Confusing the MPPT controller

[JiminDenver]

Here I go with my ignorant self again, seeing something and thinking I can figure it out. 😉

When I first got my original panels I talked to quite a few people including Mark at Rogue saying to run then on his 30a MPPT controller. I had told him they were different wattage as well as type but that didn't concern him at all. With all of my driveway test I realized that they never matched up in any way in any light. The 220w mono will gain a higher Voc in bright light than the 230w poly, but in low light it crashes while the poly still produces. Reading that somehow the controller tweaks the array made me think that the different voltages would have a adverse affect. I have never tried them together but I did know that I would have matching panels to mount.

Move forward to this spring when I got the Morningstar TS-MPPT-60 and did test adding the 230w poly into the three 250w polys as a mixed panel test. The 230w wasn't a match but it was of the same type and reacted to different light like the rest. What I saw was less output than I would have expected from the 970w total or even four 230w meaning that the whole array was being controlled by the low panel. Either should have easily maxed out the controller but the best I saw was 58 amps, close but no cigar. Looking at the grafts I saw that the array was providing over 800w at times but the controller was only using a portion of it and not much more than the three 250w panels could produce themselves.

Since my MegaWatt died I took advantage of needing to hook up something at home and ran the 230w schott poly and the 220w Canadiansolar mono together in series on the TS-MPPT-60. I set them out around 10 am in bright sun with a decent tilt/angle. The 220w had a Voc of 23.8v, to 230w 24.5v. When I hooked them in series I got 68v which would follow the concept of the lower panel controlling the voltage.

Now I know in parallel the 220w puts out 12a and the 230w puts out 15a here in Denver. In series they were maxing out at 23.8a which again would follow the concept of the 220w limiting the 230w.

What was interesting is the display on the controller was jumping up and down by a watt and a bit of a amp. It was doing it when the batteries were in absorb and close to what the 230w could do on its own so I unhooked the 220w and ran the 230w alone. As soon as I did that the watts and amps production settled to a solid amount.

So with like types the controller knows the watts are there but doesn't use them even though the load calls for it. With mixed types the controller seems to be having trouble settling. I'll have to set up the test again and do a log to see if the Vmp is changing that fast too meaning the controller can't find a sweet spot.

I know boring stuff, crude observations, probably way off base. Just posting what I see.

[MEXICOWANDERER]

Tell a Chinese panel maker he has to make a panel using five times what he is now using in (expensive) circuit trace material (for greater amperage) and he's going to do one of two things...

A) LAUGH

B) REACH IN A DRAWER FOR A GUN

Ever give thought to the idea that panel designs are intrinsictly EXCLUSIVE? Start an array of 200 panels and you are FORCED TO stay with that panel specification or suffer?

[JiminDenver]

Actually if you read the first part of my OP, the experts didn't know and suggested I run them on the Rogue 30a MPPT, even the owner. Come to think of it I haven't seen anyone post proof that the controller can lose the ability to settle on it's values or use the full potential output of the array. The concept of the weaker panel limiting is accepted, not the confused controller.

[grizzzman]

JiminDenver wrote:
Here I go with my ignorant self again, seeing something and thinking I can figure it out. 😉

When I first got my original panels I talked to quite a few people including Mark at Rogue saying to run then on his 30a MPPT controller. I had told him they were different wattage as well as type but that didn't concern him at all. With all of my driveway test I realized that they never matched up in any way in any light. The 220w mono will gain a higher Voc in bright light than the 230w poly, but in low light it crashes while the poly still produces. Reading that somehow the controller tweaks the array made me think that the different voltages would have a adverse affect. I have never tried them together but I did know that I would have matching panels to mount.

Move forward to this spring when I got the Morningstar TS-MPPT-60 and did test adding the 230w poly into the three 250w polys as a mixed panel test. The 230w wasn't a match but it was of the same type and reacted to different light like the rest. What I saw was less output than I would have expected from the 970w total or even four 230w meaning that the whole array was being controlled by the low panel. Either should have easily maxed out the controller but the best I saw was 58 amps, close but no cigar. Looking at the grafts I saw that the array was providing over 800w at times but the controller was only using a portion of it and not much more than the three 250w panels could produce themselves.

Since my MegaWatt died I took advantage of needing to hook up something at home and ran the 230w schott poly and the 220w Canadiansolar mono together in series on the TS-MPPT-60. I set them out around 10 am in bright sun with a decent tilt/angle. The 220w had a Voc of 23.8v, to 230w 24.5v. When I hooked them in series I got 68v which would follow the concept of the lower panel controlling the voltage.

Now I know in parallel the 220w puts out 12a and the 230w puts out 15a here in Denver. In series they were maxing out at 23.8a which again would follow the concept of the 220w limiting the 230w.

What was interesting is the display on the controller was jumping up and down by a watt and a bit of a amp. It was doing it when the batteries were in absorb and close to what the 230w could do on its own so I unhooked the 220w and ran the 230w alone. As soon as I did that the watts and amps production settled to a solid amount.

So with like types the controller knows the watts are there but doesn't use them even though the load calls for it. With mixed types the controller seems to be having trouble settling. I'll have to set up the test again and do a log to see if the Vmp is changing that fast too meaning the controller can't find a sweet spot.

I know boring stuff, crude observations, probably way off base. Just posting what I see.

Great job proving out what the experts already know! Keep up the great work!

[JiminDenver]

It's not just while in bulk and MPPT mode. It happens in absorb too. I put the 220w back in and ran a log. The Voc, Vmp and watts/amp input from the two panels remained steady. What the controller accepted changed constantly. Array voltage, wattage, current all bounced up and down slightly in steps and then start over again. An example is the array voltage starting at 63.23v and in seconds dropping 63.11, 62.95, 62.66, 62.26v and then back up to 63.23v to start it over.

So as for why or how, I do not know but the mixed voltage and amps of the two panels didn't set well with the controller. I'll go through the logs of the mixed polys and see if it was happening there too.

[MrWizard]

best guess an mppt set point that can't be maintained

[JiminDenver]

The mixed poly test I have logs from. I'll dig them up if they are not all ready in the series vs parallel thread.

I did say that I expected the array to follow the weaker panel, and it did in both Voc ans amps out of the controller. The question is why is the controller jumping up and down. I'm on break from fall "spring" house cleaning but I'll try to sneak the laptop out and log the effect.

[MrWizard]

panels in series must be the same AMPS

the circuit will not produce any more amps than the max flow of the smallest amp panel

12a in series with 15a ..equals 12 amps max at the TOTAL/sum voltage of the (2) panels
12a * Voltage = total watts the MPPT controller will decide the actual amps VRS voltage to the batteries

its like sticking a 3/4" coupler between (2) pieces of 1" pipe
max flow GPM is going to equal what the 3/4" can pass

[MEXICOWANDERER]

Connect the three brothers im series. Note the wattage. Then add the red-headed stepchild then see what or what doesn't happen