Beware Cheap eBay Ceramic Capacitors

Electronics hobbyists are often interested in stocking parts on the cheap, from places like ebay. Of course, we all know the maxim that "you get what you pay for". 

Recently I stocked up on various ceramic caps that I was needing from ebay, and decided to check them with the LCR meter when they arrived. Here is what I found:

• Almost all 0.033 uF caps read around 0.023 uF (i.e. -30%)
• Almost all 0.02 uF caps read around 0.015 uF (i.e. -25%)
• Almost all 0.01 uF caps read around 0.0075 uF (i.e. -25%)

Doubting the LCR meter, I checked with other parts that I had ordered from reputable places like Mouser or DigiKey. They read nominally and in some cases they read over the rated capacitance within the tolerance. It is instructive to note that none of the ebay caps were over. All were under by about the maximum tolerance (25 to 30% under).

After reading the book "Poorly Made in China" by Paul Midler, I came to realize why. Paul explains that the Chinese factories will take on orders at near cost, in order to get the business relationship started and to learn how to produce the products. Once things are going, they resort to one or more of the following practices:

1. Substitute or skimp on ingredients to increase profit
2. Come back to the importer with "price go up!"
3. Sell product on the side to bootleg markets.

I suspect that many of these cheap capacitors are being made under a strict tolerance, but on the low side with the idea that smaller capacitors are cheaper to manufacture than larger caps. Less capacitance requires less input material.

What to do About it?

A hobbyist can choose to:

1. Ignore the problem (at their project's own peril)
2. Get your money back (good luck)
3. Throw the parts away and reorder somewhere else
4. Order higher capacitor values (+30%) to arrive at the capacitance you require.

It's hard to ignore the deals like 100 for $1.31 (Cdn), or 30 for similar from the higher priced buy-it-now deals. The deals vary, but are attractively priced for the hobbyist.

One option is to try #4. Say you want to buy 0.033 uF ceramic caps. Add 30% for the actual capacitance you want and order near 0.043 uF (0.047 uF being the next value up). In this way, when you receive the 0.047 uF minus 30%, you'll have caps around 0.033 uF instead! Even if you got 0.047 uF minus 25%, you'd wind up with 0.03525 uF, which represents 0.033 uF + 6.8 %.

Voltage Rating

The capacitor's voltage rating is likely to be affected by the manufacturer tinkering with the product. While your ceramic caps may be listed at 50 Volts, it is possible that they are good for about 30% less! In other words, your caps may only be good to 35 Volts.  If this doesn't work for your design then you are best advised to spend what you need for quality components!