Dual-Battery Trailer wiring diagram

[ldivinag]

i'd use anderson power pole connectors:

http://www.powerwerx.com/anderson-powerpoles/powerpole-sets/sb175-sb-series-175-amp.html


also, the national luna kit, has a 5 minute delay from when you start the car. by default, when you start the car, the aux batts are not connected. only after a 5 minute delay AND if the system voltage is over a certain value, will the NL setup then connect the aux to the circuit.

their reasoning is that 5 minutes is good enough to make sure the primary batt gets the proper charge at startup.

on my setup, i'm thinking of buying a $30 timer delay circuit and hook that up.

or if you are cheap, a manual switch will do the same thing too. you just wait about 5 minutes after the car starts before you flip the switch to connect the aux batt(s) to the charging circuit.

of course the manual switch will still have an override portion so i can still connect the aux to main anytime, like if the primary batt is dead and cant start car.

 

[dzzz]

Modern vehicles and isolators have an extra wire that lets the regulator get a reference voltage from the main battery so the alternator puts out .7v higher to compensate for the drop.

And some isolators only have a .2 voltage drop. But I don't have much faith in either that or an extra wire to trick the alternator in a complex electrical environment. On boats when it really matters people no longer use isolators.
I bet you won't find isolators in earthroamer or unimog either.

A direct high capacity connection exposes the regulator to real voltage of the connected system. Solenoid systems don't cost much more that a good isolator. The Blue Sea system can even automatically separate banks to charge from alternator and solar simultaneously.

 

[eugene]

Its not tricking the alternator, simply giving the voltage regulator a reference source which it can't get through the diodes. I like the fact that a (diode) isolator isolates even while charging where a solonoid noise and spikes go across both batteries.

 

[tremors834]

I have this bookmarked for when I'm ready to upgrade

Amazon.com: PAC PAC-500 500-Amp Battery Isolator Relay: Automotive

The solenoid I have now was free (aka 'in the garage') so gonna stick with that for this trip and likely find some kind of delayed start relay when I can find a spot to put a 2nd battery in the truck instead of the trailer.

You could get them a bit cheaper elsewhere. $40-$50 bucks if you shop around. I've purchased a few from various places, eBay having the best price. Mcmaster Carr also carrys them, google for it.
PAC, Stinger, Cole Hersey are all the same relays. There must be one main manufacturer for them.

EDIT- So I looked further into it and noticed you posted a link for a 500amp relay. The relays I've purchased were the 200-300 amp relays, Although they both look the same. I'll leave the info above for any future searches.

 

[wrcsixeight]

I have A 1/2/both/off Switch. I usually start the engine on 1, my engine battery, then look at my digital ammeter. This usually falls from 22 to 8 amps in under 30 seconds since the only load on the engine battery is the starter, and computer memory, and my engine starts real easy.

Then I turn the switch to both, bringing my depleted house batteries into the loop. The engine note changes and the digital ammeter climbs upto 40 to 60 amps, depending on state of charge of the House batteries. Higher RPMs bring this number up to the 75 to 90 amp mark, and my single belt begins to squeal.

I have seen as high as 107 amps with a squealing belt at about 4 k rpm. This is with a 130 amp alternator. I have very thick alternator wiring and ground wiring.

This is with a cool engine/ alternator. When it is hot, these numbers are reduced by at least 30%.

I say this only to relate that a 150 amp alternator will never actually attempt to send 150 amps to a battery in a trailer over 8 awg cable. A 150 amp alternator is extremely unlikely to ever produce 150 amps. The ratings are worthless. Your Vehicles charging circuit was never designed to pass that much current anyway.

Here's a chart showing a lower rated alternator putting out more current than a higher rated alternator until the engine is above 3200 rpm:

There are adjustable voltage regulators out there which can help compensate of the voltage drop of an isolator's Diode.

Check out this product:
http://www.qualitypowerauto.com/catalog.php?item=148&catid=76&ret=catalog.php%3Fcategory%3D76
Part # QPR902A has a remote dial you can wire to your dash.

Also check out some of these weatherproof connectors

http://www.colehersee.com/pdf/Q-Connectors.pdf


And here is a definitive battery resource, with many many hours of reading, on more info than you need.
http://www.batteryfaq.org/

 

[dzzz]

Here's an article on split diode systems. It makes good points, but makes its best case on vehicles that only charge house batteries from the alternator.

 

[eugene]

Well of course if you try to pull 70A through a 70A diode its going to get hot, if you run your engine at its max rpm it will make heat too. I have a 105A alternator with a 120A isolator. Also their information about alternators isn't accurate, sure there are some that can't have an external reference but there are plenty that do. Mine runs around 15v at the alternator then the isolator drops down to the normal 14.x charging voltage.

 

[eugene]

The real issue though with either one is properly charging the second battery. With an isolator your taking the reference form the starting battery so its cutting back once the main battery is charged. With a solonoid your referencing both batteries in parallel so it could still be under/over charging one depending on the state of the other. I'm hitting against this now as I want to put a deep cycle or AGM as my secondary and they don't like the constant charging as much as a typical starting battery, they truely need a seperate charge controller. Most of your vehiicles in the USA the reason they have gone away from isolators it not to go to a solonoid but to dual alternators so each battery is charged seperatly by its own alternator. the 3/4 ton and bigger trucks all have dual alternator option available. I think I have room to add a second under the hood of mine, but a smaller truck like the OP's H3 may not have the space.

 

[evldave]

The real issue though with either one is properly charging the second battery. With an isolator your taking the reference form the starting battery so its cutting back once the main battery is charged. With a solonoid your referencing both batteries in parallel so it could still be under/over charging one depending on the state of the other. I'm hitting against this now as I want to put a deep cycle or AGM as my secondary and they don't like the constant charging as much as a typical starting battery, they truely need a seperate charge controller. Most of your vehiicles in the USA the reason they have gone away from isolators it not to go to a solonoid but to dual alternators so each battery is charged seperatly by its own alternator. the 3/4 ton and bigger trucks all have dual alternator option available. I think I have room to add a second under the hood of mine, but a smaller truck like the OP's H3 may not have the space.

Yeah it's a tight fit, and probably overkill for what I'm looking for. I'm going w/SLA 2nd battery so I don't have the constant charge/current issue, but I will ultimately have the voltage issue.

As a side note, I can't seem to find my 6ga wire but do have a whole roll of 4ga welding cable, so gonna use that to feed the rear batteries through an anderson connector. This is some fascinating discussion on voltage regulation/charging/etc., but a little beyond my capability. Think I'll stick w/a simple setup like I have a deal w/the potential issues (plus I've pretty much got everything already). I guess if I start blowing fuses, I'll know the 2nd battery is pulling >75A if it's dead enough.

 

[ntsqd]

Some reading:

http://bluesea.com/category/2/productline/overview/387

http://www.bepmarine.com/home-mainmenu-8/productcategory-44/voltage-sensitive-battery-relays

Some of these solenoids/relays can sense individual battery or battery bank voltage and only charge those which are low. Even the simplest versions require that the starting battery be fully charged before charging the 'house' battery/ies.
National Luna seems the be the brand that has caught on in this forum, but they are far from the only mfg. of this type of device. I've listed two others above and there are probably more that I do not know of. Each brand seems to have slightly different sets of features, so what works for someone else may not work for you.

 

[ldivinag]

i like that BEP MARINE one...

1. its 300 amps

2. it has the similar voltage sensing that the NATIONAL LUNA does...

and with a $30 circuit, you can add a delay function that the NL does.

 

[ntsqd]

I have the 710-125A, which I will be running in parallel with a marine combiner switch for manual over-ride for the FJ60 project. BEP offers this as a package, but I already had a different switch. I choose it because of the bolded text. No delay needed, it is built-in. Or perhaps I don't understand the delay function of the NL?

The description of the 300 isn't as clear on that point. I would expect it to work the same way, but advise checking if this function is highly desirable.

710-125A (Single Sense)

The Voltage Sensitive Relay (VSR) allows two batteries to be charged at the same time. When the engine is started and the start battery reaches 13.7 volts, the VSR engages, allowing two battery banks (start and house) to be charged simultaneously. When the voltage drops below 12.8 volts (eg the engine is stopped), the VSR disengages, separating the batteries. This system eliminates the possibility of draining the start battery and protects sensitive electronic equipment powered from the house battery from harmful engine start up spikes."

 

[dzzz]

Isn't the delay for engine crank? With computers and such on the house battery?

Blue Sea and maybe BEP don't address the "land" market and many people are more comfortable with a company that does. The national luna battery stuff looks crude compared to the marine equivalents. I also don't expect NL is made to work under water.

 

[ldivinag]

the 5 minute delay for the national luna is to make sure that the primary batt is charged fully before it goes and hooks up to the secondary...

 

[ntsqd]

So NL uses a time delay rather than sensing the voltage of the starting battery and only charging the house batteries after the start battery has reached a threshold voltage?