Li batteries at 48vdc

[2oldman]

After much deliberation and questions, I'll likely be purchasing the 48v Lithium battery pack instead of 4-12v. I liked the idea of 12v batteries for weight and ease of handling, but the possible cell-balancing issues are a deal-breaker. Looks like the 48v pack will be around 130lb. I'll just have to find a couple guys to get it in there. Once in, it shouldn't ever have to come out... at least not in my lifetime.

According to the techs at Relion, cell balancing issues can occur if discharged below 80%. And if I only went with 100a of total capacity, that's a possibility.

Relion company is redesigning their 48v 150ah pack (which I think would be more than sufficient), so I'll be waiting to see what they come up with.

[2oldman]

N8GS wrote:
Looking forward to getting back there for New years eve. If you are there maybe our paths will cross.

BTW microwave draws 132 amps, voltage drop under load is 0.12 volts on my 12 V system.

I won't be there NY, but I do pop in and out on occasion.

Wow. Mine drops 1 volt.

[N8GS]

2oldman wrote:

N8GS wrote:
If you want to understand the balancing issues better, there is a lot of info relating to prismatic cells and Top vs Bottom balancing.

Ain't this fun!

I have cylindrical cells, not prismatic. Balancing is all internal to the pack, which is why I didn't choose 4 12v in series.

Yes, it is fun!! I like pioneering!

I understand that but the principals still apply. Like you I gave up on trying to design/program my own BMS. Time will tell if parallel 12 v bats work like we think they should.
I spent a lot of time emailing and on the phone with Sean at Battle Born. Actually that is not the company name but is the brand name they are using.
I have a 100 A converter/charger for if the sun doesn't shine but have never needed it. 470 watts of tilted panels in Quartzsite has been plenty. TV on, morning and evening + computer and printer and microwave, we get by on 95 Ah very nicely. Looking forward to getting back there for New years eve. If you are there maybe our paths will cross.

BTW microwave draws 132 amps, voltage drop under load is 0.12 volts on my 12 V system.

[2oldman]

time2roll wrote:
Then set rebulk at float or 0.2 below. If the battery voltage drops below the set rebulk voltage it will revert to the absorption (58.4) voltage.

Done, thanks. Rebulk can be set lower or equal to, but not higher than Float. It's set to 55.2

I cannot understand why Outback would say such a seemingly nonsensical thing. (which it appeared you agreed with above)

[time2roll]

Yes but don't do that. I thought float was 55.2

Leave absorption at 58.4 and float 55.2 or 54.4 range.

Then set rebulk at float or 0.2 below. If the battery voltage drops below the set rebulk voltage it will revert to the absorption (58.4) voltage.

[2oldman]

time2roll wrote:
In the Floatstage, if the battery voltage falls below the ReBulk Voltage set point for at least
90 seconds, the FLEXmax will automatically initiate a new charge cycle.

If I set the Float voltage the same as Absorb, (58.4), won't the controller float at 58.4?

[time2roll]

2oldman wrote:

MrWizard wrote:

So set a really low float, like where you want to start recharging, in other words a low voltage cut off point where you go back into charge ( aka rebulk ?)

That's my plan.

You can leave float where it is and set REBULK even lower to avoid a restart before needed.

Charging in float mode should still supplement power up to the max available from solar if needed.

[time2roll]

2oldman wrote:

time2roll wrote:
May need to revisit your manual.

Outback engineer just told me to set the float same as absorb. That makes no sense. Maybe he didn't understand my question.. but this is why it's taking me so long to understand charging an Li battery.

Yes that sounds correct. REBULK voltage is the trigger point to restart the charge cycle. If voltage drops below the set REBULK voltage for 90 seconds the controller reverts back to the absorption voltage in the main program.

See outback manual page 50

In the Floatstage, if the battery voltage falls below the ReBulk Voltage set point for at least
90 seconds, the FLEXmax will automatically initiate a new charge cycle.

rebulk voltage is the restart trigger point, not the new bulk voltage.

[2oldman]

MrWizard wrote:

So set a really low float, like where you want to start recharging, in other words a low voltage cut off point where you go back into charge ( aka rebulk ?)

That's my plan.

[MrWizard]

Float means a constant steady voltage that keeps the battery from self discharge

No float on lifpo, is as far as I understand it

No applied voltage, turn off charge source

If that is the case , rebulk is no better than float, and might do more harm

If I understand this correctly, yo want to charge them to 90 percent or slightly above then turn off all charging, or hold the amps to a milliamps trickle at battery resting voltage, that will in effect do nothing

With Lifpo, is discharge recharge, no float, no sustained voltage , rebulk or otherwise

That is If I understand this correctly

So set a really low float, like where you want to start recharging, in other words a low voltage cut off point where you go back into charge ( aka rebulk ?)

[2oldman]

N8GS wrote:
If you want to understand the balancing issues better, there is a lot of info relating to prismatic cells and Top vs Bottom balancing.

Ain't this fun!

I have cylindrical cells, not prismatic. Balancing is all internal to the pack, which is why I didn't choose 4 12v in series.

Yes, it is fun!! I like pioneering!

[2oldman]

"I cannot comment on the specific voltage that you need to charge to as we do not manufacture that battery. All I can say is that you need to have your absorb and float voltages programmed to be the same value. The value needed will have to be provided by the battery manufacturer."

This is a response from Outback. I told them exactly what the battery says on it for voltages. This response makes absolutely no sense to me.

[N8GS]

2oldman wrote:

N8GS wrote:
You might want to quiz your supplier as to the need to float..

They say it's not necessary. I cannot set its duration.

Float will end when the sun goes down.
I have my Absorb time set to 30 minutes. But I may want to reset it to just 10 minutes.
If you have a temperature probe disconnect it. Temperature compensation is not used with LFP.
If your battery monitor has a Peukert function set it to 1.00 or turn it off to get accurate usage numbers with LFP

BTW LiFePO4 is now commonly being refereed to as LFP, aka, lithium-ferrophosphate, aka, lithium iron phosphate.

If you want to understand the balancing issues better, there is a lot of info relating to prismatic cells and Top vs Bottom balancing. What we are using is Top balancing and that is why we avoid using the last 15% to 20% of the capacity. If using bottom balance you would never "top off" or use the upper 10% of capacity.

Ain't this fun!

[N8GS]

pianotuna wrote:
Hi Gale,

I wanted to know the solar harvest on a bad day.

I had one rainy nasty day in Quartzsite last January where I got just 10 Ah that day. Like I said, time to read a book and save the amps.

[pianotuna]

Hi Gale,

I wanted to know the solar harvest on a bad day.

[2oldman]

N8GS wrote:
You might want to quiz your supplier as to the need to float..

They say it's not necessary. I cannot set its duration.