Dual batt setup - getting some wierd results - help needed

I mean battery posts, not terminals.

hey mate

battery is a new one, only a few weeks old. did the dual batt installation a few weeks ago so its been getting plenty of charge.

Went out this weekend gone for the first time to try the setup.

Fridge was rented - but if fridge was stuffed, then lights should still work. Cabling running from the fusebox to the plugs is all 4mm (core thickness) twin core cabling and cable from aux battery to fusebox (front to rear of the car) is 16mm2 (6B&S cable).

I dont know about valium, but i sure could do with a scotch!!! lol

cheers
Jeelan

Sounds like an earth problem to me !

"If rear earth was the problem, wouldnt the measurements show uneven voltage all the time rather than just when an appliance is attached?"

Nope, The voltages would look fine without a load (current being drawn) the moment current was drawn the loose or dirty connection would drop volts and die.

Sounds like a loose or dirty connection problem to me too!

Geoff

thanks Geoff

i think that's what the problem is. WHen i start the car up, it's all systems go and everything that is connected to the aux battery sockets lights up. Once i've turned the car off, everything runs for about 2 mins and then the lights dim/flicker and fridge goes into cutout mode.

The voltage at the battery posts still reads fine, but at the fuse terminals it starts fluctuating again.

i'll hv to recheck all the terminals and make sure they're connecting well and also check the earth and make sure its completely clean metal .

thanks again for everyone's suggestions..

cheers
Jeelan

Jeelan,

Make sure the (thin) 16mm² cable is attached FIRMLY to both the 60ah Aux (+) battery terminal and the 6 lug fuse box (+) terminal.

For *best* result - run a return 16mm² EARTH cable BACK to the AUX (-) battery.

NOW - first check the battery Voltage using BOTH Aux battery posts, then at the INPUT (+) to the fuse box, then check the OUTLET (+) side of the fuse box, with NO load and the EARTH cable attached to a good solid bolt etc for an earth ( because you too far away to use the Neg battery terminal )

Then check same positions with vehicle running and also with load (fridge) attached.

This will show you exactly where the problem is.

Mainey . . .

thanks mainey for that.

I've done pretty much as you've suggested EXCEPT that i dont have a 16mm2 earth going back to the (-) Aux -

the reason i didnt do this was because the firewall hole that i used wasnt large enough to accomodate 2 cables of this thickness plus the co-ax for my UHF. I've decided that i'll drill a larger hole through the firewall and run the earth back to the battery.

Besides that - i have checked voltage on the following

Checked voltage at Aux battery posts - 12.4V
Checked voltage at end of cable in rear of car - 12.4V
checked voltage with cable connected to fusebox - 12.4V (voltage check here was done by touching the fusebox hardware, NOT the cables directly).
Checked the voltage at the OUTPUT terminals of the fusebox - 12.4V
Dismantled a hella socket and checked the voltage here - 12.4V

Ran a load on the system - a cheap 12V compressor which kept sputtering..

Checked voltage at Aux batt posts - 12.4V
Checked voltage at fusebox INPUT terminals - 4-5V reading.
Checked voltage at OUPUT terminals on fusebox - 4-5V reading.

So i guess this means that i've got a bad connection to the fusebox OR that i'm not earthing correctly here.

the 16mm2 cable has been crimped but the crimp for this size cable has a hole that is far too big for the fusebox so i'm using washers under and above the crimp to ensure solid connection - do these washers have to be a specific type to give the best connection??

Same with the (-) terminal - i've used 16mm2 to earth but the crimp for this size cable is much larger than the attachment point on the fusebox so i've used washers to secure.

if all this is fine - perhaps the fusebox is buggered? Is there a simpler system?

I bought the fusebox without giving real thought to what i want to connect - at this point 2-3 hella style points are sufficient for me so is there a simpler, more "robust" method of connection using something like an inline fuse rather than a fusebox as such?

beyond this, the only option is to pull everything out and start reinstalling with dual core cable all the way through....

Incidently, what voltage should a fully charged wet cell battery run at normally anyway? Deep cycle that is...

I've got an Amaron deep cycle which is 60ah and 550CCA. It was a cheaper brand which i deliberately picked because i wasnt sure what my requirements would be etc. I figured once i got a better idea of what i wanted to do with my setup, if required, i could get a higher quality battery.

cheers
Jeelan

Jeelan
You have found the problem here:

""Checked voltage @ Aux batt posts - 12.4 Volts""
""Checked voltage @ fuse box *INPUT* TERMINAL --> 4.5 Volts""
""Checked voltage @ fuse box *OUPUT* TERMINAL --> 4.5 Volts""

Simply remedy it by checking the cable connections between the AUX battery terminal and the fuse box *INPUT* terminal, while using the SAME EARTH path.

Because that is where you obviously loose the Voltage...

Mainey . . .

Jeelan,
""Is there a simpler system?"" -> Yes, the most *efficient* method is to run identical (thick) battery cable from the Pos (+) and neg (-) battery terminals direct to the fuse box.

""Beyond this, the only option is to pull everything out and start reinstalling with dual core cable all the way through"" -> Yes and the most *efficient* method anyway !!

""Incidently, what voltage should a fully charged wet cell battery run at normally anyway, Deep cycle that is?"" -> 12.7 Volts

An independant charging cable, both to and from, the fuse box will eliminate Voltage drop and create a secure charging system.
You have stated the DC battery is only 12.4 Volts now, so it's not fully charged anyway!

Mainey . . .

Hi
Re washers , these form part of the circuit & must be clean bright metal ,brass is best , mild steel next, & STAINLESS last[has highest resistance ].
Mild steel will rust /corrode unless protected with grease / vaseline etc.
You definatly have high resistance joint/joints somewhere in the circuit [ citcuit meaning any where from bat +post back to bat- post.
Agree ,12.4V is not a fully charged battery should be 12. 6v min, you may need to check the bat charging circuit as well

MAINEY -

if i'm reinstalling from scratch, what is the ideal cable that i should use?

I purchased all my hardware from 12V Shop in Welshpool and took their suggestions as to cable size etc.

your earlier comments alluded that 16mm2 is *THIN* - can you pls suggest a type of cable i should be using from Aux batt to fusebox, and then from Fusebox to Hella plugs?

cheers
Jeelan

Jeelan,
I use 32mm² (2 B&S) and I only go about 2.5 Metres, I'm not suggesting you should do as I do, but look at the size of "normal" battery cable and a realistic minium of 25mm² would be more useful than 16mm² that you presently use over the 'total' distance to the Hella plugs from the Aux battery.

You can use 25mm² (or larger preferred) to the fuse box, and then use the existing 16mm² to EACH of the Hella plugs, as I understand the distance between the fuse box and each Hella plug will be reasonably short and they will only be running one 'appliance' at a time.
(I have about 1.2 Mtrs of 10mm² powering my fridge, as a comparison)

Remember; when you make the hole in the firewall, use a rubber bung, from a 'garage' or a piece of heavy duty hose or similar 'security' method to stop any rubbing of the battery cable on the (thin) sharp edge of the hole, causing it to SHORT out.


Mainey . . .

mainey

thanks for the additional info - those are some pretty thick cables.

I was initially going to use 4B&S cable but found it too thick to tuck under the door trim of Pajero. The trim werent sitting back properly over the cable so i opted for 6B&S.

i'll hv to reroute through another way i guess.

Also thanks for the heads up with the firewall hole. Again, the 6B&S was the thickest cable that could fit through the existing firewall, however i popped into Repco today and picked up some blank wiring grommets of varying sizes. Will get some hole saws and make a new hole over the weekend and cap off with the appropriate grommets.

Just one final question - basically if i have (-) going back to the Aux batt from the fusebox then i dont need to earth anything at the fusebox...is this correct? The only earth would then be at the Aux Batt itself right?

cheers
Jeelan

Jeelan,
You have to form an electrical "circuit"

This electrical "circuit" starts at the (+) terminal of the Aux battery, the (+) cable goes direct to the fuse box, and then a cable goes to each Hella plug via a fuse in the fuse box, then to the "appliance" (fridge or light) and then it returns to the fuse box Neg (-) attachment bolt or similar attachment, then the large (-) cable returns to the (-) terminal of the same AUX battery, forming an electrical "circuit" - when the fuse blows it breaks this electrical circuit.

Most fuse box's have a common earth 'bolt' (attachment) where each (-) cable from the Hella plugs (etc) bolt onto, then your larger (-) cable returns back to the Neg (-) Aux battery terminal, thus forming the electrical "circuit" - ONLY when the "appliance" is connected and activated.

Mainey . . .

"" Just one final question - basically if i have (-) going back to the Aux batt from the fusebox then i don't need to EARTH ANYTHING at the fusebox... IS THIS CORRECT ? ""

I read it as a simple question, as it clearly states "just one final question" with the " ? " at the end of the sentence, hence my reply to him.

I don't believe Jeelan is suggesting the actual fuse box is EARTHED
Just asking questions about an "EARTH" to form the electrical circuit !!

Mainey . . .

you got it Mainey - thanks again for the explanation re circuit. I'll run the (-) back to the aux battery and also get the battery checked tomorrow to make sure there's no problems with it.

cheers
Jeelan