Dual Battery Relay

Post by **Sluggo** » Fri Aug 21, 2009 6:04 pm

More than 2 years later and I'm finally actually doing this!

Just not on the originally intended Bus.

Ford Starter Relay is mounted.

To make sure I got this correct:

One big terminal to the main battery.
One big terminal to the auxiliary battery.
Small terminal marked "S" to starter.
Small terminal marked "I" to ground.

What gauge should the wire between the batteries & the relay be?

Fuses between each battery & relay + 1 between aux battery & fuse box or just one before the fuse box?

Auxiliary battery is also grounded to the body?

AirCooledNut · Post by **AirCooledNut** » Wed Aug 26, 2009 9:29 pm

For what it's worth, I'm using a battery isolator w/o issue...that means it works as intended and isn't a cheapie unit so it does keep the two batteries separated (one can't feed the other like a relay would allow). Too simple to install. Take the alternator B+ wire that goes to the starter post and instead connect it to the A-post on the isolator ("A" is for "alternator"

). The 1-post goes to the starter battery and the 2-post goes to the camping battery. Done. No-brainer.

BTW, I have the interior lights, 12v receptacle for the kids portable DVD player, and stereo/XM always running off the camping battery, through a dedicated fuse box, of course. This way the starting battery is used as designed with the extra savings of no extra stuff to drain it.

I like the isolator but a relay is a good way to go as well. There isn't ALWAYS just one way to do something and each way has its merits.

AirCooledNut · Post by **AirCooledNut** » Wed Aug 26, 2009 9:38 pm

Sluggo wrote:...

What gauge should the wire between the batteries & the relay be?

Fuses between each battery & relay + 1 between aux battery & fuse box or just one before the fuse box?

Auxiliary battery is also grounded to the body?

8-gauge wire is plenty from all the reading I've done on the subject. If you want overkill on your overkill you can use 6-gauge. On my isolator I had a brain-fart and used standard battery cables to feed the batteries. Dummy...really a waste of money when 8-gauge would've been plenty.

The aux. battery grounds to the chassis exactly like the stock starter battery. I have both of my batteries grounded directly to the engine. That way when the engine drops out it'll be flailing the batteries with it, like panicky arms

<- except not so happy. LOL

I think only one fuse is necessary and that would be at the point where the alternator B+ cable mounts to your relay (in my case, the A-post of my isolator). Beeleeb me, you don't want to have your alternator short its power feed! Very hot and melty, like a Taco Bell Mexi-melt but with metal and plastic instead of artery-choking goodness!

twinfalls · Post by **twinfalls** » Mon Aug 31, 2009 8:40 am

Sluggo wrote:I want to add a second battery for the stereo, blower, phone charger, etc. Do you need to get those kits from the various vendors? It looks like it's just a regular 30A Bosch relay & 30A fuse with the wires routed to the batteries and voltage regulator. I can get Bosch relays for a few dollars a piece. Just wanted to make sure there wasn't something special about these relays.

30A Bosch relay & 30A fuse.
This is the same as the original Westfalia set up. It works very well.

A small detail : No need for chunky 30A wires between batteries +post; Actually, 3A wire is recommended.

BTW Where is the fuse in the original Westfalia design ?
I remember an in line fuse ( a terrible source for bad contact ) on the wire to devices fed from the auxiliary battery.

Post by **Sluggo** » Fri Sep 04, 2009 3:48 pm

Got all my stuff an got it half hooked up. I'll take pics tomorrow.

*10g wire between the + battery terminals with a 30amp fuse as close to each battery as possible. Wires connected to each large terminal on the Ford Starter Relay.

*Switch wire (14g) coming from the starter coil wire to the terminal marked "S".

*Ground wire (8g) from the terminal marked "I" to mounting screw for relay.

*8g wire running from + battery terminal to 6 item fuse box with a 60amp fuse close to the battery.

*Aux battery will be grounded to the engine.

I think I'm good and safe.

twinfalls · Post by **twinfalls** » Sat Sep 05, 2009 5:06 am

Good.

You should feel the relay clicking when the engine is started, and then measure a 0 volt drop between the two +12v batteries posts.

I had trouble with bad in-line fuses; Unreliable contacts inside.
Because of this I like better no fuse and no thick wires between the batteries....Wires that would act as large fuses between batteries.

midatlanticys · Post by **midatlanticys** » Sat Sep 05, 2009 2:31 pm

twinfalls wrote: I like better no fuse and no thick wires between the batteries....Wires that would act as large fuses between batteries.

WHOA!!

I'm not sure I like the idea of skinny wires acting in place of a real fuse - could you look for a better quality in-line spade fuse fitting or even a small fuse block?

Post by **Sluggo** » Sat Sep 05, 2009 5:38 pm

midatlanticys wrote:
twinfalls wrote: I like better no fuse and no thick wires between the batteries....Wires that would act as large fuses between batteries.
WHOA!! I'm not sure I like the idea of skinny wires acting in place of a real fuse - could you look for a better quality in-line spade fuse fitting or even a small fuse block?

I don't like that idea either. I used glass buss inline fuses for the 30amp by the batteries (if I have a problem I'll change to spade fuses) and a big ass spade fuse for the 60amp between the aux battery and the fuse box. The fuse box uses normal spade fuses.

How many amps should the fuse be between the starter & relay?

Ritter · Post by **Ritter** » Sat Sep 05, 2009 6:30 pm

Sluggo wrote:
How many amps should the fuse be between the starter & relay?

Fuse amps is a function of wire gauge. There is a link somewhere that clarifies.

justgimmecoffee · Post by **justgimmecoffee** » Sat Sep 05, 2009 7:09 pm

Sluggo, so how did you secure the aux battery?

Thanks for the great write up, you give me inspiration.

Post by **Sluggo** » Sat Sep 05, 2009 7:13 pm

justgimmecoffee wrote:Sluggo, so how did you secure the aux battery?

Thanks for the great write up, you give me inspiration.

I'll be bolting 2 small steel brackets to the tray on each side of the battery and using a strap with one of those little click connectors like they have on child strollers. Haven't done it yet.

midatlanticys · Post by **midatlanticys** » Sun Sep 06, 2009 4:55 am

Sluggo wrote: How many amps should the fuse be between the starter & relay?

Does this help? "Install a 30 amp fuse on each positive feed from the relay as close as possible to the batteries." http://www.paultaylorimaging.com/VW/Lei ... /LB_6.html

Complete with a sensible approach to using fuses here: http://www.paultaylorimaging.com/VW/Lei ... LB_11.html

The full thread here: http://www.paultaylorimaging.com/VW/Lei ... /LB_1.html

Post by **Sluggo** » Sun Sep 06, 2009 9:11 am

midatlanticys wrote:
Sluggo wrote: How many amps should the fuse be between the starter & relay?
Does this help? "Install a 30 amp fuse on each positive feed from the relay as close as possible to the batteries." http://www.paultaylorimaging.com/VW/Lei ... /LB_6.html

complete with a sensible approach to using fuses here: http://www.paultaylorimaging.com/VW/Lei ... LB_11.html

and full thread here: http://www.paultaylorimaging.com/VW/Lei ... /LB_1.html

Great Link! I think the info I found was based on that site and they conveniently left a few things out. Doesn't mention a fuse on the switch wire so I guess I'm good.

Post by **Sluggo** » Wed Sep 09, 2009 10:07 am

PICS!

Ford Starter Relay
[albumimg]2810[/albumimg]

Relay, Battery & 60amp Fuse
[albumimg]2812[/albumimg]

Main Battery
[albumimg]2811[/albumimg]

Ritter · Post by **Ritter** » Wed Sep 09, 2009 11:40 am

It is so clean!

Is that a baby (starting) battery? Mine is much larger (having upgraded after my little one died and Colin made fun of it).

Itinerant Air-Cooled

Itinerant Air-Cooled

Dual Battery Relay

Re: Dual Battery Relay