I'm considering scrapping my Victron Orion battery combiner, which I installed but haven't used, and opting for a DC-DC charger (or multiple chargers). The main reason is that if the house batteries are low, the alternator will work overtime to pump enough juice to bring them back, possibly at the expense of overheating the alternator itself. Post by: Glennman

I've been researching various DC-DC units, such as those from Sterling and Victron.  I've read a lot about the Victron units getting very hot. That doesn't sound very good and could be a cause of early failure.  Additionally, the Victron units appear to be limited to 30 amps, whereas others are rated at 40 and 50 amps. I have eight Lithium-ion batteries with 3000 watts of solar power, so maybe a 30–50-amp DC-to-DC unit is all I need.

Any thoughts on this?

Post by: buswarrior

You are right to carefully protect the coach alternator from the voracious amp-consuming potential of the lithium-ion house batteries.  Are there units you are considering that let you throttle the amperage up and down?  The solar will still be charging while driving, so typically set the amps lower for a supplemental boost.  If the solar panel fails, consider increasing the unit's power output and running the alternator at a higher rate to complete the job.

Post by: Glennman

Buswarrior, those are very interesting points. I'm not sure if anything like that exists. Maybe someone will weigh in on that, too!

Post by: luvrbus

A separate one-wire alternator will regulate itself and eliminate the electronic components. The DC-to-DC chargers do get hot. 

Post by: Glennman

A separate alternator is a good idea. That being said, I don't have any problem with actually installing one mechanically, but there must be some calculation involved in determining RPMs in relation to belt and pulley sizes. Could someone provide advice on how to determine that?

Post by: buswarrior

Another alternator still doesn't stop the amp-hungry lithium batteries from running that alternator at full tilt.  There needs to be a throttle on their appetite.

Post by: TomC

I would get an inverter/charger.  Mine puts out a maximum of 130 amps.

Post by: dtcerrato

What Tom said.  Our 2800W Magnum inverter charges at 125A or can be dialed down to any increment below the max amp output.

Post by: luvrbus

People are missing the point; He wants to charge while driving without a generator.  An inverter charger needs AC current to charge.

Post by: oltrunt

I use a Sterling battery to battery charger on my little bus.  The only time it seemed a little hot was on the first trip with it, as the "new" feeling was wearing off.  I installed a switch in its circuit so it doesn't try to charge the house batteries while the alternator is recharging the start batteries at the same time.  Once the start batteries are topped off, I add the house battery load.

As a side note, the reason I went with the Sterling was to thwart the Yosemite camp host Gestapos who got their knickers in a knot when I ran my nearly silent generator to charge the house batteries when dry camping. 

Post by: luvrbus

It's not that hard to charge a system that has the same voltage.  The expensive isolators have a capacitive voltage divider that stores and regulates the volts to the house batteries.  Our Safari Trek had one.  It would heat up since the design was intended to dissipate excess voltage through heat.  That is why they have all the cooling fins on the housing. 

I have a Magnum inverter and a totally electric coach.  It will convert the DC to AC, but the engine alternator supplies the DC, and the charger does not work when the inverter is on from a DC source.  Unless you have a special Magnum, those are AC-to-DC chargers.   

Post by: windtrader

What problem are you trying to solve?   You have a start and a house battery.  The solar panels, the alternator, and the generator are energy sources.  What's the reason for the combiner, etc.?

Post by: dtcerrato

Quote from: luvrbus

You are correct, my bad.

Post by: TomC

I have three 100-amp Battle Born lithium-ion deep-cycle batteries. I also wired the "Battery Isolation Manager" available through Battleborn Batteries into the main batteries.  I highly recommend this since my 160-amp alternator charges the batteries during the drive just fine.  It is a smart isolation switch.

Post by: Glennman

Hey Windtrader, I just want to be able to charge my eight lithium house batteries off the alternator without overloading or damaging the alternator. The lithium batteries will apparently cause the alternator to run at max output if, after boondocking, the eight batteries are low, potentially reducing the alternator's lifespan. I have the Victron Multi-plus II 3000-watt inverter for charging while plugged in, and the 3,000-watt solar panels too (literally on a good day!), and no generator.  Maybe the solar panels are all I need.  I figure that adding about 30 amps of charging while driving, coupled with what I get from the panels, will at least bring the batteries up to a sufficient level to run the refrigerator.  Thanks for weighing in!

Post by: windtrader

Is this all installed, or are you still in the design and planning phase? The solar panels should be more than sufficient to charge the house lithium bank. If it isn't, then: 1) You have too much draw - add more charge capacity, 2) You have insufficient solar charging to keep the house battery charged - add more panels, if extended low solar charging, then go to the pole or an onboard generator.  3) Depending on your use pattern, adding a circuit to charge the house from the alternator is not beneficial. For example, if you spend days parked/boondocking, the bus will not travel enough to be used as a charging source. We'll assume that running the bus engine to spin the alternator to charge the house batteries is not a recommended option.  This can be done, but it is probably the least efficient way to charge house batteries.

Post by: luvrbus

A good solar panel, on average, is 200W or three amps. You have a 270-amp alternator that produces 6,000 watts. How many solar panels would you need to supply that much power?

Post by: Glennman

Quote from: windtrader

All of the above!  I’ve installed the entire system (as of this week).  Re: Design: I'm never satisfied. And for planning, I don't do it enough!

I installed the battery combiner, but I'm concerned about overloading the alternator, so I want to install the DC-DC unit instead (this still charges off the alternator, but is metered, allowing for lower-level charging). I'm not looking to completely replenish the batteries while driving, as 30 amps from the alternator charging depleted 800-amp hours of batteries will require that I drive thousands of miles to bring them back up, especially if the sun isn't shining. I think that 30 amps from the alternator (DC to DC), plus whatever I get from solar, will be enough at least to run the mini split and a 10 cu. ft., 110V refrigerator while driving, especially if the batteries are low after returning from a boondocking adventure.

I might wait for now. I will have a 50-amp shore power on our first trip to Idaho in June. So, I should start the journey with a full charge and return home with a full charge. It's only 300 miles one way, so if I get good sunshine, the batteries should still have good power by the time I reach my destinations.

Post by: luvrbus

I don't quite understand the concern about the alternator.  The regulator protects against overcharging, and if it detects too much heat, it reduces the charging rate.  The Balmar regulator is my favorite.   It is a better unit than the OEM unit IMO.

Post by: Glennman

That is very interesting luvrbus. I'll have to look into that before I scrap my battery combiner for a DC-DC charger. Is the regulator outside of the alternator? Can a "Balmar" regulator be installed in place of the factory one without replacing the entire alternator? Thanks for your help!

Post by: buswarrior

Look for the multi-stage regulator, amongst all the other lovely things that Balmar makes.

Post by: Glennman

My son works for a marine outfit. I'll see if they can order stuff from Balmar.  I can see myself with a separate, dedicated alternator.  It appears that they offer complete kits.

Post by: mqbus767

Hi Glenn, I had a similar experience about two years ago. You can read my experience here:

I wanted to directly connect the alternator to the house battery using a "smart" combiner,  but the output from the 50DN kept tripping the internal circuit breaker on the BB batteries.

What I currently have installed are three Victron Energy Orion-Tr Smart 24/24-Volt 17 amp 400-Watt DC-DC Chargers. They are expensive per watt but highly configurable and "safe". They support charging profiles for various battery types, feature engine start detection, and offer Bluetooth monitoring. I really didn't want to go this route, but I may replace it with something else in the future; however, they do work.  1,200 watts is not much, but I'm also hoping that with future solar installations, it'll be enough to run the mini-split and the fridge down the road.

I don't think the 50DN will have any issues with direct charging a battery bank, as it's rated for continuous use. I might even be able to overcome the battery CB tripping by extending the capacity one day. I tried several times working with BB and Victron techs to make it work, but none of them could tell me exactly why it wasn't working. On paper, they all said it should work.

Post by: Glennman

Thanks for weighing in mqbus767!  I read all the posts in the link you provided detailing your experience. Why didn't you go with two 30-amp units instead of three 17-amp ones? Using the DC-DC chargers appears to be a safer option than the combiner. Do you think your experience with the combiner would have been different if you used the Victron Cyrix-li-ct? You mentioned that you accidentally ordered the wrong one. Do you recommend the non-isolated or isolated model?  I have a good connection from the house bank to the bus frame for the opposing side. Additionally, I believe that one 30 amp charger will be sufficient, or at least greatly help, since I also have 3000 watts of solar, which is, of course, on a good day.

Post by: mqbus767

Hey Glenn, the 30-amp units are 12V/12V. My house batteries are 24V. When I bought the units, 17A was the largest Victron offered.  That may have changed.

The combiner route is a good option only if your batteries can handle the current from the alternator. Nothing I tried in a direct connect setup worked because the batteries couldn't take everything the 50DN was able to produce. Victron speculated that a larger bank would be able to handle it, but I was unwilling to spend several more thousand dollars to test that theory.  I may one day travel to Victron and have them inspect the system and provide advice.  If they can prove that having more batteries solves the issue, then I might consider that route.

Post by: Glennman

Which battery bank needs to be able to "handle it"? Are you referring to the house batteries or starter batteries?

Post by: mqbus767

The house batteries.

Post by: Glennman

Now that I have my system fully functional (except for charging from the alternator), I'm thinking that the 3000 watts I'm receiving from the solar panels will be all I need.  I'll be sharing my results on my "project" thread soon, but recently I ran my batteries down to 89% by running the AC for about five hours with the solar panels turned off.  Then, at about 4:30 pm, I turned on the solar panels, and the batteries were at 100% within 20 minutes. All that on a cloudy day!  The batteries recharged even while the AC was running (I had it set to 70 degrees so that it would continue to run). The AC was drawing about 850 watts, while the solar panels were generating 1700 watts, charging the batteries and powering the AC simultaneously. I am very impressed. I have yet to conduct further testing, but I may not need to charge the alternator at all. More on that later...  Thanks, everyone!