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Parallel connection problems

tcparris2

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Joined
Aug 18, 2020
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36
Hi,

I have two 320 watt 24v Renogy In parallel and getting some output problems.

During peak sunlight with no shade I was getting only 5 amps and roughly 175 Watts. I through a blanket over one panel that had an angle tilted less toward the sun and the amps went up about 0.5. I then through the blanket over the other panel and the amps were about the same as when both were exposed (5 amps).

Im worried when I first made my mc4 branch connectors I was connecting and disconnecting to test for continuity and they arced at the panel and may have done damage?

The other interesting thing is the amps do seem to add now that it’s partially shaded. One is getting 30watts the other 50 Watts and when both exposed 80 Watts.
Any suggestions for why I wasn’t doubling amps in full sun but was while shaded after the blanket test?

Thanks Taylor
 
What's your make and model of SCC? Amps Max Voc?
Is your battery full? You will not get much charging if it is near to full.

Attach a load when you take your readings.
 
PIP-2424LV-MSD aka 24v mpp solar. I had it set to charge at 10 amps with solar and though that may be it so increased to 20 to no avail. I looked at every setting again to double check there wasn’t a a setting changing the draw. I have read they will only draw according to the load so maybe that’s it :). My 24V CALB with ant BMS is showing 26.5V with each cell at about 3.310v. That’s about 70-80% SOC. The max charge on the mpp is set to 29.2 Float 27 and Ant BMS to 28.4. I’ll set these lower but trying to see what I can get out of these panels.

Ill try plugging in a 150-200 watt appliance and see if it pulls more. Thanks for that suggestion. Hopefully that’s it.
 
Max Voc for that mpp solar model is 145v and this panels are oc of 40.1. So it’s 80.2 together.
 
Max Voc for that mpp solar model is 145v and this panels are oc of 40.1. So it’s 80.2 together.
You said the panels are in Parallel so you would not double the voltage.
You would double the amps of your 2 320 watt panels.

PIP-2424LV-MSD aka 24v mpp solar. I had it set to charge at 10 amps with solar and thought that may be it so increased to 20
I dont remember what amps the MPPT is on that unit but why are you setting it to less than the max? 60A?
 
Right, yeah it’s parallel connected. My mistake, it’s just 40.1. 80.1v if series. I’m seeing a max of 37V so far.
Yes it’s 60A. I’m setting it to charge slowly to extend the life of my batteries. With 2 320 watt panels I could only draw 26.6 amps if they indeed get 320 Watts.
 
Well that 26.6 isn’t right, I was doing that math at 24v m. It’s around 17amps @ 37v.
 
Right, yeah it’s parallel connected. My mistake, it’s just 40.1. 80.1v if series. I’m seeing a max of 37V so far.
Yes it’s 60A. I’m setting it to charge slowly to extend the life of my batteries. With 2 320 watt panels I could only draw 26.6 amps if they indeed get 320 Watts.
That's wacky about extending LFP battery life by slow charging!
Where did you get that idea from?
LFP can charge at 0.5C with no problems.
Just put the setting on 60A!
How many Ah in your 24V LFP battery?

640 watts into a 24V battery is only 27A charging.
 
Will Prowse.
.

Probably won’t heat up at 0.5C rate but may as well stay on the safe side. I have used CALB 100A cells so I think that after use the C rating changes precisely because of the heating. I’m assuming they’re grade B and 0.5C but they should be 1C if new Grade A . Plus one of my cells is bad and jumps to 3.8v when charging at around 600 Watts. So the 100 watt charging rate is ideal for now to safely get a decent charge out of my bank. My ANT BMS will tell it to stop charging at 3.8v but I’ll still monitoring when charging or discharging around 500 Watts. I have a replacement cell coming.
 
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27A is not 0.5C charging on your 100Ah LFP battery.
0.3C
 
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Right, 50amp would be 0.5C. I’ve seen other videos Will Prowse does recommending max of 20 amp charging to extend life of batteries.
 
Having it limit to 10 amps of charge current is only going to pull 260 watts or so from the panels. So it makes complete sense that the current did not increase. Set it for 0.5C charge rate on the LFP and they should last a long time. If you want to extend the life, don't run them to high voltage, just set the absorb down to 3.4 per cell. You will lose a little capacity, but they will last longer. Being over paneled at 640 watts is not a bad thing. It just means you will get your desired charging current for more hours and in worse conditions. I have my 240 watt Enphase micros connected to 300 watt panels. They only ever clip at 240 watts when it is very sunny yet cool outside. No matter what your charge current is set to, once your battery is fully charged at your set absorb voltage, the power will fall off to keep from overcharging the batteries. If you want to see full power from your array, connect a 300 watt load and see if the solar will keep up.
 
Being over paneled at 640 watts is not a bad thing. It just means you will get your desired charging current for more hours and in worse conditions
He is not overpaneled.
640 watts into a 24V battery is only 27A using a 60A MPPT.
 
He was over paneled for just 10 amps of charge current though. He would get that 10 amps for a fairly long period. Not sure I fully explained. I agree, he should crank up the current. Set it for 50 amps, it will never get there, and he should see the power of the 2 panels add until the battery is fully charged again.
 
He was over paneled for just 10 amps of charge current though. He would get that 10 amps for a fairly long period. Not sure I fully explained. I agree, he should crank up the current. Set it for 50 amps, it will never get there, and he should see the power of the 2 panels add until the battery is fully charged again.
He actually reset to 20A
That's correct on 10A
I have been trying to convince him to up the setting to 60A max as you say it will never get there.
But he watched a video and thinks he is extending his LFP battery by charging at a low rate.

640 watts panels making 175 watts.
Only one may be connecting.
Does he have a multimeter?
 
Yeah I have a multimeter.

I’ll try to increase the charge rate to 60A and connect a load when there’s full Sun to see if that’s it. Just tested again in the shade and am getting 95 Watts with parallel connection. If I blanket shade one panel I’m getting 34-45 Watts and vice-versa for blanket shading the other panel. So it is likely my inverter setting. I’m just surprised it won’t pull all the way up to 10A when it’s set to max charge 10A. 10A is 370 Watts at 37V. If each panel was indeed getting 175-190watts as I tested by shading each panel with a blanket then that would be close to that 10A draw. If I charge with utility with all the same settings it will draw exactly 10A or 20A depending on how I set it. I’m sure the charge controller works different the the utility charger in this unit though so y’all are hopefully right.
 
Having it limit to 10 amps of charge current is only going to pull 260 watts or so from the panels. So it makes complete sense that the current did not increase. Set it for 0.5C charge rate on the LFP and they should last a long time. If you want to extend the life, don't run them to high voltage, just set the absorb down to 3.4 per cell. You will lose a little capacity, but they will last longer. Being over paneled at 640 watts is not a bad thing. It just means you will get your desired charging current for more hours and in worse conditions. I have my 240 watt Enphase micros connected to 300 watt panels. They only ever clip at 240 watts when it is very sunny yet cool outside. No matter what your charge current is set to, once your battery is fully charged at your set absorb voltage, the power will fall off to keep from overcharging the batteries. If you want to see full power from your array, connect a 300 watt load and see if the solar will keep up.
Yeah I’m planning on charging and discharging each cell between 3.225 and 3.35 to get close to 75% down to 25%. When I’m needing larger loads or extended time while I’m on the road or don’t have utility I’ll use more of the capacity. For now I just have lights and fans.
 
I think y’all were right. Parallel connection seems to be working good now after connected to a load and upped the charge to 40a. Interestingly I can now move it to 10a and it seems to be charging only 10a as long as I have a load on it. The battery is also drained to 26v. I think the PIP Charge controller does pull amps relative to the voltage of battery bank (max charge is 29.2) and load demand but not the charge amp draw limit setting. If I disconnect the load it still charges at 10A now. I think it was just reading to high a voltage from the battery bank. That one bad cell is so variable when charging discharging the total V jumps from 26-27.1 and I think the PIP recognizes that and tells it to draw less current. The cell is still cool to touch but I’m still concerned because the voltage of that cell is hovering 3.7-3.9while charging. Now at 3.867 on ant BMS and multimeter charging at 220watts. I’m able to get the voltage to drop below 3.8 if I add loads but uncertain this is safe. Again the cell is cool to touch still.

I’m drawing about 160 Watts from each panel now for 320 Watts. Still only getting half the rated Watts but that’s probably because the angle of the panels and wire losses. It’s also only 11:30 in October.
 
3.9 volts is too high for an LFP cell. 27.1 on the whole pack should only be 3.3875 on all 8 cells, so you have a serious balance problem. Use a good meter and measure the voltage at each cell's terminals. You may have a bad connection somewhere, or the BMS is not working correctly also. Most do not recommend going over 3.65 volts on LFP cells. If all of the voltages look ok directly at the cell terminals, then I would suspect a bad connection between cells, or a problem with a BMS lead connection. If you add up the voltage you read at each cell, it should be very close to the voltage across the entire pack. If the full pack is higher than the total of the cells while charging, it is a bad connection somewhere. And if the cell voltages do not match what the BMS is reporting, it is also a sign of a wiring problem, or a bad BMS.
 
I just have a single bad cell. Already have a new cell coming as mentioned already. I bottom balanced them all and when charging or discharging that one cell has a huge voltage drop or gain. I discovered this when I first received the cells a couple months ago. I’m reading with multimeter and it matches the BMS for all cells. The other cells stay within .002-.004 volt difference when charging or discharging. Like I said that one cell jumps to 3.8-3.9 when charging at 8amps and falls to around 3 when discharging 8 amps. The BMS works very well in cutting off charging if cell volt is too high or low. If I set the BMS to total volt high relative to what that one cell is jumping to when it goes to 3.8 it will then charge at a slower rate.

so if the total pack is at say 28v when that one cell is 3.8v and the other seven are around 3.4 while charging at 10amps, I can set the BMS high volt at like 28.4 and that will make it charge at a slower rate, say like 5 amps at which point the one bad cell drops to like 3.6. The BMS is cool in that it charges slower and slower as it approaches the total volt high and you can watch the amps/Watts charging decrease at it approaches the total volt high parameter, at which point it will keep the pack at 0w 0a even with a load on it as long as there’s a charging source (PV or utility).
So right now it will shutoff charging if any one cell hits 3.85v and then I just have to toggle with the total voltage to get the cells charged to like 3.4. When they all settle they’re all balanced within .002 volts including the bad cell.
 
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