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Connecting up 2 batteries in boot

Started by MR77LX , Aug 01 2012 06:33 PM

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#26 _torbirdie_

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Posted 03 August 2012 - 01:03 AM

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.


Very unlikely givne that the problem is over,come by jump starting.

If the cable size is too small then the voltage drop is happening along the cable, effectively reducing the available voltage at the starter. It won't matter how many batteries are added in parallel, the same voltage drop will occur along the cable restricting the voltage at the starter.

Edited by torbirdie, 03 August 2012 - 01:10 AM.

#27 _judgelj_

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Posted 03 August 2012 - 07:40 AM

Just make sure if you do go for a dual battery setup that your batteries run and charge in unicen otherwise it will be pointless for what you need. Some setups run the primary battery and only source power from the reserve when levels are low. This wont give you double cranking amps when you need it.

#28 yel327

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Posted 03 August 2012 - 07:58 AM

Is it a red starter on the black block? I have heard of problmes with people mixing up generations of starter. Is it a geared started or an original?

#29 FastEHHolden

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Posted 03 August 2012 - 01:09 PM

Test how much current it is pulling....they usually pull about 220 Amps.

My advice is use a set of jumper leads to help you diagnose it.....connect 1 lead from block to starter body andf another from block to car body....I'm willing to bet its the earth side of the circuit.

#30 rexy

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Posted 03 August 2012 - 07:35 PM

I have an 11.3 comp 383 holden with VT block and original starter in the LX sedan.
Battery in boot (600CCA)with battery earth to rear panelwork inside the boot. Extra earth from block to front chassis rail. Cranks beautifully hot or cold. Cabling is gigantic - pulled from main supply to a building under demolition.

Its hard to believe you need 1200CCA. As some have suggested above I bet its either an earth issue or starter heat soak.
The jumper cables added to make extra temp earths is easy and cheap to try.

#31 MR77LX

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Posted 03 August 2012 - 09:43 PM

Torbirdie, I have posted a thread on this before. Since then I have taken it to 3 electricians and they all said you need a bigger battery. All 3 electricians did their checks on my electrical system and said there were no problems.
However I do agree with everyone else that 1200cca is excessive
SS Hatchback, I have ordered a 900amp dry ultima battery today, same as yours. I figured I will take a gamble and just buy a descent size battery first and see what happens.
I’m running a reduction type starter motor out of a Commodore VR.
My battery is going to arrive next week. I’m hoping the problem is the battery.
I will look at re locating my earth cables again and doubling them up and see what happens.

#32 _SS Hatchback_

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Posted 07 August 2012 - 07:51 PM

hope it all works out for you , i run my cabling similair ro rexy's and no issues since fitting that battery. Think from memory i am running 95mm welding flex cable , good stuff and keep us posted how you get on

#33 MR77LX

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Posted 07 August 2012 - 10:52 PM

No problem bud. Im just waiting for my battery to arrive. It should be here with in a week.

#34 MR77LX

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Posted 08 October 2012 - 04:25 PM

Hey guys, sorry it took me a while to get back to this forum. I have been very busy with work.
The 900amp battery came and i fitted it, however it did not fix the problem.
I have tested my starter motor with 3 different electricians as well and they could not find a problem.
Today i took it for a test drive; however i disconnected the battery after i turned it on and went for a half an hour drive while the battery was disconnected. After i got back i connected up the battery to see if its starts up again after a drive and funny enough it did not start and was slow to crank. The only thing this checks i guess is the battery and obviously the problem is not a battery because it was disconnected and it’s brand new.

Any help or ideas would be great because now I’m totally lost on what to do.

#35 Stinga

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Posted 08 October 2012 - 05:42 PM

isn't it a terrible idea to disconnect your battery while the car is running??

#36 _judgelj_

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Posted 08 October 2012 - 05:53 PM

find a bloody good mechanic or sparky.. lol

#37 _torbirdie_

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Posted 08 October 2012 - 08:45 PM

If jump starting it fixes your problem then there is your indication that fitting another battery in parallel will work.


Does jump starting it still work.? and where are you making the connection for the 'jumper'


Did you get around to measuring what the voltage at the starter and the battery was when trying to unsuccessfully start it when it was hot?


By providing this info it will help getting to the bottom of the matter.

#38 MR77LX

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Posted 08 October 2012 - 09:17 PM

I did not try jump starting it but i assume it will work from previously times.

i usually jump start it from another car. My guess it that something is possibly getting hot.

I'm guessing maybe the ignition wire going to starter motor or maybe the starter motor it self even though i have physically taken it out and tested it with the electricians.

#39 _torbirdie_

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Posted 08 October 2012 - 09:41 PM

I did not try jump starting it but i assume it will work from previously times.

i usually jump start it from another car.


But where do you connect it on the car that is "jumped"?

I'm guessing maybe the ignition wire going to starter motor or maybe the starter motor it self even though i have physically taken it out and tested it with the electricians.


By measuring some voltages when cranking you can avoid guessing

#40 MR77LX

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Posted 08 October 2012 - 09:56 PM

On the car that i jump started it from i went directly off the battery, negative to negative and positive to positive.

The electrician did measure the voltage when cranking and said its all fine. (He did not tell me what the reading was however)

The reason why i suspect maybe it could be the ignition wire is because when i rang up Come racing and asked them if they had this problem before, Issy from come racing said u will need a bigger ignition wire. I told that to my electrician and he said the wire that he has ran will do the job and blamed the problem on too much compression.

#41 _torbirdie_

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Posted 09 October 2012 - 08:21 AM

On the car that i jump started it from i went directly off the battery, negative to negative and positive to positive.

The electrician did measure the voltage when cranking and said its all fine. (He did not tell me what the reading was however)

The reason why i suspect maybe it could be the ignition wire is because when i rang up Come racing and asked them if they had this problem before, Issy from come racing said u will need a bigger ignition wire. I told that to my electrician and he said the wire that he has ran will do the job and blamed the problem on too much compression.


did the auto sparky do this when it was able to start or not able to start?

Suggest you get your own measurements using a multimeter and we can eliminate some of the possibilities.

What do we want measured?

voltage across battery terminals for cold and hot when cranking.

Voltage between +ve battery and +ve starter(= voltage drop along cable) for hot and cold cranking.
Voltage between -ve batt and engine block for hot and cold

Edited by torbirdie, 09 October 2012 - 08:22 AM.

#42 MR77LX

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Posted 09 October 2012 - 01:58 PM

He did this when it was able to start and also when it was slow to crank.

I'm happy to actually measure the voltage myself and see what happens.

However I'm not the best wit electrical. If I can get som simple instructions would be great and rough reading on what each voltage should be.

#43 VitcLJ

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Posted 09 October 2012 - 06:46 PM

Ther is one thing here that hasn't been considered. This problem seems to occur when the engine has been run. Where does the exhaust run? does it go near the starter motor? The resistance change of copper is 0.393% per degree centigade, Thus if the starter motor gets hot the resistance increases and it is then unable to draw the current it needs, if its at 100 degees then the resistance is 39.3% higher. (heat soak into a starter motor is a problem just ask someone who circuit races even the six cylinder holden suffers from this problem and heat shields are fitted to help keep the starter cool) .

If you can, TAke the car for a run drive up to the hose and run water over the starter for a minute then try to start it. if it starts OK then thats the problem.

The actuallity of a circiut is that the battery also has internal resistance of about 0.020 ohms. the starter and cabling is usually about 0.040 ohms so terminal volts will drop to about 8volts under fulll cranking. Putting in a larger battery (or two in parallel) lowers the internal resistance enabling a higher cranking voltage a t the starter (when the starter is at the same temperature) When the starter is hot the voltage at the starter will actually increase as its resistance is now higher but the power available is actually less (for the technically minded Power = current squared multiplied by resistance ) as current is a squared function and resistance is linear. so (2202) * 0.040 is roughly 2Kilo watts and lets say starter is at 125 centigrade then you will get roughly 150 amps being drawn due to the resistance rise thus this condition gives (1502)* 0.060 which is roughly 1.35 Kilowatts. Its a bloody big difference (and Ive allowed for the higher voltage at the starter when hot here).

As I said before this heat soak starter problem is common, the VC VH VK HDT commodores with extractors quite often suffered from it.

Sorry to be so long winded but hopefully you will get some assistance from this to either dismiss this as the problem or confirm it.

heat shield on the starter heat wrap on the extractors and exhaust in the starter vicinity will help if this is the problem. :mellow:

#44 MR77LX

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Posted 09 October 2012 - 07:52 PM

Thanks for that info. The starter motor i have shielded only.

i have wet the starter (but not for a minute with the hose) and there was no difference. If you think i need to wet the starter for a minute with a hose then i will try that. I just poured water from like a 5L bottle for about 10 seconds.

#45 VitcLJ

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Posted 10 October 2012 - 08:29 AM

unfortunately the starter motor is a large mass of iron and copper and its the copper windings that need the cooling rather than the steel casing, its takes some time for the cooling effect from water on the outside of the casing getting to the copper coils on the inside.
The Idea you had of putting two batteries in parallel is probably the easiest cure but then you have to drag two blocks of lead around. It really wont place much more of a load on your altenator if you keep the batteries charged, the initial current draw from the altenator may be higher but as each battery is less discharged than a single would be the energy needed to replace that taken for starting is the same so the charge current will be higher for a shorter period of time, (theoretically should be half the time to get batteries back to full charge practicaities will lenghten it slightly above this)

Problems will arise if one of the batteries becomes weak or faulty (generally if it degrades rather than just loosing a cell, its internal resistance increases and it can no longer deliver the current the starter needs because you loose too much voltage across the batteries resistance.)

Its a sad fact of life engines need lots of heat to operate successfully and electrics hate heat because of resistance rises in circiuts

Aint physics a real pain in the A

#46 _torbirdie_

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Posted 10 October 2012 - 08:30 AM

He did this when it was able to start and also when it was slow to crank.

I'm happy to actually measure the voltage myself and see what happens.

However I'm not the best wit electrical. If I can get som simple instructions would be great and rough reading on what each voltage should be.


Ok, a basic cheapo digital multimeter will do. Depending on what you are measuring use the 0-20V or 0-2V scale, DC( it will be labelled as such or have an underscore line and dotted line as a symbol, rather than the AC which has the symbol(~)

Attach the probles to the where you want the voltage to be measured.

From +ve to -ve of battery.

Should see ~ 12.6 V when battery is resting.
When cranking cold, given the size of the battery , would probably see somewhere from 10.5 - 11V when cranking.

It is the hot cranking(non start voltage) that should tell a story.

If the starter motor is overloading the system(either by short or by motor being hard to turn) we will see the voltage go much lower across the battery, possibly 8V or lower.
If it remains in the 10.5 - 11V range or higher it indicates that there is a problem with the connections within or to the starter, or that the starter windings have got so hot that their resistance increases and stops the starter from allowing enough current to create the necessary torque.

Also measure the voltage between +ve of starter and engine block for hot and cold cranking. These will be lower than at the battery, more than 1V diffence(to what you see at the batt) will point to problems with your leads/connections.

Edited by torbirdie, 10 October 2012 - 08:36 AM.

#47 _torbirdie_

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Posted 10 October 2012 - 08:35 AM

double post

Edited by torbirdie, 10 October 2012 - 08:35 AM.

#48 MR77LX

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Posted 11 October 2012 - 08:43 PM

Thanks for the info Torbirdie.

Strange thing happened today with my car. It seemed to start OK when it was hot and cold.
However i did not test drive it. I just left it on for 20 min. I'm assuming that its hard to start only after a test drive. That is a bit weird cause it reached normal operating temperature at idle. In saying that when my electrician tested my electrical, he did no test drive it. He had only turned it on and tested it like i just did today. And maybe this is why he could not find any faults.

I will do another Hot test when i drive it this weekend.

Here are measurements i did today.

Voltage across battery terminals on start-up and when hot was roughly between 12.8 to 13.1V.

Voltage to starter on cold was 14.27. However when hot cranked it did drop to about 9V. I'm guessing that if my car played up that the volts from starter would to drop around 7 because i have measured that before.

Voltage between battery and engine block was about 13.8V.

#49 _torbirdie_

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Posted 11 October 2012 - 09:16 PM

Thanks for the info Torbirdie.

Strange thing happened today with my car. It seemed to start OK when it was hot and cold.
However i did not test drive it. I just left it on for 20 min. I'm assuming that its hard to start only after a test drive. That is a bit weird cause it reached normal operating temperature at idle. In saying that when my electrician tested my electrical, he did no test drive it. He had only turned it on and tested it like i just did today. And maybe this is why he could not find any faults.

I will do another Hot test when i drive it this weekend.

Here are measurements i did today.

Voltage across battery terminals on start-up and when hot was roughly between 12.8 to 13.1V.

Voltage to starter on cold was 14.27. However when hot cranked it did drop to about 9V. I'm guessing that if my car played up that the volts from starter would to drop around 7 because i have measured that before.

Voltage between battery and engine block was about 13.8V.


It sounds like you are measuring voltages with the engine running? we aren't interested in that for the moment, though it appears that there is a problem here, you are measuring 14.27V at the starter terminal and only 13.1 at the battery, assuming your alternator wire goes to the starter terminal then you have a fair amount of resistance in the wiring going from the starter to the battery.

The battery may often measure the voltage it was last charging at, turning on the headlights for a few seconds will get it to its correct level which shouldnt be any more than 12.7-8 volts.

we want voltages when the starter is being used(disconnect the coil lead so it wont start)

#50 MR77LX

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Posted 11 October 2012 - 09:48 PM

Yes im measuring the voltage while the engine is on at cold start and when motor is hot.

I will disconnect the coil lead and give you a reading tomorrow on the starter.
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