LiFePO4 Batteries: Discussion Thread for Those Using Them as House Banks

[deckofficer]

Originally Posted by mbianka

THE BIANKA LOG BLOG: ELECTRO SAILING AROUND NEW YORK: PART ONE

Considering the way I operate I still don't see the economics working for me to change out to Lith's at this time. I could replace my four 200 amp AGM's for $1,900. Lith's would cost double and that's before I start adding chargers and BMS to the costs too. That does not mean I'm not interested in them. Just I'd still like to see a bank that makes it to 1,500 charge cycles like is claimed and the balance issues be not so hands on. For now my AGM bank is pretty much hands off and I like that.

(4) of the 260 a-hr cells are now $820, less than 1/2 the price of your AGM.
Usable energy;
200 a-hr AGM at 50% DOD 100 a-hr for 500 cycles
260 a-hr LiFePO4 at 80% DOD 208 a-hr for 2000 cycles

Use the AGMs till they die, then make the switch Capt Mike, you won't be sorry.

[noelex 77]

Originally Posted by NahanniV

It's a "JST-XH" connector (.1" spacing). I got a 5 pin (for 4 cells) cable from a local hobby store that caters to electric Remote Control Hobbies. This is commonly called a balance connector in the hobby world.

[deckofficer]

Best price I could find $27.98 here. Cell-Log Cell Voltage Monitor 2-8S Lipo

I think I'll get one.

Just ordered two, their cheap.

[NahanniV]

Originally Posted by deckofficer

Best price I could find $27.98 here. Cell-Log Cell Voltage Monitor 2-8S Lipo

I think I'll get one.

Just ordered two, their cheap.

If you don't need the USB connection and logging there is also an 8M(monitor) version for half the price:

Cell-Log 8M Cell Voltage Monitor 2-8S Lipo

As far as I understand, it still has the audible alarm and an alarm port.

[deckofficer]

Originally Posted by NahanniV

If you don't need the USB connection and logging there is also an 8M(monitor) version for half the price:

Cell-Log 8M Cell Voltage Monitor 2-8S Lipo

As far as I understand, it still has the audible alarm and an alarm port.

I should have looked a little more. When you buy an item on line they show what others who bought the same item had looked at, and this one didn't show up. At least with the USB I'll be able to plot a chart and share with the good folks here. O-well, could have saved $30.

The main thing is having the alarms for over/under voltage. Set at 2.9 volts and 3.9 volts, should keep me from harming the cells during usage and charging.

[T1 Terry]

Originally Posted by noelex 77

Does anyone know the name of the input plug/socket for this cell logger.

Google doesn't give up the secret in this case.
Thanks
EV-Power | Cell Logger 8 cells / 1 battery (USB port)

This guy on EBay sells at the right price and will make plugs with longer leads if you make a sepial request 5pin JST-XH Connector Adapter plug silicone 4S 4 Cell | eBay I have bought a lot of plugs and leads from this guy, they are good quality.

T1 Terry
EDIT: The cell loggers generally don't come with a plug so it needs to be purchased seperately. i recommend fitting 2 plugs, one up near all the other monitor stuff and the other close to the battery. The reason for the one close to the battery is if you ever need to do balancing, it makes life much easier. Don't forget to fuse all the wires (no need to fuse the neg wire) a 5 amp fuse is plenty, the wires don't carry any current.

[T1 Terry]

Originally Posted by deckofficer

I should have looked a little more. When you buy an item on line they show what others who bought the same item had looked at, and this one didn't show up. At least with the USB I'll be able to plot a chart and share with the good folks here. O-well, could have saved $30.

The main thing is having the alarms for over/under voltage. Set at 2.9 volts and 3.9 volts, should keep me from harming the cells during usage and charging.

they are so cheap getting the logger one gives you a spare for the main unit. You could set one logger up in the montoring area and the other one up at the battery box with a smoke alarm wired across the alarm output wires, simply soldered to each side of the test button. Set the alarms for 0.2v higher and lower than the momitoring unit, that way is the control unit fails an alarm will warn you of a problem.

T1 Terry

[Adamante]

Originally Posted by T1 Terry

Don't forget to fuse all the wires (no need to fuse the neg wire) a 5 amp fuse is plenty, the wires don't carry any current.

How do you recommend fusing these wires - inline fuses soldered directly to the wires?

[mbianka]

Originally Posted by mrm

You stated previously, that for best longevity you like to utilise only 30% of your bank capacity. This means, that 200Ah AGM bank gives you 0.3*200 = 60Ah of usable capacity.

LiFePO delivers 70% of its capacity while claiming 7000 cycles (or 80% claiming 5000 cycles). This means that you will get the same or better usable capacity from 100Ah cells (0.7*100 = 70Ah).

To make a 48V bank you will need 15 LiFePO cells.

At current nominal (not clearance!) prices, it amounts to 15 * $110 = $1650.

So you still have $250 to spend on cell loggers, mini BMS and such

We see much better claims at present
As for 'hands off' - I have a feeling we will get there quite soon.

Well, actually I do have more usable capacity with the 8A4D AGM's I just don't tend to use them as I switch to hybrid operation. But, the additional capacity is there if I need it. It's a battery "bank" and I don't want to "withdraw" too much at any one time. It's just how I roll and it is working out pretty well so far. By not drawing down the bank too much I should get better battery life out of the bank and it also means less time for charging when I anchor. A question d0 Lith Ion's charge faster than LA?

You, you do bring up a good point with those pricing numbers for the 100 amp packs. I may have to rethink the power options when it comes time to replace the batteries. Which I hope will be a few more years down the road. By then the Lith packs may be even cheaper and the cell balancing issues solved.

[mbianka]

Originally Posted by deckofficer

(4) of the 260 a-hr cells are now $820, less than 1/2 the price of your AGM.
Usable energy;
200 a-hr AGM at 50% DOD 100 a-hr for 500 cycles
260 a-hr LiFePO4 at 80% DOD 208 a-hr for 2000 cycles

Use the AGMs till they die, then make the switch Capt Mike, you won't be sorry.

Deckofficer:

But won't I need four of the 260 a-hr cells for my 48 volt propulsion bank? That's $3280 right? Still it's more amps and cycles so I will certainly rethink the issue when the AGMS need replacing. Prices should even be cheaper and the track record will be longer by then too. I would hope the cell balancing issues should be pretty much taken care of by then too. I want to be reaching for a beer not my Fluke meter when I drop anchor.

[T1 Terry]

Originally Posted by Adamante

How do you recommend fusing these wires - inline fuses soldered directly to the wires?

Either the fuse block method or the single fuse method. Probably better the fuse bloke with a sealed cover to reduce the risk of corrosion causing an increase in resistance at the fuse connection points, these fuses have enough problems with that at the best of times.

[daddle]

Originally Posted by T1 Terry

Don't forget to fuse all the wires (no need to fuse the neg wire) a 5 amp fuse is plenty, the wires don't carry any current.

Hmmm. Seems like all the small wires of a cell logger have the same melting and burning potential and should all be fused. Should consider all the failure modes. They are all at some voltage relative to their neighbors. It's not a simple loop circuit like the 12V distribution on a boat.

An alternative could be to mount the cell logger close to the cells and use really good durable high-temperature wire (not the cheap PVC jacket). They are only sense wires. The current is very low. Use very small conductors that will generate very little heat before vaporizing themselves. Like 28 gauge. Bundle them in a durable fireproof sleeve where they route thru the boat.

All those little corroding fuses look like trouble. Especially because the LFP users are trying to accurately and reliably sense millivolt differences.

[NahanniV]

I used a 5 pin trailer harness and connector.

Each wire has a pigtail fuse soldered to it and the fuse is crimped and soldered to the terminal lug. Then the whole thing is sealed with two layers of adhesive lined shrink tubing. I don't plan to blow a fuse, but if I do it will mean re-doing the connector.

[daddle]

Are people using special insulated wrenches on those cell terminals? Yikes! Touching a wrench across the terminals of a LFP must be spectacular.

[Adamante]

Originally Posted by NahanniV

Each wire has a pigtail fuse soldered to it and the fuse is crimped and soldered to the terminal lug.

Yup, that's the way I would do it. Using any kind of a fuse holder or a fuse block, unless it has been evacuated or filled with an inert gas, creates the likelihood of corrosion. Might get away with it in an RV, but I wouldn't do it in a boat.

As far as using a thin wire instead of a fuse, that would constitute the fusible link wire situation that was discussed earlier in the thread and identified as a potential fire hazard. If you would go to the trouble of encasing it in some sort of a fireproof transparent tube (glass?), you may as well install a proper fuse.