auxiliary battery

[MountainManJoe]

I also want to run all my accessories (radio, lights, cig lighter sockets etc.) from the aux battery.

I assume the thinner red wire on the battery is for accessories, and the the thick black one is for the ignition/charging/starting circuit?

[Cobra]

I also want to run all my accessories (radio, lights, cig lighter sockets etc.) from the aux battery.

oh now you're on the same page that i want to be on i'll be watching this thread more closely now

[MountainManJoe]

I decided I want to get a battery separator (goes by many other names), such as the one by SurePower (http://www.surepower.com/separator.html). They go for as little as $60. Only $20 more than the heavy duty marine switches except they're worry-free.

I plan to get a 115 Ah, group 16 battery (12 7/8 x 6 3/4 x 9 1/8"). The best location I could come up with is right behind the last crossmember on the driver's side. I went out looking for battery trays and connecters yesterday without much luck. I'm going to go check out some marine stores today.

[MountainManJoe]

STAGE 1 - Connect inverter.

I connected two (+ and -) 6' 0guage welding cables to my starter battery. From the engine compartment, they go down and along the subframe rail (zip tied to some other tubing). Then they come up under the front of the driver seat through an oval hole I made.



For now, the inverter just sits under the driver seat. There is just enough room to slide it in. The tight fit combined with the stiff cables keeps the inverter pretty steady.



The starter battery didn't provide enough life, and forgetting to unplug things led to some sticky situations, which leads us to Stage 2...

[MountainManJoe]

STAGE 2 - Connect deep cycle battery and separator.

Costco brand battery: $100

Connected in parallel to the inverter right now.



Next the separator:


Surepower website
Product info
Installation

I picked up model 1314 for $85 from a battery distributor. All it is, is a fancy switch. It is either in connected or disonnected state, but it has all kinds of voltage sensing electronics to decide what to do. It has 3 major functions:

1. Charging: When the separator detects the main battery has reached 13.2V (charged), it engages the auxiliary battery bank. This ensures your starter battery is always charged first
2. Draining: When consuming power, the separator disengages the auxiliary bank when it drops to 12.8V, protecting your starting battery.
3. Starting: When starting the motor, the separator compares your starter and auxiliary batteries. If the starting battery voltage is lower than the auxiliary bank, it engages to assist the starting.

Here is a simplified diagram of how everything is connected. I wanted all my interior lights, headlights, radio and cigarette-lighter plugs to draw their power from the auxiliary battery, so I could run them with the engine off without worrying about draining the starter battery. That's why the fuse-box is connected AFTER the separator in the diagram:



Here is my under-hood wiring: (Again, notice the wire loom running from the separator across to the fuse-box for DC loads.)



And a close-up of the separator. It's screwed into the side of the plastic fuse-box cradle.



The whole system works marvelously, EXCEPT for one thing. If I drain the aux battery with the engine stopped, the van won't start. This is because when the starter battery voltage drops below 12.8V, the separator disconnects the aux battery (to protect the starter batter). Because the fuse-box is now disconnected from the (charged) starter battery, there is not enough charge left in the aux battery to engage the starting circuit relay. To start the van, you then have to use the manual override on the separator to temporary connect the two batteries together. But you have to work fast before the starter battery dumps all of its charge into the drained aux battery!
One solution would be to mount an override switch in the cabin. A more professional/reliable solution would be to isolate the starting circuit from the other DC loads, and have it permanently wired to the starter battery. I'll just continue using it as-is and see how things go.

[MountainManJoe]

STAGE 3 - Mount aux battery (PENDING)

This is where I want the battery to end up: (Straddling the cross-member on top of the torsion bar)

[Cobra]

you sir i would give a gold star (if i could)
you are doing basically the same thing i intend to do. I wanted to separate the run circuit (the dash cluster, ecm and starter) from the accessories (radio and other goodies) the work you are doing is giving me a major heads up on what kind of problems i may encounter.
i was initially thinking of mounting the batteries behind the rear most seats under the floor (if i ever get that damn spare tire outta there)

[MountainManJoe]

So I went out and bought a 1000W Proctor Silex kettle, and it works a lot better. I tried it with the engine running, and it reached boiling point without tripping a fault once. Next time I'll try and see how long it'll go on a full battery without the engine running.

Something else I want to explore is upgrading the alternator. Word has it there's a 300A one that'll bolt right in. I hope there's no risk of overcharging, but it should have a built-in regulator to prevent that. And speaking of regulators, I often wonder how alternator regulators behaves in more complex setups like mine, where there are high loads and multiple batteries. For instance, will they be restricting power when it is needed most. Ideally there would be no regulator on the alternator, and a charge controller for the batteries instead, but I think that can get costly.

Lastly, I could use some help. Does anyone know an accessible point under the hood where to get a start signal. In other words, an electrical contact that gets momentary voltage when the key is being turned to start. I'm sure it's easy to find on a diagram in my manual, but finding the actual physical location on the van is trickier. I would use this to connect to the aux-start terminal on my battery terminal.

[MountainManJoe]

So I found out today why the separator does NOT close when the auxiliary battery is drained. It is designed to close only when AUX battery is within 1V of the MAIN battery. This is to protect the separator from the surge of current you get when you connect a full battery to a dead one. i.e. hundreds of Amps. This begs the question, how does it reconnect?

All this emphasizes the need to isolate the starter relay from the rest of the DC loads. Just gotta find the right wire ...

[reaper]

I would highly recomend adding a gromet to where you have your wiring coming thru
the floor & adding shrink tubing to your cables at each lug end.
It is currently a potential fire hazzard & Looks like there is no fuse protection.
My recomendation is clearly for safety for you,your Family & your van.

[MountainManJoe]

Things are just temporary right now until I relocate that aux battery. You are right of course, and I did plan on making further improvements. Realistically, these things have to happen in increments.

[batmo]

I have three onboard AGMs on mine. check out the "solar safari" in members ride section for more details.

if you can justify the extra cost for an AGM batt. they can be mounted on their side so clearance isnt as much of an issue.

also no automotive altenators fully charge batteries, they all charge upto about 90% but thats it. this is not good for batteries so if you invest in high end batteries its best to also use solar or external a/c smart chargers.

and dont forget proper fusing either! low voltage/high amperage systems can be a major fire hazzard.

BTW no offence but your avatar is freakish!

[MountainManJoe]

BTW no offence but your avatar is freakish!

Thank you

AGM's are too expensive. When you consider $ per mAh per year, these cheapies from Costco are just the ticket. I may add on another battery later on if I decide to get a mini-fridge, or use a microwave. But perhaps not since there's is not that much room. One is all I need right now. I may swap in a 300A alternator too so I can run more things at once. We'll see.

[batmo]

oh I forgot, you could get that start signal right off the starter if need be.

[MountainManJoe]

So I found out today why the separator does NOT close when the auxiliary battery is drained. It is designed to close only when AUX battery is within 1V of the MAIN battery. This is to protect the separator from the surge of current you get when you connect a full battery to a dead one. i.e. hundreds of Amps. This begs the question, how does it reconnect?

All this emphasizes the need to isolate the starter relay from the rest of the DC loads. Just gotta find the right wire ...

I contacted the manufacturer, who is actually Cooper Industries.

The function that was disabling the override is not there to protect the separator as I previously thought, but rather to isolate the dead battery, and prevent it from weakening the system, so that the starter can crank. Once the engine is started, this is no longer a problem, so the aux battery is reconnected (and charged).