14 replies to this topic

[Vic Harder]

@vic

What kind of issues? Just finished install last night. Prelim testing looked good.

Before the update it would charge for a while and then shut down.  i thought it was a heat issue until the update.  

 

Note that the 100% reading is obviously bogus, or it would not be charging this much.  I resynchronized to 100% after I was sure it was full up... 

[Vic Harder]

Thanks for the info. Rando, on your set up using the ACR, do you get a full charge from the alternator. Alternators for FLA batteries usually charge at about 13.9 volts whereas lithium requires 14.6 volts. is there also a bleed off from the higher lithium battery voltage to the lower voltage truck battery? Or does the ACR take care of that? I would like to be able to keep using the ACR and not have to buy a DC-DC charger. The BLUE SEA folks did not think ACR would work with lithium.  I am using 10 gauge wire in the ACR circuit. Should the wire size be larger? This is sure helpful. Thanks

rando is very knowledgeable about LiFePo4.  I feel like a noob myself.  That said I had a Blue Sea 7622 ML-ACR in my system before I went with an Orion TR.  

 

Yes, there is bleed from the higher resting voltage LiFePo4 to the truck battery.  I think rando considers this a benefit, as LiFePo4 batteries last longer if not stored at 100% SOC.  The ACR only disconnects if the voltage is too low, so in this case it does NOT disconnect.  You could disconnect it manually, of course.

 

10g wire can be an issue.  It is good for 30A, but the voltage drop can be enough to cause the ACR to cycle through disconnect/reconnect all the time.  Voltage sense will indicate there is enough voltage to charge and it connects... once the current starts to flow the voltage drops, and it senses that and disconnects.  I ran 2g welding cable to prevent that.  4g should be enough though.

 

What is your alternator output voltage?  Mine is 14.2V at 70*F.

 

Disadvantage of the DC-DC is that your solar panels will no longer charge the truck battery.  It is nice to have that charging if you are parked for long periods of time between camping trips.  

 

rando also has outlined a circuit using a heavy duty relay to manually switch the system between DC-DC charging and using the ACR so you can have the best of both worlds!

[rando]

Thanks for the info. Rando, on your set up using the ACR, do you get a full charge from the alternator. Alternators for FLA batteries usually charge at about 13.9 volts whereas lithium requires 14.6 volts. is there also a bleed off from the higher lithium battery voltage to the lower voltage truck battery? Or does the ACR take care of that? I would like to be able to keep using the ACR and not have to buy a DC-DC charger. The BLUE SEA folks did not think ACR would work with lithium.  I am using 10 gauge wire in the ACR circuit. Should the wire size be larger? This is sure helpful. Thanks

 

I am not sure where the idea that lithium batteries need 14.6V to be fully charged came from.   It is absolutely untrue.   There are very interesting (albeit quite technical) results from some actual test that Battery Stream performed on LiFePO4 batteries with their state of charge vs the charge voltage:

https://www.powerstr...rge-voltage.htm

 

Note this are all for a single cell, so you need to multiply by 4 for a 12V battery, but to summarize the capacity vs charge final voltage for an LiFePO4 battery is:

 

12.0V = 2% SOC

12.4V = 4% SOC

12.8V = 8% SOC

13.2V = 31% SOC

13.6V = 99% SOC

14.0V = 99% SOC

14.4V = 100% SOC

14.6V = 100% SOC

 

What this tells us is that once the battery gets to 13.6V it already at 99% SOC.   Now there can be some voltage drop in the wires, so maybe going to 14V to be totally safe is worth it.   Going up to 14.6V is just increasing the risk of the cells becoming out of balance and shortening the life of you battery and there is no extra benefit.   For reference, I set my solar charger to 13.4V when in storage and 13.8V when we are actively using the camper and want the battery to be full.   On most all days the battery gets back to 100% using 13.8V from solar alone.

 

As for the ACR, yes it will stay on most of the time, and in effect the starting battery will be always float charging off your house battery.  There is not really a down side to this, particularly if you have solar to charge things back up.    If for what ever reason, your solar is not producing, then the ACR will disconnect the lithium battery at about 20% SOC, which is actually a great SOC to store it at.  Unlike lead, lithium batteries prefer to be stored at a low state of charge.   There is no risk of the truck battery being drained by the camper. 

 

The reason to get a DC-DC charger is if you need maximum charging current from your alternator.  Others suggest it is required to stop your alternator burning out from the load of charging the batteries, but with the long run of 10awg wire that you have, there is no way this will happen. Given the size of your solar system, I am guessing you don't need much from your alternator, so a DC-DC is likely not required, but you could add one if your alternator is not providing enough current.   It may actually be cheaper to add the DC-DC then to upgrade the wire.

[nixfwc]

Thanks for the info. Rando, on your set up using the ACR, do you get a full charge from the alternator. Alternators for FLA batteries usually charge at about 13.9 volts whereas lithium requires 14.6 volts. is there also a bleed off from the higher lithium battery voltage to the lower voltage truck battery? Or does the ACR take care of that? I would like to be able to keep using the ACR and not have to buy a DC-DC charger. The BLUE SEA folks did not think ACR would work with lithium.  I am using 10 gauge wire in the ACR circuit. Should the wire size be larger? This is sure helpful. Thanks

[Wildcat]

Here's my solution to the ACR question that I sort of stumbled upon with my lithium.  I have the remote ACR disconnect switch on my dashboard and just turn it to disconnect mode when I turn off the truck.  I have the same Blue Sea 7622 and installed the dashboard switch several years ago.  When I got the lithium battery for the camper I noticed the bleed-off to the truck battery, which is an Optima AGM.  I also have a Victron monitoring gauge mounted on my dash as I don't have solar and I rely upon the truck charging when I'm running the engine.  Of course using the manual connect/disconnect requires me to remember to do it, which took some training but now it's sort of automatic for me, like putting on a seat belt, I just look at the switch to turn it on when I start the truck. 

 

FYI, I am running 2ga welding wire to the the ACR and lithium battery as Vic mentioned.  It probably was not really needed and I did that before I discovered the integrated battery management in the lithium limits the amount of incoming charge from the truck alternator.  

 

The disconnect switch is not a perfect solution and I'm sort of agreeing with rando that charging to 14.5 is not really beneficial.  And it's sort of dis-heartening to look at my Victron the morning after I forgot to disconnect the ACR and see that the lithium voltage has dropped to match the truck battery (maybe I should stop looking at the Victron monitor on the dash).  When I get home I usually plug the lithium into my wall charger and it brings it up to 14.5, so it will get a full charge quite often.  My truck alternator (older Toyota) also seems to bring it up to 14.4.  I'm assuming that I might avoid the bleed off by switching to a lithium in the truck when the Optima goes out, but that's several years away (I usually get 8-10 years out of my Optima's in all my vehicles), and I'll probably have another truck by then. 

Edited by Wildcat, 10 August 2020 - 06:04 PM.