dmm’s

I am looking at picking up a better DMM in the near future. Right now I have a Home Depot $100ish meter and it has been great for a while, but I have noticed that it doesn't seem to be very accurate when it comes to measuring draw... and it quite frankly sucks when it comes to tach signals b/c the "refresh" rate seems to be very slow. I want to pick up a Fluke since they seem to be the best in the industry... but since it won't be something I use daily, I don't want to spend an arm and a leg. However it will be used both for automotive and home projects. I was thinking about either the Fluke 115 or 116. The price difference is minimal between the 2, and the 116 seems to have a thermometer built in which I'm sure will come in handy eventually. So I'm looking for opinions of the pros. What is your take on both these models? Are they decent quality for the price or should I go a little bit more for something better? Thanks in advance. KennyKenny

Owner / Technician

KKD Garage LLC

Albany, NY 12205

The 116 is primarily for HVAC applications. While the thermometer function is nice, I would suggest the 115 for your needs. You are correct that the difference in price is not much with the 115 being a little cheaper. This series of meters is extremely durable and in my opinion you can't go wrong. The sampling rate is excellent compared to the private label meters like you have now. If you buy one of these get the magnet accessory (TPAK, I think). It's a little pricey but well worth it. And be sure and get a bag for it, the C35 is a nice one and doesn't cost too much. Fluke is the standard set for everyone else, a really good choice that will last for years.Joe in Texas

One other comment, the Fluke 179 is the next meter in the Fluke line as far as features and quality goes. Normal usage by most people can't justify the difference, unless you are going to be measuring voltages in excess of 600 volts. I would guess you won't need that. The Fluke 87V is the "Cadillac" model, but it's $400. Nuff said there. I will say the sampling rate is really fast on this meter. If I want to watch movement that requires something really fast it's advisable still to have a good analog meter handy. It's just nice to see that needle move. That's where you might want an old Simpson 260 or a Triplet 630. Too many words, I know...Joe in Texas

"True RMS" may be a consideration - even for DC current measurement. I'm happy with my sub-$30 (AUD$) meters but they don't have frequency and are limited to the "standard" 10A current range (which needs to be connected in series with the load). I also have a $35 autoranging Noble NB 4000P-2 with capacitance and frequency but a 400mA limit. (DMM & leads in a flip case. Small & great for the glovebox and rough treatment.) I have been considering true-RMS clamp meters in the $150 range (400-600A AC and DC)...

For my tuppence work, your 30 $or£ meter is more than adequate for 90% of work. Flat battery? Will frankly I can give you an approx draw right off the light bulb of a Snap-On test light. You don't need a figure,just working, working slowly and blowing fuses. Sorry got out of the hospital yesterday and I'm bouncing off the ceiling.

May the ceiling survive! FYI - I bought a $10 50A current shunt - place it in series with the circuit, place a DMM across it and each 1mV is equivalent to 1A. I've used it to test starter motor currents (140A & 240A) - the 50A rating is a long-term rating but it handles higher currents for short times - it's a thermal thing so as long as the thing doesn't melt (or get annealed etc). One issue is that the shunt's "calibration" is via hacksaw-like cuts into its thick conductor. It will be these thinner cut sections that will fuse (melt) but the surrounding conductor conducts heat away quickly. THe point is, a VERY large current may fuse it very quickly, but for $10... (100A for $20 was IMO too expensive - this was an interim "ammeter" until I got a 400-600A clamp-on AC/DC true-RMS ammeter or DMM.)    Though I intend to mount a few Hall-effect current sensors (up to 600A) in my vehicle, that's for experimentation etc. IMO such measures are useless for most. What people want to know is "is the charging system keeping up?" - or maybe "how discharged is/are my battery/ies?", and a Voltmeter is best for that (an ammeter might indicate an underpowered alternator, and maybe a battery fault, but that's about it. (It doesn't even indicate the starter-motor current.)). Ammeters are only useful to get an indication of a load (as I did for starter motors). Though once upon a time ammeters were fitted to many cars, they are useless in practice... [ it only tells the battery charge or discharge current, not if overcharging, undercharging, how long the battery will last or when you have reached the recommended 20% discharge limit (for crankers; 50% for deep-cycle), or if your battery has a collapsed cell or has reached its end-of-life. ] ... and until remote shunt versions appeared, were generally a hazard and a big voltage drop. [ The un-fused alternator-battery ammeter cable was routed to the ammeter in the dash, and then back again (ie, alternator to ammeter to battery instead of a short alternator to battery cable) only to go back to the cabin & IGN switch & dash etc via fuses as per normal distribution. (The ammeter is fitted between the battery and loads-and-alternator. Hence you could not fit loads to the battery (the ammeter would show that as a -ve load current - ie, as if charging the battery by its load current.) Anyhow, even though shunts were later used {a dash-mounted voltmeter across the battery's GND cable or an inserted shunt resistor [eg, in the GND cable OR from the battery's +12V terminal - specifically between battery +12V and the alternator +12V output (often labelled B or B+) indicated "Amps" (eg, a 1V drop might mean 100A (10mV per Amp))], they lost favor due to their limitations. Apart from all the stuff a voltmeter could show, a voltmeter is cheaper anyway - an ammeter is a voltmeter PLUS a shunt resistor. Summary: Most should survive with a high-current shunt. They can then use their true-RMS or any other DMM else voltmeter to measure the current.    Why measure currents long-term or permanently? (Data logging or "smart" diagnostic purposes etc excepted.) If using an ammeter for some battery or charging-system intelligence, forget it. Forget how many Amps your battery is discharging at (assuming it's noticed, the old analog-meter scale is far from accurate!), wouldn't you rather know what State Of Charge your battery has? A voltmeter also indicates under and over charging [above ~14.5V; below (say) 13V (idling and low-RPM excepted)], and the condition of the battery - though some knowledge is required (eg, 13.8-14.4V; 12.7-~11.7V; cranking and loaded voltages).

Thanks for the memory prompt Peter, London taxis in the 1970s, nice lucrative number with the ammeter leads shorting out every time!