Lithium house bank project

[tiltrider1]

I have a 1060 AH Lifepo4 bank. Yesterday I pulled 40amps for 6 hours and 20 amps for 8 hours. It took me 5 hours at 100AH charging to get back to full. These numbers don’t exactly add up because I am not monitoring very carefully plus I still have heavy demand even while charging. I am again pulling 40 amps today. I am experimenting with how hard I can hammer the bank. My 1400 AH lead acid would have been down to 12.0v with this much use. So far I have not been down to 13.0v. This is not exact science. It is a test run to see what I can expect from LiFePo4. I do not normally spend a day watching 10 hours of TV with the wife surfing the Internet. So far I find my self more comfortable with the LiFePo4 batteries than my old lead acid batteries.

 

[Delta Riverat]

Yeah Baby!

If your bank works, don't fix it. But when it's time...do you really want to install more heavy low capacity clunkers...

Or something much better -

 

[Delta Riverat]

Hooked all the grounds up today and everything that wasn't working is working now. Aft bilge pump (the important one) and the 12 volt cigarette socket in the saloon (not so important but gets lots of use)

When I left the boat yesterday, the batteries were at 13.2. No charge overnight. Was on for 4 hours, lights on, recharged my flashlight and when I was done the batteries were still at 13.2. No big loads except the drawer fridge on the fly for 24 hours, but hey, it's hot here now and the beer is ice cold -

Now on to the engine panel, get the new lead-acid charger connected and the bridge solenoid wired and verified and then we'll be ready for some boat rides.

Soon I hope to have as much confidence in my starter batteries as I do in the LiFePO4 house bank. And soon after the house bank will grow to 880 AH. I can run House 2 (600AH) dry and switch to House 1 for another 280AH. Sort of a safety zone -

 

[SteveK]

I can run House 2 (600AH) dry and switch to House 1 for another 280AH. Sort of a safety zone

If I may, based on nothing specific, as long as you have a shunt and/or other monitors consider keeping just one bank to more easily monitor SOC, better control over charging. With LFP you do not need that extra safety net we needed with FLA

 

[Delta Riverat]

Good idea, but that would not be easily done.

However, in a way it is already. This whole project started with the idea of (2) 300AH batteries for the house and that is what is in there now. During the process I found out that what I thought was a generator battery was not. It was simply bridged over to the starboard house battery, House 1 on the helm switch. Now it is bridged over to House 2, the one in the toolbox enclosure and the shunt for the monitor is also in there keeping track of both batteries.

I bought the third Li Time battery (280 AH) after I found there was no generator battery and that will be the new House 1 after I get the other dead 4D lead-acid out of there.

 

[CMS]

I see a lot of LFP banks lacking overcurrent protection…

 

[Delta Riverat]

I installed a Blue Sea Systems 250A terminal fuse on each battery. In addition the BMS will limit continuous current to 200A.

 

[luna]

ABYC’s E-11 requires the overcurrent protection device at the battery to have an Amperage Interruption Rating equal to the battery manufacturer’s short circuit rating or 20,000 Amps @ 125 V.

Blue Seas MRBFs have an AIC of only 10,000 amps @ 12 V. which is likely fine for small LA banks, but typically not for LFP.

You may want to consider a Class T, or perhaps a NH fuse to comply with ABYC.

 

[tiltrider1]

Just so people understand, most fuses are installed to preserve the wire simple as that. However, as you get in to larger battery banks, you end up with enough power that the bank can melt down the fuse and jump across the gap. You need a fuse that is capable of withstanding the destructive power of your bank. T class fuses are usually rated for suck applications but, you need to match the fuse up not just to your wire size but also the destructive capability of your bank.

 

[Barking Sands]

On the Epoch 460 there is a 500amp, 50k AIC rated fuse inside each battery. Then I have 250 amp MRBF on each positive terminal.

 

[Delta Riverat]

According to Li Time, the BMS is good for 200A continuous and 800A for 5 seconds. I think the 250A fuse will melt long before the 5 seconds.

Just looked it up and at 3X rating (750A) the fuse will melt in 1 second.

 

[luna]

The trip delay curve has nothing to do with the fuse’s amperage interrupt ability.

In the case of a full on battery short circuit where your LFP battery will deliver 1000s of amps, the 250 amp fuse blows open almost instantly but the plasma in the fuse or the remaining fuse parts provide continuity and the current still flows. The BMS is undoubtably no match for this amount of current and is rendered inoperable.
The only thing that is stopping your 2/0 battery cable from becoming a very large red hot heating element is the Class T fuse with its higher AIC.

Unless your LI Time batteries have a fuse embedded like the 50,000 AIC. rated fuse of Barking Sands Epoch batteries, you should consider a Class T or better fuse.

 

[Delta Riverat]

There is a class T fuse (400A) already installed. I found it while down in the engine room a couple weeks ago. I have a replacement in the toolbox now in case it blows. Also a box of the 250 amp terminal fuses.

The battery spec for internal resistance is <40 milliohms. Google shows 2-20 typical. So lets use 10 for fun. At 13 volts the max current even w/o a BMS is 1300 amps on a dead (zero ohm) short.

The fuse has an interrupt rating of 10,000 amps at 14 volts. Yes I know about arcing and plasma, Pops was an electrical engineer at Detroit Edison (now DTE energy). The fuse has to be able to quench the arc. Somewhat more difficult at 2000 volts.

I feel confident in the fuse rating as I don't see 10,000 amps happening ever.

 

[luna]

I see that you now acknowledge the existence of a 400 A class T fuse in the circuit. That’s great!

Understanding that you found it in the ER a while ago and you just installed 3 LFP batteries, you should ensure it is within 7” or 42” if sheathed, of the battery post.

 

[Delta Riverat]

Today I can say that House 2 is done;

Just need to put the lid back on. But that was not the main effort today;

The start charger is on and works -

Don't worry, I'll clean up that wiring tomorrow when I install the solenoid jumpers, the 12V feed to the solenoid (helm switch is wired to ground) and see how overnight does on the start batteries. All went well, no arcing-sparking or blown breakers, I flipped the switch and went back down to the engine room and found all settings correct (defaults for flooded) and the charger jamming 40 amps (20 to each side) to the batteries. Left the boat with the charger running.

Looking forward to my visit tomorrow to see how the overnight went.

 

[Delta Riverat]

When I returned the Xantrex showed ready and charge under 10%, float mode, less than 4 amps. When I lifted 1 ground decreased to less than 2 amps. Perfect. This charger is for the 2 start batteries currently two sets of 2 6 volt golf cart batteries in series. Yeah deep cycles used for starters...but hey, they work. These golf cart batteries continue to amaze me as I have been guilty of serious abuse.

I let them dry up once. Seriously dry as in I put a gallon of distilled water in one and a half gallon in the other to fill them up. Then charged and they worked fine. Just recently as this project tells the 10 amp charger failed and they went flat as in not being able to crank the engines.

Now that I have a capable charger installed, a couple equalizing cycles will be done. I have destroyed batteries before with far less abuse than described above. When I need replacements I'll get 4 new 6 volt GC batts, which have the additional benefit of being 60 pounds each a manageable weight for me to handle alone.