Victron Energy: Alternator/Solar Charging - LFP Battery System

[luthj]

Since lithium packs don't need (or want) regular true 100% SOC charges, you can set the "synchronize" at any level you want. For optimum longevity terminating at 94-98% SOC is a good option. That is typically 6% return current at between 14-14.2V. Each pack will vary, so you can do some testing to identify what that means for your pack.

 

[shade]

Sorry, yes. Set 100% SOC

Not equalize cells

Victron calls it synchronizing SOC

From what you've said, I don't think you have a Victron battery. The Victron Smart LFP series auto balances at full charge, when tapering off at 14.2V.

Here's the BMV-700 series manual, if anyone wants to follow along. 2.2 Synchronizing the BMV is on page 10:
https://www.victronenergy.com/uploa...-700-700H-702-712-EN-NL-FR-DE-ES-SE-PT-IT.pdf

I think you'll want to disconnect all loads & charge sources to get the battery to a steady state. Rather than rely on auto-sync, I plan to charge my battery to 100% (since it's an LFP battery, I'll keep it under its true 100% capacity), and manually sync the BMV. That seems simpler to me that anything else, but I haven't actually used a BMV yet, so the auto-sync function may work perfectly fine.

I'll also have Victron charge sources, so I plan to configure them to work within the "100%" limit I've defined with the BMV.

 

[dreadlocks]

I turned off Auto SOC Calibration and do it manually when I know its full right now.. mine is mostly charged by solar and 4% return amps could just be due to solar conditions not battery state.. so I dont want it resetting to 100% soc when its really at 90% or something.

 

[luthj]

I turned off Auto SOC Calibration and do it manually when I know its full right now.. mine is mostly charged by solar and 4% return amps could just be due to solar conditions not battery state.. so I dont want it resetting to 100% soc when its really at 90% or something.

This is why a specific voltage/current combo is used. 4% return at 0.1V under absorb won't trigger 100%. Lithium has a pretty flat curve, but the BMV is an accurate enough volt meter for this purpose. The manual says plus/minus 0.3%, but it should be quite a bit better than that. So less than 40mv drift at 14V nominal.

 

[DRP]

From what you've said, I don't think you have a Victron battery. The Victron Smart LFP series auto balances at full charge, when tapering off at 14.2V.

Correct, Battle Born, but Victron 100/30 and then BMV 712

It has been doing 100% SOC sync for eight months now, no problem.

Battleborn suggests 14.4V but I have been running it at 14.3

Decided to bump to the 14.4 and the last few cycles it hit the voltage mark and then tapered to 13.6 but left the BMV at 98% and didn't reset the "last full charge" counter


OK, hit "Sync" at 14.41. "Last full charge" reset to zero and SOC reset to 100%

The 12V load has been off for today but on for the last few days monitoring.. Keep in mind I have a 12V fridge and this is an RV so there is always something on

"Last full charge" stayed at 0min 0sec for a couple of hours as voltage dropped to 13.6. LFC started counting and charge controller woke up the solar panels when I turned on the 12V load

 

[dreadlocks]

I'm running 14.2, with fixed absorb til 2A then drops to float of 13.4 which lets battery discharge to ~90% SOC and then holds it there.. dont really make it easy to auto calibrate but I prefer this profile.. I'll manually balance and calibrate it as needed and not daily.

 

[luthj]

I would personally set the sync as follows.

Votlage parameter 0.05 to 0.075V below the chargers absorb voltage. Current parameter, 5-15% greater than the chargers absorb end amps. so if you are using 6%, then set it to 6.6%. Time parameter, 1-5 minutes.

This ensures the BMV catches the full charger every time.

You guys do have have temp compensation turned off the BMV right? Most of these meters will adjust for battery temperature if you don't and typically the default is for lead. Though you could enter the compensation coefficient for lithium if the software supports it.

 

[DRP]

Shade, thanks for tolerating my hijack, but I think it all ties in to the conversation

And thanks everyone for chiming in

 

[shade]

Shade, thanks for tolerating my hijack, but I think it all ties in to the conversation

And thanks everyone for chiming in

Not a hijack in any way. I'll be running through these questions myself before long.

^ Jon's comment about temperature compensation is important, especially if the battery isn't communicating with other components. Even with Victron integration, I expect I'll be manually configuring some settings rather than relying on canned settings.

 

[dreadlocks]

If you use the Lithium profile, or start tweaking from the Lithium Profile then there is no temperature compensation, only low temp stop charge.. at least on the Victron 100/30.

 

[luthj]

I was referring to the BMV temp compensating the full sync setpoint. So a 14.4V full would become something like 15V at 10F? I don't know if the BMV adjusts its setpoints that way, but some meters do.

 

[shade]

If you use the Lithium profile, or start tweaking from the Lithium Profile then there is no temperature compensation, only low temp stop charge.. at least on the Victron 100/30.

I haven't looked into the ways my system can be controlled yet. Maybe I have it wrong, but I figure that the BMV & BMS will take care of emergency disconnects (hi/lo voltage, hi/lo temp), and the Orion-Tr & SmartSolar chargers can be programmed to control normal operations. I may also find out that the Victron profiles & other interconnected automation are perfect, and I should just let the system work how VE designed it.

I haven't worked up a wire order yet, or figured out how I'm going to get wire into the truck cab. I should work on that tonight.

 

[shade]

I was referring to the BMV temp compensating the full sync setpoint. So a 14.4V full would become something like 15V at 10F? I don't know if the BMV adjusts its setpoints that way, but some meters do.

A BMV will read battery temp if a Victron battery is used. If not, there's a BMV temp probe available to be placed on a non-Victron battery, and the BMV will use that data to trip a relay and an alarm for hi/lo temp. The BMV also allows the use of a manually entered temperature coefficient below 20°C.

68. Temperature coefficient This is the percentage the battery capacity changes with temperature, when temperature decreases to less than 20°C (above 20°C the influence of temperature on capacity is relatively low and is not taken into account). The unit of this value is “%cap/°C” or percent capacity per degree Celsius. The typical value (below 20°C) is 1%cap/°C for lead acid batteries, and 0,5%cap/°C for Lithium Iron Phosphate batteries.

Default Range Step size 0%cap/°C 0 – 2%cap/°C 0,1%cap/°C

 

[dreadlocks]

I haven't looked into the ways my system can be controlled yet. Maybe I have it wrong, but I figure that the BMV & BMS will take care of emergency disconnects (hi/lo voltage, hi/lo temp), and the Orion-Tr & SmartSolar chargers can be programmed to control normal operations. I may also find out that the Victron profiles & other interconnected automation are perfect, and I should just let the system work how VE designed it.

I haven't worked up a wire order yet, or figured out how I'm going to get wire into the truck cab. I should work on that tonight.

yeah I started w/all the LFP settings on everything but then tweaked it a little bit to be slightly more conservative, i think by default the chargers will just fixed absorb for 2h once it hits the absorb voltage of 14.2, guess that ensures balancing can go on.. I turned on expert mode and enabled it to stop absorb early at set amps and lowered the float voltage down a bit, by default it held it at like 98% SOC.. when I want to balance cells I just put float at 14.2 and keep it there until its registering no current input, then I calibrate 100% SOC, guess I could just turn it back to fixed 2h absorb too to be ultra safe incase I forgot.. I do that once a month or so in the summer, none in the winter.. I'm about to disconnect it at 50% SOC and just leave it.

 

[shade]

yeah I started w/all the LFP settings on everything but then tweaked it a little bit to be slightly more conservative, i think by default the chargers will just fixed absorb for 2h once it hits the absorb voltage of 14.2, guess that ensures balancing can go on.. I turned on expert mode and enabled it to stop absorb early at set amps and lowered the float voltage down a bit, by default it held it at like 98% SOC.. when I want to balance cells I just put float at 14.2 and keep it there until its registering no current input, then I calibrate 100% SOC, guess I could just turn it back to fixed 2h absorb too to be ultra safe incase I forgot.. I do that once a month or so in the summer, none in the winter.. I'm about to disconnect it at 50% SOC and just leave it.

That 2hr default seems excessive. I'll have to see if the system is smart enough to recognize that if the cells are reporting at equal voltage, the additional 2hr time can be skipped.