Recommendations to monitor individual batteries on my 90 kWh AGM Battery Bank

bryhan67

Can anyone recommend a good battery monitor system that can track the voltage from each individual battery? I have a 48V system that has 24 batteries at 2v each. Model is EnerSys PowerSafe DDm100-33 UPS Each of my batteries is about 290lbs.  That about 7,000 pounds of battery bank.  I would love to be able to view it on my computer and have data logging. My objective is to spot any problem batteries over time. Trying to keep the cost down to a few hundred bucks. I know there are good expensive monitors looking for something less expensive. I dont need to charge them individual but it would be a nice option.

I wonder if a BMS for LiFePo4 would work if I change the parameters to make max voltage 2.32. Maybe it could also help balance them once its fully charged. 

Also I have had no luck in finding a high amp 2v charger. my max voltage is 2.32v.  Any ideas how to bring up the voltage in one battery?

Anyone here using 2V batteries on their off grid system?

Leon20220701

you can use BMS with communication functions, then you can track every cell voltage clearly .

bryhan67

I could do a BMS but a 24 battery system tries to charge to 72 volt. Can anyone recommend a BMS only to monitor on the computer via WIFI?

Marc Kurth

I do not have a suggestion for Wifi individual cell monitoring, but I am curious what the cycle life rating is on these?

bryhan67

1800 cycles. I wonder what is a cycle? In i only use 25% every day is 4 days one cycle? 

BB.

It appears that your batteries are AGM Lead Calcium type... I did not find any information from the Mfg. about service type (deep cycle or float) and/or life (float life, cycle life).... And they are spec'ed for UPS usage (typically float/standby with few cycles).

Need to contact the Mfg. for those details (it appears).

If these are "float service" type batteries, they may have a deep cycle life of only "hundreds" of deep cycles at best. For a longer life, would need to limit discharge to 15% (to 25%?) state of discharge.

For UPS (uninterruptable power supplies), typically would be float service with only a few "deep cycles" in power outages.

If these are deep cycle type batteries that support down towards 80%-100% depth of discharge... The typical cycle life chart seems to be pretty much: based on depth of discharge... A theoretical cycle life may look like:

100% discharge = 500 cycles
50% discharge = 1,000 cycles
25% discharge = 2,000 cycles

Random Victron AGM "Telecom" (float service?) life:

https://www.victronenergy.com/upload/documents/Datasheet-Telecom-batteries-EN.pdf

Float design life @ 70ºF/20ºC 12 years
Cycle design life @ 80% discharge 500
Cycle design life @ 50% discharge 750
Cycle design life @ 30% discharge 1800

Here is a random Rolls AGM battery cycle life chart:

https://rollsbattery.com/battery/s12-240agm-re/

bryhan67

Makes since. Heat is bad too. I have a AC just for battery room/ It seems to help keep inverter and controller cooler. Gets 100+ deg here. 

bryhan67

Still looking for BMS recommendations for 24 batteries and WIFI or ethernet connection to internet
 

BB.

100F equipment room temperature is pretty high.... Anything you can do to reduce it (insulation, shading of windows, venting of hot air, possibly a bit of A/C --- Always a cost & design trade off because of the extra energy used by AC is not "really solar friendly").

In general with Lead Acid batteries, voltage drift between cells is addressed by controlled over charging (Equalize Charging). The light over charging does not damage the "100% charged" cells, and the EQ charging current will bring up the "weak cells".

For AGM batteries, a variation of EQ charging seems to be popular... EQ charging is the "normal charging voltage" (say 14.4 volts) held for 8-24 hours on an otherwise fully charged bank done once every 6 months. AGM batteries tend to say balanced better than flooded cell lead acid and may not even need EQ every 6 months.

2 volt lead acid batteries are very common for larger battery banks... However, lead acid BMS (battery management systems) seem to be rather "rare". Lead Acid batteries tend to be "more forgiving" of high and low voltages/states of charge whereas Li Ion batteries can be ruined by one transition/event outside of min/max specifications (voltage/stage of charge). Hence lots of BMS options for Lithium banks.

I have seen a few BMS for lead acid banks on the web... Here are a couple (I know nothing about them):

• https://eepowersolutions.com/products/battery-monitoring-systems/battery-monitoring-solutions-vla-vrla-nicad-systems/bms-icom-battery-monitoring-system/ (for 12 volt batteries up to 48 volts)
• https://eepowersolutions.com/products/battery-monitoring-systems/battery-monitoring-solutions-vla-vrla-nicad-systems/bds-pro-battery-cell-voltage-monitoring-system/ ("cell" based capable monitoring)

Just be careful with wiring up "per cell" battery monitors. Lots of small AWG wires with ability to get shorted and catch fire. In larger systems I worked on, we would use a resistor or fuse/fusible link per wire to protect against shorts/wiring faults for sense wiring.

-Bill

bryhan67

Thanks Bill for the info. I dis get a quote from EEpowersolutions but was out of my budget.  I do run a AC all day long and shuts off before dark. Temp stays down pretty good overnight. 

A BMS $100-500 mostly just monitor on my PC via WIFI with data loging is what I am looking for. Seems like the bad cells actually are highe voltage when charging then lower voltage at night when in use. Tricky to pick the bad ones out. 

Yes those little wires worry me. Do you have more details how to keep it safe? 

BB.

I would talk with the BMS mfg and see what they say...

There is fusible link wire--You could crimp that on the ends that attach to the battery connections. It is designed to act like a fuse:

https://www.wiringdepot.com/store/p/2497-JT-T-211F-18-AWG-Black-Fusible-Link-Wire-with-flag-8.aspx

The one I found quickly is $4.xx for a few inches of 18 AWG wire--Not cheap.

There are fusible resistors too:

https://www.elprocus.com/fusible-resistor/

It does depend on how much current the sense leads" draw. If it is just measuring voltage... It may be microAmps. You could even put a relatively high value resistor on the batttery connector and then, even if shorted, there is very little current flow and very little heat generatoed.

However, if you have "actively balancing" (pretty common on Li Ion battery BMS--Then you may be pass 1-2 amps (more or less) to balance cells. And you would need a fusible link/resitor/fuse large enough to safely carry the current.

Otherwise, using heat shrink or wire sleeving:

https://www.mcmaster.com/wire-protection-sleeving/

To protect insulation from cuts and random mechanical abrasion.

Used to drive an ~1953 GMC 1/4 ton pickup 40 years ago for work. The battery door (under passenger's feet) had a lock spring. And one day the spring fell off and right on top of the battery. Smoke and red hot steal--Got pretty exciting. Knocked the spring off the battery terminals and tossed the spring--And all was fine. But do that on a large solar battery bank--Lots of current and voltage available. Was always a concern for me.

But I don't work in the industry--So I don't know how they address the question (or if they just completely ignore the issue).

-Bill

bryhan67

Bill you seem to know what your talking about. What can I use to energies my inverter or controller so it does not create a huge spark? I have seen people use them but I am unsure what size to get. I am 48v and use 6,000 watt inverter. When connection first time shoots a huge arc.  

BB.

Yea--Inverters do have some good size capacitors on the DC input. Using good quality circuit breakers (instead of fuses, or worst yet, no breakers or fuses).

Using breakers is usually a good solution. Besides resettable (instead having a few 175+ amp fu$e$ on the shelf--Or not having spares and needing them now), they also make good on/off switches for servicing/winter shutdown, etc.

https://www.solar-electric.com/residential/circuit-protection/circuit-breakers.html?product_list_order=price
https://www.solar-electric.com/mnedc175.html

The usual answer is to just let it arc and pre-charge the capacitors (if you are not using circuit breaker/switch). Wearing safety glasses and keeping fingers/face a distance from the arc point is a good idea.

Another way would be use a cable+resistor (or large filament lamps--at least in the olden days before mandatory LED lamps) to precharge, then make the final electrical connection.

For example, say you have a 48 volt bank and want to 10 amp limit to surge current:

• V=I*R
• R=V/I= 48 volts/10 amps = 4.8 Ohms
• P=V*I= 48 volts * 10 amps = 500 Watt (surge for a fraction of a second). 

• If you get get a surplus power resistor (even 100 Watt is probably overkill), that would do your "pre-charge" nicely.

Of course, make sure you have + and - correctly wired from bank to DC inverter input (using black and red electrician's tape to "wrap" the last 6" of cables to keep polarity correct is nice).

Some DC loads use a simple large diode across the DC inputs. The simple "polarity protection" is, if power is hooked up backwards, then the diode conducts a bunch of current and blows the upstream fuse or circuit breaker (no fuse/breaker, things can get a bit more exciting--And even possibly "spot weld" the cable ring to the DC terminal connection).

You can also buy prewired disconnects and even "E-Panels" that save you having to buy your own parts and construction:

https://www.solar-electric.com/search/?q=DC+disconnect+midnite

-Bill

bryhan67

Perfect info on power resistor. I will get a 100w one. I have my busbar fused but will for sure do some large breakers when I move my system.  Got my eye on the new The Barcelona MPPT from Midnite. 600v input and up to 200amp with breakers for solar and battery built in it. 2 or those and I will be set. 

bryhan67

Bill I was looking at 100w resistors and there is a large range of options with different Ohms. What Ohms do you recommend for the 100w resistor? Thanks

BB.

In post #13 above, I showed you the math. If you have a 48 volt battery bus and want a maximum of 10 amp surge, then 4.8 Ohms would do it... You can take the above equation and if you and purchase a 5 Ohm (good price/availability), you can plug the voltage and resistance into the equation and see that the max surge would be.

• V=I*R
• I = V/R = 48 volts / 5 ohms = 9.6 Amps max surge...

10 Amps will probably not create a large spark (will still spark a little)... But better than the 100+ amps 48 volt battery bank connected to a input filter capacitor (bank).

No exact number here... 5-20 amps is probably perfectly OK. I would not pick to high of resistance... You may have other draws as the inverter is DC powered--And 1 amp may not be enough to bring the input voltage up....

These are all pure guesses on my part. You may need to experiment and see what works for you.

In old radio gear and such, I have found variable wire wound resistors (a clamp can slide up/down the resistor body and you can set the resistance you want:

https://duckduckgo.com/?q=variable+wire+wound+resistor&ia=web

I would not spend much money... If it gets "not cheap", I would be looking a heavy DC switch or a properly rated Circuit Breaker and simply use that as the switch.

You have to be careful with DC current... at 24 VDC and above, it makes for a good Arc Welder. For example, this video shows the difference between switching AC vs DC current. Basically a sustained arc can be carried above >12 VDC. And 24 VDC for arc welding is a common starring point. This video is 220 VAC vs 220 VDC--But this shows any DC arc sustaining vs AC:

https://www.youtube.com/watch?v=Zez2r1RPpWY

-Bill

bryhan67

Yikes. I always wonder the danger to my self with such large batteries. Its clear I can touch both pos and neg with no affect. But what if I am sweaty? Is there any situation that 48v can be dangerous to the human body?  I once stuck my finger 12v cig plug and it burnt me, perhaps because neg and pos is so close and moisture in my finger? Where I am is very hot and humid can be tough to stay 100% dry. Just wondering how dangers it really is. If I am playing with death or just a big shock.

BB.

In theory, 12 VDC or less is considered to be (relatively) touch safe.

Between 12 and 60 Volts is "sort of" safe to work around (with proper training, behind locked doors to keep kids/unauthorized folks out).

Above 60 Volts is not safe to touch.

You are correct, area of contact, water, salt, and such all matter.

For example, I was working on a 24 VDC aircraft power system and keep feeling like a I was sitting on a metal rail with sharp points on it--Turned out that I was getting shocked through my jeans. Was not dangerous--But could feel it.

More or less, it is current that is the danger. Say you have enough voltage (and low enough resistance) that you can get more than 10 milliamps (0.010 amps) or more through your heart--And you can stop it.

That is why it is suggested to only work with one hand on "energized circuits" (if you must). That way no current through your heart vs working with two hands.

And why you can get sparks from a Van De Graaff generator and not kill you--Because the static charge generator has very low current.

AC voltage shocks can be worse--AC current can cause your muscles to lock and you cannot let go.

DC Arcs are more sustainable--And large battery banks with high amount of available current can cause Arc Flash (like an explosion), weld metal together (no wedding rings/jewerly worn while working on power system).

When working on things you cannot "turn off" (like batteries in a bank)--Wrapping tools (screw drivers, wrenches) and their handles with electrical tape is common practice. A "diligent" electrician will re-wrap with every new job (to ensure insulation coverage is good). Wearing a face shield (against metal "spray", and any battery acid to face).

In the "olden days", getting shocked on the job for an electrician was just a risk of the trade and as long as it did not kill you--You just continued work. Old electricians were even known for "testing to see if a 120 VAC circuit was life) by just using their fingers.

Today, the realization that severe shocks can cause death hours later (heart rhythm issues???), an electrician that gets a significant shock on the job can (should) be checked into a hospital for 24 hours and monitored.

Some videos.

First is a British Telecom safety video (large 54 volt battery bank for central office). Near the end (around 6:35 minutes), they short out a battery bank that is not that much different in capacity vs a largesh home power system.:

https://www.youtube.com/watch?v=DpQeDcEpEn0

Next is 48 volt to 240 volt arc flashes:

https://www.youtube.com/watch?v=1ckk3owZz-w

And an example of 4x 60 cell (Vmp=30 volt) solar panels in series--And an example of an Arc Fault--Where an electrical connection fails (corrosion, pulled connector, etc.) and starts a sustained arc:

https://www.youtube.com/watch?v=S9a2oPCIMr0

In the end, be smart and careful. 

-Bill

bryhan67

Wow. I have so many large batteries I have considered building a small shack just for it. So if something goes wrong I dont lose the garage or house. You never know what can happen. 

BB.

Using outbuildings for batteries, running gensets, fuel storage is probably always a good idea if possible.

And some things that catch fire can have very toxic gasses/results. This article from 2019:

https://www.kcra.com/article/15-exposed-to-toxic-fumes-after-responding-to-fairfield-house-fire/27933317

FAIRFIELD, Calif. (KCRA) —

Fifteen first responders were treated for exposure to toxic fumes after helping battle a house fire over the weekend in Fairfield, officials said Tuesday.

The Fairfield Fire Department said 11 firefighters and four officers reported feeling sick after being exposed to the fumes.

Crews responded to a fire at a home on Ash Court around 5 p.m. Saturday. There, crews found 200 pounds of lithium-ion batteries in the garage, the Fairfield Police Department said. According to officials, the batteries emitted fluoride gas after being exposed to the fire.

That's when the 15 people were exposed to the toxic fumes.

The fire department also said the incident was so toxic that crews had to throw away all the hoses and boots that were exposed while battling the blaze.

Investigators are now trying to determine what kind of business the homeowner was running.

Some Lithium battery fires, when mixed with fire fighting water and known to produce Hydrofluoric Acid (I guess that is the reason for the above Fire department had to toss their equipment--And illness)--Which is some pretty scary toxic effects.

https://www.suu.edu/erm/eohs/chemical-specific-protocols/hydrofluoric-acid.html

For any significantly sized battery bank, keeping the bank in a separate building keeps your family safe, and if you have to scrap the building to the ground for cleanup--This helps to limit your losses.

There are just so many different chemistries for Lithium Batteries (more than 20?)--It is difficult to make wide ranging statements about safety/toxicity, etc. And I am no expert. So, again, due diligence when selecting, designing, and maintaining your systems.

-Bill

bryhan67

I will have with backup system over 15,000 lbs in batteries. Might even look at splitting them up also. Now I have my batteries, inverter and controller is same small room for the air conditioner. Would be a bummer to loos it all. Will try and keep a lot of good quality breakers in place.

Marc Kurth

BB. said:

Using outbuildings for batteries, running gensets, fuel storage is probably always a good idea if possible.

And some things that catch fire can have very toxic gasses/results. This article from 2019:

https://www.kcra.com/article/15-exposed-to-toxic-fumes-after-responding-to-fairfield-house-fire/27933317

FAIRFIELD, Calif. (KCRA) —

Fifteen first responders were treated for exposure to toxic fumes after helping battle a house fire over the weekend in Fairfield, officials said Tuesday.

The Fairfield Fire Department said 11 firefighters and four officers reported feeling sick after being exposed to the fumes.

Crews responded to a fire at a home on Ash Court around 5 p.m. Saturday. There, crews found 200 pounds of lithium-ion batteries in the garage, the Fairfield Police Department said. According to officials, the batteries emitted fluoride gas after being exposed to the fire.

That's when the 15 people were exposed to the toxic fumes.

The fire department also said the incident was so toxic that crews had to throw away all the hoses and boots that were exposed while battling the blaze.

Investigators are now trying to determine what kind of business the homeowner was running.

Some Lithium battery fires, when mixed with fire fighting water and known to produce Hydrofluoric Acid (I guess that is the reason for the above Fire department had to toss their equipment--And illness)--Which is some pretty scary toxic effects.

https://www.suu.edu/erm/eohs/chemical-specific-protocols/hydrofluoric-acid.html

For any significantly sized battery bank, keeping the bank in a separate building keeps your family safe, and if you have to scrap the building to the ground for cleanup--This helps to limit your losses.

There are just so many different chemistries for Lithium Batteries (more than 20?)--It is difficult to make wide ranging statements about safety/toxicity, etc. And I am no expert. So, again, due diligence when selecting, designing, and maintaining your systems.

-Bill

I know two PV contractors (customers) who will only install large battery banks in an area, not in or attached to the house. Generally, I see simple cinder block structures. You are right Bill, a battery fire can be a huge mess in terms of damage and cleanup.

Marc

Dave Angelini

Hey Marc !  Add in loss of insurance and a denied claim. This happens more than you think. State Farm agent told me once that they all come from YouTube.

Marc Kurth

Dave Angelini said:

Hey Marc !  Add in loss of insurance and a denied claim. This happens more than you think. State Farm agent told me once that they all come from YouTube.

Ouch. I cannot imagine suffering a huge fire loss, then discovering that your coverage is void. (I lost a home to fire, but State Farm was absolutely great with us.)

Dave Angelini

State Farm or most any insurance company is going to want to know the cause of the fire. Just make sure if you do a large battery system in a garage that is close to the house, or part of the house, that they have been informed and it is installed to the local code.

Offgrid often can't get insurance or it is too expensive. Look at the fire burning now in Mariposa my old home town.

https://www.youtube.com/watch?v=HsuIJf7AuJQ