My first solar off grid system

[Pieter Blackie]

Hi All, I am a long time reader but first time poster, I have been following Will for a while now and have watched every video on the channel

this is a summary of the system I have just completed

24v 3KVA Solar Inverter Charger Hybrid Pure Sine Wave PWM 50A Regulator PV 80VAC AU
2x 12V 350W Solar Panel Mono
2 x Rapid X 12V 100Ah Lithium Ion Battery LiFePO4
150A Digital LCD Watt Meter Power Analyser

I do however have a problem

My batteries takes forever to charge off solar and even connecting to mains it still takes forever
seems as if the charge to battery is limited and it looks as if the batteries BMS is the cause but how do I test this
Also does not look as if If my batteries in series want to charge higher that 27v

 

[upnorthandpersonal]

Welcome to the forum!

I did a quick Google search on that inverter. Could it be that you don't have any parameters to set, and that it's only configured for GEL/AGM? Normally you want to adjust the charge parameters to match those for LiFePO4.

 

[Steve_S]

Nice clean setup, KISS is the best way to do it !
While you did not provide Make & Model or links to the products you used (That is always most helpful as there are details we know about, quirks /foibles etc). You did provide one key detail, you are under-paneled to charge with any serious amperage.

Normal Default for LFP: 100AH Battery can output 100A for 1 Hour (1 C-Rate) and take 0.5 C-Rate 50A charge for 2 hours in your case.
The Charge Profile likely needs adjusting as well so it is tweaked for LFP and not another chemistry. Lithium Defaults are often incorrect.
Below are two items that you may want to download and save for quick reference.

RapidX battery has real capacity 100Ah which is truly worthy of your purchase.

Specifications:

* Brand: RapidX
* Nominal Voltage: 12.8V
* Nominal Capacity: 100Ah
* Charge Voltage: 14.6V
* Watt Hour: 1280Wh
* Charge Method: CC/CV
* Charger: 14.6V20A
* Standard Charging Current: 25A
* Max. Charge Current: 50A
* Standard Discharge Current: 25A
* Max. Discharge Current: 50A
* Storage Temperature: -10°C to 50°C
* Working Temperature Range: Charge 0°C to 45°C; Discharge-20°C to 50°C
* Series / Parallel Connection: NOT Support

SOURCE: https://www.kogan.com/au/buy/toughl...d-no-leak-fast-chargedischarge-li-12v-g-a4-x/

PART OF YOUR ANSWER IS RIGHT THERE !
Also their Charge Parameters are pure Horse Pucks ! 14.6V = 3.650V per Cell and that will NEVER WORK ! That is the "Hopium Factor".
14.0V = 3.500 Volts per cell, the TOP of the Working Voltage Range is 3.400, once past 3.450 cell deviation WILL occur and will be worsened if at High Amp Charging. As noted below, CC Charging to 90%/95% and then Constant Voltage Variable Current to finish off to Designated Full.

Designated Full ? WTH ??
Full Voltage Curve = 2.50-3.650 (Max Limits), Working Voltage 3.000-3.400 with Nominal being 3.200. We (the users) designate what is our 100% SOC and most choose 3.450 or 3.500 as absolute full (pending on cell grade). Appreciate that from 2.50-2.900 & 3.450-3.650 only represents roughly 3-5% of "Gross Capacity" of the cells. IE an A+ 100AH Cell will test out typically between 105-110AH "GROSS" from 2.500-3.650.
FYI, All big Commercial Packs (BattleBorn, Relion, SimpliPhi and now even SOK & AmperTime) use Grade A+ 105+AH cells in their 100AH Packs and derate them to ensure they meet compliance & spec for warranty period. Even their BMS are rated for 110A to 120A and derated.

Hope that helps, Good Luck.

 

[wattmatters]

Nice work on your first project. I did my first one this year as well. Looks like you are somewhere in Australia or perhaps NZ (just going on the style of AC power outlets).

Also does not look as if If my batteries in series want to charge higher that 27v

I think your primary problem is the batteries.

According to the specifications of those batteries, they are NOT designed to operate in series. 12V operation only.

Connecting them in parallel in a 12V system is fine but not in series to create a 24V, 36V or a 48V battery. Their BMSs are not designed for it (most likely a mosfet voltage rating issue).

To put 12V LiFePO4 batteries in series requires batteries with an internal BMS designed for operating in series (most are not). In general you are better to buy a dedicated 24V battery as it will be designed for it.

Unfortunately you are about to find out that LiFePO4 batteries designed for 24V operation are considerably more expensive than two of the Kogan specials you have.

To keep costs down you may want to consider building your own from 8x individual LiFePO4 cells with an 8s BMS. Just like Will does in his videos. Or buy a pre-built 24V battery from China via Alibaba / AliExpress but that comes with purchase risk as is often discussed on here.

Looking at your set up (you are way better at constructing things than me), it looks like you have a battery DC disconnect/isolator switch but no battery overcurrent protection (i.e. a fuse or DC overcurrent breaker). This leaves your system exposed to BMS protection only and that's a risk. I strongly advise adding overcurrent protection for your battery. Something like a suitably rated HRC fuse in a fuse holder although at these lower voltages an ANL fuse is probably as good.

 

[Pieter Blackie]

thanks @upnorthandpersonal and @Steve_S and @wattmatters
I really apricate the feedback I will review and look into the settings
What would you suggest solar wise, would another 2 panels added in series be enough
One question is the price for the rapidX a good deal, they are now on special for US $169.52 each delivered, why I am asking is I am considering buying another 2 and cut them open take the cells and build my own large 24v battery with a good quality BMS. I cant buy individual cells for that price so think this might be a option.
this is my Inverter: https://www.ebay.com.au/itm/384153814762
and yes agreed I need a fuse for protection

 

[wattmatters]

What would you suggest solar wise, would another 2 panels added in series be enough

What are the solar input specifications of that inverter? In particular what is the Voc limit (open circuit voltage limit)? this is the primary things to be concerned with - do not exceed this limit.

You panel Voc (based on earlier picture) is 22.5V.

4 x 22.5V = 90V @ STC (25°C). The colder it gets the higher the voltage will go. So it might be 4 in series will result in Voc exceeding 100V.

If your inverter has a Voc limit of 145V, then you're sweet. If it's 105V then you are close to the edge of viability depending on how cold it gets. If Voc limit is less than 100V, then 4 of those panel in series is too many, 3S is max with those panels.

One of the other issues you face is the batteries are rated for a pretty low 25A discharge rate.
26V x 25A = 650W. Take away inverter/system losses and you are going to be limited to AC loads of under 600W.

If you add a second 24V battery in parallel then that doubles the effective current capability and you can draw perhaps up to 1200W on the AC side.

cut them open take the cells and build my own large 24v battery with a good quality 16s BMS

1 x 16s BMS won't work. The "s" in 16s is for series.

You'd need 2 x BMS, one for each 24V battery.

In the end you are getting what you pay for. Don't expect matched cells, don't expect new cells. Don't expect high performing cells. You might get lucky.

This guy did a review on those batteries:

He thinks they are likely made up of grade B cells. He did a load test but without a current/coulomb measurement unfortunately, just a load lamp which indicated they only supplied 91% of rated capacity, but much room for measurement error with his approach.

 

[Pieter Blackie]

@wattmatters
so I did a bit of a test on the batteries in series
ran a heatgun off the inverter drawing 12A on the battery side and 221W at the AC 230v side, I ran the system for 9.5 hrs and batteries dropped down to 23v (preset on inverter as low voltage cutoff), I think in the end it was a good outcome for these batteries

 

[wattmatters]

I think in the end it was a good outcome for these batteries

2.1kW on the AC side from a nominal 2.4kVAh DC supply is not bad going. Good work on the test. Now charge 'em up!

 

[Supervstech]

.25C max output from the BMS… yikes.
How easily can they be opened up? Glue? Screws? Be careful!
Your pwm charger likely cannot deal with more than two panels in series, so that means, you need new charge controller, and new BMS…

 

[Pieter Blackie]

So doing some charging testing 2 x 350W panels in Series today running at around 7.5A 220w, why is it that the Watts is 100 lower than panel ratings

 

[upnorthandpersonal]

The rated power is reached in ideal test conditions only. It depends completely on where you are, what time/date of the year, exact positioning of the panels, temperature, etc. You usually never reach the ideal conditions in the real world.

 

[wattmatters]

So doing some charging testing 2 x 350W panels in Series today running at around 7.5A 220w, why is it that the Watts is 100 lower than panel ratings

2 x 350W = 700W peak output capacity.

In addition to:

The rated power is reached in ideal test conditions only. It depends completely on where you are, what time/date of the year, exact positioning of the panels, temperature, etc. You usually never reach the ideal conditions in the real world.

it might also be:

- panels are incorrectly rated
- there is a limit on the charging side

Mainly it's one of two things:

- the insolation striking the panels is less than perfect, combined with other environmental conditions which derate performance
- the loads are insufficient for the system to be pulling maximal output from the panels

What is the charge setting for the battery?

 

[Pieter Blackie]

@wattmatters thanks for tall the info greatly appreciated
I have attached the inverter manual. all settings are similar to the default
I managed to charge the batteries back to full in 15hrs over 2 days (10 hrs sun time) its been cloudy for a big part of the first day

 

[Pieter Blackie]

So I have decided to buy a JBD Smart BMS 8S 24V With Temperature Protection and Bluetooth 100A for AU$78, once it arrives I will hack these 2 RapidX batteries open and use the cells to build a 24v battery with decent charge and discharge rates

 

[wattmatters]

So I have decided to buy a JBD Smart BMS 8S 24V With Temperature Protection and Bluetooth 100A for AU$78, once it arrives I will hack these 2 RapidX batteries open and use the cells to build a 24v battery with decent charge and discharge rates

Sounds like a plan. Let us know how you go.

 

[wattmatters]

Hi Have cut one of the batteries open

I opened up a cheap RapidX $199(AU$279) LIFEPO4 - photos

Well it was easy to open up only a small bit of the lid was actually glued on, I found a couple of wires pinched and the the rest is self explanatory in the photos ... I cant believe that I had these batteries connected in Series running a 2400w inverter off them, I drew 50A for more than 30...

diysolarforum.com

Yikes.

 

[Pieter Blackie]

Ok so here is a build update, I took those nasty rapidX batteries and cut them open, you probably seen my post here
Well to make the best of what I have I cleaned it all up removed the little 12v BMS and combined the two 12v packs to create a 24v pack, I fitted a 100A JBD smart BMS and enclosed it all up in a wooden box, reused the lid of 1 of the 12v batteries for the connections , here is some photos

 

[pollenface]

Nice clean system.

What brand is that hybrid inverter? Were you able to change the charge parameters to suit your batteries?

I like your cardboard insulation, I do the same. Free (comes with beer) and works extremely well.

 

[Pieter Blackie]

Nice clean system.

What brand is that hybrid inverter? Were you able to change the charge parameters to suit your batteries?

I like your cardboard insulation, I do the same. Free (comes with beer) and works extremely well.

this is the link to the inverter https://www.ebay.com.au/itm/384153814762

the cardboard is what came with the original batteries,

now that I have upgraded the BMS the charge settings was easy and works well, the inverter was charging the batteries from mains at 30a and my solar system is charging at 7A, I need a better solar array. my panels are rubbish

 

[pollenface]

the inverter was charging the batteries from mains at 30a and my solar system is charging at 7A, I need a better solar array. my panels are rubbish

What is the orientation of your panels?

also remember that a PWM controller will sacrifice efficiency. I have a PWM controller in one of my circuits and the best I can get is 78% with optimal all-year orientation of a 72cell house panel.

I think using 60cell panels would work well with a PWM controller in a 24v system as the working voltages of the panels are closer to the charge voltages of the battery and hypothetically less efficiency loss.