I have a Renogy 40 amp MPPT charge controller. I drained the batteries down to 70% charge and when the sun came up in the solar panels went to work the charge controller never entered the boost mode. The batteries did get charged and the next day with a battery voltage of 12.9 the charge controller did go to boost phase and float phase. Is there an explanation for this that I’m unaware of or was it just a fluke?
Mppt controller did not go into boost
- Thread starter eddiek99
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sunshine_eggo
Happy Breffast!
It could have been a fluke, but...
"Boost" is the name Renogy uses for absorption, or the constant voltage portion of the charge. It's possible to get a battery fully charged with intermittent sun or excessive loads in bulk without ever hitting "boost" or float.
"Boost" is the name Renogy uses for absorption, or the constant voltage portion of the charge. It's possible to get a battery fully charged with intermittent sun or excessive loads in bulk without ever hitting "boost" or float.
Since I have your attention I have another question. My trailer has a .5 amp parasitic load on the batteries. Two 6V agm 205 amp hours. Overnight approximately 10 or 12 hours the batteries drain from 13 V to 12.8 V. Is this normal? Or is there an issue with my batteries?
chrisski
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The AGM SOC chart I just looked at put the batteries at 92% to 93% SOC. I honestly don’t keep track of SOC by voltage I used the shunt?
Have you checked to find what does this draw by pulling fuses and turning things off? THe shunt made that easy for me. I found .5 amps coming from my propane fridge and I also found my stereo needs to be turned off and another 1.2 amp, and also the inverter draws a full amp. I left the fridge on, but I found enough to save about 20 ah just by shutting certain things off I did not know even drew power.
Have you checked to find what does this draw by pulling fuses and turning things off? THe shunt made that easy for me. I found .5 amps coming from my propane fridge and I also found my stereo needs to be turned off and another 1.2 amp, and also the inverter draws a full amp. I left the fridge on, but I found enough to save about 20 ah just by shutting certain things off I did not know even drew power.
I have an amp meter. The draw on the batteries are from the radio, smoke detector, and propane leak detector. It’s .5 A. I have Amp metered and catalogued everything that uses power. Maybe I wasn’t clear the power draw of .5 A is when the trailer is not in use. That is expected because there are some things that are always on. I was just curious if the battery should drain that much in just 10 or 12 hours with only a .5 amp load.
sunshine_eggo
Happy Breffast!
Yeah. You've pulled about 6Ah out of 205, so that's about 3%.
Just letting the battery sit for a couple of days will bring it down to 12.8-12.9V with NO loads on it.
Tomthumb62
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Am I correct in that if an AGM bank never reaches boost, that’s hard on the batteries long term? Meaning if it’s always only getting charged in the float voltage, that you’re going to end up with an undercharged battery that reads a good voltage 12.9-13.2v or so)?
And am I understanding properly that the boost aka absorption voltage is only part of the equation of a sealed lead acid battery getting a proper charge - it needs a minimum C rating charge? In my case, I believe the minimum C rating charge for my 200Ah 12v bank is 0.2C or 40A, for an absorption aka boost charge. It will appear fully charged at a much lower C rate, but the actual power inside the battery is lower than if it gets a proper boost voltage and charge rate. Am I understanding all this correctly?
Thanks!
chrisski
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A minimum charge of .2 c is hard to hit on a solar charging system. Especially when max discharge is 50%, or even 80%.
I see my system slowly come up and perhaps over the course of 3 hours it reaches .2c. Also I’m guessing an AGM is a max charge rate of about .3 c.
Charging between this minimum charge rate and max charge rate can be easy to do when hooked to the grid, but is not practical for an off grid solar system.
I had lead acid, but FLA and realized there may be some degradation, but millions are in the same boat and use it.
Tomthumb62
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Thanks. Yes can’t do 0.2C on solar so I have a couple grid chargers to give them a 0.25C charge occasionally. I think we have bad batteries, going to get them tested at Oreillys soon. Without much draw, we’re getting voltage sag down to 10.3V, which sends an alarm on the inverter and it shuts down. Remove the 60-200W draw and it pops back up to 12.8 or even above 13V. Have checked Ava replaced cables so starting to think these new batteries are the problem.
chrisski
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I’m just curious about the sag…
Does this happen in full sun?
Watching my MPPTs come to life takes a few seconds from 0 to 2 kw. All the batteries at first, and then all the panels after that. This tells me those MPPTs alone would not cover a surge or make up for bad batteries.
Tomthumb62
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The sag happens in full sun as well as at night. I just put a 1600W draw on the inverter after a boost charge, voltage dropped from 13.8 to 11.1v. MPPT was taking in 15A, so theoretically it could cover the draw, but the battery couldn’t handle it.
Before this tri charger boost charge (which has never been done before but batteries are fairly new), voltage would drop to as low as 10.3V.
Also, the SCC manual says that the boost charge is a timed 2-hour setting. But it only lasted about 1 hour. At the time, I also had two grid chargers hooked up, a 15A and 20A one. For about 15 minutes, it seemed I had about 45A going into the batteries at 14.4V, but it didn’t last that long. I don’t have an amp meter that does above 20A, so I could only tell what the MPPT was doing, which went from 10a to 0.04A
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chrisski
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I do wonder how much instantaneous power a panel can provide. I’m pretty sure with the surge sag you see, the MPPT could provide the power quicker, but the algorithm slows the power from the panel down. Probably because the panel power has some sort of surge also.
Would be nice to see the math behind that, but you’d probably need to go to engineering school.
If it’s delivering 46 amps at 14.4 volts for an hour to me, this seems like the battery is nearly full.
I had an SCC with a 2 hour boost, and it seems like it would stay there longer if needed, or would stop early if charged.
Tomthumb62
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Thanks for confirming that. It makes sense, except even with a full battery we get this voltage sag. I mean the sag is happening to below 10.5V with only a fridge hooked to the inverter. 600-700w draw for about 1-2 seconds then drops to 65-70w. It usually seems to be the initial surge draw that does the nearly instant sag and trips the low voltage alarm on the inverter.
Looking forward to the advanced tests Oreilly will be doing. So awesome they do that and for free.
For good-condition AGM's to fully charge, they need to stay in CV (absorb) anywhere from C/100 to C/500 amps. And then drop to float.
This is sometimes impossible to achieve for those that are daily-cycling with solar, hence capacity loss.
A solar charge controller which has a so-called agm "equalization", that is merely .2v higher than normal, once every 28 days, and for only 2 hours is a mild-attempt to counteract this inevitability. It is entirely different from a true equalization given to flooded lead acid, which uses much higher voltages for much longer.
And, some SCC's may have a timed absorb - like 2 hours which you cannot change. This is ok for standby / weekend warriors where you have the rest of the week to make up for it.
But for daily cyclers, depending on your system, a fixed 2 hour absorb may not be enough. It is "dropping to float" too soon well before the C/100, let alone C/500 if you have that capability.
One fix for daily-cyclers if it drops to float too soon, is to raise your float voltage to equal your CV voltage, basically making Float = CV. This isn't damaging since you still may not actually reach C/100 and the sun sets stopping the process anyway. But at least you may be doing better.
Since batteries purchased at a store at not really well maintained or may be 6 month old stock or more, and combined with not charging the agm until current falls to C/100 at least, can get one off to a bad start and may possibly have to look into some downtime with recovery charging.
This is sometimes impossible to achieve for those that are daily-cycling with solar, hence capacity loss.
A solar charge controller which has a so-called agm "equalization", that is merely .2v higher than normal, once every 28 days, and for only 2 hours is a mild-attempt to counteract this inevitability. It is entirely different from a true equalization given to flooded lead acid, which uses much higher voltages for much longer.
And, some SCC's may have a timed absorb - like 2 hours which you cannot change. This is ok for standby / weekend warriors where you have the rest of the week to make up for it.
But for daily cyclers, depending on your system, a fixed 2 hour absorb may not be enough. It is "dropping to float" too soon well before the C/100, let alone C/500 if you have that capability.
One fix for daily-cyclers if it drops to float too soon, is to raise your float voltage to equal your CV voltage, basically making Float = CV. This isn't damaging since you still may not actually reach C/100 and the sun sets stopping the process anyway. But at least you may be doing better.
Since batteries purchased at a store at not really well maintained or may be 6 month old stock or more, and combined with not charging the agm until current falls to C/100 at least, can get one off to a bad start and may possibly have to look into some downtime with recovery charging.
