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totaldla · 05-20-2017, 01:30 PM

I've been pondering a large lithium-iron (the safe type) battery pack that would be housed inside the trailer (Black Rock 20RD), likely under the bed. I've done a lot of Googling on the battery technology, but I'm most concerned about the safety issues, if any. BTW, the reason for "inside" is it makes it easier to keep the battery temp within usable range.
Any thoughts on this?

Here is a link to the batteries: https://evolveelectrics.com/collections/lithium-batteries/products/calb-100ah

WownFlutter · 05-20-2017, 02:26 PM

I'm not sure if the link I'm opening via mobile is the same as what you are looking at, but that is only a 3.2v cell so you would need 4 of them to make a 12v-ish battery system...just an FYI in case you may have thought you found a good cheap way to get lithium batteries into your RV! Something like this would be more suitable as a ready to battery pack

https://evolveelectrics.com/collecti...enerdel-ec4s8p

totaldla · 05-20-2017, 07:04 PM

Yes, it takes 20 of those batteries to make a 12v 500AH array.

I wouldnt consider this with any other lithium chemistry, as the risk of fire, small as it may be, bothers me too much.

brulaz · 05-22-2017, 06:13 AM

- You will need some sort of battery management system with LiFeP, either built-in or home-brew.
- IIRC they will be destroyed if you attempt to charge when below freezing, but they can be discharged.
- They are still very expensive.

The main advantage is that LiFeP are very light.

But if weight is not a problem, a cheaper alternative for a sealed indoor battery is Firefly's Carbon Foam batteries. 116Ah and you can get 1000 cycles down to 80% DOD. These folks sell both: Firefly Oasis Battery - Carbon Foam AGM

These Fireflys can take a lot more abuse (long term partial charges) than AGMs.

For an outdoor FLA battery, Trojan's T105RE is a 225Ah 6V GC2 that can also give you 1000 cycles when taken down to 80% DOD. And they're a lot cheaper than any of the above.

totaldla · 05-22-2017, 08:39 AM

I'm attracted to lfp because
(1) weight
(2) no maintenence
(3) fast charge
(4) 80% usable capacity
(5) very long lifetime

Most FLAs are only rated to 50% dod, I'm surprised the T105E shows 1000 cycles at 80%.

brulaz · 05-22-2017, 09:07 AM

Quote:

Originally Posted by totaldla

...
Most FLAs are only rated to 50% dod, I'm surprised the T105E shows 1000 cycles at 80%.

Not sure where that 50% comes from. It's quite conservative.

How much you draw down depends upon how many cycles you want your battery to last. The T-105RE is exceptional in that regard: www.trojanbattery.com/pdf/datasheets/T105RE_TrojanRE_Data_Sheets.pdf

According to the life cycle chart of my cheaper US battery 2200XC, I can only get 675 cycles when drawing down to 80%. If I only go down to 50%, I can theoretically get 1150 cycles. But the T105RE gets ~1650 cycles at 50%, apparently because of some secret sauce, "SmartCarbon", that they add to their premium battery lines.

Batteries age also, no matter how you use them. Maybe 8-10 years is the usual max for a well maintained FLA battery, although I have heard of better. So if every year you want to draw down your batts maybe 30-60 times for a typical RVer, that's only 300-600 draw-downs over ten years. Even my relatively cheap US2200s should be able to do that, going down to 80% each time.

Full-time boon-dockers, of course, have different requirements.

brulaz · 05-22-2017, 03:02 PM

Quote:

Originally Posted by brulaz

- You will need some sort of battery management system with LiFeP, either built-in or home-brew.
- IIRC they will be destroyed if you attempt to charge when below freezing, but they can be discharged.
- They are still very expensive.

The main advantage is that LiFeP are very light.

...

Forgot another big advantage of LiFeP: they have very little voltage sag under heavy loads, no matter what the DOD.

The FLA GC2's that you can discharge down to 80% DOD and still get a respectable # of cycles, will have a much bigger voltage sag under high loads, especially when they are close to that 80% DOD.

If you go to a FLA Marine style battery, the sag is not so bad as they are designed for high loads. But going over 50% DOD will seriously reduce their lifetime.

Apparently AGM's and that Firefly Carbon Foam battery I referenced above are not as bad as FLA in terms as V sag. But the LiFeP are the best AFAIK.

Some Inverters can handle V sag better than others. As I have 4 FLA GC2s, V sag was a problem with my old inverter. When upgrading to a new 2000W inverter I was looking closely at how low the V could be before the inverter cuts out.

totaldla · 05-23-2017, 08:30 AM

Brulaz - all good points. One other positive for LFP - they charge fast.

LFP technology for a 12v 500AH setup is:
- 3x more expensive ($2600 vs $840 for T105s)
- 2.5x lighter (170lbs vs 420lbs for T105s)
- roughly 3x faster charging
- 3x longer lifetime when cycled to 80% DoD
- LFP requires no maintenance, is not corrosive, requires no venting.

LFP potentially could be "install it and forget about it" for the life of the coach.

The technical downsides to LFP is narrowed operating temperature range, and they dont "float" well.

brulaz · 05-24-2017, 03:01 AM

Guess a lot depends upon your usage patterns. If we were full-time boondockers, the long lifetimes of LiFeP would definitely be important. And as we don't use a generator, just solar, fast charge times are also less important to us.

Not sure about your pricing. If you just want the LiFeP cells, you might get 20 100Ah cells for about US$2000. But if you're concerned about safety then you want an excellent BMS with your LiFeP cells. That Bruce Schwab site I linked to before sells complete LiFeP systems with BMS, as well as the Carbon Foam batteries. The LiFeP systems are quite a bit more expensive than what you have priced (2x?). Other packaged systems I've seen are similarly high priced.

A home brew battery bank with BMS will definitely be cheaper, but some technical expertise is required. From what I understand, just ensuring that the initial cell voltage levels are the same (before applying the BMS) requires a decent voltmeter and power supply. People do it, but it's not for everybody.

totaldla · 05-26-2017, 08:37 AM

Packaged systems seem to be expensive for what they offer. BTW, "balancing" is important to do once to achieve maximum capacity, but it is not a safety issue. I think the term "BMS" gets over-hyped as LFP are actually easier than lead-acid to charge and maintain. The only "trick" appears to not float them - which programable chargers can do.

The only downside to LFP is the upfront cost IMO.