New LFP House Battery
- Thread starter SycloneDriver
- Start date
I will check when I am on the boat tomorrow.
i don’t recall seeing that menu option when i went through the settings, but maybe i missed it or it is called something else. I do have a Charge switch and a Discharge switch. The discharge switch will kill the outflow of power out of the battery. But in the photos, both batteries are showing the discharge switches as being on.
Greg
I don't see anything wrong.I don’t want to hijack @SycloneDriver’s post, but this is AlFP system related, so hopefully not egregious… if I should start a new thread, please comment,
I was checking my new Humseink LifePo4 batteries today after the batteries have been on the charger for a few days. Batt 1 showed 100% SOC and Batt 2 showed 99%. Interestingly, the BMS on Batt 1 shut off the charging switch. I assume since it was at 100% and couldn’t accept any more charge. The batteries are paralleled (see photo below).
View attachment 233092
I went out for a 2.5 hour sail today, with a light load on the house bank (fridge, VHF, stereo, CP & instruments).
When I got back, I left the charger off until I could check the BMS for the 2 batteries. Now, Batt 1 still showed 100% SOC and batt 2 was at 86% SOC.
I am not sure why these batteries, if wired in parallel, would not supply power to the house system in equal measure. Instead, it seems that one battery is doing all of the work
View attachment 233093 View attachment 233094
I have written to Humseink to see what they can tell me (if anything). I have discovered that their BMS app will not let me see what the individual cells are doing. They did say that their engineers are working on an upgrade to the app.
So, here is a crude drawing of my DC system (left out the AC side of the equation for now)...and only the house side. Left off the starter battery, switch, charger, etc for that.
View attachment 233095
Does anyone see anything blatantly wrong with this set up (I hope not, as I have sailed with it a few times now). Or could this just an issue with the batteries? One thing I could try is to install a positive and negative bus bars and hook each battery individuslly to the bus bars. But the charger would charge the bus bars (single output charger ). Not sure that changes things much. Does paralleling LFP batteries need to be different than FLA?
Greg
I am curious as to what you have the charge and maintenance voltages set at in the charger?
Does the alternator have a programmable regulator?
jssailem
SBO Weather and Forecasting Forum Jim & John
- Oct 22, 2014
- 23,160
It was a glorious sunny day, and it was time to test the solar panel charging my LFP.
A 50-watt panel is producing 36 watts. The app says that at this rate, it will take 36 hours to fully charge your battery. The battery is at 18%. So I let it go, and an hour before sunset, the battery had recovered to 25%.
My second battery was at 22%. I plugged in the 12V 25W Victron charger. When I got going, the message was that 25amps at 14.2 would take 3 hours to charge the battery.
When it was at 100%, I disconnected the battery, put it away, attached the solar-charged battery (at 25%) to the power charger, and went off to dinner. By the time I returned, it was at 75%.
A 50-watt panel is producing 36 watts. The app says that at this rate, it will take 36 hours to fully charge your battery. The battery is at 18%. So I let it go, and an hour before sunset, the battery had recovered to 25%.
My second battery was at 22%. I plugged in the 12V 25W Victron charger. When I got going, the message was that 25amps at 14.2 would take 3 hours to charge the battery.
When it was at 100%, I disconnected the battery, put it away, attached the solar-charged battery (at 25%) to the power charger, and went off to dinner. By the time I returned, it was at 75%.
This can happen when the individual cells in a battery are not balanced. The BMS will continue accepting a charge until all the cells are balanced at (or very close to) the same voltage. In use the cells will not charge or discharge evenly, top balancing returns them to equal voltages. This is pretty normal behavior for LFP batteries.
The other problem, uneven discharge between the 2 batteries seems more unusual. It may take a few charge/discharge cycles for the BMS to learn the SOC. The usual causes for the imbalance between the 2 batteries are uneven jumper lengths or the manner in which the batteries are put in parallel. The way you have wired the batteries was once the recommended method, it is still fine, however, current thinking has the batteries connected to a bus bar to parallel them and the loads taken off the bus. Buried somewhere on the Victron site is a basic wiring manual that shows the different methods of paralleling batteries. There may also be information on Calder's site, www.BoatHowTo.com.
While we're looking at the photos, the DC+ wires all need to be fused. One of the dangers of LFP batteries is the amount of current they can discharge in a short time. There should only be 2 DC+ connections on the battery, the jumper from B1 and B2 and the cable to a Class T fuse. A Class T fuse should be used because it has a higher interrupt level (AIC) than other fuses. If there is a short the power delivered from an LFP battery can arc across a blown fuse. Class T fuses prevent the arcing. All the wires after the Class T fuse can be fused with other styles of fuses. ATC fuses in inline holders or a Blue Seas fuse box will work. The fuse box is a bit neater.
Hi Troy,
My alternator (original dumb alternator), is still wired to my starter battery, so it is not in the house system.
My charger is a new 20-amp Victron.
It doesn’t say what the “bulk” setting is. I think it is around 13.5 or so.
Greg
Thanks Dave,
I was disappointed to learn that the BMS app for these Humseink batteries won’t let me look at individual cells
But I had the batteries on the Victron for a few days, so I was assuming it would have balanced the cells (and the batteries).
I turned off the discharge switch on the lower voltage battery last night, forcing the 100% SOC battery to run the fridge overnight. I will check on them today to see what the look like. Oddly, I think they were acting like “normal” a few days ago, showing a draw on both batteries. Even though they did not show an identical SOC, both were sharing the load it appeared.
I am using an MRBF fuse on the DC+ wire. Not as good as a T fuse?
Appreciate the tips.
Greg
”Bulk” is not a voltage setting. It is maximum current that the charger can apply. With a discharged battery, the voltage at that current will initially be below the absorption voltage setting. As the battery SOC gets higher, its voltage will rise. Once the programmed absorption voltage is reached the charger will reduce the charge current so as not to exceed the absorption voltage setting.
Looking at your screenshot it appears battery 2 has its discharge FETs off, even though the app is reporting they are on. Notice the difference in voltage (13.15V vs 13.38V). You can have small differences in reported voltage with paralleled batteries but not that large. Can you cycle the discharge FET switch? Maybe that will reconnect it.
I'm not familiar with that brand of battery, but 13.2V is too low a float voltage for lifepo4 chemistry.... ideally 13.5-13.8V. In the case of lithium, absorption = bulk.....
I wouldn't trust a BMS that doesn't let you monitor individual cell voltages..... just like a flooded lead acid battery, lithium batteries do require some monitoring and maintenance especially when connected in parallel. Sometimes they have to be separated to be rebalanced.
If you can't confirm cell balance, I'd use a lower charge voltage, maybe 13.8 to 14.0V.... to avoid large cell imbalances. A large imbalance could trigger the BMS to shut down the charge MOSFETs....
MRBF fuse is not recommended for a lithium battery.... get a good quality Class T fuse.
Don't forget to secure that battery!
What is the alternator output rating? Using an isolator is generally not recommended when charging lithium with a flooded/agm battery. The agm/flooded battery have a very very different charge profile than the lithium battery. They need and can take an extensive absorption phase, where as the lithium only needs about 15 minutes at peak voltage... I'd discontinue the use of the isolator immediately. If you have a programmable alternator regulator, connect the alternator output tot he house bank. If you have a dumb (aka stock) alternator, wire it to the start battery and then use a DC-DC converter to charge the house batt with a lithium profile.
If you wire the externally regulated alternator directly to the house battery, and your shore power 30A charger is also connected to the house battery, then all you need is a small dc-dc charger to charge the start battery from the house batt whenever the voltage is >= 13.8Volts.
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GregI was checking my new Humseink LifePo4 batteries today after the batteries have been on the charger for a few days. Batt 1 showed 100% SOC and Batt 2 showed 99%. Interestingly, the BMS on Batt 1 shut off the charging switch. I assume since it was at 100% and couldn’t accept any more charge. The batteries are paralleled (see photo below).
View attachment 233092
I went out for a 2.5 hour sail today, with a light load on the house bank (fridge, VHF, stereo, CP & instruments).
When I got back, I left the charger off until I could check the BMS for the 2 batteries. Now, Batt 1 still showed 100% SOC and batt 2 was at 86% SOC.
I am not sure why these batteries, if wired in parallel, would not supply power to the house system in equal measure. Instead, it seems that one battery is doing all of the work
View attachment 233093 View attachment 233094
I have written to Humseink to see what they can tell me (if anything). I have discovered that their BMS app will not let me see what the individual cells are doing
So, here is a crude drawing of my DC system (left out the AC side of the equation for now)...and only the house side. Left off the starter battery, switch, charger, etc for that.
View attachment 233095
Does anyone see anything blatantly wrong with this set up (I hope not, as I have sailed with it a few times now). Or could this just an issue with the batteries? One thing I could try is to install a positive and negative bus bars and hook each battery individuslly to the bus bars. But the charger would charge the bus bars (single output charger ). Not sure that changes things much. Does paralleling LFP batteries need to be different than FLA?
On the RV forums I subscribe to, several campers with 2 LiTime batteries were experiencing similar. Basically, one battery was going into "standby" while the other carried the load. There were various "fixes" suggested by LiTime which included taking both batteries to zero, and then resetting. Nobody wants to take LFP batteries to zero for fear of never being able to wake them again, especially on a boat.
Bottom line: it's a BMS software flaw that eagerly shuts down one battery of a parallel combo. I wonder if your battery set is using the same BMS as LiTime.
Solutions:
- download and try Solar Overkill app on your phone. This may allow Bluetooth access to more BMS functions and information. I prefer the Solar Overkill app because I know the software is being maintained. I have a Techcella battery I bought 3 months ago that has disappeared from the market, so I have no hope of the OEM app being updated.
- cell balancing on a regular basis is critical in a parallel environment
- follow factory instructions on recovery. But in LiTime's case the problem reoccurs regularly.
- go to single battery ops, either buying a larger battery or using existing batteries one at a time and switching between them. If you keep 2 batteries at any significant difference in SOC, you CANNOT parallel them.
- I went with a single larger (160AH) battery because in both personal experience and electrical engineering I have learned that paralleling batteries - regardless of type - is inherently unstable because no 2 batteries are perfectly matched. Nobody wants to talk about this until something goes wrong. And there are many, many users of paralleled batteries where nothing has ever gone wrong. In my case it was a battery fire with lead acid batteries (no BMS except me to shut things down). Others have experienced what you are going through.
- I have had many, many people tell me I'm wrong and don't know what I'm talking about. But whenever the voltage is the SLIGHTEST bit different between the 2 batteries, they will try to equalize the voltage, often with tremendous currents depending on wire size, voltage difference, and internal battery resistance. That's why the parallel configuration requires attention to details of wire lengths or placement of bus bars at equal distance from the batteries. And correct fusing. The BMS in an LFP battery is the last line of defense to protect the battery when things go wrong.
Fred W