Battery isolator installation?

[zuren]

I'm trying to get my head around installing just a single auxillary battery and having it isolated from the starting battery. I've been reading through the information at the Hell Roaring website and they have this diagram showing a "standard" 2nd battery install:



My van was already a pseudo-converted van with a 3000w inverter. There are already Pos. and Neg. cables running from the starting battery to the inverter in the back. The auxillary battery will be mounted in the cabin near where these cables emerge. I thought the isolator would go between the connections at each battery but this diagram shows differently (isolator goes between the alternator and aux. battery). I'm trying to figure out wiring changes that I'll need to make between the engine bay and the rear and wanted to know if this is the configuration that everyone else has done who have 1 house battery that is isolated.

Thanks!

[Herbie]

I recently did my dual-battery setup and I ran my cables from the starting battery, not the alternator. The only difference from that and the setup you've pictured is where the fuse is.

Running from the starting battery positive terminal, it goes to a big 150A resettable breaker, then through the isolating solenoid, then the long run of cable back to the back of the van, then through another 150A breaker, then to the positive terminal of the house battery.

Fusing/breaking both ends of the long run is key because if you ground out that cable anywhere in the middle, both "ends" will be shorting to ground.

OK, I needed to do this anyway for my own leaky memory, but here's the original "recommended" wiring from the manufacturer of my NL knockoff battery controller, followed by a craftily modified version (note my mad Paint skillz) that reflects the "reality" of wiring in my van:



One thing to note about the way I wired mine: Some people recommend powering the dual switch off of the house battery entirely, but I didn't. I probably could do it by reconfiguring a couple of things, but my reasoning is that the non-open-circuit draw is relatively low and I've got the breaker so I can isolate the solenoid completely if there's a problem, so I left it closer to the original diagram.

Note also that I ran a ground cable all the way back to the starting battery, rather than relying on chassis ground, etc.

[dwh]

To the OP:

In the pic you posted, the wire from the isolator and the wire from the battery both go to the alternator. They'll be connected together at that point anyway, so there's no difference if you run from the isolator to the alternator, or from the isolator to the battery. You'd just be connecting the isolator to the battery end of the battery-alternator wire instead of the alternator end of the same wire.

One thing to be aware of though is the wire size. You say you have a 3000w inverter - that's HUGE. 3000w / 12v = 250a !!

You need cable as thick as your thumb to support a load like that.

[zuren]

Herbie - Are there any pros/cons of doing it the way you did versus what Hell Roaring shows?

My original thoughts are how you did it. This is my current setup:

Positive
Alternator --> Main Batt. --> Breaker --(long cable run)--> Inverter

Negative
Main Batt. --(long cable run)--> Inverter

So grounding from the Neg. post to Neg. post would be easy for me, I would just need to add an extension. I have space on the passenger side wall to install another breaker, an isolator, and a 12 circuit fuse box. So my proposed setup is:

Positive
Alternator --> Main Batt. --> Breaker --(long cable run)--> Isolator --> Breaker --> Aux. Batt. --(2 splits)--> Inverter & fuse box

Negative
Main Batt. --(long cable run)--> Aux. Batt. --(2 splits)--> Inverter & fuse box

The fuse box I'm looking at is a Blue Sea 5026 that has it's own neg. bus. Grounding to chassis works but wanted the option for a better ground. I have a lead that is linked to the ignition that I capped off so I could easily extend that to the isolator as well.

Unless, anyone can point out a shortcoming with this approach, I think I'm essentially copying your setup.

[zuren]

One thing to be aware of though is the wire size. You say you have a 3000w inverter - that's HUGE. 3000w / 12v = 250a !!

You need cable as thick as your thumb to support a load like that.

Yep! I don't have pics but that is exactly what is running nearly the entire length of the van. Both the Pos. and Neg. cables are 1/2" in diameter or better. I couldn't see what gauge they are but will look tonight. I have no idea why they needed an inverter that large. This is the one that came with the van:

Tripp Lite 3000w inverter
http://www.tripplite.com/en/products...xtModelID=2560

Even on the cheap end it's a $350+ inverter.

[dwh]

Yep! I don't have pics but that is exactly what is running nearly the entire length of the van. Both the Pos. and Neg. cables are 1/2" in diameter or better. I couldn't see what gauge they are but will look tonight. I have no idea why they needed an inverter that large. This is the one that came with the van:

Tripp Lite 3000w inverter
http://www.tripplite.com/en/products...xtModelID=2560

Even on the cheap end it's a $350+ inverter.

What a beast!

That page you linked to says the package includes 25' of wire, so what you've got is probably whatever wire came with the inverter.

[dwh]

Positive
Alternator --> Main Batt. --> Breaker --(long cable run)--> Isolator --> Breaker --> Aux. Batt. --(2 splits)--> Inverter & fuse box

Only gotcha I can see is that to be completely proper, there should be a fuse/breaker between the aux battery and the inverter, and also between the aux battery and the fuse block.

[Herbie]

Herbie - Are there any pros/cons of doing it the way you did versus what Hell Roaring shows?

I'm not sure how the Hell Roaring system makes it's decisions, but I will say this, both the National Luna and IBS make it a point to caution a few things about installation: namely that the "measurement" connections that lets the unit(s) sample the battery voltages should be as close to the batteries as possible to avoid any sort of differences in voltage potential. In other words, the system is based on having an accurate measurement of the battery voltages, and if you wire the connections such that you introduce any small differences in the sampled voltage, you might lose efficiency or even create charging problems. That's the same reasoning why they urge a full ground cable for the battery and not using a chassis ground - the two batteries could end up at slightly different potentials if done otherwise.

So taking that and looking at my diagram, you can see that the biggest "flaw" is that I'm sampling the Aux battery voltage where it connects to the solenoid, rather than close to the battery. Now, it's a big cable, so the voltage drop "should" be negligible, but the reality is that every foot of cable, every connector, and every breaker in the line adds a little impedance and the chance of something going wrong. I weighed this risk against the ease of install and decided I'd rather run all the wires from the control unit to the same spot in the engine bay.

Other than that, there really isn't much difference between my diagram and Hellroarings. As dwh points out, connecting to the alternator or to the positive terminal of the battery is the same voltage potential, and really only a difference of a foot or two of cable probably.

One other difference to wiring it my way versus the Hellroaring diagram is whether the current flows through the alternator cable or not. If the vehicle's alternator cable was close to it's max safe capacity, adding the aux-charging load to the alternator side means current doesn't flow through the alternator-to-battery cable during charging, whereas it DOES flow through that cable if connected to the starting battery terminal.

On my vehicle, all the loads (including the normal vehicle loads shown on the Hellroaring diagram) are connected on the battery terminal, not the alternator, so all alternator current normally flows through that cable anyway, so I felt safe doing it that way.

[dwh]

One other difference to wiring it my way versus the Hellroaring diagram is whether the current flows through the alternator cable or not. If the vehicle's alternator cable was close to it's max safe capacity, adding the aux-charging load to the alternator side means current doesn't flow through the alternator-to-battery cable during charging, whereas it DOES flow through that cable if connected to the starting battery terminal.

True, but that shouldn't matter as long as that cable is able to handle the full output of the alternator, since even with the aux tied to the battery and the full charging current for both batteries running through the alternator wire - it won't cause the alternator to put out more than it's rated for.

[zuren]

True, but that shouldn't matter as long as that cable is able to handle the full output of the alternator, since even with the aux tied to the battery and the full charging current for both batteries running through the alternator wire - it won't cause the alternator to put out more than it's rated for.

I found the size of my wire running front to back - 2/0 AWG! I need to figure out the size of the breakers needed. The Blue Sea fuse holder I want handles 100A total. Based on your calculation and the input amps listed for the inverter, that breaker in the front of the van must be around 250A. I can't read what it is rated at.