Author Topic: Replacing my gel batteries  (Read 973 times)

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DamonHD

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Replacing my gel batteries
« on: September 09, 2017, 04:29:46 AM »
It doesn't seem nearly long enough ago since I bought my ~400Ah of 12V gel batteries for my off-grid system.

http://www.earth.org.uk/expanding-off-grid-PV-system.html

A year ago I wondered if I'd killed them a year ago, and I'm still wondering.  Anyhow it might be time to bite the bullet and replace them.

Given that loads are low (from less than 1W average for my core server load, to ~16W when taking networking gear off-grid to maybe 60W peak when powering my laptop occasionally) any sort of battery would supply the discharge current.  The primary aim is to keep my server off-grid through winter, and take other loads off too as above where possible.

I have a nice Morningstar SS-MPPT-15L charge controller for the primary array, and a cheap Chinese PWM controller in parallel for a small amount of 'extra' PV.

Question: AGM or gel for the replacements?  I know the gel should have the longer service life, but I wonder if chucking up to 15A+ peak charging current at it is what is finally killing it off, and if AGM would be more resilient?



Rgds

Damon

 

Simen

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Re: Replacing my gel batteries
« Reply #1 on: September 09, 2017, 05:12:45 AM »
Go for a 12V LiFePO4 bank. :)

You could manage with half the Ah, without sacrifice lifetime vs. LA-batteries...
I will accept the rules that you feel necessary to your freedom. I am free, no matter what rules surround me. If I find them tolerable, I tolerate them; if I find them too obnoxious, I break them. I am free because I know that I alone am morally responsible for everything I do. - (R. A. Heinlein)

DamonHD

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Re: Replacing my gel batteries
« Reply #2 on: September 09, 2017, 05:38:34 AM »
Thank you.

I'm not against LFP at all, as you see, and I'll eventually do that alongside many more kWh grid-tied for my house I hope, but for now there doesn't seem to be a good choice of solar LFP controllers*.  In fact, many of the BMSes seem to be totally proprietary and opaque.

Eg something that is MPPT and will work with my 60-cell PV panels and won't blow up with excess available input power!

But please show me that I'm wrong: I'd be happy to take that route.

Rgds

Damon
« Last Edit: September 09, 2017, 09:57:46 AM by DamonHD »

Simen

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Re: Replacing my gel batteries
« Reply #3 on: September 09, 2017, 09:47:36 AM »
I agree; there are not many (if any) solar-controllers there that really supports LFP - but most lfp-batteries would do ok with standard controllers set to 14.4V CV, as a proper controller would keep the voltage at 14.4V until the battery draws only a few amps. The BMS in the lfp-battery should manage the balancing just fine, but might struggle a bit if the cells are badly out of balance. A simple solution would be to connect a CV source for some hours, once a month, to let the bms fine-balance the cells.

I've run a 12V, 110Ah lfp battery in my caravan for a couple of years now, connected to a 15A MPPT controller and 160W of panels, and i checked the balance of the cells a month ago, and they were spot on. There is a constant load of 7Ah/day, year round (a smart-home controller and an AP) - and higher when i use the caravan. :)
« Last Edit: September 09, 2017, 09:54:11 AM by Simen »
I will accept the rules that you feel necessary to your freedom. I am free, no matter what rules surround me. If I find them tolerable, I tolerate them; if I find them too obnoxious, I break them. I am free because I know that I alone am morally responsible for everything I do. - (R. A. Heinlein)

DamonHD

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Re: Replacing my gel batteries
« Reply #4 on: September 12, 2017, 01:02:12 PM »
No more opinions?

In my situation is there any significant difference between gel and AGM?

Rgds

Damon

Bruce S

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Re: Replacing my gel batteries
« Reply #5 on: September 12, 2017, 02:12:06 PM »
Damon;
Have you thought of other battery chems? OR are these the most cost effective available?
Writing a BMS using a arduino should be child's play for you.

I'm still using my NiCDs and am getting ready to bring up another 40Ahr of them. I have gone back and re-done the packs into 11batts/setup , makes for less voltage drop and closely matches the charging regime for the solar chargers.

Hope this doesn't muddle the mix further.
Bruce S
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DamonHD

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Re: Replacing my gel batteries
« Reply #6 on: September 13, 2017, 12:02:13 PM »
Hi Bruce,

I just don't think that I can get good 60-cell MPPT into any other manageable chemistry at the moment.

Next round yes, when my Morningstar controller will be old hat and out to pasture along with me!

But again, please show me I'm wrong!

Rgds

Damon

Bruce S

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Re: Replacing my gel batteries
« Reply #7 on: September 13, 2017, 12:59:57 PM »
Damond;
In my thinking, the charging profile for the MPPT using 60-cell for 12Vdc and a good set of NiCDs (recycled or new) would be very similar to the AGM style LA batts.
There is still quite a stigma about NiCds but in reality the NiCDs are very safe with someone who won't go throwing them in the fireplace.
In your case, since I don't know if you have a good source for used NiCDs , going with AGM is probably your best bet. I do have several of the AGM work had just lying around 6Vdc 7Ahr , these are nice little units and will probably be used in front of my NiCDs once I've had time to sort them out.
I can say for certain AGM are used in all the UPSes I've had the fun times of working on. APC, Eaton, MGE all use AGMs . This is includes the units with 110Vdc on the buss.

Hope this helps
Bruce S 
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DamonHD

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Re: Replacing my gel batteries
« Reply #8 on: September 13, 2017, 01:25:34 PM »
Thanks!

Damon

Mary B

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Re: Replacing my gel batteries
« Reply #9 on: September 14, 2017, 03:46:55 PM »
Plop a decent sized lead acid on the charge controller then run the lithium BMS off that...

DamonHD

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Re: Replacing my gel batteries
« Reply #10 on: September 15, 2017, 02:29:08 AM »
I sorta kinda was doing that before.  But still, should that new LA be gel or AGM?  B^>

Rgds

Damon

mab

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Re: Replacing my gel batteries
« Reply #11 on: September 15, 2017, 05:31:24 AM »
My vote would be agm, although I'm not sure I have enough experience of gel to make an informed decision. My agm is still going 12+ years after I bought them 2nd hand, although I did follow joestue's (?iirc) advice and watered them a few yrs ago which helped, and getting the hydro running means they've been operating mostly as standby/ surge for a few years which is what they were originally built for.

DamonHD

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Re: Replacing my gel batteries
« Reply #12 on: September 15, 2017, 09:30:22 AM »
Yes, making the bank last 12 years would be good: we'll be well into Lithium-air or something by then!

Thanks

Damon

PS. Keep the ideas coming!

clockmanFRA

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Re: Replacing my gel batteries
« Reply #13 on: September 16, 2017, 04:00:41 AM »
Hi Damon,

Just returned from your neck of the woods in London, spent most of my time at traffic lights. haha.  Also got funny looks from the locals with my very French Normandy mud covered 3 year old Toyota, when I parked at my clients. Note to self,...... remember to take wheelbarrow for the Parking charges next visit !!!!!

I haven't commented on your batts, as there are a lot of very wise guys here that have oodles of more brains and experience.


However, .... I thought that I would share my last 10 years of experience with used/second hand AGM's, (real ones with soaked matt plate separators) and Sealed Lead Acid, SLA.

This summer I purchased and installed over a ton of New SLA batteries, they were called marine types Ultra deep cycle.

http://www.ebay.co.uk/itm/4-X-12V-110AH-Deep-Cycle-Battery-Numax-XV31MF-Leisure-Caravan-Marine-Boat-/191830670926?hash=item2ca9ffbe4e

2017 my Installation is now ....  a 48v 1300ah battery system, strings of batteries with copper plate/strap inter links and main 16mm battery cables are all just about the same length.


Firstly ..... I had tested 12 of those New SLA  for the last 5 years and they had all behaved very well and staying remarkably stable with at rest voltages and loading voltages. In the old photo below there are 8 up the top on test.
Up top as they only weigh 25kg each, lighter than the equivalent ah AGM's


Secondly ..... The Photo is 5 years old showing my test installation, ....... My previous used/second hand AGM's MARATHON, and those Blue ones in the Pic, forgotten there 4 letter name, were bad bad. In every day use Lasted between 1 year and 5 years, then they would no longer hold more than 12.2v after 24hrs rest period.

Most would loose a cell, either the first or the last, as the plates inside had only 6 -10mm clearance, and any buckling would have the cell rise slightly and connect with the main link bars, and that was that. And yes I took a couple apart to look see. (but folks remember there is ACID in there, in the matt separators).

The exception is those yellow POWERSAFE (Hawker Siddley) they have behaved well, five years down the line.

Those Used Second hand YUASA 6v 160ah SLA have also behaved very well over the past 5 years. The only drawback is there 6v and therefore need some careful cable connections. 


Thirdly...... I got fed up with constantly monitoring those used/secondhand AGM's, but being short of large amounts of cash, found that NEW SLA cost about the same as the so called refurbished AGM's, In the Uk anyway. Hmm, this was becoming a no brainer, but what New make was the best? at the best cost? and best weight?


Fourthly......... and importantly for me, was a comment from 'Oztules' ........
 
"Lets be clear, there is no need for a monster battery or an expensive battery, better to use golf cart ones that will last 5 years, and replace them every 5 years.
6x220ah American batteries can be found for $200, so a 24 battery bank will only be $5000 ( you will probably get more years than that as they will rarely be discharged beyond 25%... and that should give 3000 cycles)
Stylish expensive cells ( whilst I like them very much) are not necessary to produce a better system."



So hence with me going down the Leisure battery route, but I deliberately never discharge beyond 10%.

So far my testing and monitoring has revealed some interesting points, especially as I have moved down the OzInverter route, with the  OzInverter back charging and the AC coupling, where the battery bank does not have to be so massive as the GTI's feed directly into the OzInverter created AC output MINI GRID so the battery bank is not being heavily drawn upon.


Damon, Just my opinions and observations on a Simple, Robust and very Cost Effective solution that suits my situation.

 


   
« Last Edit: September 16, 2017, 04:09:00 AM by clockmanFRA »
Everything is possible, just give me time.

OzInverter man. Normandy France.

3off Hugh P's 3.7m Wind T's (9 years).  .. 5kW PV on 3 Trackers, (5 yrs) .. 9kW PV AC coupled Used/SH GTI's, on my OzInverter created Grid, and back charging with AC Coupling to the OzInverter to my 48v 1300ah batteries.

DamonHD

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Re: Replacing my gel batteries
« Reply #14 on: September 16, 2017, 06:32:36 AM »
Many thanks for that view!

I've adjusted the thresholds up a long way just now to try to be kinder to the battery bank, and I may do more
subtle stuff like raising them further in prolonged dull periods:

http://www.earth.org.uk/expanding-off-grid-PV-system.html#LESS_DoD

Right now that has pushed my bank from being in an apparently 'OK' state to 'VERY LOW', and the system should draw much less juice from it until the SoC rises significantly.

(BTW, when people ask me if I miss ever having owned a car, your experience of parking and charges is one of the reasons not!)

Rgds

Damon
« Last Edit: September 18, 2017, 12:36:16 AM by DamonHD »