FAQ Steca charge controller

What does Float, Boost and Equal mean?
1. float

Charge with available module current until final charge voltage is reached.

2. trickle charge

When the battery is full, the controller automatically switches on trickle charging (charging with the trickle voltage). This prevents the battery from discharging.

3. boost, maintenance charging

Maintenance charging cares for the battery more intensively than maintenance charging. Further applies:
The maintenance charging starts automatically when the voltage falls below 12.7V (70%). Maintenance charging can also be started manually.
Maintenance charging ends after the charging time has expired.
During maintenance charging the charging voltage is higher than during maintenance charging.
After maintenance charging, the controller automatically switches over to trickle charging.

4. equal, equalizing charge

Equalization charging avoids acid stratification through controlled gassing and thus extends the life of the battery. Further applies:
Equalization charging starts when the cycle has expired or the switch-on threshold1) is undercut.
Equalization charging ends when the charging time has elapsed or when the switch-off threshold1) is reached, whichever occurs first.
Equalizing charging is switched on in the setting "Liquid electrolyte".
What to do if the charge controller is defective?
Depending on the model, a self-test can be carried out on the device, which can provide further information on any errors that may be present (for further information, please refer to the corresponding operating manual).

If the self-test shows an error code, or if a self-test is not possible depending on the model, please contact your dealer or installer for complaint handling.
How do you calculate the necessary cable cross section?
The cable cross-section to the battery connection can be calculated using the following formula:

A = 0.0175 x L x P/(fk x U²)

A = cable cross section in mm2
0.0175 = specific electrical resistance of copper [Ohm x mm2/m]
L = cable length (positive conductor + negative conductor) in m
P = power transmitted in the cable in W
fk= loss factor (generally 1.5 %) = 0.015
U = voltage in V
Can another source be used instead of PV at the charge controller input?
The operation of our charge controllers with other sources (wind turbine, water turbine, power supply) than a PV module is unfortunately not possible. This is due to the fact that the controllers short-circuit the PV input when the battery is full, in order to avoid overcharging.
This procedure is harmless for solar modules, but has partly destructive consequences for other sources.
What should be considered when using a charge controller in cars or mobile homes?
When using the PR-controllers in a car, please note that these controllers have a positive Common Ground (=all positive connections are internally connected). For this reason, it is possible to have positive grounding at all points, but only negative at one point. In the vehicle (normally negative Common Ground, i.e. all negative lines are connected, battery minus is common ground) you can solve this e.g. by routing module and consumer lines separately. So 2 lines (+ and -) from the module to the regulator, and 2 lines (+ and -) from the regulator to the consumer.
It would also be possible to use a multiple socket for several distributors. It is only important that the connections are separated from the rest of the vehicle.
Which modules are suitable for our charge controllers?
Two characteristic values of the modules are used to select the modules or to check their suitability:
The module open circuit voltage (usually called Uoc) and the module short circuit current (usually called Isc). It should also be noted that the module open-circuit voltage is a temperature-dependent value. The value in the data sheet is usually at 25°C, so that the expected open circuit voltage must be calculated at e.g. 0°C. The temperature coefficient of the open circuit voltage (Tk(Uoc) ) is used in the following formula:

Uoc@25°C - (temperature difference in Kelvin x Tk(Uoc)) = Uoc@expected temperature

This approach applies to all our charge controllers. The corresponding limit values are given in the data sheets. For the PR regulators, e.g. maximum open-circuit voltage 47V and maximum module current vary depending on the model.
Exceeding these values leads to damage to the charge controllers.
Can several controllers charge one battery at the same time?
Yes, even up to 5 controllers can be operated on the same battery without direct communication between them. The SOC control must be deactivated on the controllers and the voltage control must be selected instead (if supported by the controller).
Are Steca charge controllers compatible with lithium batteries?
The solar charge controllers MPPT 3020 & MPPT 5020, as well as MPPT 6000-M (S) can be configured to charge lithium battery packs.
It is important that these storage devices have their own battery management system (BMS), which does not require communication with the solar charge controller.

MPPT 6000 M /S: Where are the consumers connected?
All MPPT 6000 M /S have no connection for consumers.
Consumers must be connected directly to the battery. So you have to build your own distribution somewhere there.
To protect the battery from deep discharge the consumers must have their own deep discharge protection.
Alternatively you can (only with the 6000-M) build an additional deep discharge protection by using the auxiliary contacts AUX and an additional external switching element (relay or contactor).
If you want to have information about the current consumption of the consumer, you can (only for the 6000-M) use an additional external current sensor HS400
Solsum series solar charge controller: Which solar module?
To charge the battery, it is important that the module voltage in the MPP of the module is at or slightly above the highest final charge voltage of the battery. In order for the battery to be charged, the module voltage must be higher than the current voltage of the battery. For the Solsum it is important that the module voltage is at least 10V, otherwise it goes into night mode and stops charging. Of course, the Solsum also has its own consumption, which the solar module must also cover.

The specification 5W of the PV module refers to an irradiation of 1000W/m2. If the irradiation is lower, the power of the solar module is reduced accordingly.

Here an example of the influence - the values do not belong to the present 5W module, but rather fit to a 50W module. Source: http://www.work-crew.de/photovoltaik/

If you now assume diffuse light and assume 200W/m2, i.e. 1/5 of the power, the 5W module has only 1W. This 1W at a MPP voltage of about 15V results in a possible current of 1W/15V = 0.066A. If you set the Solsum regulator's own consumption of 6mA, 60mA of charging current remain for the battery.

If you assume that you want to charge 1Ah into the battery, you would need 16.6h at a stretch with 60mA charging current.

With the 100W lamp this looks already different. Here results converted on m2 a clearly higher irradiation and thus more achievement / current from the solar module.
Solar charge controller series Tarom 4545: How can data stored on the SD card be visualized on the PC?
The SD card stores data in CSV format. No Steca/KATEK tool is available for evaluation / visualization. The user can/must individually create a representation with Excel. A description of the file content can be found in the operating instructions.

The fact that a new csv file is created every day is a little inconvenient. If you want to display several days, you must manually copy the data into a spreadsheet.

The data cannot be saved to the SD card afterwards. The storage on SD card is an online recording on the storage medium. The Tarom does not have an intermediate storage for a later re-storage. It is not possible, for example, to save the internal data logger to the SD card later. The recording starts at the time of activation. Of course, a writable SD card must also be inserted.
Solar charge controller with "SOC" charge control (State of charge) and requirements for its correct function
The SOC "state of charge" mode uses a special algorithm to determine the state of charge of the battery as accurately as possible. Based on the SOC value the discharge is stopped - deep discharge protection at <30% SOC the load output is deactivated. Based on the SOC value the charging modes (float, boost, equal) are selected. The actual charging procedure, or the type of voltage and current regulation when charging the battery is independent of the SOC. So in SOC mode as well as in voltage controlled mode there is always a U-I charging procedure.

In the voltage controlled mode a voltage value is used to activate the deep discharge protection instead of the SOC value. Also in the voltage controlled mode a voltage limit is used instead of the SOC value for the selection of the charging modes (float, boost, equal).

The SOC value can only be determined correctly if ALL charge and discharge currents of the battery are detected by the charge controller. If the battery is directly charged by another charging source or if an island inverter or here e.g. the garage door drive is directly connected to the battery, the SOC mode cannot be used in a reasonable way. The SOC value would be falsified due to the currents that cannot be measured by the controller. As a result, the state of charge (SOC value) is over- or underestimated - this may cause the deep discharge protection to react too early or too late. So if charging sources or consumers are directly connected to the battery, it is always advisable to use the voltage controlled mode.

As described above, the selection of the charging mode (float, boost, equal) depends on the SOC or voltage controlled mode. The final charging voltages for each charging mode are fixed (except for temperature and line compensation) and therefore independent of the SOC or voltage control mode. In U-I charging, the battery is always charged with the maximum possible charging current in the U phase and the battery voltage is monitored. When the actual battery voltage has reached the final charge voltage, the controller switches to the I-phase and now regulates the charge current into the battery in such a way that the final charge voltage is kept constant. As the battery's energy consumption increases, the charging current will become smaller and smaller.

Is it better to operate the system in SOC mode: - Yes, if the SOC can be determined correctly. For this purpose, no sources or consumers must be directly connected to the battery. If this is not possible due to the design, it is better to switch to voltage control. - Advantage: The SOC adapts the deep discharge protection and the automatic selection of the charging modes (float, boost, equal) to the actual state of charge of the battery and is therefore more gentle on the battery. - Disadvantage: Behaviour of the controller on SOC basis is not so transparent for the user, the user must have more "trust" in the controller, because the internal processes cannot be directly understood by the user. It is not allowed to compare the behavior of the regulator 1:1 with the voltage value of the battery or to derive it from it. Especially with dynamic processes the impression can arise that the behavior of the controller in SOC mode is not correct. Example: When switching on a (large) load, the battery voltage drops significantly downwards, but the SOC value remains unchanged for the time being and corrects itself only slowly downwards. The voltage can also drop below the deep discharge threshold in voltage controlled mode without the controller switching off its load output - if the SOC is still correspondingly >30%. In the opposite case, the battery voltage may have already reached the final charge voltage, but the SOC is not at 100% - despite the avoidable impression that the battery should be fully charged based on the voltage. The main reason for this avoidable discrepancy is that the state of charge of a lead-acid battery is not linear to the voltage curve during operation.

Is a synchronized use of the night light function possible with several charge controllers (in this example solar charge controller of the PR series)?
A synchronized switching of the night light function with several PR controllers is not possible. (our partner company Uhlmann Solarelectronik offers controllers with "swarm" function, or controllers with timer)

The PR recognizes night when: - Charge control is not active (this can be disturbed during parallel charging e.g. by a power supply or wind generator) - The module current is <= 0, which is usually the case when the module voltage is approx. 1V lower than the battery voltage. - There must be no short circuit at the module input. - The "conditions" for night are checked every 1s, if the conditions for >10s are fulfilled, the module is detected to night.

Due to the dependence on the battery voltage (module voltage must be lower than battery voltage), different switching points can occur at the light points, especially in systems with separate batteries. The detection at night is also dependent on the module voltage. If there are different conditions (e.g. also by extraneous light, dirt, shading) this also influences the switching point. Due to the dependence of battery voltage and module voltage, it is not possible to obtain an absolute value for the module voltage from The PR controller has no clock.

Deviations of 1h or even more can actually occur, depending on the characteristics and behavior of the individual light point.
Solar charge controller of the PR series: The controller displays load current although no consumer is connected. Can the controller be recalibrated?
1.) PR must be in default setting (no night or morning light function)
2.) Load is switched on (load symbol is displayed)
3.) Simulate night by darkening or disconnecting the module (moon symbol must be displayed after 10-15 minutes)
4.) Switch off load manually with right key (load symbol disappears)
5) wait a few seconds
6.) Switch load on again.
With this procedure, the load current calculation should be correctly calibrated again and 0 amperes should also be displayed when the load is not connected.
Solar charge controller with load connection: Can the voltage at the load output be limited?
No, the load output on the solar charge controller with load output) cannot be limited in voltage.
The battery voltage is always present at the load output.
At what ratio does the Solarix 2020-x2 - 2-battery regulator charge the connected batteries?
When the main battery is full, the charging power is increasingly used for the secondary battery. The secondary battery does not stop at 10%.

Technically, the expression "more power to the secondary battery" is not quite correct. At the momentary charging current both batteries always get the same, only the duration is different. The charge is always switched between the two batteries. First the main battery is charged for 90% of the time and then the secondary battery for 10% of the time. When the main battery is full, the secondary battery is given more charging time. In the example below this is only 30%, but to my knowledge it can go up to 90% for the secondary battery and 10% for the main battery. It always depends on how full the main battery remains. The duration is short, 100% time is 33ms. Related to this time duration, the current for the secondary battery is average and increases when the main battery is full.
PR series solar charge controllers: When do I use them?
The PR or all Steca charge controllers use the charge modes float - boost - equal. The "equal" mode has the highest final charge voltage. The strongest gassing occurs with the lead battery.

Since AGM batteries do not have a refill option for the electrolyte, or distilled water cannot be refilled, and since this type of battery usually has a safety valve that reacts when the internal gas pressure is too high, many battery manufacturers recommend a moderate final charge voltage. The easiest way to do this is to select the battery type GEL/AGM. With this selection the "equal charge" mode is not active and only the reduced final charge voltage of the "boost" mode is active.

However, the battery manufacturer's instructions regarding the recommended final charge voltages should be observed and complied with. This may also require that the "equal charge" mode can be used. The PR regulator even offers the advantage of being able to set the final charging voltages, see the instructions in the "Charging Voltages Menu" on the PR 1010 website. 3030 regulator.
What could be the reasons for too high battery voltages (example: battery voltage reaches 30V in a 24V system)?
The setting of the charging voltage is done in a "hidden" menu, see additional instructions (not available for all controller types)

- Selection of voltage control with/without bargraph is important and necessary if loads are connected directly to the battery.
- 30V, even if short, should not occur under normal circumstances when battery type GEL is selected. This is also independent of the SOC / voltage control setting.
o 30V could (longer) occur if the final charge voltage for equal has been changed to 30V and the equal charge mode is active.
o 30V could occur briefly (if the setting has not been changed) if charging is done with a very high charging current on a small battery.
o 30V could occur briefly (if the internal resistance of the battery is increased) if load changes (changing charging current, possibly also changing load by consumers) cause oscillations which the controller cannot adjust fast enough. An increased internal resistance can be a sign of an old / bad battery.
o An increased line resistance between battery and regulator may also be present. If necessary, check connections, cables, terminals, fuses.
o 30V could occur briefly if the consumers directly connected to the battery feed back, possibly during switching operations?
o 30V could also be caused by chargers directly connected to the battery
o 30V could occur briefly if charging sources other than PV modules are connected to the module input of the controller. Only PV modules may be connected!
Do Steca charge controllers have to be grounded separately?
Grounding is not necessary from the point of view of the devices. We do not have any existing local regulations for the installation and construction of this system, including requirements for earthing, but they must be observed. If grounding is not necessary, a grounding-free installation is preferable. If grounding is necessary, the positive pole of the battery can be grounded. Inside the Solsum all positive connections are firmly connected to each other anyway. Under no circumstances should two or more negative connections (PV -, Bat -, Load -) be grounded simultaneously / in parallel. By earthing e.g. Bat - and Load -, the switching element for the load output would be bridged by this common earth connection. As a result, the deep discharge protection for the battery would not be able to switch off. If PV and Bat - are grounded at the same time, the control circuit for charge regulation is bypassed - as a result the charge current into the battery can no longer be regulated and the battery is overcharged. If a grounding on the minus side should/must be done, it is absolutely necessary to ground only one minus potential, e.g. only BAT -!

(These grounding instructions apply to Solsum, PR, PRS, Solarix 2525/4040, 2020-x2, PowerTarom and Tarom 4545 controllers.

Solsum series solar charge controller: Is it possible to operate the solar charge controller without connected solar modules?
The Solsum can be used without a connected module as a pure deep discharge protection. The Solsum supplies itself from the battery.

(Only if a night light function should be activated for the load output this would not work)
Can a solar charge controller remain connected to the solar modules for a long time without a battery (using our PR series as an example)?
The operation of the PR controller without PV module is not an intended application, but can be carried out without damage if certain basic conditions are taken into account.

If the battery is disconnected, the PR1010 does not have a secured supply. The behavior of the PR is therefore dependent on the voltage conditions at the PV module.

If the voltage at the PV module is between approx. 10V and 13.9V (possibly doubled for 24V system) the controller will display error message E13.

In this voltage range, the PV module is operated in idle mode. If the voltage at the PV module rises to >13.6V, i.e. if the charge control is activated, the PR starts to short-circuit the PV module. Since it can/will then also short-circuit the only supply source, the controller will switch off and then restart. This state is repeated. If the short circuit current of the PV module is <15A, the PR will not be damaged. However, the device may heat up - as in normal operation.

If the voltage on the PV module is approx. <10V, the PR may not be supplied with power and the controller will not start up at all.

In operation without battery, different states can be displayed on the unit, with changing displays. This may be annoying for the user, but is not harmful for the PR controller.

However, it must be noted that the maximum short-circuit current from the PV module is below the rated current of the PR and the PV open circuit voltage will never exceed 40V. Otherwise the PR controller may be damaged. Due to the unsafe supply, no loads should be connected to the load output in this state. The loads may be subject to voltage fluctuations of the PV module that they cannot tolerate.

When reconnecting the battery, it is essential to ensure that the PV modules are disconnected first. The installation sequence must be followed: 1 - battery, 2- PV module. This is the only way to ensure that no incorrect system voltage was previously detected by the controller using the PV module. (e.g. 24V instead of 12V).

It is always advisable to use a disconnect switch between the PV module and the PR controller. Alternatively a cover of the PV modules is useful to ensure that the PV circuit and the PR controller are as de-energized as possible.
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