How to calculate bulk and fload charging voltage?

hrischo

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Joined
Nov 27, 2021
Messages
4
Hello, I am sorry if someone question that. I have solar system with
- EASUN 5.5kw Hybrid Inverter MPPT 48V
- 4x solar panels Suntech 440w
- 4x Gel battery /12v 150ah/
- and Victron Energy SmartShunt 500A/50mV (settings on smart shunt is by default only I have change battery amp to 150ah because I am using 150ah and charged voltage to 52.8v)

My question is how to calculate value of bulk and float charging voltage and low cut-off voltage. I am using SmartESS app for monitoring and make settings. I have option to select battery type (AGM, Flooded and USER). I have now selected user mode and bulk = 56.4v, floating = 54.0v and cut-off = 48.0v. I am not sure is that settings are correct. And I need help for correct setting.

On battery label have:
- Standby use: 13.50~13.8V
- Cyclic use: 14.10~14.4V

Thanks in the advance.
 
Last edited:

sunshine_eggo

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Oct 26, 2021
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Hello, I am sorry if someone question that. I have solar system with
- EASUN 5.5kw Hybrid Inverter MPPT 48V
- 4x solar panels Suntech 440w
- 4x Gel battery /12v 150ah/
- and Victron Energy SmartShunt 500A/50mV (settings on smart shunt is by default only I have change battery amp to 150ah because I am using 150ah and charged voltage to 52.8v)

My question is how to calculate value of bulk and float charging voltage and low cut-off voltage. I am using SmartESS app for monitoring and make settings. I have option to select battery type (AGM, Flooded and USER). I have now selected user mode and bulk = 56.4v, floating = 54.0v and cut-off = 48.0v. I am not sure is that settings are correct. And I need help for correct setting.

On battery label have:
- Standby use: 13.50~13.8V
- Cyclic use: 14.10~14.4V

Thanks in the advance.

14.10 * 4 = 56.4V bulk/absorption
13.50 * 4 = 54V float

Looks good to me.

In a solar system with variable charge current, Victron recommends setting charged voltage to just under absorption, not float, 56.2V.
 

hrischo

New Member
Joined
Nov 27, 2021
Messages
4
14.10 * 4 = 56.4V bulk/absorption
13.50 * 4 = 54V float

Looks good to me.

In a solar system with variable charge current, Victron recommends setting charged voltage to just under absorption, not float, 56.2V.
Thanks for fast answer. I will keep these setting, only I will change victron charged voltage from 52.8V to 56.2V.

And low cut-off voltage is enought at 48.0V?
In manual ask for 5.5kw inverter - Low DC Cut-off Voltage:
@load < 50% --> 41.0Vdc
@load >= 50% --> 40.0Vdc
but I don't know how many percentage is recommended to can use from battery.
 
Last edited:

wattmatters

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Apr 16, 2021
Messages
1,399
but I don't know how many percentage is recommended to can use from battery.
The deeper you discharge a lead acid battery the shorter its cycle life. Your batteries should have recommended charge/discharge voltages.

So it's going to depend on how long you are hoping to make the batteries last for and what your use case is.

In general you don't want to be be discharging beyond 50% of rated capacity unless you really have to. For maximal cycle life then only using 20% of capacity is better.

It comes down to your use case.

You have a smart shunt so will be able to measure how much energy is being drawn during discharge.

48V (nominal) x 150Ah = 7200Wh total nominal capacity, so
50% depth of discharge = 3600Wh (3.60kWh) - consider this your effective working limit on discharge.
20% depth of discharge = 1440Wh (1.44kWh) - this would be the limit if you want batteries to last a lot longer.

It's not quite as simple as above but it's a pretty decent starting point.

And low cut-off voltage is enought at 48.0V?

That may be perfect or problematic depending on your use case. Very much depends on your loads and what cycle life you are aiming for.

In manual ask for 5.5kw inverter - Low DC Cut-off Voltage:
@load < 50% --> 41.0Vdc
@load >= 50% --> 40.0Vdc
These are a bit low for my comfort level. That's a very depleted battery, especially when you have 4 in series.

Have a read here for some helpful information about batteries:

In particular read about lead acid battery discharging and voltages under loads.

Your bulk and float charge voltages sound on the money.
 

sunshine_eggo

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Joined
Oct 26, 2021
Messages
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Location
USA
Responding to @wattmatters to agree/supplement:

The deeper you discharge a lead acid battery the shorter its cycle life. Your batteries should have recommended charge/discharge voltages.

So it's going to depend on how long you are hoping to make the batteries last for and what your use case is.

+1

In general you don't want to be be discharging beyond 50% of rated capacity unless you really have to. For maximal cycle life then only using 20% of capacity is better.

+1

It comes down to your use case.

You have a smart shunt so will be able to measure how much energy is being drawn during discharge.

+100

48V (nominal) x 150Ah = 7200Wh total nominal capacity, so
50% depth of discharge = 3600Wh (3.60kWh) - consider this your effective working limit on discharge.
20% depth of discharge = 1440Wh (1.44kWh) - this would be the limit if you want batteries to last a lot longer.

It's not quite as simple as above but it's a pretty decent starting point.

+1

However, the Peukert effect and temperature compensation features of the Victron battery monitor make SoC reporting very accurate if you have a temp probe on and set those features up correctly.

That may be perfect or problematic depending on your use case. Very much depends on your loads and what cycle life you are aiming for.

48V will be problematic. A single heavy load even on a battery at high state of charge can pull it below 48V.

These are a bit low for my comfort level. That's a very depleted battery, especially when you have 4 in series.

IMHO, you use all the battery you need. if you're using too much, use less, buy more battery or supplement with a generator. I have the typical 42V cut off (10.5V/battery) on my Quattro. Why? Because it almost never matters... and I can change it remotely if I care. :p

I have SoC alarms set for my BMV-702/GX device, so I get notifications at various programmed alerts for SoC and battery voltage. One I get pretty regularly is the 48V warning when I'm using 2000-3500W even at a high state of charge.

@hrischo don't over-think this. Properly configure and trust the battery monitor. Don't try to have the system limit you when it's not necessary. If you're not dipping below 80% SoC, then you're going to have long battery life; 50% - good battery life; > 50% - use less power or get more battery.

There have been a handful of times I've had to run my battery down into the 30% range. The alternative was to have the propane furnace blower stop in freezing temps. The last thing I want is my inverter cutting me off at 50%.
 

hrischo

New Member
Joined
Nov 27, 2021
Messages
4
The deeper you discharge a lead acid battery the shorter its cycle life. Your batteries should have recommended charge/discharge voltages.

So it's going to depend on how long you are hoping to make the batteries last for and what your use case is.

In general you don't want to be be discharging beyond 50% of rated capacity unless you really have to. For maximal cycle life then only using 20% of capacity is better.

It comes down to your use case.

You have a smart shunt so will be able to measure how much energy is being drawn during discharge.

48V (nominal) x 150Ah = 7200Wh total nominal capacity, so
50% depth of discharge = 3600Wh (3.60kWh) - consider this your effective working limit on discharge.
20% depth of discharge = 1440Wh (1.44kWh) - this would be the limit if you want batteries to last a lot longer.

It's not quite as simple as above but it's a pretty decent starting point.



That may be perfect or problematic depending on your use case. Very much depends on your loads and what cycle life you are aiming for.


These are a bit low for my comfort level. That's a very depleted battery, especially when you have 4 in series.

Have a read here for some helpful information about batteries:

In particular read about lead acid battery discharging and voltages under loads.

Your bulk and float charge voltages sound on the money.
Thank you so much for answer.
 

hrischo

New Member
Joined
Nov 27, 2021
Messages
4
Responding to @wattmatters to agree/supplement:



+1



+1



+100



+1

However, the Peukert effect and temperature compensation features of the Victron battery monitor make SoC reporting very accurate if you have a temp probe on and set those features up correctly.



48V will be problematic. A single heavy load even on a battery at high state of charge can pull it below 48V.



IMHO, you use all the battery you need. if you're using too much, use less, buy more battery or supplement with a generator. I have the typical 42V cut off (10.5V/battery) on my Quattro. Why? Because it almost never matters... and I can change it remotely if I care. :p

I have SoC alarms set for my BMV-702/GX device, so I get notifications at various programmed alerts for SoC and battery voltage. One I get pretty regularly is the 48V warning when I'm using 2000-3500W even at a high state of charge.

@hrischo don't over-think this. Properly configure and trust the battery monitor. Don't try to have the system limit you when it's not necessary. If you're not dipping below 80% SoC, then you're going to have long battery life; 50% - good battery life; > 50% - use less power or get more battery.

There have been a handful of times I've had to run my battery down into the 30% range. The alternative was to have the propane furnace blower stop in freezing temps. The last thing I want is my inverter cutting me off at 50%.
Thank you so much for answer.
 
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