Making the right call on batteries

[john61ct]

And LFP 3-5000 cycle ratings are based off stupidly abusive operating conditions, not the use case discussed here.

Plenty of LFP banks all around the world are approaching 17, even 19 years of daily cycling and are still very close to rated capacity 90-95% SoH.

I think 10,000 cycles is doable at low C-rates.

But only with top quality cells, well cared for, staying far from the voltage shoulders forget about the min/max data sheet specs.

Drop-ins, I very much doubt it.

[dzl_]

Originally Posted by john61ct

And LFP 3-5000 cycle ratings are based off stupidly abusive operating conditions, not the use case discussed here.

The standard test conditions are in many cases more 'abusive' than what would be seen in normal solar use-cases. However its not that simple clear cut.


There are ways in which the standard testing is more abusive (0%-100% charge/discharge, and 1C rates (I believe), However, there are ways in which the standard testing is less abusive, (near ideal and stable temperature, no effect of calendar aging, no storing at near 100% SOC).


Its not as simple as saying you will exceed what the manufacturer states. If you treat your cells right, engineer your system well, learn what you need to learn to responsibly manage the system (most people don't) its very possible you will exceed the manufacturer rated cycle life. But it is far from a given, particularly considering that most people are buying cheap, and not spending the time to really understand the chemistry. Still 3000+ cycles is a long time. There are a lot of variables, some are in our favor, some are not.



Plenty of LFP banks all around the world are approaching 17, even 19 years of daily cycling and are still very close to rated capacity 90-95% SoH.

I think 10,000 cycles is doable at low C-rates.

Me to, low c-rate, modest depth of discharge, and avoiding temperature extremes. For many people its this last one that will be most difficult with a bus, and its this last one that can have a significanct effect on life of the cells.

[john61ct]

Also not as if going to and sitting at high SoC isn't easily preventable.

Once users know it's harmful to longevity

[kidharris]

Originally Posted by Mountain Gnome

I was told as a kid that 1000s (or was it 10,000s) of FLA batteries explode under the hood of a car every year and injure someone, from vented hydrogen gas. (and at the time, DieHard batts exploded the least, but I think they are just "generic" batts with a "brand name" now) No "accumulation" needed.


Look at a new pair of jumper cables. What do the instructions say? The last step in connecting them is to connect the ground to the MOTOR block, not the battery. Why? Because the spark may ignite the H2 gas. Hood raised. Open sky above. Still, it can explode and impregnate your eyeballs with debris, blow out your eardrums, throw you to the ground, cover you with acid, and maybe catch you and the car on fire.


You don't need to fan-vent your indoor FLAs. Just keep them vented at the top of a sort-of sealed box. The H2 gas is the lightest gas of all, and it will quickly find its way out the box top-vent and up to outer space. But any spark on the way will ignite it.
-Wikipedia


Don't know about the Sulphur-Dioxide gas that is vented, is it heavier than regular air? If yes, then vent it at the bottom , also.

I have always heard that most of the car starting battery explosions, especially those concerning flying acid, are because of pressure build up from clogged/restricted cell vents when the battery suddenly produces a lot of gases (from the water, acid, and whatever?. I am pretty sure the volume of the gasses generated is much greater than the volume of the liquids being electrolyzed and can over pressurize the battery case when you connect the cables. The case ruptures and sends acid flying and you don't want to be near it is why you connect the charged/good car battery jumping last when jump starting a dead battery. Hook up the dead battery first, then the good battery. True or false? I think, maybe, hooking the ground to the engine then just becomes a way of trying to ensure a good ground between the starter and battery?

[HamSkoolie]

Originally Posted by kazetsukai

The upfront cost per Wh used to be extremely competitive as well, when I bought mine it was dirt cheap, neck and neck with lead.

The only apples to apples way to compare Wh (kWh keeps the number reasonable) cost in any system designed for long term use is to compare LIFE CYCLE capability. How many kWh can be pulled from the batteries over their expected lifespan compared to the cost of acquisition and maintenance of the system. Lead acid batteries have their place but they also require significantly more maintenance and can release fewer usable Wh per dollar, per pound, and per kWh of capacity...... because they have significantly lower lifespans.

When we use this methodology, we find that even without maintenance costs in labor and materials, Lithium technology provides a cheaper cost per kWh.
Now if I'm just building a system to last long enough to get it out the door and sold.... lead acid will do that trick. And thus all the major RV companies ship out their rigs with a single, 12 volt, POS, "deep cycle" FLA battery. If it's a big expensive rig, they'll give you two. But I also bet if you ask, they'll have a very expensive "Lithium upgrade" available.

Originally Posted by kazetsukai

BMS? Wiring them in series? What bank voltage are you going for?

Yes, the BMS is included in the batteries we're going with. It's an entire system in a rack mountable package.
We haven't settled on a bank voltage yet which is the only reason they aren't already on hand. I'd prefer to keep the bank at 12vdc but that would entail large conductors. 24vdc reduces conductor size but then requires use of a buck converter to get back down to 12vdc for standard DC fixtures such as 12vdc charging ports, USB ports, lighting, etc.
36 and 48 volts will be avoided simply because, while convenient, finding components while traveling can be a challenge. The auto and trucking industries are fairly standardized on 12 and 24 volt systems and so parts on the road and in other countries should be easier.

Originally Posted by kazetsukai

I haven't heard of any LFP that will do 7000 full cycles.

The spec sheet says 7,000 @ 80% DOD. While I understand that marketing "fudges" things (I'm a business major) even at 5,000 cycles it would be over 13 1/2 years and cutting the claim by half to 3500 cycles is STILL 9.5 years.....twice the warranty and coincidentally twice the time we plan to use the rig off grid.

Originally Posted by kazetsukai

Here's an example, really. You need an extra moderating device to prevent your alternator from blowing up charging it...

Yes, these are the "devices" I mentioned. While I'm not sure we'll employ an extra alternator as that's a decision that will be made after the rig is completed and on the road for evaluation, we will be wiring it for such an installation. I can see it being useful for long term stays in winter conditions where we're moving a lot and the sun is occluded. But we're not planing on operating in such conditions as a norm so the occasional use of the genny to top off batteries when there is no sun or wind is okay with us.

Originally Posted by dzl_

Some of the things you've said--specifically the 7000 cycles bit--make me think its possible you are considering buying from or have bought from a fraudulent company I am aware of,.....

The seller I am looking at isn't presenting themselves as a manufacturer, just an importer and reseller. The cells aren't 18650's but rather prismatic cells. I've seen the internal structure (via non compensated third party) as well as several performance evaluations (again independents) and am quite impressed.
However, being a business major, I know what depths fraudulent marketers will go to so I will send you a message with the name and a link.

[HamSkoolie]

Originally Posted by kidharris

Hook up the dead battery first, then the good battery. True or false? I think, maybe, hooking the ground to the engine then just becomes a way of trying to ensure a good ground between the starter and battery?

Just did this yesterday with my 30 year old jumper cables that were manufactured for military vehicles back before they went to the Army dog proof "NATO cable" with a polarized connector. These things are designed to jump start a TANK and are basically welding cables long enough that yesterday I parked BEHIND the F150 I was working on and had plenty of cable to reach between the batteries.


So here's the deal, from a formally trained mechanic (both civilian and military schools) and the former "owner" of 120 prime movers.
Connect the dead battery first then connect the POSITIVE to the good battery. Connect the ground to EITHER the negative terminal of the good battery or a GOOD GROUND.....these days finding a good ground in the engine bay, that isn't in a place that it could get into the belt(s) can be difficult. It used to be you could just hook to the bumper but even those are plastic coated these days.
The only purpose for not going to the good battery ground was to avoid a spark that could potentially cause a hydrogen explosion. But if you've vented the area there is no such worry.


Never forget, the average person is pretty dumb when it comes to auto mechanics (well anything really).....and half the people are dumber. Standard operating procedures are written for those people because they don't understand the systems and dangers.

[kazetsukai]

Originally Posted by HamSkoolie

The only apples to apples way to compare Wh (kWh keeps the number reasonable) cost in any system designed for long term use is to compare LIFE CYCLE capability. ...

While I don't disagree, this is really value provided per dollar. Many folks want to know what they'll get with their money _now_, and dollars over energy capacity is a valid metric by which to make an educated decision. Imagine a battery tech with half the energy capacity that lasts 50 years without breaking sweat, life value eventually doesn't really matter if the capabilities don't live up to needs 'or up front cost is prohibitive.

Originally Posted by HamSkoolie

We haven't settled on a bank voltage yet which is the only reason they aren't already on hand. I'd prefer to keep the bank at 12vdc but that would entail large conductors. 24vdc reduces conductor size but then requires use of a buck converter to get back down to 12vdc for standard DC fixtures such as 12vdc charging ports, USB ports, lighting, etc.

Here's what I really don't get... why are people so adverse to buck converters? I feed several 12V fuse blocks with a dozen appliances using buck converters, its not like you need one for every appliance. I don't see the problem at all... people with large battery banks are making themselves headaches (with the MPPT, Inverter) by insisting on a 12V bank voltage _in my opinion_.

Biggest drawback I see to higher voltages is that it sort of takes alternator charge off the table,

[dzl_]

Originally Posted by kazetsukai

While I don't disagree, this is really value provided per dollar. Many folks want to know what they'll get with their money _now_, and dollars over energy capacity is a valid metric by which to make an educated decision. Imagine a battery tech with half the energy capacity that lasts 50 years without breaking sweat, life value eventually doesn't really matter if the capabilities don't live up to needs 'or up front cost is prohibitive.

Here's what I really don't get... why are people so adverse to buck converters? I feed several 12V fuse blocks with a dozen appliances using buck converters, its not like you need one for every appliance. I don't see the problem at all... people with large battery banks are making themselves headaches (with the MPPT, Inverter) by insisting on a 12V bank voltage _in my opinion_.

Biggest drawback I see to higher voltages is that it sort of takes alternator charge off the table,

I may or may not be the only one, but I love these debates/discussions of battery bank voltage. It probably receives much more attention than it deserves but there is a good bit of nuance and tradeoffs with whichever choice is ultimately made. And I find my perspective shifts a little bit, and I have new small 'ah hah' moments most time this gets rehashed.


I (currently) agree with you that people overstate the downside of a buck converter--and I used to be, and currently still partially am--one of those people.


I think--for me at least--part of the resistance is a logical frustration. Part of what draws me to higher voltage is the marginally higher efficiency in some respects. Needing to use buck/boost converters can wipe out or even reverse this small efficiency advantage. Still we are only talking about a few % one way or another.


A second negative I see is marginally more complexity. But I think this is often overstated, the additional complexity of adding one or even a few buck converters to the system is not a big deal in the realm of things.


But still, I can see the logic of preferencing 12v for small to medium-small systems.

[HamSkoolie]

Originally Posted by kazetsukai

Many folks want to know what they'll get with their money _now_, and dollars over energy capacity is a valid metric by which to make an educated decision.

As long as the decision is educated and the ongoing costs are understood and acceptable. For instance, if you need X watts in a package weighing X pounds and occupying X space it might be worth it to pay more per kWh in order to meet that spec.

Originally Posted by kazetsukai

... life value eventually doesn't really matter if the capabilities don't live up to needs 'or up front cost is prohibitive.

There does seem to be a big disconnect with Americans when it comes to paying more up front. It's the life blood of the auto industry.....just $599 down and $599 a month and you can drive off in this nice new XYZ car.......what they don't tell you is that you're loan will be upside down until the last 6 months and if it gets wrecked, your fault or not, you're going to still owe thousands.
CASH is KING for a reason, well at least to those of us who understand its power.

In the business world where it's a cost of business, that's a different equation but cash is still king.

Originally Posted by kazetsukai

Here's what I really don't get... why are people so adverse to buck converters?

No aversion here, just looking at simplicity and spares. With a 12vdc bank and no buck converter there is one less single point failure possibility and thus one less spare part. It's also easier to add a single 12vdc storage battery into a 12vdc bank.
We will probably go with 24 though and a buck converter supplying the DC bus bar.

Originally Posted by kazetsukai

Biggest drawback I see to higher voltages is that it sort of takes alternator charge off the table,

Higher voltage banks can still be charged via alternator using a device designed specifically for the job. We will likely end up with a separate alternator for house battery charging just to add another level of redundancy. Just as we will probably run our 8 solar panels as four parallel sets though 4 charge controllers just to ensure loss on a panel has minimal impact.

[john61ct]

24V even 48V alternators are a thing, in fact where the innovation is happening, balancing engine loading propulsion vs bank charging, see Wakespeed and APS.

But of course most vehicles these days aren't too flexible, mechanically wrs space available

nor electrically in jurisdictions mandating fuel economy.

And costs quickly get unreasonable compared to normal OTS gear.

[kazetsukai]

Originally Posted by dzl_

Part of what draws me to higher voltage is the marginally higher efficiency in some respects. Needing to use buck/boost converters can wipe out or even reverse this small efficiency advantage. Still we are only talking about a few % one way or another.

From my perspective, the whole DC side to my system is around a 80W draw (computer, NAS, NVR, lights...). Maybe 200W or so when the pump kicks on. Compared to the system as a whole... whatever efficiency losses I'm seeing in that conversion aren't a drop in the bucket they're a square inch or so of the condensation forming on the outside.

I setup an internet relay two weeks ago to get signal from over the hill we're on. Pair of 35Ah AGMs, Victron 100V/20A MPPT, a 12V 4G router, point-to-point wireless powered by 24V PoE. The 12V -> 24V boost converter arrived late, so I powered the PTP with a tiny 300W PSW inverter while I waited for it to arrive... before/after subbing the inverter out for the boost converter is night and day:


(To be fair inverters are generally at their highest efficiencies at high load, this load was very sippy.)

Forget cabling losses, if you compare the efficiency gains by the inverter only having to step up from 24V/48V rather than 12V, and the gains you see when you only have to run a single MPPT which itself doesn't have to step down as much to meet bank voltage, whatever you lose on the DC side with buck/boost converters isn't significant. (On large-ish systems that rely heavily on an inverter and/or has a ton of panels.)

Originally Posted by dzl_

But still, I can see the logic of preferencing 12v for small to medium-small systems.

Absolutely.

[kidharris]

Originally Posted by kazetsukai

" aren't a drop in the bucket they're a square inch or so of the condensation forming on the outside."

LOL. That's pretty clever.....but there are flaws in the logic....time, temps of water and air, and relative humidity....the condensation can continue to produce water over time and the condensation on the outside can vary depending on the RH and temps, a drop however has somewhat defined limitations. Note: "a drop in a bucket" is not all that well defined as a comparison...how big/full is the bucket? is the drop all of the water in the bucket? what is the ratio of the surface area of the bucket to the volume of water? All we really know is that there is at least 1 drop in a bucket... is the comparison of 1 drop to the unknown volume of the bucket or an unknown volume of water in a bucket?

Sorry, just killing time....avoiding going outside,,,too cold... too windy ,,,too much work... dread the results...too many dead batteries in my life...this is part of my version of humor?

[kidharris]

Originally Posted by kazetsukai

I setup an internet relay two weeks ago to get signal from over the hill we're on. Pair of 35Ah AGMs, Victron 100V/20A MPPT, a 12V 4G router, point-to-point wireless powered by 24V PoE. The 12V -> 24V boost converter arrived late, so I powered the PTP with a tiny 300W PSW inverter while I waited for it to arrive... before/after subbing the inverter out for the boost converter is night and day:
Attachment 62089

How is the "internet relay" thing working out? I think this might be a topic that interests a lot of skoolie/rv/back country people. How to get/improve cell/internet reception. Please PM me if you don't want to go public.

[dzl_]

Originally Posted by kazetsukai

From my perspective, the whole DC side to my system is around a 80W draw (computer, NAS, NVR, lights...). Maybe 200W or so when the pump kicks on. Compared to the system as a whole... whatever efficiency losses I'm seeing in that conversion aren't a drop in the bucket they're a square inch or so of the condensation forming on the outside.

Forget cabling losses, if you compare the efficiency gains by the inverter only having to step up from 24V/48V rather than 12V, and the gains you see when you only have to run a single MPPT which itself doesn't have to step down as much to meet bank voltage, whatever you lose on the DC side with buck/boost converters isn't significant. (On large-ish systems that rely heavily on an inverter and/or has a ton of panels.)

Good comment all in all, I agree with most everything (based on your context--and I think your context (most thirsty power consumers being on the AC side of the system) applies to most people building fullsize buses).


I want to hone in on the bolded part of your comment, because I think its an important point. Context. To some extent what makes the most sense will come down to your specific system design. If you've got a lot of 120V or 240v high power kitchen appliances, A/C, electric heat or electric water heater, a few % inefficiency on the DC side will be a rounding error, and counterbalanced by the factors you laid out.



For a more minimalist, low power build (as seen more often in short buses and other vehicle conversions) the DC consumers can often be the biggest consumers, and the inverter might be a seldom used or on demand nicety rather than an always on necessity. In which case the calculation would be weighted differently. But in the big picture, While I admittedly obsess over efficiency, I think these considerations are a small concern compared with other practical considerations like overall cost, inverter size, battery bank capacity, BMS selection. If you've got a large Array 12V is ridiculously cost inefficient compared with 48V or even 24V.

[kidharris]

Originally Posted by dzl_

Good comment all in all, I agree with most everything (based on your context--and I think your context (most thirsty power consumers being on the AC side of the system) applies to most people building fullsize buses).


I want to hone in on the bolded part of your comment, because I think its an important point. Context. To some extent what makes the most sense will come down to your specific system design. If you've got a lot of 120V or 240v high power kitchen appliances, A/C, electric heat or electric water heater, a few % inefficiency on the DC side will be a rounding error, and counterbalanced by the factors you laid out.



For a more minimalist, low power build (as seen more often in short buses and other vehicle conversions) the DC consumers can often be the biggest consumers, and the inverter might be a seldom used or on demand nicety rather than an always on necessity. In which case the calculation would be weighted differently. But in the big picture, While I admittedly obsess over efficiency, I think these considerations are a small concern compared with other practical considerations like overall cost, inverter size, battery bank capacity, BMS selection. If you've got a large Array 12V is ridiculously cost inefficient compared with 48V or even 24V.

Thanks for the summary, I was not getting their point.

[john61ct]

There should be no relationship necessarily between average Ah consumption per 24hrs

from the bank at 12V

and the size / type of vehicle.

The real distinctions are between

off-grid vs powered sites

mostly-solar vs genset often running

aircon used or not, electric stoves/range/heating, vs propane/other FF burned

LFP bank vs lead

You could have a dozen inverters installed, and still only use them for 10% of your total Ah per day consumption.

A mostly solar setup could have all the mod cons and comforts, far from minimalist in fact 10x as sophisticated and costly electrickery setup

in order to consume 80% less total Ah per day.

Originally Posted by dzl_

If you've got a large Array 12V is ridiculously cost inefficient compared with 48V or even 24V.

This is a head scratcher to me, if you mean array of panels, I've no idea why you would think so.

[dzl_]

Originally Posted by john61ct

There should be no relationship necessarily between average Ah consumption per 24hrs

from the bank at 12V

and the size / type of vehicle.

The real distinctions are...

Your right, its not a concrete relationship, but it is a correlation/generalization.
My observation on this site is that most people building full size buses on this site for full time use tend to build like they are building small apartments or conventional AC centric RV's in terms of appliances and consumers, whereas its common with shortie builds, truck builds, etc to go more minimalist. Its just my observation, there are many exceptions, and your distinction is more precise in many ways. But don't dwell on it, it was just an example of how different design parameters lead to different design choices.

This is a head scratcher to me, if you mean array of panels, I've no idea why you would think so.

Yes, I mean solar array.

Look at the price of charge controllers. For a good brand (i'll use Victron as an example) you pay a lot of $$ for high amperage controllers.

Say you have a 2400W Array, not massive, but sizeable. @12V you need a 200A charge controller, @24V you need a 100A charge controller, and @48V you need a 50A charge controller to capture all of the potential energy, slightly less if you overpanel a bit.

With Victron's options and pricing that looks like:
$1600 @ 12V
$800 @ 24V
$550 @ 48V

The specifics will differ somewhat with the quirks of each brands sizing and the specific array size but the principle is the same. Victron just happens to be the brand I'm most familiar with.

[john61ct]

Well for a mobile array I always reco one SC per panel anyway to optimize efficiency from a well matched panel,

and it's Victron whose excellent low pricing makes that practical.

75/10 and 75/15 often can be had for under or around $100 each

True going to a 24V bank gets double the watts, but the savings there is IMO not enough of a factor to depart from the 12V default.

It's the 48V units that get expensive to get the equivalent quality, features and conversion efficiencies.

[HamSkoolie]

WOW.....
I have come to realize that there is one more user I should just see their name and skip to the next post.

[Rwnielsen]

Well, I went ahead and ordered 16, 200Ah, 3.2v batteries (AliExpress) which will give me a 400Ah, 24v bank. I also bought a couple step down transformers, one for the water pump and one for the CDH heaters (Amazon). I plan to mount the xfmrs adjacent to their loads. Some time soon Ill get another for the lights and TV and then just play it by ear. I'm still waiting on the shipping cost of my solar panels. Spendy day.