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Battery Bank - Performance Test?

E

EasternPromise

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Joined
Oct 18, 2020
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73
Greetings,

Dumbass newb here. I've found myself in an off grid situation and playing catch-up.

My specs:
9kW Solar array ASL/CanSolar,
48V battery bank - 24x 2V Surrette deep cycle lead acid
2x Magnum Energy 400W 120/240V inverters

I'm trying to ascertain the state / degradation of the battery system. After a cloudy day I had it plunge down to 46V which if I understand correctly is the danger zone.

How do I test what state it's in and how well are the batteries performing?

Thanks all.
EP.
 
Without knowing specifics, 46V is about as low as you want to go over the course of about 20 hours of discharge. That's very roughly the 50% point.

If flooded lead acid (FLA), check specific gravity on all 24 cells after fully charged and in float mode for about 2 hours. Document them.
  1. What are your charge controller voltages set to? Bullk/absorption? float?
  2. How old are the batteries?
  3. What model batteries?
  4. DO you have a means of seeing Ah or Wh pulled from the battery via the inverters or a separate battery monitor?
  5. Do you know what your daily consumption is? Charge controllers often keep a log of daily kWh harvest.
Rolls batteries are awesome, but they don't last forever.
 
Thanks.

1. 63.3 EQ (bulk?), 60.3 Absorb, 54.6 Float
2. Batteries are 5-6 years old
3. S-1459 deep cycle wet lead acid. I need to check gravity on all units. Thanks for reminder.
4. Evening and overnight pulling between 6-12 amps. Daytime use can spike to 60+ if we have a dishwasher, laundry, kettle, toaster, etc. going
5. 2x Midnight Solar 250 controllers, 1x Midnight Solar 150 controller. Tried going into logs but couldn't pull daily data. Getting lifetime, etc., but can't find daily draws.

Thanks again. All new in this and a bit overwhelming.
 
EasternPromise said:
Thanks.

1. 63.3 EQ (bulk?), 60.3 Absorb, 54.6 Float
2. Batteries are 5-6 years old
3. S-1459 deep cycle wet lead acid. I need to check gravity on all units. Thanks for reminder.
4. Evening and overnight pulling between 6-12 amps. Daytime use can spike to 60+ if we have a dishwasher, laundry, kettle, toaster, etc. going
5. 2x Midnight Solar 250 controllers, 1x Midnight Solar 150 controller. Tried going into logs but couldn't pull daily data. Getting lifetime, etc., but can't find daily draws.

Thanks again. All new in this and a bit overwhelming.
Click to expand...

SG should be checked about 2 hours after fully charged and held at float. You should suck in and expel electrolyte 2-4 times before taking a reading. Document all 24 readings and record the date. Important to see changes over time.

Only add purified or distilled water when fully charged. If cells are not fully charged and plates are visible above the electrolyte, add just enough water to cover the plates and charge.


You have 54kWh of storage. It should be able to hold the 60A current for 10 hours before you hit 50%.

I'd stick with 63.0eq, 60.0V bulk. 54.0V float. Not big changes, but consistent with this:


Read that cover to cover for flooded cell batteries. Pay particular attention to the portion concerning equalizations.

For your charge controllers, compare the lifetime production between two consecutive mornings just before charging starts.
 
Anecdotally, I sense the bank is underperforming. Will test for gravity and look into equalization as well as compare the production - but there is no way I'm getting 10 hours of 60amps before hitting 50%. I'm seeing the charge crash overnight under limited use: less than 10A/hr.

I've noticed the batteries are a bit swollen, not much - but enough to notice. The manual claims some bloating is normal, but I wonder if they've been abused in the past - would that be an indication?

Lastly... and I apologize for the dumbassery of the question: I'm seeing different battery voltage charts all over the place. Some cite 50% at ~46V and others at ~48V, etc. How do I know what' accurate for my setup? I saw my reading at 44.6V the other morning and flipped my lid.

Thanks again...
 
My s-605 6V units have been abuse mercilessly, and they show no bloating, but some might be normal. I have some Trojan T-1275 12V that function very well, but they'll a little puffy on the side.

The problem with voltage is it's a crappy indicator of state of charge. Since the "standard" current for a battery is determined by its C20 rating, the voltage is pseudo-linear with a mostly constant slope... sorta. A fully charged battery resting voltage sitting 24 hours after its last charge should be around 51V. 46.4 is about halfway to true empty at 42V when discharging at the C20 current. Yours C20 is 56A.

Until you get this sorted, I would look to conserve power. Use your max power items only between 10am and 2pm or if you're producing enough solar to cover it. Ensure the batteries get fully charge and into float mode every day and stay that way for as long as possible.

At 5-7 years, they may be within sight of end-of life. At 50% DoD, you have about 1400 cycles:

1603260165926.png

That's 3.8 years. At that point the battery is only 80% of rated capacity, and each time you discharge to "50%" it's actually MORE than 50% since the battery has deteriorated, so your cycle life deterioration accelerates.

At 5-7 years, you could easily be down to 60% of rated due to accelerated deterioration.

Failure to maintain them meticulously can also shorten their life. Deeper discharges may make it even worse.

Checking SG 2 hours after float has been maintained will help determine if the individual cells are equally (un)healthy, or if you have problematic cells.

Another check in the morning shortly before charging starts will also show any disparities and help identify weak cells or establish they are all equally (un)healthy.
 
Ok,
So I've measured and recorded the gravities as follows:

Cell#Gravity
11190
21185
31210
41190
51200
61210
71175
81210
91180
10900
111175
121200
131175
141185
151160
161185
171225
181205
191200
201190
211200
221205
231185
241200

This was at 99% charge after about two hours resting in float mode.

They're all underperforming save for cell #17. Cell #10 is clearly the weak link. Is it common for one cell to significantly underperform in a string that works in parallel and is of same year/make? Is there potential for equalization to remedy cell #10 issue, or safe to assume I should try to replace the weakest link here.

I'll do another data set in a few days. Sun is sparse these days and am feeling the propane pinch.
 
Since you have individual cells, why not try to recharge cell #10 individually?
Obviously a power supply with CV/CT modes would be ideal.
A solar panel would produce Isc with no limit on voltage, so you would have to monitor.

Usually not recommended to replace cells in an old bank. But I suppose it would just not cycle as deeply?
If cell #10 doesn't recover, removing it and reducing nominal voltage settings from 48V to 46V would be one option.

Maybe another would be to get either AC or 48V DC supply and wire it to keep boosting that cell - a single cell active equalizer. To extend 10 hours discharge to 20, might need current equal to C/10? To do that well might need a supply with analog control, rigged to track another cell. That would be a development project. Maybe just regulated to target float voltage?
 
Thanks.

Since you have individual cells, why not try to recharge cell #10 individually?
Obviously a power supply with CV/CT modes would be ideal.
A solar panel would produce Isc with no limit on voltage, so you would have to monitor.
Click to expand...

Can I charge it while it's hooked up in series or do I need to remove it and do it standalone? It would mean killing the power in my house for a bit, etc., etc,.
Thanks.
 
EasternPromise said:
Thanks.

Can I charge it while it's hooked up in series or do I need to remove it and do it standalone? It would mean killing the power in my house for a bit, etc., etc,.
Thanks.
Click to expand...

No need to remove. Just need a power supply that is isolated. Any bench supply or PV panel would do.
Since this is lead-acid not lithium, don't need to watch as closely. It should rise linearly in time (excluding discharge due to house loads) so you can predict when it will hit target voltage.
 
I'm leaning to removing it from the bank and trying to recharge it on its own. I can't get a hold of a bench supply for a few days as our province is in crazy lockdown and the bank continues to underperform.

If cell #10 doesn't recover, removing it and reducing nominal voltage settings from 48V to 46V would be one option
Click to expand...

Do you just mean reducing what the bank charges at during bulk, absorption and float? Would I just use a linear calculation to adjust down to 46V - i.e.:

Eq.57.75
Bulk55
Float49.5

Thanks again.

I'm hoping to recover these batteries to a workable state. The 9KW PV provides enough juice during non-winter seasons but the bank has not been holding enough charge to maintain an overnight load and it's a pain.
 
Also... regarding recharging the underperforming cell. How much voltage would I optimally need to juice it with? I have a small trickle charger for a 12V batter but I suspect it's not enough. I appreciate your insights here as I'm not versed in this at all.
 
EasternPromise said:
I'm leaning to removing it from the bank and trying to recharge it on its own. I can't get a hold of a bench supply for a few days as our province is in crazy lockdown and the bank continues to underperform.



Do you just mean reducing what the bank charges at during bulk, absorption and float? Would I just use a linear calculation to adjust down to 46V - i.e.:

Eq.57.75
Bulk55
Float49.5

Thanks again.

I'm hoping to recover these batteries to a workable state. The 9KW PV provides enough juice during non-winter seasons but the bank has not been holding enough charge to maintain an overnight load and it's a pain.
Click to expand...
Yes, something like that.
Not exactly subtracting 2V from each, rather multiplying each by 46/48

I think mine (Sunny Island) starts with the nominal voltage I configure (48V default, 42 to 52V range allowed) and adjusts the others.
But if I go back and subtract 2V from nominal I'm not sure the others are automatically reconfigured.
I have 6V batteries not 2V individual cells, so only thing I could do is drop from 48V to 42V. If larger bank with 2V cells I could have started as high as 52V.

EasternPromise said:
Also... regarding recharging the underperforming cell. How much voltage would I optimally need to juice it with? I have a small trickle charger for a 12V batter but I suspect it's not enough. I appreciate your insights here as I'm not versed in this at all.
Click to expand...

A 12V charger may not be happy pulled down to 2V.
But you can connect a lightbulb in series with it to drop most of the voltage.
You could do that in situ, so no need to remove from bank.

Keep charging until it reaches absorption voltage and hold there a couple hours.
 
A 12V charger may not be happy pulled down to 2V.
But you can connect a lightbulb in series with it to drop most of the voltage.
You could do that in situ, so no need to remove from bank.
Click to expand...
I found a charger with a 6V option (NOCO G3500) and it appears to be charging. I'm not sure how to rig a lightbulb to it to reduce voltage. Will try this for a day or two and then pull it out of the bank if not seeing improvement.
 
Have a volt meter on the cell? That should show it coming up over time.

An old automotive headlamp might be 36W at 12V, 3A, 4 ohms. That's at full power. Momentary starting surge could be 10x, 30A, 0.4 ohms
If you connected a 12V charger in series with the light bulb and cell, current would never exceed 30A, might be dropped part way toward 3A.

store.propridehitch.com

Battery Charger - NOCO - GENIUS5 - ProPride Hitch

An integrated thermal sensor detects the ambient temperature and alters the charge to eliminate over-charging in hot climates and under-charging in cold climates.
store.propridehitch.com store.propridehitch.com

Doesn't appear to have an ammeter, so just have to watch voltage.
Says 3.5A, so after a day or two would have put in 200 Ah.
How many Ah was that cell? 1000 Ah? If so, give it a week or two.
Being a 6V charger may go to 7V or more eventually. Monitor and don't exceed absorption voltage for one cell.
 
Hi all.
So I've worked with Rolls and they've been great at helping me troubleshoot and get the bank back to operational through winter months. Spent some money on propane for the gennie - but that is what it is.

I've now isolated two very sulphated batteries and pulled them out of the bank. The bank performs much better at 44V vs. 48V with overnight charge maintained much better, and voltage not dropping off as much towards the morning. Admittedly, having more daylight has helped.

I'm now at a point of trying to recover the two isolated cells on a standalone basis. The gravities on both are below 1100.

As mentioned - I have the NOCO Genius5 charge and am struggling a bit to understand how to go about this without doing damage to either batteries or charger. Charger has a 6V option, so should I connect the two 2V batteries in parallel and monitor for cell voltage? For a desuplhation cycle, isn't the intention to overcharge for a while and see if the gravity recovers?

Thanks, and apologies again for the newbieness of the Qs.
 
Even with cells in series, that would be 4V battery and 6V charger.
I think you want a regulated voltage source (supply with both CC and CV modes) so you can charge 2V cell fully, then boost voltage to vendor's spec for equalizing.

Some people talk about a pulse charger that's supposed to knock sulfation loose, but I don't know about that. Could try vendor's recommendation.
 
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