question

championc avatar image

Would a MPPT 150/35 for 48v still need / use 3 x Battery Balancer units ?

Hi all,

I'm planning a solar installation with Panels setup in series to make 48v. I see that I would need the MPPT 150/30 Charge Controller. However, the documentation for the controller referred to equalizing of batteries but I am assuming that this would only be for 2 x 12v batteries in series whereas I'm planning for 4 x 12v = 48v.

Documentation for the Battery Balancer unit confirms that 3 x Balancer units are needed for 48v.

Therefore, if I want battery equalization, am I correct in saying that i would not need Balancer units if I went with 24v but at 48v I'll still need 3 x units ?

However, if I went with 24v and had 2 sets of 12v battery pairs in parallel, can the Charge Controller equalize batteries in Parallel ?

MPPT - Solar Charge ControllerBattery Balancer
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6 Answers
JohnC avatar image
JohnC answered ·

Your plans seem fine. No comment on that inverter thingo.. :)

Take another look at your panel stringing plans though. You don't have to match '24V' panels to a Victron mppt as you might with a pwm unit. The '150/' in your specced model's name is telling you the max Voc that it can accept in a string. For 6x standard sort of panels, the Voc might be ~43V. Strung 3x would fit, 4x too many, and 2x possibly inadequate in poor light/sunup/sundown. With 6x panels, go 3S2P for best results - simpler wiring too.

https://www.victronenergy.com/blog/2014/03/28/matching-victron-energy-solar-modules-to-the-new-mppt-charge-regulators/ Bit dated now, but still relevant.

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Paul B avatar image
Paul B answered ·

The MPPT units do not balance individual battery's as I think this is what you are referring to and then if you have lead acid range of batteries you should balance them regularly or at least check each battery to make sure the battery voltages are similar. the victron battery balancers do that.

to be clear you would need balancers for 24 volt systems and 48 volt systems.

equalization in the MPPT is for flooded batteries and its used to remix the batteries liquid every now and then due to stratification of the different chemicals in the acid when a battery is not moved around much, this raises the voltage so the batteries bubble away and thus remix there liquids.

in my opinion Lithium Phosphate batteries with a good bms are the way to go these days. much better life by quite a magnitude and much deeper cycle depths and thus usually half the capacity batteries are needed, plus balancers are not needed as the BMS does this for them and for a different reason.


Hope this is what you were getting at here


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JohnC avatar image
JohnC answered ·

Hi Champion. Personal opinion - I'd much rather have a single string of 48V with no balancers, than a double string of 24V with a balancer.

For a few reasons, but balancing current through each string is to me a bigger issue than balancing a 'midpoint' V.

Besides, if your intended mppt is sized for panels/loads @ 48V it will need to be doubled in size @ 24V.

By the way, Victron don't make a 150/30. A 100/30 or 150/35 is close? The /35 for 48V. https://www.victronenergy.com/upload/documents/Datasheet-BlueSolar-and-SmartSolar-charge-controller-overview-EN.pdf

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Apologies, typo on my part - I intend buying a 150/35

championc avatar image
championc answered ·

This would be my intended setup now. The inverter on the right is a Sun GTIL2 Grid-Tie Inverter


solar-home-1.jpg (158.7 KiB)
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JohnC avatar image
JohnC answered ·

Ahh ok, more batts.. Yeh, lock in 48V.

You'll note I have an ingrained hatred of multiple strings of Pb batts. I'd be prepared to go 2x strings, but not more. I went for 6V batts to keep individual unit weight down, and would have immediately added another string (with at least monitoring) if needed. Thankfully one string sufficed..

6V batts are common in golf carts, and 2V individual cells in forklifts. You could consider all..

2V batts have another advantage in a 48V bank - lose one cell, bypass it, adjust your charge settings a touch, and continue on with 48V.

Picky now, but you've noted "48V" on your pv. Typically for a 150/ mppt the panels would be in 3x strings for a 48V bank, and maybe ~120V in operation. Your grid-tied inverter I can't comment on. Frightens me actually.. :)

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championc avatar image
championc answered ·

Thanks @JohnC

Overall, does my setup and approach look correct, based on my diagram ?

I'm planning to install the panels as 2 x 300w @ 24v in series, three times thereby giving me 48v x about 27a. For the batteries, I'm getting them (Yuasa SWL2500EFR) free from a UPS in work. They are swapped about 2 years before their stated EOL. I know they may only have a short lifespan but I feel that batteries are possibly going through a real transition right now, so who knows what might be available in a year or two (thanks mainly to Electric Car development).

The short potential lifespan made me determined to install the Battery Balancers to extend the life of them as much as possible.

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