Digital Multimeter Question

Joe Myerson · Post by **Joe Myerson** » Sep 5th, '07, 21:17

In the past, my old Tiller Pilot tended to blow fuses, so I stopped using it. Recently I decided to try once more, just to see what would happen.

I plugged it in, and NOTHING happened. The fuse didn't blow, but no matter how I turned the compass dial or moved the unit, there was no movement of the rod.

So I got out my as-yet-unused Radio Shack digital multimeter. I saw that it required a small 12-volt battery (no. 23), and my local hardware store had one.

The meter also comes with a small manual, written in a language that I, as a non-electrical engineer, could not really understand (although even I could figure out how to put the battery in).

I installed the battery, set the meter to the appropriate voltage, and the display read "OL." I put the probes into the plug, and it would flash "OL," followed by various numbers, starting at about 1.54 and flashing up to about 6.5.

This didn't make sense, so I turned it off quickly.

Then I turned the meter on without attaching the probes. It flashed "OL," followed by various numbers, starting at about 1.54 and flashing up to about 6.5.

When I looked up "OL" in the manual, it said I should turn the meter off immediately, because it was getting excessive current.

Could it be that I must use a Radio Shack battery, rather than any size 23?

Any ideas? And any suggestions where I can learn how to use a multimeter correctly?

Thanks,

--Joe

PS I know that there are several electrical engineers on this board. If one of you has the answer to this question, please phrase it in words of one syllable.

Oswego John · Post by **Oswego John** » Sep 5th, '07, 21:59

Joe Myerson wrote:
If one of you has the answer to this question, please phrase it in words of one syllable.

Hi Joe,

The bat tree must be the right size to fit, but more imp or tant, it must be of the right volt age.

O J

Sea Hunt · Post by **Sea Hunt** » Sep 5th, '07, 23:26

Hello Joe:

I have trouble changing a light bulb, but the following may be what happened.

"OL" probably stands for "overload". If you had the meter set to measure either current (amps) (A) or voltage (V) and actually connected the meter's leads/probes to a circuit to be tested, and you got an "OL" reading, it should mean the amps or voltage you are trying to read exceed the meter's range of measurement. This is unlikely given the low voltage and low amp systems on most small sailboats.

"OL" may also appear on some meters when you initially set up the meter to measure resistance/ohms (the symbol is sort of an upside down "U" with feet) if the leads/probes are not attached to whatever you are trying to measure the resistance of.

Before taking the meter back to Radio Shack, you may want to recheck your battery placement and reset the meter, etc.

As for reading material, I am not sure if it is still in publication, but a good one is "How to Use Your Multimeter". It is authored by Alvis J. Evans and GB Electrical, Inc. and published by Master Publishing, Inc. in 1991. Their phone number is (was) 214.907.8938. The book does not appear to have an ISBN number that I could find.

The above notwithstanding, I would strongly recommend you wait to hear from someone on this board who actually understands electricity and meters before attempting to rely on anything I have suggested. I am still trying to figure out how to put in that light bulb.

Fair winds,

minke · Post by **minke** » Sep 6th, '07, 00:52

Was the meter set to DC??

Leo MacDonald · Post by **Leo MacDonald** » Sep 6th, '07, 05:00

Was the meter set to DC Volts?

Al Levesque · Post by **Al Levesque** » Sep 6th, '07, 07:19

I am puzzled by the 12 volts. The most likely battery voltage would be 1.2 volts. Is the 12 volt battery common?

Ed Haley · Post by **Ed Haley** » Sep 6th, '07, 09:48

In responding to your original problem of blown fuses or nothing happening with the AP, my suggestion is to try a larger fuse, say a 10 amp to replace a 5 amp. If the fuse still blows, then check your AP. I'm not trying to be facetious but it appears that not enough current travels through the fuse to run the AP.

It may be that the fuses you were using were too low in amperage to begin with. Check with the owner's manual (find it on the internet if you don't have one) to see what size fuse it takes.

Normally the inline power fuse is there to protect the electronic device initially installed. But sometimes the same fuse for one device is used when upgrading and it isn't the right one. Anyway, try larger fuses and see if it works.

Russell · Post by **Russell** » Sep 6th, '07, 10:59

Ed Haley wrote:In responding to your original problem of blown fuses or nothing happening with the AP, my suggestion is to try a larger fuse, say a 10 amp to replace a 5 amp. If the fuse still blows, then check your AP. I'm not trying to be facetious but it appears that not enough current travels through the fuse to run the AP.

I would check the manual before putting in a large fuse, and certainly not put in anything larger then the correct size. Its a fair point that its possible the one being used is too small thus causing it to blow, so its worth check if you havnt already to make sure the right size is being used. But you should never put in a larger fuse then the correct size, especially if its blowing a lot, you will likely just destroy your AP.

Oswego John · Post by **Oswego John** » Sep 6th, '07, 13:46

Joe and all,

It's too difficult to break down in a post composed of one syllables, all that is contained in a booklet written in Engineerese.

There is a web address that might be of benefit to anyone that has any electronic gizmos on their boat.

http://www.doctronics.co.uk/meter.htm

After browsing that page, be sure to click "Back To Contents"

Here are some random thoughts I find helpful when trouble shooting electrical and electronic instruments.

I own several types of meters. Namely digital, analog and clampon. Some are high end and others are fairly cheap. If you suspect one meter is acting strangely, test it with another meter.

Because a meter doesn't work, don't throw it away. Some meters have fuses inside the case to protect it from the user's boo-boos.

Generally, you check for amp load in series. Some meters can't handle high amps, just milli-amps. Here's where a clamp-on meter comes in to play.

When taking readings with a clamp-on style meter, don't clamp on around both the positive and negative wires in a cable. Only read one of the wires. Reading positive and negative at the same time they will negate themselves. The same goes for reading a twisted pair.

As previously stated, switch the selector switch to the proper range before testing. AC circuits, switch to AC. DC, likewise. If in doubt about which voltage scale to use, start at the highest range and, watching the scale, work your way down to the most accurate reading. The same goes for reading resistance in ohms.

The battery in a digital meter is used for several things. It powers the display and possibly a backlight. When testing for resistance or conductivity on a dead circuit, the test is powered by the meter's battery. All other tests are powered by the instrument's power source. (usually 12v DC)

In analog or digital readings, if the battery is low, you won't get true readings.

Read the accompanying literature of the unit to ascertain the proper fuse size and wire size, taking into consideration the distance of the unit from it's power source.

Look for a tag or label attached to the case or chassis of the unit. Look for the amount of power or wattage it consumes under full load. Measure the power supply voltage at the unit. Divide the voltage into the wattage and that will give an idea of the normal amperage the unit draws..

This post could go on and on. There are literally hundreds of tips on troubleshooting techniques that could be stated. These all come with practice and experience.

One last suggestion. If you intend to take your meter back to Radio Shack, first go for the $5.00 and purchase a Radio Shack battery and install it. By using another make battery, you might void any guarantee.

BTW, 12V, #23 is the proper battery.

Good luck,
O J

seadawg · Post by **seadawg** » Sep 6th, '07, 15:33

If ohms is selected on your meter then ol would be a normal indication. In this mode touching the meter leads together should display aproximatly 0.0 ohms. Just a thought.

Oswego John · Post by **Oswego John** » Sep 6th, '07, 16:39

Seadawg,

You are correct. By touching the probes together, you are creating a dead short circuit. This will occur in any of the three resistance modes.

The use of one of these modes is a good way to check continuity. By holding a probe on either terminal of a fuse or a light bulb, etc, you can check if a fuse is blown or not, or check if the lamp filament is intact. It is also a way to check the internal continuity of a circuit

With a dead short, the digital readout should read 0.0 and the needle should swing full scale on an analog meter face. This action is powered by the meter's battery, not by any other outside power source.

O J

Parfait's Provider · Post by **Parfait's Provider** » Sep 6th, '07, 17:34

OL appears on my Radio Shack multimeter fairly often. When you connect it to something, it seems to read very accurately. I think OL might be the equivalent of infinity in the resistance mode (ohms).

I doubt the battery is 12 V. Mine takes two AAs, which are 1.5 volts each. I am certain they are connected in series for a total of 3 volts.

What model multimeter do you have?

Joe Myerson · Post by **Joe Myerson** » Sep 6th, '07, 18:42

Thanks to all for keeping your responses clear, even when using words of more than one syllable.

I'll have to wait two days to check out your suggestions, as the meter remains in my took kit, which is stored onboard.

As for the fuse size: This is an old unit that takes very small fuses. I had to travel to several marine stores to get a sufficient number of them, because few places still carry them. I got the specs from the manual, which I do have.

However, one thing I didn't think to check was the integrity of the circuit from the battery to the cockpit socket. I thought it would be easy to use the meter, instead of crawling into the port locker, removing the top of the battery cover and checking to make sure the leads are connected to the terminals.

As for the other suggestions: I'll send a report after visiting the boat.

Best to all, es pe ci al ly to OJ for his one syl lab le an swer.

--Joe

Parfait's Provider · Post by **Parfait's Provider** » Sep 6th, '07, 20:04

Joe,

While you are chomping at the bit to get to the boat, if you don't have a test lamp, make one. It will not only let you know where there is 12 VDC, but it will tell you where there isn't a sufficiently low resistance path to light a bulb. The VOM will not tell you that because most have fairly high impedance input circuits.

Even better, you don't have to figure out how to hold the meter, read it, and position two leads at once.

All you need is a 12 Volt bulb, an appropriate socket, a couple of wires, preferably stranded and definitely insulated, and some alligator clips.

CruiseAlong · Post by **CruiseAlong** » Sep 7th, '07, 08:25

Most of the meters I saw at Radio Shack took a lower voltage battery but there was one yellow, 15 function digital multimeter which took a "A23" battery which is a 12 VDC battery (sort of a half length AAA battery) which, unfortunately, is the same physical size as a "N" 1.2 VDC battery. I found this out when I accidently placed a "A23" into my boats clock. It, of course really wanted the "N" battery...no damage by the way....I did not see that there was no "." between 12 and 1.2
And I am a EE.

Generally, the "OL" is a reading of "over range" or "overload". On the resistance or ohms scale, it would mean a higher resistance than the maximum scale range you have the meter set for. For instance, it will read "OL" if you have it on the resistance scale and the leads are not connected to anything because the resistance between the leads is very large. For a DC voltage or AC voltage, it would mean a higher voltage than the scale you selected can read. In your case you will want to use a DC voltage scale greater than 12 VDC (volts direct current). One should never use the resistance scales (ohms) or turn through the resistance scale selection when connected to electrical wiring which is powered with voltage. It will blow the internal fuses or damage the meter. Only use the resistance scales with power removed.

To test the meter you can select any resistance scale or DC/AC scale with the leads plugged in. Without connecting to any electrical wiring, just touch the test lead probes together...the reading should go to zero.....i.e. measuring 0 volts or 0 resistance. If it does not, consider that the meter is faulty, has a blown internal fuse or the wrong battery...or weak battery.

I should also point out that there may be a couple of lead insertion sockets to choose from on your meter where the leads can be connected. These are generally labeled "COM" for "common" which is the negative voltage/resistance lead connection or black lead connection. The red lead connection may be different base on what you intend to measure. For resistance it may be labeled "OHMS", "R x1", "R x 100", or have an omega symbol which looks like an inverted "U" with flat lines off of its tips. For alternating voltage (VAC, or AC), for direct voltage (DC)...you of couse want VDC ffor this application. To measure current amperage, the socket is generally labeled "A". Each meter has slightly different symbols.

From what you describe:
1. Unit was blowing fuses with correct fuse size occasionally.
Does not work at all now...first test is to see if 12 VDC is reaching the unit....answers if it is the unit or the wiring.....

Cause: Pilot is motor driven....can draw more amperage if the voltage drops through a wire resistance to the unit. Wire can also be too small or long which makes the resistance too high or... have a loose or corroded wiring connection. Wiring fuse may also be correct amperage but be a "fast blowing, fast time blowing" rather than "Slo Blow, slow time blow" fuse which is generally used for motor application. There may be an internal pilot unit fuse which has now blown too.

At this point it is best to divide the possible problem in half by first testing for voltage at the unit connection.

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