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|You could find more information bellow or you could consult our web site for futher information.|
|Model||Input Vdc||Voltage Range||Channels||Remote on Input||Notes|
|PVFB 24/24-32||24||1-8 A||4||Current limiting to avoid voltage dips|
|PVFE 24/24-12||24||1-6 A||2||Channel reset remotelly|
|PVFE 24/24-20||24||1-10 A||2||Channel reset remotelly|
|PVFE 24/24-24||24||1-6 A||4||Channel reset remotelly|
|PVFE 24/24-40||24||1-10 A||4||Channel reset remotelly|
|The EU, USA and many other countries are considering to increase the safety requirements and probably in the future the electronic fuses will be mandatory in many applications and not only a way to save time and money.|
Why should we protect the output of our power supplies or DC loads?
Wires are very expensive. We always try to save money in our machine or system by using the minimum wire diameter.
|We will also try to use the minimum number of power supplies. In this way we not only safe money but also avoid many other problems like leakage currents, inrush currents and ECM problems.|
It is also more and more popular to use a distributed arquitecture. This means we use a power supply to get a DC bus, also getting the isolation, then we use local small DC/DC converters non isolated (Points of Load) to power each local load. With this method is faster and cheaper to develop new systems and also more flexible to expand our application.
Sometimes we forget about very important issues. What will happen if we have a short circuit in one branch? Some power supplies have a shutdown behavior in case of a short circuit or overload. This is fine for some installations were we have maintenance people, but in many other cases this is not the desired behavior. If we have an unattended installation we do not what to send someone to check what happen or just to restart the power supply that failed due to a peak current or isolated problem.
|For these reasons it is more common to see power supplies that do not shut down in case of an overload. Some units are over power, offer higher power in case of a overload to try to start motors and other heavy loads. Others have a hiccup behavior and will be all the time attending to re-start in case of a short circuit or overload. In all this cases what will happen is that all the current will flow to the shorted branch. Since we use small wires for that load because we did not thing about a short circuit that wire might burn out. If this does not happen at least the load with the short circuit will be probably heavily damaged because all the current if flowing inside without any limitation. Also voltage of the system will go down and all the other unaffected loads will be off because all the power is going into the shorted load.|
|If we are able to open and isolate that branch in a short time we will avoid a total shut down of our system and also will reduce the damage suffered by the shorted load and will prevent from fires.|
|To avoid these problems we can use fuses. But fuses must be also manually replaced. We also need to use fuses that are able to stand the peak and turn on currents but that in case of a short circuit will be melted. Power supplies that have a big overload current can help to trip these fuses.|
|We can also use circuit breakers. Circuit breakers usually need 10 to 20 times higher current than their rated current to trigger the solenoid they have inside. For example a C1A circuit breaker is a 1A and needs 10 to 20 amps to be triggered in a fast way. Of course with a smaller current it will be trigger because of temperature and it will take a long time. When we have long cables the circuit breakers do not work properly because the power supplies have not enough current to trigger the solenoid.|
|To know if we can trigger a circuit breaker in a safe way (usually in less than 10 ms) we can make some simple approach of calculations.|
|For example for a 3A circuit breaker we need 60 Amps to trigger the magnetic part. This means the resistance should be less than 0,4 Ohms (R= V/I). We need to know the wire diameter. We will take the resistivity of the copper at 20ºC Y= 62,5 m/Ωmm2 . If we use a flexible wire it’s real length is 2 times the length of the cable because it is twisted. So using a 1,5 mm2 wire.|
|0,4 Ohms = 2 x Cable length / (62,5 m/Ωmm2) x 1,5|
We can find out that to trigger a 3 A circuit breaker with a 1,5 mm2 we can use a maximum cable length of 18,75 meters. Of course we also need a power supply able to have 60 Amps a 24Vdc output, this will really mean that the real length will be much more smaller than this calculation. Which is also one of the big problems, we need many times to test the circuit breakers. If we use a too big one we will not trigger it in case of an overload, if we use a small one it will be triggered with the turn on currents. In many cases a circuit breaker won’t work or won’t be reliable. We also need to think about the temperature changes and how does affect the wire resistance.
For this reason the only safe, reliable and easy option are the electronic fuses. The electronic fuses have a powerful microcontroller that check the real current, voltage and that will trip the branches faster than anything and in a safe way. We can also program the units to accept peak currents and to have a delay time.
Block offers electronic fuses of 2 or 4 channels with currents of 1 to 6 or 1 to 10 Amps. You can adjust the output current of each channel in 1 to 1 steps.
The PVFE series can be remotely connected, so we can avoid sending someone just for an isolated failure. We can implement sequences to try to restart the channel before calling for the maintenance.
Also these electronic fuses keep in their memory the last failure as well as the maximum currents for each channel. So even if we were not present when we had the failure we can easily find out what happened.
The LCD display shows the instantaneous current for each channel, so we can easily find out wrong calculation and adjust our system to the real power consumptions. This also offers us a more flexible way to expand our application.
We will not have any more problems with long wires and we can be safe with a reliable protection. Even if one branch has an overload or short circuit the other branches can work safely. The PVFB series has also a active current limitation, so in case of an overload the current flowing into a channel will be limited to 1,5 times the nominal current to a maximum of 10 Amps.
The LCD display, RS-232 communication port, relays, active 24VDC signals helps us to monitor our system with detailed information. We can also safe and load configurations with the free software so we can safe time in the installation.
|The remote On for PFVE series and the active current limitation for PFVB series make these electronic fuses unique in their kind and a state of the art product.|
|For further information you have available technical information about PFVE serie , PVFB serie or both of them.|
Do not hesitate to contact our sales department to consult prices and availability.