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MPT-7210A Questions
#21
ALL chargers that are cheap you need to connect battery first. Thats a common rule. I have tried the other way around and killed many devices Tongue

and YES if you have a BMS that disconnects you can in worst case kill the charger! I know that because i have had that happen. The newer controllers today are better in that sense since they had to adapt them to Lithium that have BMS.
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#22
Since it's raining today, I decided to take the time to upgrade my MPT-7210A a bit. Put it in a soon-to-be weather resistance enclosure (waiting for the 3D printed vent/shrouds to finish, which I will attach to the 2 holes in the side of the box and seal with silicone sealant), and added a coax cable and external antenna to the ESP8266 (as well as adding some code which should allow it to reconnect if it drops connection), since so far I have not been able to successfully get data from my MPT-7210A except the very first day I installed it, and 2 days ago when I was fussing around with the panel location and reconnected the panel.

 


Here is the data from 3/11 when it did work at least:

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#23
I have had one of these units for around 2 years. It was feeding a 24V (2x12V 110Ah) setup from 3 x 100W 18Vmp panels in parallel.

The thing would power up from the solar input (regardless of battery) first thing in the morning with the fan slowly accelerating as the voltage climbed - it ended up as a psudo alarm clock for me for a month....

The main issue I had was the tracking accuracy because it seemed to have issue with cloudy days when the output from the solar dropped faster than the internal software expects. This results in an over draw from the unit and it drops the output to zero as a result and then starts to build the output again.

As an extreme solution and experiment I wired up a pack of 10 x 500F supercapacitors (as a buffer to the inpout and through that this would then both prevent the cloud issue and help optimise the cloude edge peaks. The supercap pack would actually store around 4Wh of energy.

What ended up happening was the tracking pulled the voltage down to the minimum value (10-12V input) at times and then not allow the voltage back up, so my conclusion was that adding any additional capacitors on the input would potentially reduce the overall energy captured.

What was beneficial though )very very marginal) is that I could disconnect the solar when it was very low input and allow the capacitors to charge up enough to then allow this energy to go through the unit. Without them the unit would not power up properly or the fan would use the power. Again, this is so marginal that it would not even recover the cost of a single supercap.....

Other than that they are a good unit with a nice display.
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#24
completelycharged There is no tracking function built into it. Its manual and you need to set the power point voltage your self. If its not set properly the unit will walk all around the place.

So if you want a proper MPPT tracker then this unit is not the right one Smile
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#25
(03-14-2018, 01:28 PM)daromer Wrote: completelycharged There is no tracking function built into it. Its manual and you need to set the power point voltage your self. If its not set properly the unit will walk all around the place.

So if you want a proper MPPT tracker then this unit is not the right one Smile

There is some degree of tracking, look at the chart in the post by rev0 and the pattern of output through the day. Explain the circuit behaviour between 0 and 1hr for the W and V in the chart ? In the chart 1-2.25hrs is clear sun with a couple of clouds/interruptions - the profile of V and W outpout either side seems more like basic tracking to me.

I have tried setting the Vmp level and experimented a lot with the unit, the basic issue is the units seem to have a difficulty tracking quick output decrease from the solar, whcih a passive component device would never have.

If you set the Vmp way higher than your actual Vmp for the solar panels the unit will track close to the actual Vmp in bright sun.... or at least my unit does (and it is 2yr old so may have older firmware programming)... might be just my unit.
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#26
If I can get my logging working reliably (currently it seems to only work when powered by the USB port, doesn't like when the voltage of the charger slowly ramps up), I'll do some science with the Vmp settings to see what produces the highest output.
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#27

Correction - 12s capacitor pack. Had to take one set of the resistors off - scavenged for a different project while away.
Had a balancer for them, but it was terrible because the (chinese sourced) capacitors have that much variation between them (tollerance around 30%).
The resistors were efective means of 24x7 bypass balancing for the caps - basic higher the V more I... and did not run them anwhere near the limit becauase of the poor quality of the caps.
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#28
Yes i know it does some kind of tracking and its useless Tongue I tested it for 2 hours and then i ditched it and only use it for smaller tests Smile

The thing when setting it higher is that it drags down to what it can push through kind of. if you have a smaller panel like 20W it will behave very weird but if you have bigger panels it works better. Though not sure if its different from unit to unit but the units I have had none of them tracked even close. Comparing to any of my other devices none of them worked more then when full sun and when the point was set properly. Outside that they where atleast 20% below the others Big Grin
The Ultimate DIY Solar and build place
YouTube / Forum system setup / My webpage  Diy Tech & Repairs

Current: 10kW Mpp Hybrid | 4kW PIP4048 | 2x PCM60x | 83kWh LiFePo4 | 10kWh 14s 18650 |  66*260W Poly
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#29
Mike still seems to be liking his. It's definitely a great value if nothing else, $27 and it's still quite a step above a cheap PWM controller. 

Anyhow, finished my mods, debugging the ESP8266 logger was a pain in the butt. Apparently, it does not reliably start when the voltage is slowly ramping up (like when the sun rises and the panel voltage slowly creeps high enough to turn the charge controller on). I had to add a power on reset circuit that holds the ESP module's reset line low until the input voltage exceeds ~10V. It's just an op amp that compares the 3.3V LDO voltage to the divided down internal 10.6V buck converter output. When the buck converter output is high enough, reset goes high and lets the ESP8266 boot up. At first I tried controlling a USB power enable switch, which would just switch 5V on when this same thing happened, but it was still unreliable. So far this seems to work, we'll see how it does in the real world. 

Here's the simplified system schematic as it is today:

 

And here's the final weatherproofed box, added a couple vents where the air will circulate and the wires will exit. Used silicone sealant around these 3d printed vents, hopefully this keeps the water out:

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#30
I think yehu came up with the best idea for these units: He has removed the front panel and added a big fan in their place cooling the whole unit from atop. He's placed the panel with the LCD screen alongside. You can see that in a couple of his videos, although he hasn't made one specifically for the MPT7210A unit.

I also believe these units are quite good for their price, give lots of control over the charging parameters and can be used as DC-DC boost converters reliably. However, a 100Wp panel is the minimum (says so in the chenglish manual), the tracker just doesn't work right under a smaller panel.

I would also appreciate it if it was a buck as well as a boost converter. This unit, being a boost converter, needs to be wired to at least an 8s battery, since most modern solar panels have an MPPT voltage of around 30V.
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