LifePO4 GBS Amp Hour Testing 2.5v to 3.6v per cell

[karrak]

I have a 70 amp charger, approx 2000 watts of panels.

Storage wise daily I need approx 1kwh for fridge, 1kwh for freezer and 1kwh for misc. We use more if the sun is good during the day if we are home, pumping water and clothes washing.

My 2 x PL40 pwm charge controllers are synced by another unit but there voltages have wandered a little and they are approx .2V difference. I have them set to try to compensate but they get confused at times and rerun absorb. I would prefer just one controller, there are a lot more options now than 10 years ago,

yes I could set up autostart for the genset.

Summertime temps would be around probably say 25c to 30c. We get a few days up to 35c but not many much over 30c. 12c on a winter night for us is freezing.

I want my system as simple and reliable as possible.

Sounds like an LFP battery around 5-6kWh would do the job and work well with your current equipment. One good thing about LFP batteries is that you can add to them at a later date. This doesn't work well with lead acid batteries.

I agree with you that it is probably a good time to upgrade to a new MPPT controller.

Your temperatures look fairly benign to me, much better than our summertime temperatures. Your mean daily summer temperature would be around 23^oC-25^oC

The big issue with DIY LFP battery systems at the moment is battery management and system integration. I would think you need a battery management system that will make sure that no individual cells go outside their safe operating voltage range and will automatically turn your generator on when the battery SOC gets to say 20%. This may require relays and other bits and pieces that Dax has mentioned in his last post. The complexity of the BMS is dependent on how many of the functions of the BMS you are prepared to do manually, how much risk you are prepared to take, and how much you want to spend. Do you have much knowledge of what is available and what is required?

Simon

[Sunking]

Unbelievable 3Kw @ 12V = 275A (including inverter 10% overhead) and none have burned ?
How do you manage the 12V distribution in a house, with inverters scattered all over? That's a lot of copper, is it all encased in conduits labelled DC throughout the house?

Just this one comment excerpt is enough to show you as a hack, ready to burn houses down,

Spot on Mike. So why do you let this guy on here who knows nothing? For Pete's sake he cannot do simple math and calls himself a designer. He is a FRAUD!

[Sunking]

we stick with 12v, as they are the cheapest components compared to 24-48v and do the job.

This statement here proves you are an idiot with absolutely no understanding what so ever of physics or electricity.Not to mention extremely dangerous asking to burn houses down.

[Bala]

Sounds like an LFP battery around 5-6kWh would do the job and work well with your current equipment. One good thing about LFP batteries is that you can add to them at a later date. This doesn't work well with lead acid batteries.

I agree with you that it is probably a good time to upgrade to a new MPPT controller.

Your temperatures look fairly benign to me, much better than our summertime temperatures. Your mean daily summer temperature would be around 23^oC-25^oC

The big issue with DIY LFP battery systems at the moment is battery management and system integration. I would think you need a battery management system that will make sure that no individual cells go outside their safe operating voltage range and will automatically turn your generator on when the battery SOC gets to say 20%. This may require relays and other bits and pieces that Dax has mentioned in his last post. The complexity of the BMS is dependent on how many of the functions of the BMS you are prepared to do manually, how much risk you are prepared to take, and how much you want to spend. Do you have much knowledge of what is available and what is required?

Simon

I have an understanding of setting up a bms from reading n here, I am warming to lfp so am studying requirements a bit more. Still have a bit of time. I don't have a problem with relays and electrics, so am happy that I can set up a system.

[dax]

Dax, could you give us the technical specs for the batteries that you use. In particular the maximum charge and discharge rates, and the recommended charge and discharge rates.

Does your modulisation go as far as having separate sets of PV solar panels for each battery module?

I am enjoying your responses to Sunking, you have a good way with language. As you have said Sunking's antics don't help with anyone trying to learn anything.

Thanks,
SImon

Our cells maximum constant charge current is 75amp, discharge is 150amp and max burst discharge is 250amp.
We use 750w x 24v of panels per 60amp controller, most installations of ours are 1000-2000amp lifepo4. Passive homes don't use much energy and have between 3-6kw of panels so 4- 8 controllers into 2-4 x 500amp lifepo4 packs. Some use the packs separately through individual inverters and some use them in a parallel bank through one inverter, personally prefer a number of inverters to make the system more fail safe and that's the way we are heading.
We build fail safe systems, if one set or component goes down, the rest can carry on providing energy.

I'm just an illiterate mate, can't spell, read, write or add up, according to some. The problem with deranged ideological egotists is, they are so far up themselves they don't have a clue outside their simple controlling programming. Creativity and lateral innovation is way beyond them, all they can do is repeat their imbedded mantras of I'm right and everyone else is wrong, no matter the facts.

What these idiots fail to grasp is the majority of those looking for information regarding solar control and storage, is understandable information. Not a load of semantic technical garbage the average person can't and don't want to understand. When you are deeply insecure in your narrow window on life and can see your programming going out the window because it doesn't fit the reality, clones always jump on the band wagon and throw infantile idiocies around like confetti.

[dax]

Unbelievable 3Kw @ 12V = 275A (including inverter 10% overhead) and none have burned ?
How do you manage the 12V distribution in a house, with inverters scattered all over? That's a lot of copper, is it all encased in conduits labelled DC throughout the house?

Just this one comment excerpt is enough to show you as a hack, ready to burn houses down,

Now what can anyone say to something so infantile, ludicrious and stupid as what you've posted. Or is it you have no real life experience outside an office or school room and no clue of what or how a real off grid lifepo4 system works. It's plain to see you've not read my posts, just jump on the band wagon in a childish attempt to beat your sagging chest.

However just to amuse you, a 3kw inverter, would never draw 275amp at once or constantly. In an off gird system it would be lucky to get over 1.6Kw at any one time and that would be a large appliance starting draw. I've posted many times, our installations are 240v wired and for the ignorant, that means inverters are situated in the module, connected within 10-20cm of the controller above the pack, or bank. They then connect to each 240v circuit in the house, if you can understand that complicated explanation, or is plain simple understandable language beyond you.

[smily03]

Dude...chill. We're just concerned, because what you posted sounds really dangerous without some further explanation...

3000 / 13.6 = 220, and 220 * 1.2 = 264. Unless you're seriously undersizing your OCPD, you'd have to be running some serious wiring, otherwise you're risking fire. Even if loads are only really ever 1kw, but the inverter is capable of doing more, you have to size the wiring for what the inverter is capable of drawing unless you're going to size your OCPD for the size of the wire you're running. Because something could always short out or act up and make the inverter pull its maximum load, and if your inverter to battery wiring is undersized...oops.

[jflorey2]

However just to amuse you, a 3kw inverter, would never draw 275amp at once or constantly.

If it never draws 275 amps it's not being used as a 3kW inverter. If you install a 3kW inverter and downrate it to 1.6kW, great - but in that case might as well just install a good 1.6kW inverter.

In an off gird system it would be lucky to get over 1.6Kw at any one time and that would be a large appliance starting draw. I've posted many times, our installations are 240v wired and for the ignorant, that means inverters are situated in the module

No, that doesn't mean that. 120V and 240V inverters are readily available with a wide variety of mounting options.

The more you post, the more it sounds like your success has been due to luck rather than technical competence and an understanding of the issues involved.. I hope for the sake of your customers that your luck doesn't run out.

[Mike90250]

Now what can anyone say to something so infantile, ludicrious and stupid as what you've posted. Or is it you have no real life experience outside an office or school room and no clue of what or how a real off grid lifepo4 system works. It's plain to see you've not read my posts, just jump on the band wagon in a childish attempt to beat your sagging chest.

However just to amuse you, a 3kw inverter, would never draw 275amp at once or constantly. In an off gird system it would be lucky to get over 1.6Kw at any one time and that would be a large appliance starting draw. I've posted many times, our installations are 240v wired and for the ignorant, that means inverters are situated in the module, connected within 10-20cm of the controller above the pack, or bank. They then connect to each 240v circuit in the house, if you can understand that complicated explanation, or is plain simple understandable language beyond you.

Vacation time for DAX. Take a chill pill.
In your zeal for something, you are now posting seriously dangerous practices, and are unable to comprehend why it is bad.
Many lurking neophytes read these posts and with no knowledge of electricity, they are likely to follow the easy way you describe.

WTF does any style of battery have to do with what I said? Zero..

If you build a system with a 3Kw inverter, you ABSOLUTELY have to plan on that inverter providing 3Kw, and nearly all inverters will provide more till they reach thermal limits and shut down.
So you HAVE to design wiring to safely provide 3Kw - does not matter what sort of battery sources the power, or how far the wires run.

[Mike90250]

Banning users:
I generally let things run, but when bad advice is given, corrected and then attempts to justify bad advice, it's time for a ban. As someone else said,

success has been due to luck rather than technical competence and an understanding of the issues involved.

[SunEagle]

Banning users:
I generally let things run, but when bad advice is given, corrected and then attempts to justify bad advice, it's time for a ban. As someone else said,

I agree. While dax may have had some knowledge concerning LFP batteries he continued to show he had no knowledge concerning electrical safety or even the understanding why the currents would get so high on 12volt system making them dangerous regardless of what the battery chemistry used to fed the inverter.

While Math may not be important for some people and for every trade when it comes to designing electrical wiring circuits it is a must.

[karrak]

If it never draws 275 amps it's not being used as a 3kW inverter. If you install a 3kW inverter and downrate it to 1.6kW, great - but in that case might as well just install a good 1.6kW inverter.

No, that doesn't mean that. 120V and 240V inverters are readily available with a wide variety of mounting options.

The more you post, the more it sounds like your success has been due to luck rather than technical competence and an understanding of the issues involved.. I hope for the sake of your customers that your luck doesn't run out.

How do we know the 3kW is not the peak rating, allot of the Chinese manufacturers quote the peak rating rather than the continuous rating?

Dax has said that the 12 volt inverter is part of the module and is connected to the battery via 30cm of cable. Where is the safety issue if he has used the correct size cable, the correct fuses and the cable terminations have been done correctly?

I agree that from a technical point of view it is better to run higher voltages and lower currents but as Dax has said the system he has works. How many times do we see commercial considerations overriding technical considerations?

Simon

[SunEagle]

How do we know the 3kW is not the peak rating, allot of the Chinese manufacturers quote the peak rating rather than the continuous rating?

Dax has said that the 12 volt inverter is part of the module and is connected to the battery via 30cm of cable. Where is the safety issue if he has used the correct size cable, the correct fuses and the cable terminations have been done correctly?

I agree that from a technical point of view it is better to run higher voltages and lower currents but as Dax has said the system he has works. How many times do we see commercial considerations overriding technical considerations?

Simon

The problem is not that the "system works" 99 times out of 100. It has to be safe and has to meet code. Which means it has to be designed with the proper wire size and OCPD to protect that wire.

Things may cost more over here in the US but our insurance companies would quickly make a decision to blame a home owner for not following safe practices should a fire start due to their handiwork where the end resulted in not getting any compensation from the insurance company for the damages that occurred by using an unsafe electrical device. This is something we tress here on the forum about not using unlisted UL solar devices because they are both illegal and dangerous.

[karrak]

The problem is not that the "system works" 99 times out of 100. It has to be safe and has to meet code. Which means it has to be designed with the proper wire size and OCPD to protect that wire.

Things may cost more over here in the US but our insurance companies would quickly make a decision to blame a home owner for not following safe practices should a fire start due to their handiwork where the end resulted in not getting any compensation from the insurance company for the damages that occurred by using an unsafe electrical device. This is something we tress here on the forum about not using unlisted UL solar devices because they are both illegal and dangerous.

I totally agree with you. There are the same considerations here in Australia.

As far as I can see Dax is just stating what equipment they use in their system. I would be surprised if the equipment he sells is unsafe and doesn't comply with the regulations.

If Dax was recommending using long lengths of cable that were only capable of carrying 100A to the inverter without any fuses and using a vice to crimp the crimp lugs onto the cable then yes you have every right to criticise him.

Simon

[SunEagle]

I totally agree with you. There are the same considerations here in Australia.

As far as I can see Dax is just stating what equipment they use in their system. I would be surprised if the equipment he sells is unsafe and doesn't comply with the regulations.

If Dax was recommending using long lengths of cable that were only capable of carrying 100A to the inverter without any fuses and using a vice to crimp the crimp lugs onto the cable then yes you have every right to criticise him.

Simon

The problem is that while Dax is probably using safe circuit design and equipment he has been very secretive in what his systems are comprised of which leaves some of us guessing which requires some of us to be completely trustful in what he says he can supply.

Since I am an Electrical Engineer that type of thing raises red flags and brings up questions that Dax did not want to answer.

I am not mad at him. I just wanted more information concerning his design but also understood maybe why he did not want to give up the "keys to the kingdom" by answering my questions.