My RV has 2 Trojan T105 6V batteries that give me 225ah. (really 100ah to 50%). they are both being re-charged daily by 200W of solar running Victron MPPT and BMV equipment. I have lots of 18650 checked and tested cells that I can use to build a "supplemental" battery pack for longer RV boondocking runs. I would like to build a DIY 18650 100ah+ portable/luggable battery that I can plug into the existing 12v RV power system to give it some better runtime. is it wise to mix energy solutions like Lead Acid and Lipo? can/should the solar be able to recharge BOTH solutions if they are both 12v? (I'm guessing not). the Trojans don't have a BMS and just soak in as much voltage as they can get so if that voltage also goes at the BMS/charger built into the Lipo will that work?
18650 supplemental 12v RV battery
- Thread starter dpackham
- Start date
LiPo is a pure shit solution for 12V. 3S operates below the working range of FLA and 4S operates above the working range of FLA.
Taking a pure shit solution and then running it in parallel with FLA is like shit on shit with a side of shit that can catch fire.
Yes. "shit" is apparently my word for the day.
Taking a pure shit solution and then running it in parallel with FLA is like shit on shit with a side of shit that can catch fire.
Yes. "shit" is apparently my word for the day.
3S works from 7.5V to 12.6V - most inverters cut off at 11V, and this range is below the voltage that FLA/AGM can be charged.
4S works from 10V to 16.8V, but typical FLA/AGM charging peaks at 14.8V with the NMC cells at only 3.7V each - probably around 50% charged.
7S for 24V and 14S for 48V work great.
And of course, you need a robust BMS to prevent destroying the cells by taking them out of limits.
4S works from 10V to 16.8V, but typical FLA/AGM charging peaks at 14.8V with the NMC cells at only 3.7V each - probably around 50% charged.
7S for 24V and 14S for 48V work great.
And of course, you need a robust BMS to prevent destroying the cells by taking them out of limits.
Yes you can use 3s li-ion to augment your trojan batteries. I have a 312ah li-ion batterybank (3s) that augments my 220ah 4s lifepo4. And previously I used a 94ah 3s li-ion pack(handbuilt with 18650) that augmented my 102ah agm battery.
As long as the lead acid is charging from the solar panel you can connect your 3s(as long as its not empty) into it, and it will charge that way or you can use a boost/buck converter to charge the 3s which is a safer way to do it since the boost/buck can be set to 12.6 volts and limit the amps. Just don't charge while the solar is not producing power because the li-ion will drain the lead acid until they equalize.
Li-ion is the 18650 cylinder cells, lipo is the more dangerous pouch packs. 18650 is just as safe as lifepo4 as long as you don't overcharge or puncture them. Make sure you have a good hi quality bms, that you tested to work on you li-ion pack.
When the solar panel is producing power and your batteries are about the same voltage (example 12v agm, 3s li-ion or 4s lifpo4) you can connect together, whichever battery is the weakest will receive the most amps from the solar system. I connected agm, and li-ion to my lifepo4 to topped them off, with no sparks or other type of problems. Just try not to connect a completely depleted battery to the system because the depleted battery will also start draining the full batteries. It's why I use a boost/buck converter that can limit amps output.
Picture of my first 3s 94ah li-ion pack (168 cells), this was a solid performer, I retired it when I moved to lifepo4.
This is a picture of my 312ah li-ion batterybank. I use the mobius 26ah battery pack and connected 12 of them in parallel. I spent about 450 dollars to buy all 12 of them. I charge this from my lifepo4 battery with a boost/buck converter. The only weakness of this pack, is you need to have a good charging system to charge something this massive. With limited sunlight this pack has been at 10 percent (about 10 volts) for the past 2 weeks. But even at 10 percent it still runs my 200 watt inverter and my 12 volt fridge. Everyday I charge just enough to get me through another day, my lifepo4 is not much better at 20 percent, my 240 watt panel/20a mppt is barely charging over 500ah of lithium.
As long as the lead acid is charging from the solar panel you can connect your 3s(as long as its not empty) into it, and it will charge that way or you can use a boost/buck converter to charge the 3s which is a safer way to do it since the boost/buck can be set to 12.6 volts and limit the amps. Just don't charge while the solar is not producing power because the li-ion will drain the lead acid until they equalize.
Li-ion is the 18650 cylinder cells, lipo is the more dangerous pouch packs. 18650 is just as safe as lifepo4 as long as you don't overcharge or puncture them. Make sure you have a good hi quality bms, that you tested to work on you li-ion pack.
When the solar panel is producing power and your batteries are about the same voltage (example 12v agm, 3s li-ion or 4s lifpo4) you can connect together, whichever battery is the weakest will receive the most amps from the solar system. I connected agm, and li-ion to my lifepo4 to topped them off, with no sparks or other type of problems. Just try not to connect a completely depleted battery to the system because the depleted battery will also start draining the full batteries. It's why I use a boost/buck converter that can limit amps output.
Picture of my first 3s 94ah li-ion pack (168 cells), this was a solid performer, I retired it when I moved to lifepo4.
This is a picture of my 312ah li-ion batterybank. I use the mobius 26ah battery pack and connected 12 of them in parallel. I spent about 450 dollars to buy all 12 of them. I charge this from my lifepo4 battery with a boost/buck converter. The only weakness of this pack, is you need to have a good charging system to charge something this massive. With limited sunlight this pack has been at 10 percent (about 10 volts) for the past 2 weeks. But even at 10 percent it still runs my 200 watt inverter and my 12 volt fridge. Everyday I charge just enough to get me through another day, my lifepo4 is not much better at 20 percent, my 240 watt panel/20a mppt is barely charging over 500ah of lithium.
Li-ion is all types of Lithium chemistry that uses Lithium ions to transport charge including LCO, LMO, NMC, LFP, LYP, NCA, LTO and other experimental types.
Your assertion that Lithium NMC or LMO is as safe as LFP is laughable while describing a system that requires a lot of special effort and rules to do this and not do that. Your system leaves a lot of capacity on the table that's not usable from the 18650 bank.
Rube Goldberg would be proud.
Gasoline is just as safe as water as long as you don't ignite it or drink it
Well, it's easy, you just need to do 3.5S for 12 V...
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