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| ET5410 Electronic Load mod: add external sense |
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| mawyatt:
Agree putting the PTC Fuse in series with the Resistor and not directly with the Sense lead is probably better. If a big enough power resistor is used, that can withstand the peak current, then the SBD can be omitted. You can compensate for the PTC resistance by matching a pair for equal ~0 current resistance. Or possibly even better, use a matched pair of PTC fuses in place of the 10 ohm resistors, then no need for the SBD or the Resistors!! Best, |
| MF-jockey:
*** A safe 4-wire mod with PTCs *** Inspired by mawyatt, I looked at the data sheets of common PTCs from TDK/Epcos. For a safe solution even at higher voltages, I can recommend the TYPE B59860C0080A070, https://www.mouser.com/ProductDetail/EPCOS-TDK/B59860C0080A070?qs=MD70nW2XBGhXaRINHeKp0g%3D%3D. This PTC has a transition temperature of around 80°C, so it doesn't get that hot when switched off. The cold resistance is around 15 ohms, which is very suitable for this application. In general, PTCs with 10 to 25 ohms are suitable. See also the EPCOS data sheet as first appendix. A lower value reduces the influence of the 2-wire measurement. A higher value improves the 4-wire measurement, especially at high currents (higher voltage drop in the load lines). Since I couldn't get hold of the PTC B59860C0080A070 so easily, I had other common PTCs (10 Ohm, 150°C) in stock, but I ordered Polyswitch 250V 0.1A from Aliexpress on suspicion https://de.aliexpress.com/item/1005004908820722.html. These turned out to be a stroke of luck for this purpose, suitable resistance around 10 Ohm and quick response at relatively low temperatures. Knowing that the resistance increases after response, I connected 6 of the 10 PPTCs directly to 32 V DC. After a short current surge (approx. 3 A) they limit at around 40 mA. When they cool down they have a resistance that is around 15% higher, which is hardly a problem here. I have summarized the measured values in the attached table. Today I installed two of these PPTCs in my ET5410A+, it works well as expected. |
| MF-jockey:
Thermostat for fan, according to the mod by ceut -> there is a problem with ET5410A+ I got myself some 45 °C temperature switches and after testing them I installed one in the fan cable of the ET5410A+. Unfortunately, the device was no longer usable. The fan symbol appears at the top right and all inputs are blocked. The software of the ET5410A+ works differently in terms of fan monitoring than the older one in the ET5410. The fan only has two connection cables, monitoring is done using a 0.5 ohm resistor via the current flow. I will now build a solution with an additional resistor to achieve the necessary current flow. |
| klausES:
Satisfied the fan monitoring with a minimum current by resistance and a decent temperature curve control to the fan, (with a adjustable quiet minimum speed, because a complete standstill fan is not good for other components). |
| MF-jockey:
A sensible fan control according to temperature would be the responsibility of the manufacturer, especially since all the components for this are installed. Instead, a medium speed is set when the device is cold and when a higher power is set, it is regulated to full speed, even when the device is still cold. This is a quick solution and no programmer has thought about a quieter device. After analyzing the circuit, I assume a current threshold of less than 80 mA. There are two different solutions for activating the thermostat solution. Firstly, a parallel load resistor to the fan and thermostat so that the monitoring detects current flow. The fan can stay off until the temperature threshold is reached, but is not monitored. Secondly, a bridging resistor on the thermostat that lets the minimum current for the fan monitoring through. This slows the fan down until the temperature threshold is reached. I chose the second solution and determined the maximum resistance value with a potentiometer. At 27 ohms, the fan just about starts safely. For a little safety, I soldered 20 ohms onto the thermostat. This means that the fan runs much more quietly until the cooler reaches the switching temperature of the thermostat. |
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