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It is worth noting that while the PV input on the Tracer xx20AN units might be rated at 200v, also so are ALL of the parts on the PV input line. So the 200v rating is not a "safe max", but rather an "absolute maximum" rating. Their xx15AN units are rated @ 150v--with 150v parts inside.
Sounds like typical advertising. And that's exactly how i treated it. Max Open Voltage is 136V on my array. I don't like tempting fate with things that can cause fires. And the voltage is high enough that i can easily max out the controller with 10AWG cable.
Also worth noting that I had a Morningstar Tristar blow up on me (bright orange flash) after the umpteenth MODBUS restart command. Their customer service was exemplary...but it's worth noting that things happen even to "the big guys'" products too.
Yeah, absolutely. And honestly, the likelihood isn't all that reduced. Maybe a little from improved quality control, but not enough for significantly reduced scrutiny.
I'm planning to buy a second 10420AN, if that tells you where my opinion stands.
5 minutes ago, NotMario said:And the voltage is high enough that i can easily max out the controller with 10AWG cable.
Yeah, that's what I like about 'em 😉. Doing the same with my system...maxed with 10AWG cable.
5 minutes ago, NotMario said:I'm planning to buy a second 10420AN, if that tells you where my opinion stands.
My ONLY complaint with the two 8420AN units that I have...is that their regulation is VERY slow (i.e. tens of seconds to react). This means that if you were running one to 100% with a load, and turned the load off...it will significantly overcharge the battery for up to a minute as it slowly throttles down. Not a problem for SLA...but not the best for Lithium-based batteries.
"The" solution I read somewhere was to set the "overvoltage disconnect" setting...in other words, when the output voltage rises too high (because of the controller's slow regulation), it cuts out entirely...coming back in when the "overvoltage reconnect" setting is reached. Haven't bothered to configure 'em that way on my system at this point though.
Worth noting: "Ampinvt" has been slowly becoming more visible...but their MPPTs have a serious flaw with cloudy weather MPPT tracking. If it's cloudy, dollars to donuts that you'll find the solar panels pulled all the way down to battery voltage, oftentimes resulting in less than half the available power output...
2 hours ago, Sid Genetry Solar said:My ONLY complaint with the two 8420AN units that I have...is that their regulation is VERY slow (i.e. tens of seconds to react). This means that if you were running one to 100% with a load, and turned the load off...it will significantly overcharge the battery for up to a minute as it slowly throttles down. Not a problem for SLA...but not the best for Lithium-based batteries.
Very interesting. Do you mean the voltage spikes too high? My historian reports Load drop from 2041W -> 291W results in 25.86V -> 26.71V. But it was only running @ 50% capacity at the time.
Might need you to elaborate more on this. I want my LI's to last... lol
By the way, there's a Windows (gasp) application to activate LI optimized charging. Not sure if that may have some heuristics for this problem.
Very interesting. Do you mean the voltage spikes too high? My historian reports Load drop from 2041W -> 291W results in 25.86V -> 26.71V. But it was only running @ 50% capacity at the time. Might need you to elaborate more on this. I want my LI's to last... lol
Basically. It might not be a huge amount--but when I had my inverter OVP setting with a rather tight tolerance, the inverter would OVP shutdown on a random basis (load dependent) due to the voltage "surge" when a large load would turn off. My "solution" was to drop the "aborb/float" voltage of the Tracers, leaving the proper "absorb/float" cycle to be handled by the Morningstar Tristar (which has exemplary voltage regulation).
Peak battery voltage on my 16S LFP bank (from the Tristar's perspective) is 57.0v; the spec max given on the Tristar is 56.5v for "absorp." As the Tracers are set ~55v peak (think I disabled "absorp" on them), that means we have a 2v "overregulation" from the Tracers. I know I saw my battery bank up to 58v at one point (caused by the Tracers) before I adjusted settings. 3.625v/cell isn't too bad, except that my shunt balancers clamp ~3.55v, so they got pushed pretty hard.
By the way, there's a Windows (gasp) application to activate LI optimized charging. Not sure if that may have some heuristics for this problem.
I would be somewhat surprised if so, as this is a regulation issue...not a configuration setup issue. However, I'd be curious to run a MODBUS sniffer on the output of the Windoze program to see what exactly it sends the Tracers for Lithium modes--as the "Lithium" modes can't be accessed from the MT-50 Epever external meter. About all I did was set the temperature compensation to 0...though if the Tracers can be set to automatically refuse to charge <32F, that'd be really dandy...
Also worth noting that there is no "charger on/off" listed in the Tracer MODBUS specification--but rumor has it that the PAL-ADP-50AN "parallel adapter" for the Tracers CAN turn chargers on/off via MODBUS. That just means that they haven't documented the on/off controls....
I got the impression that the LI mode followed a different code path. IIRC, there was a very different set of options.
Don't remember seeing an option for cold charge protection on the Tracer. But my batts have it built in. (to my pleasant surprise)
What charge voltage do you target? I currently target 3.65v/cell, but it sounds like you think that's a bit high?
Highest i've seen the tracer push is just under 30v, and that lasts... a few seconds now that i think about it... long enough for the historian to see it.
The BMS kicks in at 29.2v anyway. So maybe that's saving my bacon. This whole system was set up in January - learning curves, you know.
1 hour ago, NotMario said:The BMS kicks in at 29.2v anyway.
1 hour ago, NotMario said:Don't remember seeing an option for cold charge protection on the Tracer. But my batts have it built in. (to my pleasant surprise)
Some MPPT units (such as the Morningstar Tristar) are liable to blow themselves up if a BMS "disconnects" the battery from the MPPT (for whatever reason) while solar is still connected.
Pretty simple why, actually...while I haven't confirmed this, it's a viable hypothesis I think:
...they use high voltage parts for the PV power line (i.e. all the way to the top FET of a synchronous buck converter)...
...then in a desperate bid to increase efficiency as much as possible, they use LOWER voltage FETs/diodes for the remaining circuitry on the "battery voltage" level.
This works fine until a BMS abruptly removes the battery load from the circuit due to overvoltage. Suddenly all that's left between 4,000W of solar energy and overvoltaging some 80v parts are a half-dozen 1,500uF, 80v caps. They get slammed with 136vDC (due to the duty cycle), and the magic smoke is released...
This potentially can get a lot worse if the MPPT devices short straight through due to failure: in this case, the BMS will get a nice direct 136v of solar panels across it's switching devices (highly unlikely that they're rated for this), resulting in the BMS shorting through, and the batteries are then faced with a nice high voltage baking session until interrupted by unspecified possibilities.
1 hour ago, NotMario said:What charge voltage do you target? I currently target 3.65v/cell, but it sounds like you think that's a bit high?
I try to go for 56.0v "float" and 56.5v "absorb" (just a little "topping" charge at the start of the day). This works out to 56.5 / 16 = 3.53vpc and 56.0 / 16 = 3.50vpc. There isn't much capacity in LFP above ~3.40vpc (as the "base battery voltage" is usually ~53v, or 3.31vpc), though in order to get a significant charge current, you have to have some headroom (i.e. much faster to fill a container if the incoming water is of a notably higher pressure than the container itself!)
Some people say that the higher the "float" voltage, the shorter the battery lifetime. I'm not a battery scientist, but with that in mind (as well as the fact that there is very little capacity >3.4vpc anyway), I settled for ~3.5vpc as a happy medium. Worth noting that when I tried increasing the distance between absorb/float, the system would actually pull the batteries down to "float" voltage over ~10 minutes. My goal was for the batteries to "drop down" without being "pulled down" when the system switched from absorb to float.
Not all LFP batteries are rated for 3.65vpc--some are rated to 3.60v. Depends on the manufacturer; it should be noted in the spec sheet.
Some people say that the higher the "float" voltage, the shorter the battery lifetime. I'm not a battery scientist, but with that in mind (as well as the fact that there is very little capacity >3.4vpc anyway), I settled for ~3.5vpc as a happy medium.
Neither am I but it's definitely a thing. The higher the cell voltage the shorter the cell life. 3.375 seems to be a safe long term voltage from what I've read, and this is also Victron's default lifepo4 'float' voltage so that's good enough for me.
Some MPPT units (such as the Morningstar Tristar) are liable to blow themselves up if a BMS "disconnects" the battery from the MPPT (for whatever reason) while solar is still connected.
So, when i designed the system, my 200A alternator was a core component. Alternators have a very similar issue to what you're describing, so i gave this problem a lot of thought.
There is a parallel LA that will take the load, or the charge punishment as the case may be. Essentially a big, fat, slow cap.
The voltage swing when hitting 100% Disconnect is around 29.2 -> 31. I haven't determined the long term effects on the LA yet, but since it pretty much always stays charged, at least that factor is in good order...
I am watching this possible issue very closely as these [continuous duty] alternators are very expensive. (The MPPT stuff doesn't hold a candle) The LA seems to have been a decent KISS solution. I hope i'm not grossly miscalculating on this one. 😕
Some people say that the higher the "float" voltage, the shorter the battery lifetime.
Yeah, my understanding is that the batts live longer if you can average them below 50%. (Kind of opposite from a LA) The way i've built/configured my system is generally to avoid high SOC - aside from solar/wind, of course.
Generally floating a LiFePO4 is not necessary. Probably better to not float it at all if you can configure that. (My BMS protect does this implicitly... caveats above notwithstanding)
Thanks for the charge voltage info. These batts are rated at 3.65, but i think i'll lower my charge target a bit. It only seemed logical to use the rating at the time. 😕
Great great info in this thread. Thanks.
It's not float in the lead acid sense. It's more about providing current from the solar array to what ever loads you have. If you have no loads at all there is no need to make current available to the lifepo4 for > 9 months, assuming it doesn't need to be in a high state of readiness for use.
What <a contenteditable="false" data-ipshover="" data-ipshover-target="/profile/41-thebutcher/?do=hovercard" data-mentionid="41" href="/profile/41-thebutcher/" rel="">@TheButcher said 😉...the "float" mode is for powering loads, not necessarily "maintaining" the batteries. Their current should go to practically zero anyhow once fully charged.
I like the idea of running the batteries close to their "neutral" voltage (Victron spec of 3.375 * 16 = 54v), though I also like the idea of making sure the LFP cells are balanced whenever full charge is reached.
At least in my experience, you have to take the LFP cells past 3.4vpc in order for any cell SOC imbalances to become obvious. My shunt balancers are hard-set at 3.55v trigger voltage (could be changed, though). Setting "absorb" to 3.57 and "float" to 3.375 would result in the batteries being microcycled every time the MPPT decides to run an "absorb" cycle.
Besides, let's face it: when a charger has a maximum output amperage that they stick to (like Morningstar), you get more watts out of the controller the higher the battery voltage 😉.
<a contenteditable="false" data-ipshover="" data-ipshover-target="/profile/133-notmario/?do=hovercard" data-mentionid="133" href="/profile/133-notmario/" rel="">@NotMarioSounds like you've thought it through with the lead-acid bank...that'll definitely protect your MPPTs/alternators from BMS units abruptly opening the circuit without warning. I didn't even think of that.
Ah, i have never heard "float" used in that manner. I see what you mean...
Soft of like the MPPT controller is acting as another batt string. As load increases, the voltage drops and the controller compensates by supplying more power. Duh.
Frustratingly, i wont have a windows machine for a couple weeks to adjust the Tracer targets. 😕
Can't do it with the MT-50 in LI mode, as noted earlier.
Frustratingly, i wont have a windows machine for a couple weeks to adjust the Tracer targets. 😕 Can't do it with the MT-50 in LI mode, as noted earlier.
Would be handy if you could somehow "sniff" the MODBUS commands sent to the units for hacking purposes...yeah, not the easiest thing to do without a DSO or some programming of an external MCU.
It uses a USB->Serial adapter. So i could use pcap to sniff the USB commands (which should unwrap to raw data on the serial).
At least in my experience, you have to take the LFP cells past 3.4vpc in order for any cell SOC imbalances to become obvious. My shunt balancers are hard-set at 3.55v trigger voltage (could be changed, though). Setting "absorb" to 3.57 and "float" to 3.375 would result in the batteries being microcycled every time the MPPT decides to run an "absorb" cycle.
I take Victron's lead on this again, because they seem to know what they are doing. Their default strategy for lifepo4 is 'float' at 3.375, 'absorb' at 3.55. On the first 'absorb' cycle of the day hold the battery at that voltage for some period of time or until battery current has fallen to some low level to give the BMS time to balance the cells at a point on the charge curve where the low balancing current of the BMS can actually do the job. After that is completed don't pull up to absorb voltage again unless the battery dips 300mV below float for a few minutes, but if this is triggered just pull up to absorb voltage then immediately release back to float. The default settings seem to handle things well enough with no, or just a low number of re-bulks. Their default lead acid rebulk offset voltage is 30mV (from memory) for comparison.