Does the MPPT push VDC above max 60VDC that Lynx Power-In can handle

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harlov asked Jun 17, '24

Does the MPPT push VDC above max 60VDC that Lynx Power-In can handle

Hello all

I am wanting to implement the Lynx Power-in into my 51V battery bank (2x 100Ah), as well as into an MPPT for near future solar. Currently I have both batteries running in parallel through a single 125A NH00 gBat fuse & 50mm2 cables, into my 3kVA MP-II.

I am aware this isn't optimal, as each should rather run through their own 125A fuse, before combining back at the Lynx, which is where my below research starts.

I have recently watched many videos on arcing and how severe it can become, so it's my main priority to avoid this. Am also aware that only the internal POS & NEG terminals of the Lynx should be used for battery terminals, and not the external two mounting holes on the left side, (which are designed for connecting to another Lynx). Rubber caps on to avoid anything making a connection between them and causing an arc.

I looked at the VDC of the Lynx Power-In, which as per the manual specs in Section 8 https://www.victronenergy.com/media/pg/Lynx_Power_In/en/technical-specifications-lynx-power-in.html it says:

Minimum: 9 VDC
Maximum: 60 VDC

My battery’s 54.5V is well within this, so all good thus far, but the issue comes in when you add the MPPT, with higher VDC solar into the mix.

This is because, In the same manual, in section 4.1.3 https://www.victronenergy.com/media/pg/Lynx_Power_In/en/system-design.html it shows that you can connect both your battery bank and solar arrays, which is where i am getting confused.

From what I am seeing/understanding, it's very under-specced for the high voltages that will exist, within a solar array in series, which will easily surpass the max VDC.

Because, in order to even power the MPPT, the voltage needs to be at least +5V above battery as per the MPPT manual section 9 https://www.victronenergy.com/media/pg/Manual_SmartSolar_MPPT_100-30__100-50/en/technical-specifications.html.

Given this and my battery at 54.5V at 100%, we can round this off to 60V, which is inline with the Lynx Power-In’s max 60 VDC, but what happens when I have even 3x 425W solar panels with a Voc of 38V and best case a VMPP of 32V. (Factoring in using a 150/100 MPPT to give some voltage headroom).

Even with a lower and closed circuit VMPP, 32x3 can = 96V, which is far above the Lynx max of 60V.

So am I not understanding something here, or should you not actually connect a Lynx to an MPPT, with anything more than 2x panels that fall below the 60VDC limit?

Also, wouldn't the battery VDC be added to this, increasing the total VDC even further to 96+54 = 150VDC? (EDIT: nevermind, I soon realized that the Lynx is in parallel, so V wouldnt increase)

Thanks

MPPT Controllers lynx distributor

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Answer 1 · 2024-06-17T10:12:23Z

harlov answered · Jun 17 at 10:12 AM

Pics of links, for reference

mppt-specs.png (59.2 KiB)

lynx-power-in-system-example.png (107.2 KiB)

lynx-power-in-specs.png (65.6 KiB)

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Answer 2 · 2024-06-17T10:21:01Z

harlov answered · Jun 17 at 10:21 AM

OK posed the question to GPT and said the following which makes sense, which is a detail I didn't know:

"The high voltage from the solar panels (e.g., 114V) is handled by the MPPT controller directly and should not pass through the Lynx Power In. The MPPT controller steps down the high voltage to the battery voltage level and manages the charging process.

The output from the MPPT (which is regulated to match the battery voltage, e.g., 54.5V) is what should be connected to the Lynx Power In. This ensures that the voltage within the Lynx Power In does not exceed its 60VDC limit."

Can anyone confirm this so that I am 100% sure and clear. Thanks

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Answer 3 · 2024-06-17T10:22:13Z

kevgermany answered · Jun 17 at 10:22 AM

The solar arrays always go through a solar controller, never direct.

As long as the controller is set up correctly, with absorption voltage set according to battery maker's instructions, the Lynx system will work correctly. The solar controller drops the panel voltage to battery requirement levels.

I.e. the system is designed for and fully capable of running in a 48V setup.

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Answer 4 · 2024-06-17T10:40:14Z

harlov answered · Jun 17 at 10:40 AM

thanks for confirming :)

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Answer 5 · 2024-06-17T12:07:28Z

harlov answered · Jun 17 at 12:07 PM

@kevgermany Quick follow-up question

So say the hypothetical incoming max power is (3x 31.3VMPP = 93.9V) * (13.58 IMPP) = 1275W.

As this then gets stepped down by the MPPT to 54.5V, it would then also increase the amp current to deliver the equivalent watt power of 1275W / 54.5V = 23.4A through to the Lynx?

Therefore in terms of cabling and fuses,

Between panels and MPPT: you would use cables rated for 15A or more, with a DC fuse rated lower than cable, but higher than the 13.58 IMPP amperage (to avoid any power loss), while also making sure the fuses can handle a voltage far exceeding the 114Voc, to protect from arcing?
Then, between MPPT and Lynx: cables rated for higher than 24A, with a fuse rated lower than cable. I assume arcing is still possible here, but less damaging than what the fuse between the panels and MPPT has to deal with - similar to battery cables and fuse?

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Answer 6 · 2024-06-17T13:37:37Z

kevgermany answered · Jun 17 at 01:37 PM

You should be using solar cable between the panels and mppt. Preferably with mc4 connectors. There are inline fuses for solar with mc4 connections. Solar cable comes in different sizes for the differing currents.

Make sure the cable you use to the lynx isn't too big for the MPPT. Yes fuse it below the cable rating. Also take voltage drop into account for sizing. It can be significant at high current over longer runs if the cable is too small.

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