Flooded Cell Vs AGM

[Ray,IN]

If your battery charger is not AGM friendly, add the price of a new charger to your total bill.

[Jim & Alice]

Yes, Daveh, please update us down the road on how this works out for you. I have some similar thoughts in mind for next year.

Jim

[reed and elaine]

Posted before on subject. We have a 9.6 kW-hr CALB battery bank (4 x 180 amp-hr batteries @ 12 V nominal in series, i.e. 16 cells in series for a 48 V nominal battery bank). We have had system in operation since June of last year and have had zero problems. We have been basically solar autonomous except for a few days in Spokane when we were in full shade and temperature was around 100. Normally we have enough solar/battery to run a/c but not those days without sun.

 

General wisdom seems to have each cell to be in float at 3.4 V but there are a lot of discussions about this on Aussie fora and on Cruising/Sailing forum (4000 posts in 200+ page thread). Lots of Aussies are using top/bottom balancing (arduous project) and then setting maximum voltage to be this 3.4 V per cell. Most systems used in OZ are 4 cell batteries (12 V nominal) and battery management system (BMS) may not be necessary. We do run a/c or microwave and BMS may be desirable (we do not run them simultaneously). Son (who designed/fabricated system) trialed the inverter and battery bank by running the a/c and m/w simultaneously for a draw of around 3.5 kW or .35C. It was interesting to watch the BMS monitor demonstrating the balancing of the individual cells, battery by battery. BMS may be prudent for battery banks of more than 4 cells. Jury is out on this at current moment.

Reed and Elaine

[Daveh]

Yes Reed, I need to reread some things but I was going to use 3.6 for the initial charge with all cells in parallell. As I understand the procedure you just let them hit that number and then stop, allowing then to settle back down to 3.4 and then just sit there all hooked in parallell for a couple weeks. That would be the top balance part. I do not thiink I will do the bottom balance. I will have very small didgital readouts on top of each battery, I will also use cell loggers to monitor the pack with low and high alarms.

[reed and elaine]

Daveh

 

Have read a few writeups on different fora of the technique of top and bottom balancing and it is apparently straightforward but arduous. Our BMS takes tod3.5 at absorb and drops to 3.4 V at float.. Apparently you do not want to get above 3.6 V per cell.

 

Reed

[Daveh]

Interesting article by technomadia about loss of capacity in Lifepo4. I have been planning on a lower charging voltage. Also, I agree with them that the environmental temp of the batteries shows up in the specs but seems to be ignored in practice except on the extreme ends. I am thinking of moving my batteries inside. http://www.technomadia.com/2015/02/living-the-lithium-lifestyle-3-5-year-lithium-rv-battery-update/b

[Jack Mayer]

If you read some of the boating forums and a few other places you will see that the ambient temperatures have been discussed fairly often. This is the problem with Lithium...it is still "experimental" for use in RVs for most people. Most don't want to pay the required attention to it and obsess over managing the batteries. Not that it is a whole lot of work....but you have to get it RIGHT. Or you throw most of the money out. So for most people an AGM bank - that you can totally "set and forget" is still a good option. I'll almost certainly run Lithium in our next coach, but it still requires some attention.

[Vladimir]

The cost is not hard to justify is you are getting old, have arthritis in both your hands and your knees. Yes, you can get down (with kneepads) and check the cells/fill when necessary, wipe, etc., but boy does that take the joy out RVing for that day. So if you can afford it, why not?

 

Barb

 

I replaced my wet-cell batteries at my solar house with AGM's two summers ago. I finally looked at them a couple of days ago. Yep, look good.

 

Barb, you forgot to mention battery acid burns in your clothes. I believe at one time every t-shirt I had came complete with a hole in it.

 

Granted I had 12 huge wet-cell batteries to fill and maintain. I would fill a shopping cart just with distilled water!!! Nothing wrong with wet lead acid batteries, except the time, energy, and acid burns in your clothes.

[skyking]

Read technomadia's report yesterday, they covered this topic very well on the lithium solar experience for 2 1/2 years.

[Jack Mayer]

To me, here is the bottom line......

 

1. If you are price driven there is no choice - it is wet cell golf cart batteries from Sam's/Costco. They work well, and should last 5 years or more if taken care of and not cycled deeply.
2. If you want "set up and forget" it is AGM. For brands, "choose your poison"...but Fullriver has AGMs with a good warranty, good reputation and significantly less cost than Lifeline. The AGMs have significant performance benefits over the golf cart.
3. If you are a hobbyist and want the benefits of the Lithium, and initial cost is not an issue, then the Lithium is probably at the point now that they are worth buying. Still not "setup and forget" but rational for most people that are "interested" in batteries and are willing to put in the work to set them up.

​The Lithium have significant benefits over all other battery types. If cost is prorated over lifetime then they are probably "around" the cost of AGMs. But you have to pay pretty close attention to them to get the most out of them. And you have to be realistic in actual field performance....the 80% drawdown many talk about is not what I'd do in practice. I'd design for a 70% drawdown. And I'd factor in the decline in the bank right up front...although that may be manageable.

[reed and elaine]

Not sure why folks believe you have to monitor and pay close attention to LFP. We have been solar autonomous (except for perhaps 5 days at 100 F in shade when we hooked into line power) for 21 months. Our son installed the system with a first class BMS which has worked superbly. I do amuse myself (being somewhat OCD at times) by watching the battery monitor to see how it is charging/discharging. We do watch the fuel level (as the EV folks call battery level) in W-hrs when we are in inclement weather or boondocking in shade (happens in rain forests) and we decide what energy management level we need to use.

Reed and Elaine

[Jack Mayer]

You have to monitor/test them to determine how fast they are declining. I suppose you could say the same on any battery, but you are more incentivised on an expensive bank like LFP. But you are right - other than that they don't really need any real attention if properly set up. I assume yours are in an environmentally "friendly" location? I edited my post above to be clearer.

[Daveh]

Veryy gradually working my way through the 4000+ post thread on LiFePo4 at CruiserForum. Although we have talked on this board about the efficiency in charging lithiums, I was reminded by that board that this another area where the cost efficiency of LiFePo4 needs to be considered. I'd have to look back but I don't recall we considered this in cost comparisons.

 

 

The general consensus is that LFPs are 95% efficient, so if you take 100Ah out of a cell, you need only put 105Ah back to restore it to the same SoC. Subject to Peukert adjustment, of course.
Lead acids, by comparison, are only 80% efficient. Plus they require an often lengthy absorption phase, whereas LFPs do not.

[Jack Mayer]

That has been mentioned someplace, Dave. It is a consideration for those really wanting higher performing batteries.

 

A close cousin of that point is "how" are you getting power back in.....solar is all well and good. And is typical. BUT, if genset charging how powerful of a charger do you have available to you. It is no good to have a fast charging/"take all the power you can push" battery bank if you are charging with a 45 amp charger.

 

A discussion of components best suited for LFPs is an interesting discussion to have.

[Yarome]

A discussion of components best suited for LFPs is an interesting discussion to have.

 

X2. That would make for a good new thread. We can talk all you want about the performance benefits of LFP's, but what's required in the "backbone" to really take full advantage of those benefits?

[Daveh]

I certainly am interested in that discussion. As I said, right now I am working my way through the cruiserforum LFP thread. As part of that process I am cutting and pasting to a word document those posts most relevant to our RV purposes. I then hope to go back through once more and narrow things down and organize by issue. Off the top of my head the issues are (1) wiring--parallel vs series (2) battery monitoring or management systems (3) appropriate charge voltage settings for different types of equipment i.e. shore, alternator, solar, and (5) how to determine the battery state of charge with LFP's together with the best charge cycle lengths.

 

They do have some discussion of specific equipment choices but much of it deals with items we would not be interested in such as marine motor alternators. They do discuss specific brand battery management-monitoring systems but most of that discussion focuses on whether there is even a need for battery management, as opposed to monitoring, in smaller applications..

 

As far as I know, Jack's proposed new thread would cover new ground especially in the RV industry. As an additional starting point it would be good to know the equipment set up of those already utilizing LFP batteries. I have had some correspondence with Bill Joyce on this issue. My actual retirement is next week so as of right now I have the batteries and some unopened equipment boxes.

[dreamstreamer]

We installed four GC-2's three years ago, with the Flow-Rite watering system. Basis for the watering system was to water lower (difficult to access) batteries. Watering system turned out far better than we expected. No more acid-eaten rags or clothes. No potential exposure to chemicals each month. Watering requires ten minutes max monthly. Water in batteries restores to uniform heights across all cells. Quick-connect fittings are easily reachable yet out of the way.

 

The lithium batteries constraint on cold charging isn't unique - our PDI Intellipower shows very low charge rate when batteries below freezing. When we use our genset (winter NC sun can be weak) after an hour of low current input, the charge rate starts ramping up automatically. Fun to watch the effects via the Tri-Metric monitor. Rest of the year, our 250watts panel keeps batteries well-charged.

 

I am price-sensitive. The GC-2's were much lower cost for me, even with two watering manifolds. Not really so much a difference about maintenance, spending ten minutes every month to squeeze the bulb and put the kit away. Annual maintenance is identical, checking all connections, insulation, and case condition.

 

We'll go GC-2's again, or the tall scrubber batteries (L-16's?) next time. Currently thinking at least another two-three years. We'll see.

 

Interesting thread, excepting a snarky comment. Thanks all for so much interesting info. Great forum, eh?

[Daveh]

Here is a piece of Lithium specific equipment------ http://www.progressivedyn.com/pdfs/lithium_battey_chargers_lit.pdf. Sounds like they do away with the absorption and float whichmight make sense. The 14.6 voltage cut off will fry your batteries though. For right now the appropriate LiFePO4 charging equipment for small applications seems to be the higher end stuff that gives you complete freedom to avoid factory presets.

[Jack Mayer]

I agree - you want a charging system that can be totally tailored by the user.

[Jim & Wilma]

X2. Progressive is promoting the use of the BMS as the charge manager. I think of the BMS over voltage and battery bank cutout relay as a safety device to protect the batteries and as such shouldn't be used in this fashion - you end up with only one level of protection.