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

[Maine Sail]

Originally Posted by T1 Terry

Charging with a constant voltage of 13.8v is very slow to get the last 10% or more in, fine if you have plenty of time, a higher charge voltage is required if time is limited but you need to get near fully charged before you stop the charge cycle.

I have not found this to be slow at all, but perhaps for Li it is slower in the top end.. I don't find my bank really limiting much until into the high 90's as a % of charge. Just yesterday I was still pumping 24A of current in at 99% SOC and it was declining.

It ran the alt at full tilt for a solid 30 minutes before the current began to reduce when the bank hit the target voltage. Unlike LA batteries, when I say "reduce", it went from 130A down to 125A and very slowly tapered but I was already into the high 90's (above 96% SOC) when this occurred.

I had dropped the bank back to 81% SOC then fed it with the alt. Initially it was running at about 151A then when it got warm settled in at about 132A to 128A. I walked up to the sail loft and when I got back 30 minutes later the alt was still in the 110A range but the banks was nearly full or as full as I'd need in a short run.

I have never in my life seen a bank get back to 98-99% SOC so fast especially at 13.8V.... Yes, I could certainly push higher, but for now I am choosing to manually push the voltage up for the BMS to balance but only when the cell logger shows me the cells are "out". Thus far, after about 60 cycles, the cells are still in-balance to within 0.01V.... No complaints.

You are 100% correct that a single v-belt will easily get destroyed. An alternator not up to the task will also get fried. I am also using an alternator temp sensor to cut field based on alt case temp. Mine will run in the high 120A range for a long while and still remain below the alt temp limit.... I am using a 10 cog "J"/Jason industrial serpentine belt to drive the alt..

[NahanniV]

Maine Sail:

Are you using your LiFeP04 bank to start your engine ?
Any problems, or imbalance caused by this ?

How did you end up managing your backup AGM ?

Cheers,
JM.

[Maine Sail]

Originally Posted by NahanniV

Maine Sail:

Are you using your LiFeP04 bank to start your engine ?
Any problems, or imbalance caused by this ?

How did you end up managing your backup AGM ?

Cheers,
JM.

Starts the engine with vigor. No issues.. Course my engine starts in a duration of about .75 seconds.. The AGM is charged via a Duo Charge for now or BOTH if I decide I needed that. I may still wire an A/B to the solar to give it absorption voltage every now & then..

[roetter]

Originally Posted by T1 Terry

...

A few things we found,
it's better to limit the alternator max current to around 60% of it's capacity, easier on the drive belts and on the alternator itself, slipping drive belts add a lot of heat into the alternator rotor and they don't live long when you do that. Methods of limiting that output are varied, mine was to use an inverter and mains charger, unfortunately I had already stuffed the alternator by that stage.
.......
T1 Terry

Hi T1 Terry

I would like to get more information on how you drove and controlled an inverter from the alternator to run a regular charger. I would like to drive a Victron Multi charger from the two alternators on my cat. It would be easy to program the Multi charger values with a PC connection to experiment with the LiFePOs.

Rolf

[hellosailor]

I have seen an alterantor belt literally hump up like an inchworm and climb off a pulley when a heavy load kicked in, so proper tension and alignment become critical if the alternator ig oign to engage a heavy load. Which is why some external regulators have a "soft start" to prevent that shock on the belt.

But in my limited experience I've never seen an alternator actively regulated to a set % of it's full capacity. That could easily be done with conventional power regulator circuits but that would also be pointless. An alternator's coils should saturate as the load comes up, and given adequate cooling the first thing to overheat is normally the diodes. By using oversize diodes that can tolerate the max output, you turn the alternator itself into a limiting factor. Or, have an alternator shop rewind it with less feet of thicker wire, which should reduce the output and raise the heat tolerance, again self-limiting it without the need for a regulator.

Of course some alternators are specified as "farm and industrial" use rather than automotive, and they usually can handle heavy loads much better as well.

Either way it should be a fairly simple job.

[Maine Sail]

Originally Posted by hellosailor

I have seen an alterantor belt literally hump up like an inchworm and climb off a pulley when a heavy load kicked in, so proper tension and alignment become critical if the alternator ig oign to engage a heavy load. Which is why some external regulators have a "soft start" to prevent that shock on the belt.

But in my limited experience I've never seen an alternator actively regulated to a set % of it's full capacity. That could easily be done with conventional power regulator circuits but that would also be pointless. An alternator's coils should saturate as the load comes up, and given adequate cooling the first thing to overheat is normally the diodes. By using oversize diodes that can tolerate the max output, you turn the alternator itself into a limiting factor. Or, have an alternator shop rewind it with less feet of thicker wire, which should reduce the output and raise the heat tolerance, again self-limiting it without the need for a regulator.

Of course some alternators are specified as "farm and industrial" use rather than automotive, and they usually can handle heavy loads much better as well.

Either way it should be a fairly simple job.

Limiting alternator output is quite common with external regulation. With the Balmar regs you can set this with belt manager or just dial it back. The alts run cooler, the belts last longer and when the owner is ready to address his belt and pulleys he already has the "large" alternator and all he needs to do is turn it up... The alt temp sensors do the exact same thing by reducing the field when the alt heats up beyond safe levels....

[hellosailor]

Maine-
You're right of course but I wasn't really thinking of that as regulating the alternator. They all work by lowering the self-excitation, which in turns limits the amount of power that can be produced. Which of course IS effective regulation...I was just thinking the other way around, of letting the "black box" run as hard as it wanted to, and performing the regulation out side of it. (Rather than by feedback from the regulator and back into it.)

[T1 Terry]

Originally Posted by Maine Sail

Limiting alternator output is quite common with external regulation. With the Balmar regs you can set this with belt manager or just dial it back. The alts run cooler, the belts last longer and when the owner is ready to address his belt and pulleys he already has the "large" alternator and all he needs to do is turn it up... The alt temp sensors do the exact same thing by reducing the field when the alt heats up beyond safe levels....

I was thinking or a similar idea to control alternator output, pulse width modulation to achieve a desired max current output, then as the load reduced the on pulse could be extended.
The Inverter and charger will probably be the easiest to do though, I'ce already rewired my feeds into the inverter to drive it from either the start battery or the house battery, with provision for both to be on just in case the start battery is flat so I can use the house battery to power the starter. Needed this a few time while we were away, even when the Li batteries were on their knees with a cell at 2.85v under load, there was still heaps there to start the 4 cyl diesel with a great deal of enthusiasm :lol:

Hi T1 Terry

I would like to get more information on how you drove and controlled an inverter from the alternator to run a regular charger. I would like to drive a Victron Multi charger from the two alternators on my cat. It would be easy to program the Multi charger values with a PC connection to experiment with the LiFePOs.

Rolf

I used 2 H/D 12v solenoids with a 100% duty cycle wired to self illuminated rocker switches. One solenoid in the positive cable from the start battery to the inverter, the other solenoid in the cable from the house battery to the inverter. With both solenoids switched on, the two batteries are linked at the inverter, when the engine was running, I turned the house battery solenoid off and turned the battery charger powered by the inverter on. You can't use a combined inverter/charger, the battery charger must be a stand alone unit small enough for the alternator to be able to run 24/7, about 60% of the alternator output is about the limit. If I'd had the presence on mind to do this in the first place rather than on the side of the road 2 weeks into the trip, I could have saved myself a lot of headaches, 6 fanbelt replacements and a stuffed alternator, live and learn I guess. I just ran out of time to fit the solar panels before I left, so the emergency back up became the main charging system, and it wasn't up to the intended task by a long shot.
Turns out, the previous owner had a lot of electrical problems, the alternator was changed a few times, the last time they fitted an 11A section belt pulley instead of the required 13A section pulley, the load tore the belt v section in minutes, a 120 amp alternator with a single pulley is asking a lot in the first place, using the wrong pulley was a recipe for failure. There is no room to fit a double pulley or a flat belt pulley, there are 3 belts on there now and it's a climb inside and underneath to remove each belt, luckily it's the middle belt that's the problem but the radiator and fan shroud doesn’t provide much room to work in. at least in a boat you don’t have these things in the way so life’s a bit easier there, but I did have the side of the road to stop on when a belt left the building, you don’t get that luxury in a boat.

T1 Terry

[Maine Sail]

Arghhhhhh.

Somewhere in the process of installing my bank I lost the cell level volt sensing cable for my Cell Log 8S (the multi-pin one).

I now can't seem to figure out what that part number is or if ANYONE in the USA stocks it? I know it was a separate line item when I ordered the Cell Log 8S but now can't put my fingers on it.

The Cell Log 8S took 7 weeks to get here from Hobby King so I hate to go through that again for a $2.00 part........

Part number anyone? USA source?

[neelie]

If its the 5 wire mini plug with tails, PM me your address, I'll throw one in the mail.

I have a couple of spares.

I'm in Hong Kong - you should get it in a week,

Cheers

[NahanniV]

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.

Here is the Canadian company listing where I bought mine:
http://www.greathobbies.com/producti...od_id=TGHX1012

I'm sure you can find one locally.

[CharlieJ]

RC-
Here is where I got my 8S JST-XH Pigtail. The company's name is appropriate ;-)

Progressive RC
6906 15th Ave NE
Seattle, WA, 98115
(443) BATTERY

[T1 Terry]

these people make very good quality plug and lead set eBay Australia: Buy new & used fashion, electronics & home d
i am trying to get them to make the pug and leads for the alarm port, the wires that come with the Junsi cell logger are very flimsy and break off at the plug ib no time.

T1 Terry

[ebaugh]

An interesting chart from Balqon I had not seen before. Only a glossy sales brochure with no detail on what testing was done to derive the chart. But it clearly shows the hopeful case for ROI on LFP banks.

[Talbot]

Originally Posted by ebaugh

An interesting chart from Balqon I had not seen before. Only a glossy sales brochure with no detail on what testing was done to derive the chart. But it clearly shows the hopeful case for ROI on LFP banks.

It also shows that the AGM batteries are not the panacea that their advocates claim.