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Old 08-15-2021, 09:00 PM   #1
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Lithium Conversion – HELP, We’re Taking the Plunge!!

Okay, here’s the deal… We do a fair bit of boondocking with our 2018 Forest River Sunseeker 2400W (Mercedes Sprinter 3500 Chassis) and have been less than impressed with the usable battery power available from our conventional lead acid batts. We upgraded about two years ago to a pair of larger 12v Group 31 Duracell AGMs (210ah total), but even that gives us only 105ah to play with before dipping down below 50% depth of discharge.

So, the time has come… We’re taking the plunge and upgrading to lithium (LiFePO4). Obviously, not everyone NEEDS lithium, and YES they’re EXPENSIVE, but for us and the way we like to use our coach off-the-grid, I think they’ll be worth it. I’m not here to debate all the pros & cons because we’ve already made our decision & passed the point of no return by ordering hardware – to include a single 200ah lithium battery small enough to be a drop-in fit for the entryway battery compartment and an upgraded switchable lithium board (PD4060CSV) for our original Progressive Dynamics PD4060K 60-amp charger converter.

Now, here’s where we need some HELP from those who have gone before us: how did you handle the issue of lithium charging via the stock Mercedes alternator? One of the distinct advantages of lithium batteries is how quickly they can be recharged. However, we understand that’s also a potential disadvantage because they can draw so much amperage from your alternator (100+) that it can overheat and/or burn out, especially if the engine is idling or charging at relatively low rpm … NOT GOOD!

Now, as we all know, Mercedes specifically advises against extended idling of our diesels (for emissions reasons) and we rarely ever do, so I’m thinking perhaps we are at less risk of alternator damage, but I’d prefer not to take any chances. Accordingly, it sounds like we have at least four options:

1) DO NOTHING… Just say a quick prayer and keep on truckin,’ especially if others who have gone before us can attest (and provide meaningful stats) that nothing bad occurred. Of course, doesn’t mean it can’t or won’t happen, but at least it’d be a helpful data point.

2) DISCONNECT the ignition trigger wire from the standard Precision Circuits Battery Isolation Monitor (BIM) in the stairwell, which would thereby preclude the lithium battery from ever being directly charged by the alternator. This was an option described by the lithium experts at Battle Born and, while it certainly limits the risk of alternator damage, it also eliminates a critical source of charging power whenever shore power or generator power is unavailable due to noise or fuel restrictions.

3) MODIFY the standard Precision Circuits BIM by swapping out the existing internal solenoid with a much smarter and lithium-specific solenoid module called the Li-225. This device will basically allow high-amperage charging from the alternator but also LIMIT its duration to a specific duty cycle (about 15 min on, then 20-25 min off), which allows the alternator to cool down and avoid damage.
4) Same as #2, but also somehow INSTALL a dedicated DC-to-DC charger which takes DC power from the alternator-charged chassis battery under the driver’s seat and powers a stand-alone programmable battery charger to directly charge the lithium battery at a much lower & more stabilized amperage level (typically 30-40).

At first glance, I think Option 4 represents the SAFEST solution for best overall alternator protection, but I’m concerned about the relative difficulty of the install, especially if it involves having to run a lot of new electrical wiring. Hopefully, others have gone down this path before and can share. However, at this point, I’m really only interested if their experience is specific to our Class C Sprinter RVs, as many of the other installs I’ve seen were performed on other platforms and lack applicability to our MBS electrical system.

Really anxious to hear from any fellow Class C MBS operators willing to share their lithium upgrade experience, especially with regard to advice/recommendations on the alternator issue, but also eager to learn about any other "extra" system upgrades I might want or need to consider. Let the adventure begin!!
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Old 08-15-2021, 10:28 PM   #2
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I converted my 2012 Solera MBS about a year and a half ago. Documented my conversion on the forum - links in my post #3 in this thread:

https://www.forestriverforums.com/fo...ml#post2503040

I went the dc-to-dc converter route. Mounted the converter on the front wall of the first storage compartment behind the starirs. Disconnected the relay between the house and chassis batteries in the BCC on the left side of the stairs. Also connected to both the house and chassis batteries and picked up the required ignition signal for the converter (by splicing into the ignition signal wire) in the BCC.

Noted that (per the Sprinter forum) Mercedes “upfitters guide” says “maximum 40 amps” to an auxiliary battery. I chose a 20 amp dc-to-dc, which draws (per its spec) up to 50% over its output current (or 30 amps). A 30 amp unit would potentially exceed the reported 40 amp limit.

FYI, Jim
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Old 08-15-2021, 11:06 PM   #3
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Thanks Jim, yes I recall running across your install during my research and it was actually one of the better documented (and more applicable) threads I saw. Good job!

The DC-to-DC charger is my preferred approach (and your comments about sizing are helpful), with the Li-225 BIM Mod my backup plan (don't really like Option 1 or 2 at all, ha!) What I'm hoping you can confirm for me is that you were able to source all the required electrical hookups for the new DC charger right from the BIM (or battery bay), WITHOUT having to run a lot of new cable runs throughout the vehicle.

If I understand what you're saying, most everything we need is already contained within the BIM and we can simply splice into that and run some new leads to wherever is most convenient to locate the new charger. In my case, the 200ah lithium battery I picked is only 19" long and the battery bay is 27.5", so I should have an extra 8" or so to play with right in there. If it won't fit there, I have a similar storage bay to yours that might work. Any chance you can provide a more detailed step-by-step description (or photos) of the electrical side of your mod?

Also, anything else you elected to change back then, or anything you would have done differently based on knowledge gained since the upgrade?
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Old 08-16-2021, 02:16 AM   #4
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My 2012 preceded Forest River’s incorporation of the Precision BIM. My unit uses the Custom Products SDC-107A well detailed by rk06382 ( Robert) in this thread:

https://www.forestriverforums.com/fo...7a-194843.html


I believe the links above show I have converted from my initial Banggood monitor to an AiLi monitor to gain “battery fuel gauge” capability. Had to reset the Banggood between charge and discharge cycles and manually keep track of charge status.

As I’ve also mentioned elsewhere, I would likely choose a different converter were I to do it again. The PD simply drives the 14.6 volts and stays there. Battleborn recommends charging to that level, but then dropping back to ~13.6 volts if leaving the converter connected long term. I believe WFCO now offers a converter that does this stepdown.

All the connections I needed were accessible in the BCC on the side of the stairwell.
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Old 08-16-2021, 09:35 AM   #5
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Roger that, thanks for the update!

Especially glad to hear I'm likely to find all the connections I need to wire up the DC charger right there in the BIM. Think I'll be going with a Victron Tr-Smart DC charger (w Bluetooth) for my install, primarily based on the fact I already have the Victron 500A Smart Shunt (w Bluetooth) - an amazing battery monitor that is fully programmable right from my smart phone and will also be able to communicate with the DC charger.

Yes, I've learned about the shortcomings of my PD charger/converter with the lithium upgrade - that is, continually charging at a steady-state 14.6v. Not sure why they couldn't have somehow designed it to incorporate a tailored lithium charge algorithm (especially for the $200 they're getting). That said, I went with that option because it's supposed to be a pretty easy drop-in replacement (and also retains the ability to switch back to a conventional lead-acid charge profile if/when needed). Most folks say they just flip the breaker to interrupt charging for long term lithium storage (which shouldn't be stored in a topped-off state anyway). Guess that's just another reason why the DC-to-DC charger is the best alternator option, as it can be programmed for whatever charge voltages work best and can fully top off the lithiums for proper cell balancing.

BTW, what type of in-line fuzing did you use on your DC charger? Brand and sizing would be helpful if you can recall?
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Old 08-16-2021, 09:52 AM   #6
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Sorry - don’t recall what fusing I used. Suspect I used a 30 amp glass fuse in a “twist open” inline connector (I usually have a few around the house) - typically from Ace hardware.
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Old 08-16-2021, 10:23 AM   #7
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DC to DC

The Victron dc-to-dc devices may be more efficient than the Renogy. You may be able to stay below Mercedes' 40 amp number with a 30 amp output Victron. I measured 27 amps with 13.6 volts input for 20 amps out with my Renogy. Haven't measured a Victron - their spec sheet looks promising though.
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Old 08-16-2021, 11:01 AM   #8
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Good to know, as my preference right now is to go with their 30 amp unit. Sounds like other folks have gone that route in a desire to get best charging rate and still managed to keep their alternator draw down below 40 amps.

Planning to go with the less expensive and easier to wire "non-isolated" version, which is for applications like ours where the chassis & coach batteries share a single common ground for the negative side. As I understand it, the more costly "isolated" DC chargers are basically for those applications like boats and fiberglass shell RVs where the chassis & coach batteries do NOT share a common ground.

Can you confirm that's how you wired yours?
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Old 08-16-2021, 11:01 AM   #9
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A link to some (speculative) thoughts I posted a while ago about the Mercedes 40 amp limit for auxiliary battery charging:

https://www.forestriverforums.com/fo...it-215973.html

Of note, I haven’t heard of anyone having a problem - and I believe those with a Lithium BIM are likely violating the Mercedes “limit” under some conditions (like low state of house battery charge).
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Old 08-16-2021, 11:07 AM   #10
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Yes, I'd certainly agree those who've made NO changes to their MBS alternator charging system are overtaxing their alternators at some point - especially if the lithium batts have been substantially discharged and are hungry for maximum amperage (I think most lithium BMS units will tolerate as much as a 100+ amp rate for bulk charging).

If they've survived without damage, I'd submit they've just been LUCKY...
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Old 08-16-2021, 11:08 AM   #11
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Quote:
Originally Posted by Iceman from McMurdo View Post
Planning to go with the less expensive and easier to wire "non-isolated" version, which is for applications like ours where the chassis & coach batteries share a single common ground for the negative side.

Can you confirm that's how you wired yours?

Yes, I wired my Renogy with a common ground. It is a “non-isolated” device. Don’t know if Renogy even offers an “isolated” version…
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Old 08-16-2021, 11:16 AM   #12
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Quote:
Originally Posted by Iceman from McMurdo View Post
Yes, I'd certainly agree those who've made NO changes to their MBS alternator charging system are overtaxing their alternators at some point - especially if the lithium batts have been substantially discharged and are hungry for maximum amperage (I think most lithium BMS units will tolerate as much as a 100+ amp rate for bulk charging).

If they've survived without damage, I'd submit they've just been LUCKY...
From what I’ve read on the forum here, I believe Forest River’s lithium option uses the Lithium BIM approach.
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Old 08-16-2021, 12:24 PM   #13
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You've done the converter/charger upgrade. Now all that's left to do is swap out the BIM for the Li BIM-225.

I've got over 30K miles with my setup. It's wonderful to see the SOC climbing on my Victron BVM-712 as I drive to the next campsite.
Do you really need an inverter?
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Old 08-16-2021, 01:17 PM   #14
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Hmmm, TomAR has me curious now about the Li-225 BIM modification vs the DC-to-DC charger. My understanding was it was one OR the other, not both. So, presumably, he's not suggesting both - just saying he chose to go with a lithium mod to the stock charger/converter and do the Li-225 BIM mod instead of adding a DC-to-DC charger. Or, am I missing something??

At any rate, I am curious indeed to hear from those who've gone exclusively with the Li-225 BIM mod to see how it's working out in real life on the MBS platform. I think I'd still be concerned about overtaxing the stock alternator during that 15-min burst of max amperage flow to the lithium battery bank, so would be immensely helpful to know from him (or others) who have monitored exactly how many amps are being sucked out of the alternator when connected thru the Li-225. I bet it's gotta be a LOT...

BTW, when I asked the experts at Battle Born about which option would be better for my specific MBS with a 200ah lithium battery bank, they recommended the DC-to-DC charger route for maximum safety & flexibility. They stated the Li-225 BIM mod was primarily designed for larger battery banks of 300ah or more, although they didn't elaborate as to the rationale.
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Old 08-16-2021, 01:18 PM   #15
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I added a DC-to-DC to my system -
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Old 08-16-2021, 02:07 PM   #16
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I've got a pair of 100Ah BB batteries, fitting into the step well, with the PD Li- converter/charger. No solar, no inverter. Battle Born initially told me I did not need the Li-BIM. That was a mistake; I wasn't getting any charge while driving. We were on the road from PA to Alaska and had to get a Li-BIM shipped to a campground where we were at for more than a few days. Fortunately it fit right in. Was soooo happy to see it charging while driving.
With the Victron, I could look at the charging amperge to the batteries, but I'm doing all the driving. Never seemed to have a problem, but it wouldn't quite charge up to 100% like when on shore power.
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Old 08-16-2021, 02:31 PM   #17
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Thanks robo44, sounding more & more like the DC charger option is the best overall solution, just depends on how difficult the wire-up might be for each of our individual RVs.

Frankly, ease of installation was the driving reason I was initially leaning toward the Li-225 BIM Mod (vice the DC charger), because it looked like a simple solenoid swap-out within the BIM itself with no external wiring changes req'd. However, as I think Tom says, I can essentially tap into those same BIM points and wire up the DC charger.
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Old 08-16-2021, 02:47 PM   #18
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Thanks for chiming in TomAR, appreciate your insight! So, sounds like you just went with the Li-225 and have had no issues charging your 200ah lithiums, correct?

As I understand it, the lithium voltage curve is substantially higher than std lead-acid batteries and that's why our standard BIMs won't allow the alternator to charge a coach battery bank of lithiums at all - it doesn't typically see a low enough voltage to think they NEED any charging. While this means there's minimal risk of alternator damage with the std BIM, it also means you're typically NOT gonna have the option of alternator charging at all... Which is why they invented the Li-225, which uses a smarter processor to figure out the voltage differences and connect when appropriate, and then ONLY for a limited duty-cycle of 15 on and 20 or so off.

If possible, can you please share what kind of amperage flow you observed from the alternator whenever the Li-225 connected? Perhaps it's not as massive as I imagine??
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Old 08-16-2021, 02:49 PM   #19
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I mis-read your initial post. All this charger talk made me read it again.
I swapped out the stock PD charger/converter (PD4060K) to the Li-compatible version (PD4060LICSV); cost me $270. It fits right into the stock 'power center' where all the circuit breakers are.
https://www.progressivedyn.com/lithi...acement-units/

I have not monitored amperage into the batteries while driving, but I'm happy that it charges.

When we first hit the campground and plug into shore power, the PD charger really sucks in the juice. Can't use the microwave or (electric) hot water heater for the first 20-30 minutes because all the shore juice is going into the batteries.
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Old 08-16-2021, 02:50 PM   #20
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Quote:
Originally Posted by Iceman from McMurdo View Post
Hmmm, TomAR has me curious now about the Li-225 BIM modification vs the DC-to-DC charger. My understanding was it was one OR the other, not both. So, presumably, he's not suggesting both - just saying he chose to go with a lithium mod to the stock charger/converter and do the Li-225 BIM mod instead of adding a DC-to-DC charger. Or, am I missing something??

At any rate, I am curious indeed to hear from those who've gone exclusively with the Li-225 BIM mod to see how it's working out in real life on the MBS platform. I think I'd still be concerned about overtaxing the stock alternator during that 15-min burst of max amperage flow to the lithium battery bank, so would be immensely helpful to know from him (or others) who have monitored exactly how many amps are being sucked out of the alternator when connected thru the Li-225. I bet it's gotta be a LOT...

BTW, when I asked the experts at Battle Born about which option would be better for my specific MBS with a 200ah lithium battery bank, they recommended the DC-to-DC charger route for maximum safety & flexibility. They stated the Li-225 BIM mod was primarily designed for larger battery banks of 300ah or more, although they didn't elaborate as to the rationale.


I think you need to do more research on the Forum on this subject as there is a ton of info by all of us who have gone the 2X Battle Born 100AH, the Progressive Dynamics PD4060 LICSV Converter and the LI-BIM 225 Battery Isolation Manager. After running the system for over 3 years I have had no problems and it charges very fast off the Alternator, the Generator, Shore Power and Solar. I have run extensive tests monitoring all Current with my Victron-712 and don't ever remember seeing over 65 Amps going into the Batteries from the Alternator even when the batteries were discharged down to under 50% SOC. Further with the Chassis Running, the LI-BIM has a timer circuit on for 15 minutes and off for 20 minutes, then retests and repeats as necessary.

I have had no problems with my system and believe the key is being able to monitor all current flow and battery conditions at any given moment.
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