3.2v 280Ah LiFePo4 Batteries - Cycle Life Numbers?

[Steve_S]

I'd like to point out that making generalized comments based on Assumptions is generally not a bright idea.
Blanket Generalized statements help no-one and does not further understanding & knowledge.
Appreciate that saying LF is less efficient than HF without evidence of such is well... a tad dubious at best.

Every manufacturer makes many different inverters, their specs vary a LOT ! Even within the same brand. I use a Samlex EVO-4024 and it is 94% while the EVO-2212 is only 90% Efficient, and these are both Low Frequency.

As for Standby Power Usage (Samlex EVO-4024)
No Load Power Consumption in Standby Mode (Inverting/ charging are suspended) < 5 W
No Load Power Consumption in Power Saving Mode < 8 W
No Load Power Consumption in Normal Mode (120 VAC Output, Typical) 25 watts

When looking at Inverters, ALWAYS LOOK AT THE SPECS and see what the efficiency is an how it is determined. Tier-1 & Tier-2 Products will have this information in their documentation. Tier-3 and "Value" systems rarely have much in the form of decent documentation and such information is hap hazard.

The Experts explain the differences between High & Low Frequency Inversion:
Inversion Methods Explained: High Frequency vs Low Frequency

Inversion Methods Explained: High Frequency vs Low Frequency | Magnum Dimensions

Understand the difference between high frequency and low frequency inverters with this quick article.

www.magnum-dimensions.com

 

[Dzl]

I'm designing the setup so that everything besides the fridge and cooking appliances are run off 24V.
I'll only be cooking here and there so I'll just switch on the bigger inverter for that.

My understanding is that running a 3000w inverter for ONLY a 120w fridge is less efficient than running a 200-300w inverter?
If it's just as efficent at low power draw then I'll save the cash and just buy a big 3000w inverter to use 24/7.

I think your understanding is right in theory, larger inverters usually have larger idle power draw, and I think I remember hearing inverters are somewhat more efficient towards the top of their power rating. But I think both of these factors are most relevant either as general observations or for comparing between inverters of the same product line/manufacture. There are other factors that will effect efficiency as much or more.

But I'm not aware of any <1000W LF inverters, are you?

One thing you can consider if you haven't already bought the fridge, is just getting a 24V fridge and skipping the second inverter. Most "12V fridges" made for marine and rv applications are designed to operate at 12v or 24v.

 

[Dzl]

I'd like to point out that making generalized comments based on Assumptions is generally not a bright idea.
Blanket Generalized statements help no-one and does not further understanding & knowledge.
Appreciate that saying LF is less efficient than HF without evidence of such is well... a tad dubious at best.

Steve, While I largely agree with your point in the abstract and generally respect your opinion, I find your generalized comment, directed at my generalized comment, just a bit offensive and off target. Here is what I wrote:

You may want to consider flipping this around. As I understand it, LF inverters [tend to*] have higher no-load power draw, so using one for your 'always-on' fridge inverter will cost more in efficiency, also I'm not sure if there are any LF inverters available at that low wattage (but this last point is just speculation and might be wrong).

Was there a particular inverter you had in mind?

I am specifically talking about no-load power draw, for an always on single purpose inverter. And asked if there was a specific inverter in mind. I stand by that general observation and think that it was sufficiently specific in the context of OP's general question/situation, and hope that it was sufficiently clear that its my understanding based on what I have observed not some infallible law of nature.

That said, I mostly agree with you, when you make generalized observations, there will usually be exceptions to the rule. And there other factors outside LF/HF that will make as big or bigger differences. But we make generalizations every day out of convenience and necessity, the article you linked to (which I like and have linked to myself in the past) makes plenty of generalizations.

I do very much agree that comparisons are most useful within a specific manufacturer, or product line, or at the very least between products of the same "tier"/level of quality (but its worth noting the concept of 'tiers' in particular is a huge generalization).

Every manufacturer makes many different inverters, their specs vary a LOT ! Even within the same brand. I use a Samlex EVO-4024 and it is 94% while the EVO-2212 is only 90% Efficient, and these are both Low Frequency.

A few more general observations I've noticed: WIthin a specific inverter line from a specific brand (1) higher input voltage is usually marginally more efficient as a % (2) higher wattage is usually marginally more efficient as a % (3) higher power inverters often but don't always have higher no load power consumption.

Your Samlex Evo is a good example of the specific point I was trying to make regarding OP's situation. For the application (single purpose, always on inverter for a ~100-200W load), the Samlex Evo (which I regard as one of the best value/quality inverters) would be a poor fit. The lowest cost 24V model costs about ~$800, with an idle power draw of over 20W (~500Wh per day). I have read on this forum, that fridges usually aren't compatible with inverter eco modes, if this is true, that means the 'energy cost' of the inverter will rival that of the fridge itself.

In my eyes, to make the dedicated inverter option practical, it must be affordable and it absolutely must have low idle power draw, otherwise any efficiency gains from a two inverter setup will be quickly swallowed up by no load consumption.


Edit:
OP, if you want to learn more here are two threads on LF and HF inverters, some good discussion and resources sprinkled throughout
Low Frequency Inverters
Low or High Frequency Inverters

 

[idontknowwhatimdoing]

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or the link the the selection of their 24v

8S Lifepo4 Battery Board - Shop Cheap 8S Lifepo4 Battery Board from China 8S Lifepo4 Battery Board Suppliers at JBD Battery PCB Board Store on Aliexpress.com

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There is the 8s version.

I'm getting 2 4s version you mentioned https://www.aliexpress.com/item/32858179124.html?spm=2114.12010612.8148356.8.22b399cfvxYqIN for my 8 cells. One 12v 4s in my car and one in the shed.

 

[CitizenCane]

But I'm not aware of any <1000W LF inverters, are you?

Yeah there's lots around,the ones I've seen are usually sold by 4wd/auto stores to plug into a cigarette lighter socket.

just getting a 24V fridge and skipping the second inverter.

Yeah this was my initial plan, but I've heard these draw a lot more current than a modern efficient household AC fridge.
They're also stupidly expensive, if I wanted to buy Engel / Dometic units they'd be three times the cost for half the volume of just a regular domestic fridge.
The only real benefit, besides the convenience, is that they are more suited to being bashed around on off road tracks.

There is the 8s version.

Cheers for the link.
My system is 8 x 280ah 3.2v cells, so 24v 280A (if I understand that correctly).
So I'll need to get at least a 280A capacity 8S 24v BMS won't I?
The biggest that seller seems to stock is 120a.

 

[idontknowwhatimdoing]

Cheers for the link.
My system is 8 x 280ah 3.2v cells, so 24v 280A (if I understand that correctly).
So I'll need to get at least a 280A capacity 8S 24v BMS won't I?
The biggest that seller seems to stock is 120a.

Capacity and CC don't have to match. Depending what your draw is mate. 100A one gets you 2400w.

 

[Dzl]

Yeah there's lots around,the ones I've seen are usually sold by 4wd/auto stores to plug into a cigarette lighter socket.

Are you sure you are actually referring to Low Frequency inverters, and not maybe confusing that with "Pure Sine Wave" or some other spec. I suspect these cheap small inverters are not low frequency, and posisbly not even true pure sine.

Yeah this was my initial plan, but I've heard these draw a lot more current than a modern efficient household AC fridge.
They're also stupidly expensive, if I wanted to buy Engel / Dometic units they'd be three times the cost for half the volume of just a regular domestic fridge.
The only real benefit, besides the convenience, is that they are more suited to being bashed around on off road tracks.

Yes efficiency and being purpose built for applications where they need to be rugged are the two major benefits I can think of.

You have to consider the cost of the second inverter in the overall cost. If you truly want a low frequency inverter to run the fridge and a separate inverter for everything else. The LF inverter might end up costing more than just buying the 24V fridge.

I think you should go back and revisit what a low frequency inverter is, and make sure that we are on the same page about that. From the sound of it, you might be misunderstanding the term.

Cheers for the link.
My system is 8 x 280ah 3.2v cells, so 24v 280A (if I understand that correctly).
So I'll need to get at least a 280A capacity 8S 24v BMS won't I?
The biggest that seller seems to stock is 120a.

I believe you are still misunderstanding this concept. Battery capacity (Amp-hours) and BMS throughput (Amps) are two separate and not directly related numbers. BMS is sized on loads/current, not battery capacity/stored energy.[/QUOTE]

 

[CitizenCane]

I suspect these cheap small inverters are not low frequency, and posisbly not even true pure sine.

I was looking at something like this for the fridge:

300W / 600W Pure Sine Wave Inverter 24V DC to 240v AC Camping Boat | Alternative Energy Supplies |

Buy 300W / 600W Pure Sine Wave Inverter 24V DC to 240v AC Camping Boat from Kogan.com. This model is used in a wide range of application including remote homes, RVs, sailboats and powerboats. It will operate most televisions and VCR, personal computers, small appliances and tools such as drills...

www.kogan.com

Not the most efficient but I haven't really started shopping around yet, I'll probably find something better.
It doesn't actually specify whether it's LF or HF.
Correct me if I'm wrong, but, it doesn't matter much if the fridge never gets near it's limits.
It'll only draw about 120w max, so 300w will be fine?

Speaking of efficient did you get around to building your DC-DC powered PC yet?
Pretty keen on doing that myself, but (surprisingly) it doesn't seem like many people do that, outside of small form factor PC building enthusiasts.

100A one gets you 2400w.

Thanks for the tip.
I'm going to be using more than that at certain times so I think I should go for more like a 150a - 200a BMS, something like this:

48.6US $ |Lifepo4 24v 8s 80a 100a 120a 150a 200a 18650 Battery Pack Management System Balanced For Solar Inverter - Battery Accessories & Charger Accessories - AliExpress

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There's no reason not to get an oversized BMS for a bit of future proofing I assume?

 

[Dzl]

Speaking of efficient did you get around to building your DC-DC powered PC yet?

I didn't, I went a different direction in the short term and got a laptop (which can be charged via either AC or DC depending on the charger. In the future I will probably still build a DC powered computer, and I like the look of this company. It looks like they build very high quality products, and if something like the PicoPSU can't provide the power you need (I think they max out around 190W right?), these guys make higher powered DC power supplies. The other cool thing about these PSU's is they can be DC-DC or with an additional module can be AC-DC so they are pretty flexible.

I think combining the power supply I mention, with an AMD Ryzen 3400G (or the newer version just coming out), you would have a pretty powerful and pretty efficient DC computer.

Thanks for the tip.
I'm going to be using more than that at certain times so I think I should go for more like a 150a - 200a BMS, something like this:

There's no reason not to get an oversized BMS for a bit of future proofing I assume?

I fully agree, oversize it if you can. With FET based BMS' (like the ones you are considering), it is definitely a good idea to oversize the BMS (for extra capacity if you need it in the future, but more so because you don't want to be using these BMS at full nominal rated capacity (some people go so far as saying to stay under 50% of rated capacity, but that's on the far conservative end, I would think somewhere between 50% and 80% of rated capacity sounds about right, but that's just speculation).

 

[JoeHam]

Also consider the Intel NUC computer lineup.

Over the years I have built an I3, I5 and I7 version of these. All with SSD and they are quite efficient. Most come with DC powerbricks which obviously can be replaced by pure DC.

 

[Dzl]

Also consider the Intel NUC computer lineup.

Over the years I have built an I3, I5 and I7 version of these. All with SSD and they are quite efficient. Most come with DC powerbricks which obviously can be replaced by pure DC.

NUC and NUC like PC's are good options if the small form factor works for you. External power brick so easy enough to convert to DC (they are like 19VDC right?)

 

[CitizenCane]

I like the look of this company. It looks like they build very high quality products

Thanks for the tip, I've ordered one of their DC-ATX PSUs. Just what I was looking for.

Also consider the Intel NUC computer lineup.

I'll definitely consider an Intel NUC for a NAS / Server (if I don't build a RasPi version)
But I've already got most of the bits for a pretty beefy gaming rig already so I'll went with the HDPLEX 400W Hi-Fi DC-ATX Power Supply as Dzl suggested.


I think the I've worked out the best choice for a BMS: the Chargery BMS8T 8S 600A BMS

600A is more than I need right now, but I'd rather get an oversized BMS and be able to add more cells later, than have to upgrade the whole setup.

The listing says "You also buy our 1S , 4S , 5S or 8S balance module to use with the BMS together."
Unfortunately the S8 Balance Module is out of stock.

I found what looks like to be the same one at another seller, but for $159. Seems ridiculously pricey.
There are alternatives like this one for only $10.17.
Or even this one for $2!

Looks like the cheaper ones don't come with cables but I'm not afraid of a little soldering.
Won't they do the same thing or am I missing something?

 

[Dzl]

Thanks for the tip, I've ordered one of their DC-ATX PSUs. Just what I was looking for.



I'll definitely consider an Intel NUC for a NAS / Server (if I don't build a RasPi version)
But I've already got most of the bits for a pretty beefy gaming rig already so I'll went with the HDPLEX 400W Hi-Fi DC-ATX Power Supply as Dzl suggested.

Cool, what GPU are you going with?

I think the I've worked out the best choice for a BMS: the Chargery BMS8T 8S 600A BMS

600A is more than I need right now, but I'd rather get an oversized BMS and be able to add more cells later, than have to upgrade the whole setup.

Again (not to kick the shit out of a twice dead horse), BMS current rating (amps) and battery capacity (amp hours) are separate things. Divorce these two specs in your mind. The current rating of the BMS you buy now will have no effect on your ability to add more cells in parallel later. It will have an effect on maximum total current. Point being size the BMS on load current, not battery bank size, you can grow your battery bank without needing to upgrade your BMS.

If this still isn't clear or i'm misunderstanding you, let me know and i'll try to reframe it differently

As to what we said earlier about it being smart to oversize your BMS. This applies to FET based BMS', but with a BMS like the chargery, the current rating relates to the shunt and maybe the relays not the BMS itself, I think you may want to double check that there aren't any downsides to oversizing the BMS (it may be non-optimial for the shunt to be oversized). Someone who knows more about Chargery or Shunts can maybe confirm or dismiss this concern.

 

[Steve_S]

As to what we said earlier about it being smart to oversize your BMS. This applies to FET based BMS', but with a BMS like the chargery, the current rating relates to the shunt and maybe the relays not the BMS itself, I think you may want to double check that there aren't any downsides to oversizing the BMS (it may be non-optimial for the shunt to be oversized). Someone who knows more about Chargery or Shunts can maybe confirm or dismiss this concern.

The Relay/Contactor is what handles the Amperage flowing through it is a BMS such as a Chargery.
The shunts must also be appropriately sized to handle the maximum Amps that will e possibly pulled.

DZL is quite correct, Amp Hours, has nothing to do with the amount of Amps being pulled from the battery bank.
In plumbing terms, AMPS = the amount of water pressure in the pipe, where amp hours is how long you can keep that pressure up.

BTW: I use an HP EliteDesk NUC (Desktop brick "HP EliteDesk 800 G2 DM 35W") for my main computer as it is very power frugal in comparison to my heavy workstation The brick power supply is marked as 19.9V @ 3.5A. Quite a nice machine even though it is dated a bit now and even runs heavy 3D Simulation Software which typically needs an NVidia GTX Video to fully render (quite a surprise really).

 

[CitizenCane]

what GPU are you going with?

I was going to get a RTX2080, but I think I'll hold off as the 3000 series will be out soon, and it's going to take a month or so to get my DC-ATX PSU anyway.

I actually have all the bits for a water cooled CPU / GPU, so if I think it can hold up to living in the back of the van I'll give that a shot.
Probably be the first van-based water cooled battlestation

I use an HP EliteDesk NUC (Desktop brick "HP EliteDesk 800 G2 DM 35W") for my main computer as it is very power frugal in comparison to my heavy workstation

Yeah the NUC seems like a winner, not really a fan of laptops unless I'm not going to be using them at a desk. too hot and expensive.
I've got my eye out for a cheap NUC to use for my new NAS.

 

[Dzl]

I was going to get a RTX2080, but I think I'll hold off as the 3000 series will be out soon, and it's going to take a month or so to get my DC-ATX PSU anyway.

Super powerful GPU but It'll suck a decent bit of power won't it? What's the TDP?

I was considering the 1660 Ti, can't compare to the 2080 in terms of raw performance but its top of the line in terms of performance per watt. With pretty modest power consumption overall (120W max)

 

[CitizenCane]

Yeah the 2080 will suck alotta power (about 250w under full load I think)

I'm using a 1070 at the moment that I bought partially considering power usage and using it off batteries. It's pretty frugal.

Problem is I already have all the bits for liquid cooling. besides the GPU water block, so I'd prefer to get a card that has inbuilt water cooling (like a Gigabyte RTX 2080 waterforce) but they're only available on the top end cards. Maybe I'll look for one second hand.

The cost of getting a separate GPU water block is like $300. Hard to justify the cost.