Motorhome LiFePO question with existing non-LiFePO charger.

[RvShark]

Hi All!

Apologies for what is a hypothetical question! I have read a ton of LiFePO battery conversion posts, but none that really seem to lay out what would happen if I replaced my flooded lead acid batteries with LiFePO. I have a triplite RV1250 inverter/charger and a simple voltage readout at the information panel of my 2017 Tiffin Open Road 32SA with 4 6v 215Ah golf cart batteries. The triplite can charge at 55amps.

I'm wondering what would happen if I directly swapped the 4 6v batteries for 2 or 3 lipo 100Ah batteries (I would get a smart shunt for monitoring since the voltage readout wouldn't be enough, and also probably a dc-dc charger to limit the amperage from my alternator.) I know the trip-lite isn't ideal for LiFePO, but battleborn actually has a blog post about using it with their batteries (I assume "lesser" batteries would be similar and that it's not something special about battleborns?)

Blog post: Battleborn with Triplite

Additional info I requested from Triplite:
Phase 1 of the charging process starts at 10.5V
and ramps up to 14.5V over 10 minutes.
Phase 2 goes from 14.5V to 13.8V.
Phase 3 holds 13.8V.

Basically I'm wondering what would actually happen. Would it take forever to charge? I know it wouldn't take the batteries to 100% (from what I've read) but wondering what would it be like compared to my current system. BTW, raining for days and days at our location, so extra time on my hands lol! Thanks for any info or insights!

-Mark

 

[Mark_K5LXP]

Not sure what the "ramps up to 14.5V over 10 minutes" part means. That's the absorb phase for lead acid and it would need to be a lot more than 10 minutes. Basically though, a typical lead acid charger does not stay at an elevated voltage long enough to completely charge lithium. Lead acid would be 80% charged by the time it hits absorb voltage but lithium needs this from start to finish. The Progressive Dynamics charger with it's pendant can be manually put into absorb mode so this is one option for lithium, or you can get a new converter that correctly charges lithium without intervention. You can try and see what your particular converter can do, or can be configured to do and go from there but at face value, if it's "stuck" on a lead acid profile you may not conveniently reach 100% with a lithium pack. This may be a don't care depending on how much of that capacity you want or need.

Mark B.
Albuquerque, NM

 

[touchracing]

3 main options are to use only your existing converter (so long as it won’t exceed 14.6 volts during bulk charge) and live with the reduced capacity. Second choice is to replace the converter with something better suited for LiFePo. Third is to supplement your existing converter with an additional LiFePo compatible charger powered by shore or solar.
Also i’d recommend a dc-dc charger for a motor home to better isolate the different battery chemistry if nothing else.

 

[Gary RV_Wizard]

A couple of points to consider...

• The 4 x 6v batteries have a max capacity of 430 AH, or at least they did when new. 2 or 3 100AH lithiums have a 200-300 AH max capacity. We can quibble about how much you choose to discharge the lead-acid batteries (50%, 80%, etc) but the bottom line is that you 2 x 100AH is less total amp-hours of power available when that rainy day comes. 80% discharge on a 430 AH battery bank is 344AH, so you would want at least 3 of the 100AH Lipo to have equivalent capacity.
• The stage 1 (bulk) charge mode of the Triplite holds 14.5v more than 10 minutes. Even a lead acid battery wouldn't charge much if the bulk charge mode quit that soon. Most chargers hold that at least 30 minutes and some indefinitely until the battery no longer accepts a high amp rate. I looked for a better explanation of their charge management but didn't find any on the spec sheet.
• The Triplite has some dip switches that can alter the charging and min/max voltages used. Look at your Triplite manual to see if that might help get a more effective charge.
• I see various estimates of how effective an LA charger will be on a lithium battery and I'm sure the specifics depend on the charger and the battery BMS involved, but none of the estimates I've seen are less than 80% of full charge and most were higher.