Is it known what it draws?
It could be that it is pulling too much energy …

Some relevant technical info here: Does the Metris have muli stage battery recharging? which mentions the up-fit guide max 40A.

 

Icerabbit has a good point on what it's drawing. If you have an O'Reilly's Auto parts store nearby you might be able to borrow an amp meter. Most of their stores will loan out tools for free. With an amp meter, you'd know for sure if that's the problem.

Its a safe bet that the Metris alternator has built in protection for a variety of electrical faults such as over voltage, under voltage, etc. If the VSR is trying to pull too much amperage, the battery warning light would be a logical indicator.

You didn't say how quickly the battery fault comes on. The VSR might have a delay before it begins pulling power- the instructions hopefully provides that info. If so, any known delay that corresponds with the activation of the battery would support the idea that is pulling too many amps.

Nor did you say anything about the new battery. Ideally it should be similar in size as the starter battery (about 100 amp hours) and also an AGM..... If its much larger, say 200 amps hours, that would also be a reason for an excess amount of power being used.

 

delete

 

Thanks, y'all. @RansomRidge , I'm using a 100amp AGM battery as the aux, brand new.
The light doesn't come on until I start driving- I can idle in the driveway indefinitely. But it pops on within a couple hundred yards on the road. The VSR has an LED indicator when it's working- and it'll claim to be working while I'm idling in the drive.

Indeed, that link that @icerabbit posted looks very informative. I'm headed out of town for the weekend, but will definitely look into this more in-depth next week and report back.

 

The Mercedes docs say the second battery should be the same battery.

If you read some of the docs on the battery to battery chargers and smart alternators you tend to leave totally believing that the only way to even have a second battery charge with a smart alternator is to use a dc-dc charger. The buck/boost of the charger means you don't have the problem you have with the voltage sensitive relay.

 

@pounce , thanks for that reply. I might just order a charger and be done with it. Think this would do the trick? Amazon.com: Victron Energy Orion-Tr IP43 12/12-Volt 30 amp 360-Watt DC-DC Converter, Isolated: Automotive

 

@pounce , thanks for that reply. I might just order a charger and be done with it. Think this would do the trick? Amazon.com: Victron Energy Orion-Tr IP43 12/12-Volt 30 amp 360-Watt DC-DC Converter, Isolated: Automotive

That's the model I planned to try, but I have not seen anyone else using it with our van. I cannot vouch for it. The Redarc products offer similar and also potentially give you a solar input. Cost more, but you would expect that.

 

It should be here Tuesday. I'll let you know how it turns out.

 

That model takes 6ga and smaller in case you wondered about connections.

 

Hive you tried putting it on a battery charger to get it fully charged first? If so, it shouldn't draw much from the alternator. If it still gives the warning, you have some other problem.

 

@pounce
I installed the DC/DC charger that I linked above. Definitely addressed the issue with the alternator/battery warning that led to my original post. I did a ten minute drive after installation and had no problems.
Otherwise, it seems to work, in that the "on/off" light on the charger unit comes on and my aux battery is at 13.1v.

Thanks for the help, everyone.

 

Great. Curious where you mounted it.

 

It's currently under the passenger seat, in the rear cubby next to the emergency battery. The plastic cover for the cubby is removed.The aux battery is between the seats. The plan is to incorporate the battery under a console that's in the works. The fuse panel is on top of the seat base, between the rails. I removed the foam cover that usually resides there and used it as a template to make a twin out of 1/4" plywood. To this I screwed the panel.
We'll see how the temperature/venting holds up with the charger mounted here. There's a much more ventilated spot I could mount it, but I'd rather keep everything fairly tidy in this area, and I don't want battery cables spanning the whole vehicle.
The charger unit has a function to add an on/off switch. I'm not sure under what conditions that would be desirable, but I'm definitely thinking about doing it.

I wish I'd done this from the start. I think all the bits and pieces I bought for the other setup probably equaled this in price, and didn't work. Ugh. This is the easy button and works correctly. As well, the other setup took up a 16" square board and had wires all over the place. This charger unit is only about 7" square. Again, the part I used is a Victron Energy Orion-Tr DC/DC Isolated Converter, 12v/12v 30amp. Looks like this:

I bought it on Amazon for ~$215 at this link.

 

If you have time for some images and extra details along the way, I will certainly look forward to them!

I'm no stranger to DIY, but I am green when it comes to vehicle "mods"and am still hoping to wire up a few things in my cargo bay, down the road

 

I'm glad this charger worked out because it's on my list. Still trying to work out what ac charger to pair with it so I can charge with shore power. I'd like to get a 50a charger, but Victron has a 30a waterproof ip67 one that could be handy. Might give the option to mount it outside. I like their smart charger because it can do lifepo4 and it can be switched to power mode to simply supply 12v to devices. The app also let's you see the last 10 charges in detail.

The other question is do I get the smart shunt. I think I wll if I go with over 200ah lifepo4 battery.

I was thinking of a battery between the seats like the option, but not sure now. Having swivels installed and maybe a webasto under the driver's seat if we can get parts. If I do the heater the vent needs to be at the center out the side of the driver's seat.

The other thought is doing 600ah along with charger and inverter under the van where the spare is today. Just delete the spare.

 

Glad the OP got it fixed. I just returned from a 4,500 mile vacation (20 days on the road). My Renogy 30A DC-DC Charger/MPPT performed perfectly both driving and while parked using solar. For "shore power," I just wired up a MEAN WELL RSP-500-24 DC Power Supply to connect to the DC-DC Charger solar input. This simulates solar and generates 30 A current when plugged in. My solar panel is a compact Renogy on a folding stand that I set up beside Metris while parked for camping. I debated the 50 A charger, but it wouldn't help much because the slow part of charging my 95 AH house AGM is the last 5 to 10 amps up to full capacity. That can take several hours. The one bad thing on the Renogy DC-DC is that it limits alternator current to 15 Amps whenever it senses ANY solar current. That's part of why I set my solar panel up to fully disconnect while driving. I don't think the Redarc has this issue.

In general, Victron products are viewed as more "premium," kinda like Dometic vs. ICECO, but the Renogy charger and inverter have been swell. Incidentally, I've had to push the inverter up over 1000W a few times -- it sounds an alarm but keeps on working!!!

My longest stay on the trip was 7 nights over 9,000 feet in upper Ten Sleep Canyon (Wyoming). Even my minimal (100W/95AH) solar/AGM setup was ample for daily ICECO, MaxxFan and lighting use. My AGM had degraded to about 12.2 volts and 55-ish AH by the end of my stay at Ten Sleep.