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Old 01-06-2021, 08:44 AM   #11
Join Date: May 2017
Posts: 30
Where to wire DC-DC charger

I hope it is appropriate to post this here rather than starting a new thread altogether. I've been following this thread with great interest as I have decided to make the switch to Lithium batteries for some time and have a setup that is essentially the same as Sloya's. But I have a question related to the discussion here.

My SMB is a 2017 144 high-top Sprinter built out by SMBW in early 2018. Like Sloya's mine has 200w of solar, Zamp 30amp controller, Magnum MS 2000w inverter/charger, and the Blue Sea 7620 automatic charger relay. I have recently added the PN2146 Contura switch to the mix as well. My current batteries are 2 105amp AGMs.

I plan on replacing the current batteries with 2 100 amp Lithium batteries. (Probably going with Relion's RB100-LT, primarily for the internal heating system which seems like a really good feature.)

From Sloya's information I am pretty confident that just dropping in the new batteries and making sure the Magnum ME-RC and Zamp settings are correct will yield pretty good results. But, for reasons expounded on by folks on this thread, I also plan on adding a DC-DC charger.

My question is, where should I wire in the DC-DC charger? Being the extreme novice I am I am confused by how it will interact with the Magnum Sense module and the Automatic charging relay. My basic wiring diagram is shown in the attached image. (I think/hope I drew everything correctly.) Can someone just tell me where on this schematic I should be placing the DC-DC charger? Thanks--the information I am gaining from the electrical discussions on this forum are nothing short of amazing!


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Old 01-06-2021, 09:26 AM   #12
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The quick answer is that the DC to DC charger generally replaces the ACR. The input from front of the van to ACR would go to the input of DC to DC. The house side of the ACR will go to the output of the Dc to DC. Remember that most DC to DC chargers will require fuses on both input and out put.

The input ground to the DC to DC could come directly from the battery, or connected negative ground bar. Depends pretty much on the recommendation of your DC to DC charger.

The output ground could also go to the same ground bar or you could attach to the non battery side of the BMK shunt or inverter side. Also you need to check the size of the cable from negative ground bar, as drawn it would be to small and is shown attaching to inverter frame. I would expect that there is a path from ground bar to the shunt. It could just be the way you have drawn it.

You could wire the DC to DC in parallel to the ACR, but that could bring some other issues that you would need to take into account.


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Old 01-06-2021, 10:06 AM   #13
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Thanks Greg. Your answer that the DC to DC charger replaces the ACR makes sense to me except for one thing. I donít think DC to DC chargers provide the function that the ACR does as far as automatically disconnecting the house and chassis batteries thereby protecting the chassis battery when the house batteries get too low do they? Thatís an important feature.

I almost feel like the DC to DC charger should be connected to the house side of the ACR and then the three wires now connected to the house side of the ACR should go to the output side of the DC to DC charger. In other words, connect it in series I guess. But that idea likely just shows my degree of ignorance about how this stuff all works.

Regarding your comment on the cable from the negative ground bar, the one I drew just is there to ground the inverter chassis I believe. There are other wires going to the ground bar that I did not draw in for some reason. Iím pretty sure everything is properly grounded at this point (i.e. as it came from SMBW).
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Old 01-07-2021, 05:40 AM   #14
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Originally Posted by Scalf77 View Post
You could wire the DC to DC in parallel to the ACR, but that could bring some other issues that you would need to take into account.
One issue I see wiring the DC-DC charger in parallel with the ACR is that when the engine's running, both the ACR and the DC-DC charger would be sending voltage to the lithium house batteries. The voltage going to the lithium house batteries from the ACR would be equal to the output of the engine's alternator, typically less than 14v. And the voltage from the DC-DC charger would be the lithium charging profile programmed in it, typically, 14.4-14.6v. The issue arises because the ACR will allow the higher voltage of the DC-DC charger to backfeed into the starting batteries, potentially overcharging and damaging them. A workaround for this would be to leave ACR in the off position using the 2146 Contura switch. At that point the only benefit to keeping the ACR in the circuit is for the rare times you may need to tie the two battery banks together to jump start the starting battery, something that could be accomplished by a set of jumper cables and/or a jump starter like https://www.audew.com/Audew-2000A-Pe...l?rmmds=search
2006 E350 SMB RB50 6.0 PSD
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Old 01-07-2021, 07:01 AM   #15
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To be clear I am not recommending that you would run the ACR and DC to DC at the same time. Yes, it would be switched off in normal use, but available for backup or emergency jump start. You also would need to make sure how the DC to DC would handle it when you went to perform a jump start. You most likely would need a remote off, and or additional switching for inputs or outputs of the unit. If using a dual DC to DC with solar, you may want to still use solar to top off starters, which means you would need to be able to isolate the input the DC to DC charger.

The following is a diagram of my old rig. I essentially have an additional Blue Sea Solenoid on both the input and output of the KISAE DMT1250. The ACR is in parallel with DC to DC. The remaining Blue Sea device is a disconnect for the Fuse panel.

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Old 01-07-2021, 09:45 AM   #16
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Thanks Porschedpm and Greg for the additional information. After the earlier posts, I did some more reading and now realize that dc-dc chargers do in fact prevent the house batteries from draining the chassis battery (at least when the engine is off) so that is not a concern. I'm planning on removing the ACR and 2146 Contura switch and replacing them with the dc-dc charger.

I will miss the Contura switch but can work around that. For one, I will put in a toggle switch in the ignition line from the dc-dc charger so that I can disconnect the house and chassis batteries even when the engine is running. (I also plan on using circuit breakers on either side of the charger so could just use those rather than adding a toggle switch I suppose.) As far as an emergency jump, I will either use jumper cables or that nifty jump starter porschedpm pointed out. One of my main goals is to keep the system as simple as possible so wiring the ACR in parallel someway is definitely out.

I know some dc to dc chargers come with built-in MPPT solar input. I am quite happy with my current ZAMP solar controller/charger setup so will stick with that. (Unless it will cause other issues?) That's kind of counterproductive as far as the keep it simple goal goes, but it does keep it simple as far as minimizing the necessary changes associated with converting to lithium batteries.

As far as the choice of dc-dc chargers goes, I'm thinking of getting the Renogy 40A model. I'd like to go to 50A for quicker charging but think staying at 40A will be better for alternator help. The only thing that makes me hesitate on this choice Renogy is significantly cheaper than the Redarc or KISAE alternatives. That makes me a bit nervous but the Renogy seems to get good reviews and few complaints that I've seen.

Greg, that is some system diagram for your old rig. It's snowing here today so it is perhaps a good time to sit in front of the fireplace and challenge myself with seeing how much of that I can figure out!
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Old 02-12-2021, 05:48 PM   #17
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Hi all, I also just upgraded my house batteries and wanted to share here since my setup is a little different. Hopefully this will help anyone considering converting on a Ford SMB.

Original set up - 2008 Ford with EB 50 conversion by SMB West. I had a 4D AGM mounted on a tray behind the rear axle, Tripp Lite Inverter Charger, Blue Sky 2000E solar charger, with Sure power Separator.

New set up - 2 100AH Battle Born Batteries, Redarc BCDC 1240D Dual Input Charger and Victron BMV-702 Battery monitor. I kept the Tripp Lite Inverter Charger for now.

A little about why I chose these components

Battle Born Batteries - From what I was able to determine these are extremely well made batteries. They are made in the US and they have fantastic customer service and are willing to work with DIYers. They were really helpful in designing my set up. There is a great video of a tear down of one of their batteries on Youtube. https://youtu.be/G5E30u-66VI

Redarc DC-DC charger. Again great customer service you can call a US number and talk directly with them in Australia. These chargers are built specifically for 4x4's so they are tested for harsh vibrations, heat, cold and moisture. Take a look at the videos on their website of what they do to test their equipment. This will replace the Blue Sky solar controller (mine had an intermittent fault) and the battery separator. If you are switching to Lithium batteries you really need a DC-DC charger because an alternator is not designed to charge lithium batteries. The batteries won't charge properly and it can fry the alternator. I also liked that this charger prioritizes the solar power first and then supplements with power from the alternator. I opted for the 40 amp because I have a single alternator but they also offer a 50 amp version.

Victron Battery Monitor BMV-702- As stated earlier in this thread you can't use voltage to estimate charge level of a lithium battery because the voltage is very consistent and then drops off a cliff when the batteries reach near zero charge.

I kept the Tripp Lite Inverter/Charger because it should be fine for bulk charging the batteries. It doesn't have a lithium setting and their customer service is terrible, they weren't able to give me any of the specs. for float voltage for the two setting it has and all they could tell me was what is in the manual. This may get changed later when the bank account has some more $$ available.

First task - remove battery, I disconnected the terminals while the tray was in place so as to not damage the cables, then used a floor jack with blocks of wood to lower the tray. It was a little sketchy but I really wasn't concerned with damaging the old battery. Just keep your hands and feet clear because the battery weights 100+ pounds.

I had to grind the two pieces of angle off the tray that held the old battery in place. I then welded a new piece of flat steel across the drivers side end of the tray for support before cleaning and repainting it.

I found 2 QuickCable Group 27 battery boxes fit in the tray and used pop rivets in the corners of the boxes to attach them to the trays. I chose the rivets because they won't work loose with vibrations and they and low profile and won't wear on the bottom of the batteries. I used a Sawzall to cut the handles off the boxes and tin snips to cut the ends and sides of the tops to allow for the cables to come through. The batteries have a little extra space in the boxes and no way to tie them down so I used foam pad around and under the batteries. This will keep them from sliding around in the boxes plus give them a little insulation.

Ready to go back in:

I purchased cables with the batteries from Battle Born and installed split loom on them before installing. I also re-routed the negative cable, from what is shown in the picture, so it wouldn't cross the positive cable. This leaves the negative outside of the boxes but I would rather it chafe on the chassis then short to the positive.

I was able to get the batteries and tray back in without the use of a jack because these are much lighter. I was able to push the passenger side up on to the frame rail then get a bolt in the drivers side to hold it in place. It is better to have two people for this but it is doable by yourself. Once I had it in place I put both bolts in the passenger side with the nuts on just up to the point where the bolt threads came out the back of the nut. Then I lowered the drivers side and propped it on a short (approximately 12") piece of 2x4. This gave me enough room to get the cables connected and the tops on the boxes.

Now for the interior wiring. I completed all of this prior to re-installing the batteries so the only live wire was to the start batteries. First thing is to remove the back seat to get access.

I removed the battery isolator located on the bulk head behind the passenger side wheel well. Be-careful and tape off the live connection to the start batteries so you don't have any fireworks. There are two small gauge wires to the isolator you will not need. One is black and is the negative, I took this loose from the ground terminal on the wheel well and removed it completely. The other runs the the ignition and joined the batteries when starting. I cut this one off and taped the end as it isn't needed.

I then unraveled all of the negative leads. They are all connected beside the inverter in split loom and electrical tape and held together by a clamp nut. I mounted the shunt for the monitor on the wheel well and was able to use all the existing cables. I cut them to length and crimped and soldered eyes so that they were all able to connect to the shunt.

I ran the power for the shunt to the terminal the powers the main fuse block which is right next to the wheel well. Note this is also where the wire from the solar connects, you will need to splice to this when installing the charger.

I mounted the Redarc charger near where the separator was located and crimped and soldered all of the leads together. The only new cable I needed was a 12" piece of #6 wire to connect the ground for the charger to the shunt. The wiring instructions for the Redarc charge are really good and all of the wires are color coded. I mounted the fuse between the charger and batteries next to the charger.

Here is everything done:

I mounted the battery monitor where the Blue Sky solar controller was mounted behind the drivers headrest. I was originally going to use aluminum plate, but I had a piece of oak cabinet toe kick trim that was the perfect size and thickness, and, since I have "oak" cabinets it matches. I used the face plate of the old controller as a template then cut a hole in the middle with a hole saw for the gauge. I took the back out of the shelf that runs over the counter top (2 screws behind snap covers) and took the back out of the cabinet behind the sink (6 screws plus the shelf rails on one side) and was able to run the Cat 5 cable that connects the shunt to the gauge. I used a couple do door shims to create enough space between the paneling and bottom of the cabinet to push the cable up from below the cabinet.
There was a lot of extra Cat 5 cable and for now it is under the seat next to the shunt. I have the tools to cut and splice new ends on Cat 5 but haven't done it in over 10 years so I need to practice a little before cutting it to length.

Total cost about $2500 with approximately 20 hours of time to complete.

To keep the batteries topped up while the van is parked, I keep it plugged into shore power but turn the inverter/charger off once the batteries are fully charged (there is a switch on the inverter to do this). I have a 1.5 amp battery minder/ charge that I plug into the 120 volt outlet behind the drivers seat with it plugged into the 12 volt plug on the dash. The dash plug is always hot so this keeps the start batteries topped. The Redarc charger turns on when the start battery voltage exceeds 13.2 volts so this will also keep a float charge on the house batteries to make up for the parasitic draw from CO detector and furnace / water heater thermostats.

I hope this helps anyone upgrading to lithium batteries on an older SMB. It really wasn't hard and only special tool needed is to crimp the large eyes on the battery cables. I was lucky enough to borrow one from a friend, who also helped me with the welding. My welding skills are only suitable for wheel barrows and and demo-derby cars.

So far we have done one trip with the new batteries and I am very happy with the results. We camped on the Washington coast with almost no solar for 3 nights. The furnace ran the entire time and we did not conserve on running lights on the morning we were leaving we still had 45% remaining in the batteries. It is nice not to have to worry about running the batteries to low and damaging them or trying to guess the charge remaining by voltage which only really works with no load on the batteries.

I am happy to answer any questions.
'08 SMB 4X4 6.0PSD EB 50 (96K)
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Old 02-13-2021, 10:17 AM   #18
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I am still personally troubled w switching to Li for our rig usage. The low temp cut outs are a deal killer. (High temp might be as well but that is far less of a worry)

Last ski season 2019/2020 we were gone for 10 weeks skiing out of the van. The first five to six weeks we never saw an air temp above 30 F. outside the van. The ice build up on the axles, fenders, under the van never melted. The wind chill factors present under the van while of driving had to be near 0 F. Multiple nights we had sub 0 F outside temps. So, Lithium battery placement exposed under the van is not going to work for us, certainly in the winter.

Placement inside the van in the environmentally controlled space would work but it would require using valuable inside space for batteries vs under the van for our currently installed 2 x 175AH AGM's.

Amongst the solutions I have considered are cutting a hole in the floor to create an insulated battery compartment which I could route some heat from the cabin. I would likely go with a single 200Ah SOK Lithium which would give me 160 usable Ah which is comparable to the usable AGM. I would actually gain considerable capacity in winter time usage since the AGM's lose 1% of capacity for every 1 Celsius deg change below 25 C (75F). At 5F (-15 C) the AGM bank capacity is reduced by 40%. The 175 usable Ah drops to 105 for our current AGM setup.

The upside is AGM's are far more tolerant to changes in charging at different temperatures without being compromised. Having Lithium w lots of solar or driving w DCDC chargers are all dependent on having batteries warm enough (or cool enough) to accept the charge.

Just some musings for a Saturday morning. I am interested in how others are solving this low temperature constraint.
Beastie 3: 2002 7.3 EB Cargo: Agile TTB, CCV Mid Top, Custom Walk Through, Lots of stuff added. BlingMyRig.com
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Old 02-13-2021, 10:29 AM   #19
Join Date: May 2017
Posts: 30
Since my batteries are inside the van, the Battle Born batteries with the built-in heater work quite well because I'd never let the interior get real cold while using the van and when it's being stored I can just turn the heaters off. They don't draw much current but if mounted outside the van in constant cold temps like you describe, I wouldn't think they'd be a good option because over time that low current draw from the heaters, which would be on all the time would add up. (According to Battle Born, once the heaters kick in, they don't turn off until the battery temp reaches 45 degrees.)
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Old 02-13-2021, 11:14 AM   #20
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Very interesting thread. I'm in the same boat currently planning a Li upgrade as part of a general overhaul to the van interior (upgrading most/all of the electrical actually). I'm challenged with whether to reuse the battery tray under our E350 RB or move the batteries inside. I'd like to keep them outside because our interior space is quite limited in a RB vs. an EB or Sprinter/Transit, etc. I wasn't excited about Battle Born's heating solution since it draws current from the battery to keep the batteries up to temp at all times and you have to use an on/off switch (I picture myself forgetting to turn this off when not needed). Two alternatives I've found are ReLion and LiFeBlue. They both function by using charge current to first warm up the battery if it is too cold. Once up to temp, the current will charge the battery. Fully automated, heating only when charge is needed. I'm not sure how efficient it is though - you might spend all day with your solar trying to warm up the battery and never actually collect a charge. It definitely seems like a nice feature if you plan to top-up with shore power in colder weather or something similar. LiFeBlue is MUCH cheaper than ReLion and they are releasing their next gen now (website not updated, but I talked to a sales rep who said they're ready to ship). The next gen is actually a few hundred bucks cheaper than what they have on their website and they have a 200 ah version ($1600) that ReLion doesn't. We probably won't do a ton of cold weather camping, and it will probably only be for a weekend when we do. I'd imagine topping up the charge with shore power in Dec-March where it's cold near Salt Lake and driving south to the desert where it'll be a bit warmer. So maybe it's not even worth the extra $ for the LT.

So, what're your thoughts? Anyone have experience with these LT batteries? Am I overthinking this? Just move them inside? Looking forward to your insight and wisdom!

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