Basic Multimeter Question
June 20, 2013 8:53 AM Subscribe
I have a multimeter, and a I have a hub dynamo built into my bike wheel.
I want to attach the multimeter probes to the wires that power my front light, and see what, if any, power comes through those wires when I spin the wheel.
What do I set on the multimeter to see that happen? PS: I know nothing about electricity.
Given that you know nothing about electricity, what do you want to DO with the meter reading results? Are you just trying to verify that it basically works? Are you trying to figure out if it's usable for a specific purpose?
posted by RustyBrooks at 9:03 AM on June 20, 2013
posted by RustyBrooks at 9:03 AM on June 20, 2013
Are you trying to figure out why the light doesn't work? or something else?
posted by mr vino at 9:30 AM on June 20, 2013
posted by mr vino at 9:30 AM on June 20, 2013
Right out of the dynamo, it will be AC, not DC. Should be in the range of about 20 volts (probably a 12 VAC dynamo, that will overclock to 20-30 volts if you spin the wheel really fast).
posted by Doohickie at 9:34 AM on June 20, 2013
posted by Doohickie at 9:34 AM on June 20, 2013
A multimeter will measure the difference in voltage (in volts V) and current (in amperes A) between two points. Think of voltage as "how much power" and current as "how much power is flowing".
There are two types of power:
alternating current (AC)
direct current (DC)
Alternating current acts like a sine wave where the voltage changes over time, and is what is fed to the outlets in your home. If your bike light is incandescent, then your dynamo is producing AC.
Direct current has a constant voltage. A direct analog would be power coming out of a AA battery. If your bike light is LED, it needs to be fed DC. Your dynamo can have an additional circuit to convert AC to DC.
You can set the multimeter to measure AC or DC. It will measure up to a certain sensitivity. If the multimeter is set to 20V AC, then it can measure up to 20V and not over. In this setting, too small of a voltage will cause the meter not to display anything. This will require you to up the sensitivity to something like 2V AC.
posted by dobi at 9:38 AM on June 20, 2013
There are two types of power:
alternating current (AC)
direct current (DC)
Alternating current acts like a sine wave where the voltage changes over time, and is what is fed to the outlets in your home. If your bike light is incandescent, then your dynamo is producing AC.
Direct current has a constant voltage. A direct analog would be power coming out of a AA battery. If your bike light is LED, it needs to be fed DC. Your dynamo can have an additional circuit to convert AC to DC.
You can set the multimeter to measure AC or DC. It will measure up to a certain sensitivity. If the multimeter is set to 20V AC, then it can measure up to 20V and not over. In this setting, too small of a voltage will cause the meter not to display anything. This will require you to up the sensitivity to something like 2V AC.
posted by dobi at 9:38 AM on June 20, 2013
I should add that most multimeters denote AC and DC by a symbol:
~ Alternating Current (AC)
____
- - - Direct Current (DC)
posted by dobi at 9:44 AM on June 20, 2013
~ Alternating Current (AC)
____
- - - Direct Current (DC)
posted by dobi at 9:44 AM on June 20, 2013
Response by poster: mr vino, yes -- the light works only intermittently.
posted by sandettie light vessel automatic at 9:46 AM on June 20, 2013
posted by sandettie light vessel automatic at 9:46 AM on June 20, 2013
Response by poster: My object is to to see if the link from the hub to the light is flaky or if it's the light itself.
posted by sandettie light vessel automatic at 9:51 AM on June 20, 2013
posted by sandettie light vessel automatic at 9:51 AM on June 20, 2013
To test if a link is good/bad (vs whether dynamo is generating) you want the "resistance" feature of the meter. Might be labelled something like /\/\/\/\ (a saw-tooth).
The values that matter to you are "infinity" and "not infinity/close to zero" -- if you hold the probes apart, you should see infinity (or something like it) because there's infinite resistance (ie no electricity flows). Touch the probes together, and you'll see zero, or something very close to zero (there's next to no resistance, so electricity if flowing).
So put the probes on two ends of a wire/connection, and see if you get infinity, or something close to zero, to tell if the connections are good or not.
posted by k5.user at 10:37 AM on June 20, 2013
The values that matter to you are "infinity" and "not infinity/close to zero" -- if you hold the probes apart, you should see infinity (or something like it) because there's infinite resistance (ie no electricity flows). Touch the probes together, and you'll see zero, or something very close to zero (there's next to no resistance, so electricity if flowing).
So put the probes on two ends of a wire/connection, and see if you get infinity, or something close to zero, to tell if the connections are good or not.
posted by k5.user at 10:37 AM on June 20, 2013
k5.user, that may or may not work. A dynamo probably doesn't have a continuous path, it's like a generator, that uses magnets and loops of wire to generate electricity.
Hooking up the meter, setting it to 20V AC will probably work. Turn the wheel, see what you get. You may have to turn it at a considerable speed to get a good reading. I don't have enough experience with these dynamos to know if hte output is buffered or instantaneous - that is, I don't know if your output is directly proportional to the speed of the wheel Right Now or if it's averaged out by some kind of intermediate storage
posted by RustyBrooks at 10:49 AM on June 20, 2013
Hooking up the meter, setting it to 20V AC will probably work. Turn the wheel, see what you get. You may have to turn it at a considerable speed to get a good reading. I don't have enough experience with these dynamos to know if hte output is buffered or instantaneous - that is, I don't know if your output is directly proportional to the speed of the wheel Right Now or if it's averaged out by some kind of intermediate storage
posted by RustyBrooks at 10:49 AM on June 20, 2013
Response by poster: When the light is working as expected--it is an LED--it will go from steadily-on to blinking to off, depending on the speed of the wheel. One brisk spin with my hand can produce a second or two of "steady".
Thank you everybody--this gives me much to start with! I may well follow up this evening.
posted by sandettie light vessel automatic at 10:57 AM on June 20, 2013
Thank you everybody--this gives me much to start with! I may well follow up this evening.
posted by sandettie light vessel automatic at 10:57 AM on June 20, 2013
Think of voltage as "how much power" and current as "how much power is flowing".
Better to think of voltage as "how much (electrical) pressure" or "how much (electrical) force" and current as "how much electricity is flowing" or "how fast charge is moving." Power has a precise definition: the product of voltage and current.
posted by Mapes at 11:07 AM on June 20, 2013
Better to think of voltage as "how much (electrical) pressure" or "how much (electrical) force" and current as "how much electricity is flowing" or "how fast charge is moving." Power has a precise definition: the product of voltage and current.
posted by Mapes at 11:07 AM on June 20, 2013
RustyBrooks -- I took the comment, "to see if the link from the hub to the light is flaky" to mean irrespective of the dynamo. Thus, the resistance check. (ie the plug/socket/wires that go from A to B are correctly transmitting power.)
posted by k5.user at 11:15 AM on June 20, 2013
posted by k5.user at 11:15 AM on June 20, 2013
When the light is working as expected--it is an LED--it will go from steadily-on to blinking to off, depending on the speed of the wheel. One brisk spin with my hand can produce a second or two of "steady".
That is expected behavior for a dynamo driven light. Some lights have a "standlight" feature that stores electricity to keep the light lit (sometimes at a dimmer setting) for several minutes when the wheel isn't rolling, it doesn't sound like your light has that feature.
A really good source of info on stuff like this is BikeForums.net. Register as a member (free) and go to the forum called something like "Gadgets and Lighting" and the people there should be able to help you figure out what you've got and if it's working correctly.
posted by Doohickie at 11:34 AM on June 20, 2013
That is expected behavior for a dynamo driven light. Some lights have a "standlight" feature that stores electricity to keep the light lit (sometimes at a dimmer setting) for several minutes when the wheel isn't rolling, it doesn't sound like your light has that feature.
A really good source of info on stuff like this is BikeForums.net. Register as a member (free) and go to the forum called something like "Gadgets and Lighting" and the people there should be able to help you figure out what you've got and if it's working correctly.
posted by Doohickie at 11:34 AM on June 20, 2013
If it doesn't always light "as expected", my first bet is on the wiring. It can become brittle and break. Fortunately that's one of the cheaper things to replace in the system.
posted by Doohickie at 11:36 AM on June 20, 2013
posted by Doohickie at 11:36 AM on June 20, 2013
Like Doohickie says, what you are describing is totally typical of a dynamo-driven bike light without a standlight option. The light will only seem constant when you travel at adequate speed. If you want continuous light at lower speeds or at rest, you need to obtain a new bike light. Look for one that specifies it is compatible with hub dynamos and has the "standlight" option.
posted by werkzeuger at 8:37 AM on June 22, 2013
posted by werkzeuger at 8:37 AM on June 22, 2013
Response by poster: werkzeuger-- I think I have not been clear. The light will stop suddenly for no reason while I'm rolling. Like, just stop working. I fully grasp the "contingent upon the wheel turning" part.
Rarely, simply tapping the light with my foot --again, while I'm moving--will bring it back.
Still have not had time to test any of this advice, but again, thanks to all of you.
posted by sandettie light vessel automatic at 10:54 AM on June 22, 2013
Rarely, simply tapping the light with my foot --again, while I'm moving--will bring it back.
Still have not had time to test any of this advice, but again, thanks to all of you.
posted by sandettie light vessel automatic at 10:54 AM on June 22, 2013
Ahh, thanks for the clarification. That indeed sounds like an intermittent break in the wire, maybe where it goes into the light. The "continuity" or "ohms" setting on the meter will help you track down bad wires and connections.
posted by werkzeuger at 11:59 AM on June 22, 2013
posted by werkzeuger at 11:59 AM on June 22, 2013
Response by poster: Followup, FWIW: It was the Axa-brand LED light itself that was broken. A postmortem revealed that some controller-looking chip had come completely off its little board.
I now have a Lumotec Lyt that I am entirely happy with, and have not altered the wiring at all.
posted by sandettie light vessel automatic at 5:38 PM on August 26, 2013
I now have a Lumotec Lyt that I am entirely happy with, and have not altered the wiring at all.
posted by sandettie light vessel automatic at 5:38 PM on August 26, 2013
This thread is closed to new comments.
posted by deadmessenger at 8:55 AM on June 20, 2013