Upgraded 24v to 48v. Now Low wattage from the FX80

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spdas
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Upgraded 24v to 48v. Now Low wattage from the FX80

Post by spdas »

Aloha, going from 24v batteries to 48v system with FX80 controller and 48v VFX inverter, I notice the charge controllers are not putting out as much wattage at 48v as they were at 24v. Here are the specs. 3 panels (9 strings) all put in 55v to the controller and the controller is putting out ~51v to the 48v battery. Could it be that the FX80 controller is not working effeciently at incoming voltage of 55v converting to 51v? Would it be better to go up to 6 panels in the string and bring in 100-110v to the controller? Do you think the incoming of 55v from the panels and outgoing 51v to the battery is a factor? Francis.
raysun
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Re: Upgraded 24v to 48v. Now Low wattage from the FX80

Post by raysun »

The FlexMax charge controllers need 1.5V difference between IN (panel) voltage and OUT (battery) voltage in order to charge.

IN = 55 and OUT = 51 should be sufficient. However, PV arrays are not static, and its logical to expect the voltage to vary. 51V is fairly minimal for a 48V nominal battery charging voltage. What type of battery is employed?

In any event, increasing the string voltage will assure plenty of voltage differential between IN and OUT.

The absolute maximum IN voltage limit is 150V, so strings of 6 would probably be fine if the total V(oc) is below the limit.
spdas
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Re: Upgraded 24v to 48v. Now Low wattage from the FX80

Post by spdas »

Thanks for the reply.
I have 2 flooded 48v forklift batteries @ 850 ah each. I can double up the string to make ~ 105v each. I should up to 55v volts or so with fully charged batteries, but only getting up to ~51.5 after the end of the day. incoming Volts always is staying 2 volts or so above outgoing, even when a cloud passes. The concern is that when I was running the 24v, the end of the day would top off at 28v, so I was expecting at least 55v using the current 48v system. (there must be "clipping" going on inside the FX80 that is minimizing/conserving the amperage output, being so close to the input/output voltage setup). thanks francis
raysun
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Re: Upgraded 24v to 48v. Now Low wattage from the FX80

Post by raysun »

1700AH is a big bucket to fill.

I suspect the charge controllers are not completing a Bulk phase and entering Absorb. Most likely due to the amount of charge the battery needs.

The FM80 "buck" circuitry is quite efficient. If the voltage differential is maintained (1.5V) the chargers will pass full available current.

Rather than it being a limitation internal to the FM80, the MPPT circuitry is more likely its being forced to pick a PV Array voltage that is not at the optimal power point. Its likely too high on the V/I curve for maximum power. Setting up the arrays so there is more voltage "headroom" will allow a more optimum power point to be selected.

20220617_073557.jpg
Early morning array activity. Two panels in series for 108V(oc). Note the IN voltage is substantially below that point. The 54V(oc) of a single panel would not permit optimum power point to be selected.
spdas
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Re: Upgraded 24v to 48v. Now Low wattage from the FX80

Post by spdas »

Aloha, I will increase the headroom by adding a panel to the string to make 72v optimal incoming. (It seems the panels will keep the high voltage pretty much constant in full sun or cloud days and ONLY the amperage will vary).

Also I never understood the advance settings in the FX80. I have 3.0 hours absorb time set, but are the other settings relevant--(they are at default factory)
EDIT the panels are older 200w 18.10V 11.05A at peak.
thanks Francis
raysun
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Re: Upgraded 24v to 48v. Now Low wattage from the FX80

Post by raysun »

Increasing the string voltage will be a big help.

I figured these were older panels.

What is the exact configuration / model of the battery?

Which Island are you on?
spdas
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Re: Upgraded 24v to 48v. Now Low wattage from the FX80

Post by spdas »

Aloha, I am on Oahu-Barbers Point. I have been off-grid for 15 years and have 5 different systems running our factory. (Mig Welders, grinders, office refrig's a/c's, air compressor etc)

In this system there are 3x36v 850amp flooded forklift batteries tapped to make 2x48v. ie each 48v battery is comprised of the 36v PLUS 12v of the "middle battery" leaving 12v in the middle of the middle battery unused, but acting as a spare cell in case a cell of the 48v goes bad in the future. This system is for office. These batteries are fairly new. (the office also has another separate system @24v running the computers, video surveillance, etc.

The warehouse has another 48v system on the Radian 8048. Also has another system running an electric forklift charger.
Francis
Last edited by spdas on Fri Jun 17, 2022 11:22 am, edited 1 time in total.
raysun
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Re: Upgraded 24v to 48v. Now Low wattage from the FX80

Post by raysun »

Does the battery manufacturer provide a spec sheet with charging information?
spdas
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Re: Upgraded 24v to 48v. Now Low wattage from the FX80

Post by spdas »

Does the battery manufacturer provide a spec sheet with charging information

Yes I am sure it does, but have not looked it up yet as I am no-where near "Topping out" I guess it is near ~55v. I have not seen it go into absorb yet. I am a little cautious to not use the max charging info from the manufacturer, because it assumes you are charging a battery from low voltage up to full charge with various bulk/absorb cuttoff points. Whereas in this off-grid setup, using the battery all day, it may stay in Bulk all day and boil off because we are drawing off all day
3x875 ah batteries.jpg
3x875 ah batteries.jpg (10.37 KiB) Viewed 253 times
. So I set bulk a bit lower. But we are not at that point yet @51v. What do you think? thanks Francis
raysun
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Re: Upgraded 24v to 48v. Now Low wattage from the FX80

Post by raysun »

I think it looks like a classic "thick plate" flooded lead acid deep cycle battery. For their intended usage (higher discharge forklift power) and rapid cycling demand they are generally designed with high charging voltages in mind.

The lower discharge rate for off-grid cycling can use a lower charge voltage, but I'd guess 51V is too low. The standard FLA Absorb charge target is 2.4-2.45V per cell, or 57.6-58.8V.
The Absorb Time will be dictated by either measuring the specific gravity (it should reach full charge at the end of Absorb), or net charge current (roughly 3 - 4% of the C20 AH rating of the battery.)

Float voltage of 2.24V per cell, or 54V for the battery.
spdas
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Re: Upgraded 24v to 48v. Now Low wattage from the FX80

Post by spdas »

Aloha, yes these batteries will take a 200-250 amp charge to start and I am teasing them with my total 30-40 amp panel input,
I will now increase the headroom by adding a panel to 72.4 is the next step. Calculations of 3 panels at 18.1 v each gives 54.4v and even though the FX80 is showing 55-56 v, it is struggling. Let's see if the extra panel making 72.4v to 55v output helps. thanks, Francis
spdas
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Re: Upgraded 24v to 48v. Now Low wattage from the FX80

Post by spdas »

Aloha, tried to add one panel, but changing the wiring would be too time consuming, so I "put into series" two strings and have 108v at idle and 75v when it is hooked unto the FX80. It is MUCH better and I think there is a "Sweet spot" for incoming voltage for the FX80.
To demonstrate, I have another FX80 powered by another set of panels that is coming in at idle 140V and when hooked up to the FX80 it is 115v in. This second FX80 is putting out 19amps

(I have 2 sets of panels)

#1 set of panels is 5300 total watts
AND previously was setup at 55 incoming and 51 battery outgoing and producing 15amps
NOW is setup at 75v incoming loaded volts and 51 battery outgoing and producing ~50 amps!

#2 set of panels is total 5400 watts
NOW is setup at 115v incoming loaded and 51 battery outgoing and producing only ~19amps!

Both sets of panels have the same total wattage, but one is less than 1/2 output through the FX80 compared to the other. francis
raysun
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Re: Upgraded 24v to 48v. Now Low wattage from the FX80

Post by raysun »

There's lots of conditions that will affect the current output of a solar panel/array: orientation to the sun; shading; dirt; electrical mismatch between panels; surface temperature; age; etc.

The 2nd array may well have some faulty wiring, or panels that have been degraded by weathering.

It may take some detective work to run down the performance issue. Starting with an inspection of the panels and connectors.

With a voltmeter, and clamp-on ammeter attachment, each panel may need to be tested for output.
spdas
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Re: Upgraded 24v to 48v. Now Low wattage from the FX80

Post by spdas »

Aloha, will need to do the detective work for sure, but the simple putting the 3 panel in series with another 3 panel at the combiner box, sure points to the FX80 having a sweet spot, as before output was 15A now 50A.

""AND previously was setup at 55 incoming and 51 battery outgoing and producing 15amps
NOW is setup at 75v incoming loaded volts and 51 battery outgoing and producing ~50 amps!"" (all I did was to put to series one string to another).

Both arrays are in full sun, cleaned, same age, same wiring, but will as you suggest check the amps out on each panel or string and connectors. Will try equalize the batteries.
So you know how much voltage I can safely put into the VFX3648? thanks Francis
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Re: Upgraded 24v to 48v. Now Low wattage from the FX80

Post by raysun »

Aloha, will need to do the detective work for sure, but the simple putting the 3 panel in series with another 3 panel at the combiner box, sure points to the FX80 having a sweet spot, as before output was 15A now 50A.
Its not so much the FM80 having a "sweet spot", rather its the PV array that has the "sweet spot". That is precisely what Maximum Power Point Tracking (MPPT) controllers do, they continually tune the incoming Voltage/Current to transfer the maximum power the array is capable of generating. That Maximum Power Point is constantly shifting as the sun or shadows move across the array, as the panels heat up and cool off, etc.

Having the nominal array voltage so close to the battery voltage gave precious little "room" in which to find maximum power. Increasing the string voltage permits the MPPT to find better array power points along its V/I curve.

If the other array, when configured identically, does not generate similar power, then there is a constraint or defect somewhere in the system. The most likely area is the one most exposed to the elements - the array itself and its wiring - so that's the place to start looking.
spdas
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Re: Upgraded 24v to 48v. Now Low wattage from the FX80

Post by spdas »

I have been fooled by checking Voltage, rather than Amperage, so will check tomorrow. Even junk smashed panels produce the rated voltage! But also, I have a great KWH thirst, 2 fridges, one a/c and 2 pool pumps running today. Produced 23KWH today, expect 30 tomorrow. We are still at battery 49.5v. and as you say 1750 is a huge AH bucket to fill. francis
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Re: Upgraded 24v to 48v. Now Low wattage from the FX80

Post by fcwlp »

When you switched from a 24V to 48V system with the same array you were operating your panels on the steep portion of the IV (current voltage) curve or in other words not the "sweet spot." General guideline if you work with the OB array design tool is to keep the maximum temp Vmp => 64V. Keep in mind that the maximum temp is actually the temperature of the panel not the ambient. Your solution to add a panel is the typical solution when switching from 24V to 48V.
spdas wrote: Fri Jun 17, 2022 7:59 pm So you know how much voltage I can safely put into the VFX3648? thanks Francis
Target a max Voc of <145V at your coldest ambient temperature for the FM80 CC. The VFX3648 only sees the battery voltage, the maximum voltage allowed is 68V. I have batteries that I typically equalize at 64V.
spdas
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Re: Upgraded 24v to 48v. Now Low wattage from the FX80

Post by spdas »

ok thanks, will eq tomorrow or Sunday at 64v. (if I can get the KWH up pushing over 56v battery voltage). I assume I will start bubbling 55v or so. francis
spdas
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Re: Upgraded 24v to 48v. Now Low wattage from the FX80

Post by spdas »

Checking amperage. I just have an Old School clamp-meter that only has 200 or 1000 amp settings, so bought this one on Amazon. Is this what I need? thanks Francis
https://www.amazon.com/ACM91-Auto-Rangi ... NrPXRydWU=
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REC Alpha 440W panels - 2 arrays: each of 4 strings of 2 in series
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Re: Upgraded 24v to 48v. Now Low wattage from the FX80

Post by raysun »

That should work.
spdas
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Re: Upgraded 24v to 48v. Now Low wattage from the FX80

Post by spdas »

Aloha, I got that clamp meter (below) and amps do not even come close to amps shown on the FX80 (both in and out) or amps going to the inverter. And seems to get different readings every time. Is it a piece of junk or am I expecting too much to compare amp readings with the FX80? Or you pay for what you get?!!
Do I need to spend $300 for a Fluke or do you know of any in the $100 range? thanks Francis



https://www.amazon.com/ACM91-Auto-Rangi ... NrPXRydWU=
raysun
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Outback IBR3 battery enclosure
REC Alpha 440W panels - 2 arrays: each of 4 strings of 2 in series
Honda EU7000is gas fuel generator

Re: Upgraded 24v to 48v. Now Low wattage from the FX80

Post by raysun »

There's not all that much to these clamp-on ammeter, so even a cheap one *should* work OK. They can be susceptible to stray external fields, so positioning can make a difference.
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