LiFePO4 - The future for off-grid battery banks?

[Sunking]

Am I not understanding something correctly about the Grid Tie and how it works?

Tommy L sends....

Maybe not. There is no way to control where the power goes.

If your systems is generating more power then your home uses, the excess goes out to your neighbors. If you are consuming more power than the system is generating, then the grid makes up for the shortage.

[TommyL]

You cant have a portable gridtie system. Well not legally anyway in any country I know of. It has to all be installed to that areas regulations . Those ebay plug into wall socket grid tie inveters are to the best of my knowledge not legal anywhere and for good reasons.. example say you have a circuit that is rated for 20a and its already carrying 16a and you plug an inverter into it putting out 6a you are now opperating that circuit above its rating, now mabe overheating and a free fire.

Good Day John,

I thought from all my reading to date that the Grid Tie inverters energy would be used first.
The 16amps 1900watts Grid consumption would be reduced to 1200watts and the Grid Tie would
supplement the rest 6amps or 700watts.

Am I not understanding something correctly about the Grid Tie and how it works?

Tommy L sends....

[john p]

You cant have a portable gridtie system. Well not legally anyway in any country I know of. It has to all be installed to that areas regulations . Those ebay plug into wall socket grid tie inveters are to the best of my knowledge not legal anywhere and for good reasons.. example say you have a circuit that is rated for 20a and its already carrying 16a and you plug an inverter into it putting out 6a you are now opperating that circuit above its rating, now mabe overheating and a free fire.

[TommyL]

Is there a good or great portable solar expandable Grid tie with battery charging system?

Tommy L sends...

[TommyL]

JOSCO yes standard adjustable output voltage PWM CHARGER..
Here is a repeat of that post explaining all..

IF anyone is interested this is how I have set up 3 x100ahr LiFePo4 batteries for charging by solar and for use with MSW inverter..
Im not claiming this is the correct way or even the best way to do it,, But dont tell me it wont work as all 3 systems been in use over 2 years now almost 3 years with NO PROBLEMS
Charger a 30a PWP 12v charger set to output 14.8v with no equalization..
Battery cell over charging 1x 3.9V 1watt zenner diode and 1x10ohm resistor across each cell
One low voltage sensor set to disconnect the inverter and anything else connected to the battery pack at 10v
Facts as found out the expensive way by me are if you discharge a cell below about 2.2 v it will be destroyed even if done just one time only.
If you over charge above about 4.4v they have a very short life.
If you look at charts from the manufacturesr you find there is little power above 3.8v and it stays fairly constant until about 2.5v then hits a brick wall.
So use between those 2 voltages and all is well with the world.
I have never found a MSW inverter that has problems with operating between 15.5v and 10.5 v and that is the usual specs given by most MSW invereter manufacturers..

Thank you John!

Tommy L sends...

[TommyL]

TOMMYL read my post #26 it explains it .I hope, thats the big advantage if you using a lot of cells if one becomes faulty very easy to just replace that cell only,keeps costs of replacements los as you are not throwing away good cells also.

Totally agree! Not for the "Set and forget" style people. I've been building, fixing, making, designing, prototyping all my life. I enjoy
being involved and tweaking my work.

I look forward to readying your post/threads! I appreciate your input!
I have around 100 38120HP (Red) Headway cells. I've been testing them. Low resistance cell.

My plan is to bring in 1,000 or more pcs for commerce.

Tommy L sends...

[john p]

TOMMYL read my post #26 it explains it .I hope, thats the big advantage if you using a lot of cells if one becomes faulty very easy to just replace that cell only,keeps costs of replacements los as you are not throwing away good cells also.

[TommyL]

Tommy l if you use the 10ahr cylinder cells its very simple to make a BMS for them unfortunately its not as easy to upscale to the much larger(100to 200ahr)cells

What do you have up your sleeve for the 10ahr cylinder cells?

Although they are not the cheapest of the LiFePO4 storage per w/h, I do like the
the ease of switching out a problem cell without loosing too much money

Tommy L sends.....

[TommyL]

Hi,

You question was asking about charge efficiency too

My pack came with a BMS - and as mentioned above you should use larger format cells - say 100Ah 3 in parallel * 16 in series - or 300Ah cells 16 series, generally there isnt too much price penalty either way.

I am currently designing a flyback charge balancing BMS for cell and supercap I was hoping to sell - it's 3 to 5A and doesnt bleed power through resistors, hopefully superior, with full reporting via RS485/232 - a while away for now though as I have other projects nagging.



Regards,

Steve.

I stand corrected!
Super capacitors are very interesting. I look forward to the day that you test your new device.
Lots of Experimenting/Observing and taking notes continuing in my future.

I appreciate your input!
Take care...

Tommy L sends....

[steveg]

Thank you for the links..... but my question was....

What are you using for BMS?
Do you have a build thread?

Tommy L sends....

Hi,

You question was asking about charge efficiency too

My pack came with a BMS - and as mentioned above you should use larger format cells - say 100Ah 3 in parallel * 16 in series - or 300Ah cells 16 series, generally there isnt too much price penalty either way.

I am currently designing a flyback charge balancing BMS for cell and supercap I was hoping to sell - it's 3 to 5A and doesnt bleed power through resistors, hopefully superior, with full reporting via RS485/232 - a while away for now though as I have other projects nagging.



Regards,

Steve.

[john p]

Tommy l if you use the 10ahr cylinder cells its very simple to make a BMS for them unfortunately its not as easy to upscale to the much larger(100to 200ahr)cells

[TommyL]

A quick google search gave me :

Charge Efficiency PbA

http://photovoltaics.sandia.gov/docs/PDF/batpapsteve.pdf

http://www.powerstream.com/SLA.htm

For LiFePO4 see figure 5
http://www.batterypoweronline.com/eprints/TI_0510.html

Thank you for the links..... but my question was....

What are you using for BMS?
Do you have a build thread?

Tommy L sends....

[steveg]

Hello Steveg!

Very clean install! Does anyone actually have "Charge Efficiency" comparison between LiFePO4 and AGM/Wet Cells?

I'm testing Headway cells. A 32ah 12v pack can provide current to 2.5C (80amps) and give their full rating 24 minutes.
The 12v/50ah rated AGM drawing 1.6C (80amps) only lasted 12 minutes.

41lbs
AGM 13.2v (no load)
AGM 11.5v (80amp load applied)
AGM 10.5v (at 12 minutes)


10lbs (closer to 15lbs with busbars)
LiFePO4 13.2v (no load)
LiFePO4 12.6v (80amp load applied)
LiFePO4 12.26v (at 20 minutes)
LiFePO4 11.0v (at 26 minutes)

AGM lasted 12 min vs LiFePO4 26 min
The LiFePO4 was still at 12.29v at the 20min mark.
I ran this test using 800watt resistant load (8 100watt light bulbs on light board)
and a Xantrex 1000watt Inverter.

What are you using for BMS?
Again, Very nice clean install!

Tommy L sends...

If your Lead Acid bank is not large enough, there is no doubt that voltage sag occurs.

A quick google search gave me :

Charge Efficiency PbA

http://photovoltaics.sandia.gov/docs/PDF/batpapsteve.pdf

http://www.powerstream.com/SLA.htm

For LiFePO4 see figure 5

http://www.batterypoweronline.com/eprints/TI_0510.html

[Mike90250]

What are you using for BMS?

Agreed - the BMS for Li based batteries, is a problem. That usually leaves users to either cobble together something of their own, or risk battery damage by going without a BMS.

[TommyL]

The charge efficiency of LiFePO4 is very high and we live in the top 30-40% of the battery so I expect my lifetime of the cells to be high.

Hello Steveg!

Very clean install! Does anyone actually have "Charge Efficiency" comparison between LiFePO4 and AGM/Wet Cells?

I'm testing Headway cells. A 32ah 12v pack can provide current to 2.5C (80amps) and give their full rating 24 minutes.
The 12v/50ah rated AGM drawing 1.6C (80amps) only lasted 12 minutes.

41lbs
AGM 13.2v (no load)
AGM 11.5v (80amp load applied)
AGM 10.5v (at 12 minutes)


10lbs (closer to 15lbs with busbars)
LiFePO4 13.2v (no load)
LiFePO4 12.6v (80amp load applied)
LiFePO4 12.26v (at 20 minutes)
LiFePO4 11.0v (at 26 minutes)

AGM lasted 12 min vs LiFePO4 26 min
The LiFePO4 was still at 12.29v at the 20min mark.
I ran this test using 800watt resistant load (8 100watt light bulbs on light board)
and a Xantrex 1000watt Inverter.

What are you using for BMS?
Again, Very nice clean install!

Tommy L sends...

If your Lead Acid bank is not large enough, there is no doubt that voltage sag occurs.