A "cheap" LiFePO4 drop-in update

[Don L]

Just an info update:

I have now had my $306 100Ah LFP drop-in Power Queen batteries 11 months (they are cheaper now). They are still babies really for LFP batteries and I have 4 of these for a 400ah house bank. These batteries have mostly only been charged by solar. They of course charge via the alternator while motoring and once in a while they get charged via battery charger either using shore power or my Honda EU2200. For the most part they operate in the range of 60-100% state of charge. So far the biggest problem turned out to be the idiot that installed them (me) not tightening all the terminals.

Since it has been cloudy for 4 days it seemed a good time to test them for the first time before heading out again in couple of months. So I just let them run down a couple days and then hurried the discharge along today by turning on every DC load I could. I finally stopped after -342Ah, which works out to be 14.5% charged by the math and was 19.6% by the battery monitor that has a PF of 1.05 programed into it. Voltage after a 10 minute wait with all DC power off was 12.67V, which works out pretty much to be about 15% SOC on most curves.

So my cheap batteries look good!!! they may have gone up in voltage more, but I wanted to turn the lights back on. In normal operation I never would have let my batteries get so low and the only time would be if I was gone a long time and solar failed or it was cloudy 4 days.

And to note I made NO changes to my electrical system at all changing from acid batteries to the LFPs. I had a "cruiser" type system already and all I did was change the various setpoints. Right now the charger is running on an AGM setting that will charge back o 14.1V and then float at 13.4V. That probably wouldn't be 100%, but who cares and I probably will turn it off once batteries are back in the 90% range.

Now I will say this, the same great things could have been written about my last set of FireFly carbon foam acid batteries at this time of use. Those lasted 2.5 years and then died a death that exactly matched partial state of charge problems they were not suppose to have.

 

[Barking Sands]

That sounds perfectly viable to me!

 

[DavidM]

400 Ah of Li batteries puts quite a load on your propulsion engine’s alternator. What kind of alternator do you have and how has it worked out?

David

 

[Don L]

400 Ah of Li batteries puts quite a load on your propulsion engine’s alternator. What kind of alternator do you have and how has it worked out?

David

I have a 100amp Balmar I have reduced to 70 amps with my regulator belt management feature. My 50 hp engine doesn't even notice it. Alternator is 22 years old.

 

[Delta Riverat]

Yeah, that's what I'm planning too. Reduce output and never worry about it.

 

[Don L]

Yeah, that's what I'm planning too. Reduce output and never worry about it.

Well I recommend you also program setpoint low enough to never trip BMS and have a temperature sensor on alternator to protect it just in in case

 

[DavidM]

Yes the Balmar temp system is a good way to protect the alternator. As I recall it cuts the alternator output in half when it measures 180F+ case temp.

David

 

[Don L]

Yes the Balmar temp system is a good way to protect the alternator. As I recall it cuts the alternator output in half when it measures 180F+ case temp.

David

You have to check what is programmed into the regulator. My ARS-5 was defaulted to 105C. Which is funny because Balmar recommends 100C. I changed mine to 90C and have not seen it go above 83C.

 

[DDW]

Don't know about the ARS-5, but the 614 has some problems in this regard. It will progressively cut back the field current as the temp reaches the limit, then hunt up and down overshooting a few times before stabilizing. It can go low enough that the charge voltage and current drops, then the regulator thinks it should go to float. At least I think that is what happens. I've seen it a few times, derate due to temp then end up in float prematurely.

Even the Wakespeed 500 hunts when it hits the temp limit, though it did not mistake that for done like the Balmar. The best solution I could come up with is to see what the field current % was once stable and still charging hard, then set the field current limit to just above that. The result of this is the temperature approaches the limit more asymptotically, so the current/temp software servo loop can deal with it without overshooting so badly.

 

[twistedtree]

It’s a classic PID feedback control loop to handle such a thing.

 

[Don L]

Don't know about the ARS-5, but the 614 has some problems in this regard. It will progressively cut back the field current as the temp reaches the limit, then hunt up and down overshooting a few times before stabilizing.

All I can say is that my 100 amp alternator with an ARS-5 with a B-4 reduce and a 90C temp setpoint I have watched put out 70 amps for hous at 83C temp with no hunting etc.