? - Voltage Regulation when Charging an LFP Battery

[luthj]

13.8-14.0 is perfect for LFP charging. Enough to compensate for moderate voltage drop, and still get good rates. Without the diode boost that is about why my vans alternator makes. My plans are to do direct LFP charging down the road, in order to take advantage of the 100A or so I can charge at.

 

[john61ct]

I agree about the voltage, but current still needs limiting (for the sake of both sides), and stopping at a healthy stop-charge point.

 

[shade]

I agree about the voltage, but current still needs limiting (for the sake of both sides), and stopping at a healthy stop-charge point.

I'll keep current limiting in mind as the system comes together. I can program the external BMS to disconnect below 100% SoC.

Thanks again for your help. I'll revisit this once I have some real world data about the system's behaviour.

 

[shade]

the 160Ah battery is going away Victron says, so grab them now while on sale.

Ordered.

 

[john61ct]

I'll keep current limiting in mind as the system comes together. I can program the external BMS to disconnect below 100% SoC.

Those two are not related.

If you have no current limiting device between your alt/VR output and your LFP, you can easily damage the former, put an infrared or other temp gauge on the hot bits and disconnect at 60°C or so.

And going faster than a 0.3-4C rate will hurt the longevity of your bank.

All this at low voltages, it's low SoC where the bank pulls the most amps.

 

[shade]

Those two are not related.

If you have no current limiting device between your alt/VR output and your LFP, you can easily damage the former, put an infrared or other temp gauge on the hot bits and disconnect at 60°C or so.

And going faster than a 0.3-4C rate will hurt the longevity of your bank.

All this at low voltages, it's low SoC where the bank pulls the most amps.

I know current limiting and SoC concerns aren't the same. I think I have enough control to be reasonably certain the charge disconnects in the plan will prevent continuous charging at 100% SoC, and I'll check to see if they'll disconnect at a user defined charge rate.

Current limiting is another matter, and I'll be doing just as you said about monitoring alternator output and heat. With the battery at a low SoC, I could mitigate heat at the alternator by simply disconnecting alternator charging after X minutes to allow a cooling period.

Group speculation has been very helpful, but I think it's time to go forward with actual testing. I can easily add some form of voltage regulation to the circuit later.

 

[john61ct]

Yes rebuilding alts isn't that big a deal, but you definitely want to do your experimenting on a cheap LFP bank, not those Victrons.

CTEK and Renogy make cheaper lower-amp dcdc units, but setpoints are not user adjustable.

 

[shade]

My plan is to rely mainly on solar charging. When alternator charging, I'll actively monitor what's going on by the VE phone app and the BMV-712 monitor. If I can't watch what's happening, I won't allow alt charging. The LFP battery is for part time use, so it's not like I'll be regularly charging via the alternator. If I fall asleep, the battery's internal BMS disconnects charging above 4.2V/cell, the external BMS disconnects at 16V.

I may end up with a DC-DC charger, but I'm waiting to see what Victron announces in November. Like I said, I'd rather stick with VE products for better integration and interoperability. If Victron doesn't have a DC-DC option I want, I may end up with another make, but it'd be silly to go that route this close to their announcement.

I'm also exploring using a Balmar small frame alternator with external regulation, or some other replacement alternator with a Balmar MC-614.

 

[dreadlocks]

thats kinda how I'm doing it, my Victron SmartSolar is by far the best charge source I have for my LFP and I feel completely comfortable leaving it unsupervised and let it do its thing.. so its primary and other charge sources require manual intervention in default mode.. I keep my shore charger circuit flipped off so I can get home after a long day on the road and plug it in w/out worrying about it.. when I go hook that charger up if its needed its then monitored physically.

but LFP is unlike lead, it'll suck up unhealthy levels of current.. pretty much whatever you can give em.. it'd take 1C if you can find a 160A source.

 

[shade]

thats kinda how I'm doing it, my Victron SmartSolar is by far the best charge source I have for my LFP and I feel completely comfortable leaving it unsupervised and let it do its thing.. so its primary and other charge sources require manual intervention in default mode.. I keep my shore charger circuit flipped off so I can get home after a long day on the road and plug it in w/out worrying about it.. when I go hook that charger up if its needed its then monitored physically.

but LFP is unlike lead, it'll suck up unhealthy levels of current.. pretty much whatever you can give em.. it'd take 1C if you can find a 160A source.

The 160Ah battery maxes out at 320A, so my puny 130A alternator can't hope to exceed that on its best day. It's possible the alternator could dump 100A or so into it briefly before dropping off. Higher than 0.4C, but not catastrophically high as far as the battery is concerned. The recommended charge is 80A or less.

A 50-75A DC-DC charger with user defined parameters would be a good fit, and I hope that's what Victron is being tight lipped about.

 

[dreadlocks]

how much solar you think you can fit? just a single 325W? tha'll probably do the job most days.

 

[shade]

I'm starting with one and will see how it goes. I have room for two, and I'll design for expansion during the assembly. I'd rather not add more weight up high, so I may have a smaller 100W-ish panel for remote positioning.

 

[1leglance]

I'm starting with one and will see how it goes. I have room for two, and I'll design for expansion during the assembly. I'd rather not add more weight up high, so I may have a smaller 100W-ish panel for remote positioning.

OH OH OH that reminds me of something I have been meaning to learn about....
Like you I am going to start with a 360w panel (LG residential) but I would like to be able to park under a shady tree and put out a folder which would obviously be something smaller.
My understanding is that if I just add that folder inline with the big boy then the entire system is throttled down to the weakest panel.....yeah? So I should add the folder with it's own solar controller direct to the battery or to some other point in the system (where?)......am I anywhere near correct or way off?

 

[dreadlocks]

you run a second controller sized appropriately for your portable set.. wont drag nothing down.

Victron is working on having multiple solar controllers sync via bluetooth networking, the'll coordinate charge profiles and behave like a singular unit much like very large (industrial output) solar controllers.

I'm waiting for this feature to hit before buying another controller for my 2nd Panasonic HIT residential panel, tho its not required w/latest firmware.

 

[shade]

OH OH OH that reminds me of something I have been meaning to learn about....
Like you I am going to start with a 360w panel (LG residential) but I would like to be able to park under a shady tree and put out a folder which would obviously be something smaller.
My understanding is that if I just add that folder inline with the big boy then the entire system is throttled down to the weakest panel.....yeah? So I should add the folder with it's own solar controller direct to the battery or to some other point in the system (where?)......am I anywhere near correct or way off?

You'll want a separate controller per panel. Otherwise, there's no way for a single controller to do its MPPT sampling effectively between dissimilar panels.

Also, some Victron controllers can be networked.