I´m working on a project who uses some canbus data, data logging in a SD card, bluetooth and realtime clock. These components are working great together with the arduino Uno. But, the final task of the project involves to send pulses to two solenoids (together, they draw around 11 amps in a very short period of time - around 20 pulses in one second and, after the pulses, will be on for 10 to 15 seconds). My first idea was use a solid state relay to do this job, but it´s very hard to find one for DC. My primary input is DC 12V provided from my motorcycle. So, I´m considering to do this job with a transistor. But I´m very newby on this, and I don´t know how to locate de correct components and assembly then together.
Some of you already do somethig like that ? If yes, every advice will be welcome.
If you rule out general advice from people who haven't, you are eliminating most of the useful feedback you can get. Think about how many people actually did... very few. If you want that, go search for similar projects.
Was also going to suggest this might need a MOSFET which would be more efficient. Probably something like an IRF540 (the 520 is a bit borderline for a requirement of 5.5A per solenoid). These already have a built in snubber diode. Will almost certainly need a heatsink. I doubt those controller boards will adequately dissipate the heat on their own.
Still, as per aarg, it would be good to see a description/diagram (even a hand drawn one) of what you are trying to achieve.
Power supply
Power drivers (FETs), and protection
Possibly cooling, certainly a good heatsink
Your control logic
Noise suppression on the power rails anddriver wiring
Kicking a solenoid at 20Hz is probably getting close to the limit - depending on the throw of the armature.
You have stated that you derive the 12V from your motorbike supply, which is fine, but the details of your project is lacking.
You need to state why you need the pulses, although I could hazard a number of guesses and say you don't need to pulse relays in this way, unless it is for something very specific. Even so, normal relays don't like being pulsed fast, given there is a little thing called remanence, which determines how fast a relay is released.
More detail will help to identify your needs, rather than just trying to give you an answer which is completely wrong for the actual task.
Back-emf of an inductor produces a higher voltage on the drain of the fet, which could reach breakdown/avalanche voltage (some fets don't mind).
The body diode inside the fet can't stop that (wrong way round).
A diode across the load limits voltage on the drain to "supply + 0.7volt".
Leo..
You are absolutely correct! I have evidently been looking at some dodgy reading material. The Snubber diode IS placed across the LOAD and not the switching device. That's an embarrassing error on my part!
Freewheeling diodes are Transient suppression diodes(TVS) and although a normal diode can be used, there are diodes designed to do this more efficiently. This is nothing like the internal diode on a MOSFET, which (from past reading) is used as a Voltage clamp.
A TVS has a bigger junction area, than a standard diode, so suppresses the transient a lot faster and its response time is quite fast, unlike a standard diode.
You also have to note that unlike a normal diode, the Voltage can vary, depending on which device you use.
As far as DIY designs are concerned , then a standard diode will suffice.
TVS diodes are zener diodes on steroids, and are AFAIK not commonly used for back-emf protection. They are commonly used to protect power supplies from over-voltage.
They could be used across the switching element, if faster release of a relay is needed.
Nonsense.
A TVS, Schottky diode or common 1N4004 are all 'turning on' equally fast.
Leo..
Using the term nonsense is just downright insulting, but if you think something said is wrong, just state your reasons. We are not children around here so don't act like one.
TVS diodes are used in many applications and are designed for that task and have a high repetitive characteristic, unlike Schottky (which is fast) and 1N400x series which is slow by a magnitude for comparison.
I have been using some P6KE51CA in a recent design which have a response time of 1.0 pS min something even a Schottky diode does not achieve. As you say,in this case at least, these particular ones,are used in a power application where the Voltage cannot exceed 75V,
A Schottky diode has fast switching capabilities, which is good for PSU's and RF but they also have a 0.2V forward Voltage and an equally lower reverse Voltage breakdown some as low as 10V, which is useless in many other applications
There is no use lumping all diodes into one basket and saying they are similar.
My point being that there are many different types of diode and they all have different jobs
As we all know, there are shorcuts to achieving an end result which is adequate.
If the relays in this circuit are attempting to switch 11A at pulse speeds of 20/s, then get rid of the relays, and use opto isolated MOSFET for switching.
If there is a diode across the coil there is no spike to suppress because the diode allows the current to continue flowing when the supply is interrupted. As long as there is a low resistance path for the current the inductor does not need to create a high voltage to attempt to maintain the current.
As for switching speed, it does not matter. Rectifier diodes have high capacitance due to their large junction area. Above some frequency, which will depend on the diode, the capacitance effectively shorts out the junction, maintaining the current from the inductor. The junction capacitance charges, the charge carriers move and start combining at the junction and it conducts. If you are concerned that there might be some brief open circuit period between the power being removed and the diode conducting, there isn't.
Nice, but this is an Arduino forum where we don't use hundreds of GigaHz. For practical purposes, a Schottky diode has a response time in the nanoseconds, and so does a 1N4004. You don't seem to find those specs in the datasheets. They only list recovery time, which is irrelevant when used for kickback of a relay. I had a paper about that, but I can't find it after upgrading my PC.
Leo..