exactly what degree of incline gives perfect comfort for touring and yet still allows her to apply the dual control footbrake when my inner teenager gets over-excited.
She has promised to come with me on a TVRCC trip to the land of kilt and deep fried mars bar in June, so I must look after her creature comforts. Aircon ✅ (roof comes off), heater ✅ (been repaired three times), heated seats ✅ (told her to remove the seat pad and sit on a hot water bottle - I have Tuscan seats). What more can a woman desire?
I have just spaghetti junction, ECU and the fuse box left there now.
I am planning on fixing some timber strips to the floor and walls to support it, with some sort of quick release catches each side, so that it stays put until access is required. I will be consulting with Erin (Mrs Dawes) as to exactly what degree of incline gives perfect comfort for touring and yet still allows her to apply the dual control footbrake when my inner teenager gets over-excited.
She has promised to come with me on a TVRCC trip to the land of kilt and deep fried mars bar in June, so I must look after her creature comforts. Aircon ✅ (roof comes off), heater ✅ (been repaired three times), heated seats ✅ (told her to remove the seat pad and sit on a hot water bottle - I have Tuscan seats). What more can a woman desire?
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