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Hello From Westbrook, Maine
#11
(02-12-2019, 06:16 AM)iscience Wrote: I like your setup.
How long have you been using the MakeSkyBlue chargers, and have you had any issues with them?
I want to use one but I'm worried about my BMS disconnecting (and possibly reconnecting) my battery while it's still getting solar input, if any cells become over-charged/discharged, I don't suppose you've tried it?

iscience,

I have been using the MakeSkyBlue MPPT controllers since ~ July 2018. I do to some extent like them and will continue to use them for a while.
I did have a problem with one of them where the mosfets blew up and it was difficult to get a "warranty replacement". but after I bought another one from a different vendor and a $40.00 replacement motherboard from the original vendor, the original vendor promised to send me a free replacement unit with the new firmware etc, I haven't seen it yet. In the final analysis I replaced the mosfets on the blow up one and now have 2 spares. If I ever get the promised one I'll have 3 spares. Dodgy

All in all they work OK the do very well with MPPT tracking and are pretty quick to respond. Programing is relatively easy once you get to know how it all works and it is a set it and forget it scenario. There is no wifi or data output, other than the screen, so you have to monitor them differently or manually. I have noticed that the voltages are off a little between units and that they will go into float mode (I have them set up for my Lead Acids) at different times even though they are all set up the same. I think the discrepancy in Voltage sensing and the lack of them being able to communicate with each other causes that. On one of them the fan has become noisy during cold startup but I will replace it with a better fan in the future. Eh you get what you pay for. Do be aware of "fakes" watch out for firmware versions as some of them claim the newest but it is just a hacked version of the latest with a newer version number hacked into it.
When I go for my 18650 powerwall I will definitely look for a better and single MPPT solution. As I have 3000 Watts of solar panels and in the summer they produce almost 50A I will probably find a 80A MPPT solution.

As far as the BMS uncoupling the batteries from the MPPT I don't know why it would as that should be programmable as an overvoltage and overcharge safety net. The MakeSkyBlue has a Li setup and you can set the top voltage with it. The system basically goes into standby when the voltage you have set it for is reached. The controller just won't allow anymore current to flow. So the BMS should really never come into play as you would have the MPPT set for example in a Nominal 48V system to 56V and the BMS over voltage protection at 58V. Believe me I have seen my Voltage on my panels hit over 100V and nothing gets to my batteries because they are full. This happens pretty quickly on a very sunny day and I am frustrated that I am wasting all this solar juice hence I want to build a powerwall to absorb all that wasted energy.

Hope this helps
Wolf
If 18 X 650 = 2200+mAh then we have power! 
May all your Cells have an IR of 75mΩ or less Smile
Last count as of 6/10/2019
Total Number of Cells                          5940
Cells  >80% of Capacity                      4334
Cells <80% of Capacity                       1605
Cells ≥2200mAh & ≥ 80% & ≤75mΩ    2800 +236
For Info Google Drive
Not your average Wolf       
            Cool



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#12
@Wolf: Good to see a fellow Maineiac/Mainer on here. I wish I were still in Maine now. Moved away after joining the U.S. Navy about 12 years ago. Currently in Washington State. I myself will be building a powerwall, I'm in the long process of harvesting and testing now. I plan to have around 10-15 kWh to start and move up over 30 kWh since that seems to be my daily usage on the grid. I will wait a bit to add solar (Washington kind of sucks for that) but eventually will add it to help offset the cost of power. I may even add a couple of wind turbines.
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#13
(03-01-2019, 05:40 PM)chamele0n Wrote: ................. I will wait a bit to add solar (Washington kind of sucks for that) but eventually will add it to help offset the cost of power. I may even add a couple of wind turbines.

Wind turbines sounds great but with all the rain maybe a private dam is in your future. Tongue

Yep been in Maine since 85 and never looked back. Love it here even with the snow.
I'm trying to figure out a system to get juice out of melting snow. LOL
Wolf
If 18 X 650 = 2200+mAh then we have power! 
May all your Cells have an IR of 75mΩ or less Smile
Last count as of 6/10/2019
Total Number of Cells                          5940
Cells  >80% of Capacity                      4334
Cells <80% of Capacity                       1605
Cells ≥2200mAh & ≥ 80% & ≤75mΩ    2800 +236
For Info Google Drive
Not your average Wolf       
            Cool



Reply
#14
(02-12-2019, 12:12 PM)Wolf Wrote: As far as the BMS uncoupling the batteries from the MPPT I don't know why it would as that should be programmable as an overvoltage and overcharge safety net. The MakeSkyBlue has a Li setup and you can set the top voltage with it. The system basically goes into standby when the voltage you have set it for is reached.

Thanks for the quick reply (sorry I somehow missed the notification and only just thought to check).

I mean the situation where a single cell is bad and the BMS disconnects the charger to protect it - so the pack voltage is still within the normal range. As far as I can tell this is what might happen:

1) cell goes over max voltage while charging
2) BMS disconnects charger
3) ** possible damage to charger ** (from battery disconnect)
4) charger output voltage increase to maximum value set

Then, it either needs to be all reset manually, or (ideally) it would do the following automatically:
5) BMS reconnects charger once cell has been balanced to below threshold voltage
6) ** possible damage to charger and/or other electronics ** (initial inrush current due to charger voltage being higher than battery voltage - but should be quite brief?)
7) continue charging as normal, possibly back to (1)

Ideally, the BMS would keep cells balanced and this never occurs, but I prefer to know just in case.
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#15
(03-09-2019, 01:23 PM)iscience Wrote:  As far as I can tell this is what might happen:
1) cell goes over max voltage while charging
2) BMS disconnects charger
3) ** possible damage to charger ** (from battery disconnect)
4) charger output voltage increase to maximum value set

Then, it either needs to be all reset manually, or (ideally) it would do the following automatically:
5) BMS reconnects charger once cell has been balanced to below threshold voltage
6) ** possible damage to charger and/or other electronics ** (initial inrush current due to charger voltage being higher than battery voltage - but should be quite brief?)
7) continue charging as normal, possibly back to (1)

Ideally, the BMS would keep cells balanced and this never occurs, but I prefer to know just in case.

Iscience,

You do raise an interesting point to which I don't really have a proper answer to. At this point my BMS experience is limited to lead acids. and that is a pretty simplistic unit I built.

The only thing that I can think of that might work is a "Super Capacitor" before the BMS disconnect to maintain the illusion of a battery bank still hooked up to the charge controllers as to fool them into thinking the battery is full so that they can throttle back.
The issue is if there is a shunt trip there is definitely something wrong and it should not have an automatic reset.
Alarm bells should be ringing and a fire extinguisher should be close by. Although lithium creates its own O2 just like magnesium the fire would be hard to put out.

I was contemplating this type of dampener "Capacitor" to be able to charge 2 battery banks separately from my charge controllers. If 1st bank = full, auto switchover to 2nd bank and the charge controllers would never know. The charge controller would not have a ~58V to 0V to ~50V shock. The charge controllers do have some capacitors in them but they bleed off pretty fast.

Would it work I don't know.

Wolf
If 18 X 650 = 2200+mAh then we have power! 
May all your Cells have an IR of 75mΩ or less Smile
Last count as of 6/10/2019
Total Number of Cells                          5940
Cells  >80% of Capacity                      4334
Cells <80% of Capacity                       1605
Cells ≥2200mAh & ≥ 80% & ≤75mΩ    2800 +236
For Info Google Drive
Not your average Wolf       
            Cool



Reply
#16
Yeah, it's something I've been thinking about but I'm not game to try it and risk breaking something. You're right anyway, it's safer to force a manual check to make sure nothing has gone wrong. I'd probably want to know if a cell is needing a lot of balancing.

I think the solution for now is to add an extra disconnect on the solar input to the charger, so it'll all turn off and stay off.
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