| Electronics > Beginners |
| Voltage "divider" after PSU to highten the resolution? |
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| hli:
Remember: a power supply is not a measurement device. Its intended to _supply _power_ to your device, that it also measures voltage and current is mainly so you can adjust its settings, and get a sense about overloading. When you want to do precision measurement, use a DMM (or e.g. a µCurrent). Yes, there are PSUs out there that can measure very precisely too, but as you did already discover this combination has its price. |
| FriedMule:
Yes you are right and I thought, if I could get / buy a PSU, I could always use a meter to adjust it by, no need for advanced DMM, "just" a great resolution. |
| ArthurDent:
As others have pointed out, finding a power supply with the specs you mention is not an easy (or cheap) task. Resistors are the worst way to try to get this resolution because they only give you a ratio (at no load) and the ratio error will increase with load. If you want 10 volts at 10x more resolution and you use a 10:1 divider you get 10x more resolution at 10x less voltage so you have to increase the voltage into the divider by 10x (or 100 volts) to get your required 10 volts out and resolution wise you are right back where you started except you no longer have a regulated output – it is load dependent. If your supply only has local sensing and you set the power supply output to 10.00 VDC and use two 3 foot number 18AWG (1.2mm) wires with a 1A load, the load will only see about 9.95 VDC. If your load varies from zero to 1A then the load will vary 50 millivolts caused by the lead drop, that on top of whatever load regulation the supply has. Trying to build your own supply will be a huge problem unless you have unlimited funds to devote to research and development. Besides needing a supply with remote sensing capabilities as has been pointed out, the supply has to be temperature stable and able to maintain its stability and accuracy over some extended time period. Drift can be a big problem with low end power supplies. That is why the price you have to pay for precision goes up exponentially. Resolution can be meaningless if the other supply errors are large enough to mask the resolution problem. Below is a photo of my HP e3632A bench supply similar to the HP 6632A supply beanflying has. Supplies like this can sell used for up to $1000 (I paid FAR less) but they are one way to get what you need. This video about the HP e3632A gives some good information to describe what you’re talking about. The second photo is of one of my stable references that has been on for several months and has an output of 10.00000 VDC as read on my HP3457A meter. That precision comes at a cost and a lot of time for burn-in. You have to ask yourself if you really need what others have said you are wishing for. One common way to eliminate lead drop would be to build the necessary regulator right at the circuit you’re building so the lead length is an inch or so and if you need 10 VDC then feed the input to the board regulator with the higher necessary voltage. |
| FriedMule:
Thanks. great info and video. I have found this Maynuo M8851 model but can't seem to find a datasheet. http://www.maynuo.com/english/pro.asp?tid=35 I know that it only goes to 6V but better then nothing, it do on the other hand, goes sky high in Amp: 60!! |
| Calvin:
Hi, its under the folder Download at the top of the page. Wouldn´t be the 8811 (30V/5A) or the 8831 (30V/1A) be closer to Your needs? Welectron offers the Manyuo electronic loads ... maybe they can also supply for the power supplies. regards Calvin |
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