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

[nebster]

Originally Posted by sparrowhawk1

Well here's a low voltage disconnect that I'm going to have to get something like regardless. I was hoping there would just be a simple programmable disconnect for let's say 14 volts or 13:8.https://www.amazon.com/Victron-BPR00...069&psc=1&th=1
It also says that it can be a charge interrupter. But I want something that will measure the voltage at the battery and disconnect it between the panels and an mppt.

You can use a BP for that. To open the high voltage side you’d need a separate contactor rated for that side and driven by the BP’s external output. But with the BP specifically, in that scenario you’d be paying for an expensive FET gate rated for battery voltage and high currents, but only using the device as a glorified voltmeter.

But, why do you want to disconnect on the high voltage (panel) side in the first place? Why not just have the monitor tell the charger to stop charging, or simply open the charge side?


Anyway, some of your options become less reasonable depending on what else is going to be in your system — what other chargers, loads, etc, you have at play. For example, it doesn’t do much good to design just for the solar disconnect if you also have three other sources, two of which are hard to program correctly. At that point it might make sense (be more reliable, simpler, and/or less expensive) to move the charge control hardware and logic to a different point in the circuit.

I can’t promise you that anyone here will do free design work for you, but you might want to start your own thread and lay out your system in its entirety, to have a chance at getting reasonable advice.

[sparrowhawk1]

I have an existing mppt controller, it says not to disconnect from the battery when the panels are connected. It's changing the higher voltage into higher amperage which I would think would be less of a problem for a switch if one at all. For $60 I can get a 100a low voltage programmable disconnect I would like to do the same for the high voltage maybe 50a, just for the solar. Thank you for any links for this type of device.
PS. Right now my panels are parallel so we're only talkin about 20 volts or 40 or so in series if I switch.

[nebster]

Originally Posted by sparrowhawk1

Nebster. What voltage are you stopping at to get 92%? thanks

54.40V at 0.22C with one hour of absorption.

But those numbers won’t help you much, because there are a lot of real world factors that can change the needed voltage.

For example, I have 6 feet of 2AWG cable between each of my batteries and a bus bar, plus an inline fuse. That stuff creates a small but important voltage drop. So my voltage is artificially “high” because I’m not taking my reading directly at the cells.

For another example, the meter in my charger may be off by a little bit compared to yours. I don’t care much how accurate it is; I just want it to be precise, so it yields repeatable results.

If you want to use the same approach, you have to set the whole system up and then experiment. Gradually increase the CV voltage threshold and/or the absorption timeframe and/or the absorption rate termination point, and measure how much energy goes in. After a few tries, you can get it dialed in pretty much wherever you want, as long as your charge rate is the same.

It’s much tougher to do that with variable charging like from PV. I have my PV set much lower on the charge curve to ensure that it never over-trickle-charges. But that works well for me, because PV is usually supplementary charging for my pack; we need to run the genset regularly when we are off grid unless the weather is perfect. So I just have it set at a lower stopping point, somewhere around 80%.

[newhaul]

Originally Posted by sparrowhawk1

Price? Link? Also is it adjustable to exact voltage or does it just have a lithium selection. Newhaul same question for the controller you're using. Thanks. Also in the past controllers have had small terminals, I like using heavy gauge wire so if Max gauge wire is known maybe pass it on too. If I have a programmable controller or high and low voltage disconnect I don't think I would go with a drop in.

as I stated my controller is programmable to the .01 volt. I provided a link to the controller in an earlier post. I also being a power miser myself ( the biggest load is my 400 watt inverter and my holding plate refrigeration . I run the boat through my charge controller 30 amp load ( also setable to the .01 volt for disconnect and reconnect .
All is listed in the tech manual .
It logs both ah in and ah out that way. Also can show instantaneous amps in or out.
( I paid $23 for mine )

that all means I can accurately monitor the system with the push of a button.

[newhaul]

Originally Posted by sparrowhawk1

I have an existing mppt controller, it says not to disconnect from the battery when the panels are connected. It's changing the higher voltage into higher amperage which I would think would be less of a problem for a switch if one at all. For $60 I can get a 100a low voltage programmable disconnect I would like to do the same for the high voltage maybe 50a, just for the solar. Thank you for any links for this type of device.
PS. Right now my panels are parallel so we're only talkin about 20 volts or 40 or so in series if I switch.

a respectable breaker like this inline between the panels and charge controller.
https://www.amazon.com/Bussmann-CB28...R3REMMGCRYCR0V

[sparrowhawk1]

Thanks again newhaul. I went to the link you showed me and it didn't have those specs but that seems like it will do everything I need for a low price. I'll dig a Little deeper for the specs but you answered my questions(actually gave me better advice) [emoji106] I currently have a 100 amp fuse for my lead acid.

[sparrowhawk1]

Okay I just downloaded the manuals they also sell this controller. I've got my homework cut out for meAttachment 194043

[sparrowhawk1]

Hit send too soonAttachment 194044
That price is just for the accessories
164.99 for the controller.
Still going to study even though I have the solution with the cheaper controller.

[Checkswrecks]

Originally Posted by KTP

I know LiFePO4 batteries are one of the safest lithium chemistries but how are your thoughts on the dangers of hydrogen flouride gas if the batteries start going up in smoke (unlikely that they would cause a fire but I was reading a paper that seemed to indicate a large bank could produce grams or possibly even kilograms of hydrogen flouride)?

You see some of the puncture testing and volumes of some sort of smoke coming out of the battery but most of the videos are really focused on the fire danger or in LFP case, the lack of fire. They don't seem concerned with what is in all of that smoke.

If you were on a crossing, out 2000 miles in the Pacific and the battery pack started emitting this much smoke, would it be a situation where you could just sit on the bow for a few hours and wait for everything to burn down or would you need to keep some sort of 3M filter mask on board so you could go down below and turn things off? Hydrogen flouride I think can cause blindness too, so maybe a full face mask?

Or is this just not a concern with LFP? Since it doesn't usually or ever really catch on fire?

A burning LFP battery is very similar to a plastics or electronics fire with the primary smoke products being CO and CO2, which make it really hard to breath. There is a hydrogen and oxygen release which can combine with humidity to create acids, making it very hard to see and to breath.

Again, the way to stop any battery fire is flooding it with lots of cooling water. Before that is needed, you can go a long way to prevent a fire with your system design, maintenance (largely checking connections and cell voltages), and handling.

[newhaul]

Originally Posted by sparrowhawk1

Okay I just downloaded the manuals they also sell this controller. I've got my homework cut out for meAttachment 194043

https://www.ebay.com/itm/EPEVER-MPPT...edirect=mobile

You might just like this better than windy nation

Only 145 with the Wi-Fi option

[Evenstar]

Originally Posted by sparrowhawk1

Okay thanks. I still don't understand why it wouldn't make more sense just to get a high and low voltage cutoff.

If the cut off works on the cell level and monitors every cell...maybe. You can't just do it by bank voltage. And you want to watch for cutting everything off. You don't want to shut the whole boat down as indicator of charge completion, so a dual bus setup would work better. You may want to monitor voltage to cut off the load bus at one upper level the charge bus at another level.



My BMS monitors cell level voltages and temps, high/low current & charge, etc.


At some point it seems like you're re-inventing the wheel.

[rgleason]

Newhaul, my first goal was to recharge my modest needs of 80-130ah (perhaps a little more sometimes) with a 200ah lifepo bank with a new alternator while leaving and entering harbor (1/2 hr each way). Then I was advised that .5C would reduce the life of the lifepo batteries and I realized that some solar (not much, but enough, 50w-100w) would help compensate for the loads, so decided to not go above .35C and perhaps run the engine a little longer (not something I really want to do). All of this is still very hypothetical, except I've bought a Gen3 VSR Alternator Regulator and need to find space and make brackets for a 150-200a large frame alternator (throttled back).

So in thinking about this further, I think the question I should have asked, is how much difference would charging at .5C occasionally, say 25% of the time, make in cycles/life?


The only reason I am considering LiFePo is because we are on a mooring and I can't stand running the engine for 5 hours to top off the LFA batteries frequently, and I do not like the frequent maintenance charging to 100% required by LFA. We are not liveaboards, but do a fair amount of cruising all summer.


Do you think the 100watts of solar would alleviate the need to switch to LiFePo, with our use?


I managed to recover my (2) old T105's from sulfate grave, so now I have four of them working well. I could just install them all (one set would replace my 14 year old west marine gel - cables are big enough) and use that for the next 4 years, but I really don't want to deal with recharge to 100% all the time!!!

[CatNewBee]

Originally Posted by rgleason

Newhaul, my first goal was to recharge my modest needs of 80-130ah (perhaps a little more sometimes) with a 200ah lifepo bank with a new alternator while leaving and entering harbor (1/2 hr each way). Then I was advised that .5C would reduce the life of the lifepo batteries and I realized that some solar (not much, but enough, 50w-100w) would help compensate for the loads, so decided to not go above .35C and perhaps run the engine a little longer (not something I really want to do). All of this is still very hypothetical, except I've bought a Gen3 VSR Alternator Regulator and need to find space and make brackets for a 150-200a large frame alternator (throttled back).

So in thinking about this further, I think the question I should have asked, is how much difference would charging at .5C occasionally, say 25% of the time, make in cycles/life?


The only reason I am considering LiFePo is because we are on a mooring and I can't stand running the engine for 5 hours to top off the LFA batteries frequently, and I do not like the frequent maintenance charging to 100% required by LFA. We are not liveaboards, but do a fair amount of cruising all summer.


Do you think the 100watts of solar would alleviate the need to switch to LiFePo, with our use?


I managed to recover my (2) old T105's from sulfate grave, so now I have four of them working well. I could just install them all (one set would replace my 14 year old west marine gel - cables are big enough) and use that for the next 4 years, but I really don't want to deal with recharge to 100% all the time!!!

You can't kill a LFP with 0.5C, they are designed to swallow 1C all the time and for fast charging 3C.

During the winter I juced up my 1kA LFP with the e Onan generator and the 5kVA Quattro (220A charger) plus 2x40A legacy charger. In 2h the battery was full again (almost 600Ah charged) and I could heat the cat for hours on the LFP bank. Simply awesome.

[JmanC]

Originally Posted by sparrowhawk1

All the charge controllers I've ever used have said not to disconnect from the battery when the solar panels are connected. So it seems to me drop-ins would be harmful to my controller. I would think the easiest way around this is to have a sensor on the battery and have a disconnect where the panels go into the charge controller. Recommendations appreciated.

Not sure if this is the same thing. But i have disconnected my agm from my chargers (sterling AC and victron mppt 50A) during bulk and absorb stages a good dozen times in testing and they seem to handle this abrupt disconnect fine.

[Pete7]

Originally Posted by rgleason

Do you think the 100watts of solar would alleviate the need to switch to LiFePo, with our use?

If it does and I don't see why not, it will be a shed load of dollars cheaper. What is a 100w rigid panel and a 75/10 Victron MPPT? about $200 say.

Your numbers are similar to ours. Just downsized the house bank to 2 x Gp24s (160AH), so not really tested them yet. However, the previous bank was 220AH of FLA, actually ordinary 200 cycle truck batteries rebadged. Charged with the alternator for short bursts and 80+30w of solar managed okay during the summer so long as it didn't rain for more than 2 days straight.

2 years ago 80w panel swopped out for 150w rigid panel, plus 60w suitcase panel for in harbour or at anchor. Now were were using the electric slow cooker to cook and still have spare power. Bit limited in the depths of winter but batteries always sat at float. So these ordinary batteries lasted 7 years. Sure we were down below the recommended 80% capacity replace point but it didn't matter. Even during the winter allowing the panels to charge the batteries up after we left the boat meant they were full when we returned next.

Was it worth the investment, absolutely, wish I had gone to 150w initially. I sold the Honda 20i because we just didn't use it anymore. Oh and not using shore power means the anodes last longer too.

Pete