Testing USB cables with ADUSBCIM USB Checker 2

Introduction

There are many ways to get USB cables. You can get them from dollar stores for 110 JPY, you can get them from well-known manufacturers for 500–3,000 JPY, or some of them come bundled with various devices.

How do you know if the more expensive cable or worth it or not? How do you know if the bundled USB cables are good or not? Since I was curious, I bought “ADUSBCIM USB Checker 2”, a device which can check cable connectivity and measure the cable’s internal resistance.

ADUSBCIM — surprising, it’s a device made locally in Japan

For data transfer, the connectivity of the cable (marked “connection” on the tester) is the important part. For charging, the internal resistance is the important part as high resistance can cause charging to be slower and energy to be wasted.

Test Results

Now, let me share the test result of some cables I have lying around. For each cable, I will share the length, resistance and resistance per meter. Resistance per meter doesn’t matter in actual use, but longer cable naturally have higher resistance, so it can provide a fairer comparison.

The documentation of what each display means can be found here.

#1 — Xiaomi 1.5M USB-C cable (5A)

1.5m, 189mΩ, 124mΩ/m

As you may be able to see from the discoloring, I’ve used this cable as my daily driver for quite some time. It has quite low resistance value for its length, as expected of a cable from a well-known device manufacturer.

#2 — Unknown 0.6m USB-C cable

0.6m, 233mΩ, 388mΩ/m

I think this cable came with some Anker charger or power bank, but I’m not 100% sure. Despite being short, the resistance is a little bit high.

#3 — Vention 1.08m USB-C cable

1.08m, 142mΩ, 131mΩ/m

While Vention is not a well-known brand, it is not a random brand either. This cable is being sold in Thailand for 119 THB per (~540 JPY) and this test shows that its product is decent.

#4 — Vention 0.58m micro-USB to USB-C cable

0.58m, 218mΩ, 375mΩ/m

Unlike the previous Vention cable, the resistance is higher despite the cable being shorter. Perhaps the manufacturing standard is higher for USB-C to USB-C cables?

There’s a 5.1kΩ resistor on the USB-C side of the cable telling the connected device to act as a host, which makes sense since the micro-USB side can only act as a peripheral.

#5 — Sanwa Supply 1m USB-C cable (5A)

1m, 165mΩ, 165 mΩ/m

This cable is from a local brand in Japan and costs 1,590 JPY. The selling point is that one of the connector can be freely rotated so I wondered if that rotation support results in higher resistance, but it seems like no.

#6 — Apple 2m USB-C cable (5A)

2m, 161mΩ, 80mΩ/m

This is the cable that came bundled with MacBooks. Out of all cables, this has the lowest resistance per meter, as expected of Apple.

#7– 0.15m cable from an HDMI adapter

0.15 m, 107 mΩ, 713 mΩ/m

This is a very short cable from an adapter for connecting a MacBook to an HDMI screen with PD passthrough and USB input. Since this cable can transmit videos too, it has all the connections and not just the normal 5 connections.

#8— HP Display 1.8m USB-C cable (5A)

1.8m, 187mΩ, 103mΩ/m

This is the USB-C cable that comes with my HP Display. Despite being quite long, the resistance is less than 200mΩ.

#9 — Watts 1m USB-A to USB-C cable

1m, 208mΩ, 208mΩ/m

This USB-A to USB-C cable is being sold at Watts for 110 JPY. For its price, I think the resistance is quite decent, showing that not all cheap cables are bad. (However, only the internal resistance is being tested here, not other factors like durability.)

The checker also shows that a 56kΩ resistor connected, telling that the device can only pull 500mA. This is required for USB-A to USB-C cables per the standard. (There were multiple non-compliant cables back in 2015, see this article for more details.)

#10 — Watts 1m USB-A to USB-C cable with USB-C to USB-A OTG adapter

1m, 297mΩ, 297mΩ/m

This is the cable back in #9 connected to a USB-OTG adapter, producing a weird USB-C to USB-C cable. On the A-side, we can see a 5.1kΩ cable forcing the connected device to act as a host. So essentially, this is a one-direction USB-C cable.

The reason I have this combination of cable is because I have an out-of-spec digital photo frame. It has a USB-C port but would only work with USB-A to USB-C cables and not USB-C to USB-C cable. I suspect that it does not know how to negotiate which device is the host and which device is the peripheral.

One other reason I tested this is to see the if the adapter results in additional resistance and yes, it does. So adapters should be avoided when charging high-current devices when possible.

#11 — Motteru 2m USB-C cable

2m, 275mΩ, 137mΩ/m

This is another local brand in Japan. This cable is being sold for around 1,660 JPY. Compared to Apple and HP cables, the resistance is on the high side, but should still be acceptable.

#12 — “at.Q” 0.7m USB-C cable

0.7m, 159mΩ, 227mΩ/m

I got this cable for 110 JPY from Seria. While it’s a bit short, the resistance of the cable is satisfactory.

#13 — DAISO 1m USB-C cable (5A)

1m, 198mΩ, 198mΩ/m

I got this cable for 330 JPY from DAISO. I’ve decided to try this because I’ve found that 5A cables generally offer lower resistance and to see whether more expensive cables from the dollar store are necessarily better or not.

While the resistance is not bad and per meter, it’s better than the #12 “at.Q” cable, I do not think it’s worth the extra 220 JPY for this.

#14 — SwitchBot Hub USB-A to micro-USB cable

1.5m, ≥1100mΩ, ≥733mΩ/m

This is the cable used to power the SwitchBot Hub Mini. This is the first time I’ve seen a “HIGH” display on the checker, indicating that the resistance is above 1,100mΩ.

For using with the SwitchBot Hub Mini, this is not necessarily bad because the power draw is very small, negating the impact of the resistance. However, one should not use this cable for high power applications.

#15 — M5StickC USB-A to USB-C cable

0.8m, 484mΩ, 605mΩ/m

This cable came with the M5StickC for charging. It’s one of the cables with the highest resistance here and also does not support data transfer, as indicated by the lack of connectivity of the D- and D+ lines.

As with the SwitchBot cable, this is not a problem when used for its original purpose, but it should not be used for high power applications.

Summary

These are the trends I saw so far:

• Cables from major manufacturers are generally very good, especially those bundled with devices expecting high power draw.
• E-marked cables are generally better than non-E-marked ones as they have to be rated for 5A current.
• Do not use USB cables from low power devices for other purposes as they may support just the bare minimum.
• Cables, even cheap ones, are generally good enough. (This might not apply to cables from less reputable sources.)

Does all this matter?

Resistance matters in cables because it causes voltage drop, which can slow down charging due to power being lost in the cable. The voltage drop can be calculated using the equation V=IR.

The USB specification allows 0.5V drop across Vbus and 0.25V across Gnd. Since the checker cannot measuring resistance separately for Vbus and Gnd, I will use a simplified 0.75V drop across Vbus and Gnd combined. (Another caveat is that while the specification specifies the resistance for the cable only, the resistance measured by the checker includes the resistance for the checker’s own receptacle as well)

Below is the calculated voltage drop for 3 situations.

#1–5W (5V1A) charging

This is “slow” charging used in older phones. Since the amperage is low, the voltage is not that large even with slightly higher resistance.

All resistance values shown here are still within spec for this use-case. (Note: the USB-C spec forces cables to support 3A or 5A, but for practicality, I will consider only the amperage actually being used.)

#2–10W (5V2A) fast charging

This is the original fast charging where the amperage is increased but the original USB voltage of 5V is still used.

We can see that even with only 200mΩ resistance, our power loss in the wire is 8%. This is quite larger than I actually expected. A cable with 500mΩ would cause 20% power loss and voltage to drop to 4V, which is not suitable for charging. (Smart devices would detect the voltage drop and lower the power draw to reduce the power loss in the cable.)

Any cable with higher than 375mΩ resistance would be considered out-of-spec for this use-case.

#3 — 15W (9V1.67A) USB-PD fast charging

This is modern fast charging where the voltage is increased so that charging can be done with lower current (and thus puts less requirement on the cable).

The power loss is lower because of 2 reasons:

1. The current is lower resulting in lower voltage drop according to V=IR.
2. More importantly, the total voltage is higher. A 0.5V drop on a 5V source is a 10% loss, but a 0.5V drop on a 9V source is a 6% loss.

Any cable with higher than 450mΩ resistance would be considered out-of-spec for this use-case.

Which cable would I use

Ideally, I would want my cable to have at the lowest amount of resistance possible. Practically speaking, 200mΩ seems like a reasonable value to target. For longer 2m cables used with USB-PD fast charging when power loss is not a concern (e.g. using a wall adapter and not a power bank), 300mΩ seems reasonable.