Klein CL390 Clamp Meter Review: How I Tested a 10-Year-Old Solar Panel’s Voltage and Amps

If you have an older solar panel, a clamp meter tells you how much it has really degraded.

I used the Klein Tools CL390 AC/DC Clamp Meter to test the open circuit voltage and short circuit current of a used solar panel that’s about 10 years old.

In this Klein CL390 clamp meter review, I’ll cover the meter, the voltage test, the current test, and what the numbers say, the pros and cons, and who it’s for.

Products Used in My Klein CL390 Video

👉 Klein Tools CL390 AC/DC Clamp Meter

For business inquiries and collaborations: luisangel@aemind.com

Affiliate Disclosure: If you purchase an item through the links provided, I may receive a commission from the Amazon Influencer Program, at no additional cost to you. Thank you for supporting the channel.

What Is the Klein Tools CL390 Clamp Meter?

The Klein Tools CL390 is an AC/DC clamp meter that measures voltage and current, which makes it handy for checking solar panel output.

Key Features

• AC and DC measurement
• Clamp-on current readings
• Voltage testing with leads
• Useful for solar, automotive, and home electrical work

Open Circuit Voltage

The panel’s original open circuit voltage was 32.8 volts. Lately, I’ve been measuring it at around 27 to 29 volts.

Short Circuit Current

The original short circuit current was 8.05 amps. On a regular sunny California day, I’ve been measuring 5 to 6 amps.

What the Numbers Say

After some quick math, I calculated a voltage drop of about 13% over the last 10 years. The panel still produces energy, even with a lot of damage from sun and years of loads.

Would I Buy a Used Panel?

I wouldn’t recommend buying a used panel like this one for an off-grid home system with battery backup. I’m mainly using it for testing and learning how panels perform over the years.

Things to Consider Before Buying

• Safety: Follow the meter’s safety ratings when testing panels and wiring.
• Conditions: Readings change with sunlight and temperature, so compare on similar days.

Klein CL390 Pros and Cons

Pros

• Measures AC and DC
• Easy voltage and current checks
• Great for solar testing
• Trusted tool brand

Cons

• More meter than casual users need
• Readings depend on test conditions

Who Is It For?

The Klein CL390 is great for DIY solar owners, electricians, and anyone troubleshooting electrical systems.

Frequently Asked Questions

Can it measure DC current?

Yes. It’s an AC/DC clamp meter.

What did my old panel read?

Around 27 to 29 V open circuit and 5 to 6 A short circuit, down from 32.8 V and 8.05 A.

How much had it degraded?

About 13% by my calculation over 10 years.

Should I buy a used panel?

I wouldn’t for an off-grid home system.

Final Verdict

The Klein Tools CL390 Clamp Meter made it easy to see how much my old solar panel has degraded. It’s a solid tool for solar testing.

Watch My Klein CL390 Review

In my video, I test a used solar panel with the Klein CL390. You can watch the full video on my YouTube channel, Ryzzun Reviews:

▶ Klein CL390 (How to Use) Multimeter Testing Solar Panel Voltage & Amps

👉 Klein Tools CL390 AC/DC Clamp Meter

For business inquiries and collaborations: luisangel@aemind.com

If you purchase an item through the links provided, I may receive a commission from the Amazon Influencer Program. Thank you for supporting the channel.