Any ideas for improvement?

[AF_Bob]

I know it's too late, but If you're anything like me I build a system and then justify changing it or building a better one.

Anyway once I got my hands on a battery with a bluetooth BMS I realized I wouldnt want to be without one again, sold all my prefab batteries and built new ones with BT BMS ($60 each from JBD). That way you can keep an eye on the actual coulomb counter SOC and capacity of each battery from your phone, keep an eye on each cell voltage, battery temp, adjust the balancing settings as needed/if needed and check to see if loads are balanced between batteries. Also they will have low temp cutoff and sometimes even heating option.

I assume the extra cost is probably not much different than the cost of a good shunt and with BT in each battery you get a lot more data and cell level data. Anyway if you end up building another system at some point, I can vouch for the BT being an awesome feature and hopefully that will become the standard because it wont add much cost for manufacturers so why not.

Believe me when I say, "I should have gotten batteries with bluetooth." If I had known how much it would cost to just monitor the battery capacity, I definitely would have purchased batteries with a bluetooth BMS that let me know the capacity. Oh well, if I build another system, it will be much different.

 

[Rocketman]

The amp counting that the bms’s do is not as accurate as the shunt based battery monitors.

Often it is good enough… but from what I have read on this site from other users - the bms process doesn’t count low amps very well. If your draws are high amps - no issues - but if they are very low draws - I have read it can get out.

 

[AF_Bob]

The amp counting that the bms’s do is not as accurate as the shunt based battery monitors.

Often it is good enough… but from what I have read on this site from other users - the bms process doesn’t count low amps very well. If your draws are high amps - no issues - but if they are very low draws - I have read it can get out.

Thanks, Rocketman. I never realized there would be such a steep learning curve for solar. When I joined the Air Force in 1974, I went into electronics and got my FCC First Class Radiotelephone License with radar endorsement as well as a General Class Amateur Radio license...but LIFEPO4 batteries weren't a "thing" and solar wasn't big then either. Now that I'm 69 years old, I feel like I need to go back to school. I still enjoy tinkering with stuff and hopefully I'll get smarter on solar very soon.
I tested my Victron SCC yesterday and topped off my two 12V LIFEPO4 batteries in series in about 20 minutes with four 100-watt solar panels. I took the voltages this morning on each battery, and there is a .2V difference so I wired them in parallel and I'll leave them like that for a day or two to see if they balance.
I also discovered one of my new 100-watt solar panels is only producing about 50 watts, while the other 3 provide 100 watts in bright sunlight. The fact that the panel is giving me exactly HALF of what the others give at any point in time, I wonder if half the panel's cells are not connected. I haven't had them for a month so I can still return the pair via Amazon but I hate to send them both back when only 1 is bad. I sent a message to Ecoflow asking if I could just return 1 of them (they came 2 in a box) so I'll see what they say. Nothing is ever easy!
Thanks again for the patience it must take to respond to my questions and concerns. Colleges could probably offer degrees in LIFEPO4 technology alone, with minors in charge controllers, shunts, balancers, etc.
Merry Christmas and Happy Holidays!

 

[AF_Bob]

If you have Victron mppt - get the Victron shunt!!!

One reason is you can set up a Bluetooth network and the shunt will send the voltage, current at the battery to the mppt. This helps with voltage losses and current draws.

It is well worth it keeping the software working as it should.

Also, if your inverter is a Victron that has the VE.Bus (looks like a network RJ45 cable), at some point look at getting a Cerbo or other GX device (or roll your own w/a Raspberry Pi). You can use the Cerbo to control the on/off/charger only/inverter only and input amp limit. But it’s real job is to talk to all the other Victron items and summarize them on its screen (and send the data to the internet (if you have it) - VRM.

Rocketman, thanks for the advice. I finally saw the Victron IP65 SmartShunt go down in price today (went from $130 to $117) so I purchased it. I got the Victron IP65 shunt since it's weatherproof and the wires are all built-in/sealed so I can do the mid-point wiring between the 2 LIFEPO4 batteries in series. I don't know a thing about setting up a bluetooth network, but hopefully I'll figure out how to make the Victron SCC feed the readings to the Victron SmartShunt. Thanks again!

 

[Rocketman]

The manual is good- if you have any questions- just ask

 

[AF_Bob]

The manual is good- if you have any questions- just ask

Rocketman, When you have a minute, I’d appreciate your thoughts on 2 questions concerning my Victon IP65 SmartShunt:

• I read that the SmartShunt draws 12mA, which equates to 11.52AH every 40 days (11.52% of my 100AH capacity). Do you recommend adding a switch on the little positive wire of the shunt so there isn’t a constant 24/7 12mA draw from the battery?
• If so, and I add a switch, do I have to reprogram the Shunt every time I turn it on?

 

[Rocketman]

If you will be putting it in a closet and not using it for months on end - then maybe…

If it has a little solar panel or any “charging” - then no.

There is a setting on the Smartshunt to use the last SOC. (That may not be the default).

One issue with lithium’s is the bms’s use power too, so if you put it away for a while - you need to set a schedule that says - once a quarter- you need to recharge the lithium’s. Thus the Smartshunt low draw will be recharged with that.

 

[AF_Bob]

If you will be putting it in a closet and not using it for months on end - then maybe…

If it has a little solar panel or any “charging” - then no.

There is a setting on the Smartshunt to use the last SOC. (That may not be the default).

One issue with lithium’s is the bms’s use power too, so if you put it away for a while - you need to set a schedule that says - once a quarter- you need to recharge the lithium’s. Thus the Smartshunt low draw will be recharged with that.

Thank you! I've been playing around with the SmartShunt for the past hour or so and it seems to work great. I updated the firmware and the app software and I adjusted the settings for LIFEPO4 (things like Leukert 1.05 vs 1.5, etc.) and the Mid-point monitoring works. It displayed 0.3% deviation, which surprised me a little since I fully charged both batteries, left them connected in parallel for a few days, and they measured the exact same voltage on both batteries about 2 weeks ago when they were NOT connected. When I disconnected the SmartShunt today and no longer had the batteries in series, one measured 13.57V and one measured 13.64V so I can see how the SmartShunt displayed the deviation. Since the alarm defaults to 2% deviation, I guess perhaps 0.3% is not a big deal. Although I ordered the 2 batteries at the same time, the S/Ns were different lots.
I wonder if the Victron SCC (when charging in series) keeps them balanced. When I used the SCC to fully charge both batteries in series and disconnected them later, they read exactly the same. Perhaps the BMSs (like you mentioned) don't use NASA precision components and without being used, the batteries just drift off.

If it doesn't hurt the batteries to top them off with solar charging once a week, I'll plan on doing that. The Victron manual mentions you can put a switch is series with the small red cable so I guess I could do that for long-term storage. When I disconnected the SmartShunt and re-connected it, it immediately updated the App readings and although I didn't check everything, the settings that I remember changing remained the same so perhaps it's all non-volatile memory. I read that the SmartShunt automatically updates the SOC when charged.

I'm very glad I purchased the shunt and you were right in telling me to buy the Victron shunt since I have the Victron SCC. I'll play with the network option once I get everything wired into my RIGID 2.0 case on wheels. It's going to be a tight fit since I keep adding things, but I feel much better accurately knowing what the SOC is. I appreciate all your help.

 

[Rocketman]

The network is easy!

In settings go to the VE.Smart Networking on your shunt, create it. Then do the same on the mppt.

 

[AF_Bob]

The network is easy!

In settings go to the VE.Smart Networking on your shunt, create it. Then do the same on the mppt.

Thank you very much!

I plan on trying to mount my SCC, SmartShunt, 24V-12V converter, Fuse Block for low power connections (light, USB outputs, fans, etc.), on a 1/4" piece of vertical plywood during the next few days and then wire everything up. Due to getting the SmartShunt, I needed to order 2 smaller 2AWG cables and I'm still waiting for those to arrive.

Once everything is installed in the box and working, I'll setup the VE.Smart network. I'm assuming that will transfer some values from the SCC and make the system more accurate. I may have a question or two once I setup the network. As always, I appreciate your help.

 

[Hedges]

I tested my Victron SCC yesterday and topped off my two 12V LIFEPO4 batteries in series in about 20 minutes with four 100-watt solar panels. I took the voltages this morning on each battery, and there is a .2V difference so I wired them in parallel and I'll leave them like that for a day or two to see if they balance.

Wired in parallel, to get them to balance you ought to charge and hold in the voltage range where balancing by BMS occurs.
Simply sitting in parallel may or may not accomplish much balancing. Maybe if previously charged high enough it would? But charging should.

 

[AF_Bob]

Wired in parallel, to get them to balance you ought to charge and hold in the voltage range where balancing by BMS occurs.
Simply sitting in parallel may or may not accomplish much balancing. Maybe if previously charged high enough it would? But charging should.

I was lucky enough to get them to match, but once I put them in series and used them, they didn't stay matched. I also tried charging each battery with a LIFEPO4 battery charger to full. They read the same voltage with a voltmeter, but then after putting them in series (24V system) and using them or letting them sit for a week, they don't stay matched. Today, 1 was 13.57 and one was 13.64 (0.7V difference). My SmartShunt displayed 0.3% deviation and the alarm defaults to 2.0% so perhaps anything under 1.5% or so is OK.

 

[Hedges]

It may be fine the voltage is different. In the middle 80%, voltage can be almost the same but SoC very different. Past the knee, voltage shoots up but SoC could be close. If voltages diverge, you need charging voltage enough lower that it stops without either battery having a cell run past high voltage disconnect.

13.57V is 3.39V/cell. What voltage range does the BMS require to balance? What voltage do you charge to, and for how long? Then what float voltage?

 

[AF_Bob]

It may be fine the voltage is different. In the middle 80%, voltage can be almost the same but SoC very different. Past the knee, voltage shoots up but SoC could be close. If voltages diverge, you need charging voltage enough lower that it stops without either battery having a cell run past high voltage disconnect.

13.57V is 3.39V/cell. What voltage range does the BMS require to balance? What voltage do you charge to, and for how long? Then what float voltage?

I got the Li Time 100 Amp MINI pouch batteries. I believe the manual said to use 28.4V +/- 0.2V absorption, 26.4-26.8 Float. I've used a LIFEPO4 20 Amp at 12V or 24V at 10A (depending on whether I'm charging them in parallel or series) or a Victron 100-15 Solar charge controller. I don't have any info on the BMS inside the new Li-Time MINI batteries.

 

[Hedges]

Can't talk to the BMS to see what cell voltages are?

Does manual say how long to hold absorption, and were you able to set SCC for that? I would expect balancing to occur then, not during float. Your measured voltage is just above float, an entire volt below absorb. Maybe more time to balance would help, not sure.

What matters is that when you cycle, it avoids disconnecting for high cell voltage. You may get divergence between the two batteries eventually, have to periodically do full charge for each.

 

[AF_Bob]

Can't talk to the BMS to see what cell voltages are?

Does manual say how long to hold absorption, and were you able to set SCC for that? I would expect balancing to occur then, not during float. Your measured voltage is just above float, an entire volt below absorb. Maybe more time to balance would help, not sure.

What matters is that when you cycle, it avoids disconnecting for high cell voltage. You may get divergence between the two batteries eventually, have to periodically do full charge for each.

Looking at the demo feature of the Victron Connect App (for the solar charge controller 100-15), it appears that I can set the Absorption voltage (Demo shows 28.8V), Float Voltage (Demo shows 27.60V), and Equalization voltage (Demo shows 32.4V but I didn't think you used equalization on LIFEPO4 batteries. The App defaults to automatic equalization DISABLED). I only had the charge controller hooked up for a few hours to test out my 400 watts of solar panels (4 X 100 watts in series). I'm still in the process of checking everything out before installing everything inside a toolbox on wheels. The new Li Time 100Amp MINI batteries don't have bluetooth so I have no idea about how the BMS works or what voltage the individual cells inside the battery are. Once everything is up and running, I was planning to limit the SOC on the batteries to 90% and never go below 30% SOC...but perhaps that's a pipe dream...or not a good idea.

 

[Hedges]

Correct you don't use an elevated equalization voltage for LiFePO4. You could set it to same as absorption, to do no harm. You could use "equalization" with extended time at absorption to get battery to balance further. Without BMS communications you may not know if it did anything, or maybe it will affect how much voltage drops after a while when disconnected.

Documentation for the battery may be the only place to see what absorption voltage should be used to allow balancing.

Limiting SoC to anything but a charge voltage, whatever percentage knee of the curve represents, is difficult. I think knee is above 90%. Have to count Ah in and out to determine SoC, e.g. charge fully for known SoC, then partially empty/fill while keeping track. Occasionally full charge to reset to 100% then draw down.

 

[AF_Bob]

Correct you don't use an elevated equalization voltage for LiFePO4. You could set it to same as absorption, to do no harm. You could use "equalization" with extended time at absorption to get battery to balance further. Without BMS communications you may not know if it did anything, or maybe it will affect how much voltage drops after a while when disconnected.

Documentation for the battery may be the only place to see what absorption voltage should be used to allow balancing.

Limiting SoC to anything but a charge voltage, whatever percentage knee of the curve represents, is difficult. I think knee is above 90%. Have to count Ah in and out to determine SoC, e.g. charge fully for known SoC, then partially empty/fill while keeping track. Occasionally full charge to reset to 100% then draw down.

I'm attaching what's on the Li-Time website for the 100Amp MINI battery. It doesn't give too much info. I appreciate all the info you gave me, and I'll see what I'm able to find regarding equalization with extended time at absorption. Once I fully charge the batteries and use the Victron SmartShunt, I'm hoping to be able to stop the SOC at 90% since I don't plan on using it much unless the power goes out at my cabin. I have a VTOMAN Flashspeed 1500 and an Ecoflow River 2 Pro for short power outages, as well as a 3500 Watt (4200 peak) gas inverter-generator if all else fails. I'm basically building a 2,560 WH 24V system as a learning experience and to be able to replace individual items if they fail. With the VTOMAN and ECOFLOW, once the warranty is over, I'm guessing they'll become useless if they malfunction...especially in a SHTF scenario.

 

[Hedges]

"Charge Method：CC/CV Charge Voltage：14.4V ± 0.2V Recommend Charge Current：20A (0.2C)"

That would be 3.6V per cell. People building batteries here typically parallel top-balance once to 3.65V, then operate lower.
Could be that occasional charge to 3.6V would be good to get it rebalanced.

"Charge Temperature：0℃ to 50℃ / 32℉ to 122℉"
"Low-Temperature Protection：N/A"

Avoiding charging below freezing is left as an exercise for the buyer.

 

[AF_Bob]

"Charge Method：CC/CV Charge Voltage：14.4V ± 0.2V Recommend Charge Current：20A (0.2C)"

That would be 3.6V per cell. People building batteries here typically parallel top-balance once to 3.65V, then operate lower.
Could be that occasional charge to 3.6V would be good to get it rebalanced.

"Charge Temperature：0℃ to 50℃ / 32℉ to 122℉"
"Low-Temperature Protection：N/A"

Avoiding charging below freezing is left as an exercise for the buyer.

If I set my Solar Charge Controller for 28.8V absorption, that would give me 3.6V per cell for 8 cells in series. Since my Victon SmartShunt is set for mid-point monitoring, I'll make sure I take action for any deviation above 1%. It was indicating 0.3% yesterday and I've hardly used the batteries for anything other than to test the 2000 Watt pure sine wave inverter by making 16 oz of coffee and drawing 800 watts for about 5 minutes. Once I get the 2 additional 1-foot 2AWG cables I need (as a result of buying the SmartShunt) and put everything into the box, I'll start using it for a while to monitor the midpoint of two 12V batteries in series and exercise the batteries more often. Since Li Time states the batteries are rated at 4,000 cycles at 100% DOD and 6,000 cycles at 80% DOD, they should last a while.