Small 12v 100AH LiFePO4 battery system for use in a camper

RandyP

Adventurer
I am considering a small 12v 100AH LiFePO4 system for use in a camper.

In the past I had a popup camper with Two 125AH Lifeline AGM Battery. Used a RedArc DC-DC with solar controller battery charger, Bogart TM1025 Monitor, two 130W 17v photo cells, an IOTA dc converter with three stage battery charging voltage controller (good for AGM Battery charging from shore power). I liked this setup. Usually never discharged bellow 90% nightly and recharged to about 97% during the next day using solar. Ran the heater Fan, CPAP, 12v refrigerator, lights, fans and sometimes a bed warmer blanket for 15 minutes.

I will use the RedArc BCDC 1240D battery/battery charger with solar controller in the new lithium Ion Battery setup.

I will use two Grape Solar 180w monocrystal panels Vmpp 19.67vdc, Voc 24.6vdc.

I am struggling with choosing a monitor. I do NOT need one that is made for lead acid batteries. The LiFePO4 battery does not have all the problems of a lead acid battery when charging or discharging. I do not need to put back in 110% of the Discharged AH to get the battery up to 100% charge.

Any help in choosing a Battery Monitor would be greatly appreciated.

Also struggling with a shore power charger choice. Looks to be a pretty simple charging routine for LiFePO4 . Start charging when Battery gets to 10.5V min, charge at 14.2-14.5 V until battery is 100% charged. No Need for absorb or float charge. Do not exceed 14.6 volts charging. Never Equalize the LiFePO4 battery.

Have not found a simple charger that works as described above. 40-60A charger would be preferred.

Any help choosing a battery charger would also be appreciated.

RandyP
 

RandyP

Adventurer
I found this quote a Progressive Dynamics 9100L owners Manual:
"OPTIONAL REMOTE SHUTDOWN MODULE
Your INTELI-POWER 9100L converter is equipped
with a Remote Shutdown Module interface. The
converter can be shutdown using either a high or
low side control, or by connecting two wires by
means of a mechanical switch or relay contacts.
This allows the battery management system to
shutdown the converter after battery charging and
balancing are complete."
Can I use this for the Discharge state sensor (12.x volts) and full charge state sensor (14.4 V) when charging LiFePO4 Battle Born 12v Battery?

RandyP
 

dreadlocks

Well-known member
you just need the high side for the charger, and the BMV-712 can provide this for you.. I use the battery protect relay to drop the battery when it gets over set voltage, then it stays disconnected while the charger is running so all 12v appliances are then running off the Progressive Dynamics.. this works well for my use, since I can plug it in and forget it.. if its long term storage like I have it in now, I turn off the charger and let battery get to bout 45% from the fridge and other stuff then pull the manual disconnect and power the Progressive Dynamics back up so the lights and stuff still work over the winter.

If you dont wanna use a solid state relay to disconnect battery (recomended) the BMV could be instructed to shut down PD charger at certain voltage and not recharge again until a bit below the floating charge, this would be minimal amount of protection required from cooking battery but could lead to unwanted cycles if you have any loads left on.. ie, if you left a light on it could go from 100%-90%-100% over and over instead of just happily running off shore power and leaving the battery alone.

Low Voltage Disconnect w/LiPo is hard, it holds voltage until its nearly discharged, the difference between 20% floating and 80% w/load is not that great.. I use the BMV to calculate state of charge @ 20% then drop loads, the highest voltage the Battery Protect disconnects on its own is like 12.2v and that ends up being ~3-5% SOC, so its the last line of defense until the internal BMS takes over, and by then it may be too late.
 
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RandyP

Adventurer
…..I use the battery protect relay to drop the battery when it gets over set voltage, then it stays disconnected while the charger is running so all 12v appliances are then running off the Progressive Dynamics...…..
Is the battery protection relay a separate device, from Victron Energy ?

Low Voltage Disconnect w/LiPo is hard, it holds voltage until its nearly discharged, the difference between 20% floating and 80% w/load is not that great.. I use the BMV to calculate state of charge @ 20% then drop loads, the highest voltage the Battery Protect disconnects on its own is like 12.2v and that ends up being ~3-5% SOC, so its the last line of defense until the internal BMS takes over, and by then it may be too late.
So do you use the battery 12.2v setpoint on the Battery Protect Disconnect along with the 20% battery SOC level as derived from the BMV ? I read that the BMV resets the 100% charged point nearly at every charge cycle, because without thei reset it is not too accurate as a state of charge device.

RandyP
 

dreadlocks

Well-known member
yes, Victron Battery protect is a solid state relay with built in LVD (low voltage disconnect) and an external input that I have wired to BMV Relay Output

The BMV calculates SOC through a shunt, it does auto recalibrate but not because its inaccurate.. its to maintain accuracy without intervention, its one of the most accurate methods you can use really, especially with LiPo since trying to calculate SOC off just voltage is nearly impossible.

normally the Battery Protect internal LVD does nothing, thats just incase I over ride the BMV after it shuts down.. I have a 'reserve' switch in parallel with the BMV that I can flip if I really want that last 15% of battery.. it will shut down before battery is completely flat if I've disabled the BMV's protection in an emergency.
 

RandyP

Adventurer
you just need the high side for the charger, and the BMV-712 can provide this for you.. I use the battery protect relay to drop the battery when it gets over set voltage, then it stays disconnected while the charger is running so all 12v appliances are then running off the Progressive Dynamics.. this works well for my use, since I can plug it in and forget it.. if its long term storage like I have it in now, I turn off the charger and let battery get to bout 45% from the fridge and other stuff then pull the manual disconnect and power the Progressive Dynamics back up so the lights and stuff still work over the winter.
…..
Finally putting it all together.
"you just need the high side for the charger, and the BMV-712 can provide this for you"
think I can get the high side of the battery charge from the BMV-712 SOC point or battery voltage point.
Do not fully understand the statement above.
"I use the battery protect relay to drop the battery when it gets over set voltage, then it stays disconnected while the charger is running so all 12v appliances are then running off the Progressive Dynamics.."
So is this the same relay you use for the battery low voltage disconnect or is a second relay?
Can the BMV-712 provide the fully charged battery state signal and the fully discharged battery state signal for use in one relay or does it have to be two relays.

RandyP
 

dreadlocks

Well-known member
BMV-712 supports 2 batteries, basically it has 2 voltage monitors.. instead of hooking it up to two batteries you hook it up to both side of the battery protect, lets say the 'starter' battery is set to the load side and the house battery is hooked to the battery side.. I then hooked the relay output on the BMV up to the input on the battery protect.

AC Constant Voltage Charger/Converter is connected to load side.

BMV-712 you configure (through BT app) the relay behavior, It has high/low voltage settings for battery and high/low voltage settings for starter (aka load).. You set the relay to disconnect the battery when: battery voltage > 13.8v-14.2v (pick one in that range) OR when starter voltage > 14.2.. (also when battery low is under desired voltage and low SOC, those are diff settings)

What this does is, when battery hits full charge voltage (14.2v) the BMV disconnects the load/charge from the battery, now the battery will start shedding a few volts to get to its resting voltage.. normally this would trigger the relay to reconnect charger in an endless loop.. but when we disconnected the battery from the charger the load side is now ~14.6v and the 'starter' voltage being high keeps the battery protect disconnected while plugged into shore power.. when you unplug shore power everything cuts out for a few seconds and then the battery protect reconnects the battery..

Set a delay on reconnecting the relay so a short voltage drop on the load side (say fridge kicks on and it dips a little on inrush) it has plenty of time to recover (high voltage trigger) and cancel reconnecting the battery.

I've got an over-ride switch to the battery protect wired in parallel with the BMV relay, I call this my reserve switch incase I want to play dangerous games and go past my safety limits after reaching a low SOC.. but this switch also lets me force reconnect the charger to the battery manually if warranted for any reason.

This lets you plug it in, walk away and it'll fully charge the battery, then auto-disconnect it when charged and then run everything off the AC/DC power supply.. finally it'll revert back to battery when shore power is lost.

I've considered extending this setup so it also kills the generator when fully charged, then I could fire up genny and then go hit some trails and it all shuts down when everything charged back up.. but I'm hoping my pending solar install will greatly reduce the need for the generator for recharging.
 
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RandyP

Adventurer
Thank you for the detailed explanation of how you are using the BV battery protect relay interfaced with the BMV monitor to protect the L-ion battery from over/under charge and integrate the PD-4100L charger/converter into the system. Very well thought out and clever. I will use this information.

I am using a BattleBorn LiFePO4 100AH battery.

But note that I have a RedArc BCDC1240D Battery to Battery charger with MPPT solar controller to add to the power supplies for the LiFePO4 battery.

This device uses a MPPT solar controller that routinely maximizes the solar voltage/current operating point to get he most out of the solar panels as the sun conditions change. This causes some changes in battery charge output voltage from the BCDB while it maximizes monitors from solar panels.

The BCDC also routinely looks back at the vehicle alternator/battery voltage to verify that that system is at 13.2v or greater (batteries fully charged) before it delivers current to charge the camper battery. To monitor the vehicle battery voltage it interrupts the current from the vehicle momentarily to see the voltage of the battery without effect of voltage drop caused on the wires feeding the BCDC from the vehicle battery.

I would like to add this power supply to the house battery side of the V BP battery protector as noted in your setup above so it is seen as another power supply for the battery and protects the battery from over/under voltage.

I think this would work. Wonder if I might need to change the voltage threshold and delay settings in the VB712 monitor relay controller feature to compensate for the RedArc MO ?

Do you have sketch of the power wiring for your setup. I am developing ROUGH (hand drawn) sketch of my power wiring. I can jpg it and send it your way. I do not know how to post a picture here. Perhaps we could share power wiring sketch pics thru email or a messaging services ?

I have nearly every component of the system. Still waiting on fuse holders/fuses, the PD battery charger/converter, a ground buss bar. Will get wire, lugs, enclosure locally as needed. Very close to putting this system together.

Have a first of February trip to Arizona Organ Cactus monument planned. Would like to have this system up and running by then. Rain is forecast here for the next week. Could be a challenge adding the Solar Panels to the roof in the rain.

Thanks for any help or suggestions you may have.

RandyP
 

dreadlocks

Well-known member
Here's a quick diagram I whipped up of my setup, I dont have the solar hooked up yet but I will here before April.

Camper Wiring (2).png

The DC-> DC Charger does make things a bit more complicated, I'm not certain this is how solar will be wired up at this point.. I'm pretty sure the Victron MPPT charger will let me safely charge a lithium at whatever charge profile I want, I think the first try will be testing to see if this is adequate/safe enough and if so I'll let the MPPT Controller's own smarts decide when to charge and cut it out of the BMV logic.
 
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RandyP

Adventurer
What software program did you use to whippup the diagram ?
Thank you for the diagram. I see that all the power supplies will be on the load side of the battery protect relay. I see your bypass switch (reserve switch) for the battery protect relay. This a power and control diagram. Nice.
RandyP
 

RandyP

Adventurer
Looks like the starter battery voltage input to the BMV712 comes from the PD charger/converter internals. Could it be tied to the PD output '+' terminal as well ?
RandyP
 
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