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Battery banks, parasitic loads and low sun hours

SHTF Power Anyway

Power Pig
Joined
Oct 7, 2021
Messages
285
Location
PNW
Hello forum members!

I'm looking for a bit of feedback. We are running 2 Sol-Ark 12k's with 10 Fortress eFlex batteries in an off-grid format using almost 15kwh of PV.

This winter, the parasitic load was killing us. What I've finally found out is that we have a parasitic draw of 30 watts for each battery and the same for the Sol-Arks which, in total, eats 8,640 watts of power in 24 hours (often more than our PV uptake on dark days). This leaves no room for actual loads in our world as we have poor solar uptake for days and days at a time. A generator is not an option for us for personal reasons. Wind and hydro aren't options either. So here's what I'm looking for:
  1. What kind of parasitic load do you have with your equipment?
  2. Do you have suggestions for replacing the eFlex batteries with another model or brand that would substantially lessen this load? I'm considering switching the battery bank to Fortress eVaults (x3) but wanted to see if anyone else has suggestions.
  3. Is there a good place to sell gently used equipment if we decide to replace the battery bank?
Thanks to any and all who can offer their thoughts.
 
Any way to shut down one of the Sol-Arks? Low sun should reduce maximum draw maybe within the single inverter.
 
First thing I would do is shutdown one of the inverters. Your batteries and lack of solar don't justify needing the load capacity. Secondly is there a heater or a balancer in the batteries that is consuming the power?

Currently our house runs 4 glycol circulation pumps for floor heat, boiler, Two freezers. An inline fan and a fridge/freezer. I am using between 500-700 watts per hour overnight.
 
Any way to shut down one of the Sol-Arks? Low sun should reduce maximum draw maybe within the single inverter.
Yes, I can shut down one most days, really. I only have 4kwh attached and could shut down at night. It's just a matter of taking the system off parallel but the biggest waste is the battery bank.
 
Those are expensive batteries. Are you sure they waste 30 watts? Could there be another problem?
That's what their rep told me. I'd asked before and never got a straight answer. Now I know. I thought I was missing a bunch of power... Now I know why.
 
Yes, I can shut down one most days, really. I only have 4kwh attached and could shut down at night. It's just a matter of taking the system off parallel but the biggest waste is the battery bank.
My single sol ark 15k will eat over 100 watts per hour idle. Usually triple that when fully loaded. idle most of the time as it's always in use off grid.
 
Sol-Ark specs say their idle load is 60 watts so x2 that's 120 watts.

8640 divided by 24 hours = 360 watts per hour = 120 (sol arcs) = 240 watts unaccounted for. That's a lot of power.

As @myles said, do the batteries have heaters? Because that would sure do it.

Are you sure you don't have a bunch of wallwarts plugged in? Those little phone chargers and stuff add up fast.

What you really need to do is measure current draw coming out of the batteries.. and measure that draw at the battery. Which leads me to ask: How did you come up with this 8640 number?

A funny little story...
Last year, we ran into the same situation.. short winter days, no sun, grid down, batteries running low... I'm watching my current draw using the BMS software and I'm up in the 500 watt range and wondering what the heck? We unplugged all the freezers, unplugged all the little wall-warts, turned off lights we weren't using, etc. I even disconnected the stupid transformer going to the doorbell ! Still pulling more juice than I should and pulling my hair out.

Get this.. turns out that my mig welder was drawing 75 watts! Huh? The mig welder has a big honking power switch on the front.. turn it off and it goes CLUNK.. it shouldn't draw any power.. Nope.. when I unplugged the 240 line feeding it, my house current dropped.

You need to hunt that parasitic load down and it's probably going to require some footwork and turning breakers off.
 
First thing I would do is shutdown one of the inverters. Your batteries and lack of solar don't justify needing the load capacity. Secondly is there a heater or a balancer in the batteries that is consuming the power?

Currently our house runs 4 glycol circulation pumps for floor heat, boiler, Two freezers. An inline fan and a fridge/freezer. I am using between 500-700 watts per hour overnight.
I agree that in the winter when solar uptake is low, I don't need the 2nd inverter. That inverter was to run our house when it's summer and power is plentiful. I'll be swimming in power in the summer with all my PV. But I do need it during times of uptake to bring in the 4kwh of PV attached. The larger loss is from the batteries themselves.

I would love your setup. We spent all our resources on building the system but our house and infrastructure were already in place so we don't have the built in efficiencies a normal off-grid would have. Right now it's just our shop run off solar in the winter. And that shop has several freezers and a refrigerator and our water pump in it. That draw is surprisingly minimal. I was running our solar system without loads then comparing to running the shop without break. The difference in power usage was actually quite minimal. I'm bleeding from the parasitic load specifically.

So I'm wondering what's normal for a battery bank. There are no heaters but there are BMS in each battery and the 30 watts was a number given to us by Fortress.
 
@MurphyGuy that is fascinating! Another parasitic load story. New house so things are new and still learning. But I was putting my daughter to bed and I heard a hum outside (winter time). Turns out it was the A/C mini split either heating a frozen coil or something even though AC was off for months. Turned the breaker off. Bam freeed up 100W! Live the free power gains. Every watt matters overnight off grid
 
Sol-Ark specs say their idle load is 60 watts so x2 that's 120 watts.

8640 divided by 24 hours = 360 watts per hour = 120 (sol arcs) = 240 watts unaccounted for. That's a lot of power.

As @myles said, do the batteries have heaters? Because that would sure do it.

Are you sure you don't have a bunch of wallwarts plugged in? Those little phone chargers and stuff add up fast.

What you really need to do is measure current draw coming out of the batteries.. and measure that draw at the battery. Which leads me to ask: How did you come up with this 8640 number?

A funny little story...
Last year, we ran into the same situation.. short winter days, no sun, grid down, batteries running low... I'm watching my current draw using the BMS software and I'm up in the 500 watt range and wondering what the heck? We unplugged all the freezers, unplugged all the little wall-warts, turned off lights we weren't using, etc. I even disconnected the stupid transformer going to the doorbell ! Still pulling more juice than I should and pulling my hair out.

Get this.. turns out that my mig welder was drawing 75 watts! Huh? The mig welder has a big honking power switch on the front.. turn it off and it goes CLUNK.. it shouldn't draw any power.. Nope.. when I unplugged the 240 line feeding it, my house current dropped.

You need to hunt that parasitic load down and it's probably going to require some footwork and turning breakers off.
Sadly, the 30 watts was the figure from the battery manufacturer who also confirmed my math. He said each battery would draw 30 watts and each Sol-Ark would be the same. 12x30x24 = 8640

I do believe the Sol-Ark is actually higher than 30. I don't have confirmation of the parasitic number from Sol-Ark directly but I had one person tell me their 2 Sol-Arks eat 3 kwh per 24 hours.
 
I agree that in the winter when solar uptake is low, I don't need the 2nd inverter. That inverter was to run our house when it's summer and power is plentiful. I'll be swimming in power in the summer with all my PV. But I do need it during times of uptake to bring in the 4kwh of PV attached. The larger loss is from the batteries themselves.

I would love your setup. We spent all our resources on building the system but our house and infrastructure were already in place so we don't have the built in efficiencies a normal off-grid would have. Right now it's just our shop run off solar in the winter. And that shop has several freezers and a refrigerator and our water pump in it. That draw is surprisingly minimal. I was running our solar system without loads then comparing to running the shop without break. The difference in power usage was actually quite minimal. I'm bleeding from the parasitic load specifically.

So I'm wondering what's normal for a battery bank. There are no heaters but there are BMS in each battery and the 30 watts was a number given to us by Fortress.


Do you fortress batteries have a BMS that is calling for balancing of cells when discharging? If so I would change that to only balance when charging and cell exceeds 3.4v.
 
Sadly, the 30 watts was the figure from the battery manufacturer who also confirmed my math. He said each battery would draw 30 watts and each Sol-Ark would be the same. 12x30x24 = 8640

I do believe the Sol-Ark is actually higher than 30. I don't have confirmation of the parasitic number from Sol-Ark directly but I had one person tell me their 2 Sol-Arks eat 3 kwh per 24 hours.
Do you batteries communicate with the solark? Just spit balling here...
 
Sadly, the 30 watts was the figure from the battery manufacturer who also confirmed my math. He said each battery would draw 30 watts and each Sol-Ark would be the same. 12x30x24 = 8640

I do believe the Sol-Ark is actually higher than 30. I don't have confirmation of the parasitic number from Sol-Ark directly but I had one person tell me their 2 Sol-Arks eat 3 kwh per 24 hours.

Something is wrong.. unless there's a heater on the battery, there is no reason for it to draw 30 watts.. Seriously, 30 watts is enough juice to actually cause the battery box to get warm..

I think you should call them back and talk to someone else.. 30 milliwatts is more reasonable. Even under cell balancing at a worst case situation, I can't imagine a BMS dissipating 30 freaking whole watts..

My bull$h1t detector is going off. I can't imagine any battery sucking 720 watts a day just sitting there.. I strongly suggest you call back and talk to someone else, you might have either misunderstood them or the person you talked to was high on drugs. Really.. 30 watts for a battery is a design flaw.
 
@MurphyGuy that is fascinating! Another parasitic load story. New house so things are new and still learning. But I was putting my daughter to bed and I heard a hum outside (winter time). Turns out it was the A/C mini split either heating a frozen coil or something even though AC was off for months. Turned the breaker off. Bam freeed up 100W! Live the free power gains. Every watt matters overnight off grid
We carefully turned off all circuits we knew we didn't need and, when weather was supposed to be good for a few days, we ran our first test running our entire house including the 2.5 ton furnace and we left the water heater on. I put a UPS next to me so when power went out, it alerted me with an alarm. We tripped the system only twice and our usage for the night was surprisingly little in comparison to what we lose to the system itself with zero loads. I thought that in and of itself was freaking nuts!

I know there are no heaters in the batteries because they didn't want me to leave them in an environment less than 40 F (even though they're supposed to be good to 32 F while operating and 20 F while in storage). They suggested leaving them on so that the heat generated from their operation would keep them warm. I'd had 4 of 10 batteries showing a BMS alarm for temperature issues when the shop where the system is located never fell below 38F and the battery bank was tucked into R19 insulation for the night. They literally suggested I use more power to put heat mats under the batteries. smh

I do like Fortress for a lot of reasons but that was not the right answer for me.

I did ask them about using their larger 18.5 batteries and specifically asked if it was the same 30 watt draw for the BMS on those. They said they "believed" it was. I could try to sell what I have and reinvest in just 3 and save myself 5 kwh in a 24 hour period but I know I'd lose my arse in that transaction. The larger batteries are over $10k. And I paid $3,500 for the 5.4 kwh batteries that I have now. Not sure what anyone would pay for a used battery but I'm trying to do the research and kick the idea around. To be honest, I'm one of those "nut jobs" who thinks we're going to need to be ready for grid-down either because we'll be refusing to comply or because we'll have no money left for the electric bill when they make everyone swallow CBDC's. So we're not doing anything but trying to engineer our way into survival if that happens. We'll have enough fuel to get us to the scene of the crash of our system though! lol
 
Do you batteries communicate with the solark? Just spit balling here...
Yes and communication issues have been resolved. They told us Sol-Ark changed some of their software which rendered their communication protocol invalid so they had to retool. Now that this excuse is out of the way... lol
 
Yes and communication issues have been resolved. They told us Sol-Ark changed some of their software which rendered their communication protocol invalid so they had to retool. Now that this excuse is out of the way... lol
Every little feature on that fortress battery takes power. Operating the BMs. The comms etc. I'd minimize any features possible on it except high and low voltage disconnect if possible on the bms and to only balance while charging.

If I understand balancing right. My chsrgery balances at I think 1.0A. Take that over a pack of 48V. It's over 50 watts getting moved from one cell and put into another cell. There will be losses on the way also adding up to parasitic load.

You need more batteries. Start researching diy lifepo4. Better bang for buck if you can handle getting your hands dirty and learning a whole bunch of good stuff
 
Take a 30 watt old fashioned incandescent light bulb and plug it in.. Wait 15 minutes and then try to touch it. (be careful because you will burn yourself)

Go ahead, put that 30 watt bulb in a metal tool box and come back in an hour and you will find the entire tool box is warm.
 
Every little feature on that fortress battery takes power. Operating the BMs. The comms etc. I'd minimize any features possible on it except high and low voltage disconnect if possible on the bms and to only balance while charging.

If I understand balancing right. My chsrgery balances at I think 1.0A. Take that over a pack of 48V. It's over 50 watts getting moved from one cell and put into another cell. There will be losses on the way also adding up to parasitic load.
That doesn't make sense. 1) If your BMS is balancing and shuffling energy from one cell to another, then its not actually USING that energy, meaning that energy is not being dissipated as heat and wasted. 2) Assuming for a moment that your chargery is NOT an active balancer, but is instead a passive balancer (dissipates heat through resisters to bleed down high cells), then it is not balancing all cells at the same time, and not always balancing period. In fact, most BMS's only balance when charging or over a certain voltage. So even if your BMS did go crazy and need to balance cells, I still can't see it drawing anything near 50 watts... the BMS box would get so hot it would start damaging things.
 
Something is wrong.. unless there's a heater on the battery, there is no reason for it to draw 30 watts.. Seriously, 30 watts is enough juice to actually cause the battery box to get warm..

I think you should call them back and talk to someone else.. 30 milliwatts is more reasonable. Even under cell balancing at a worst case situation, I can't imagine a BMS dissipating 30 freaking whole watts..

My bull$h1t detector is going off. I can't imagine any battery sucking 720 watts a day just sitting there.. I strongly suggest you call back and talk to someone else, you might have either misunderstood them or the person you talked to was high on drugs. Really.. 30 watts for a battery is a design flaw.
Thank you for that feedback. This is what the guy actually said to me:

"
Here is a typical estimate of your self consumption by the equipment.

Parasitic load calc.
energy storage: (10) eFlex +54000 Wh x 80%= 43200 Wh usable

Loads:
Battery(10) eFlex BMS ~30W x 10= 300Wh
Inverter (2) SolArk 12k ~30W x 2= 60Wh

Total consumption from equipment load= 360Wh x 24 hours = 8.640kWh (8640Wh) per day

Calc number of days: 43200Wh / 8640Wh= 5 days
Conclusion: Although the Parasitic load should be considered in battery sizing, it is not a major concern for this low consumption application.

Though I appreciated the information, I was dumbfounded at "it is not a major concern for this low consumption application". What he is saying is that I can run my system idle for 5 days before I run out of power... GREAT! Uh, except I'm supposed to be able to use that power, not put a bow on it and pat myself on the back for being able to generate and waste power!
 
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