Replace battery or bank?

RandomJoe · April 2013

Looks like I have one T-105 going bad. I'm going to get the bank fully charged then equalize then load-test but I expect I'll be buying at least one new battery if not just replacing the whole bank. I'm curious what others think about it...

I have a 48V system, 8 T-105s that were bought Feb 2009 so four years old. This morning it's been gloomy and I had a load on the bank - about 11A so no capacity problem. I had roughly 47.5V across the bank (from the Outback system - the three DC voltage measurements are all slightly off, CC or FNDC or inverter) which I was surprised to see that low but I was at 80% SOC so decided to just watch it.

A short while later it was down to 45V! Ouch... Grabbed the Fluke and measured each battery, 5.7-5.9 on each except one in the middle of the bank - 3.8V!

I switched back to grid, the voltages rose, and the low cell was only about 0.5V behind the others. I now have the inverter charging the bank at about 21A, voltages are all up between 6.6-6.8V on each battery with the low one now 6.5V - only 0.15V behind the low end of the others. So it doesn't appear to be a *dead* cell. I'll go ahead and try equalizing and load-testing, can't hurt, but I'm also looking at battery options, which leads to my question for today.

I've been planning ahead for bank replacement, of course it will have to happen *sometime*. I had thought I would switch to L16s when I do, for a little more capacity, but I wasn't planning on doing it quite this soon. I have $1800 saved toward a new bank, and could shuffle some funds around to go ahead and do it, or I could just buy a single T-105 to replace the bad one.

Granted, the rest of the bank is likely nearing end of life and the new one is going to see a relatively short life, but that's just $150 now and a very quick and easy swap-out vs (at a quick glance online) $2800 and possibly new battery cables.

On the other hand, another battery could be ready to die tomorrow...!

For those with battery banks, if you were at 4 years old would you just replace the one bad cell or go ahead and replace / upgrade the whole bank?

BB. · April 2013

Re: Replace battery or bank?

I like to go with the risk/reward method...

The $150 is not even sales tax these days (at least in California). And what is the risk if your bank dies--Is it going to take a week to get new batteries+wire them up and leave you at risk (losing $500 worth of food, $YYY worth of fuel to keep a genset going with an angry spouse at home while you are traveling for work, etc.)... Or is a "non-event"... Just go down to the battery shop, pay your money, and they come out on a truck in the afternoon...

Also, can you find a used battery for even less out of pocket cash?

-Bill

Cariboocoot · April 2013

Re: Replace battery or bank?

A). I wouldn't let the battery Voltage get below 48 to begin with. What's up with that?

. Check the SG on all; likely the lot of them need replacing - possibly due to chronic undercharging.

Four years is about 1 year shy of what a manufacturer would say you can expect. With that premature failure of one you can say goodbye to the rest in a hurry. Plug a new one in there and it will get dragged down right away.

Funny, but lead-acid battery systems could actually benefit from the intensive cell-by-cell management necessary with lithium types. I can see a line of 2 Volt cells, each with its own Volt meter ...

westbranch · April 2013

Re: Replace battery or bank?

What is the SG reading(s) cell wise? They might tell a slightly different story than Voltage alone does... Like Marc said, they may all be failing.

RandomJoe · April 2013

Re: Replace battery or bank?

Well, I certainly didn't intend for it to get below 48V! I was surprised to see the 47.5V, but it was also under a 11A load and down to 80% SOC so... Wasn't sure, I rarely run a very high load for any length of time, my loads tend to be light but constant. This morning I fired up a bunch of computers that don't normally run all at once.

Undercharging might have been an issue earlier in life, I initially had around a 5% charge rate, but added panels until now I could actually exceed 20% if no loads on a bright, sunny day. Normally the bank gets to float by noon though, and if I remember right I even extended the absorb time.

I was thinking similar thoughts on the BMS. I think I will put together another Arduino clone to monitor voltage across each battery (would be sweet to have each cell but that'd be tricky). I can put together the essentials of an Arduino for less than $4 in parts. Add a few more resistors for voltage dividers and calibrate. Only real cost will be how I transmit the data back to my automation system, I have some XBee wireless modules I've been playing with ($25 each) or I could use RS485 (free if I grab the ICs from some old control boards in my stash). Hey, another project to add to the stack!

Wouldn't really "manage" anything, but at least I could keep a running log of individual battery performance. (Or the computer could - it's much better at that sort of thing that I am!)

I am fortunate in that my battery bank isn't any sort of critical. If it dies, I just stay on grid power until it's fixed. I do like to keep it operating though, and also use it for load-shedding during the summertime "peak month" period.

I'm not sure about battery availability, haven't been looking lately. We have a "battery warehouse" in town where I bought the first bank. They had a pallet of T-105s when I went there before. Don't know if they keep L16s on hand, but since lots of commercial equipment uses them I would assume so. Not sure about the "RE" versions, they might be harder to find. Warranty coverage would be the only issue, otherwise I don't know if the "RE" versions are worth the extra cost / reduced capacity.

I've never bought a used battery. Got a few for free - and they were worth every penny... :roll: Not sure where I'd buy used around here aside from something like Craigslist - and I'm too darn cynical for that. I just *know* I'm going to get ripped off!

Eric L · April 2013

Re: Replace battery or bank?

'm not sure about battery availability, haven't been looking lately. We have a "battery warehouse" in town where I bought the first bank.

I would bet there are quite a few battery distributors around OKC, and I would start contacting them and even visiting them, and once you have a couple of quotes on L-16s, bring them with you to the other distributors because they will sometimes negotiate on price, IME. FWIW, after some haggling like this I got 8 new L-16s for less than $1800 last year.

Photowhit · April 2013

Re: Replace battery or bank?

11 amp load at the batteries (48 volt) or 11 amp load at 120 off the inverter? even at 48 volts with the batteries at 80% SOC that is a very large load and I would expect substantial voltage drop. Not sure you have a huge problem, even at 48 volts with 4 year old batteries at 80% SOC(220 x .8=176 Amps) your drawing 16% of your capacity every hour with no thoughts to reduction of battery capacity. If it's 11 amps at 120 that's a huge load.

RandomJoe · April 2013

Re: Replace battery or bank?

It was 11A from the battery bank, or around 550W total load. I usually don't get that high for any length of time, and rarely go over it. Worse, I almost never run those kinds of loads completely off the battery bank, I usually run them at midday with good sun. So I don't have a lot of experience with how the bank reacts "normally" to those loads.

I usually never see the bank voltage drop below 48V, the only times I remember it doing so were last summer when running a mini-split straight off the panels at midday. Each time a cloud passed over the bank would be hit with a 30-36A load and naturally that caused a significant voltage drop - but they handled it fine for the (at most) few minutes before the cloud passed.

Looking through my database, it appears this sagging started 14 April - that's the first day I had <48V for more than a brief surge or for less than 6-8A (@120VAC) load. Hasn't happened every day, but on the 14th, 19th, 21st and today. There are even a couple 44V readings where the fridge started!

Have to admit I didn't even think about checking SG until it was mentioned here!

I do check it on occasion, though probably not as often as I should. I'll do so shortly.

Blackcherry04 · April 2013

Re: Replace battery or bank?

RandomJoe wrote: »

It was 11A from the battery bank, or around 550W total load. I usually don't get that high for any length of time, and rarely go over it. Worse, I almost never run those kinds of loads completely off the battery bank, I usually run them at midday with good sun. So I don't have a lot of experience with how the bank reacts "normally" to those loads.

I usually never see the bank voltage drop below 48V, the only times I remember it doing so were last summer when running a mini-split straight off the panels at midday. Each time a cloud passed over the bank would be hit with a 30-36A load and naturally that caused a significant voltage drop - but they handled it fine for the (at most) few minutes before the cloud passed.

Looking through my database, it appears this sagging started 14 April - that's the first day I had <48V for more than a brief surge or for less than 6-8A (@120VAC) load. Hasn't happened every day, but on the 14th, 19th, 21st and today. There are even a couple 44V readings where the fridge started!

Have to admit I didn't even think about checking SG until it was mentioned here! I do check it on occasion, though probably not as often as I should. I'll do so shortly.

I'd number them all, ck the SG's, find the low ones and move them around in the bank location, do a EQ and see how they react. I shuffle mine once a year and clean up all the connections. Some will tell you it makes no difference on Batteries in series. It probably doesn't on paper, in real life it does.

NorthGuy · April 2013

Re: Replace battery or bank?

Blackcherry04 wrote: »

I'd number them all, ck the SG's, find the low ones and move them around in the bank location, do a EQ and see how they react. I shuffle mine once a year and clean up all the connections. Some will tell you it makes no difference on Batteries in series. It probably doesn't on paper, in real life it does.

Depending on the setup, there could be temperature variations between locations.

RandomJoe · April 2013

Re: Replace battery or bank?

Equalizing has helped some. I got sidetracked today, didn't get to work on the bank until this evening. Loads were off it, so the panels brought it to float and held it there all day. I checked SG before EQing, then again after 1 hour of EQ. It's obvious there's a problem with cell 6C, but it is coming up. Don't know if it's possible to recover from something like this though.

When I first took the measurements, I was surprised to see such a spread between the other cells too, but looking at Trojan's info on the batteries they say not to EQ unless more than 0.030 out or below 1.235. Of course I had a few cells below 1.235 so the EQ is warranted, but otherwise (with the exception of 6C) the spread was still less than .030. The numbers look low compared to the numbers for fully charged in Trojan's brochure - 1.277 for 100% - but my bank has *never* read that high, even brand new. 1.250-1.260 was it for the original six batteries. The last two (#4 & 5 in the list below) were bought in Dec 09 - 8 months later - when I went from 12V to 48V battery bank. They were - and still are - a bit higher.

In the past I've never seen much variation in SG at all, I've also never EQed much. Usually just 15-30 minutes after filling with water to help it mix.

Now doing a second 1 hour EQ, see what that does.

I'll also note that it's not possible to get extreme precision with my hydrometer - only has markings every 0.025, have to interpolate between those marks. Wonder what one of those fancy digital models cost? (Only place I've seen one is in Trojan's data sheet!

) -- HOly COW! Just went searching. $2400 for a pretty basic one!

Cell
At Float
1 Hr EQ
2 Hrs EQ
3 Hrs EQ

1A
1.230
1.250
1.250
1.250

1B
1.250
1.250
1.250
1.250

1C
1.230
1.240
1.240
1.250

2A
1.225
1.235
1.240
1.250

2B
1.245
1.245
1.250
1.245

2C
1.230
1.230
1.250
1.250

3A
1.250
1.250
1.250
1.245

3B
1.240
1.250
1.250
1.250

3C
1.245
1.250
1.250
1.250

4A
1.250
1.265
1.265
1.260

4B
1.250
1.265
1.265
1.270

4C
1.250
1.270
1.260
1.260

5A
1.250
1.255
1.255
1.260

5B
1.250
1.265
1.265
1.270

5C
1.255
1.270
1.265
1.260

6A
1.230
1.240
1.245
1.240

6B
1.245
1.245
1.250
1.250

6C
1.150
1.190
1.190
1.205

7A
1.245
1.245
1.245
1.245

7B
1.240
1.250
1.250
1.250

7C
1.230
1.245
1.245
1.240

8A
1.245
1.245
1.245
1.245

8B
1.245
1.250
1.245
1.245

8C
1.245
1.250
1.245
1.245

Blackcherry04 · April 2013

Re: Replace battery or bank?

Don't be afraid to EQ for the time it takes, it could take 3-4 hours. Why don't you pull out the 8 lowest and work on them ?? Then slip them back in and do some more on all of them ?? Here is where it'd be nice to have a 12 V charger or a variable power supply where you could just work on one or two at a time with the EQ, you don't need a lot of amps, just the volts.

Cariboocoot · April 2013

Re: Replace battery or bank?

What BC said is a very good idea.

I'll guess that #6 is the one with the really low Voltage. Hate to say it, but that looks like collapsed plate/shorted cell there.

RandomJoe · April 2013

Re: Replace battery or bank?

I was thinking about doing that, I have all the 12V gear from the original setup and could even just reconfigure the FM80 for 12V since I obviously wouldn't have the 48V system in action.

Just finishing up a third hour of EQ right now, after the second hour some values had risen a bit more but the bad cell was still 1.190.

Updated the table above with the latest numbers. The bad cell came up more, all others are pretty much topped out. Hm, I may just hook the one bad battery to my variable power supply. Don't need to cook the others unnecessarily...

Blackcherry04 · April 2013

Re: Replace battery or bank?

I think Bill mentioned finding a used battery, I have 3 golf courses close by. They always have a bunch of 6v batteries they have removed this time of the year sitting around, they will usually sell one for the core charge. I guess always buy one new from Sams.

They actually look like they are doing ok, except for the one, The longest I ever went with a EQ was 18 hrs, as long as you control the temperatures you'll be ok. Use your power supply, that is the best thing I ever bought, I got a 0-50 amp and volt, it's a snake charmer. I use it off the Inverter and disconnect that string, pull that battery out of that string and hammer it. One battery will only take a few amps DC.

I take a paint pen and always number a bank when I commission it, it makes it easier to track each battery.

Once you get the SG's up, take a look at your charging regimen, your going to have to increase time or voltage or both.
.

RandomJoe · May 2013

Re: Replace battery or bank?

I went ahead with replacing the bank. The bad cell would come up some (but not nearly enough) with vigorous equalizing but would drop back off quickly with any load at all.

I bought Crown CR390s for replacements, which bumped me from 220AH to 390AH. Of course I knew L16-style batteries are heavy. It's one thing to "know" that, though - quite another to *see* it as you load almost 1/2 ton of batteries in the bed of your small (S-10) pickup...!

Got them home, wired them in, proceeded to reprogram the Mate interface. Good GRIEF there are a lot of different places to put the same information, between the inverter, charge controller and FNDC monitor. Had to break out the manual to make sure I covered them all...

The bank is now fully charged, all readings recorded (SG in all cells leveled out between 1.260 and 1.265) and the system is back to normal operation. 8)

Replace battery or bank?

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