Lithium upgrade for 21 Georgetown 31L5

[frogman12477]

Hello all. Wondering if anyone out there with a 31L5 has upgraded to lithium with additional solar panels.
Thanks
Frank

 

[VKSheridan]

Frank, we run a 2023 GT7 (36D7) which is close but not close enough to call same as your GT5 but have upgraded to 800 Ah LifePo4 and 400 additional watts of solar power.

First thing is you’ll need to replace your BIM 160 with a Li-BIM 225 battery isolation manager. This will prevent your alternator from overheating when charging the lithiums which will accept pretty much all the amperage your alternator can produce.

Next, determine if your converter can charge lithium or if it’s just designed to do lead acid batteries. I believe your coach came equipped with a Progressive Dynamics PD9100. If so, it will need to be upgraded to a PD9100L or compatible charger. Because LifePo4 batteries can charge at higher amperage and voltage, using the PD9100 will pretty much limit their performance down akin to AGM.

Lastly, your solar controller is a Merlin TravelPro 30 which can be set for sealed, gel or flooded or user. Using the information from your battery OEM, go to user settings and set it as directed. If you’re going roof mounted, connect your additional panels with splitters at the PV connector on the roof that your existing panel uses.

I prefer portable panels versus roof mounted because I like to park in the shade and shade diminishes panel performance. I also wanted scalability and being limited to 30 amps output that the TravelPro 30 produces felt limiting so I installed a separate 60 amp MPPT Solar Controller and left the factory set-up alone. I’m currently using four 100 watt 10BB panels connected in parallel and they allow the controller to output an average of 28 amps an hour. I might add 4 more panels just cuz.

Here’s a component location diagram for your rig to help you figure out where all these components are. Your BIM160 will be in the house battery compartment.

After upgrading, our coach is night and day. It takes a fraction of the time to recharge the batteries which saves generator wear and the ability to drain them past 50% reserve without damaging them yields more capacity in the same space. No corroding terminals, no gassing, can store them inside and stacked AND they’re lighter. They’re the bees knees!

Hope this helps!

 

[NXR]

First thing is you’ll need to replace your BIM 160 with a Li-BIM 225 battery isolation manager. This will prevent your alternator from overheating when charging the lithiums which will accept pretty much all the amperage your alternator can produce.

I do not see current limiting as part of that product's capabilities in its documentation. That normally requires a DC-to-DC converter box as well as a lithium-capable BIM.

A DC-to-DC converter not only limits the amount of current drawn from the alternator to avoid damaging the alternator when lithium batteries are almost depleted, it steps up the alternator voltage to a level that is high enough to fully charge lithium batteries.

Depleted lithium batteries have a very low internal resistance that looks like a short circuit to an alternator. Many a person has smoked their alternator due to the lack of a DC-to-DC converter.

Ray

 

[TitanMike]

I do not see current limiting as part of that product's capabilities in its documentation. That normally requires a DC-to-DC converter box as well as a lithium-capable BIM.

A DC-to-DC converter not only limits the amount of current drawn from the alternator to avoid damaging the alternator when lithium batteries are almost depleted, it steps up the alternator voltage to a level that is high enough to fully charge lithium batteries.

Depleted lithium batteries have a very low internal resistance that looks like a short circuit to an alternator. Many a person has smoked their alternator due to the lack of a DC-to-DC converter.

Ray

Li-Bim's don't limit current as a DC-DC charger does. They do limit the amount of load on an alternator over time as they switch on for a short period then off for a period to allow heat to be dissipated from alternator. Not the best method, that would be a DC-DC charger, but the Li-Bim allows for charging chassis battery from converter as well as emergency starting of engine should chassis battery be dead.

Li-Bims are often the choice of those upgrading to LiFePO4 in MH's as it's a simple change. Adding a DC-DC charger can be more complex as a new location is required for charger and often wiring changes.

 

[VKSheridan]

I do not see current limiting as part of that product's capabilities in its documentation. That normally requires a DC-to-DC converter box as well as a lithium-capable BIM.

A DC-to-DC converter not only limits the amount of current drawn from the alternator to avoid damaging the alternator when lithium batteries are almost depleted, it steps up the alternator voltage to a level that is high enough to fully charge lithium batteries.

Depleted lithium batteries have a very low internal resistance that looks like a short circuit to an alternator. Many a person has smoked their alternator due to the lack of a DC-to-DC converter.

Ray

Ray, unlike a battery that lacks variable voltage to strengthen the rotor windings to increase amp output, the regulator controls the output current of the alternator, not the load.

DC to DC converters are used when you’re try to charge a battery using current sent through a seven pin connector. That isn’t the case on a motorhome.

The myth that fully depleted lithiums are practically a dead short is also incorrect. Unless you bought your battery from TEMU, LifePo4 batteries have built in circuitry to limit what goes in and what goes out to protect them. That is why lithiums don’t need to have a multi-phase charge profile.

Lastly, you need to share your smoked alternator story with Forest River because the very Li-BIM I referred is currently OEM STANDARD on 2025 models with the Lithium option.

 

[bikendan]

Hello all. Wondering if anyone out there with a 31L5 has upgraded to lithium with additional solar panels.
Thanks
Frank

Moved thread from the General Community Discussion section to the Motorhome section's Georgetown sub-forum since the OP's questions are specific to a Georgetown product and are not general community discussion questions.

 

[TitanMike]

LifePo4 batteries have built in circuitry to limit what goes in and what goes out to protect them.

That built in circuitry is the BMS and but it does not control current that goes into the battery. Only what comes out. Charging is limited only when cell voltages reach a max value and then the BMS shuts things off

The issue that arises in MH's is there are often multiple batteries in parallel and that means charge current draw can be multiplied by the number of batteries in parallel.

If max charge rate for 100 ah lifepo4 battery is .5C Now connect 4 100ah batteries in parallel and potentially 200 amps could flows. Now the alternator is seriously overloaded as it's already powering all the other essential power draws of a modern engine and "creature comfort" devices.

(My two Lifepo4 batteries in parallel can draw 270 amps while charging and not exceed mfr's .5C rate)

Again, Motorhomes have this issue more than towables as the 7-wire connection has current limiting characteristics in itself.

Another overlooked factor with increased loads on alternators when charging lifepo4 batteries is their cooling. Buried deep in the engine compartment they need cool air to keep them alive. Sadly that's often lacking as their fans are all to often moving to slow due to heavy traffic and idling. The solution would be to use water cooled alternators on MH's like other heavy duty applications but 200amp units costing from $1,000 up to $2200+ I don't see that happening on most MH's sold today.

Lifepo4 batteries DO require multi-phase charging algorithms. Most mfrs spec a Bulk rate (constant current) to rapidly charge, an absorption rate (constant voltage) to facilitate cell balance; and then a float rate (usually around 13 5v) to maintain charge while connected to shore power or solar.

DC-DC chargers are excellent for this as they provide the tailored charge profile reccomended while preventing overload of alternator.

 

[MikeW-ESC]

I have a 2021 GT5 31L5, and recently switched from AGM batteries to LiFePO4 batteries. I really like the new setup, but there were a few surprises. I installed two WattCycle 300Ah (280Ah) 12V batteries in the same location as the original AGM batteries. They were a tight fit side to side, but with a small bend in the mounting hole for the J-bolt they made it. I changed the BIM to the Li-BIM as VKSheridan suggested. I haven't had any problems with this. The batteries charge at a little over 100 amps when driving (well within the rating of both the generator and the batteries). The charge for 15 minutes and the generator rests for about 20.

I had to change the converter on my 2021, because it could not be set for lithium batteries. I went with the PD9380V to be able to charge the batteries more quickly at 80 amps. I ran into two problems with the converter installation. (1) The 80 amp converter has a 20A 120V plug (one vertical and one horizontal blade) rather than the "standard" 15A 120V plug (two vertical blades), so it doesn't fit in the outlet. (2) Our converter is in the power bay at the rear of the coach on the driver side and the batteries are at the front of the coach on the passenger side. As a result of the long wire run between them there is a significant voltage drop at high current between the converter and the battery. This limited the charging current to 40A or less. To get around these two problems I installed the converter in the storage bay next to the battery bay with new #2 wires to the battery control box. I also installed a new 20A 120V circuit to that bay, since the outlet in that bay is shared with all the other outlets in the coach. If you were not so worried about quick charging you could just go with the 60A PD9360V converter and install it in the same place as the old converter. It would just be a plug and play.

I check into the solar controller and found that the TravelPro 30 that came with the coach can be programmed to custom battery settings that will work for Lithium. The only catch is that you need to use a remote interface to set up the settings. I found the EPEVER MT50 for $20 at Inverters R US, and used that to reprogram the TravelPro. I just have the factory 100W solar panel, so we don't get much from the solar, but at least it will still charge.

I already had a Victron Smart Shunt to monitor the old battery state of charge. If you don't have one I would very much recommend it. The existing battery monitoring will not be of much use with the Lithium batteries. The have a very stable 13.2V output until they are close to fully discharged.

We've done a couple of small trips and a bunch of testing at home on the setup and it's working well for us.

 

[VKSheridan]

That built in circuitry is the BMS and but it does not control current that goes into the battery. Only what comes out. Charging is limited only when cell voltages reach a max value and then the BMS shuts things off

The issue that arises in MH's is there are often multiple batteries in parallel and that means charge current draw can be multiplied by the number of batteries in parallel.

If max charge rate for 100 ah lifepo4 battery is .5C Now connect 4 100ah batteries in parallel and potentially 200 amps could flows. Now the alternator is seriously overloaded as it's already powering all the other essential power draws of a modern engine and "creature comfort" devices.

(My two Lifepo4 batteries in parallel can draw 270 amps while charging and not exceed mfr's .5C rate)

Again, Motorhomes have this issue more than towables as the 7-wire connection has current limiting characteristics in itself.

Another overlooked factor with increased loads on alternators when charging lifepo4 batteries is their cooling. Buried deep in the engine compartment they need cool air to keep them alive. Sadly that's often lacking as their fans are all to often moving to slow due to heavy traffic and idling. The solution would be to use water cooled alternators on MH's like other heavy duty applications but 200amp units costing from $1,000 up to $2200+ I don't see that happening on most MH's sold today.

Lifepo4 batteries DO require multi-phase charging algorithms. Most mfrs spec a Bulk rate (constant current) to rapidly charge, an absorption rate (constant voltage) to facilitate cell balance; and then a float rate (usually around 13 5v) to maintain charge while connected to shore power or solar.

DC-DC chargers are excellent for this as they provide the tailored charge profile reccomended while preventing overload of alternator.

Mike, there’s a couple of things with your reply that just isn’t right.

Your alternator is regulated. It cannot produce more amperage than its design so even if you had the ability to flow 400 amps, your alternator will only put out what the regulator allows and at worst, what it’s windings can handle.

A DC to DC charger is the best you can hope for with your Flagstaff Micro-Lite because you’re not running battery cables between your house batteries and your alternator. Unfortunately for you, you have to run your power through a 7-pin connector that should never see more than 5-8 amps.

A GT5 doesn’t have that problem.

The cable to the BIM is sized by FR to the alternator’s output. And that is why factory LifePo4 installations use a Li-Bim. It optimizes the fast charge benefit of LifePo4 by capitalizing on the alternator’s output rating, not the limitation of a hitch connector.

I’m not speaking from opinion, I own a GT7 that has logged 20,000 miles so far letting my factory F53 alternator charge my 800 Ah of batteries. If I had experienced any issues or system distress, I’d be saying that. But the people that taught me were right. It works and it works great.

Safe travels

 

[NXR]

Apparently there is no way to delete a post anymore so this'll have to do.

 

[MikeW-ESC]

I was worried about possible alternator overload with my 560AH LiFePO4 battery installation, but monitoring the alternator current charging the batteries, even when they are heavily discharged, I have never seen more than 100A of current from the alternator, well within it's rating. I believe that the wire length and the various connections between the alternator and the battery are the limiting factor. The batteries require about 13.8V to charge at 100A, and the alternator is regulated to 14.4V max, so there's only a voltage drop of about 0.6V. At 100A this means 6 milli Ohms. The 20 or so feet of 1 AWG wire in the positive leg from the chassis battery is almost half of that, so when you add the connection resistance through the BIM, battery fuses, the additional wire from the alternator to the battery and the resistance of the ground line I think it's very likely that there is around 6 milli ohms in the charging loop. This amount of resistance does seem to protect the alternator from excess current draw.

 

[TitanMike]

Mike, there’s a couple of things with your reply that just isn’t right.

Your alternator is regulated. It cannot produce more amperage than its design so even if you had the ability to flow 400 amps, your alternator will only put out what the regulator allows and at worst, what it’s windings can handle.

A DC to DC charger is the best you can hope for with your Flagstaff Micro-Lite because you’re not running battery cables between your house batteries and your alternator. Unfortunately for you, you have to run your power through a 7-pin connector that should never see more than 5-8 amps.

A GT5 doesn’t have that problem.

The cable to the BIM is sized by FR to the alternator’s output. And that is why factory LifePo4 installations use a Li-Bim. It optimizes the fast charge benefit of LifePo4 by capitalizing on the alternator’s output rating, not the limitation of a hitch connector.

I’m not speaking from opinion, I own a GT7 that has logged 20,000 miles so far letting my factory F53 alternator charge my 800 Ah of batteries. If I had experienced any issues or system distress, I’d be saying that. But the people that taught me were right. It works and it works great.

Safe travels

Most alternators on the road today are not current limited. Only voltage limited. Current limiting regulators went by the wayside when generators were replaced by alternators.


New "smart alternators are controlled by the ECM using a current sensor on battery's negative cable only to reduce output once starting battery is recharged in order to reduce power draw on engine to save fuel.

Traditional alternators are self limiting as their efficiency is reduced ad the current output reaches design limits.

To repeat, the main issue with charging a lifepo4 battery directly from an alternator isn't really that it's harmed by over-current but lack of cooling. This is why Li-Bim's use a on/off method of controlling heat buildup in the alternator.

 

[VKSheridan]

I was worried about possible alternator overload with my 560AH LiFePO4 battery installation, but monitoring the alternator current charging the batteries, even when they are heavily discharged, I have never seen more than 100A of current from the alternator, well within it's rating. I believe that the wire length and the various connections between the alternator and the battery are the limiting factor. The batteries require about 13.8V to charge at 100A, and the alternator is regulated to 14.4V max, so there's only a voltage drop of about 0.6V. At 100A this means 6 milli Ohms. The 20 or so feet of 1 AWG wire in the positive leg from the chassis battery is almost half of that, so when you add the connection resistance through the BIM, battery fuses, the additional wire from the alternator to the battery and the resistance of the ground line I think it's very likely that there is around 6 milli ohms in the charging loop. This amount of resistance does seem to protect the alternator from excess current draw.

Mike, I’m not so sure it’s the resistance in your cables limiting the alternator output but rather the PCM controlling the voltage regulator doing the magic.

The reason I sat this is the 2015 and newer F53’s come from factory with a variable voltage alternator (aka “smart alternator”) that has a PCM managing the regulator and field windings, thus controlling the output.

The house batteries are never connected to the alternator exclusively or independent of the coach battery so there’s never an opportunity for the PCM to read just the house batteries and command the alternator accordingly. The chassis battery is kind of a capacitor in the circuit if ya think about it. Pretty ingenious to this kid.

One other benefit that the DC to DC crowd often overlooks is chassis battery charging when connected to shore.

Yep, your Li-BIM senses charge voltage from both the alternator AND your inverter/converter/charger which means it’ll let your inverter charge your chassis battery while you’re charging your house cells. DC to DC chargers don’t do that….

Here’s a link to the Li-BIM Product Data Sheet that explains to isolation better than I can.

 

[VKSheridan]

Most alternators on the road today are not current limited. Only voltage limited. Current limiting regulators went by the wayside when generators were replaced by alternators.


New "smart alternators are controlled by the ECM using a current sensor on battery's negative cable only to reduce output once starting battery is recharged in order to reduce power draw on engine to save fuel.

Traditional alternators are self limiting as their efficiency is reduced ad the current output reaches design limits.

To repeat, the main issue with charging a lifepo4 battery directly from an alternator isn't really that it's harmed by over-current but lack of cooling. This is why Li-Bim's use a on/off method of controlling heat buildup in the alternator.

Mike, the Ford F53 chassis in OP’s GT5 doesn’t use a traditional alternator nor an IBS at the negative post. It is equipped with a “smart alternator” whose windings are not just controlled by the regulator but the PCM as well. In fact, this novel little jewel of electrical generation even has load shed capabilities that coincides with your idling at a stop concern but I digress.

The popular statement is a lithium will fry an alternator because they have lower resistance to flow, hence charge faster. The resistance of the average 100 aH LifePo4 is 4-40 milliohms. Interestingly, the average 100 Ah AGM battery’s internal resistance is 4-6 milliohms. Because they share such close resistance, that’s is why you can connect them in parallel to charge them. The difference between the two at the same voltage and flow is the charge acceptance is far superior on a LifePo4 than AGM thus less time needed to charge.

Can you burn up an F53 alternator? Of course but you’ll need about 1,600 Ah of batteries fully depleted and 10 hours of driving to do it. Or have a killer boom box that sucks the resin off the windings….LOL

Did you know both the BIM160/225 used for years with AGM set-ups and the Li-BIM 160/225 have solid state voltage and amperage sensing designed to prevent overburdening the charging system? Whether it’s the alternator or the inverter, it’ll isolate if the loads get crazy and both have some common cycle characteristics.

Here’s a document from Battleborn that says the Precision Electronics Li-BIM cycles 15 minutes on, 20 minutes off under certain conditions. I don’t see any documentation from Precision Electronics that confirms or denies it but if it does cycle the load, I’m thinking it’s more because it can be installed on a myriad of voltage sources, including solar.

If I had concerns for heat, it wouldn’t be because I’m changing battery type from AGM to LifePo4 but rather changing the reserve capacity to recharge from fully depleted 200 Ah reserve to fully depleted 1,200 Ah reserve. That will increase the duty cycle whether it’s AGM or Lithium but again, lithium will hit 100% in much less time at the same amperage and will gladly accept more if the PCM would kindly let the alternator do it!

Sorry so wordy but thank you for the conversation.