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

[Overlord]

Thank God for your BMS then , as by now i could have caused serious damage
mine was set Absorb 14.4 and float 13.8

[electric1]

Originally Posted by chris smith

Thank God for your BMS then , as by now i could have caused serious damage
mine was set Absorb 14.4 and float 13.8

I doubt there would be serious damage, these cells are pretty resilient, it takes repeated abuse or severe overcharge/over-discharge to damage them.

Drop both voltages by 0.2V and you should get better results.

[Overlord]

have just done it. will wait and see what happens on a hot day. Anchored off Grand Cayman at the moment

[atoll]

i have an 800 amp bank of ni cad wet cell as batteries in 1.2v cells any reccomendations on charging and use as house batteries

[DaleM]

I just roughed in my solar / Lifepo4 battery bank over the weekend. Nothing blew up and the batteries charged. Here are the details:

The batteries are (4) 3.2 volt HiPower 200 amp cells bought used. They were initially balanced to 3.7 volts each. I wired them together to get 13.? volts using battery cable and lugs. The bank fits into a old plastic milk crate and drops into a locker in the boat. No BMS fitted. The existing 200 AH lead acid batteries stayed in place and are charged by the existing 120 volt charger or the engine alternator. The 1, 2 both switch picks which system is used.

Solar is mounted on the bimini. Solar is (2) 175 watt, 35 volt panels going through a Morningstar TriStar 45 MPPT controller with a separate output screen so I can read the battery state of charge. I programed it to charge at 13.8 and float at 13.6 to the LifePo4. The MPPT has a battery sense wire so the battery voltage is very accurate. Solar does not charge the LA yet.

The system charged the bank quickly with no problems. It was interesting to watch the amps quickly drop off as the bank reached 13.8. I shut it off when I left the boat just in case I screwed up in the installtion. I'll look it over next weekend before I go live 24/7.

Here are things I learned:
Panels cost a lot to ship. Cheaper high voltage panels require an expensive MPPT charger to get the useable amps down to 12 volts. Higher priced panels and a cheaper controller may have worked as well. It is a pain to program the MPPT charger but that is the only way to not cook the batteries. All of this requires fuses and disconnect switches on every wire to make sure nothing gets fried. This is not an install it and forget it system like we treat lead acid batteries. It costs a lot but I have doubled my battery capacity in a small space. Momentarily combining both batteries seems to do nothing. The 13.8 volts does not seem to have enough voltage difference to push power to the charged lead acids.

Costs to do this:
Batteries used $600
(2) 175 watt solar cells $500 + $200 for shipping = $711
MPPT controller and remote meter $500
Wires, disconnects, fuses etc. $230

Total about $2,041
What do I get for that? A system I can pull two days of 60 to 70 amp hours out of with no sun before I switch over to engine charged bank.

What I plan to run on the system when we leave the dock:
small Engel fridge 22 AH
Small watermaker 16 to 20 AH
TV up to 12 AH
Everything else 10 to 20 AH, all LED lights, no radar, no SSB, no electric windlass on a 34 Pearson.

I thought I'd post this summary for those after me. Thanks to all on this forum for talking about Lifpo4 and solar.

Dale
Your mileage may vary, I am not an expert, this may be dangerous, don't try this at home, use at your own risk.

[bill good]

Interesting the specs on the cells going into service as starter battery for my boat indicate nom. voltage 3.2V & since there is not a lot of power usefull at higher levels a 3.3v 5watt zener & 1 OHM 2 watt resistor across each cell allows 14.2V alternator to give a equilizing charge on startup & with a battery charger & solar available & will bleed back to approx 3.3v per cell without then when the zener stops discharge with no elevated charge voltage final cell voltage remains above 3.2v & bal within 2MV. Analog + KISS. cost $2.00 per cell retail. So not top or bottom bal. but operating level bal. All parts used have 300% above specs so what is wrong given it is a 12V system?
Regards Bill (system under test)

ps for Atoll sounds like aircraft batteries & they have a special charger also keep away from L/A as vapour from the L/A may kill them. Balance on service intervals.

[electric1]

3.3V zener is too low, you need at least 3.45V potential to charge these cells, or 3.5V-3.6V if you want decent charge rate. Full resting voltage will settle at 3.4V, then it will work for a while until it drops to 3.3V and only later down the road to 3.2V. Your 3.3V zener will spend too much time in open state and will waste too much power and get too hot.

And this system still does not give you per cell monitoring for HVC/LVC, which is more important than balancing alone.

[T1 Terry]

Hi Chris,
If you have access to AC mains power buy one of these http://http://www.hobbyking.com/hobb..._GENUINE_.html IMax charger balancers (around $40) and 2 http://http://www.ebay.com.au/itm/5p...item1e5dcf0032 plugs ($2.50 ea) with wiring and a http://http://www.hobbyking.com/hobb...idproduct=9282 Junsi cell log 8 ($28) so you can monitor the cell voltages while you are not on the boat by down loading the info to your computer.
The Balancer charger can charge an individual cell with settings to charge LiFeP04 cells so you can get the low cell up to where it should be, then plug in the JST-XH 5 pin plug and set the unit to balance the cells. Once it's finished you can unplug the unit and put it in the cupboard for next time.
The Junsi cell logger will record all the cell voltages so you can watch to see if there is a problem cell by following the graphs produced on your computer.
The bulk charge on the FlexMaster should be set to 14v, this is the area the most problems will be cause as the cells run away to high voltage very quickly once full so a high bulk charge will allow one cell to race away far more than is safe and the HVC will shut down the charge before the system can drop into absorb and float.
The system we developed to use the alarm port of the Junsi cell logger turns the charge off for 5 mins to allow the system load to pull the high cell down and then reconnects the charge, it will continue to do this until the other 3 cells catch up as any voltage above 3.4v in any one cell has virtually no capacity so it burns off quickly so very little is removed from the other cells, just the excess from the high cells, they soon self balance.

How long have you had the BMS fitted? Why didn't the shunt balancing bring all the cells in line, I thought that was what they were designed to do? Might be worth checking that the low cell isn't because one of the shunts is continually discharging dragging that cell low.

T1 Terry

[deckofficer]

A couple of questions. Are all types of Ni cads designed to give best life by almost full (90+% DOD)? On bank sizing for LiFePO4, I've always been told to size to a series string only, if possible for desired capacity.

[T1 Terry]

Hi Bob,
Sorry, I know very little about using Ni Cad cells as house power batteries although I have been told by a few people using them that over voltage spikes have a good effect on clearing the crystal build ups and the same effect memory charge as deep discharging but I've never experimented with it so I'll leave that in the "here say" folder.

With LiFeP04 cells unless you have a very sophisticated system that can evenly share the load and charge between multiple battery banks you will have much better results by building capacity by paralleling cells and linking these clusters in series to build voltage, balancing is much easier and in my experience in a 4 series cell battery they will self balance if not over charged, 3.6v is the absolute max charging voltage in any one cell group in my opinion and has worked the best in my systems.

T1 Terry

[mrm]

The recorded session of prof. Jay Whitacre from Carnegie Mellon University, discussing the LiFePO4 chemistry had been already referenced in this thread, but a long time ago and I think it is worth repeating, as most of questions asked recently on this thread are answered there in great detail. The first hour is a discussion of the battery chemistry and may appear too detailed to some without background in chemistry (although it explains a lot!), but around 1hr 10min he starts answering very practical questions and it is worth to carefully listen to this part at least.

Robotics Institute: Videos

Marius

[JoeFish]

Originally Posted by mrm

...but around 1hr 10min he starts answering very practical questions and it is worth to carefully listen to this part at least.

Robotics Institute: Videos

Marius

Marius,

Thanks for posting this. Very informative.

Best,

J

--
Bonne Amie

[bdbcat]

Folks...

First post, read the whole thing first. Good reading.

Just took delivery of 12 pcs CALB 180AH cells.
Unfortunately, the wrong bus bars were shipped. Too short. sigh.....

CALB offers to replace the bus bars if I send them back to China first. Now, shipping $50 worth of copper halfway around the world, twice, in order to enable a $3K battery bank makes no sense to me.

I need to make forward progress on this project. So, I modify the short bars by opening their holes so that they fit, albeit with somewhat less contact area. In my configuration, I expect to see only about 40A max through each bar, so should be OK. But not great....

I ask CALB to sell me new, correct bus bars at full retail. What's $50 in the grand scale? No can do. 500 pcs minimum quantity without cell order. sigh again.....

And so we come to my question:
Anyone know of a source for CALB 180AH cell interconnects, or an economical flex braid interconnect good for 40-50 A?

Thanks
Dave

[Cotemar]

I have made battery interconnects before out of copper tubing.

1) Cut copper tubing to length.
2) Hammer tube flat.
3) Drill two holes.

Better than any interconnect you can buy

[bdbcat]

Cotemar....

Thanks for the idea. I can do that...

Do you worry about lack of flexibility? Maybe more important in auto application, with higher vibration potential....But this is going on a 50 ft motor yacht. Not too much vibration in the battery compartment.

Thanks
Dave