3 Group 27s with some wiggle room? Or 4 GC2 Sardines?

[KendallP]

.
EDIT: Regarding Question 2 below, the guys in the first few replies got me thinking I can suppress my OCD and get by adding water with a watering system when I would normally just inspect. If they're full, I'll know it because they won't take any water.


The slide-out battery tray in this motorhome is designed for 3 group 27s. It currently has 2 new ones and a slightly older one that tests almost as new via they hydrometer. The tray can also probably fit 3 29s and maybe 3 31s. All with about 3/4" between them horizontally like so...

______
I_____I
______
I_____I
______
I_____I


The tray will also just fit 4 Deka GC2s in 2 vertical pairs thusly...

___ ___
I....I I....I
I....I I....I
I__I I__I
___ ___
I....I I....I
I....I I....I
I__I I__I


Each pair might have 1/8" of gap between them, left to right. And maybe 1/2" between the top pair and the bottom pair.

Also... the back vent caps are going to be very hard to check and fill without removing the front pair of 64 lb batteries... at chest level. There was a time when I could load an awkward, 120lb 4D in and out of a tight battery compartment solo, no problem, but... I guess I'm gettin' old.

The benefit of the GC2s would be...

1. 460 Ah vs roughly 300

2. Greater deep cycling durability / longevity

3. And easier to recover from progressive sulfation incurred by successive 50-90% charges.

That's if the tray can stomach an extra hundred pounds or so.

Questions:

1. How bad would it be if the 4 Dekas were sandwiched together with no gap between them?

2. How big of a boondocker does one have to be to remove a pair of GC2s every time one needs to check the electrolyte of the other pair? Let alone top them off...
.

[KendallP]

I just came across mena's signature. Still shows the L16s... and 740 Amp hours.

So then he had to have had 4 of them. That's almost 460 pounds of lead and plastic in a motorhome!

Peukert was definitely his friend.

I recall that they were the best fit for his basement battery box vs. 6 or 8 GC2s. The only downside to those tall batteries was enhanced stratification.

[KendallP]

pianotuna wrote:
KendallP,

IIRC mena66 did jump to LiFePo4.

That is my recollection as well.

He was a mild climate dweller / camper... and power boondocker. I had talked him in to a pair of L16 (if not 4) early on since he had basement space he was willing to use... and that worked very well.

Then he started looking into LiFePo4 when no one else was talking about it.

Haven't spoken with him in quite awhile. If he's still RV-ing, I imagine he's invested in a good amount of solar.

[pianotuna]

KendallP,

IIRC mena66 did jump to LiFePo4.

[KendallP]

Grit dog wrote:
Every time I read one of these threads I feel like it’s Groundhog Day or 50 First Dates, the movies. We’ve even got self proclaimed battery geeks arguing with other battery geeks about their terminology and definition of 6v vs 12v.
If this is what getting old and having a RV produces, I’m selling mine tomorrow!
This stuff ain’t that difficult and the OP already understands batteries, was just looking for some creativity about how to best fill his battery cabinet.

LOL

If ever there was a more astute post... I'd like to see it.

That said... I'm glad LFPs were brought up. I haven't been heavily active around here for many years. Shoot... it may have been 10 years since I last remember discussing the new LFP tech... which was WAY out of reach back then. mena66 had been looking into it.

And now it's to the point where the cost/benefit definitely works... for the right camper.

But yeah. If you think THIS is bad...

It ain't got nuthin' on the ol' PD v. IOTA converter days of yore.

I'm just getting to know some of the guys on this thread, but BFL13 and I brainstormed some discoveries on these forums that were not to be seen anywhere else at the time. Progressive sulfation or Progressive Capacity Loss (PCL) is probably the best example.

And pianotuna made a lot of positive contributions as well.

MEXICOWANDERER goes without saying... so long as you can decipher his poetic mix of sarcasm and high-tech engineering parlance.

I still find these forums to be the best around for some really top-notch tech info. Sometimes you just have to separate the wheat from the chaff to find it.
.

[KendallP]

time2roll wrote:
I only have two jobs. Although my side business is sporadic on-call that varies from very busy to minimal.

Yeah, I can piss way further.

🙂

That SOK looks pretty intriguing. Thanks!

[KendallP]

pianotuna wrote:
The top of the line LiFePo4 units do have blue tooth monitors integrated. At least some of the monitors do a state of charge.

The exact mechanism for SOC has never been made clear in any of the reading I've done. I do not think that it is necessarily voltage based--because the very best voltage based unit is the Smart Gauge--and it does not work with LiFePo4. That is speculation on my part. Coulomb counting? Maybe.

There are some batteries that tell porkies about their bms--saying it does have a cold weather disconnect--when nothing of the sort is inside the box.

If I were not a cold weather camper LI would be worth considering. But I'm not, and I'm no longer full time. SiO2 fit me like a glove. I'm set up to fit seven of them.

Yeah, Will Prowse seems to be impressed with this smart, budget Chins unit with heaters. Still a chunk of change, though.

[Grit_dog]

Every time I read one of these threads I feel like it’s Groundhog Day or 50 First Dates, the movies. We’ve even got self proclaimed battery geeks arguing with other battery geeks about their terminology and definition of 6v vs 12v.
If this is what getting old and having a RV produces, I’m selling mine tomorrow!
This stuff ain’t that difficult and the OP already understands batteries, was just looking for some creativity about how to best fill his battery cabinet.

[time2roll]

pianotuna wrote:
The exact mechanism for SOC has never been made clear in any of the reading I've done. I do not think that it is necessarily voltage based--because the very best voltage based unit is the Smart Gauge--and it does not work with LiFePo4. That is speculation on my part. Coulomb counting? Maybe.

Yes the BMS has a coulomb counter along with some voltage set points so that it never needs a manual reset.
I believe the charge characteristics actually make the charge level easier to track properly. Virtually no peukert adjustments or long absorption times.

[time2roll]

KendallP wrote:

time2roll wrote:
I found self assembly to be a fun project and saved a bunch of money.

I still work for a living. A lot.

Time is money... and more precious.

I only have two jobs. Although my side business is sporadic on-call that varies from very busy to minimal.

SOK has an app that should give capacity. Probably need two of these.

https://www.us.sokbattery.com/product-page/sok-12v-206ah-lifepo4-battery-bluetooth-built-in-heater

[pianotuna]

The top of the line LiFePo4 units do have blue tooth monitors integrated. At least some of the monitors do a state of charge.

The exact mechanism for SOC has never been made clear in any of the reading I've done. I do not think that it is necessarily voltage based--because the very best voltage based unit is the Smart Gauge--and it does not work with LiFePo4. That is speculation on my part. Coulomb counting? Maybe.

There are some batteries that tell porkies about their bms--saying it does have a cold weather disconnect--when nothing of the sort is inside the box.

If I were not a cold weather camper LI would be worth considering. But I'm not, and I'm no longer full time. SiO2 fit me like a glove. I'm set up to fit seven of them.

[KendallP]

You know... I'm so used to being Peukert centric. Capacity is king... and so forth.

But without my trusty calculator, I have to wonder if 200 Ah total / 180 Ah worth of usable power... just might equate to 215 or so. And would certainly be more than the current 142 Ah usable.

If yes, then the cost vs GCs is a wash.

Now with 100A of charge power, I would be at the recommended max, but... OK. So I don't get a gazillion cycles. I just get short generator run times instead. Boo hoo.

All that said... I imagine I would have a hard time stopping at just 2 - 200A LFPs.

Now... how do I tell SOC with these thing?

[KendallP]

time2roll wrote:
I found self assembly to be a fun project and saved a bunch of money.

I still work for a living. A lot.

Time is money... and more precious.

[KendallP]

BFL13 wrote:
Some days you can't pee a drop.

And some days you pee several drops without meaning to.

Or... so I'm told.

Yeah, almost 4 times the cost of a GC2 equivalent is not in the cards. LFPs look to be closer to 50% more per usable Ah... if a watering system is factored in. Not bad.

Looks like I could get 3 decent 100 Ah 12V units with 100A BMS each... for around $1,050. Maybe a hair less. This would provide a usable 270 Ah vs. 215 for 4-GC15s with watering system for about $650.

And I forgot... the current G27s are rated at only 95 Ah. So for three, that's about 142 usable. 270 would nearly double that.

[KendallP]

pianotuna wrote:
What is ESSENTIAL for LiFePo4, is having a proper battery management system. It must be able to do a cold weather disconnect at -4 F.

Thanks, Don.

Yeah, I don't have enough time on my hands to roll my own.

If I decided to go the LFP route, it seems to me that the solution would be to...

1. Mount the LFPs under the bed (if they'll fit)... which is over the current battery tray, so it wouldn't take a lot to drill a hole or two.

2. Kill the temp compensation of the Xantrex

3. Keep the float off while in storage during the hot summers

Not 100% set and forget, but not exactly rocket surgery either