A digital multimeter (DMM) can be extremely handy item to have around the house. While these are often seen in the hands of electricians, automotive mechanics, or technicians, an inexpensive multimeter can also serve the homeowner quite well, whether it’s testing for battery charge on the car, repairing appliances, testing batteries in the remote control, measuring resistance on a circuit, or for a myriad of other electrical tasks around the house.
Recommend this product?
The days of inexpensive U.S.-made electronic equipment appear to be over in the case of the basic DMM. Most are made in China these days, even for some affordable models of the more prestigious ‘professional’ brands. After much searching in vain for a U.S. made model under $100, I decided to forego the battered used 'pro' models offered on the auction sites or in pawnshops for a new, basic model that was affordable. I settled on the Cen-Tech Model 90899 7-Function Digital Multimeter sold by Harbor Freight Tools®.
The Cen-Tech Model 90899 as sold by Harbor Freight® measures a compact 2 7/8” wide x 5" high x 1" deep, weighs around 4.4 ounces with battery, and has been offered over the years in various colors, typically yellow, red, or black. It has the features of a basic digital multimeter, including 3.5-digit resolution with a ½” tall LCD display, auto zero adjust, an over-range indicator, a low battery indicator, a fuse and diode-protected circuit, and the ability to measure DC volts (1000v maximum), DC current (200 milliamps - 200u, 10 amp maximum), AC voltage (200v and 750v settings, 750v maximum), and a resistance range in ohms (200 - 2000k). Also featured is a transistor checker, a function for testing the charge state of 9v and 1.5v batteries, and a setting for testing voltage drop in diodes.
This particular model is double-insulated and conforms to IEC-1010 electronic measurement standards in category I (designed for measurements not directly connected to mains). It comes with an instruction pamphlet, a nine-volt battery, a 250 mA fast-acting replaceable fuse, and 30-32” test leads with shrouded banana plugs that fit the meter’s receptacles. As a basic, consumer-grade DMM, the Model 90899 has none of the additional luxuries of more expensive multimeters, such as auto-ranging, a sample-and-hold function, or even an auto-off shutoff. Affordable is the operative word for the Model 90899. It normally retails for about $4 but can often be found on sale for as little as $2.49 plus tax.
Although other retailers sell similar 7-function DMMs of the same size, features, and general circuit design (notably the DT-830 series from all-sun®), the Model 90899 from Harbor Freight® is somewhat unique in that it has a separate on-off slider switch, rather than incorporating this function into the rotary adjustment dial as found on other models.
Product Operation and User Interface
The Cen-Tech works much as any other basic digital multimeter. There is a rotary dial that controls the main measurement functions, along with a separate on-off switch.
After the test leads are plugged into the appropriate ports (jacks) and the probes connected to the circuit/battery/wire, the dial is turned to the function range desired, and the power switch is turned on for a measurement. As with most consumer DMMs, there is an additional 10ADC port for DC current measurements up to 10 amps (note that this port has no fuse protection, and is limited to current measurements of no more than 10 seconds).
If the circuit voltage is unknown, I like to set the selector switch on the meter to the highest range available, then power up the circuit before reading the meter. The range can be reset downwards as needed for an accurate reading.
The Model 90899 uses two test leads with conductive tip probes, one red, one black. The test probe leads, while functional and fitted with adequate protective shrouds, are of bottom-level quality, and it is advisable to check these for signs of poor connections. I tend to replace these at the outset with better quality versions available at electronic stores or the various auction sites. It’s also useful to get an extra set of test leads with either alligator-type or micro-hinged jaws that will grip a wire/lead without having to hold the probes with each hand.
One disadvantage to the compactness of the unit is the spacing of the ports (jacks) for the leads. They are narrower than the .75” standard, and so will not accommodate the dual banana plugs used on some test leads or probes, forcing one to use single banana plugs for each red and black lead.
With no auto-off feature, this is not the model to get if you are forgetful about turning off the power switch when you are finished using the meter. Replacing batteries is also something of a pain, as the battery compartment is very tight, and secured by screws. I found that not all brands of replacement 9v batteries will fit this compartment, as battery manufacturers do not always adhere to the nominal battery dimensions for a 9v cell. The Energizer 9v cell proved to be the ticket: thinner and more compact than most other brands, it fit perfectly. However, given the cost of this multimeter, it might be easier to buy a whole new unit rather than bother with a battery change.
While unscrewing two screws and removing the back of the unit to change batteries is cumbersome, this does avoid the annoyance of lost sliding battery compartment lids.
Accuracy and Construction/Manufacturing Quality
In a temperate operating environment the Model 90899 has a published specification accuracy of +- 0.5% for DC voltage up to 200 volts, an accuracy of +- 1.2% for AC volts up to 750v, a DC current accuracy of +- 1.0-1.2% from 200mA to 200uA, and an a accuracy of +- 1.0-1.2% when measuring ohms on the resistance scale. Sampling rate is 2.5 times per second.
In actual use, I find the Model 90899 is accurate enough for most around-the-home electronic measurement providing the circuit and LCD are functioning correctly, and the battery has sufficient charge. Even more critical uses aren’t necessarily beyond this model’s capability. Since I can afford to buy several units, I can use two or more of them simultaneously for tasks as measuring the individual bias voltage/current on the output sockets of my stereo tube amplifier.
I once compared two of these Cen-Tech DMMs with several others owned by a friend by taking them to an electronics hobbyist with a recently-calibrated professional multimeter to measure current, voltage, and resistance accuracy. To my considerable surprise, one of my 90899 meters was off by only 1% on the resistance and voltage scales, while the other gave the same exact readings as the reference meter. My friend's more expensive DMMs fared worse than mine.
The squared-off shape of the Model 90899 is useful for standing the unit on end when taking measurements, and its compact dimensions fit into the smallest of tool bags. The LCD display is thoughtfully recessed to prevent damage from accidental contact with other items, though this isn’t a total safeguard. The display can be hard to read in very bright or dim light, and there is no backlight for low light conditions. Another point to note: the ports for the test leads are soldered directly to the circuit board, which can be damaged if too much pressure is exerted on the ports when plugging in the test lead wires.
On the plus side, the inexpensive nature of this unit is such that you can buy more than one, keeping them handy in places where one might be averse to keeping a more expensive meter. Used at work, they don’t ‘walk away’ nearly as often as more expensive electronic gear, and they make perfect gifts to those family members and friends who don't have one, and are always calling to borrow your own.
Nevertheless, as with any electronic item costing so little, quality control can be an issue. In my experience, most issues with these cheap multimeters arise shortly after purchase with units that were incorrectly assembled or manufactured.
After purchasing and examining several of these basic 7-function DMMs of various model designations (DT-830B, DT-830D, etc.) I can only recommend the Harbor Freight® version (Cen-Tech Model 90899), which has a separate on-off slider switch. In my experience, it appears to outlast similar versions that incorporate the power switch into the rotary dial. Additionally, the Model 90899 exhibited noticeably better soldering and assembly quality over that of its nearly identical cousins. It still uses regular 9V battery leads connected to the usual vinyl contact pad, while others, such as the DT-830D from all-sun®, had battery 'connections' in the form of coil springs crudely soldered to the circuit board.
During the last few years I have purchased six of these Model 90899 DMMs, and I still own five; one was replaced after two days' use by Harbor Freight® for a malfunctioning display, while the other was discarded after the plastic casing broke after a drop onto the garage floor. The others still work fine, and have more than repaid their purchase price, which isn't much more than the cost of replacing the 9v battery.
To ensure a better chance of getting a properly-constructed unit, I always test a newly-purchased model against a resistor of known resistance, which can at least verify accuracy of the resistance scale. If you or a friend already own an accurate, recently-calibrated DMM, once can compare voltage and current readings to see if the new unit gives identical or near-identical readings. Needless to say, a low battery or blown fuse will also prevent correct readings, and it’s not unheard of to get a new meter that has a low or dead battery if too much time has elapsed since it was originally assembled and packaged.
It must also be remembered that a frequent cause of damage to a multimeter is incorrect usage, such as incorrectly connecting the meter to a powered circuit, and I’m never too proud to re-read the instructions when I’m hazy on the correct procedure. For example, with the meter set to ohms, the test probes should never be applied to a live circuit (with current flowing). Also, never turn the rotary dial of the multimeter to the DC volts ("DCV") or the DC amps ("DCA") function when measuring AC voltage. It’s also not recommended to switch between testing modes with the multimeter connected to a live circuit. With its limited fuse protection, CAT I certification, and 10-amp limit, the Model 90899 is not a good choice for measuring high-amperage DC current.
While I generally hesitate to recommend such inexpensive electronic tools, the overall performance of the Cen-Tech Model 90899 7-Function DMM is excellent, particularly given its price point. It gives us all the ability to keep two or more basic multimeters on hand when needed, and without much regret if they become lost, damaged, or break after a period of use.
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