A summary

[AJMike]

Having spent the last week asking questions on this forum and the last couple of days speaking with techs at some of the hardware companies that are involved I thought I would summarize what I (think I) have learned. If any of this is incorrect please post and tell me so. This is all about using Lithium batteries in our Winnie Fuse.

1) In a discussion with Battle Born about alternators and Lithium batteries I was told that high output alternators (like the one in our Fuse which is rated at 210 amps) need to be protected when using Lithium batteries; the batteries themselves do not need to be protected as they can handle input as high as 100 amps each battery and have their own monitoring system, but the alternators will output so much current that they themselves can be damaged and reverse spikes can also damage them. BB recommends a DC-DC charger to protect them. They sell a Sterling 60 amp (about $400) but Renogy makes 20 amp, 40 amp and 60 amp alternatives for less money. I have no information about how good the different units are but in one of RV-ing with Tito videos Tito spoke highly of the Renogy model.

In any case I believe that the DC-DC charger is basically an inverter/transformer of sorts that provides a steady output voltage for charging the batteries and protects the alternator from any spikes on the line. It was not clear where voltage spikes might come from since the source would be the battery and associated wiring.

2) In the same discussion with BB that I mentioned above I was also told that low output alternators also needed protection when charging Lithium batteries, although the reason seemed a bit vague. In any case I was told that if the alternator output was low it should be protected by a battery isolator instead of a DC-DC charger.

My understanding is that BIM does its work by switching the alternator-to-battery circuit on and off at regular intervals so that the alternator is not connected to the batteries for any extended period of time.

3) Choice of a DC-DC charger also determines recharge time of the batteries when charged from the alternator since the output from different models varies. A 60 amp charger will recharge faster than a 40 am charger which, in turn, will charge faster than a 30 amp charger, but the batteries themselves don't care and are happy to charge at any rate up to 100AH or down to almost 0AH.

4) I checking about the inverter/charger I exchanged emails with Progressive Dynamics who made the PD9245C in the Fuse. The tech was very clear that the unit we had would charge Lithium batteries without any issue as it was, but since its output was normally limited to 13.6 volts (or so) it would not fully charge them.

He offered 2 solutions. One was the addition of a remote device that would allow the user to temporarily set the output voltage to 14.4 volts manually for about 4 hours and then would automatically revert to 13.6 volts. The second was to replace the unit with one specifically designed for Lithium batteries. This means that I could use the existing charge controller to fully charge any Lithium batteries if I was willing to push the remote button when either starting the generator or hooking up to shore power, or ignore it if I was willing to live with a charge of only 13.6 volts.

I still have some questions:

a) How do the various models of DC-DC chargers compare? Is the Sterling model better than the Renogy? Or are all relatively the same quality?

b) If the PD9245C is charging Lithium batteries at 14.4 volts, either using shore power or the generator, and then switches back to 13.6 volts at the end of the 4 hours, will that degrade the voltage in the Lithium batteries? Or will it remain at 14.4 volts? I assume the inverter/charger is one-way but I don't really know.

c) Adding 2 100AH Lithium batteries would allow the use of a larger inverter than the 1000 watt unit in the Fuse. Has anyone added a 2000 watt inverter? And if so how do the BB (or other) Lithium batteries handle it?

d) The fact that a conversion would not automatically require a new inverter/charger means that the cost of a Lithium installation is about $500-$600 lower than the estimate that was given to me. The fact that there are less expensive DC-DC chargers further reduces the price by about $150-$200 and the fact that the BB batteries are on sale (and lower cost than some of the Chinese batteries) saves another nice piece of change.

All that together means that it may be practical for me to go to Lithium after all. The initial total conversion estimate of > $3500 made me decide to go back to my initial idea of larger and heavier AGMs, but this has reduced the price to the mid $2000 range so perhaps it is possible. Over my budget, but not by all that much. Of course I would probably add the Lithium inverter/charger next year but that is a different budget.

I would appreciate any corrections and suggestions. I knew nothing about all of this before I started posting questions and all of the answers, which sometimes were very different, helped me learn as well as know what questions to ask when I called places like BB and Progressive Dynamics.

Thanks for all of the help.

[DavidM]

You made a very good summary of your findings so far. I am no LPO expert but have lived with FLAs extensively as liveaboard boater. I am also a pretty smart (my say so) engineer. See comments in bold below:

Originally Posted by AJMike

Having spent the last week asking questions on this forum and the last couple of days speaking with techs at some of the hardware companies that are involved I thought I would summarize what I (think I) have learned. If any of this is incorrect please post and tell me so. This is all about using Lithium batteries in our Winnie Fuse.

1) In a discussion with Battle Born about alternators and Lithium batteries I was told that high output alternators (like the one in our Fuse which is rated at 210 amps) need to be protected when using Lithium batteries; the batteries themselves do not need to be protected as they can handle input as high as 100 amps each battery and have their own monitoring system, but the alternators will output so much current that they themselves can be damaged and reverse spikes can also damage them. BB recommends a DC-DC charger to protect them. They sell a Sterling 60 amp (about $400) but Renogy makes 20 amp, 40 amp and 60 amp alternatives for less money. I have no information about how good the different units are but in one of RV-ing with Tito videos Tito spoke highly of the Renogy model.

In any case I believe that the DC-DC charger is basically an inverter/transformer of sorts that provides a steady output voltage for charging the batteries and protects the alternator from any spikes on the line. It was not clear where voltage spikes might come from since the source would be the battery and associated wiring.

Your understanding of a B2B charger is correct. I think the reason for a B2B charger is to force the chassis alternator into thinking it is serving a low voltage load like a discharged FLA battery and it converts that low voltage input to a higher voltage output which the batteries require. It also limits current from the battery to keep from putting too much load on it.

2) In the same discussion with BB that I mentioned above I was also told that low output alternators also needed protection when charging Lithium batteries, although the reason seemed a bit vague. In any case I was told that if the alternator output was low it should be protected by a battery isolator instead of a DC-DC charger.

Probably to limit the load on the low output alternator so they don't burn out.

My understanding is that BIM does its work by switching the alternator-to-battery circuit on and off at regular intervals so that the alternator is not connected to the batteries for any extended period of timeha

What is a BIM? I understand what a BMS is but a BIM, no.

3) Choice of a DC-DC charger also determines recharge time of the batteries when charged from the alternator since the output from different models varies. A 60 amp charger will recharge faster than a 40 am charger which, in turn, will charge faster than a 30 amp charger, but the batteries themselves don't care and are happy to charge at any rate up to 100AH or down to almost 0AH.

True but doesn't Mercedes recommend not pulling more than 40A continuously from the chassis alternator for an external load?

4) I checking about the inverter/charger I exchanged emails with Progressive Dynamics who made the PD9245C in the Fuse. The tech was very clear that the unit we had would charge Lithium batteries without any issue as it was, but since its output was normally limited to 13.6 volts (or so) it would not fully charge them.

He offered 2 solutions. One was the addition of a remote device that would allow the user to temporarily set the output voltage to 14.4 volts manually for about 4 hours and then would automatically revert to 13.6 volts. The second was to replace the unit with one specifically designed for Lithium batteries. This means that I could use the existing charge controller to fully charge any Lithium batteries if I was willing to push the remote button when either starting the generator or hooking up to shore power, or ignore it if I was willing to live with a charge of only 13.6 volts.

I followed the thread on what voltage to charge LPO batteries at but came away totally confused by the conflicting information. I think a larger charger (and wiring) would be helpful to limit generator running time and if you have to buy a new converter then by the Li capable one.

I still have some questions:

a) How do the various models of DC-DC chargers compare? Is the Sterling model better than the Renogy? Or are all relatively the same quality?

I have some experience with most of them:

Sterling is a fairly new entrant into the DC electronics field, but so is everyone. I don't particularly like their website which only talks in platitudes, not facts

Renogy is also a newcomer and is loved by Amazon apparently. I do like the straightforward approach of their website and got a quick response from a technical inquiry.

Redarc is another, Australian firm that has a US office that responded quickly to my inquiry. Their B2B with two inputs combines an MPPT solar controller with a chassis aternator charger in one device.

Victron is a very competent supplier of DC electronics and would bet my RV on their performance.

b) If the PD9245C is charging Lithium batteries at 14.4 volts, either using shore power or the generator, and then switches back to 13.6 volts at the end of the 4 hours, will that degrade the voltage in the Lithium batteries? Or will it remain at 14.4 volts? I assume the inverter/charger is one-way but I don't really know.

Yes there is effectively a diode in the circuit that makes it one way.

c) Adding 2 100AH Lithium batteries would allow the use of a larger inverter than the 1000 watt unit in the Fuse. Has anyone added a 2000 watt inverter? And if so how do the BB (or other) Lithium batteries handle it?

They should handle it fine. Two Battle Borns can supply up to 200 amps.

d) The fact that a conversion would not automatically require a new inverter/charger means that the cost of a Lithium installation is about $500-$600 lower than the estimate that was given to me. The fact that there are less expensive DC-DC chargers further reduces the price by about $150-$200 and the fact that the BB batteries are on sale (and lower cost than some of the Chinese batteries) saves another nice piece of change.

A small nit. The PD converter is not an inverter/charger, it is only a charger. Most RVs use separate chargers and inverters.

All that together means that it may be practical for me to go to Lithium after all. The initial total conversion estimate of > $3500 made me decide to go back to my initial idea of larger and heavier AGMs, but this has reduced the price to the mid $2000 range so perhaps it is possible. Over my budget, but not by all that much. Of course I would probably add the Lithium inverter/charger next year but that is a different budget.

I would appreciate any corrections and suggestions. I knew nothing about all of this before I started posting questions and all of the answers, which sometimes were very different, helped me learn as well as know what questions to ask when I called places like BB and Progressive Dynamics.

Thanks for all of the help.

[Winterbagoal]

I guess it depends on who you ask?

https://www.youtube.com/watch?v=Kl_sLR1S6Mw

[powercat_ras]

One thing to consider is that the rate of recharge starts to drop gradually once the batteries reach 90% charged, you may find that it takes a good while to get that last 10% of charge into the batteries, in particular that last 5%.

> If the PD9245C is charging Lithium batteries at 14.4 volts by adding the remote panel and manually triggering it for 4 hours, after 4 hours will the lower voltage degrade the batteries?

No. For a short the batteries will be supplying all 12 volt loads, but when a Lithium battery comes off the charger and is supplying load, its voltage rapidly drops from 14 volts to 13.4 volts as the first few percent of stored power is delivered.

So, once your OEM 9245C converter/charger drops out of the manual 14 volt bulk charge mode, in a short time any load on the 12 volt system will be provided by the 9245C at which point the Lithiums will still be over 95 % charged.

[AJMike]

Originally Posted by DavidM

You made a very good summary of your findings so far. I am no LPO expert but have lived with FLAs extensively as liveaboard boater. I am also a pretty smart (my say so) engineer. See comments in bold below:

> What is a BIM? I understand what a BMS is but a BIM, no.

Battery Isolation Manager. See here.

> True but doesn't Mercedes recommend not pulling more than 40A continuously from the chassis alternator for an external load?

The Fuse is mounted on a Ford Transit 350 HD Chassis, not a MB, but perhaps there is a similar restriction. In any case the BB tech told me that he thought that the "sweet spot" (his term) for charging was about 40-45 amps so I would probably want to stay in that range.

And thanks for the DC-DC charger recommendations. I don't want to spend any more than I have to, but I also don't want to end up buying junk.

> A small nit. The PD converter is not an inverter/charger, it is only a charger. Most RVs use separate chargers and inverters.

Thank you for the correction. The tech kept talking about inverter/chargers and it was not something I was familiar with, so that is helpful.

[powercat_ras]

One solution you could consider to keep the power drawn from your OEM alternator limited to less than 40 amps being used to recharge your lithium coach batteries would be to connect an inverter to your chassis 12 volt system and use it to drive a PD9130LV (30 amp output converter designed for Lithium). This would limit draw on the chassis 12 volt system to about 33 amps when the Lithiums were charging to 90%, then the amps would drop from 33 towards 0 as charge increased from 90% to 100%.

You could use an inexpensive modified sine wave 1,000 watt inverter. The PD9130LV is an electronic converter and will work fine with a MSW 120 volt input.

[AJMike]

Originally Posted by powercat_ras

One thing to consider is that the rate of recharge starts to drop gradually once the batteries reach 90% charged, you may find that it takes a good while to get that last 10% of charge into the batteries, in particular that last 5%.

> If the PD9245C is charging Lithium batteries at 14.4 volts by adding the remote panel and manually triggering it for 4 hours, after 4 hours will the lower voltage degrade the batteries?

No. For a short the batteries will be supplying all 12 volt loads, but when a Lithium battery comes off the charger and is supplying load, its voltage rapidly drops from 14 volts to 13.4 volts as the first few percent of stored power is delivered.

So, once your OEM 9245C converter/charger drops out of the manual 14 volt bulk charge mode, in a short time any load on the 12 volt system will be provided by the 9245C at which point the Lithiums will still be over 95 % charged.

Well, that is good news. It was pretty much the only thing (other than the cost ) that I was concerned about.

I would expect to upgrade to the Lithium charger in a year or so. I can handle the initial cost now and the later cost later. I just did not want to spend all of that right now. And I think I can live with 95% charge on 200AH of battery power.

One question that has bothered me about charging any battery in an RV. There are potentially multiple charges being applied at the same time - solar and alternator when driving, solar and generator or solar and shore power when camped. Do they all get applied to the battery at the same time? Or is there an order of precedence so that only one source is used to charge?

Not really important, but I am a curious guy.

[AJMike]

Originally Posted by Winterbagoal

I guess it depends on who you ask?

Not much information. What is a "high quality" alternator?

In this odyssey of the last week or so I called Relion among others. They referred me to a sales guy who I also spoke with, but the answers he gave me were very different from the FAQ listing on their webpage, so I don't know what is right.

The issue here is that most places tell me I need a DC-DC charger but some say I don't need anything (as in the video) if I have a good quality alternator. Since almost all newer RVs would seem to have good quality alternators I just don't know what is true.

When a place tells me I need a charger I end up wondering if I really do need one or if they are trying to sell me an additional piece of equipment. On the other hand if I destroy an alternator the cost of replacing it is going to come out of my pocket so perhaps it is best to be safe rather than sorry.

In the end I just don't know which path is best on my own so I ask question here and generally get great information. While I am still very ignorant about all of this I am much more informed than I was last week, and most of that is from the responses to my questions.

[AJMike]

Originally Posted by powercat_ras

One solution you could consider to keep the power drawn from your OEM alternator limited to less than 40 amps being used to recharge your lithium coach batteries would be to connect an inverter to your chassis 12 volt system and use it to drive a PD9130LV (30 amp output converter designed for Lithium). This would limit draw on the chassis 12 volt system to about 33 amps when the Lithiums were charging to 90%, then the amps would drop from 33 towards 0 as charge increased from 90% to 100%.

You could use an inexpensive modified sine wave 1,000 watt inverter. The PD9130LV is an electronic converter and will work fine with a MSW 120 volt input.

Thanks for the suggestion. Presumably the same converter could be used to replace the current 9245C for the shore power. I need to look up the cost of the inverter as well and see if that would be a better solution than a 40 amp DC-DC charger.

[DavidM]

I think that you will find that the difficulty in wiring an inverter powered from the chassis alternator to power the converter outweighs the costs of a dedicated B2B charger. A Renogy 40A B2B charger costs about $200.

David

[Winterbagoal]

Originally Posted by AJMike

Not much information. What is a "high quality" alternator?

In this odyssey of the last week or so I called Relion among others. They referred me to a sales guy who I also spoke with, but the answers he gave me were very different from the FAQ listing on their webpage, so I don't know what is right.

The issue here is that most places tell me I need a DC-DC charger but some say I don't need anything (as in the video) if I have a good quality alternator. Since almost all newer RVs would seem to have good quality alternators I just don't know what is true.

When a place tells me I need a charger I end up wondering if I really do need one or if they are trying to sell me an additional piece of equipment. On the other hand if I destroy an alternator the cost of replacing it is going to come out of my pocket so perhaps it is best to be safe rather than sorry.

In the end I just don't know which path is best on my own so I ask question here and generally get great information. While I am still very ignorant about all of this I am much more informed than I was last week, and most of that is from the responses to my questions.

Yes, most newer vehicles are probably outfitted with "high quality" alternators from the factory. With all sorts of regulators and safeguards on them for just this sort of thing. Relion doesn't seem to think there's a problem.

If a vendor stocks something, they must see a demand for it. Like a DC to DC charger? The question is, who created the demand for them? The vendors selling the products, or the people that have blown up their alternators with lithium?
I have yet to read about someone "destroying their alternator" by adding lithium batteries to the battery bank group being charged by it. I googled the heck out of it, and only got numerous recommendations from websites and vendors on how to avoid it, not that someone actually lost an alternator to lithium charging. The problem seems to be characterized as a sudden disconnection of the lithium batteries causing the alternator to suddenly have no where to send the charging current, resulting in a fatal voltage spike. Most lithium batteries have a cutoff that's much higher than what the average alternator can produce at full load in actual real time use. Or, alternately, that the lithium batteries are so far drained that the demand for current/voltage will overwhelm the alternator's ability to produce it, however most lithium batteries have a charge current curve that tapers to accept/demand lower voltage/current as it approaches full. Like most batteries. I'm speculating that in either case, if the chassis battery is still connected in the mix, and accepting charge, it should handle this extra current/voltage drop or spike, until the alternator's voltage regulation system lowers or raises the output to match the perceived battery charging demand. Kind of like a cooling system overflow reservoir? Maybe bad analogy, I can't think of a better one at the mo.
The final decision is still yours. I'm just playing Devil's Advocate here. I'm not a lithium/alternator charging expert, nor am I an electrical engineer. I'm just trying to learn, like you, and am applying some basic logic to what I've learned to date.
I'll still keep an eye on your off grid solution quest, and will let you know the moment my alternator fails. I hope that will be quite a long time from now.

[AJMike]

Originally Posted by Winterbagoal

Yes, most newer vehicles are probably outfitted with "high quality" alternators from the factory. With all sorts of regulators and safeguards on them for just this sort of thing. Relion doesn't seem to think there's a problem.

Just to add some confusion to the mix -

One of the local shops that BB recommended to do the install send me an estimate for all the work. Part of that was the installation of something they called a BIM - battery isolation manager - which seems to be this item:

https://battlebornbatteries.com/shop...ation-manager/

The item number (BIM-225) matches the number on the BB page and this shop is a BB recommended installer, so I am pretty sure this is the item.

The shop says that they will install anything I want, from any manufacturer, but that they have been installing this for a very long time as part of their lithium battery upgrades and have never (they were very clear they meant never) had a customer report an issue.

The thing is that this item is about $180 and the shop, which charges for pretty much everything they do, does not charge for the installation of this BIM which implies to me that it takes no real work. The DC-DC charger costs $400 and the installation estimate for it was 2 hours.

Given all of that I have to ask if the DC-DC charger is recommended because it is better or because it generates more profit. I don't know. Theoretically I would think the charger is better because it serves both to provide a steady constant current and isolates the alternator from spikes while the BIM only connects and disconnects the alternator from the battery at set time intervals. Surely the DC-DC charger is better from an engineering point of view, but is it really better from a practical point of view.

If no one has ever complained about issues with the less expensive model then I assume it does what it was designed to do, and at lower cost. Of course there is also the issue of how long the alternator will take to fully charge the batteries - the BIM switches on and off, 15 minutes on and 20 minutes off so the batteries are only getting charged about 43% of the time - but I am not sure that it matters much during a 5 or 6 hour drive.

[AJMike]

Originally Posted by Winterbagoal

Most lithium batteries have a cutoff that's much higher than what the average alternator can produce at full load in actual real time use.

Among the many things I do not know is what the average alternator output is, but the one in my Fuse can output 210 amps. Unless I misunderstood (which is always possible) the BB tech mentioned 100 amps as the high figure for what the battery could accept. Assuming that there is only one Lithium battery in the circuit that would seem to be more than it can accept. If the batteries are wired in parallel and if the current is split evenly between them it is still slightly higher than the batteries can accept.

Given that I suppose it is possible that the battery might cut out of the circuit while the alternator is running.

Still, that assumes a lot of "if"s.

[Winterbagoal]

Your modern, high quality, alternator is rated at 210A at 6,000 rpms (standard output rating?). It won't typically put out anywhere near that. The built in VR (voltage regulator) and the ambient temperature (temperature sensing?) under the hood will reduce the output accordingly. Also, it will only put out as much power as the VR will safely allow, or that the load demands, below that limit.
The prior comments are based on my opinions and experiences, and all my prior qualification caveats are still in effect.
Go with the DC to DC charger if it's in the budget. You'll sleep better.
I would go with the Renogy 40A model.

p.s. Speaking of muddying the waters, the battery shop that has "never had a customer reported problem" may have such a good record because they're installing a largely unnecessary piece of hardware. The B2B (DC to DC) chargers may just be placebos devised to sell hardware, as you've suggested once or twice. Wouldn't be the first time. I will again admit, I don't know. Just my opinion. I hope they're like insurance policies. If you spend the money and get one, and it never gets used, is that a good thing, or bad?
How much is a new alternator, installed?

[AJMike]

Originally Posted by Winterbagoal

p.s. Speaking of muddying the waters, the battery shop that has "never had a customer reported problem" may have such a good record because they're installing a largely unnecessary piece of hardware.

Yes. That is the basic question, isn't it.

Originally Posted by Winterbagoal

Go with the DC to DC charger if it's in the budget. You'll sleep better.

I assume there is also the question of whether or not the lithium batteries ever get fully charged. The alternator output is 13.6 volts or so, so it can not fully charge lithium batteries to 14.4 volts no matter how many amps it puts out. Presumably the DC-DC charger ups the voltage to 14.4 volts and fully charges the lithium batteries.

And a good night's sleep is not a bad thing ...

Originally Posted by Winterbagoal

If you spend the money and get one, and it never gets used, is that a good thing, or bad?

In my view that would be a very good thing.

[DavidM]

My understanding is that the Sprinter alternator is "smart" in that it is controlled by a sophisticated algorithm that is configured for the OEM chassis battery. It raises the voltage when it senses that the alternator is significantly discharged and then drops off towards 12.7 when it senses a full charge. It is measuring amperage, voltage and time to process its algorithm.

But that algorithm probably isn't right to fully charge a LPO battery. The B2B if installed presents a low voltage, high amperage load to the alternator's CPU and "fools" it into producing more amps and the B2B converts that low voltage to the high voltage that the LPO battery needs as well as limits current to the B2B's rating. A 40A rating would be best because that matches Mercedes recommendation.

Maybe the smart alternator is smart enough to sense an LPO in the circuit, but I doubt it. The B2B deals with this as well as protects against too much current. The Renogy 40A is only $200 and I believe it is a good investment to get the most out of your LPO batteries as well as protect the alternator. BTW a Bosch alternator for a Mercedes sedan is about $1,000.

David

[Winterbagoal]

Originally Posted by AJMike

Yes. That is the basic question, isn't it.



I assume there is also the question of whether or not the lithium batteries ever get fully charged. The alternator output is 13.6 volts or so, so it can not fully charge lithium batteries to 14.4 volts no matter how many amps it puts out. Presumably the DC-DC charger ups the voltage to 14.4 volts and fully charges the lithium batteries.

And a good night's sleep is not a bad thing ...



In my view that would be a very good thing.

re: "I assume there is also the question of whether or not the lithium batteries ever get fully charged."
Aha!!! That's where the Zamp solar panels (which you also have) and ZS-30A CC come into the picture. While they aren't guaranteed to always "finish the job" in all weather conditions, a little bit of sun, and setting it to the proper charging algorithm (either Lithium or AGM, as they're the same) will complete the charging process to FUL on that Zamp CC display. I'm at 32F and sunny here in Ontario, Canada, and my batteries are fully charged by the combintion of shore power/PD9245C and the sun's rays coursing thru my solar setup. I just checked them a few minutes ago.

[AJMike]

Originally Posted by Winterbagoal

re: "I assume there is also the question of whether or not the lithium batteries ever get fully charged."
Aha!!! That's where the Zamp solar panels (which you also have) and ZS-30A CC come into the picture.

That touches on a basic question of mine. Assuming that I am driving and have a DC-DC controller, there is charging input from both the alternator and the solar panels. Do both charge simultaneously? Or is only one charge input allowed? And, if so, how is that determined?

Same question about running the generator when camped. Two inputs - generator (or shore power) and solar? Do both charge simultaneously?

I don't know or I would not ask, but I would assume that there is only one charging input at any time and I would have assume that was the higher voltage. If the alternator charges at 13.7 volts and the solar at 14.4, then my assumption would imply that only the solar power gets applied, but that would not be good as the alternator can put a lot more power into the batteries for any given time.

[AJMike]

Originally Posted by DavidM

My understanding is that the Sprinter alternator is "smart" in that it is controlled by a sophisticated algorithm that is configured for the OEM chassis battery. It raises the voltage when it senses that the alternator is significantly discharged and then drops off towards 12.7 when it senses a full charge. It is measuring amperage, voltage and time to process its algorithm.

But that algorithm probably isn't right to fully charge a LPO battery. The B2B if installed presents a low voltage, high amperage load to the alternator's CPU and "fools" it into producing more amps and the B2B converts that low voltage to the high voltage that the LPO battery needs as well as limits current to the B2B's rating. A 40A rating would be best because that matches Mercedes recommendation.

Maybe the smart alternator is smart enough to sense an LPO in the circuit, but I doubt it. The B2B deals with this as well as protects against too much current. The Renogy 40A is only $200 and I believe it is a good investment to get the most out of your LPO batteries as well as protect the alternator. BTW a Bosch alternator for a Mercedes sedan is about $1,000.

David

Our RV is on a Ford chassis but I assume what you wrote about the MB alternator applies to the Ford as well.

I am going to order a DC-DC charger today. The only question is which one. As you mentioned the Renogy is only $200 and is my default choice but Victron also makes chargers and I was going to check with them (if I can find a local number to call. Their webpage does not seem to have a US support number).

Their webpage contains a lot of DC-DC chargers (or converters as they call them) but I have no idea what the difference between "isolated" and "non-isolated" converters is and so no idea which would apply in my case. As much as I have learned this last week or so from posted question and answers and calls to the product techs I clearly still don't know very much.

[Winterbagoal]

Originally Posted by AJMike

That touches on a basic question of mine. Assuming that I am driving and have a DC-DC controller, there is charging input from both the alternator and the solar panels. Do both charge simultaneously? Or is only one charge input allowed? And, if so, how is that determined?

Same question about running the generator when camped. Two inputs - generator (or shore power) and solar? Do both charge simultaneously?

I don't know or I would not ask, but I would assume that there is only one charging input at any time and I would have assume that was the higher voltage. If the alternator charges at 13.7 volts and the solar at 14.4, then my assumption would imply that only the solar power gets applied, but that would not be good as the alternator can put a lot more power into the batteries for any given time.

Depends on the state of charge of the batteries at the other end of the charging sources. They will all charge, or not, based on their individual ability to test and determine the SoC of the battery bank. If they sense a need for more current, they'll send it. If they detect the batteries are full, they won't. It's not an issue or a problem that you need to worry about.