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Voltage tester idea

4K views 26 replies 11 participants last post by  jorn85 
#1 ·
I do not have a wired in voltage meter. The Bene 32s5 has idiot lights on the panel for 11,12,13. Not sure how they are useful at all.

It is a bit of a hassle to get to the batteries.

If I would get a cigarette lighter plug and put a couple of alligator clips on it can I simply plug that into the 12 volt plug then to my meter and use the main battery switches to select the battery I want to check?

Will this work?
 
#4 ·
It will work fine. One thing to remember is where the lighter plug is wired. Any load between the battery and the point where the lighter is wired will cause a small around of voltage drop. This is probably at your panel so turning off loads will give you the best measurement.

Also be careful with the exposed wires. You could easily blow a fuse if they touch. If you want to use this often you might wire a series resistor of 100 to 1k. Then it's no big deal if you short the alligator clips.
 
#5 ·
David, it will work but I'd suggest two other options.

One being a plug-in voltmeter, the display is on the "lighter" plug itself. Digital or LEd bars, both are available.

The other is to buy a pair of "pygmy" hippo clips from Rat Shack, crimp a run of duplex wire and a fuse onto them, and bring out the leads direct from the battey for a "cleaner" reading.

In either case the voltage will be a good reference for you, relative to the charge state of your batteries, but subject to all the usual ways to misread the information. Starting with the accuracy of the meter, no matter what kind you have, and whether it has been calibrated. I finally stopped wondering which meter was wrong and by how much, and built a little "10.00" voltager reference supply. That's all it puts out, and exactly what it puts out, accurate to a few thousandths of a volt. So when I need to know if my meter is on drugs, or just a little slow, I check to see if it says "10.00" when it is connected to the calibration source.
As the Wicked Queen said, "Meter meter on the wall, who's the foulest of them all?"
 
#8 ·
You chase down a handful of electronic parts that Radio Shack won't have, and then most important of all, buy some breathe mints because an (mini in this case) Altoids tin is the most effective way to put a case on anything. Small project boxes are incredibly expensive.<G> Of course the Altoids box doesn't LOOK very commercial, and I suppose the TSA would be closing down airports if they even saw it (good lord, a metal case with wires and a battery!) but if I wanted to keep it under a sawbuck, that was how it had to happen.

Or maybe I should have splurged on the fancy case and taken it to West Marine? (VBG)
 
#10 ·
I use one that plugs into a cigarette lighter socket. Like this:

The only problem is that the socket is a bit of a distance from my boat's batteries, so there is a bit of a voltage drop (even more so if I use the socket on the forward bulkhead).
 
#12 ·
I had the same question when I bought it, so I compared it to my Tenma digital multimeter (which was fairly high-end when I bought it 20 years ago). Essentially, the little plug-in meter was spot on (to within the precision of its readout, anyway).
 
#20 · (Edited)
Probably pretty accurate. Multimeter hardware isn't expensive and DC voltage is the easiest thing to measure. At work we have all fluke meters but at home and the boat I have 3 of these:
http://dx.com/p/auto-range-digital-multimeter-9636

As for the OP's question what Mainsail and Hello said are exactly right. You can't have voltage drop without current. If there's no current between where you're measuring and the battery it will be 100.00% accurate.

To put it in perspective a regular self-powered multimeter has 10+ Megaohms equivalent input impedance - you could measure your DC voltage a hundred miles away with 16 gauge wire and it would be less than 0.1% off due to voltage drop from the meter.
 
#14 ·
That's just an image I found on the net of the same model as the one I have.
 
#16 ·
Actually, I'm in the process of upgrading some of the wiring on the boat right now. The little plug-in meter is being replaced with a hard-wired one (and an "(ON)-OFF-(ON)" toggle switch, so I don't have to switch the master switch back and forth to test both banks). However, I am going to run heavier gauge wire to all the plugs to avoid voltage drops.
 
#19 ·
Stu-
"Could you not deliberately oversize the wires from your bank to your voltmeter? "
Voltmeters always draw SO little power in the sense leads, that you'd really have to try hard to find a wire guage small enough to have any voltage loss on that run.
Even one of the "self powered" two-lead LED types, what is the total consumption? Maybe 100mA?
 
#21 ·
Let's see, E over I equals R, yes? So

12
----------
10,000,000

and the meter draws 0.0000012 amps, 12 millionths of an amp?

and the folks at calculator.net say:

Voltage drop: 0.0051
Voltage drop percentage: 0.043%
Voltage at the end: 11.9949

Not too bad! I suppose instrument rounding and errors might mean it could show 11.9 instead of 12.0 but from a hundred miles away...(VBG)

OTOH, having seen the way my "good" meters of various ages disagreed (by .2 volts) and the way a HF special couldn't meet it's own specs, I put zero faith (actually, 0.000000000 faith) in meters that have no specs at all, like those specials at dx. Which is why I finally decided to get out the soldering gun and put a 10.00 volt precision reference source in a mini Altoids tin, so there's no guessing, and I *know* when my meters are fibbing. The reference source is good beyond 4 digits, so when I hook it to a meter the meter had damn well say 10.00 or it gets re-educated, as the Chinese would say.
I'll be interested to see how the meters HOLD calibration, now that I've got a way to check on them.
 
#22 ·
OTOH, having seen the way my "good" meters of various ages disagreed (by .2 volts) and the way a HF special couldn't meet it's own specs, I put zero faith (actually, 0.000000000 faith) in meters that have no specs at all, like those specials at dx. Which is why I finally decided to get out the soldering gun and put a 10.00 volt precision reference source in a mini Altoids tin, so there's no guessing, and I *know* when my meters are fibbing. The reference source is good beyond 4 digits, so when I hook it to a meter the meter had damn well say 10.00 or it gets re-educated, as the Chinese would say.
I'll be interested to see how the meters HOLD calibration, now that I've got a way to check on them.
My Fluke meters are all calibrated, my cheapies not so much, but I'd love to grab one of these chips. Got a link?????
 
#24 ·
Maine-
Me and the chips are in different places this week, so I can't tell you offhand but I went with Linear, who offer accuracy to better than 0.05% (that's not a typo) so when they say "10.00" they really mean it. And internal temperature compensation, so basically if you don't need gloves or icepacks to work, it doesn't either. Damned thing just hums along and says "Ten! Nyah-nyah-nyah-nyah! TEN!" all day long.

The main limit is output power, i.e. only use it with the usual high-impedance meters. It won't work with the source-self-powered LED voltmeter displays from China, minor drawback.<G> Other than that, it pretty much doesn't give a damn what's connected in the way of power supplies, takes a wide range of those as well.

Seems like a lot of chipmakers have been coming up with all sorts of interesting "twelve volt" management devices in the last year or two. Multiple regulators, convertors, I've got to be thinking the "solar" industry is driving some of this.
 
#25 · (Edited)
Seems like a lot of chipmakers have been coming up with all sorts of interesting "twelve volt" management devices in the last year or two. Multiple regulators, convertors, I've got to be thinking the "solar" industry is driving some of this.
What did you use as a power source? Linear the type or brand?

12V is also used in the automotive world which is becoming more and more computerized. So there are tons of neat and robust 12V power management chips out there because of the automotive overlap. I've tried to think of ways to incorporate them into the boat.

In particular there are fantastic solid state switches with internal over-temperature and over-current limits. I've incorporated these into a couple designs and personally short circuit tested them (hold the + wire and - wire and then quickly mash them together) and scope traced the results. They work. Basically reset-able fuses that, in theory, can't be burnt out under any circumstances.

I considered using these when I re-did my panel. I could have had the switch on the panel only switching control current with the actual switch/fuse solid state device behind the scenes. However at the end of the day it's hard to beat the simplicity of actual switches and fuses.

Also there is an opportunity to build a cross between the bluesea relay and the echo charger for about $10 component cost. A comparator and a solid state 20-30A switch. It would limit current to 20-30A meaning you could get away with smaller wires but would lack the charging smarts of the echo charger.

Anyway, another overly long engineering rant. You can tell I've been thinking (dreaming) of ways to make money doing marine electrical design.
 
#26 ·
Linear as in the company, LT. Power source was easy, a 12 volt alarm "fob" battery is readily available and much more compact than the next simple choice, which would have been a couple of 9v batteries in series. But that would have filled a standard size Altoids tin and given me a decade of battery power, didn't want to go there.<G>

Maybe I should sell my spares as kits? (VBG)

A few years ago all the players were saying cars would move to 48VDC in order to power the electrical power steering, electrical AC, all sorts of things. Now, they're saying gee, it would cost too much to use 48VDC rated switches and wiring. Funny thing, huh?

I'd prefer "dumb" switches and breakers. No worries about noise pulses, rfi, odd things the microelectronics can do. Heck, I've "repaired" a car fuse with a chewing gum wrapper in order to get home. Can't do that with microelectronics.<G>

"Also there is an opportunity to build a cross between the bluesea relay and the echo charger for" You'd probably be reinventing a "Hellroarer" a solid state (high power FET I think) version of the Yandina/West isolator, which is the grandpappy of the Echocharger and all that stuff.

I'm still waiting for "one ring to rule them all", i.e. a modular charge controller that would be able to integrate alternator, solar, wind, and run them all efficiently together without making blind assumptions. I had some ideas on how to do it, isolate and integrate, but it all comes back to "Gee, this is gonna cost" no matter how small and cheap they can sell the brains for it.
 
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