August 7, 20196 yr Hi, I am mostly off grid (or at least should be). At the moment i have 490AH @ 48V. I started with AGM cells. They failed after a year and then decided to change to VRLA's. The specs of the VRLA's indicated that for my usage i could expect 16 years. I did not expect 16 years but did expect them to last a few years. After a year I already started getting failures. The supplier does not seem to be interested despite all of the information I gave them. I am considering going Lithium and i wanted to ask others about their experiences with Lithium? I have spent a lot on batteries and i dont want to spend more and end up in same situation in a years time. if you are using Lithium; how is your experience and how long have you been running on them? Will they be the final solution to my problems?
August 7, 20196 yr @andrew9484, You pose a very valid question. First off, I don't have LFP batteries (yet), but in planning my next system, this will probably be on my shopping list. Having said that, I am of the opinion that for very long life, the best bat is those very tall 2V cells. In the old days they were make of glass, so you could actually see what the cell plates etc looked like. I remember looking after a 48V bank for a telephone exchange in my vac work days in 1979! Measured SG with that bulb thingy and recorded it in a logbook. Those batteries will probably last a long as the exchange (>20years?). They must have cost a pretty penny then (and more today), but if you normalise the cost to a per year cost, they probably cost less that anything else on the market. The 2V cells banks will give you: - long life (10 -20 years), if maintained/looked after - lots of Ah to runs many things stuff items during the night - lots of exercise managing the bank!, but I'm sure you get auto watering kits these days - extremely high upfront cost (you need to buy 24 cells!) - need space & ventilation - Easy to add BMV, but useless if you don't have any Blue or Green + ICC equipment. - Failure of one 2V cell not critical, just remove cell and adjust changing regime accordingly. This will be the sign to replace the whole bank - Backache during install/moving this lot! With LFP you will get: - Ability to use most (80% of your Ah) - 10 years of life - Reasonable value for money, as LFP is slowly decreasing in price, despite our countries exchange rate woes. - no special room requirements, maybe just an area that does not heat up too much in summer - integration into Blue & Green + ICC is relative easy - failure of a bank in a multiple bank is not critical - can add more capacity at any time With all other types (AGM/VLRA), you get: - Lowest cost per Ah, but LFP is catching up - High cell failure rate (last approx 1-2 year, if lucky). Failure of one battery will render your bank useless! Just read all the horror stories here on PF - Need to ventilate room - Monthly maintenance (cleaning, watering & equalizing) - Easy to add BMV, but useless if you don't have any Blue or Green + ICC equipment. - Balancing easy via HA's - Can't expand bank after the first couple of months (6 max) i.e. don't mix old and new batteries Lastly, if your planning LFP, then you need to look into the compatibility of the LFP's BMV to "talk" to the Inverter. Inverters are pretty dumb devices, but i hope the next generation of them will "talk" directly to inverters, as well as management (e.g. Venus ESS , ICC etc) systems. With software you can do anything...but someone needs to write the damn code, and then management need to make it available at reasonable pricing (free upgrade) to the market. The jury's still out on this. The list above probably needs more input, I'm sure it will come with time....
August 7, 20196 yr @Sidewinder About terminology: VRLA - Valve Regulated Lead Acid. Simply means that it is sealed and hydrogen buildup is catered for via valves. Not meant to be topped up, so easy maintenance, but more limited lifespan than accessible cells. Easier to operate safely than open cells where hydrogen buildup has to be considered in the room design. You get VRLA batteries using all flavours of inner designs: AGM, Gel. You get them in 2 V blocks, 6 V blocks, 12 V blocks.... Flooded - you have access to the electrolyte, they're not sealed. More maintenance is possible. As with VRLA, you get flooded batteries that use AGM to contain the electrolyte, and you get flooded batteries that use Gel to contain the electrolyte. AGM - Absorbent Glass Mat. Battery electrolytes are kept in absorbent mats between the plates. Reduces the chances of acid spill, and offers a few other advantages in terms of performance and life expectancy. Most prevalent design on the market. AGM is a popular design for deep cycle batteries. Not all AGM batteries are deep cycle batteries. GEL - electrolytes are kept in a gel-like paste between the plates. Supposed to give more cycles due to less opportunity for hydrogen to escape, but will typically be more finicky in terms of float voltage, and will generally be able to give less current than a similar sized AGM. Regarding lithium - why do you really want the battery to speak to the inverter? The main reason would be to know the SoC, but why do you want to know that? It adds convenience, but personally I don't see it as a dealbreaker. My VRLA batteries can't tell me what their SoC is (with the exception of Northstar's ACE equipped batteries, though I've seen very few of them around), and the VRLA's silence has never bothered me. That said, my experience is in a pure DC environment, so my requirements might differ a bit. In theory the lithiums should give you much better cycle performance than most VRLA options, but the proof is in the pudding. I guess we'll have a better idea in a few years. About the 2 V cells - you do get unsealed 12 V blocks as well which you can top up when necessary, and they're generally cheaper than sealed options. But then you have to be careful of hydrogen leakage - that's why those old exchanges had dediacted battery rooms complying to fairly stringent ventilation requirements.
August 7, 20196 yr 27 minutes ago, Tacet said: hydrogen buildup is catered for via valves VRLA batteries usually have the ability to recombine the hydrogen up to a cetain point, so that the venting valves only opens if you exceed this capability (that's when you hear the whistling sound).
August 7, 20196 yr 11 minutes ago, plonkster said: VRLA batteries usually have the ability to recombine the hydrogen up to a cetain point, so that the venting valves only opens if you exceed this capability (that's when you hear the whistling sound). Yep, which is why the room requirements for VRLA batteries is simpler than for flooded cell batteries. Dry-out is still the main reason for VRLA failure, though; as you said, the recombination is only effective up to a certain point. That's where flooded cells have the advantage - they're refilled with maintenance.
August 13, 20196 yr On 2019/08/07 at 9:59 AM, Tacet said: Regarding lithium - why do you really want the battery to speak to the inverter? The main reason would be to know the SoC, but why do you want to know that? It adds convenience, but personally I don't see it as a dealbreaker. Absolutely agree with this. There have been some discussions recently on adding a BMV to Lithium batteries on which I initially agreed with, but upon reflection, the main benefit I see is to only get an accurate SOC. If one does not use SOC to do switching on your inverter then it only adds an aesthetic function. My Mecer...and I think most inverters do switching on battery voltage. After comparing, my inverter,s battery voltage is almost identical to the BMV voltage. Am I overlooking something here?
August 13, 20196 yr On 2019/08/07 at 9:59 AM, Tacet said: The main reason would be to know the SoC, but why do you want to know that? 1 hour ago, GVC said: Am I overlooking something here? The main reason you want the BMS to talk to the inverter is to stop charging and discharging when a cell is dangerously high or low. But this functionality is only half useful with a non-hybrid inverter. Let me explain. With a hybrid inverter, power can be "mixed", so if the battery says "please only discharge with 25A", then the inverter will feed up to 1250W (at 50V) into the AC side and the rest just comes from the grid. In an extreme condition, the inverter can switch to bypass and all your loads simply run from the grid. This allows the BMS in the battery to dictate the limits, and in the long run this means you're treating the battery well and extending its life. With an off-grid situation, or with a non-hybrid inverter, the BMS is not in charge of the discharge side. The loads are. The loads determine how much they are discharged with. If the loads exceed the battery's recommended discharge rate, it is left up to the battery to decide what to do. Most of them will allow you a grace period, and then they will throw the main contactor and switch off the DC power. In that way they still protect the battery, but in a rather harsh way (plunging you into darkness). With a hybrid inverter and comms, this disconnection can be avoided. It is still useful to have the inverter stop charging if the battery so desires. So the basic rule still stands: The battery/inverter connection is primarily a first level of battery protection, it allows the inverter/charger to back off and avoid the second line of protection: A disconnection. In terms of what a BMS should do, SOC is like the third item on the list 🙂 Many BMSes don't even do SOC (or voltage, or current, see my post above about the VE.Bus BMS and miniBMS).
August 13, 20196 yr I agree with the BMS, but my question is...what are the benefits of fitting a BMV to lithium batteries besides the more accurate SOC? Especially if one does not use SOC for switching.
August 13, 20196 yr 5 minutes ago, GVC said: ... what are the benefits of fitting a BMV to lithium batteries besides the more accurate SOC? From what I gathered, and I stand to be corrected: 1) If your inverter cannot use the BMV SOC data, then it is just for one's own info. 2) But if your inverter can use the data from the BMV then it is a very good idea to better manage the inverters "usage" of the bank. Like I set like when to charge the bank and to what SOC.
August 13, 20196 yr 6 hours ago, GVC said: I agree with the BMS, but my question is...what are the benefits of fitting a BMV to lithium batteries besides the more accurate SOC? Especially if one does not use SOC for switching. No benefit.
Join the conversation
You can post now and register later. If you have an account, sign in now to post with your account.