question

tex260z avatar image
tex260z asked

MPPT with separate port BMS alternative wiring

Hi Guys,

So my Van build is still working a treat after two and a half years, 12 volt 200 amp hour LiFePO4, Separate port 200/50 amp BMS, Victron 75/15 MPPT, BMV-712 (networked) 2 x 195 watt panels, and a 1500 watt Latronics inverter (schematic attached).

So now I have another project. I have been gifted a brand new 40 cell 3.2v 32650 LiFePO4 battery.

As this battery is configured flat (see pic), I am intending to fit it to the back of the solar panel I use it as a complimentary power system for my portable fridge.

I already have a spare Victron MPPT, and a small separate port BMS ready to go. However, unlike the van setup I have no inverter in the system, so this leaves me wondering about the best configuration for the three devices.

These are the two alternatives I have come up with, any suggestions or advice will be appreciated.

fridge-battery-ver1.jpgfridge-battery-ver2.jpg

fridge-battery-system.jpg

Lithium Battery
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5 Answers
tex260z avatar image
tex260z answered ·

Just to clarify, I received a long winded email complaining that my question was not direct and simple enough and I didn't follow the forum rules! This person also cautioned me me regarding attaching anything to the back of the panel. So, in order to keep to the original question as simple as I could I left out a lot of information, like I ran a solar based business for 25 years, and we manufactured devices in precisely this configuration, i.e. critical marine signaling equipment installed on the back of the panels. To this end we used a product that will insulate up to some 600 degrees Celsius, and is only 5mm. thick, and that is what I will be using.

I was also criticized for including the Van system schematic, I figured it was fairly informative in the circumstances, but apparently no.

I don't really see how anyone could ask the question any simpler, after all a picture is worth a thousand words right? I also note looking through the forum this morning that most of the "simple questions" end up the endless paragraphs for clarification, so I don't really see the point.

Note, I also did an extensive search on my question in the forum and came up empty.

Anyway at the end of the day the person who emailed me confirmed my thoughts that Victron don't give a [moderator edit: removed unnecessary epithet] about their customers, and I already knew their dealer/distributors knowledge is confined strictly to the easy mainstream questions.

So as I belong to many other forums I think I will give this one the flick as I don't appreciate being insulated for trying to pose a question as clearly as possible in the first place.

Adios

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tex260z avatar image
tex260z answered ·

Seriously! no one?

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Gerardo avatar image
Gerardo answered ·

Hi Tex,

I would rather connect both P- and C- to the BAT- in the MPPT, and the load connected straight away to Load output of the MPPT.

That way you have double level of protection (BMS and MPPT) and more versatility with the load configuration in the MPPT (streetlight, etc).

Regards,

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tex260z avatar image
tex260z answered ·

Thanks, but P- is not bi directional.

2 comments
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Gerardo avatar image Gerardo commented ·
Hi Tex,

The P- is not bidirectional, but when you connect both P- and C- to the same point (BAT- in the MPPT in this case), the path becomes bidirectional.

The reason PCMs come with charge (C) and load(P) connections separatedly is because sometimes you want to isolate the charger from the load.

In your example, because the MPPT acts as both charging through solar and discharging through load output, you can connect P- and C- together. Does it make sense?

And you have more versatility in your system.

Regards,

1 Like 1 ·
tex260z avatar image tex260z Gerardo commented ·
PCM? Did you mean BMS?
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Justin Cook avatar image
Justin Cook answered ·

Moved to "Modifications" section for discussion of non-supported systems; might have better luck/input in there!

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