Victron dc-dc charger wiring question

msmolow

2019 Unity CB / 2018 Chas
The weather has finally improved and I am planning the Victron dc-dc Smart charger install.

The charger will be in the same bay as my solar charge controller and Cerbo GX.

That bay contains a buss bar I added that directly connects to the Mercedes ground point above the rear axle. It's in the bottom right of this photo:


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Here is the Victron wiring diagram:


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Any thoughts on running both negative wires (coach and starter) from the dc-dc charger to that buss bar rather than to the battery negatives as shown? If that is acceptable practice it will makes things much easier.
 

TampaSteve

2018/2019 Unity CB
@msmolow, old dead thread, but which way did you finally go? I'm exploring dc-dc chargers. If I replace my 2 Battleborns with the slightly larger Lithionics 125 ah, the combined 250 ah would probably dissuade me from using my Cole relay isolator to directly charge the new Lithiums. There is already a scary 90-100 amps flowing at times and I wouldn't want to put even more load on the alternator. For me it seems that would be about the floor I'd need to get a decent enough charge rate but thats a substantial efficiency loss. I'm guessing using the chassis ground for the battery negative would work, but add even more loss, but was wondering what you experienced.
 
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Bawareca

Member
If you think about it for a practiucal purpose , the chassis is a conductor with infinite thickness. There will be way more voltage drop in a 20' of 1 gauge wire than in a 20' of chassis.
I did not measure the current draw of my Renogy 40w, but will do so soon. I doubt it will be at 70% efficiency, but we'll see.
 

hoosierrun

Active member
@msmolow, old dead thread, but which way did you finally go? I'm exploring dc-dc chargers. If I replace my 2 Battleborns with the slightly larger Lithionics 125 ah, the combined 250 ah would probably dissuade me from using my Cole relay isolator to directly charge the new Lithiums. There is already a scary 90-100 amps flowing at times and I wouldn't want to put even more load on the alternator. Related question, have you ever measured the actual efficiency of the charger? I read a post on Amazon that the Renogy 60 amp DC-DC charger put out 55 amps but drew 80. For me it seems that would be about the floor I'd need to get a decent enough charge rate but thats a substantial efficiency loss. I'm guessing using the chassis ground for the battery negative would work, but add even more loss, but was wondering what you experienced.

Steve, I mentioned in another post that I am using the Sterling BBW1260 with good success with my Battleborns. It is basically installed in-place of your isolator relay and IRD. It has battery cable studs that accept the ring lugs that were originally on your Cole Hersee relay. Just transfer the wiring over. Takes 2 to 3 minutes. It has it's own fused ground wire that you can either attach to the chassis ground or to either battery negative post. You set up the lithium charging profile using magnetic swipe over the edge of the case (magnet included or use your own). The unit functions the same as the non-waterproof Sterling, but really easy to install (took me 10 minutes, and another few minutes to set it up). On the Unity, you would probably need to remove the passenger seat to make the connections and screw the unit down. I am well over a year using it and it works great. There is an optional remote specific to this unit which I did not buy. I can see everything going on with my Victron smart phone battery monitor. I never had to touch the unit since I put it in. Like any DC to DC converter, it is rated for input amps so you know that the alternator max draw is truly the rating (60 amps) The output will be about 47 amps (inherent losses in the conversion plus the cooling fan). Subtract your refrigerator amps if running on DC and the remaining is what you will have going into your batteries. Here is the unit I bought: https://www.amazon.com/Sterling-Battery-Battery-Charger-12V-12V/dp/B019BVKR6U Below is a picture of what the unit looks like without the cover on it. The left side is the house side and the right side, the chassis side. Blue wire from your IRD (ignition sense) goes on the center terminal block. The other 2 smaller wires are for my step and stabilizer circuits (may or may not be present on your unit). Also, you can see the fused ground wire (coiled). On my rig, the grounding bus is adjacent, so I just attached it there.

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TampaSteve

2018/2019 Unity CB
Thanks I would have thought that mounting this under the seat would not provide enough airflow? But I gather you are saying that isn't the case.

I had resigned myself to having install it remotely near the battery so the under seat would be advantageous. The Renogy I have been looking at seems clearly too big to even consider.

I managed to install a new relay without removing the passenger seat, but I don't recall seeing a ground there. If I am not mistaken somebody said on a Unity it can be found under the driver's seat.

Reading the few Amazon reviews one said it cut off with the Lithium profile if the MPPT charger was on. I wonder if you have had that issue or used the AGM work around mentioned.

Edit: It looks like the newer Sterling is much larger, which is probably why I originally focused on the lower cost Renogy if I have to mount it elsewhere anyway.
 
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hoosierrun

Active member
I think it is very possible that it could cut off when you are charging with solar.... or at least cut back on charging amps, depending on state of charge. It is looking at the house battery voltage to determine how much current and voltage to apply, and the solar could apply enough voltage to fool it into thinking the battery is charged more than it really is. It is a good question to look into further. I don't know if Sterling Tech support or Bay Marine could address that issue. If it is a concern, I would pursue that. It has not been a problem for me because my cheap Go Power controller and wimpy solar does not effectively charge my Battleborns beyond about 80% since it only has a standard AGM profile. I continue to maintain full output from my unit (45 to47 amps or 32 with fridge on 12 VDC). I really can't address the heat dissipation issue. Other posters with Unity's have had a problem with the conventional Sterling 60 amp unit under the seat. Perhaps a grill or vent? ... but with that leather shroud, it might not look too good to cut through it. Your idea to install it away might insure no problems, but adds a lot more work to the project. Yeah the Serenity has all this under the driver's side dinette and there is a grill out the front by the driver's side.

To be safe for the ground wire, it would probably be best to use that channel between the seats and pick up ground at the starter battery negative. The seats are bolted to the floor with some big star bolts, so one of those bolts might work too.

Like all these projects, it is never as straight forward as it first seems. Let us know how you make out.
 

TampaSteve

2018/2019 Unity CB
If you think about it for a practiucal purpose , the chassis is a conductor with infinite thickness. There will be way more voltage drop in a 20' of 1 gauge wire than in a 20' of chassis.
I did not measure the current draw of my Renogy 40w, but will do so soon. I doubt it will be at 70% efficiency, but we'll see.
Probably the Amazon review was screwy in hindsight. Renogy claims something closer to 90% efficiency. So in your case did you have or run a starter battery negative, or did you just use the chassis ground?

I realize the current loss wouldn't be huge, but was concerned about other issues going with the ground as a starter negative.
 

hoosierrun

Active member
Just used a Chassis ground in my case. I figure the original system (IRD and relay contactor) used the chassis ground and it often supplied more amps than my Sterling, so I can't see that it would matter. The Mercedes battery uses Chassis ground and the LTV battery uses chassis ground. Only my Magnum has a separate pair of cables going to the battery. I have not been able to locate the ground for the solar controller and I don't see it going into the battery housing, so it must be grounded to the chassis somewhere.
 

erutan

2007 144" High Roof 2500
I used a Sterling Power DC to DC charger before - it died after 2-3 years, the replacement I got sent was DOA.

Given that my 180A alternator puts out 14.1v most of the time (depends on draw), I just put in a ~$20 heavy marine switch where my battery to battery charger was and it works fine. With ~350A of LiFePo4 I'm not overcharging (I'll never get above .5C given other electrical needs in the van) and it's simple with nothing to fail. It doesn't charge quite as fast as it's not upsampling the voltage, but it's been fine for years. In the summer I don't bother with it as my solar is enough, but it's critical in wintery months.

Note: I talked this over with someone that has been installing solar setups (and batteries) for a decade+ and they saw no issue with it.
 
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TampaSteve

2018/2019 Unity CB
I have 200 ah of LFePo4 now. Using a $30 200 amp Cole relay for alternator charging. Works great, but I have seen it running 100 amps when the batteries are low. I am thinking of upgrading to 150 AH battery. I'm not concerned about overcharging - but that I'd fry my stock Mercedes alternator over time especially if I am stuck idling with a near depleted battery bank.

I used a Sterling Power DC to DC charger before - it died after 2-3 years, the replacement I got sent was DOA.

Given that my alternator puts out 14.1v most of the time (depends on draw), I just put in a ~$20 heavy marine switch where my battery to battery charger was and it works fine. With ~350A of LiFePo4 I'm not overcharging (I'll never get above .5C) and it's simple with nothing to fail. It doesn't charge quite as fast as it's not upsampling the voltage, but it's been fine for years. In the summer I don't bother with it as my solar is enough, but it's critical in wintery months.
 

erutan

2007 144" High Roof 2500
I've never had to idle to charge up my batteries, if it comes down to that in winter months I'll find a reason to take a little drive for a walk/hike or do a shopping trip. I'm usually around 70A when idling and it can get above 100A when driving.

The alternator is going to putting out a lot of amperage regardless, the charger will just be adjusting the voltage, unless you have a limited amperage charger and a small bank to fill. Iif you're thinking of making a 350A system getting a charger that'll only do 20-30A an hour doesn't seem very effective unless you're doing a lot of highway driving. My solar and battery monitor are Victron, I'm a fan of how everything talks to each other, but it looks like the higher amperage ones aren't "smart" yet? https://www.victronenergy.com/dc-dc-converters/buck-boost-dc-dc-converter-25a-50a

I ran my Sterling 12120 since early 2016, replaced it with the marine switch in 2018, only installed solar in spring 2020 FWIW. I can't speak for truly long term results, but a stock alternator is ~$370 (not including the inconveneince of when it might fail!) vs the $500+ I wasted on my sterling charger. Here's what victron has to say about the risks of charging off an alternator: https://www.victronenergy.com/blog/2019/10/07/careful-alternator-charging-lithium/
 
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erutan

2007 144" High Roof 2500
re: mounting a made my own little mounting block behind the drivers seat... made more sense when I had an actual charger on it:
 

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hoosierrun

Active member
Probably the Amazon review was screwy in hindsight. Renogy claims something closer to 90% efficiency. So in your case did you have or run a starter battery negative, or did you just use the chassis ground?

I realize the current loss wouldn't be huge, but was concerned about other issues going with the ground as a starter negative.
I would inquire from other users as to what they are seeing in the way of charging amps from their Sterling or from other manufacturers DC to DC converters. You have to completely turn off any solar contribution to measure accurately. I am only seeing about 80% efficiency when I measure at the actual battery (using Victron 712 battery monitor). I have run the fridge on propane at times just to get the current up to 47 to 49 amps. I know the propane solenoid and a few other minor draws take about an amp to 1-1/2 amps. Also, the converter has a cooling fan. Do the manufacturers take that into account with their efficiency specs? It certainly is possible that I could be getting some degradation from not running dedicated ground wires, but my voltages seem to be in-line with the lithium charging profile. Still hard to say for sure because the current really tapers off at 95% and above SOC.
 

hoosierrun

Active member
I've never had to idle to charge up my batteries, if it comes down to that in winter months I'll find a reason to take a little drive for a walk/hike or do a shopping trip. I'm usually around 70A when idling and it can get above 100A when driving.

The alternator is going to putting out a lot of amperage regardless, the charger will just be adjusting the voltage, unless you have a limited amperage charger and a small bank to fill. Iif you're thinking of making a 350A system getting a charger that'll only do 20-30A an hour doesn't seem very effective unless you're doing a lot of highway driving. My solar and battery monitor are Victron, I'm a fan of how everything talks to each other, but it looks like the higher amperage ones aren't "smart" yet? https://www.victronenergy.com/dc-dc-converters/buck-boost-dc-dc-converter-25a-50a

I ran my Sterling 12120 since early 2016, replaced it with the marine switch in 2018, only installed solar in spring 2020 FWIW. I can't speak for truly long term results, but a stock alternator is ~$370 (not including the inconveneince of when it might fail!) vs the $500+ I wasted on my sterling charger. Here's what victron has to say about the risks of charging off an alternator: https://www.victronenergy.com/blog/2019/10/07/careful-alternator-charging-lithium/
The big problem I see with the Victron video is that is not how we set up our charging systems. It is not real world. For our Mercedes motorhomes, we just tap the starter battery (through the fuse block at the battery) for our converters or for a contactor. The starter battery acts like a big tank or a storage capacitor, essentially absorbing any spikes or back feed surges that might occur. The DC to DC converter generally sees a pretty clean DC source without the alternator trash unless someone were to hook it up directly to an alternator without the starter battery in parallel. The video shows an alternator directly charging a lithium battery.

I ran your method for over a year, just using the contactor and IRD. It does work OK but I could never get near 100% SOC (more like 80 to 85%). I didn't even know that until I installed the Victron 712 monitor and observed charging behavior while my wife drove. It seems that the Mercedes alternator targets the starter battery by voltage regulation. It slowly backs off charging voltage in attempt to keep the starter battery from cooking or over charging. Since the lithium battery requires a higher voltage, no (or very little) current is pushed into it and it doesn't get charged up very fast. 8 hours of driving could only take the batteries up to 80%. Sure, most people have solar to take it to 100% if driving in the day time, but I don't have much solar and don't count on always driving on bright sunny days. My only solution was installing a DC to DC converter.

Try checking your voltage and current with solar disabled and after you have driven for 45 minutes (don't shut off the vehicle). Unless you have an older Sprinter, I'll bet you see the alternator voltage at the starter battery about 13.8, not the 14.5 that you start out at. It only makes sense because 14.5 for many hours would be overcharging the AGM battery that Mercedes puts in the newer Sprinters. The older lead-acid batteries used in Mercedes were far more tolerant of voltages in the 14+ range, but they needed to be re-watered periodically.
 

erutan

2007 144" High Roof 2500
My alternator doesn't start out at 14.5, it puts out a fairly steady 14.2 to 13.9 depending on what load I'm pulling - I'm on a 2007 so that might qualify as "older" though. :)

My Sterling DC to DC charger connected to the positive terminal on the starter battery as recommended by them... ended up just putting in a marine switch where it was inline with my old fuses in (I flip it after I turn on the engine, so that would protect from the largest spikes I imagine). I do get above 85% charge without solar - was up by the Olympic Peninsula from late november to a ~week ago and had days where I'd only get 20-40w in, with a max of 270 depending on cloud cover, but very few days over 140w or so and was able to bring it up to full when going on a long drive on a rainy day. It does definitely slow down as the charge gets higher, but between it and my large bank it's "good enough", solar just makes it that much better, though everyone's needs and experiences are different!

I was using a DC to DC charger from spring 2016 to spring 2018, then a marine switch without solar until spring 2020, and a marine switch with solar since. I do prefer the marine charger (it's a bit faster, and the auto-disconnect is nice), but I personally haven't found it necessary and regret the ~$500 and many many hours spent troubleshooting it. :/
 

hoosierrun

Active member
I'm thinking of upgrading to the the BBW12120. With the optional remote, you can decrease the current in 10% steps via a button push on the remote (unfortunately it is not a wireless/Bluetooth remote yet). As far as I know, this feature is only available on the waterproof BBW versions of the Sterling. I'm running 4 Battle Born batteries now and really need to take more advantage of the vehicle alternator for charging. To be safe, I could program a de-rate of 80 to 90 % (96 to 108 amps input) on a BBW12120 and more than double my charging amps (with fridge on DC) from what I have. I would have the recommended lithium charging profile with this unit. Plus I could periodically check the alternator temperature with an infrared thermometer as a test and see how hot it is getting when driving long periods.. That could be useful data, but at this time, I don't have any data to determine the danger or undesirable temperatures that could cause harm to the alternator. So far, with the 60 amp Sterling BBW model I have not had to touch or even look at it since I set it up. I view its proper operation via the battery monitor, Victron BM712. The LTV Serenity has a fairly large storage compartment with a vent grill where the old IRD contactor relay was installed from the factory, so I don't envision any overheat or half power output issues.
 

erutan

2007 144" High Roof 2500
My first BBW12120 began charging very intermittently after a year and change of use, then finally died after two years. The replacement they sent was DOA.

Maybe they’re better now, but I basically went over all my wiring again assuming the second one had to work and taking it out of my system ‘fixed’ it.
 

hoosierrun

Active member
My first BBW12120 began charging very intermittently after a year and change of use, then finally died after two years. The replacement they sent was DOA.

Maybe they’re better now, but I basically went over all my wiring again assuming the second one had to work and taking it out of my system ‘fixed’ it.
That is really sad to hear. Did you run a dedicated ground back to the house battery set? I don't know if that makes a difference, but it is recommended by Sterling. I did not on my installation, at least not yet.
 

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