Aux Battery Electrical Setup Help

Not that anyone has asked... There are tradeoffs between a crossover connection (acr or solenoid) and a Bat-to-bat (B2B) charger.

Dick alluded earlier to the concept of “charging profiles” when he said your AGM battery would need topping off, and anyone contemplating adding an Aux battery would be well advised to read up on the concept. The condensed version is that different batteries have different charging needs, so pairing different batteries with a single charging source will fail to meet the needs of one of those battery types. An extreme example would be pairing LiFePO with a Lead-acid battery: the voltage differences alone make it a bad idea, but LiFePO batteries are destroyed by over-charging, while lead-acid require a maintenance trickle current to stay at 100%. The variations aren’t this extreme when combining flooded lead-acid, gell-cells, or AGM types, but these still have different preferred voltage and current preferences.

Enter the B2B charge controller: this is a device that takes energy from one source (usually an alternator, but can be anything) and uses it to supply a charging current to a bank of batteries based on its type and state of charge. That last bit is important, as it has a direct impact on recharge times and how long your system will go before your battery needs replacement. You will care a lot more about this when managing a bank of $2,000 lithium cells, but it’s still worth knowing with a $200 AGM battery, though it may not justify the premium cost of a B2B charger.

Part of the charging profile of any battery is the “bulk” phase, during which the current is limited to an upper boundary specified by the manufacturer. This is as fast as the chemical reaction can go, and exceeding it may damage the cell, particularly with sealed lead-acid batteries like gell and AGM. Joining the (+) terminals of batteries is an option only when they are of similar chemistry and construction, and at a similar voltage, otherwise the inrush current can exceed the profile current. So this is another factor in favour of a B2B charger, but as a rule of thimb, if you keep the aux battery voltage within one volt of the engine battery this never becomes an issue, and a solar or shorepiwer setup can keep the aux battery topped up.

A crossover switch wins in simplicity, price, and current capacity. You also can’t pull power backwards through (most) B2B chargers, so they won’t allow the engine to crank from the aux battery. Nor will a small B2B flow enough current to keep up with a big drain on the aux battery, so if you’re heating a casserole in the microwave and you want to pull 150 amps through the inverter for half an hour, you’ll want a crossover switch available in the system so you can meet that demand using the 200 amp engine alternator rather than pulling it from your aux bank (you probably also want a 24 volt system, but that’s another topic). But if your aux battery is anything but a flooded lead-acid battery, the engine alternator will not be capable of maintaining a 100% charge, and will never push up into the desulfurization voltages required for full lifespan, so the solar or shore power charger will need to perform that duty.

Have fun out there,

-dave

Nautamaran said:

Okay, that's a good start. I can see what you're thinking now...
I've rearranged your drawing a bit so it flows a bit more logically and makes the source and load connections easier to visualize (my drafting instructor would still cringe - but he's long dead so...)

The alternator is already connected to the PDC, so you'll tie in there with a new PDC fuse and a cable large enough to HELP crank, but also to fully power your inverter, so at least 100 amps.
That cable runs up under the driver's seat to a new crossover relay (ACR) and then the aux Bat(+).
A fuse on the line between the ACR and aux bat(+) would be a good idea. The Aux battery bank grounds back to the alternator via the chassis, so the aux bat(-) must be connected to the chassis ground with an equally big cable.

Another big cable feeds your 1000 watt inverter through a (100 amp) breaker. The inverter ground cable (also big) ties to the battery negative (or the chassis ground lug, your choice).

You'll want a 20 amp breaker between your solar charge controller and your aux bat(+) as a charge disconnect, and a (30 amp?) breaker between your "Fusebox" and aux bat(+) as a master load switch.
If you chain the bat(+) from breaker to breaker avoid needing a (+) bus. (all #10 or #12 wires)
The fuse box then distributes power out to your loads.

The Neg(-) Bus collects the grounds from the fuse box loads and charge controller, and connects to the aux bat(-) terminal (or the chassis ground lug, your choice).

That still stacks two big cables on your aux battery(+). If space is tight you could feed the inverter's breaker from the aux-side lug of the ACR switch, especially if you are locating the inverter on the driver's side anyway?

My opinions... worth every penny you're paying for them

-dave

Click to expand...

thanks dave.
wouldnt the inverter and fuse box be protected by the 100a+ fuse to the bus bar?
if i plan on putting the electrical behind the drivers seat, would connecting the inverter to the bus bars, be fine/make sense?

isdehart said:

thanks dave.
wouldnt the inverter and fuse box be protected by the 100a+ fuse to the bus bar?
if i plan on putting the electrical behind the drivers seat, would connecting the inverter to the bus bars, be fine/make sense?

Click to expand...

Yes, you could wire and fuse the bus bar for 100+ amps, but that limits you to a fuse box that can accept that much current. Remember that these main breakers/fuses protect the transmission and distribution device, and the fuses in the fuse box control the devices downstream of them. It will depend on your physical layout, but you will likely want three breakers for solar panels, fuse box, and inverter, each with a (shared?) route to the aux bat (+). You could put a 100+ amp fuse at the aux battery terminal, then run a big (+) line to a disconnect switch feeding the inverter, then continue on to your fuse box and solar controller from the unswitched side of the disconnect (creating a chained “bus” from the battery-side connectors with smaller wires. Just be sure that everything is sized appropriately to carry the combined loads, and avoid any over-fused (unprotected) runs of wiring or devices.
Codes vary by industry, but the basic requirement is that nothing be connected to a power source (alternator, battery) without first going through an appropriately sized protective device (a fuse or breaker).

-dave

Nautamaran said:

Yes, you could wire and fuse the bus bar for 100+ amps, but that limits you to a fuse box that can accept that much current. Remember that these main breakers/fuses protect the transmission and distribution device, and the fuses in the fuse box control the devices downstream of them. It will depend on your physical layout, but you will likely want three breakers for solar panels, fuse box, and inverter, each with a (shared?) route to the aux bat (+). You could put a 100+ amp fuse at the aux battery terminal, then run a big (+) line to a disconnect switch feeding the inverter, then continue on to your fuse box and solar controller from the unswitched side of the disconnect (creating a chained “bus” from the battery-side connectors with smaller wires. Just be sure that everything is sized appropriately to carry the combined loads, and avoid any over-fused (unprotected) runs of wiring or devices.
Codes vary by industry, but the basic requirement is that nothing be connected to a power source (alternator, battery) without first going through an appropriately sized protective device (a fuse or breaker).

-dave

Click to expand...

cool thanks dave. made alot of sense.

terminal mounts: https://www.ebay.com/itm/Blue-Sea-2340-Battery-Terminal-Mount-BusBars/253095911207?epid=1137749488&hash=item3aedb11f27:g:SDwAAOSwxh1Znzcr

how does this look? https://drive.google.com/open?id=1bge2K0Brz2SYr62qgjg0Ze3emzaf5sWa

Diagram looks much better (though I didn’t review it very closely)

One tip: you won’t have to dig into the MB J19 connector as described in the aux battery instructions if your van has the EK1 option (“Body Builder’s strip”), as it includes a D+ signal that is energized only after the alternator starts charging. This is the perfect trigger wire for your Stinger crossover switch. Here’s where to look:
https://sprinter-source.com/forum/picture.php?albumid=770&pictureid=4854

-dave

ps: This sort of thing gives you a fuse right at the aux bat(+) terminal:
https://rvpartssource.com/Blue-Sea-2151

New member, first post.

2006 Dodge Sprinter, cargo, ~115,000miles just purchased.

I have purchased an alternator to battery charger (similar to the battery to battery charger) from Sterling to recharge an aux battery bank. It is the biggest one they make, to my knowledge, at 120amps. My T1N doesnt have the 200amp alternator, so I think this is sufficient to handle the power output of the alternator.

Question is, does anyone think there would be a problem attaching this device (high amp draw) to the Powder Distribution Center (PDC) with a 120amp fuse in the unused position for the AC?

Sterling advises to go off alternator direct. However, if Im reading the body electrical schematics correctly, the PDC is tied to alternator with sufficiently sized 1awg or so wire. Does this sound right? And doable?

It will then travel to fuse and + bus bar.

Thanks,

Dave

You read that right... the alternator's output comes into the PDC on the left fuse, and you can come out with a new fuse and load on the empty slot that MB uses for the rooftop A/C.

Can you post a link to your A2B charger?
Is it by-directional for boosting the start battery or just for charging?

-dave

Possibly handy image:



--dick

The factory harness can handle the load. But you will see some voltage drop. I would just tie to the alternator straight. There are two large output studs that can be used.

Nautamaran said:

Diagram looks much better (though I didn’t review it very closely)

One tip: you won’t have to dig into the MB J19 connector as described in the aux battery instructions if your van has the EK1 option (“Body Builder’s strip”), as it includes a D+ signal that is energized only after the alternator starts charging. This is the perfect trigger wire for your Stinger crossover switch. Here’s where to look:
https://sprinter-source.com/forum/picture.php?albumid=770&pictureid=4854

-dave

ps: This sort of thing gives you a fuse right at the aux bat(+) terminal:
https://rvpartssource.com/Blue-Sea-2151

Click to expand...

ok, thanks dave.

if we connect the stinger/acr (+) to D+...we'd still run it though an empty fuse location on the oem panel?

or could i pop that blue sea terminal fuse block on the D+?

Midwestdrifter said:

The factory harness can handle the load. But you will see some voltage drop. I would just tie to the alternator straight. There are two large output studs that can be used.

Click to expand...

Cool. Where are the two output studs to tie in to alternator?

On the back of the alternator. One has the main harness attached, the other is shorter in length, and has nothing on it. The much smaller stud lower down is the D+ signal from the instrument cluster. Don't mess with that.

isdehart said:

ok, thanks dave.

if we connect the stinger/acr (+) to D+...we'd still run it though an empty fuse location on the oem panel?

or could i pop that blue sea terminal fuse block on the D+?

Click to expand...

The Stinger's COIL (the weak signal that causes the heavy current contacts to operate) is connected to the D+ terminal.

The thick wire from the alternator/starter-battery/PDC is then connected to one of the Stinger's big posts, and the thick wire continuing on to the house battery is connected to the other Stinger big post.

The stinger will have another small terminal, that goes to frame ground (it's the other half of the coil's connections).

The D+ should not be used to power any other form of loads.
If you want the Sprinter's battery to power some loads, that what the other two posts on the EK1 terminal strip are for: one for "always on", and the other for "switched by ignition".

--dick

Yup... what Dick said.

The EK1 strip signals are fused at the panel on the side of the seat.
The Terminal 15 and D+ signals are further isolated by relays from the rest of the van’s electrical system.

“Body Manufacturer, Terminal 30” is directly connected to the battery (+) and fused at 25 amps.
“Body Manufacturer, Terminal 15” is hot when the key is in pos’n 2 or 3, and is fused to 15 amps.
“Body Manufacturer, D+” is hot only when the alternator is charging, and is fused at 10 amps.

There’s also a separate fuse for the D+ relay’s trigger coil... leave that alone as it ties directly to the instrument cluster’s D+ output and overloading it can, among other things, disrupt the van’s charging system.

You can use the EK1 strip’s D+ terminal to trigger your Stinger, and there is a grounding lug on the floor under the seat (follow the brown wires) that you can use to ground the Stinger’s trigger coil, though I don’t know that that lug is sized to handle a large current such as an inverter’s 100 amps?

-dave

Midwestdrifter said:

On the back of the alternator. One has the main harness attached, the other is shorter in length, and has nothing on it. The much smaller stud lower down is the D+ signal from the instrument cluster. Don't mess with that.

Click to expand...

Cool, so you would tie the stinger directly to the alternator and then trigger the stinger with D+ on the EK1?

Nautamaran said:

Yup... what Dick said.

The EK1 strip signals are fused at the panel on the side of the seat.
The Terminal 15 and D+ signals are further isolated by relays from the rest of the van’s electrical system.

“Body Manufacturer, Terminal 30” is directly connected to the battery (+) and fused at 25 amps.
“Body Manufacturer, Terminal 15” is hot when the key is in pos’n 2 or 3, and is fused to 15 amps.
“Body Manufacturer, D+” is hot only when the alternator is charging, and is fused at 10 amps.

There’s also a separate fuse for the D+ relay’s trigger coil... leave that alone as it ties directly to the instrument cluster’s D+ output and overloading it can, among other things, disrupt the van’s charging system.

You can use the EK1 strip’s D+ terminal to trigger your Stinger, and there is a grounding lug on the floor under the seat (follow the brown wires) that you can use to ground the Stinger’s trigger coil, though I don’t know that that lug is sized to handle a large current such as an inverter’s 100 amps?

-dave

Click to expand...

Thanks dave. i would have to put in a heavier fuse for the D+ after tying to stinger relay?

Sounds good to me. Remember to fuse appropriately if smaller than the factory wire. Which has a 200A fuse if I remember correctly.

isdehart said:

Thanks dave. i would have to put in a heavier fuse for the D+ after tying to stinger relay?

Click to expand...

No, the 10 amps is plenty to run the relay coil, and is all the tiny wire can deliver.
The D+ should ONLY be used for small stuff like relay triggers etc.

Run a small wire from the EK1 D+ terminal to the small trigger(+) bolt, then a second small wire from the small trigger(-) bolt to the ground lug on the floor under the seat. That will get the Stinger solenoid switch to close when the engine is charging.

You will then want to put a big fuse at the PDC or alternator output lug, run a cable to the large lug on the "Starting Bat" side of the Stinger, then put another big fuse on your aux Bat(+) terminal and run a cable to the other large lug on the "Aux Battery" side of the Stinger.

Run a grounding cable from the Aux.Bat(-) to the chassis, and you've got the charging system.

-dave

Midwestdrifter said:

Sounds good to me. Remember to fuse appropriately if smaller than the factory wire. Which has a 200A fuse if I remember correctly.

Click to expand...

Would this still allow me to start with aux battery if something happens to starter batt?

isdehart said:

Would this still allow me to start with aux battery if something happens to starter batt?

Click to expand...

Fuse size is determined by cable size; cable size is selected based on what you want it to do. So use the same size (or larger) cable as feeds the starter, then the max fuse for that size. If the fuse blows, you've protected the cable from overheating.

-dave