Battery Isolators, Separators, Switches & More (updated 2020)

[Scalf77]

Yes, you can it just monitors voltage. You just need to understand that it is reading the voltage at that location, and will be susceptible to voltage drop depending on the wire size and current being drawn. It may flag some unwanted under volts responses. When the vehicle is off, it should still be pretty accurate.

-greg

[posplayr]

Originally Posted by Scalf77

Added a couple of more DC to DC charger options.
Another unit that has some promise is from Renogy the [URL="https://www.renogy.com/dcc50s-12v-50a-dc-dc-on-board-battery-charger-with-mppt/"] Another feature is that solar can be used to trickle charge the starting battery once the house is charged. Add in Renogy BT-2 Bluetooth adapter and you get a unit with some respectable features.



-greg

So I have been going over these threads looking for solutions for LiFePO4 using a DC to DC Charger. Almost all (except the DCC50S) are unidirectional which only provides for alternator charging of the LifePO4 house batteries.

For a bidirectional solution (for Lithium using a DC-DC Charger), unless I missed something the only option that allows Start battery charging is the DCC50S; is that correct?

[Scalf77]

So , the one of the key features listed for the DCC50S is to provide trickle charge feature via solar if the house battery is fully charged to the start battery.
I have never used this unit so I am only going on documentation provided by Renogy. Conceptionally this is not a feature outside of possibilities, as long as they managed to isolate the start battery from the input DCC50S DC to DC converter and have a separate trickle charge device for a standard start battery.

I believe at least one forum member has this unit installed on their rig. I am not a big fan of Renogy products, but found this unit did have some interesting features, that peaked my curiosity, which led me to showcase it in this post.

-greg

[BCam]

Here's a link to Will Prowse's positive review of the DCC50S:

https://www.youtube.com/watch?v=JtAUrS4zNSA

There's a 10% discount coupon code (WillProwse) in the comments, that may or may not work since the video dates to Nov 2019. One limitation he mentions in his summary near the end is that the input voltage limit is low (25V), making connection of panels in series impractical.

[posplayr]

Originally Posted by BCam

One limitation he mentions in his summary near the end is that the input voltage limit is low (25V), making connection of panels in series impractical.

I was pretty excited about this product for a few days till it dawned on me that there was that 25V PV limit .


(probably back in 2017) I had hoped that they would do a design upgrade to increase that PV voltage limit but apparently, they took some shortcuts in this design that precludes removing this obvious limitation.

Basically, you are stuck with paralleling 100Watt panels.

The other thing, I'm not thrilled about is the common grounds for solar, load, and DC to DC charging and the assumption that both battery banks are connected to chassis ground.

Other than that, this is as close to a "plug and play" solution for a lithium solar/charge controller setup as you can get today.

[posplayr]

Originally Posted by Scalf77

So , the one of the key features listed for the DCC50S is to provide trickle charge feature via solar if the house battery is fully charged to the start battery.
I have never used this unit so I am only going on documentation provided by Renogy. Conceptionally this is not a feature outside of possibilities, as long as they managed to isolate the start battery from the input DCC50S DC to DC converter and have a separate trickle charge device for a standard start battery.

I believe at least one forum member has this unit installed on their rig. I am not a big fan of Renogy products, but found this unit did have some interesting features, that peaked my curiosity, which led me to showcase it in this post.

-greg

The thrust of my question is really to confirm that there does not seem to be any bidirectional LiFePO4/LA charging solutions involving DC to DC chargers. For example on Battleborn's website, they recommend this Li-BIM . There is no DC-DC in the mix and they even state that it is an either-or situation.

Connecting Your Battle Born Batteries and Lead-Acid Bank with a Battery Isolator
To ensure battery safety, you need an isolating unit in line between your starting battery and your lithium house bank. You need this unit in line because lithium sits at a higher voltage and requires different charging parameters than lead acid. An isolating unit will disconnect the line between the batteries so that your lithium batteries do not continuously feed power into your starting battery. You can isolate your two battery banks with a battery isolator or a DC to DC charger depending on your system needs and preferences.

I think everybody's "needs and preferences" would be to have bidirectional charging so the underlined statement is simply an evasive way of saying there is no accepted commercially available solution. Even without more details about the DCC50S charging, we can conclude that it is technically feasible but nobody seems to want to address the issue.

I suspect it is partially a liability issue. This industry stance is consistent with another prevalent recommendation to not mix battery chemistries although it has been shown to be beneficial (within certain controlled conditions) to directly connect LiFePO4 and LA in a house battery bank.

https://www.youtube.com/watch?v=tAuPfgZgXec&t=2s

https://www.youtube.com/watch?v=sqT27KbxRec

https://diysolarforum.com/threads/mi...lifepo4.18041/

I don't think Clark invented the concept, but his video has prompted quite a bit of discussion on the subject. For example here is some discussion going back to 2019.

https://community.victronenergy.com/...d-lithium.html


From my analysis of what is being proposed (and I think you have mentioned in the past) that LiFePO4 drop-in replacements are almost compatible with LA charging. But more importantly, LiFePO4 charging is not in any way detrimental or dangerous for LA. This is the case with DC-DC charging which is almost a universally accepted requirement when moving to LiFePO4. Given the typical distance between the vehicle start battery and alternator presents too large of a voltage drop to charge a large bank of LiFEPO4 without having the step up capability of an DC-DC charger.

So if the DC-DC is given and there is no danger of LA abuse with LiFePO4 charging and then there is largely no incompatibility, but there are significant synergies in this mix (as discussed in the videos). The main issue is connecting batteries where there is a Hi SOC/Lo SOC mismatch between LiFePO4 and LA respectively. This also happens to have largely the same set of requirements for House LiFePO4 charging LA Start batteries.

I'm coming to the conclusion that an integrated solution where we can at the least do maintenance charging of the start battery when LiFePO4 bank has sufficient SOC is not only very possible but highly desirable. Further, a parallel connection of LA and LiFePO4 house batteries should be included in the mix. So conceptually this is coordinated management of mixed LA/LiFePO4 house with a LA start batteries.

Sounds perhaps complicated or dangerous or both? Maybe not.

[Scalf77]

Originally Posted by posplayr

I was pretty excited about this product for a few days till it dawned on me that there was that 25V PV limit .


(probably back in 2017) I had hoped that they would do a design upgrade to increase that PV voltage limit but apparently, they took some shortcuts in this design that precludes removing this obvious limitation.

Basically, you are stuck with paralleling 100Watt panels.

The other thing, I'm not thrilled about is the common grounds for solar, load, and DC to DC charging and the assumption that both battery banks are connected to chassis ground.

Other than that, this is as close to a "plug and play" solution for a lithium solar/charge controller setup as you can get today.

All good points, but if you want to look at the other side of the coin.

The 25V PV limit certainly does limit you to parallel connections and "12V" panels technology. But for our vans, limited roof space, camp site shading issues, parallel connections are probably the better way to go. There are also panels well over 100 watts that will work (180,190).

The common ground issue is also pretty standard. For many that are looking to upgrade to lithium and are looking for a DC to DC charger, chances are they would already have a system the grounds are already common.

-greg

[posplayr]

Originally Posted by Scalf77

All good points, but if you want to look at the other side of the coin.

The 25V PV limit certainly does limit you to parallel connections and "12V" panels technology. But for our vans, limited roof space, camp site shading issues, parallel connections are probably the better way to go. There are also panels well over 100 watts that will work (180,190).

-greg

Renogy is certainly marketing the DCC50S to more than just SMB owners. There are many FET's offering with voltage limits at the 100Volts + .

The fact that they have not improved on the PV spec tells me that they took shortcuts in reusing an existing design that had a 25V PV limit. This is unfortunately for something that is at what would otherwise be considered the pinnacle of performance for bidirectional charging.

[BCam]

I know I raised the issue initially, but, from a practical standpoint, is the 25V limit that big a deal, particularly for most Sportsmobiles and vans?

The wire runs are short so I don't see a real need to minimize amp flow, which would be the main benefit of wiring panels in series as opposed to parallel. The DCC50S maxes out at 600W input, which shouldn't be an issue for most Sportsmobiles and vans

[posplayr]

Originally Posted by BCam

I know I raised the issue initially, but, from a practical standpoint, is the 25V limit that big a deal, particularly for most Sportsmobiles and vans?

The wire runs are short so I don't see a real need to minimize amp flow, which would be the main benefit of wiring panels in series as opposed to parallel. The DCC50S maxes out at 600W input, which shouldn't be an issue for most Sportsmobiles and vans

I think there are many factors other than the technical like cost, aesthetics or operational that would dictate which way you might want to go.

For example, I can imagine that a desirable setup (assuming you have any shade to park in) would be to run a combination of panels like a 200W rooftop and a 200W portable. You can then park in the shade and still get 200W standing off in the sun at a distance. Then these would most likely be in a parallel configuration and would work well with the DCC50S. Basically, this is a 200W system because it is either the 200W rooftop or the 200W portable. You might even want to forgo the rooftop mount and just go 400W of usable portable. For the cost of the panels, I could also see just putting it all into a bigger LiFePO4 battery bank and have a reliable DC to DC charging system that will not burn up your battery. For a weekend solar panels might be an unnecessary pain. If you plan to boondock for a week or more, then the solar option could save you from having to run the engine for a DC-DC recharge.

The 12V panels are more expensive than say a residential 300-350W panel but shipping costs are another big factor. For example, Renogy lists a 200W 12V panel for $300 on sale for $250 and shipping is included.

https://www.renogy.com/200-watt-12-v...e-solar-panel/

Here is a Canadian Solar panel for $220 plus $275 is shipping LOL

https://www.ebay.com/itm/37362309069...IAAOSwTrxgWLlS

We have a couple of spare panels for the house so I mounted a 355W for "free" nominally 9A @ 38V so it would not work with the DCC50S.

Having said all that, it makes me cringe to see an array of 12V panels mounted with combiners. The routing of the wires flailing in the wind using glue down zip tie holders.

With a single panel, I cut off the solar connectors in order to pass through the roof using a waterproof 1/2 clamp shell that is low enough in profile so that it all lays underneath the panel. Other than the panel itself, nothing is in any direct sunlight. I then installed new connectors inside the van) that connect to the solar cables that run to the charge controller. So there are no connections on the roof and the only one set inside until you get to the screw terminals at the solar charger controller.

It is worth mentioning that I resigned myself to not have moveable panels in this setup. But I'm in AZ and the overhead sun is very common .
However, with LiFePO4 and the DC-DC charger, I'm more interested in maximizing alternator charge performance which has the potential to almost supplanting solar. Now that I'm moving to LiFePO4, to a large extent, I'm looking a DC-DC charging as a primary method with solar perhaps as secondary for battery bank replenishment.