Bulk vs Float charge in Voltronic Inverters

nrm21

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Apologies if this has been asked before but I couldn't find in search results. Most of you have (I believe) MPP Solar PIP's but all are Voltronic power anyway so I think they are the same as all the other brands. Can someone explain to me the behavioral differences between these 2 settings?

I cannot set (Bulk) CV lower than Float though I think I should be able to. My assumption is that Bulk (CV) is the voltage where, above this, it will start cutting back on the amperage from the Solar to keep the battery from going over that voltage. Ok so then... what is float charge?

BTW: I'm using Lifepo4's not Lead-acid so I'm in user defined mode.
 
Float charge is when the batteries are minimally discharged and are "floated" back up to full charge. It is also called trickle charging in lead acid chargers. For LiIons, you set the Bulk and Float to the same value. This effectively turns "off" float charging. It is possible you need to lower one and then the other to get them both to the desired value. I would assume you'd lower Float then lower Bulk as Float should always be <= Bulk
 
Ok so float is useless for Li-Ions then? Yeah I have them both at 58.4v right now. Seems a little high but my battery is a bit undersized so the "apparent voltage" goes up significantly past the real voltage of the cells. When they reach 58v as soon as I stop charging my batt immediately drops back down to around 55v
 
If you're running 14s, your numbers should be:

14 * 4.2 = 58.8 (max)
14 * 3.8 = 53.2 (nominal)
14 * 3.2 = 44.8 or (min)
14 * 3.0 = 42

If it's charging to 58, and the dropping to 55 when it stops, then you have an issue somewhere. Lithiums shouldn't do that. That's a LeadAcid thing. You might want to check your connections to verify everything is tight and soldered/bolted correctly. 3V drop after charge is a lot.
 
14 * 4.2 = 58.8 (max) is a bit high to my liking... 14 * 4.1 = 57,4 V is safer and betterfor long life... :)
If the voltage is dropping after charger cut-offindecatesthe batteryisnot fully charged at all...
Charging should stop only when the cv pointis reached .... and charge current is dropping (in my case set at< 10 A )
 
I was just stating the absolute max and pointing out the voltage oddity.

Charging should shift from CC to CV only when the cells have reached about 4.1V. So actually, because the unit was designed for lead acid, and it's being used with Lithium, then it would be a good idea to stop at 4.1V, as wim said. The safety factor here is that you aren't charging at CC when the cells should be being ramped down off of CC and switched to CV only mode.
 
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It would be high for 14s... but I'm using Lifepo4 (3.2v) not Li-Ion (3.7v) so... I have 16s instead of 14s.

Still a tiny bit high but as I said, I believe they aren't getting charged to full anyway because as soon as I remove the solar the drop to 55v is immediate not over several mins (as is the behavior of a truly full battery). So I believe the extra voltage is a result of "phantom boost" (like the opposite of "voltage sag") since the battery is a bit small for the application.
 
Are the lifepo4 max charge 3.6v,3.65v,3.7v,3.75v?I have seen all theses values on different lifepo4 cells.
a 3.6x16= 57.6v
at 3.65 x 16=58.4v
at 3.7 x16=59.2v
at 3.75x16=60v

lifepo4 are suppose to be tolerant of being overcharged

later floyd
 
It does depend on which LiFe you have..for instance my CALB cells are fully charged at 3.65v.
I think some LiFe 18650 can go to 4.2
Best to check data sheet
 
Generally 3.6v (my headway's are anyway) and I'm pretty sure Calb, Thundersky, Winston, Sinopoly, A123, and just about anyone who sells LiFePO4 cells are also somewhere around that.
And yes they are more tolerant of OC (and just about everything else) than other battery types. You really have to work hard to get them to burst into flames, safety is one of their appeals.

IMO they are the best type to use for home powerwall applications. Now if you're getting free used 18650 cells out of laptops or power drills well... beggar can't be choosers. But if your buying new, I dunno why someone would go with a less safe and more expensive (total lifetime number of cycles) cell chemistry. Only thing they lack is the ability to put lots of Ah inside a small space. But that's not a prob if they are sitting on a shelf/floor all day.
 
LiFePo4 generally drops a bit more when resting than LiIon does! That is important to know as well.
 
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