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Connecting up 2 batteries in boot

Started by MR77LX , Aug 01 2012 06:33 PM

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#1 MR77LX

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Posted 01 August 2012 - 06:33 PM

Hi All,

Some of you may know that im having some electrical issues with my 383 stroker.

I need to fit a 1200 CCA amp battery in my boot. However a 1200 CCA Odyssey battery is $750.

That’s allot on money to spend on a battery i believe.

I'm looking at other options and considering to fit 2 batteries instead. (600 CCA each)


Would both batteries give me 1200 cranking amps and does it put more load on the alternator if i connect up both batteries? What are the positives & negatives?

Thank You

#2 _Bomber Watson_

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Posted 01 August 2012 - 06:38 PM

Yes it will double your amps and yes it will put more load on the alternator.

If you do it probably use a dual battery system like they use on fourbies.

Why on earth do you need 1200cfm though?? My landcruiser Diesel only has 720 lol.

Cheers.

#3 yel327

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Posted 01 August 2012 - 07:06 PM

2 x 600's in parallel will be the similar to 1 x 1200, in either case you'll want a decent alternator. Biggest problem will be the size of the cables from the boot to the starter and engine, if they are too small then it will offset what you are trying to achieve. Agree with Bomber, why such a big battery requirement?

#4 _CHOPPER_

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Posted 01 August 2012 - 07:24 PM

It sounds like his current battery cables are inadequate. I had a set of leads made from 1000 amp welding cables in 1998. The stuff is currently about $20/metre from welding supply places.

#5 shadey1963

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Posted 01 August 2012 - 07:24 PM

Using a cable size calculator came up with this:


Voltage Drop and Cable Size Calculator for ELV Solar Power Systems
Allowable Voltage Drop 1 % Run Length 2 m Current Demand 1000 A System Voltage 12 V Voltage Drop 0.06 mV/A.m Recommended Cable Size 70 mm2

#6 _CHOPPER_

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Posted 01 August 2012 - 07:27 PM

The ones I got made are 95mm2

#7 shadey1963

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Posted 01 August 2012 - 07:34 PM

Sounds fair

#8 rodomo

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Posted 01 August 2012 - 07:57 PM

Something else is wrong I reckon?
You shouldn't need 1200cca
VE Commodore only has 600cca and they're in the boot.

#9 _CHOPPER_

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Posted 01 August 2012 - 08:03 PM

As I said 30 mins ago, the cable size he currently has is probably too small. Which would give the illusion of the battery being inadequate.

#10 MR77LX

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Posted 01 August 2012 - 08:29 PM

I agree, 1200 CCA is massive.

The problem im having is my car starts up perfect but when i turn it off, its cranks very slow.

If i leave it for a few hours it will start up fine. I have had 3 electricians’ looks at it and they all reckon it’s the battery. When they jump start it, its starts first go. I recently had my starter tested and it was all ok. I’m using thick welding cables which i have sent and got the ends professionally pressed as well. All 3 electricians have tested the voltage drop form various positions and can’t find any problems.

So I guess to sort out whether it’s a battery problem or not, the cheapest way is to fit 2 batteries and see what happens.

#11 _Bomber Watson_

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Posted 01 August 2012 - 08:31 PM

Or replace the current battery??

Cheers.

#12 MR77LX

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Posted 01 August 2012 - 08:34 PM

I have replaced the battery twice.

The one that i have now is actually a 660.

#13 _Bomber Watson_

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Posted 01 August 2012 - 08:36 PM

Isnt this a common issue with 308's due to the starter location? Gets hot and doesnt want to work? Have they tested it hot?

Electrics make my head hurt.

Cheers.

#14 MR77LX

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Posted 01 August 2012 - 08:42 PM

Mine is a 304 block stroked to a 383 and its injected.

#15 _Bomber Watson_

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Posted 01 August 2012 - 08:43 PM

Same thing?

Most trucks run around 1200cca, just why i find it hard to believe you might require it.

Cheers.

#16 MR77LX

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Posted 01 August 2012 - 08:49 PM

well yea its very similar.

I dont think i need the full 1200cca but i dunno. Im confused cause all three electricians said you need to double the power.

I am running 11:1 compression but surely that doesn't need 1200cca.

This is why i want to try 2 batteries, its allot cheaper than buying an odyssey battery.

#17 _Bomber Watson_

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Posted 01 August 2012 - 08:53 PM

True that, perhaps look at picking up a N70 and see if that improves the situation, there 720 from memory, about $100.

Cheers.

#18 _SLR Goat_

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Posted 01 August 2012 - 08:57 PM

how many earth connections do you have seen before high comp motor when hot cranks slow or wont crank at all a couple more earth connections fixed it

#19 MR77LX

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Posted 01 August 2012 - 08:59 PM

Originally i was going to buy a PC 1750 odyssey battery for $450. It has 930 cca.

However i didn't go with it cause knowing my luck i get it and it probably still doesn't fix the problem.

#20 MR77LX

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Posted 01 August 2012 - 09:02 PM

i have an earth running from negative battery all the way to front of chassis and an earth from chassis to block and another earth from boot chassis to battery again.

#21 _SS Hatchback_

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Posted 01 August 2012 - 09:20 PM

i used to have a few issue with slow starts when warm or hot, im running single 95mm sq welding cable to the front, one in the rear to the chassis and one in the front from chassis to block and i made a heat shield for the starter as it was only having issues like you said when hot. Make sure your thermos arent running while trying to crank your engine too but besides that i changed to a 900amp dry ultima battery and never looked back , never changed a thing and it cranks easy every time , try find a mate who has one and just try it its all i had to change and not to mention i feel even when leaving the car for 3 or 4 weeks it still starts with no issues

By what your saying it seems you cables and setup should be fine, anyway it worked for me as i was pulling my hair out too

#22 MR77LX

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Posted 01 August 2012 - 09:28 PM

Yea i have done very similar with the cables and also made a heat shield for the starter.

I have no thermos in mine so im fine there. I can’t find any anyone that would lend me there battery for the day that’s why i might just connect up 2 batteries and see what happens.

#23 _SS Hatchback_

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Posted 01 August 2012 - 10:12 PM

Just make sure you use large cable from one battery to the other aswell.

Pity you cant ask a specialised battery place their thoughts and say can i return it if it doesnt help :)

#24 _torbirdie_

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Posted 03 August 2012 - 12:00 AM

I agree, 1200 CCA is massive.

The problem im having is my car starts up perfect but when i turn it off, its cranks very slow.

If i leave it for a few hours it will start up fine. I have had 3 electricians’ looks at it and they all reckon it’s the battery. When they jump start it, its starts first go. I recently had my starter tested and it was all ok. I’m using thick welding cables which i have sent and got the ends professionally pressed as well. All 3 electricians have tested the voltage drop form various positions and can’t find any problems.

So I guess to sort out whether it’s a battery problem or not, the cheapest way is to fit 2 batteries and see what happens.

If jump starting it fixes your problem then there is your indication that fitting another battery in parallel will work.
Have you posted this prob before.....or was this someone else.?
Did you get around to measuring what the voltage at the starter and the battery was when trying to crank it when it was hot?

Will you need a bigger alternator, probably not. Larger alternators are needed for larger electrical loads while you are running the car, so unless you have added a whole lot of accessories then standard alternator should suffice. A standard battery draws about 5 A when fully charged, so if you have two that doubles to 10 A, your alt should cope with another 5A.

What is important is that you don't fall for the folly of running a separate wire from the alt to the battery, leave the setup as it is with the alt wire going to the starter terminal


Edited by torbirdie, 03 August 2012 - 12:12 AM.

#25 _torbirdie_

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Posted 03 August 2012 - 12:23 AM

Ideally you need a smarter setup when battery located at distance from the alternator. The reg needs to be able to output at a higher voltage when charging current is high to overcome volt drop but drop off when the current load decreases as well as revising where your electrics get their feed form to protect them from higher than 14.5v

Edited by torbirdie, 03 August 2012 - 12:24 AM.

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