View Full Version : Requesting help hooking up house batteries and charging from alternator

09-24-2013, 04:44 AM
First I'll say this, I've held off posting this until I read some (long) existing threads, talked to a LOT of people locally, etc, but electrical is something I know NOTHING about, and everything still isn't crystal clear, especially with so many varying (and potentially dangerous) opinions I've received.

Here's what I've bought:

Two Marine AGM batteries : 79ah each (158ah total)
Made a pair of 4g, 9" red and black wires to connect them
1000 amp inverter
6 switch marine breaker box
xantrex linkpro

The plan: Build a battery box under my bed/on top of the wheel well, and run a cable from the alternator, under the van, and up through a drilled hole near the wheel well, to the batteries.

What I'm still unsure about: using some pretty little chart I found, and assuming an eventual upgrade to the 150a alternator, it showed I'd need 4/0 cable... roughly 17 feet from alternator to battery, and 17 more from battery back to the ground. Does that sound right? The stuff was huge, very expensive, and they didn't even have close to 34 feet in stock. I had a guy trying to sell me 6g for this application, but I don't think that's right, so I ran away as fast as I could... :idunno:

Also, I crawled under the van to check the size of the post on the alternator, so I think I'm good there, but where is the ground? I know the engine block, but I didn't immediately see it?

Last thing, everyone on here was saying I needed a 200a relay between the alt and battery. I've had trouble finding one locally, and every single person I've mentioned it to looked at me like I was stupid and said it was completely unnecessary. Am I gonna die?

I've been driving around for two days now trying to figure this all out and get it pieced together, and frankly, I'm exhausted and lost! haha. Many thanks in advance! I've learned so much from this sight already, yall are great. Hopefully, with a little help, I'll be up and running here in a few days :cheers:

09-24-2013, 06:08 AM
The way to simplify an install like this is to locate the batteries as close to the alternator as you can. Advantages?

1) Less expensive cable to buy.
2) Sometimes you can drop the sizing.
3) Less potential for a voltage drop.

The relay switch or isolation is nice to have but not really necessary.

I'm hooked straight in without any relay. 200 amp is pretty big as well, for a 150 amp alternator that will never put out an actual 150, nevermind exceeding 150.

Just remember not to drain those batteries more than 50% of capacity.

Nothing here is terribly dangerous other than to your wallet. ;)

09-24-2013, 06:31 AM
Great advice! That's actually what I got to thinking after writing that... for purposes of getting some weight off the rear axle (eventually gonna be a motorcycle back there) as well as shortening that run, I may build a box right behind the drivers seat, which would double as a raised platform for the fridge that currently resides in that location... less bending to get in the fridge, minus 10 feet of cable (12 bucks a foot, that's a $120 savings, minimum, or more by dropping to 3/0 or 2/0), 100+ pounds off the rear axle, and my panel can go on the wall above the fridge, a space I didn't have a use for until now. Awesome!

I think all that's left is finding that ground on the engine block. It's a 2005, anyone know? I also wonder if there is a plug or something I can go through behind the drivers seat vs drilling through the floor. I'll figure that out tomorrow.

Thanks SullyVan :thumbup:

09-24-2013, 09:01 AM
I put my second battery in the left seat pedestal, and ran the big wire up through an existing rubber boot in there. There's a gap in the bottom so you can feed wired through to underneath/behind the plastic step on that side, and from there up that side pillar or further into the back.

09-24-2013, 09:58 AM
The location is driving your cable size due to voltage drop, get it closer and you will be able to use a smaller gauge cable, you should be able to work this out from the chart you are using?
For the same reason keep the invertor close to the battery!

The sprinter has loads of ground studs, you don't need to run back to the engine block, you just need to run to a convenient stud. In the UK there is one on the engine side of the bulkhead just below and beside the cabin air intake and just above the battery, however since this is the passenger side here and would be your drivers side I'm not sure if the position will be the same. The ground from the van battery is connected to this stud (along with a lot of others) so it is definitely suitable.
There is also one under one or both seats which is used for a factory installed auxiliary battery.

For the engine ground, on mine, well first you have to understand that my engine was withdrawn before Sprinters went to the US, and that it has a manual transmission, however the basic layout looks the same on later engines so I'll tell you where it is!
Crawl under the van to my passenger side (your driver side) of the engine until you reach the line where the transmission is bolted to the engine. There should be a bare braided wire running from a stud on the chassis to one of the bolts that secures the transmission to the engine. MB will not have moved the location of the chassis stud, although the engine end might use a different bolt. It is probably worth checking the condition of the braided wire and renewing if it is frayed, but I wouldn't run your battery negative direct to the engine as the vibration will damage it - thats why the engine link is a bare braid that is nice and flexible and easy to inspect. Some people would advise upgrading the braid or doubling it up, I would first try to find out if the engine electrics on a 2005 monitor resistance on the ground, just in case upgrading or doubling (which will reduce resistance) might cause unexpected errors.

09-24-2013, 01:55 PM
Please note: If you have the relay, you don't need isolation Diodes. The benefit with not using isolation Diodes is that the voltage drop across the Diodes (0.7 volts) goes away - while 7/10 of a volt may not seem like much - its the difference between a fast recharge of your aux battery and and very slow recharge of your aux batteries (it may take days to recharge them).

The people that are confused by adding the relay (you can order them from Amazon.com) are probably not aware of battery charging systems and don't really know what the effects of voltage drops in the line are.

What the relay does is connect the Aux Battery up to the Alternator power directly when the engine is running and disconnects it when its not. So you can't drain the main engine battery when you use the AUX battery (and the engine is not running). Isolation Diodes provide a similar function (preventing the AUX battery use from draining the main engine battery), but they do it by using a Silicon power diode that reduces the charging voltage by 7/10 of a volt.

If you read up on Lead/Acid battery charging, you'll see that this is a huge issue if you need to recharge your AUX battery quickly.