Voltage sensing wire relocation

I'm gonna be reworking the wiring in my truck soon and need a hand finalizing some things.
If we can figure this out in a simple way, it'll be a cheap to free write-up that'll let anyone with aftermarket accessory electrical components make their alternator work like it's supposed to!

This will especially help all us crazy expo guys wire up our complex systems to work correctly.



TL;DR:
Our alternator has a voltage sensing wire that it uses to adjust its output. Stock, it's connected to your stock fuse block. You bump the stereo with the headlights on and the seat heaters etc, the alternator "sees" this voltage drop and ramps up to keep everything around 14v. If the engine is just idling, it drops output to keep from from overcharging and frying your battery.
When you put your own fuse block on and wire up a ton of extra lights air compressor etc, the alternator can't see all this power being used and won't ramp up output to compensate until the battery drops enough to affect your stock fuse block.
This results in slow charging for dual battery setups, aux breakers tripping for no reason, battery isolators acting up, dim lights etc. Relocate this sensing wire correctly and your alternator will run everything at 100% And put less stress on all components.

The goal is to land this wire at the furthest and highest draw component in the circuit so it and everything in between will always be at full voltage.

I've got an sPOD relay switch block that controls most of my components and lights, but I've started to outgrow it.

My overhaul will include the big 3 upgrade, get a 250+ amp welding alternator, consolidate the negative leads for my water pump, air compressor and bed mounted crap and most importantly, relocate the voltage sensing wire from my alternator.

In the meantime, If I can figure out the relocation, I can pull all 130 amps out of my alternator before I finish the full wire harness.

Here's my wiring schematic I've got planned.

 

I think my mistake is landing it on the 12v plug in the bed. First issue is that until I have something plugged in and running, the circuit won't be complete and it'll always read zero volts. Second, that plug is supplied by the spod relay panel that has a breaker. If I pop the breaker it'll again see zero volts.

Where else should I land it?

 

sub'd

 

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Hmmm. My plan does have a set of disconnects front and rear for jump starting/ etc.



Maybe I could jump a resistor paralleled between the hot and ground a couple inches before the connector and tap the volt sensing wire there... That would complete the circuit but shouldn't short anything. And would be the furthest point most at risk of a voltage drop when used.

 

Yea def want to know more about this. I too have my aux fuse panel hooked up to my secondary battery and after extending camping trips where I run that battery down because of all my accessories, my Blue Sea ML-ACR won't automatically charge the secondary battery when it has low voltage. I have to manually link them until the secondary battery has charged a decent amount, then I can put it back on auto mode.

My set up:
Optima Red (House) and Yellow (Aux) batteries
Blue Sea ML-ACR Automatic Charging Relay
Blue Sea Aux Fuse Panel
High output 250a alternator
Big 4 upgrade

 

Got a theory.
One way to confirm this would actually fix it would be to compare the live voltage of your truck using something like a scanguage through your obd port under your dash, with your two live volt guages and hook a volt meter up at the furthest point away like plugging a fan into a cigarette plug in the bed hooked up through your aux terminals.

Keep the truck running,
Turn on all your lights and fridge- everything and let it run for a couple hours at idle.

You SHOULD See really low voltage on whatever you have running on the 12v plug in the back, low voltage on your secondary battery, decent voltage on your main and perfect voltage on your scanguage in the cab that monitors the voltage on the oem fuse block.

I think it might drop the voltage on your main enough to prevent your battery isolator from allowing you to charge both batteries.

Try it and let us know!

 

^ Yea I'll have to try it out. However, I've bought and sold a scan gauge and ultra gauge over the years lol. I'll have to get a hold of one some time to try this

 

I have one of these to continuously moniter system voltage:

LCD Cigarette Lighter Voltage Digital Panel Meter Volt Voltmeter Monitor for Auto Car Truck PatternName: 1piece

http://www.amazon.com/Cigarette-Lighter-Voltage-Digital-Voltmeter/dp/B0092KVYGI

 

Oh that's way cheaper. I'm sure autozone will have something like that. That'll do what you need too

 

Hey MJ,
The ACR has a low voltage lockout @9.5v and reset at 10v. Placing the sensing wire somewhere else won't help the ACR reconnect the two batteries. Because the ACR isolates the Aux batt in a UV condition, it's waiting for the aux batt to stabilize its voltage from a deep discharge. This can take a very long time depending on the health of the batt.

 

That's my point though. When the truck is running, there shouldn't EVER be anything below 12-14v. Even when it's running he's having that second battery stay low. If his big alternator isn't compensating for all the crap he's using, it'll only give it a trickle charge. If he moves it to his positive terminal block that both batteries and all of his extra accessories are wired to, it'll keep the voltage up at all times.

That's not to say he can't drain the battery that low when the truck is off.
And that's assuming he wired it up right. I saw someone post on the dual battery thread the correct way to wire up the blue sea panel.
Regardless. Point still stands.

 

Correct, but MJ stated that his aux batt goes low when he's camping running his fridge and lights with the truck off. His blue sea acr is doing its designed function keeping the batt separate until voltages are within cutoffs.
In the case where the truck has been off while camping and stuff, moving the sense wire will help recover aux batt voltage faster only after he manually connects the batteries from the acr.

 

@Spencer - Mike is right. My aux battery drains when long-term camping and truck is off. Thought you understood that and still determined that relocating the voltage sensing wire would help.

But yea Mike, that's exactly what I was talking about: I know the ML-ACR has the low voltage lockout, but it's also the thing that irritates me lol. Because let's say when the battery gets drained when I go camping (Not like when we camp and wheel throughout the trip, this is when I camp and don't move the truck for days), and it's time to leave camp, everything on my aux battery doesn't work until that battery gets somewhat charged. That includes my alarm, headlights (bc I have HIDs - ballasts hooked up to aux battery), and off road lights (like if I leave camp at the butt crack of dawn and it's complete dark out). Not to mention the fridge not being able to go back on or even my air compressors if I need to air back up.

I think what will eventually be needed is to replace my aux battery. I think it's 4 years old and for the first 3 years it was my primary battery with everything hooked up to it. When I went dual batteries I moved it to my aux battery bc it's a Optima yellow top and works as a deep cycle batt.

 

$73 Charge guard-Select

http://www.amazon.com/ChargeGuard-Select-Vehicle-Management-System/dp/B00B62LFNM

This is a charge guard that's designed to disconnect power from the battery with a desired set time and low voltage disconnect. I use these in our work trucks to turn off our radios after a set time and protects from draining the battery too low. Kinda pricy but is an option.

These yellow tops aren't the best deep cycle batteries for the type of use we use it for. The reserve capacity is very limited and the number of deep cycle drains isn't great either. A 4 yr old battery is typically when it goes down hill. It'll start a truck but won't provide desired capacity.

 

https://www.tacomaworld.com/index.php?threads/400536/

Here ya go.

I didn't realize you didn't move the truck or let it idle for a long while to keep the charge up!

Either way, doing this will still help, though perhaps not a much of a performance gain as a new battery could.

 

Yea a new battery is on the list. I'll probably have to go with the Optima again though. The biggest thing for me is the size. I probably can't fit any other battery in both locations

 

That group buy can get other sizes, I know 31m is common secondary/dual size.

 

I'd go with the northstar. ever since optima started making them in mexico I've heard and seen nothing but trouble out of the damn things. My dad has been through a ton of them recently- one of his trailer ones crapped out FIVE DAYS after warranty ended, his other one crapped out 6 months after warranty coverage, the jeep one is now on it's second one that failed under warranty for free replacement.... time for a new "best battery out there" it seems.

if I hadn't seen him first hand replace all of these optimas I wouldn't have started to pay attention to all the people bitching about them recently.

 

@Spencer I'm late to the party here, but Mike @tacozord has done a phenomenal writeup on relocating the voltage sense wire in his build thread located here.