Totally off topic: Anyone interested in a group purchase of LifePo4 cells?

[PrivatePilot]

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Right now it has 200 amp hours of AGM. I have been thinking about adding 300 amp hours of lithium and a 50 amp DC/DC charger and calling it good.

With 200ah of AGM you’ve really only got 100ah usable before you get into damaging discharge territory, so with the setup I’m looking at you’d be basically tripling your available amp hours.

Sounds like it would be exactly what you’re looking for in the end. I’ll keep you in the loop with pricing and such if you’re interested. I may be pulling the trigger on the cells in the next 3-4 weeks.

 

[GreyGhost]

View attachment 58599

Just flashed across FB. 3.6kwh for $4000.

As per above post I’m building around 3kw for around $1K or under. Again, DIY vs prefab pays.

That's entertaining marketing. Yes, I may be able to lower my energy bill so it is technically correct but 3.6 kWh of arbitrage will never pay off the $4000 capital cost yet alone time value of money. You might save $0.40 per day so maybe you would break even in 27 years if it was still working and you ignored time value of money.

 

[PrivatePilot]

View attachment 58602

Now I know where some of the home brew batteries I’m seeing on FB marketplace and the likes are coming from. Some of them are so terribly constructed though it’s evident a lot of people doing these tear downs really don’t have the faintest clue what they’re doing aside from “lithium battery good”.

 

[woot]

Now I know where some of the home brew batteries I’m seeing on FB marketplace and the likes are coming from. Some of them are so terribly constructed though it’s evident a lot of people doing these tear downs really don’t have the faintest clue what they’re doing aside from “lithium battery good”.

The bonus with buying packs is that I didn't have to do any welding. Just had to cut away all the stuff I didn't want, folded it in half to make them fit better, connected my bms to the same spot that theirs was and wrapped everything in the biggest heat shrink aliexpess offers (which happened to be perfect) and used the old bus bars to connect 4 packs together.

It's definitely sketchy (I had a few big sparks even with my tools all wrapped in tape) but I trust my DIY as much as someone else's DIY or cheap batteries from China and it would have been $thousands to buy new as opposed to getting a battery and making profit.

 

[PrivatePilot]

What’s the highest ah’s you’ve constructed so far? One problem I can see with constricting high AH packs using small cells like this is balancing - I think the BMS I saw with the highest cell count function was still only 32 cells.

 

[woot]

What’s the highest ah’s you’ve constructed so far? One problem I can see with constricting high AH packs using small cells like this is balancing - I think the BMS I saw with the highest cell count function was still only 32 cells.

I've only built the one battery but had to do allot of reading.

more cells on your BMS is for going more in series which will give you higher voltage. The more in parallel will give you AH.

When cells are in parallel they are constantly balanced with each other. If the +'s and -'s are all tied together then power flows freely between cells and they equalize. Even when building batteries in series it is good practice to connect them first in parrallel to make sure they are all equal and then build your battery to the number of series and parrallel connections that you need.

depending on battery chemistry you probably need 4s or 6s to get to 12V but you need a high Amp discharge capacity on the BMS. it should be rated in both peak and continuous. If they only quote one then it is likely peak current.

32 cells in series will likely get you over 100Vdc

 

[PrivatePilot]

When cells are in parallel they are constantly balanced with each other. If the +'s and -'s are all tied together then power flows freely between cells and they equalize.

Yes, I understand setting up a series parallel setup, but having packs of series cells tied together without any individual balancing just just group balancing once they’re paralleled can be based on my knowledge….risky.

The concern from the way I see it is If one of the individual cells in a pack of (say, 10 cells) goes bad and you’re pounding amps into that series pack while charging the overall pack via parallel, the high cells will try to reach equilibrium with the lower/dead/dying cells and as a result create all sorts of heat issues through the bus bars. Enough heat and bad things start happening. Thing is the BMS may not detect this as if you’re using a 4s BMS with 4 packs of 10 Lifepo4 cells in series and then paralleled, all the BMS is going to see is 4 “cells” in its eyes, not 4 packs of 10 (actually 40) cells, and therefore has no way to manage that really well.

Maybe I’m overthinking it, but when you’re getting into hundreds of AH’s, careful balancing of each *individual* cell seems to be Imperative, not just balancing banks of series cells then paralleled.

 

[GreyGhost]

Yes, I understand setting up a series parallel setup, but having packs of series cells tied together without any individual balancing just just group balancing once they’re paralleled can be based on my knowledge….risky.

The concern from the way I see it is If one of the individual cells in a pack of (say, 10 cells) goes bad and you’re pounding amps into that series pack while charging the overall pack via parallel, the high cells will try to reach equilibrium with the lower/dead/dying cells and as a result create all sorts of heat issues through the bus bars. Enough heat and bad things start happening. Thing is the BMS may not detect this as if you’re using a 4s BMS with 4 packs of 10 Lifepo4 cells in series and then paralleled, all the BMS is going to see is 4 “cells” in its eyes, not 4 packs of 10 (actually 40) cells, and therefore has no way to manage that really well.

Maybe I’m overthinking it, but when you’re getting into hundreds of AH’s, careful balancing of each *individual* cell seems to be Imperative, not just balancing banks of series cells then paralleled.

Does anyone do individual cell balancing? I thought even ev's only looked at strings of a certain length. Small cell size means you would need hundreds or thousands of channels in bms each monitoring voltage and temp. Probably not a bad idea to look at your pack with an ir camera while charging on a routine basis though. That would quickly light up areas requiring investigation.

 

[backmarkerducati]

For the application maybe Lithium Iron aka LFR aka LiFePO4 might be a more user friendly alternative. Not as energy dense as the colbalt etc. versions but more user friendly and less firey. They can be had in 12v versions... (have had one in the bike for a long time now).
***
Nevermind, I missed read the title, you are already looking for these.... duh on mu part!

 

[crankcall]

I’m interested in all this dialogue, we have a young lady that has just installed a 48v motor in a 30ft sailboat , the batteries from her engineer are all ganged 6v lithium Po to produce 48v . Her plan is solar panels and a wind turbine to create extra electricity when away from the dock . It’s been a 14k investment in a 4K boat ….

I’ve just ordered two Victran super cycle AGM 12v batteries which allegedly can be taken to 0 charge and recover , I used a carbon foam battery setup (essentially AGM) for about 5 yrs and through poor battery management killed it


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[crankcall]

We are planning a sprinter van conversion in the next yr or so and I’m testing the Victran agm batteries in another application to see if they will work in my van app. Roof deck will be solar panels , a wind turbine can be deployed when parked and I’m aiming for infinite time away from a charger .


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[GreyGhost]

We are planning a sprinter van conversion in the next yr or so and I’m testing the Victran agm batteries in another application to see if they will work in my van app. Roof deck will be solar panels , a wind turbine can be deployed when parked and I’m aiming for infinite time away from a charger .


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Just leave the turbine up while driving and you will have infinite range.


I know, I know, perpetual energy and all but so many people don't get it I have little faith for our future.

 

[crankcall]

The biggest thing I'm finding in all these systems , your can Thomas Edison your way through this , or contact a systems engineer that will "sell" you what you need , and its REALLY expensive.
Having got out of a bunk one night in a motor coach to find you couldnt put yiour feet on the floor, a battery bank of lead acid batteries was 'boiling' since the Xantrax charger pooched , we evacuated into the grass and started pulling out plugs

 

[Scuba Steve]

We are planning a sprinter van conversion in the next yr or so and I’m testing the Victran agm batteries in another application to see if they will work in my van app. Roof deck will be solar panels , a wind turbine can be deployed when parked and I’m aiming for infinite time away from a charger .


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I found it cheaper and easier to buy what I wanted from Winnebago than try and build it (been there never going back) prices are about 30% less after exchange if you buy from the southern states New item by Scuba Steve

 

[PrivatePilot]

Does anyone do individual cell balancing? I thought even ev's only looked at strings of a certain length. Small cells mean you would need hundreds or thousands of channels in bms each monitoring voltage and temp. Probably not a bad idea to look at your pack with an ir camera while charging on a routine basis though. That would quickly light up areas requiring investigation.

Actually, yeah, after doing some more reading, it seems that larger banks using series/parallel only balance the packs in parallel. I guess the key to this is that each individual cell in the series packs however must be reasonably balanced and matched *before* assembly.

@woot if you don't mind me asking how much did you pay for that giant pack? I'm guessing that was off an old TTC bus or something?

Victran super cycle AGM 12v batteries

Ouch, only 300 cycles at 100% DOD. It seems like they *can* do it, but you're still penalized pretty seriously for having actually done it.

 

[crankcall]

My hope is I never hit 100% often, if ever , but I’d like to know it’s not fried if I do .
Best intentions often come with penalty’s.


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[woot]

@woot if you don't mind me asking how much did you pay for that giant pack? I'm guessing that was off an old TTC bus or something?

$400. I was told it was off of a Ottawa transit bus. I think it was from a Hybrid bus.

 

[Mad Mike]

I'm looking to build a mega Lithium Iron Phosphate battery bank for our camper. I want to eliminate the need for running our generator for overnights while boondocking while still being able to run our little 2200BTU air conditioner overnight for sleeping, charge my laptop, run the electric stove, etc.

I've hunted down some good prices on cells from a very reputable dealer, and ordered a BMS today from one of the manufacturers (JK) on AliExpress.
The cells look like they'll be around $600-$800 from the source I'm looking at for high 280ahx4s.

I may opt for 200ah cells to save a few bucks if something good comes along price wise. 200ah will do what I want, but 280ah is just that little bit better for not a lot less price.

They also have more traditional sizes - a 100ah pack (with a full 100ah ussable, unlike lead acid where only ~50ah is actually usable) could be built for around $400.
Anyone interested, respond here.

My goal is to save some coin on shipping - the more batteries ordered together the better the shipping deal will end up being.

I'm curious -- if you drive an EV, why not look at an inexpensive way to tap its battery system? Seems to me a small backup gennie would provide you with some peace of mind as it could both power your camper and recharge your EV in a pinch?

 

[PrivatePilot]

I'm curious -- if you drive an EV, why not look at an inexpensive way to tap its battery system? Seems to me a small backup gennie would provide you with some peace of mind as it could both power your camper and recharge your EV in a pinch?

I’ve done exactly this (for both camping as well as whole-home backup during outages, but…

- Often when we’re towing with the Volt the battery is near or fully depleted, so using the car for power would mean that the engine would be starting and stopping reasonably frequently. I have my doubts that this is efficient from a fuel consumption standpoint versus the generator, and in some campground situations nobody camped nearby is going to want to hear and engine starting and shutting down every 5-10 minutes either, regardless of how quiet the Volt engine is…..it’s still going to be something that would certainly drive *me* crazy if I was in a tent nearby, so I’m sure it would bother others. Hence also why I can’t use the generator either.

- The only way to recharge the Volt is with a shore power connection, which of course if we had, I’d just run the AC from that instead.

I should do some testing (perhaps this weekend) out of curiosity and see how long the Volts battery, fully charged, will run a 300-400w AC load before it switches to engine. But I can’t imagine it would be more than 8-10 hours, so this would be a 1 night solution, beyond which we’re back to no AC power again without noise.

 

[crankcall]

I did not enjoy camping near anybody with a gen set, the deisel pusher buses idling are a close second.
I'm told by people that do this for a living the electronic chargers (BMS) are the usual culprit in a short life system, and failing to understand how heat affects the system. The guy we are talking with builds systems for people that will spend 150+ days running a number of electric systems continuous off grid , at the end of it it may be more than we can afford ( company is OceanPlanet in Maine) . We may have to dumb down our expectations.

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