LiFePO4 Batteries, Alternator, Li-BIM-225 and DC-to-DC Charging Question

JohnGarziglia

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I have a question on alternator charging of LiFePO4 batteries which hopefully does not plow through ground already discussed in other posts. Apologies for the length of the question but I wanted to give adequate details.

The alternator in the OEM setup in my motorhome is connected to the house lead acid batteries through a merge solenoid which is controlled by Spyder electronics allowing for: (1) the alternator to charge the house batteries once the chassis batteries are full; (2) allowing for a shore connection or the generator to charge the chassis batteries once the house batteries are full; and (3) bridging the house and chassis batteries together to allow for an emergency start of either the engine or the generator. For the exact specs of this OEM setup, see: https://liferebooted.net/2018-phaeton-40ih/Spyder-Battery-Merge-Spec.pdf.

Here is the setup I am contemplating. I intend to install LiFePO4 batteries in place of the OEM lead acid house batteries. In order to keep from burning out the alternator, I will install a Precision Circuits, Inc. Li-BIM 225 (https://www.precisioncircuitsinc.com/wp-content/uploads/2019/10/00-10041-26x-Li-BIM-Rev1.pdf) in accord with its specifications in place of the merge solenoid. The Spyder controls of the merge solenoid described in the link in the above paragraph will be decommissioned. Instead the dash switch for manually connecting the batteries together in an emergency start situation, which previously went through the Spyder controls, will go directly to the appropriate connections on the Li-BIM 225 along with a 12 volts ignition connection.

But, as the literature for the Li-BIM 225 states, the alternator connected through the Li-BIM 225 will not fully charge the LiFePO4 house batteries. In addition, due to the cycling characteristics of the Li-BIM 225, it will charge the house batteries for only a portion of a drive, disconnecting the charge to keep the alternator from overheating.

Is there any reason why I could also not install two 30-amp DC-to-DC chargers between the alternator and the LiFePO4 house batteries to allow the alternator to continue charging the house batteries at a lower current when the Li-BIM-225 disconnects? This would allow for a fast charging of the LiFePO4 batteries with a high current (the motorhome has a 250-amp alternator) for an initial time period, and then when the Li-BIM 225 disconnects the alternator from the LiFePO4 house batteries keeping the alternator from overheating, the charging of the LiFePO4 house batteries would continue at no more than 60 amps through the DC-to-DC charger.

I have not seen anyone else use both a Li-BIM 225 battery isolation manager, and DC-to-DC chargers, with an alternator. Is there any reason this setup should not work – am I missing something? Any observations and advice are much appreciated.
 

Zwy

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I have a question on alternator charging of LiFePO4 batteries which hopefully does not plow through ground already discussed in other posts. Apologies for the length of the question but I wanted to give adequate details.

The alternator in the OEM setup in my motorhome is connected to the house lead acid batteries through a merge solenoid which is controlled by Spyder electronics allowing for: (1) the alternator to charge the house batteries once the chassis batteries are full; (2) allowing for a shore connection or the generator to charge the chassis batteries once the house batteries are full; and (3) bridging the house and chassis batteries together to allow for an emergency start of either the engine or the generator. For the exact specs of this OEM setup, see: https://liferebooted.net/2018-phaeton-40ih/Spyder-Battery-Merge-Spec.pdf.

Here is the setup I am contemplating. I intend to install LiFePO4 batteries in place of the OEM lead acid house batteries. In order to keep from burning out the alternator, I will install a Precision Circuits, Inc. Li-BIM 225 (https://www.precisioncircuitsinc.com/wp-content/uploads/2019/10/00-10041-26x-Li-BIM-Rev1.pdf) in accord with its specifications in place of the merge solenoid. The Spyder controls of the merge solenoid described in the link in the above paragraph will be decommissioned. Instead the dash switch for manually connecting the batteries together in an emergency start situation, which previously went through the Spyder controls, will go directly to the appropriate connections on the Li-BIM 225 along with a 12 volts ignition connection.

But, as the literature for the Li-BIM 225 states, the alternator connected through the Li-BIM 225 will not fully charge the LiFePO4 house batteries. In addition, due to the cycling characteristics of the Li-BIM 225, it will charge the house batteries for only a portion of a drive, disconnecting the charge to keep the alternator from overheating.

Is there any reason why I could also not install two 30-amp DC-to-DC chargers between the alternator and the LiFePO4 house batteries to allow the alternator to continue charging the house batteries at a lower current when the Li-BIM-225 disconnects? This would allow for a fast charging of the LiFePO4 batteries with a high current (the motorhome has a 250-amp alternator) for an initial time period, and then when the Li-BIM 225 disconnects the alternator from the LiFePO4 house batteries keeping the alternator from overheating, the charging of the LiFePO4 house batteries would continue at no more than 60 amps through the DC-to-DC charger.

I have not seen anyone else use both a Li-BIM 225 battery isolation manager, and DC-to-DC chargers, with an alternator. Is there any reason this setup should not work – am I missing something? Any observations and advice are much appreciated.
I'd forget the Li-BIM and just use a DC to DC charger that has isolation. You could leave the Spyder in place, you just wouldn't be able to charge the chassis battery off the house battery due to isolation of the DC to DC. All you really need is an isolated DC to DC and install it between the Spyder and the house batteries. You will have to determine the safe charge current setting for the DC to DC based upon the alternator rated output and duty cycle.
 

JohnGarziglia

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Using just the DC-to-DC charger has the flaw of not allowing my solar panels to charge the chassis battery when needed. It removes one of the functionalities of the battery and solar panel setup in the motorhome that I desire to keep. The other functionality it removes is the use of the dashboard "Aux Start" switch which manually connects the house and chassis batteries together for emergency starting of the engine or generator situations.

Conversely, keeping just the Spyder system in place with either the Li-BIM 225 would result in two systems (the Spyder system and the Li-BIM 225 circuitry) competing with one another as to when to merge the batteries with uncertain and possibly undesired results. Also, just using the OEM merge solenoid with the Spyder system would eliminate the safety mechanism in the Li-BIM 225 circuitry that keeps the alternator from overheating.
 
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MoreTequila

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If I were you I would first talk to Tiffin's tech support since you have such a sophisticated controller. You might not have to reinvent the wheel since they probably have had many customers that have switched from lead acid batteries to LiFePO4 batteries. Your 250 Amp alternator is massive and just needs its current restricted so it does not try to feed all 250 amps to the new battery(s). It should be able to run steady state at 60 amps all day long without overheating.

So I'd think you'd just want a proper DC to DC charger that has a charge curve that matches your specific brand LiFePO4 battery's published charge curve. That would be plug and play and all you need to add it in between the transfer switch and the LiFePO4 battery (IMHO).

I am going to convert my RV LA house batteries to LiFePO4 soon too. I plan to add the matching DC-to-DC charge controller for charging while driving and replacing the existing 120VAC LA charger (when plugged into shore power) with one made for my LiFePO4 batteries. My existing RV electrical system already knows when to switch things, now I just need to make sure the LiFePO4 battery gets the right voltage and current that matches the brand battery I am going to buy.

Oh! I would think there will also be a need for a temperature sensor in the mix too to automatically manage charging when temperatures get too high or too low for the LiFePO4 battery. Don't want to damage the battery in extreme temps.

Hopefully someone that has done this before will chime in with their experiences too.
 

time2roll

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I would try to go as is. Get a DC clamp-on ammeter and see what is actually happening before you engineer a solution.
 

JohnGarziglia

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If I were you I would first talk to Tiffin's tech support since you have such a sophisticated controller. You might not have to reinvent the wheel since they probably have had many customers that have switched from lead acid batteries to LiFePO4 batteries.
Oh! I would think there will also be a need for a temperature sensor in the mix too to automatically manage charging when temperatures get too high or too low for the LiFePO4 battery. Don't want to damage the battery in extreme temps.

Hopefully someone that has done this before will chime in with their experiences too.
Thank you for your observations. The issue with Tiffin and its use of the Spyder system (which controls most of the electronics in the coach) is that Spyder (and possibly Tiffin) absolutely refuses to modify or update its systems to accommodate lithium batteries. Therefore, Tiffin "recommends against" the installation of lithium batteries in its pre-2021 coaches. But yes, if the Spyder system in our 2017 motorhome could be modified for lithium batteries, that would be the way to go. I am using a Victron MPPT solar charger, a Victron inverter/charger and a Victron DC-to-DC charger, all able to be specifically set to the parameters of the LiFePO4 batteries I have.

With respect to temperature, the lithium batteries each their own BMS built in, plus have heaters that kick in below 32 degrees so I think I am OK with temperature variations.
 

JohnGarziglia

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I would try to go as is. Get a DC clamp-on ammeter and see what is actually happening before you engineer a solution.
That I have done. The alternator charging the LiFePO4 batteries through the Li-BIM 225 goes into a greatly reduced current mode and almost no charging when the LiFePO4 batteries are at about 80% charge which comports with the product literature for the Li-BIM 225.
 

MoreTequila

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Thank you for your observations. The issue with Tiffin and its use of the Spyder system (which controls most of the electronics in the coach) is that Spyder (and possibly Tiffin) absolutely refuses to modify or update its systems to accommodate lithium batteries. Therefore, Tiffin "recommends against" the installation of lithium batteries in its pre-2021 coaches. But yes, if the Spyder system in our 2017 motorhome could be modified for lithium batteries, that would be the way to go. I am using a Victron MPPT solar charger, a Victron inverter/charger and a Victron DC-to-DC charger, all able to be specifically set to the parameters of the LiFePO4 batteries I have.

With respect to temperature, the lithium batteries each their own BMS built in, plus have heaters that kick in below 32 degrees so I think I am OK with temperature variations.

And thank you for yours!

When I replied above I had just watched one of Will's YT videos on the battery I am planning to buy (Ampere Time 12V 200Ah Lithium Iron LiFePO4) and he noted it does not have a low temp cutoff so that was stuck in my brain when I was replying. But you are correct that most other manufacturers have both high and low temp cut off built in their batteries from the factory.

I guess there must be some engineering reason Tiffin won't modify the system for LiFePO4 probably also related to liability or something along those lines (legal and lawyers LOL). But this shouldn't be rocket science. My RV is a 2002 Dynamax Class B on a Ford E350 chassis so it uses all old-school analog components.
 

Short_Shot

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So I'd think you'd just want a proper DC to DC charger that has a charge curve that matches your specific brand LiFePO4 battery's published charge curve.
This is a thing, but kind of not. At least in the sense that it's not limited to some kind of predefined curve and you need to hunt through brands to find one that matches.

A good lifepo4 charger charges at constant (limited) current until the max voltage is achieved and then holds that voltage (by switching to constant voltage) until the charge current reaches a threshold that is considered fully charged.

Then, depending on settings it might switch to a float voltage which is a bit below resting voltage for a fully charged battery, or it might just stop charging entirely if float is disabled.

A better one let's you configure the voltages involved in these transitions yourself.

At any rate there's little need to go out of your way for a specific lifepo4 charger that just happens to "match" your brand of battery. Just get a programmable one.

Especially since very few lithium battery sellers provide one that "matches" their stuff and a third party one almost certainly will not.
 

Zwy

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Using just the DC-to-DC charger has the flaw of not allowing my solar panels to charge the chassis battery when needed. It removes one of the functionalities of the battery and solar panel setup in the motorhome that I desire to keep. The other functionality it removes is the use of the dashboard "Aux Start" switch which manually connects the house and chassis batteries together for emergency starting of the engine or generator situations. Conversely, keeping just the Spyder system in place with either the Li-BIM 225 would result in two systems (the Spyder system and the Li-BIM 225 circuitry) competing with one another as to when to merge the batteries with uncertain and possibly undesired results.

That's why don't use the Li-BIM. It isn't needed. If you want that capability to charge the chassis batteries from solar, you leave the Spyder intact as I mentioned and simply install a battery cable and switch to bypass the DC to DC. You actually already have what you need in place with the "Aux Start" switch, it is there to bypass the current isolator. Simply turn it on when you want that to occur. Now if it is a solenoid, there might be some parasitic draw, which probably won't be an issue if your solar is producing. It might not be a continuous duty solenoid, but that can be rectified by swapping it out.

Also, just using the OEM merge solenoid with the Spyder system would eliminate the safety mechanism in the Li-BIM 225 circuitry that keeps the alternator from overheating.
Again, dump the Li-BIM and use a DC to DC charger with the current Spyder system.
 

JohnGarziglia

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That's why don't use the Li-BIM. It isn't needed. If you want that capability to charge the chassis batteries from solar, you leave the Spyder intact as I mentioned and simply install a battery cable and switch to bypass the DC to DC. You actually already have what you need in place with the "Aux Start" switch, it is there to bypass the current isolator. Simply turn it on when you want that to occur. Now if it is a solenoid, there might be some parasitic draw, which probably won't be an issue if your solar is producing. It might not be a continuous duty solenoid, but that can be rectified by swapping it out.


Again, dump the Li-BIM and use a DC to DC charger with the current Spyder system.
Thank you for your observations. But, from everything I have read about the current Spyder system working with the merge solenoid, it will run the alternator at full current into the LiFePO4 lithium house batteries without any safety time-out to prevent alternator over-heating. I understand there is some controversy about lithium batteries and alternator over-heating but I am not seeking to debate that here but rather simply accept it as a potential danger. Putting only a DC-to-DC charger in place of the merge solenoid eliminates any maintaining of the chassis batteries charge by the solar panels, shore power or generator.

--> Rather, my question is whether the system I describe above has any operational or electrical downsides, or anything I am missing? Or more simply put, will it work over the long-term in an automatic way to accomplish with the LiFePO4 house batteries the three purposes of: (1) the alternator charging the LiFePO4 lithium house batteries when the engine is on; (2) the solar panels, a shore connection or the generator keeping a full charge of the lead-acid chassis batteries once the LiFePO4 lithium house batteries are full; and (3) manually bridging the house and chassis batteries together to allow for an emergency start of either the engine or the generator.
 

eXodus

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Thank you for your observations. But, from everything I have read about the current Spyder system working with the merge solenoid, it will run the alternator at full current into the LiFePO4 lithium house batteries without any safety time-out to prevent alternator over-heating.
put in shunt and a Meter on your dash.

Charging for years with 180A alternator + solenoid to a lithium bank - never saw more then 100A flowing - usually like 60A.
Disclaimer - I use the Chassis of RV as ground and have 25FT of 0/2 gauge el cheapo CCL wire to the batterie - which introduces "plenty" of resistance to (0.2 Ohm) to slow down the charging of the LFP.

Further I got a 125A reset-able breaker going towards the batteries - so in case the alternator should ever deliver more the 125A it cut's charging until I reset it.

Modern alternators (2000 an later) are usually microprocessor controlled and don't really burn out anymore)
 

Zwy

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Thank you for your observations. But, from everything I have read about the current Spyder system working with the merge solenoid, it will run the alternator at full current into the LiFePO4 lithium house batteries without any safety time-out to prevent alternator over-heating. I understand there is some controversy about lithium batteries and alternator over-heating but I am not seeking to debate that here but rather simply accept it as a potential danger. Putting only a DC-to-DC charger in place of the merge solenoid eliminates any maintaining of the chassis batteries charge by the solar panels, shore power or generator.

I don't think you quite understand what I'm referring to. You don't replace the merge solenoid with a DC to DC, you simply install the DC to DC after the merge solenoid. This will control the current from the alternator. The wiring for the DC to DC is already present and nicely sized to boot.

You might have to add one cable if you want the ability to charge chassis battery from solar or give an Aux start function. It just would depend on what functionality you want and how the current system is wired.
--> Rather, my question is whether the system I describe above has any operational or electrical downsides, or anything I am missing? Or more simply put, will it work over the long-term in an automatic way to accomplish with the LiFePO4 house batteries the three purposes of: (1) the alternator charging the LiFePO4 lithium house batteries when the engine is on; (2) the solar panels, a shore connection or the generator keeping a full charge of the lead-acid chassis batteries once the LiFePO4 lithium house batteries are full; and (3) manually bridging the house and chassis batteries together to allow for an emergency start of either the engine or the generator.
It can be done quite easily combined with the current Spyder system. Remove the Li-BIM, it is unneeded and just adds a host of problems and complexity.
 

JohnGarziglia

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I don't think you quite understand what I'm referring to. You don't replace the merge solenoid with a DC to DC, you simply install the DC to DC after the merge solenoid. This will control the current from the alternator. The wiring for the DC to DC is already present and nicely sized to boot.

You might have to add one cable if you want the ability to charge chassis battery from solar or give an Aux start function. It just would depend on what functionality you want and how the current system is wired.

It can be done quite easily combined with the current Spyder system. Remove the Li-BIM, it is unneeded and just adds a host of problems and complexity.
I guess I do not understand. I am not trying to be argumentative but it appears that installing the DC-to-DC charger after the merge solenoid then limits charging to one way only -- from the alternator to the house batteries, eliminating the charging of the chassis batteries by the solar panels, shore power or generator. You state that "adding one cable" can enable the charging of the chassis battery from solar, shore or generator, but I do not understand from where to where that cable would run. If that cable is run from the house batteries to the house battery side of the merge solenoid, then that cable is essentially permanently connecting the output of the DC-to-DC charger to its input. If the cable runs from the house batteries to the chassis side of the merge solenoid, then that is permanently connecting the house and chassis batteries together in parallel which is certainly not desired. Without the addition of the referenced cable, the Spyder system which controls the merge solenoid will now be seeing on the house battery side of the merged solenoid not the voltage of the house batteries which voltage reading controls whether it triggers on or off (see attached file), but rather no voltage at all and an undetermined resistance from the DC-to-DC charger which may or may not trigger the merge solenoid to merge thus enabling the DC-to-DC charger to operate at all, and will almost certainly not trigger the merge solenoid to unmerge. Like I say, I do not understand what you are proposing. If you could show a rough wiring diagram, that would be helpful. Thanks.
 

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MoreTequila

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... You don't replace the merge solenoid with a DC to DC, you simply install the DC to DC after the merge solenoid. This will control the current from the alternator. The wiring for the DC to DC is already present and nicely sized to boot ...

This is exactly what I am going to do on my RV. That way - whether connected to 120 VAC shore power or driving my RV down the road - I will have ample DC voltage/current supplied to my Renogy 40 Amp DC-to-DC charger to recharge my LiFePO4 battery. Note: I will have to change my PowerMax 55 Amp 3-stage AC to DC converter to fixed output (@ 14.6 VDC) to properly drive the Renogy when I am plugged into shore power.
 
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Zwy

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I guess I do not understand. I am not trying to be argumentative but it appears that installing the DC-to-DC charger after the merge solenoid then limits charging to one way only -- from the alternator to the house batteries, eliminating the charging of the chassis batteries by the solar panels, shore power or generator. You state that "adding one cable" can enable the charging of the chassis battery from solar, shore or generator, but I do not understand from where to where that cable would run. If that cable is run from the house batteries to the house battery side of the merge solenoid, then that cable is essentially permanently connecting the output of the DC-to-DC charger to its input. If the cable runs from the house batteries to the chassis side of the merge solenoid, then that is permanently connecting the house and chassis batteries together in parallel which is certainly not desired. Without the addition of the referenced cable, the Spyder system which controls the merge solenoid will now be seeing on the house battery side of the merged solenoid not the voltage of the house batteries which voltage reading controls whether it triggers on or off (see attached file), but rather no voltage at all and an undetermined resistance from the DC-to-DC charger which may or may not trigger the merge solenoid to merge thus enabling the DC-to-DC charger to operate at all, and will almost certainly not trigger the merge solenoid to unmerge. Like I say, I do not understand what you are proposing. If you could show a rough wiring diagram, that would be helpful. Thanks.
Are the chassis and house battery negatives are common or isolated? From the diagram you supplied, it appears they are not isolated, you need a non isolated DC to DC charger.

After looking at your diagram, you will need a cable and heavy duty switch to enable charging the chassis battery from the LFP bank, or a DC to DC charger that allows you to charge from the house to chassis battery (expensive option but would work) You have several choices on the switch, from a remote controlled solenoid http://www.fastronixsolutions.com/Battery Power Accessories/continuous solenoid.htm to a manual switch. https://www.amazon.com/gp/product/B00Y63TQLG/ref=ppx_yo_dt_b_search_asin_title?ie=UTF8&th=1




The cheapest, easiest and probably something that you should do is simply by installing an AC to DC charger/maintainer where you can charge the chassis battery from your solar thru the inverter. Something like a NOCO could easily accomplish this. Simply put the AC side on a switch so you can control the charger with mounting the charger permanent.
 
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