14.7v lithium battery in 12v system

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Andrew-clark

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I am currently converting a van to a family camper, and have got to planning the electrics. I was planning a 12v system charged from the van and from a solar panel. It will run a small compressor fridge, led lights, some USB charging ports and a diesel heater.

I have been offered some used, but good condition, 14.7v 46Ah lithium batteries which were surplus to requirements elsewhere.

My question is whether it is possible to incorporate such a battery into a 12v setup?

 
Andrew,

Yes, it is.  I see people doing it all the time, but there are some considerations vis-a-vis the new battery. You will need a Renogy (or other) DC-DC charger to maintain the LiFePo from the main engine alternator. 
You will probably want two of those to maintain the reefer for more than a day. 
If the reefer is AC and you plan to run it with an inverter, remember that the DC current required will be 10 TIMES the AC.  So, it will need BIG wire to the house bank.  In spite of what others may tell you, a pure sine inverter is not required.  An induction motor (they all are) will hammer the modified square wave round at a small and acceptable cost.

Matt
 
Sure. First of all, that "12v system" is more like a 13.3v-14-4v system, so not really far off.  At 12.0v the system is just marginally functional (a 12.0v battery is only 50% charged) and the alternator in a car or truck puts out a steady 13.6v-14.4v while the engine is running. RV converter chargers typically manage to 13.6v.  Thus that LiFe at 14.7 isn't way out of line.

To keep the lithium batteries at optimal voltage & state-of-charge, that DC-to-DC charger (or transformer) is the best bet to improve any charging source that normally operates at a lower voltage. The solar panel regulator may already be able to adjust up to the desired level.
 
Matt_C said:
Andrew,

Yes, it is.  I see people doing it all the time, but there are some considerations vis-a-vis the new battery. You will need a Renogy (or other) DC-DC charger to maintain the LiFePo from the main engine alternator. 
You will probably want two of those to maintain the reefer for more than a day. 
If the reefer is AC and you plan to run it with an inverter, remember that the DC current required will be 10 TIMES the AC.  So, it will need BIG wire to the house bank.  In spite of what others may tell you, a pure sine inverter is not required.  An induction motor (they all are) will hammer the modified square wave round at a small and acceptable cost.

Thanks Matt. The fridge will be a small 12v dv fridge.

Thanks for the suggestion regarding a renogy charger. Do you suggest this because of the higher voltage, or because of the lithium battery? Am I correct in assuming you haven?t seen others use any additional parts in their 14.7v set up over and above a normal 12v system?

Matt
Click to expand...
 
I have a 13 cu ft 12v refrigerator that will run for more than a day on (2) 4 year old lead acid golf cart batteries.  I'm going to replace my batteries with lithium and will either buy a dc to dc charger or a battery isolator like this one  https://www.amazon.com/Battle-Born-Batteries-Lithium-Isolation/dp/B07DY8S815.  I haven't finished my research so haven't decided which will work best for me. 
 
Andrew-clark said:
I am currently converting a van to a family camper, and have got to planning the electrics. I was planning a 12v system charged from the van and from a solar panel. It will run a small compressor fridge, led lights, some USB charging ports and a diesel heater.

I have been offered some used, but good condition, 14.7v 46Ah lithium batteries which were surplus to requirements elsewhere.

My question is whether it is possible to incorporate such a battery into a 12v setup?
Click to expand...
I think a little caution is needed here.
Have you verified that the surplus batteries you have are LiFePO4 chemistry?  14.7 volts is the very top of the "charging" voltage for LiFePO4 batteries. 

--  The typical voltage of LiFePO4 12V batteries are in the low to mid 13 volts when in use.  We do charge the batteries with voltages from about 14.0 to 14.5 or so. 
--  There are other Lithium batteries built with chemistry other than LiFePO4 that have higher cell voltages. 
--  If you have batteries that are made with higher voltage cells then you may need to charge them with voltages in the 15-15.5 volt range. 
--  Also Lithium batteries made of chemistries other than LiFePO4 may not be as safe. 
 
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