120 vs. 144cells on an MPPT 100/20-48

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porcini asked Oct 23, '18

120 vs. 144cells on an MPPT 100/20-48

Hello,

I noticed that you offer the 100/20 as a 48V-Version, although that product isn't promoted on the VE-website?

The advantage is that this controller is a very cheap solution as the 150/35 is almost twice the price. But it's also a niche because there come a lot of problems with the 100V limit. I will explain my thoughts.

At normal conditions it will be possible to use both, two 60-cell and two 72-cell panels in a row.
But when it is getting hotter there is a problem when using two 60-cell panels combined with a lead-acid battery. The cell temperature entails the MPP-Voltage to be at the same level as the battery charging voltage, so the charge controller has to set its operating point above the MPP of the PV. That means losing energy. If an equalize-charge is neccessary that could even be a problem. Probably a solution would be to use Pylontech LiFePO4 and such batterys, as they operate at lower voltages. But in an off-grid-system these aren't allowed?

When it is getting colder two 72-cell panels are a problem, too. The open circuit voltage rises above the 100V limit. I don't know how much tolerance there is until the charge controller gets broken, but in winter it would definitely exceed its specs. So there are a few questions I have:

1. Does this charge controller have a PV-overvoltage-protection?

2. When using ESS with feed-in the MPPT normally works at the MPP of the PV. Is it getting more careful when it works near the limit and avoids to get over 100V if that is possible (feed in enabled, batterys empty) or does it still try to find its MPP no matter if that would be above 100V?

3. The bigger 150V models don't work above 145V. How does the 100V-Version? Does it still work at 101V or will it shut down and show an error? At which voltage that error appears?

4. Do you think that the charge controller can be used with 144cells when reaching 102V in the winter (with losing warrenty) without getting broken soon?

5. Who is this controller designed for? In Western Europe it's not an optimal solution. Neither with 120cells nor 144cells. Probably 144cells in Africa would work great.

Thank you!

regards,

porcini

MPPT Controllers temperature overvoltage

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Answer 1 · 2018-10-23T10:22:24Z

Guy Stewart (Victron Community Manager) answered · Oct 23, 2018 at 10:22 AM

1. As in all MPPT's the PV string open circuit voltage is a STRICT AND HARD LIMIT. Exceeding this voltage by even 1V can lead to permanent damage to the unit. In this case, under no circumstances (including cold weather) should the PV array exceed the MPPT voltage limit.

2. While this might help in theory, it should not be relied on that the Maximum Power Point (MPP) is sufficient to keep the voltage under the limit. You must design for open circuit voltage on the PV side to protect the charge controller.

3. At 101V, the 100/20 48V unit is likely to be damaged and no longer functional.

4. Definitely not. This unit is not to be used in any condition or circumstance where the OPV of the panel exceeds the rating.

5. It is designed for low maximum battery voltage applications (eg 55.2V) for BYD lithium, in warm climates where temperatures do not get cold and cost must be kept low.

It is an IDEAL product to support a larger AC PV array in a BYD and Victron system, where a DC solar charge supply connected to 2 x 60 cell panels is able to bring the system back from a black stop situation. It is very cost effective.

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porcini commented · Oct 23, 2018 at 11:04 AM

Thanks, just wanted to be sure that the 72cell-panels aren't possible then. These would fit better, so I could have a little bit more PV-power. But it wouldn't be profitable when I had to use the 150/35 instead for a few more percent of PV.

All in all your last passage is almost exactly I want to use it for! :) except the fact I cannot use the AC-PV at the output, because it is too large :(

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