Battery Bank Hard Stuck

foxburrow

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Oct 5, 2021
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Hello y'all,

I have a battery bank of 4x SOK 12v 206aH batteries, series and parallel, to make a 24v system. The rest of my components are Victron:
24v 3000w Inverter
MPPT 150/85 Charge Controller
Victron Battery Monitor

I had contacted SOK to get the specs to fill in the fields on the Victron App for both the Charge Controller and the Battery Monitor. According to the manufacturer, the Max Charge Voltage for the battery bank should be 29.2v.

We are entering the rainy season where I am in the PNW and I suspect my generator will become my greatest ally in maintaining charge of my battery bank. On 4th day of no sun (second time charging up my battery bank) the generator is going and the monitor reads 27.07v and stayed at that charge voltage for over 1 hour. When I shut the generator off the battery monitor read ~26.6v. I plugged in my laptop (~150w) the voltage dropped immediately and stabilized at 26.47v. The generator ran for a total of 4 hours and charged from 24.03v - 26.47v (generator delivering 1.16kW to the battery bank). This is the second time I have had to use the generator with similar results, the first time after I turned off the generator the Battery Monitor reading 26.8v. Voltage immediately dropping to ~26.6v when low wattage item plugged in. Anyone have any idea on why the system would be hard stuck on charging past 27v? How do I get my bank to reach full capacity at 29.2v?

I am new to off-grid systems, but a former apprentice electrician (AC/grid).

Thank you for your time and reading.
 

sunshine_eggo

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While LFP and lead acid cells have very closely overlapping charge voltages/ranges of operation, LFP charge/discharge profiles are very flat.

You have 412Ah of 25.6V LFP or 10.5kWh.

When you started charging at 24.03V, your battery was at an extremely low state of charge - likely < 20%. The 4 hours of charging likely only increased your charge by about 10%.

The vast majority of charging occurs in the vicinity of 3.4V/cell. Higher voltages are only achieved at the very end of the charge. Example curve:

lfp-la.jpg


Note the comparison with lead-acid.

You are likely over-utilizing your system beyond what you can supply daily. Assuming you have a multiplus, do you have it properly configured for charging from a generator?

The voltage drop you describe is to be expected when the battery is at a low state of charge.
 

foxburrow

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While LFP and lead acid cells have very closely overlapping charge voltages/ranges of operation, LFP charge/discharge profiles are very flat.

You have 412Ah of 25.6V LFP or 10.5kWh.

When you started charging at 24.03V, your battery was at an extremely low state of charge - likely < 20%. The 4 hours of charging likely only increased your charge by about 10%.

The vast majority of charging occurs in the vicinity of 3.4V/cell. Higher voltages are only achieved at the very end of the charge. Example curve:

lfp-la.jpg


Note the comparison with lead-acid.

You are likely over-utilizing your system beyond what you can supply daily. Assuming you have a multiplus, do you have it properly configured for charging from a generator?

The voltage drop you describe is to be expected when the battery is at a low state of charge.
Thank you helping bring me to a place of deeper understanding. The chart was helpful and I went ahead and ordered an MK3-USB, so I can make sure that the inverter is programmed properly for my generator.

And you're right, I have been using the system pretty hard. I am building a home and pushing through it so I can be warm before Winter hits. This means table saws, planer, chop saw, etc. running 6+ hours a day. This was no problem when I set the system up here at the tail end of Summer (saws would just take the energy right off the panels), but it is getting to be an issue now with 4 day stretches of gray and rain.

I'll run the generator for now with my tools and will look forward to ensure the inverter is programmed properly.

Thanks again for tipping me off.
 

noenegdod

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Thank you helping bring me to a place of deeper understanding. The chart was helpful and I went ahead and ordered an MK3-USB, so I can make sure that the inverter is programmed properly for my generator.

And you're right, I have been using the system pretty hard. I am building a home and pushing through it so I can be warm before Winter hits. This means table saws, planer, chop saw, etc. running 6+ hours a day. This was no problem when I set the system up here at the tail end of Summer (saws would just take the energy right off the panels), but it is getting to be an issue now with 4 day stretches of gray and rain.

I'll run the generator for now with my tools and will look forward to ensure the inverter is programmed properly.

Thanks again for tipping me off.
Just a few thoughts:

  • You have a generator delivering a little over 1000 watts to your bank. Is this the max continuous out put of your generator? If it is, good. If not, look at fuel consumption charts for generators based on load and you will find the best approach is to max out your generator.
  • Having said the above, instead of using your generator to operate your tools, you can program your multiplus to take the maximum current your generator can provide, while you are using your tools. The generator will see a constant maximum load (its most efficient state) and never sit idle wasting fuel in-between tool usage. When you use your tools, the generator will supply current through the multiplus but there is no conversion losses, it is just a straight pass through.
  • If you have a quiet generator and do not have neighbors it would disturb and it wont bother you, you can run it at night. This obviously wont work in all circumstances but it is how I plan to utilize mine while I am bush camping when no one is around. I have no problem falling asleep to the hum of my nice quiet yamaha inverter generator. Just pull the cord and it will run till it runs out of gas.
 

foxburrow

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Just a few thoughts:

  • You have a generator delivering a little over 1000 watts to your bank. Is this the max continuous out put of your generator? If it is, good. If not, look at fuel consumption charts for generators based on load and you will find the best approach is to max out your generator.
  • Having said the above, instead of using your generator to operate your tools, you can program your multiplus to take the maximum current your generator can provide, while you are using your tools. The generator will see a constant maximum load (its most efficient state) and never sit idle wasting fuel in-between tool usage. When you use your tools, the generator will supply current through the multiplus but there is no conversion losses, it is just a straight pass through.
  • If you have a quiet generator and do not have neighbors it would disturb and it wont bother you, you can run it at night. This obviously wont work in all circumstances but it is how I plan to utilize mine while I am bush camping when no one is around. I have no problem falling asleep to the hum of my nice quiet yamaha inverter generator. Just pull the cord and it will run till it runs out of gas.
Thanks for delivering me more information.

I have an old Honda EM 3500 SX that came with the property I just purchased. I do not have the manual, but when I looked up the specs online it says that it's Rated Output is 3kVA (Max 3.5kVA), how that converts to kW... I am unsure. Any advice on figuring that calculation?

When I get my MK3-USB adapter, I'll look into the programming options.

Generator is very loud, but luckily I live on a heavily wooded 30 acres. I walk halfway off the property and no longer hear it. Besides, my whole community is off-grid (primarily generator dependent), so the noise is unlikely to disturb those who are very used to it.
 

foxburrow

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Messages
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Just a few thoughts:

  • You have a generator delivering a little over 1000 watts to your bank. Is this the max continuous out put of your generator? If it is, good. If not, look at fuel consumption charts for generators based on load and you will find the best approach is to max out your generator.
  • Having said the above, instead of using your generator to operate your tools, you can program your multiplus to take the maximum current your generator can provide, while you are using your tools. The generator will see a constant maximum load (its most efficient state) and never sit idle wasting fuel in-between tool usage. When you use your tools, the generator will supply current through the multiplus but there is no conversion losses, it is just a straight pass through.
  • If you have a quiet generator and do not have neighbors it would disturb and it wont bother you, you can run it at night. This obviously wont work in all circumstances but it is how I plan to utilize mine while I am bush camping when no one is around. I have no problem falling asleep to the hum of my nice quiet yamaha inverter generator. Just pull the cord and it will run till it runs out of gas.
P.S. I just wrapped up ship lapping some boards and came inside to check the monitor. The inverter has switched from Bulk to Absorption and it went from 1.19kW being delivered, down to about 350w continuously.

Turned off the generator and the battery voltage read 28.73v. Voltage dropped by .01v a second until it is equalizing out in the high 27v range (currently 27.93v, but still dropping slowly).

From what y'all have told me, it seems like the missing ingredient is programming the inverter with the rest of my equipment.
 
Last edited:

noenegdod

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Messages
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So if you are using a generator still, turn it off. No point in running a 3500 watt generator for 350 watts.

When you get the MK3-USB check to make sure current isnt being limited. Another thing to check is the voltage that it is charging at. Measure the voltage at the charger and at the batteries. If you have much drop that will reduce the current. I have not read up on this but you can have the charger increase its voltage based on actual battery voltage by as much as 1 volt ( on a 12v unit not sure about a 24) to help overcome system drop.
 

sunshine_eggo

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IIRC, default is 28.8V for a Multiplus, so you shouldn't be too far off on the voltage.

The other considerations are AC input limitations (how much to pull from generator/grid) and charge restrictions (you can specify a % of max output as a limit). With perfect charging at peak bulk, you are limited to 70A * 28.8V = 2016W of charging output from the MP.

If your AC input is limited to 15A (I think that's the default to avoid overloading a typical 15A circuit), you're going to be down to 1800W peak.

You also need to consider your generator output and configuration:


If you're in 120/240V split phase mode, the generator won't deliver more than 12.5A to the 120VAC circuit, so 1500W max.
 

Rocketman

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If you plan on keeping using this power setup - look at adding a Victron Cerbo & touch. This will put all the data in one place. Also make sure the battery monitor (BMV712? Or Smartshunt?) is setup correctly for you batteries.

That way you can look at a glance and see your battery is at 20% state of charge or it’s at 98% state of charge.
 

foxburrow

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So if you are using a generator still, turn it off. No point in running a 3500 watt generator for 350 watts.

When you get the MK3-USB check to make sure current isnt being limited. Another thing to check is the voltage that it is charging at. Measure the voltage at the charger and at the batteries. If you have much drop that will reduce the current. I have not read up on this but you can have the charger increase its voltage based on actual battery voltage by as much as 1 volt ( on a 12v unit not sure about a 24) to help overcome system drop.
When you say the charger, do you mean opening up the inverter and putting a meter on a certain point?
 

sunshine_eggo

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When you say the charger, do you mean opening up the inverter and putting a meter on a certain point?

When charging, measure the DC voltage at the inverter lugs and at the battery terminals. Excessive voltage drop will cause the MP to decrease charge current due to wiring/connection losses thus prematurely slowing the charge rate.

Wires of insufficient gauge or improperly torqued connections will cause voltage drop.
 

foxburrow

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IIRC, default is 28.8V for a Multiplus, so you shouldn't be too far off on the voltage.

The other considerations are AC input limitations (how much to pull from generator/grid) and charge restrictions (you can specify a % of max output as a limit). With perfect charging at peak bulk, you are limited to 70A * 28.8V = 2016W of charging output from the MP.

If your AC input is limited to 15A (I think that's the default to avoid overloading a typical 15A circuit), you're going to be down to 1800W peak.

You also need to consider your generator output and configuration:


If you're in 120/240V split phase mode, the generator won't deliver more than 12.5A to the 120VAC circuit, so 1500W max.
Very helpful, thank you.
 

foxburrow

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Oct 5, 2021
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If you plan on keeping using this power setup - look at adding a Victron Cerbo & touch. This will put all the data in one place. Also make sure the battery monitor (BMV712? Or Smartshunt?) is setup correctly for you batteries.

That way you can look at a glance and see your battery is at 20% state of charge or it’s at 98% state of charge.
BMV712 is set up using the specs Battery Manufacturer sent me. And the Solar Charge Controller is set up accordingly as well. Thanks for the recommendation, I've gone ahead and put those on my wish list for when I have enough dough to shell out for upgrades.
 

foxburrow

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When charging, measure the DC voltage at the inverter lugs and at the battery terminals. Excessive voltage drop will cause the MP to decrease charge current due to wiring/connection losses thus prematurely slowing the charge rate.

Wires of insufficient gauge or improperly torqued connections will cause voltage drop.
Using 2/0 welding wire from batteries. Can't recall on generator wiring, but it is either 12 or 10 gauge. Next time I throw on the generator (likely tomorrow), I'll check out the voltages. Wiring snug and secure... I was an apprentice electrician for awhile and did a lot of main service panel installs... So I would hope by now I at least got wiring down 😜.
 

foxburrow

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IIRC, default is 28.8V for a Multiplus, so you shouldn't be too far off on the voltage.

The other considerations are AC input limitations (how much to pull from generator/grid) and charge restrictions (you can specify a % of max output as a limit). With perfect charging at peak bulk, you are limited to 70A * 28.8V = 2016W of charging output from the MP.

If your AC input is limited to 15A (I think that's the default to avoid overloading a typical 15A circuit), you're going to be down to 1800W peak.

You also need to consider your generator output and configuration:


If you're in 120/240V split phase mode, the generator won't deliver more than 12.5A to the 120VAC circuit, so 1500W max.
Hi sunshine_eggo,
I got my MK3-USB and accessed the settings, but under the general tab it won't let me increase the incoming AMPs above 50A. I disabled "Current limit overruled by remote" and still no luck.
Cheers,
FB
 

foxburrow

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You can see that the plus sign is greyed out. When typing in 70.0A and saving, it shows no change from 50.0A on the general tab. This is regardless of whether "overruled by remote" is selected or not.
Victron Inverter Settings 1.png
 

sunshine_eggo

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That's how much you're pulling from the generator. Can your generator supply 50A @ 120V? No.

You need to configure the inverter to correctly draw from the generator on the AC input side and then output no more power than that on the DC output side.

Have you figured out what mode your generator is operating in, and what current it can supply to the MP? Per the manual linked above, in split phase mode, each leg can only supply 12.5A. In 120V only mode, there are other limits.

Here are your limits:

1636047760358.png
The maximum you can get at 120V is receptacle #1 @ 30A. In your situation, I would set that to 27A. If long runs trip a breaker at 27A, I would set it to 24A.

On the charger screen, you need to set the charge current to be below what the AC input can provide. For the 27 and 24A suggestions above:

27A * 120V = 3240W; 3240W/28.8V = 112.5A (round down to 100A)
24A * 120V = 2880W; 2880W/28.8V = 100A (round down to 90A)

If you're plugging into one of the 20A receptacles, set limit to 18A on General and 18A * 120V = 2160/28.8 = 75A (round down to 70A) on Charger.

If you're in split phase and running at 12.5A only, set limit to 11A on General and 11A * 120V = 1320/28.8 = 45.8A (round down to 40A) on Charger.

Also, disable PowerAssist on Inverter page.

Worth reading:


EDIT: Also, Disable UPS function in Grid.
 
Last edited:

foxburrow

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That's how much you're pulling from the generator. Can your generator supply 50A @ 120V? No.

You need to configure the inverter to correctly draw from the generator on the AC input side and then output no more power than that on the DC output side.

Have you figured out what mode your generator is operating in, and what current it can supply to the MP? Per the manual linked above, in split phase mode, each leg can only supply 12.5A. In 120V only mode, there are other limits.

Here are your limits:

View attachment 71302
The maximum you can get at 120V is receptacle #1 @ 30A. In your situation, I would set that to 27A. If long runs trip a breaker at 27A, I would set it to 24A.

On the charger screen, you need to set the charge current to be below what the AC input can provide. For the 27 and 24A suggestions above:

27A * 120V = 3240W; 3240W/28.8V = 112.5A (round down to 100A)
24A * 120V = 2880W; 2880W/28.8V = 100A (round down to 90A)

If you're plugging into one of the 20A receptacles, set limit to 18A on General and 18A * 120V = 2160/28.8 = 75A (round down to 70A) on Charger.

If you're in split phase and running at 12.5A only, set limit to 11A on General and 11A * 120V = 1320/28.8 = 45.8A (round down to 40A) on Charger.

Also, disable PowerAssist on Inverter page.

Worth reading:


EDIT: Also, Disable UPS function in Grid.
Thanks for the learning lesson @sunshine_eggo, it is all starting to make sense now. I went ahead and configured it accordingly, based off of your instructions/explanation. Cheers!
 

sunshine_eggo

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Would appreciate a follow-up to include:
  1. Generator mode (120 or 120/240V)/connection (which port is feeding the MP).
  2. AC input limit setting.
  3. DC charge current setting.
  4. Confirmation that UPS mode and PowerAssist are disabled.
  5. Observed charge power or current from generator when battery is at a known lower state of charge.
The hope is that you can pull 27A with the generator in 120VAC mode and get something north of 100A of charge current to the batteries. This should allow you to reduce charge time and improve your Ah/gallon consumed.
 

foxburrow

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Would appreciate a follow-up to include:
  1. Generator mode (120 or 120/240V)/connection (which port is feeding the MP).
  2. AC input limit setting.
  3. DC charge current setting.
  4. Confirmation that UPS mode and PowerAssist are disabled.
  5. Observed charge power or current from generator when battery is at a known lower state of charge.
The hope is that you can pull 27A with the generator in 120VAC mode and get something north of 100A of charge current to the batteries. This should allow you to reduce charge time and improve your Ah/gallon consumed.
1. Generator mode 120 to port 1 (29A receptacle).
2. AC input limit 27A.
3. DC charge current 70A. Which to my understanding is the most my Multiplus can deliver?
4. They were both disabled by default.
5. Started generator today with battery bank at 24.1V. The charging current is sitting at around 45A. So my charge is only about half of your said 100A.
 
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