Products > Test Equipment
DL24 Atorch type electronic loads: considerations on how to choose the best mosf
Silicium81:
--- Quote from: elecdonia on February 07, 2023, 03:44:50 pm ---I should have mentioned that the 4 ohm series resistor is an option which only needs to be used when the voltage of the power source being tested is higher than what the MOSFETs can easily handle.
I agree that we don’t need the 4 ohm resistor when the source voltage is <20-30V. My recommendation to use the series resistor applies only to situations where the voltage is high enough to overstress the MOSFETs, for example when I described load-testing a 48V power source.
I frequently use an older load tester with only a single MOSFET to measure the Ah of power tool batteries (12V-18V). In this case I do not add any series resistance. But on a few occasions where I was testing a power source with 48v-60V, then I added the 4 ohm series resistor.
So, rather than making the 4 ohm series resistor a permanent component of the load tester, my idea is it can simply be wired into the test circuit temporarily when needed.
--- End quote ---
It's a good idea to dissipate some of the power in an external resistor. It can be convenient to use car headlight bulbs. These are generally 50W bulbs under 12V, i.e. a resistance of approximately 3 ohms crossed by an intensity of 4 Amps.
By using a headlight bulb, we know that the voltage drop will be 12V under 4A, easily allowing resistive arrangements to be made
It is therefore sufficient to place in series with the battery to be discharged a bulb for 4A, two bulbs for 8A.
The diagram is this (for 8A):
elecdonia:
--- Quote from: Silicium81 on February 07, 2023, 04:56:59 pm ---It's a good idea to dissipate some of the power in an external resistor. It can be convenient to use car headlight bulbs. These are generally 50W bulbs under 12V, i.e. a resistance of approximately 3 ohms crossed by an intensity of 4 Amps.
--- End quote ---
+100 for suggesting 12V incandescent light bulbs of appropriate wattage. Multiple 12V light bulbs can be connected in series or in parallel if needed. All incandescent light bulbs have a built-in current limiting feature: Their resistance when the filament is hot is much larger than the resistance when it is cold (dark). This causes them to work like a current limiting device.
For many years I've used a ""dim-bulb tester" to safely apply AC mains power to items I am repairing. This works just as well with low-voltage bulbs as it does with mains voltage bulbs. Please note that the light bulbs must always be traditional "incandescent" bulbs. Not CFL or LED.
Filippo52:
Elettronia
Ok now everything is clear;
I agree perfectly with you that this is for the higher voltages that put the mosfet in more difficulty.
I had said that you need various resistances if you make different uses that you have to insert or remove from the connection each time.
It is an effective solution if you have a few different situations to deal with
Otherwise it becomes a bit uncomfortable and if you have to have many high wattage resistors even expensive.
That's all, however yours is a simple idea to implement even now that linear power mosfets are not on sale
a greeting
Filippo52:
12 volt incandescent bulb for automotive it is exactly the method I used before I had an electronic load.
It is very cheap.
Electronic load is the "automatic solution" for all for the entire operating range of the electronic load.
Unfortunately DL24 is a Chinese product. It's cheap but has many flaws, including the seller's unacceptable arrogance.
let's say that in the end we have a good "semi-automatic" product that tries to combine the advantages of the two solutions: cheap and with a wide range of action
Everbrave:
--- Quote from: Silicium81 on February 01, 2023, 09:34:56 am ---
Hopefully they will be ok:
--- End quote ---
The operating point you draw means 450W which is much more than the max. allowed dissipation power Pd of 280W! At 100V, I assume you get max. 2A (rather 1A) from a IRFP264.
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