FAQ Steca charge controller

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?
Operating our charge controllers with sources other than a PV module (wind turbine, water turbine, power supply) 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 sometimes has destructive consequences for other sources.
What should be considered when using a charge controller in cars or mobile homes?
When using 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 negative only at one point. In the vehicle (normally negative common ground, i.e. all negative lines are connected, battery negative is common ground), you can solve this, for example, by routing the module and consumer lines separately. So 2 lines (+ and -) from the module to the controller, as well as 2 lines (+ and -) from the controller to the consumer.
It would also be possible to use a multiple socket for several distributors. It is only important that the connections are separate 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 and 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 specified in the data sheet is usually at 25°C, so that the expected open circuit voltage must be calculated at 0°C, for example. To do so, 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 specified in the data sheets, e.g. maximum open circuit voltage 47V and maximum module current for the PR controllers, depending on the model.
Exceeding these values will lead to damage the charge controllers.
Can several controllers charge a battery at the same time?
Yes. Up to 5 controllers can be operated on the same battery pack without direct communication between them. The SOC control must be deactivated on the controllers and the voltage control 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.
More information: Link
MPPT 6000 M /S: Where are the consumers connected?
None of the MPPT 6000 M/S have a connection for consumers.
Consumers must be connected directly to the battery. It is necessary to build in your own distribution somewhere there.
To protect the battery from deep discharge, the consumers must have their own deep discharge protection.
Alternatively, it is possible (only with the 6000-M) to build in additional deep discharge protection by using the auxiliary contacts AUX and an additional external switching element (relay or contactor).
If you would like to gave information about the current consumption of the consumer, it is possible (only with the 6000-M) to use an additional external current sensor HS400.
PR series solar charge controller: How do I set the different charge voltages?
Instructions for setting the various values (deep discharge protection, restart voltage, final charge voltage, etc.) can be found here
Solsum series solar charge controller: Which solar module?
To charge the battery, it is important for the module voltage in the MPP of the module to be 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 for the module voltage to be at least 10V. Otherwise it will go into night mode and stop charging. Of course, the Solsum also has its own self-consumption, which the solar module also needs to cover.

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

If we now assume diffuse light and 200W/m2 , i.e. 1/5 of the power, then the 5W module only has 1W. This 1W then at MPP voltage of approx. 15V results in a possible current of 1W/15V = 0.066A. If we assume that the Solsum controller's self-consumption is 6mA, there is still 60mA charging current left for the battery.

If we assume that you want to charge 1Ah into the battery, you would need 16.6 hours of charging current for 60mA.

The situation is different with the 100W lamp. Here, converted to m2, this results in significantly higher irradiation and therefore more power/electricity from the solar module.

Tarom 4545 series solar charge controller: How can data stored on the SD card be visualised on the PC?
Data are stored on the SD card in CSV format. No Steca/KATEK tool is available for evaluation/visualisation. The user can/must create a representation with Excel individually. A description of the file contents can be found in the operating instructions.

The fact that a new CSV file is created every day can be somewhat inconvenient. If you want to display several days, you will have to manually copy the data into a spreadsheet.

The data cannot be saved to the SD card afterwards. Storage on the SD card is an online recording on the storage medium. The Tarom does not have intermediate storage for re-storage at a later point. It is not possible, for example, to save the internal data logger to the SD card later. The recording begins at the time of activation. Of course, a writeable 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 detect 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 of the load output is deactivated. The SOC value is used to select the charging mode (float, boost, equal). 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 voltage controlled mode, a voltage value is used to activate the deep discharge protection instead of the SOC value. Likewise, in voltage-controlled mode, a voltage limit is used instead of the SOC value for selecting 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 charged directly by another charging source or if an islanding inverter or, for example here the garage door drive, is connected directly to the battery, there is no sensible use for the SOC mode. 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) would be over- or underestimated and may cause the deep discharge protection to react too early or too late. So, if charging sources or consumers are connected directly 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 control mode. The final charge voltages for each charging mode are fixed (apart from temperature and line compensation) and therefore independent of the SOC or voltage control mode. With 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 charging current into the battery so the final charge voltage is kept constant. As the energy consumption of the battery 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 may 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 adjusts 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 gentler on the battery. - Disadvantage: The behaviour of the controller on a SOC basis is not as transparent for the user; the user must have more ‘trust’ in the controller, as the internal processes cannot be directly understood by the user. It is not allowed to compare the behaviour of the controller 1:1 with the voltage value of the battery or to attempt to derive it from this. Especially with dynamic processes, it is possible to have the impression that the behaviour of the controller in SOC mode is not correct. Example: When switching on a (large) load, the battery voltage drops significantly, but the SOC value remains unchanged for the time being and may only correct itself downwards slowly. The voltage here 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, while the SOC is not at 100% – in spite of the 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.
What angle is best for the Steca solar charge controller displays in terms of readability?
Right: Klick

False: Click
Is synchronised use of the night light function possible with several charge controllers (in this example, PR series solar charge controllers)?
Synchronised switching of the night light function with several PR controllers is not possible. (our partner Uhlmann Solarelectronic offers controllers with a swarm function or controllers with a timer)

The following is required for PR to detect night: - Charge control is not active (this could be the case with parallel charging, e.g. via a power supply unit or wind generator) - The module current <= 0, which is usually the case when the module voltage is approx. 1V lower than the battery voltage. - There may not be a short circuit at the module input. - The conditions for night are checked every 1s, if the conditions are fulfilled for 10s, night is detected.

Due to the dependency on the battery voltage (the module voltage must be lower than the battery voltage), different switching points may occur at the light points, especially in systems with separate batteries. Night detection also depends on the module voltage. If there are different radiation conditions here (e.g. also due to extraneous light, dirt, shade), this also has an influence on the switching time. Due to the dependence of battery voltage and module voltage, it is not possible to give an absolute value for the module voltage. The PR controller does not have a clock.

Deviations in the switch-on times of 1h or possibly more can occur in reality, depending on the properties and behaviour of the individual light points.
PR series solar charge controller: The controller displays load current although no consumer is connected. Can the controller be recalibrated?
1.) PR must be in the default setting (no night or morning light function)
2.) Load is switched on (load symbol is displayed)
3.) Simulate night by darkening the module or disconnecting it (moon symbol must display after 10-15 minutes)
4.) Switch off the load manually with the right button (load symbol disappears)
5.) Wait a few seconds
6.) Switch the load on again.
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This procedure should calibrate the load current calculation correctly again and 0 amperes should also be displayed if 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 terms of voltage.
The battery voltage is always present at the load output.
At what ratio does the Solarix 2020-x2 - 2-battery controller charge the connected batteries?
Once the main battery is full, the charging power is used more for the auxiliary battery. The auxiliary battery does not stop at 10%.

Technically, the expression ‘more power to the auxiliary battery’ is not quite correct. Both batteries always get the same instantaneous charging current; it is only the duration that 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 auxiliary battery for 10% of the time. Once the main battery is full, more charging time is provided for the auxiliary battery. In the example below, this is only 30%, but as far as I am aware, this can also go up to 90% for the auxiliary battery and 10% for the main battery. This always depends on how full the main battery remains. The time duration is short, 100% time corresponds to 33 ms. In relation to this period of time, the average current then increases for the auxiliary battery once the main battery is full.

PR series solar charge controller: When do I use the ‘AGM/GEL’ setting?
The PR and all of the Steca charge controllers use the float – boost – equal charging modes. The ‘equal’ mode has the highest final charge voltage. This is also when the strongest gassing occurs in the lead battery.

As AGM batteries have no possibility of being refilled with electrolytes or distilled water and this type of battery usually has a safety valve that responds if the internal gas pressure is too high, many battery manufacturers recommend a moderate final charge voltage. The easiest way to do this on the PR is to select the GEL/AGM battery type. When this is selected, the ‘equal charge’ mode is not active and only the reduced final charge voltage of the ‘boost’ mode is active.

Basically, however, the battery manufacturer’s instructions on the final charge voltages recommended by it should be observed and adhered to. This may also require the charging mode ‘equal’ to be used. The PR controller even offers the advantage of being able to set the final charge voltages; see the instructions ‘Menu: Charging voltages’ on the website for the PR 1010 - 3030 controller.

What are possible causes for excessively high battery voltage (example: the battery voltage reaches 30V in a 24 volt system)?
The charging voltage is set in a hidden menu; see additional instructions (not available for all controller types)

- Selection of voltage control with/without bar display is important and necessary when consumers are connected directly to the battery.
- 30V, even if only briefly, should not occur under normal circumstances if the GEL battery type is selected. This is also independent of the setting of the SOC/voltage control mode.
o 30V may occur (for longer) if the final charge voltage for equal has been changed to 30V and the charging mode equal is active.
o 30V may occur briefly (if the setting has not been changed) if charging a small battery with very high charging current.
o 30V may occur briefly if the internal resistance of the battery is increased and, as a result, oscillations occur during load changes (changing charging current, possibly also changing load from consumers) that the controller cannot regulate quickly enough. An increased internal resistance can be a sign of an old/bad battery.
o There may also be an increased line resistance between the battery and the controller. If necessary, check connections, cables, terminals, fuses.
o 30V could occur briefly if the consumers connected directly to the battery supply power, possibly during switching operations?
o 30V could also be caused by chargers connected directly 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 earthed separately?
Earthing 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 earthing is not necessary, an earth-free installation is preferable. If earthing is necessary, the positive pole of the battery can be earthed. Inside the Solsum, all plus connections are always firmly connected to each other. Under no circumstances may two or more negative connections (PV -, Bat -, Load -) be earthed 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 no longer be able to switch off. If the PV- and Bat- are earthed at the same time, the control circuit for charge regulation is bypassed and the charging current into the battery can no longer be regulated and the battery is overcharged. If earthing on the negative side is to be performed, it is essential to earth only a negative potential, e.g. only BAT -!

(These earthing 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 a solar module connected?
The Solsum can be used purely as deep discharge protection without a module connected. The Solsum gets its supply from the battery.

(The only way this would not work is if a night light function is to be activated for the load output)

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Can a solar charge controller remain connected to the solar modules for a longer period of time without a battery (using our PR series as an example)?
Operation of the PR controller without a PV module is not an intended application, but this can be carried out without causing damage if a few basic conditions are taken into account.

In the case of a disconnected battery, there is no secure supply for the PR1010. Therefore, the behaviour of the PR is dependent on the voltage conditions at the PV module.

With a voltage at the PV module between approx. 10 V and 13.9 V (possibly double values with a 24 V system), the controller will issue the error message E13.

In this voltage range, the PV module is operated virtually in idle mode. If the voltage at the PV module rises to >13.6 V, i.e. the charge control is activated, the PR starts to short circuit the PV module. Since it will also short circuit the only supply source, the controller can/will go out and then restart. This state will then repeat itself. If the short circuit current of the PV module is <15A, the PR will not get damaged. However, heating may occur at the unit – as in normal operation.

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

During an operation without a battery, various states may be displayed at the unit, with alternating displays. This may be annoying for the user, but it is generally not harmful for the PR controller.

It must be noted, however, that the max. short circuit current from the PV module is below the rated current of the PR and also that the PV open circuit voltage never reaches 40 V. Otherwise, the PR controller may get damaged. Due to the unsafe supply, no consumers should be connected to the load output in this state. The loads may be subjected to voltage fluctuations from 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 observed: 1- battery, 2- PV module. This is the only way to ensure that no incorrect system voltage was previously detected by the controller based on the PV module. (e.g. 24 V instead of 12 V).

It is always recommended to use a disconnector between the PV module and the PR controller. Alternatively, it makes sense to cover the PV modules so that the PV circuit and the PR controller are as de-energised as possible.
What does ‘float’, ‘boost’ and ‘equal’ mean?
1. Float

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

2. Trickle charge

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

3. Boost, maintenance charging

Maintenance charging maintains the battery more intensively than trickle charging. In addition:
Maintenance charging starts automatically when the switch-on threshold falls below 12.7 V (70%). Maintenance charging can also be started manually.
Maintenance charging ends after the charging time has elapsed.
The charging voltage is higher during maintenance charging than during trickle charging.
After maintenance charging, the controller automatically switches to trickle charging.

4. Equal, equalisation charging

Equalisation charging avoids stratification through controlled gassing and therefore prolongs the life of the battery. In addition:
Equalisation charging starts when the cycle has elapsed or the switch-on threshold 1) is not reached.
Equalisation charging ends after the charging time has elapsed or when the switch-off threshold 1) is reached, whichever occurs first.
Equalisation charging is switched on in the ‘Liquid electrolyte’ setting.
What should be done if the charge controller is defective?
Depending on the model, a self-test can be carried out on the unit, which could provide further information on any faults that may be present (for more information, please refer to the relevant operating instructions).

If the self-test shows an error code, or if no self-test is possible depending on the model, please contact your specialist dealer or installer for complaint handling.

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