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

[wholybee]

Originally Posted by CatNewBee

A normal good stock alternator can do the job without any changes. Neither the alternator nor the LFP will die a sudden death when motoring in a regular setup on a boat with charge distribution diodes and a lead acid start battery.

You will be surprised how low the actual charge current in reality is, that arrives in the LFP through the wiring, a 120A Yanmar alternator on a catamaran can push maybe 40A in the battery bank 5 to 8m away, it will not overheat.

If you want to fry it, use lead acid batteries and run the inverter and watermaker while motoring, that would do the trick.

If you only get 40A out of a 120A alternator with an LFP battery, something is limiting it. I get 90A out of a 70A alternator if I disconnect the temp probe and don't reduce the output in the regulator programming.

[CharlieJ]

@CatNewBee:

A normal good stock alternator can do the job without any changes. Neither the alternator nor the LFP will die a sudden death when motoring in a regular setup on a boat with charge distribution diodes and a lead acid start battery.

You will be surprised how low the actual charge current in reality is, that arrives in the LFP through the wiring, a 120A Yanmar alternator on a catamaran can push maybe 40A in the battery bank 5 to 8m away, it will not overheat.

You just could not be more wrong.

Most alternator manufacturers spec their stator temperature at 100C to 110C. I prefer staying under 100C which leaves some charging capacity unused.

I recently commissioned a high end trawler with a Cummins main engine and a large case 24VDC/80A alternator. The LFP bank was 5 x 24VDC @ 200Ahr each. The output from the alternator went to a 24VDC AGM start battery and the output from the start battery went to a 50A buck/boost converter and thence to the LFP bank. I depleted the bank to about 30% DOD and started the M/E. My partner was monitoring the buck/bust converter on a laptop and I was monitoring the alternator temperature with a FLIR camera.

After about 20 minutes, the highest temperature on the alternator was 100C and I thought we were good. At the 30 minute mark, the highest temperature on the alternator was 103C. I had my partner trim the buck/boost output to 40A and within two minutes, the highest temperature on the alternator was 98C.

Look at the videos I posted upthread and look at MainSail's photos above. This is real world stuff. Properly wire a stock alternator into a LFP system with no controls on the output and you will burn up the alternator.

[bill good]

From when LIFEPO4 went on the cat.2011. 300a/h bank. Small 1GMs would not get above 1600 RPM because of the load reflected back to the stock alternators. Any attempt to increase power would stop the engines. Also low RPM is where most alternator overload will show up. Answer in this case was to fit frequency sens. relays set to bring alternators on line at 1800 RPM. No alternator issues.


Present boat 300A/H LIFEPO4, DC-DC converter with the first 7mins run time charge limited 20A to allow 70A standard alternator to recharge the start battery, warm up belts etc & expect engine to be above idle for 40A. All Automatic.

So far new install is working 100% Removed nearly 200kg lead. New battery, control ccts & case 28kgs.

Regards

[captianjuan]

Hi all. im about to gear up for a lithium conversion. I have question about I should go about achieving my desired ah for the bank. for example, to achieve 1200ah I could use 3, 400ah bank or 4, 300ah banks. could anyone tell me the differences and pro's con's?
thanks for the info.

[CatNewBee]

Originally Posted by captianjuan

Hi all. im about to gear up for a lithium conversion. I have question about I should go about achieving my desired ah for the bank. for example, to achieve 1200ah I could use 3, 400ah bank or 4, 300ah banks. could anyone tell me the differences and pro's con's?
thanks for the info.

less bigger cells is always better.

[LeighC]

I think that Victron video is not a good scenario because even at 3000 RPM its alternator speed is too slow, looks not even quite on to one
Most diesels have about a 3 to one belt ratio or more, & no one tries to charge at an idle, more like 1200 to 1500 ERPM (1500 X 3 = 4500RPM) or where ever the sweet spot is, usually for less vibrations etc & the higher the revs the better the belts like it also, let alone cooling.
The gearing on that Victron set up needs to have a larger pulley on the electric motor if it would drive it, just to make it more real life.
Just my 2c worth

[fxykty]

Originally Posted by captianjuan

Hi all. im about to gear up for a lithium conversion. I have question about I should go about achieving my desired ah for the bank. for example, to achieve 1200ah I could use 3, 400ah bank or 4, 300ah banks. could anyone tell me the differences and pro's con's?
thanks for the info.

Most recommendations are to parallel first to the desired capacity, then series to the desired voltage, so that you only need a single 4-cell BMS, and to avoid paralleling batteries. The following are all based on creating a 12V battery bank.

The simplest option is to use single cells in series (4S) but I’m not sure that anyone makes 3.2V cells larger than 1000Ah so you wouldn’t be able to make a 1200Ah battery, if that size is critical.

The next simplest is to put 2 or 3 or 4 cells in parallel to create a 3.2V battery of the capacity you want and then to put 4 of these batteries in series to get the voltage you want (e.g. 2P4S if you parallel 2 cells first). You could still use a single BMS, but it wouldn’t manage the individual cells. That is less important as cells in parallel will stay very close to each other. 4 individual BMS would be used if you want to manage each individual cell. This would also mean that the BMSes must be able to work together to manage the battery as whole properly and is generally considered more complex than really needed. If you were to use 300Ah cells you could make your battery 4P4S.

Finally, you could build 2 or 3 or 4 individual batteries at the voltage you want using either of the previous two topologies and put them in parallel as you’ve suggested. That will require a BMS per pack and each battery would be handled independently. This is most redundant but also most complex and expensive (lots of connections, care taken to ensure cable lengths for each battery pack are equal in length, using BMS that work together to manage charging and load cut offs). Your optimum topology would be xP4S 2P, with each battery being 600Ah and using 150Ah cells if x=4.

I’ve seen recommendations to never use cells larger than 200Ah in a boat due to vibration and shocks, though I’ve also not heard of any large-cell banks failing in that way. Maybe that advice is dated?

[CatNewBee]

Originally Posted by fxykty

Most recommendations are to parallel first to the desired capacity, then series to the desired voltage, so that you only need a single 4-cell BMS, and to avoid paralleling batteries. The following are all based on creating a 12V battery bank.

The simplest option is to use single cells in series (4S) but I’m not sure that anyone makes 3.2V cells larger than 1000Ah so you wouldn’t be able to make a 1200Ah battery, if that size is critical.

The next simplest is to put 2 or 3 or 4 cells in parallel to create a 3.2V battery of the capacity you want and then to put 4 of these batteries in series to get the voltage you want (e.g. 2P4S if you parallel 2 cells first). You could still use a single BMS, but it wouldn’t manage the individual cells. That is less important as cells in parallel will stay very close to each other. 4 individual BMS would be used if you want to manage each individual cell. This would also mean that the BMSes must be able to work together to manage the battery as whole properly and is generally considered more complex than really needed. If you were to use 300Ah cells you could make your battery 4P4S.

Finally, you could build 2 or 3 or 4 individual batteries at the voltage you want using either of the previous two topologies and put them in parallel as you’ve suggested. That will require a BMS per pack and each battery would be handled independently. This is most redundant but also most complex and expensive (lots of connections, care taken to ensure cable lengths for each battery pack are equal in length, using BMS that work together to manage charging and load cut offs). Your optimum topology would be xP4S 2P, with each battery being 600Ah and using 150Ah cells if x=4.

I’ve seen recommendations to never use cells larger than 200Ah in a boat due to vibration and shocks, though I’ve also not heard of any large-cell banks failing in that way. Maybe that advice is dated?

Winston makes 5000Ah and 10000Ah cells too. 1000Ah are pretty close to 1200Ah (actually they deliver 1300Ah when new and used at 0.3...0.5C)

[captianjuan]

Originally Posted by CatNewBee

Winston makes 5000Ah and 10000Ah cells too. 1000Ah are pretty close to 1200Ah (actually they deliver 1300Ah when new and used at 0.3...0.5C)

do you recommend a supplier for Winston batteries? Im in the states but in Hawaii.

[Steve_C]

Originally Posted by captianjuan

do you recommend a supplier for Winston batteries? Im in the states but in Hawaii.

Definitely contact Julia Yu, sales@skypowerintl.com

She is immensely helpful and is the best method for direct sales. I have recently purchased 8 1000AH Cells and am extremely satisfied.

[fxykty]

Originally Posted by Steve_C

Definitely contact Julia Yu, sales@skypowerintl.com

She is immensely helpful and is the best method for direct sales. I have recently purchased 8 1000AH Cells and am extremely satisfied.

Agree, she is awesome if you want Winston cells. She also suggested combining my order with another order she’d received to the same destination, which meant my shipping cost was half. The cells arrived very well packed, had sequential serial numbers, and were within 0.015V of each other charged at just under 3.2V each.

Julia is also on Cruisers Forum.

[blondjohn]

I'd appreciate criticism, comments and suggestions on the attached design sketch for conversion to LFP for the house bank on our full-time liveaboard. If I was starting from scratch I would buy canbus everything but we already own most of the older equipment shown, plus spares of the same on board. The theory of operation includes the ability to isolate the LFP bank (at 50% SOC) when connected to shore power and run the house loads from the engine bank with float from the Prosine 2.0 inverter / charger. This is the reason for the extra switch between the charge bus and the starting battery bank. Note that the Blue Sea ML RBS 7713 solenoids have a manual switch for manual isolation of the house bank. Note also that the Prosine inverter function has a programmable low voltage shut-off so I feel comfortable connecting the Prosine to the charge bus. BMS wiring is not shown but I have purchased a TAO centralized BMS. The system will be programmed with a cascade of audible alarms and disconnects.

Thanks!

[donradcliffe]

Originally Posted by blondjohn

I'd appreciate criticism, comments and suggestions on the attached design sketch for conversion to LFP for the house bank on our full-time liveaboard. If I was starting from scratch I would buy canbus everything but we already own most of the older equipment shown, plus spares of the same on board. The theory of operation includes the ability to isolate the LFP bank (at 50% SOC) when connected to shore power and run the house loads from the engine bank with float from the Prosine 2.0 inverter / charger. This is the reason for the extra switch between the charge bus and the starting battery bank. Note that the Blue Sea ML RBS 7713 solenoids have a manual switch for manual isolation of the house bank. Note also that the Prosine inverter function has a programmable low voltage shut-off so I feel comfortable connecting the Prosine to the charge bus. BMS wiring is not shown but I have purchased a TAO centralized BMS. The system will be programmed with a cascade of audible alarms and disconnects.

Thanks!

Off the top of my head. Where is the BMS? Solenoids are big parasitic draw unless you use latching. What is the duogen doing? Why not a VSR battery combiner? Why not a isolation switch for the LFP instead of the Start? Is the BMS max current big enough for the starters, windlasses, microwave? Why 920 ahr? Daily energy budget at anchor and underway?

[blondjohn]

Originally Posted by donradcliffe

Off the top of my head. Where is the BMS? Solenoids are big parasitic draw unless you use latching. What is the duogen doing? Why not a VSR battery combiner? Why not a isolation switch for the LFP instead of the Start? Is the BMS max current big enough for the starters, windlasses, microwave? Why 920 ahr? Daily energy budget at anchor and underway?

Hi Don,
Thanks for your questions and comments. The TAO BMS will be mounted next to the batteries. Each group of "4P" will be treated as a single cell by the centralized BMS. The solenoids are "Blue Sea ML-RBS 7713 Remote Battery Switch with Manual Control Auto-Release" and draw 13mA when on. I intend to have 3 in the system for 39mA parasitic draw. That is less than one amp per day. The Balmar Duocharge is keeping the engine bank full by trickle charging from the house bank while preventing the engine bank 2 from being drawn down by house loads. I already own the Duocharge so I decided to see how it performs in the new system before I consider replacing it with a larger and more sophisticated DC to DC converter. The BMS is centralized and does not carry any house load current. We typically use about 300 A per 24 hrs at anchor. More at sea. We have been spending years at a time in places where it is very difficult if not impossible to get batteries shipped in. The house bank is sized to allow individual cell failure and still have adequate capacity. It is also sized to continue providing adequate power for an extended period as the batteries approach end of life and begin to lose capacity. And finally, in what should really should be a separate discussion, there is a lot of data showing that LFP battery life is extended by limiting charge level and depth of discharge. I'm still studying, but it looks like cycling between 80% and 40% SOC could provide significantly longer service life than running between 100% and 20% SOC. Remember I'm trying to optimize for extended service life, not weight or cost per total amps provided during the service life of the batteries.

Thanks again for your time to question my system design.

[Simi 60]

Originally Posted by CharlieJ

@CatNewBee:

. Properly wire a stock alternator into a LFP system with no controls on the output and you will burn up the alternator.

Not just LFP
I killed off two large frame continuously rated alts hooked up to our old AGM bank
Didn't even bother with alt charge on the new LFP bank