Win a Tenma Power Supply

I would like to set this power supply up to be able to rapidly test USB cable performance. I have a large collection of USB cables that is still growing. It seems every device comes with yet another USB cable.However not all cables are the same and sometimes they don't perform well enough, usually because they incur too much voltage drop when higher currents are drawn. I have tested lots of different USB cables to show how variable they can be, but what I really need is a way to quickly test cables. If the test isn't quick, I won't do it, and when a problem crops up, it always takes too much time to isolate it to the cable and then find a better cable.

A dual supply allows the input and the output voltage of the cable to be monitored while the cable is in use by a target device. To do this one supply would be set for a voltage of 5V and a current limit of 1 A (or more if needed). The other supply would also be set for 5 V but the current limit would be set very small, say 1 mA. Each supply output would be connected to a USB connector so a cable could be connected between the supplies. The supply set to a small current would also be connected to the target device (but unable to supply enough current to power it) When a test USB cable is connected between supplies, the target device would get enough power to run.

The target device current would be the sum of the currents from both supplies (basically the high current output plus 1 mA).

The voltage to the target device would show on the low current supply voltage meter.

The voltage drop in the cable would be the high current voltage minus the low current voltage.

The voltage drop could also be determined by shorting the cable at the low current end instead of connecting it to the second supply and the load.

In that case the high current supply would go into current limit and if the current was 1 A, its voltage display would equal the voltage drop in the cable.

This application uses 2 supplies and both current meters and both voltage meters. and utilizes both voltage and current set points.

To make the tests quick I would design a PCB with 2 sets of USB connectors and 2 sets of banana plugs. One set of connectors would have its power pins in parallel and connected to one set of banana plugs while the other set of USB connectors would also be connected in parallel, but connected to the other set of banana plugs. There would also be a switch to short out one side and an output USB connector for a target device.

The tester would be able to test any cable by itself or any cable powering any target device simply by plugging the cable in or plugging in the cable and the target device.

Here is a picture showing some of the USB connectors that might be installed on a PCB to mate to arbitrary USB cables:

Of course these connectors would also allow the power supply to power or charge several USB devices at the same time.

I would like to set this power supply up to be able to rapidly test USB cable performance. I have a large collection of USB cables that is still growing. It seems every device comes with yet another USB cable.However not all cables are the same and sometimes they don't perform well enough, usually because they incur too much voltage drop when higher currents are drawn. I have tested lots of different USB cables to show how variable they can be, but what I really need is a way to quickly test cables. If the test isn't quick, I won't do it, and when a problem crops up, it always takes too much time to isolate it to the cable and then find a better cable.

A dual supply allows the input and the output voltage of the cable to be monitored while the cable is in use by a target device. To do this one supply would be set for a voltage of 5V and a current limit of 1 A (or more if needed). The other supply would also be set for 5 V but the current limit would be set very small, say 1 mA. Each supply output would be connected to a USB connector so a cable could be connected between the supplies. The supply set to a small current would also be connected to the target device (but unable to supply enough current to power it) When a test USB cable is connected between supplies, the target device would get enough power to run.

The target device current would be the sum of the currents from both supplies (basically the high current output plus 1 mA).

The voltage to the target device would show on the low current supply voltage meter.

The voltage drop in the cable would be the high current voltage minus the low current voltage.

The voltage drop could also be determined by shorting the cable at the low current end instead of connecting it to the second supply and the load.

In that case the high current supply would go into current limit and if the current was 1 A, its voltage display would equal the voltage drop in the cable.

This application uses 2 supplies and both current meters and both voltage meters. and utilizes both voltage and current set points.

To make the tests quick I would design a PCB with 2 sets of USB connectors and 2 sets of banana plugs. One set of connectors would have its power pins in parallel and connected to one set of banana plugs while the other set of USB connectors would also be connected in parallel, but connected to the other set of banana plugs. There would also be a switch to short out one side and an output USB connector for a target device.

The tester would be able to test any cable by itself or any cable powering any target device simply by plugging the cable in or plugging in the cable and the target device.

Here is a picture showing some of the USB connectors that might be installed on a PCB to mate to arbitrary USB cables:

Of course these connectors would also allow the power supply to power or charge several USB devices at the same time.

Great idea D! Maybe it exists and I haven't found it yet but a procedure for testing USB cables would be nice. Jame's goal is to simplify the testing and minimize the equipment required.

Sean

Or alternatively use a DMM

Good point. A good DMM should be able to measure milliohms well enough to get cable resistance, which is pretty useful.

However, even if it is a fancy 4-wire DMM, you would still need to calculate the voltage drop. And a DMM doesn't stress the wire with the full current it is expected to carry. Neither instrument is ideal, but if I had a choice I would use the power supply solution. Even purpose-built cable testers are not ideal, since they often require set-up and boot time and I am not aware of any that have all the USB connectors built-in. Ultimately it boils down to what instruments you have on hand and your preferences of which to use.

How much have you seen the resistance to change when increasing the current from close to 0 up to 1A?

I don't think wire resistance changes much at DC, even if it heats up it isn't a big concern, I just like the convenience of not having to calculate the voltage drop at whatever current the target device consumes.

There is also always the possibility that the high current will expose a poor wire joint that wouldn't be detected by a DMM.

Use a fixed small value resistor in series with cable and two instrumentation amplifier to amplify the low voltages. One instrumentation amplifier to measure voltage across know low value resistor and other to measure voltage across resistor + wire.

Love the suggestion. How about we combine your idea with mine to support any model of Raspberry Pi connected. An additional port could be added for testing cables.

If we get selected we could do rock paper scissors to see who they ship the unit to:) Maybe it would be Christmas and Santa's elf made extra

Sean