DC-DC charger for my 2019 Micro Minnie 2108DS

[tinglett]

I finally decided it was time to add a DC-DC charger to my lithium setup. My gear is mainly Victron so I went with the Orion Tr-Smart 12/12 30A charger.

Of course those with motorhomes use these devices to protect their alternator from the endless thirst of a lithium battery bank, but this isn't the problem at all for us travel trailer folks. Instead we battle with the voltage drop over the long run of (undersized) wire from the alternator to the trailer battery. Without the DC-DC charger the best I would see is 8A at 12.96V, which dribbles fairly quickly down to 4A (or less) as the batteries charge. My 180A OEM alternator would never notice this load. The batteries need a higher voltage in order to take a charge, and under 13v won't cut it. They really want over 14v.

One "fix" is to run heavy gauge wire from the alternator back to the trailer. I've seen some do that in forums and it works well, but what a lot of work that is. The DC-DC charger is another "fix". It'll take what it can get (voltage drop and all) and use those watts to charge the battery at proper voltage.

And it does. I setup the DC-DC convertor profile to LiFePO4 (it says 14.0V). I drained my 200AH of LiFePO4 (battleborn) batteries down to 75% and then tried the new setup. The voltage drop was all the way down to 8.7V. But no matter, it was still charging my batteries at 13.46V at 24A! Nice!

Was it worth almost $250? Maybe. It certainly helps a lot in providing a recharge as we move from location to location, but continuous 24A will take a lot of hours to recharge our 200AH battery bank. But the project was fun...so I'll take that as the reason .

[Bcborn]

I like that always thinking, Nice Job

[RocknRoll]

Thanks for the post, especially how you detailed the reason not just the process.

[creativepart]

I have a motorhome, and I installed the Victron Orion charger to - as you say - save my alternator.

It does that... but is it necessary? I'm not sure of that. First it seems I don't leave a campsite with my 400ah lithium battery bank all that low. And, I have 300w of solar on my roof that adds charge to my batteries all the time I"m driving.

So, yeah, I leave a campground with 60% State of Charge (SOC) and arrive with 100% SOC but I'm pretty sure half of that is coming in from my solar panels while I drive.

And, then in the summer months we are running the generator while we drive to keep the motorhome cool inside so that when we arrive the RV is still livable. That charges the LFP batteries while we drive as well.

I guess if I was going from dry camping to dry camping over multiple days I may feel the D2D charger was invaluable. But I'm not. I wish I had lived with the system with out the Victron Orion for a few trips before purchasing this device. I may have discovered I didn't really need it all that much.

PS. Lithium batteries are such a game changer that it really alters the way you use and think about your RV's power needs.

[tinglett]

Well, the maiden voyage with the DC-DC charger produced some good news and bad news.

First, the good news is that it worked well. My trip home was only about 75 miles, for about 1 hour 20 minutes. When I first started at the campsite we were in shade of trees so the solar was producing nothing, but the DC-DC charger was giving the batteries 25.9A @ 13.33V (345W) with the 200Ah of battery at 35% SOC. After the run home the batteries were at 54% SOC and 28.2A was going in at 13.53V. Solar was adding to the charge (I have 300W worth of panels). It was overcast and the solar controller claimed it produced 90Wh over that time. I'll call that about 6.6Ah or 3.3% SOC. The net is that I put in about 16% SOC via DCDC and 3% SOC via gray-sky solar in about 1.5 hours. Another 3 hours of driving would have topped it off. Good to know.

The bad news is that I found bad interaction with my RedArc brake controller, and I suspect this could be a problem with anyone's brake controller. I need to talk to their technical help, but I found the controller faulting and I think it's due to the heavy voltage drop. I bet the controller is powered by the same 12v line that feeds the battery. I'm speculating and will report back, but my guess is that I'll be needing to find another 12v source under the dash to power the brake controller. That shouldn't be too difficult, but it'll be a pita.

[tinglett]

Here's a follow-up on the saga about the brake controller. I've found many others fighting the same trouble on various forums.

I had installed my RedArc brake controller myself and went back to the docs to remind myself how that went. My vehicle is pre-wired for a brake controller and included a wiring harness and a place to plug into the vehicle wiring. Sure enough, the 12v power feed comes from the same battery feed that goes to 7-pin #4 (black), which is the circuit loaded down for battery charging.

This is not good. This 12v supply not only powers the brake controller electronics, but it also provides the current to feed to the brakes via 7-pin #2 (blue). I've read that the brakes will want up to 3 amps each. I believe the reason my brakes seemed to be working was that when I'd apply them the voltage would droop more, the DC-DC charger would finally go under the voltage threshold and stop drawing power, and then the voltage would be back for the brakes. This happens too slowly for driving.

The simple solution is to tap the 12v supply for the brake controller from somewhere else. The manual is very clear it should come straight from the battery via an inline fuse and had I wired it this way it would have been just fine. I'm about to winterize and put the trailer away for the season so I'll pick this up next spring. My temporary solution (if I get the trailer out early) is to either disable the DC-DC charger or tweak the charge settings (via bluetooth). In experiments with the charge settings I found the threshold is at around 13.4 volts to the battery. At 13.5 volts the battery sucks 24 amps, but at 13.4 it drops to 11.5 amps, and at 13.35 it drops to 10 amps. At 10 amps the voltage drop from the tow vehicle is only down to 12v and everything works fine...even with brakes applied (as I've tested so far). With these numbers you can see what lithium batteries really need for fast charging. You really need more than 13.4 volts.

Another thing I'd like to do is beef up the wire gauge in the trailer. Does anyone make a trailer cable with heavier gauge wiring for black/white? I haven't found anything better than 10 AWG so far.

[Marine359]

Good job installing the Orion Todd. You do good clean work.
We bought one, but returned it because, frankly, our 300w rooftop pv array will give us over 1Kwh even on cloudy travel days. And adding another panel is cheaper than buying the Orion. The fridge uses about exactly 4 amps coming through the 7-pin. So, just with solar, we usually arrive with a “full tank” of battery power. I suppose if we lived in the PNW, we’d put in an Orion.

[No1Hunter]

I installed one (isolated version), but I ran fused 6awg (+ & -) from the TV's battery terminals to the 50amp Anderson reciprocal on the back bumper and Then ran a set of 6awg cables with an Anderson connector to the DC-DC charger. 6AWG is the minimum recommend cable size for the DC to DC charger, per Victron (16+ feet).

To be truthful, I haven't had the need to use it, as our 400 amps lithium battery bank has kept us powered on our 5 day/4 night trips (never been below 30% SOC). We stayed in the same place, were off-grid, and were always parked in the trees. So, no charging from our solar panels.

I did add an Anderson connector to my air compressor, so I can plug it in to the TV without having to turn the TV around and lifting the engine hood.