- Thread starter
- #21
I don't remember - I think it's 14+ due to lithium, but I never changed it from initial set up a few months ago. I'll check that though, as it's bugging me. Have to remember how to do that.
Controller/solar/battery question (5 Viewers)
- Thread starter Tennessee Jed
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It would be better to have more information to make sense of all this.
That graph above in post 19 could simply show the controller going from float to absorption to float on the battery side, depending on settings. Nothing wrong with that. The question is whether the fridge was going or not at the time.
I'm sure you do realize that if you put your smartshunt next to the battery, as you normally would, the current displayed in the graph above does not necessarily reflect the current coming out of the load port of the controller, which is what you seemed to have connected the fridge to earlier.
Does your controller provide power from the battery on the load port if there is no power coming from the panel?
That graph above in post 19 could simply show the controller going from float to absorption to float on the battery side, depending on settings. Nothing wrong with that. The question is whether the fridge was going or not at the time.
I'm sure you do realize that if you put your smartshunt next to the battery, as you normally would, the current displayed in the graph above does not necessarily reflect the current coming out of the load port of the controller, which is what you seemed to have connected the fridge to earlier.
Does your controller provide power from the battery on the load port if there is no power coming from the panel?
- Thread starter
- #23
OK. Drawing this to a close - I solved it, and I guess I'm an idiot, but in my defense this is the first time I've heard of this.
It was exactly as someone said here - the 5v difference issue. My battery sat at around 13.5 volts and I was getting max 16 - 18 volts from the solar panels. So there was almost no time at which I had more than a 5v difference.
I reconnected the panels in series, not parallel, and problem solved. I only get half the amperage but it starts charging in a soft twilight and before it would take full sun after 10am to kick things on. You can see the situation after I kicked on the panels, it immediately started charging. These numbers are low because it was early morning on a cloudy day so I was only getting about half an amp, but like 30+ volts.
The incoming amperage started off at about 1/2 amp and is steadily rising as the sun comes up. So it's charging and the battery is taking the charge as expected.
It was exactly as someone said here - the 5v difference issue. My battery sat at around 13.5 volts and I was getting max 16 - 18 volts from the solar panels. So there was almost no time at which I had more than a 5v difference.
I reconnected the panels in series, not parallel, and problem solved. I only get half the amperage but it starts charging in a soft twilight and before it would take full sun after 10am to kick things on. You can see the situation after I kicked on the panels, it immediately started charging. These numbers are low because it was early morning on a cloudy day so I was only getting about half an amp, but like 30+ volts.
The incoming amperage started off at about 1/2 amp and is steadily rising as the sun comes up. So it's charging and the battery is taking the charge as expected.
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- Thread starter
- #24
Thanks for suggestions and help. For future reference, don't assume that panels connected in parallel (maximizing your amperage) and an MPPT controller are going to necessarily be the best solution. For my setup, which is kinda common, wiring in series doubles the voltage coming off the panels and guarantees that you'll start charging sooner and keep charging longer, albeit at a lower amperage. At least the charger will turn on.
Good news! FYI, yes you only get 1/2 the amps in series, but 2x the voltage & therefore the same watts from the solar charge controller to the battery. Plus a little less wire resistance between the panels and the charge controller. Win-win.
FWIW, in the OP you kept saying" 18 watts ) which as shown in your pic of controller is actually V. 17 volts is low, like shaded or evening time. 18 to 21 is oper range in my exp. Does your controller have a charge indicator aside from the amp reading ? It seems like your controller knows the batt voltage, is getting some input from solar but not connecting charge mode. Could be a setting for the batt voltage threshold, could be the solar input is not enough to trigger the turn on of charging batt, could be the connecting device for charging solar to batt inside controller is bad. You said 2 panels, if you test them independently what sthe output voltage ? could get a 30 dollar amazon controller to hook up and see if system works as normal.
- Thread starter
- #27
Coming back to this. It's been working great, but after about 5 days I need to turn the fridge off to let the battery fully charge. It will eventually (based on sun) get down into the high 20% range but if the fridge is off, will charge to 100% in about 8 hours of good sun.
Now I have another question. The fridge has been off for several days and the battery is always at 100% when I check it, just haven't needed to keep the fridge plugged in. What do you think of this charge pattern over the past couple of days:
It seems like about every 12 hours, I lose approx 1 volt of battery charge, then the charge controller blips for a minute or two and it's back up to 100% (about 14.4 volts) then it drops to about 13.4, then back up. Extremely consistent.
Do you think this means I have a parasitic drain? There are no loads on the battery at all. Curious to hear your thoughts. Those little blips from the CC can't provide any significant power. Seems odd to me.
Now I have another question. The fridge has been off for several days and the battery is always at 100% when I check it, just haven't needed to keep the fridge plugged in. What do you think of this charge pattern over the past couple of days:
It seems like about every 12 hours, I lose approx 1 volt of battery charge, then the charge controller blips for a minute or two and it's back up to 100% (about 14.4 volts) then it drops to about 13.4, then back up. Extremely consistent.
Do you think this means I have a parasitic drain? There are no loads on the battery at all. Curious to hear your thoughts. Those little blips from the CC can't provide any significant power. Seems odd to me.
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^ you are not 'losing' 1V every 12 hours. LiFePO4 batteries (well, most batteries) will 'float' at a 100% charged voltage that is NOT the same as what the charger is 'topping' up to. e.g. your alternator will charge your starting battery up to 14.4V (give or take), but the battery will be 100% charged at 12.8V (sitting voltage)give or take.
You should do some reading on charging LiFePO4 batteries and voltages that should be used to charge, float, start charging etc.
Your charge controller is basically seeing the battery voltage get to a point that it wants to top it up. Typically a LiFePO4 should be charged once it gets to below 3.4V (per cell), so, around 13.6V for 4 cells. Your charge controller is being more 'friendly' and not doing that until maybe 13.4V.
Charging too often or maintaining a voltage above the 'sitting voltage' is detrimental to the batteries long term performance.
All is good.
cheers,
george.
You should do some reading on charging LiFePO4 batteries and voltages that should be used to charge, float, start charging etc.
Your charge controller is basically seeing the battery voltage get to a point that it wants to top it up. Typically a LiFePO4 should be charged once it gets to below 3.4V (per cell), so, around 13.6V for 4 cells. Your charge controller is being more 'friendly' and not doing that until maybe 13.4V.
Charging too often or maintaining a voltage above the 'sitting voltage' is detrimental to the batteries long term performance.
All is good.
cheers,
george.
George is correct. What you see is normal, even without parasitic drain. The key here is that there is likely no significant state of charge difference between the maxs and mins you see in the sawtooth pattern. The difference in seen voltage is likely just the controller kicking on and off but the charge of the battery is the same since it is full. There is no real loss of charge between the 2 when the voltage is seen to decrease. You can tell because it only takes a minute to go from min to max, so there is no actual charging going on, the controller is just "activating" the battery then so to speak and the high voltage is a "superficial" artifact voltage. If you had had a significant drain, the charge would actually go down and it would then take some time for the controller to bring the battery back to 100% with a significant current seen. You should see this easily if you have the smartshunt connected properly at the battery, it will likely show 100% charge all the time.
The slow decrease in voltage is the "surface effects" dissipating, it's a voltage thing, not a charge thing. For LiFeP 12V batteries for instance, the usual desired charging voltage is 14.6V, but if you let the battery settle after that without the controller on and even fully disconnected, it will go to about 13.4V or so, and yet be still fully charged, contrary to what some people may think. The voltage at which the controller kicks back in (around 13.4 or 13.5V in your case) is defined in the settings. If you set it a bit lower than that, you will likely not see the controller kick back on for days if there is no drain on the battery, because the battery will stay at around 13.4V at 100% charge for a long time.
There is something similar going on with lead acid batteries, but it's a bit different in how it shows with a controller connected in that there is a normally a set float voltage that is higher than the rest voltage, unlike for LiFeP batteries. But if you fully disconnect the controller when it's been absorbing for a bit at 14.4V, the battery will slowly go to about 12.7V without losing any charge.
All these voltage values can be set to anything you want with a good controller.
BTW, this is why they always tell you to give the battery an hour or more to rest after charging to measure its true voltage. If you measure the voltage immediately after charging, it will be a lot higher than the true resting value.
The slow decrease in voltage is the "surface effects" dissipating, it's a voltage thing, not a charge thing. For LiFeP 12V batteries for instance, the usual desired charging voltage is 14.6V, but if you let the battery settle after that without the controller on and even fully disconnected, it will go to about 13.4V or so, and yet be still fully charged, contrary to what some people may think. The voltage at which the controller kicks back in (around 13.4 or 13.5V in your case) is defined in the settings. If you set it a bit lower than that, you will likely not see the controller kick back on for days if there is no drain on the battery, because the battery will stay at around 13.4V at 100% charge for a long time.
There is something similar going on with lead acid batteries, but it's a bit different in how it shows with a controller connected in that there is a normally a set float voltage that is higher than the rest voltage, unlike for LiFeP batteries. But if you fully disconnect the controller when it's been absorbing for a bit at 14.4V, the battery will slowly go to about 12.7V without losing any charge.
All these voltage values can be set to anything you want with a good controller.
BTW, this is why they always tell you to give the battery an hour or more to rest after charging to measure its true voltage. If you measure the voltage immediately after charging, it will be a lot higher than the true resting value.
- Thread starter
- #30
Thanks. Makes sense. I'm used to a full volt "drop" being a lot, but I see what's going on now.
Along those lines, keep in mind too that LiFeP batteries -unlike lead acid- have a very flat discharge voltage curve. IOW, they will stay around 13V during most of their discharge process and then drop hard quickly after that when they are about done. Which is why it's hard to judge the SoC of a LFP battery from voltage only. (And why you want a Smartshunt or equivalent to tell you what the SoC actually is.)
