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

[newhaul]

Ok here is a serious question as I am new to MPPT finally doing some programing via Bluetooth
Now my controller can be programmed for just about everything I set it to charge up to 14.0v just like my pwm but now I can also program when it starts charging again on the down slope . Set to 13.5v now but any issues with potentially taking it lower say down to 13.0v or even 12. Something to take advantage of my full bank size and a bit deeper cycling ?
250ah and I use about 25 to 30 ah a day 200 watts solar.

[fxykty]

Originally Posted by newhaul

Ok here is a serious question as I am new to MPPT finally doing some programing via Bluetooth

Now my controller can be programmed for just about everything I set it to charge up to 14.0v just like my pwm but now I can also program when it starts charging again on the down slope . Set to 13.5v now but any issues with potentially taking it lower say down to 13.0v or even 12. Something to take advantage of my full bank size and a bit deeper cycling ?

250ah and I use about 25 to 30 ah a day 200 watts solar.

It’s not very good to use voltage to control charging as the resting voltage curve is so flat between the knees (~ 10-90%). SOC is better to use - do you have a BMS that has an accurate SOC calculation?

But if you want to use voltage, 11.8-12.0V is reasonable for restarting solar charging, if you’re comfortable dropping the SOC to <20%. Are your solar conditions consistent enough to go that low? Otherwise, consider 13.0V to be closer to 50% SOC. Depending on your usage, there are going to be times when your consumption is higher than your solar charging.

[newhaul]

Originally Posted by fxykty

It’s not very good to use voltage to control charging as the resting voltage curve is so flat between the knees (~ 10-90%). SOC is better to use - do you have a BMS that has an accurate SOC calculation?

But if you want to use voltage, 11.8-12.0V is reasonable for restarting solar charging, if you’re comfortable dropping the SOC to <20%. Are your solar conditions consistent enough to go that low? Otherwise, consider 13.0V to be closer to 50% SOC. Depending on your usage, there are going to be times when your consumption is higher than your solar charging.

No not 12 volts but 12 something. Like 12.8 or even as low as 12.5

No the Daly does not have that capability hence my shunt and monitor gauge.

My consumption is rarely higher than production except when weather is so bad that I get no solar charging . Hence I'm adding a wind generator for those times.
But you have answered a question and it seems 13.0 is a legitimate possibility for charging .

[sparrowhawk1]

https://youtu.be/6vTaCkTVl7I

if I can find it I'll post the video where he discusses why you want the charge and float to be the same. But it's basically the fact that the voltage doesn't drop unless you have high loads so under light loads you can discharge your battery quite significantly before the voltage drops enough for your solar to start charging again. I have experience with this personally because I currently have 280 amp hour battery Bank, I have a peak of about 25 amps solar and will consistently get in the lower 20s in the middle of the day on an average sunny day. My BMS has Bluetooth so I can see exactly what's happening and I can also make adjustments. I'm using an old school mppt controller set to 14.2 volts and it works fine except for two problems even though 14.2 is the industry standard I think it's too high Although because it does not have a external voltage meter the actual battery voltage is only 14 to 14.1 I would rather have it stop at 13:8. my battery has always been fully charged when it hits that voltage or at least 98% so no reason to go higher. But the real problem is it absorbs for 2 hours and then goes to float at 13.2 worst case scenario is when the battery is fully charged right at the end of the day and over the night I discharged my battery about 40%, but it never drops below the 13.2 so the next day my battery doesn't receive charge from the panels unless I use a high load which drops the voltage enough for it to go back into bulk. I could use the settings on the BMS to prevent these two problems but I don't want the BMS disconnecting my charge controller from the batteries when 'high' amperage is coming in from the panels. And it's really not that much of an inconvenience, I usually make tea or coffee in the morning anyway using electricity.
Edit : I didn't watch the video first, I pulled it out of my library and I thought this was a two-parter but obviously this is the video where he explains what I just explained.
I know there are a lot of people that can't download videos so I hope this helps.

[newhaul]

Originally Posted by sparrowhawk1

https://youtu.be/6vTaCkTVl7I

if I can find it I'll post the video where he discusses why you want the charge and float to be the same. But it's basically the fact that the voltage doesn't drop unless you have high loads so under light loads you can discharge your battery quite significantly before the voltage drops enough for your solar to start charging again. I have experience with this personally because I currently have 280 amp hour battery Bank, I have a peak of about 25 amps solar and will consistently get in the lower 20s in the middle of the day on an average sunny day. My BMS has Bluetooth so I can see exactly what's happening and I can also make adjustments. I'm using an old school mppt controller set to 14.2 volts and it works fine except for two problems even though 14.2 is the industry standard I think it's too high Although because it does not have a external voltage meter the actual battery voltage is only 14 to 14.1 I would rather have it stop at 13:8. my battery has always been fully charged when it hits that voltage or at least 98% so no reason to go higher. But the real problem is it absorbs for 2 hours and then goes to float at 13.2 worst case scenario is when the battery is fully charged right at the end of the day and over the night I discharged my battery about 40%, but it never drops below the 13.2 so the next day my battery doesn't receive charge from the panels unless I use a high load which drops the voltage enough for it to go back into bulk. I could use the settings on the BMS to prevent these two problems but I don't want the BMS disconnecting my charge controller from the batteries when 'high' amperage is coming in from the panels. And it's really not that much of an inconvenience, I usually make tea or coffee in the morning anyway using electricity.

I can adjust my epever tracer. MPPT. In almost every aspect. If iirc my absorb is set to 10 min. At 14.2. And no float. Restart charging currently at 13.2v not on the boat atm

[mitiempo]

System I just set up for a customer. 400 AH Calb cells.

All charging sources - MPPT, DC to DC, and shore power charger set at 13.8 volts. All Victron. No float or set to a low 13.2 volts, minimal absorption if any. You only give up a few AH keeping the top at 13.8.

BMS set at 14 volts (3.5 per cell). When the first cell hits 14 volts all charging is stopped. Should never happen.

BMS shuts off loads at 2.8 volts per cell - 11.2 for the bank.

Expect it to be a trouble free battery bank for years.

[newhaul]

Originally Posted by mitiempo

System I just set up for a customer. 400 AH Calb cells.

All charging sources - MPPT, DC to DC, and shore power charger set at 13.8 volts. All Victron. No float or set to a low 13.2 volts, minimal absorption if any. You only give up a few AH keeping the top at 13.8.

BMS set at 14 volts (3.5 per cell). When the first cell hits 14 volts all charging is stopped. Should never happen.

BMS shuts off loads at 2.8 volts per cell - 11.2 for the bank.

Expect it to be a trouble free battery bank for years.

Sounds like a good set for a customer .
We all know as the DIY guys we tend to push things a bit but we also monitor things quite a bit more than the average boater we do this work for .

[CatNewBee]

13.5V for float. 13.2V is way too low.

[mitiempo]

Originally Posted by CatNewBee

13.5V for float. 13.2V is way too low.

My preference is no float at all. 13.2 gives me what I want - no current going in.

[fxykty]

Originally Posted by mitiempo

My preference is no float at all. 13.2 gives me what I want - no current going in.

Same, no need for float.

[sparrowhawk1]

Did you watch the video? There is no such thing as float with lifepo. the charger just goes to whatever voltage you set and holds it there, no ions flowing. Unfortunately my charger float settings cannot be adjusted and the problem with that is my battery can go below 40% probably even 50% before the controller will turn back on. The worst case scenario is if it's gone into float at the end of the day the next morning I'm 40 to 50% down but the voltage is still above 13.2 so all day long all the solar panels do is keep up with my demands so the next night I use another 40 to 50%........ But like I said the easy workaround is to just put a high load on it momentarily to drop the voltage so that it will go back into bulk. But if I leave the boat unattended my batteries are going to needlessly deep cycle.

[newhaul]

Originally Posted by sparrowhawk1

Did you watch the video? There is no such thing as float with lifepo. the charger just goes to whatever voltage you set and holds it there, no ions flowing. Unfortunately my charger float settings cannot be adjusted and the problem with that is my battery can go below 40% probably even 50% before the controller will turn back on. The worst case scenario is if it's gone into float at the end of the day the next morning I'm 40 to 50% down but the voltage is still above 13.2 so all day long all the solar panels do is keep up with my demands so the next night I use another 40 to 50%........ But like I said the easy workaround is to just put a high load on it momentarily to drop the voltage so that it will go back into bulk. But if I leave the boat unattended my batteries are going to needlessly deep cycle.

My refrigerator kicks on and voltage goes from resting of 13.8 right down to 13.2 and solar kicks in and that's when I'm only down 20% on my lfp bank. I don't need to do anything it's all automatic

[newhaul]

Originally Posted by sparrowhawk1

Did you watch the video? There is no such thing as float with lifepo. the charger just goes to whatever voltage you set and holds it there, no ions flowing. Unfortunately my charger float settings cannot be adjusted and the problem with that is my battery can go below 40% probably even 50% before the controller will turn back on. The worst case scenario is if it's gone into float at the end of the day the next morning I'm 40 to 50% down but the voltage is still above 13.2 so all day long all the solar panels do is keep up with my demands so the next night I use another 40 to 50%........ But like I said the easy workaround is to just put a high load on it momentarily to drop the voltage so that it will go back into bulk. But if I leave the boat unattended my batteries are going to needlessly deep cycle.

Watch the video again listen to the first statements . It says the charger he is using is for lead based chemistry. Not lfp.

[sparrowhawk1]

Originally Posted by newhaul

Watch the video again listen to the first statements . It says the charger he is using is for lead based chemistry. Not lfp.

It's only called lead-based because you can't adjust the float and can only lower the bulk to 14.2. It's what I have and that's why it can be a problem with lithium. But I was thinking of getting another refrigerator and not an engle this time. But I'm pretty sure the voltage has to go below 13.2 for a period of time for my controller to kick back into bulk. I'm not advising anyone to do anything just telling you my experience of why having a float voltage lower than the bulk voltage is bad ( exactly what the video was about). if I had a fully adjustable controller I would set it 13.8 bulk 13.8 float. My experience is it hits the bulk voltage and then 0 amps go in. the solar panels only put juice into the loads zero goes into the battery. I have Bluetooth on my BMS so I can see exactly what is happening sometimes a little bit of amps will go from the battery into a load and then the solar panels will put a couple amps back into the battery but but for the most part it's 0% amperage flow.

[newhaul]

Originally Posted by sparrowhawk1

It's only called lead-based because you can't adjust the float and can only lower the bulk to 14.2. It's what I have and that's why it can be a problem with lithium. But I was thinking of getting another refrigerator and not an engle this time. But I'm pretty sure the voltage has to go below 13.2 for a period of time for my controller to kick back into bulk. I'm not advising anyone to do anything just telling you my experience of why having a float voltage lower than the bulk voltage is bad ( exactly what the video was about). if I had a fully adjustable controller I would set it 13.8 bulk 13.8 float.

Don't know your controller but my tracer is lfp fully programmable and to kick it on to charge only takes a few seconds below set voltage.