Recomended MPPT input voltage for a 48 volt system
littleharbor2
Solar Expert Posts: 1,991 ✭✭✭✭✭
Typical recommended MPPT nominal voltage input for a given system is double the battery bank voltage. I am contemplating switching my system over to 48 volts from 24 volts. I have 72 cell panels series wired 3s x 3p, Midnite classic 200. I am curious as to how the approx. 130 voc. , 105 vmp. will work into a 48 volt bank, this being 1 1/2 times the nominal voltage, not double. At the present time this 3s x 3p configuration is charging my 24 volt bank and being 3 times nominal it creates more heat than I am comfortable with, especially in the warm Baja climate.
2.1 Kw Suntech 175 mono, Classic 200, Trace SW 4024 ( 15 years old but brand new out of sealed factory box Jan. 2015), Bogart Tri-metric, 460 Ah. 24 volt LiFePo4 battery bank. Plenty of Baja Sea of Cortez sunshine.
Comments
With 72 cell panels in a 48 volt system, if you put them 2 in series the voltage is barely high enough in hot weather and you may have to put the Classic in 'legacy' mode. Three in series is perfect for a 48 volt system and is a good reason to have a classic 200 rather than a classic 150.
--vtMaps
2.1 Kw Suntech 175 mono, Classic 200, Trace SW 4024 ( 15 years old but brand new out of sealed factory box Jan. 2015), Bogart Tri-metric, 460 Ah. 24 volt LiFePo4 battery bank. Plenty of Baja Sea of Cortez sunshine.
I still have that 4024 and 4548 in the shed? Are you in Mexico now? I am asking for a friend.
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2.1 Kw Suntech 175 mono, Classic 200, Trace SW 4024 ( 15 years old but brand new out of sealed factory box Jan. 2015), Bogart Tri-metric, 460 Ah. 24 volt LiFePo4 battery bank. Plenty of Baja Sea of Cortez sunshine.
Agree with vtmaps ...
With 72 Cell PVs, on a 48 volt system, you really have little choice. Strings of three PVs on a 48 V system is sufficiently high to allow EQing almost any Flooded battery with hot PVs and a relatively cool battery.
MidNite Solar has added a Footnote to their String Sizer Results, regarding minimum Input voltage for MPPT CCs, like the Classic:
"With MPPT controllers the higher the input voltage the less efficient they are. This is not a large value but it will add up to a little more heat in the controller and a point or two less in efficiency. BUT you also have to be careful not to have the input voltage to low. Most all MPPT controllers will want to see a minimum of 130% of the actual high battery voltage. So if we have a 48v battery and it has an Equalize voltage if 62.3 volts than we would multiply that by 130% and we would need a minimum of 81 volts on the input on the hottest day of the year in order to have enough headroom for the MPPT to work".
So with 72 Cell PVs, and a 48 V Flooded battery, strings of three PVs is the minimum, and with 60 Cell PVs strings of three is even better, as it easily meets minimum Vin required at a lower Vin to the CC.
On the 48 V systems here, one runs strings of three 72 cell PVs (106 STC Vmp strings), and another runs strings of three 60 cell PVs (92 STC Vmp strings), on Classic CCs. Both systems could run lower Vin to the CCs, but we need to run what the available PVs.
Vic
Looks like you have more SW's than you need. Getting any tuna off Catalina?
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Can you really have too many SW's
They are pulling in nice Bluefin daily on the backside if the Island
2.1 Kw Suntech 175 mono, Classic 200, Trace SW 4024 ( 15 years old but brand new out of sealed factory box Jan. 2015), Bogart Tri-metric, 460 Ah. 24 volt LiFePo4 battery bank. Plenty of Baja Sea of Cortez sunshine.
No Prob on the Baja express. I think Downwind Marine got it done on the HF a few hours ago.
htps://offgridsolar1.com/
E-mail [email protected]
I joined this forum because I had a similar question regarding input voltage. I too live in Baja, a little bit north of Todos Santos. I'm bringing a couple items down while building my house, but I don't yet need as much as I'm planning on bringing (5000 48v watt hybrid inverter and LiFePO4 48v 100ah battery). It comes in a kit but I didn't want to buy the panels in the states and risk being harassed or charged at the border for them so I'm planning on buying them down there (Any leads appreciated; the place near me is expensive and very few options) so I wanted to make sure I had the minimum voltage required which isn't specified anywhere; it just has the operating range voltage. But the kit comes with 6 x 200 watt panels which are each 12 volt, so that puts it at 72 volts. I don't yet know the voltage on the panels either, so that's my issue. The store has 550 and 340 watt panels but aren't getting back to me about manufacturer or model. I already have 2 x 200 watt 12v panels so if I had to add those on top of the panels I buy, that would be ok too. So I guess worst case scenario is I'd just have to buy more panels for the MPPT to function. Is that correct? If the panels are 40v and I buy 2, it should be more than what the kit came with. I see the date on this as 2016, so I hope you guys still use this.
For a typical LiFePO4 a 12 volt battery may take around 14.2 to 14.6 volts charging... Then the array minimum MPPT voltage rating should be:
There is another thing to watch out for... As panels get cold, the Voc (voltage open circuit) voltage rises... The minimum temperatures in Winter for Todos Santos are around 12C, so you will not see too much Voc voltage rise in winter... So you have to look at the Vpanel-max input rating for your MPPT controller to figure out the maximum Voc-array for the maximum number of panels in series.
-Bill
I recently bought 4, 550 watt panels here in San Felipe for $1,000.
2.1 Kw Suntech 175 mono, Classic 200, Trace SW 4024 ( 15 years old but brand new out of sealed factory box Jan. 2015), Bogart Tri-metric, 460 Ah. 24 volt LiFePo4 battery bank. Plenty of Baja Sea of Cortez sunshine.