question

tombe avatar image
tombe asked

24V works 48V doesn't. ???

Hello,

I have a slight problem with my off grid system and sincerely hope one of you can help.

I am currently running:

4 x 230 Ah (C20) parallel in series (24V 460Ah)

1x MPPT 150/85,

2,9 Kw solar array (3 strings @ 66V)

Lynx distributor

BMV712.

Cerbo.

ECTIVE 24V/1kw invrter

Multiplus II 48V/3000W

My plan is to change from 24V to 48V, so I connected the 4 x12 batteries in series adding a Multiplus II 48V/3000W inverter/charger. (running on factory settings for now)

Now here is my problem: running the 24V system on the old 1kw inverter worked fine and the MPPT charged the battery bank correctly. (Bulk-Absorption-Float). 800 -1500W

Changing to the 48V however, my MPPT does not come out of Bulk and the solar array does not charge with more than 70-200 W, plus the battery does not accept more than 54V even though 66 are supplied.

I then changed everything back to 24V and the panels charge a good 800W and the MPPT goes into Absorption after a couple of minutes. All good again.

I retightened all the connections to torque, checked the fuses, went over the V.Connect settings of the MPPT as well as the BMV712, but no luck. Battery voltage does still not come above 54V and hence MPPT stays in Bulk.

Stumped and happy for any input at this time.

Thanks

Tom

MPPT Controllers48v battery
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1 Answer
wkirby avatar image
wkirby answered ·

Your PV Voltage is not high enough for a 48V system.
You might be seeing 66V, but that is not the Voltage for peak power. The MPPT tracks for the highest power point but it can only scan down to the (battery Voltage + 1V). The peak power foint for your array is likely below (battery Voltage + 1V) and so you don't get as much power as you do when you are on a 24V system.

When running on your 24V system under the same weather conditions, have a look at your actual PV Voltage when the system is making 800W, it's probably around about 50V - 53V?

For your 48V system, you need to increase your PV string Voltage so that your peak power point Voltage is shifted higher. Perhaps you can re-configure your array to 2 strings with more panels per string, but still staying under the 150V limit of the MPPT?

I experienced the same problem when I upgraded to 48V from 24V.

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tombe avatar image tombe commented ·
Thanks for that. I will certainly try that and report back
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tombe avatar image tombe commented ·

It’s done and it works. Thanks again for your help

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wkirby avatar image wkirby ♦♦ tombe commented ·
Excellent, good to hear it's working again.
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