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Old 10-26-11, 01:19 PM   #1
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Many Ebike repairs/builds might be easier with an oscilloscope

I'm trying to figure out how to go about converting my 27 inch Raleigh to use an electric front hub, and so Ive been looking at a lot of the posts from people who have had various problems to try to get a feel for the ebike landscape. As I do it I keep thinking to myself that these motors aren't our parents DC motors, they appear to be quite sophisticated and I am guessing that there may be complex phase relationships one may need to get a feel for whenever one needs to troubleshoot a problem between the controllers and the hubs.

It may be a lot easier to figure out what's going on with an oscilloscope.

Even an ancient single or dual trace scope might be extremely helpful. In fact, the fact that older scopes are next to useless for most modern electronics applications but still quite useful in these electromagnetics applications means that people can sometimes pick one up for a song.

A word of warning.. too.. Most of the cheaper modern, solid state USB scopes - which are designed for mostly digital and low-level analog electronics may not be able to handle 48 volts and the inevitable spikes without a special and oftentimes expensive probe that reduces the voltage by some multiple. (x10 for example)

The manufacturers state that but I doubt if bike people are often that familiar with the kind of applications that kind of scope is mostly used in.

Someone who might be comfortable in both worlds are robotics people. If you know one, ask them. With the fact of potential gotchas in mind for those who don't do some research, there are dozens of "small signal scope" products out there that make owning an oscilloscope suddenly now affordable for anybody with a computer. There are a bunch of very cheap combination scope/logic probe tools on ebay that are so versatile and cheap that it makes sense to buy several so you can take both kinds of measurements at the same time. A logic proble might also be useful with these controllers hubs if they use switching transistors - which I suspect they probably do, less heat.

The new style scopes use your computer running specialized software as the screen, and they plug into the USB input. They are based on programmable logic devices... some of them combine an 8 or 16 channel logic probe with a single or dual channel digital storage oscilloscope, signal generator, JTAG device, etc. You can get an entire electronics bench worth of tools in a tiny little device. Some are so tiny (and sometimes inexpensive) that the leads and their clips end up being the biggest physically (and sometimes, even the most costly) part of the package.

The solid state devices are delicate and easy to accidentally brick with static electricity if you are not careful connecting them. Older scopes are much more robust.

You guys who do a lot of ebike work should keep your eyes peeled for oscilloscopes in pawnshops, garage sales, etc. You might find a nice one for under $100-200.

Especially if you can find an old Tektronics or HP at that kind of price, grab it! It happens.

With each individual channel of a scope, you can see what's happening on a wire, on two axes, voltage or current vs. *time*.

If you can't afford one of the above, I would suggest keeping and using an ANALOG multimeter in preference to a digital one. You can often figure out better whats happening from a moving meter than wildly changing digits.

But you still may be struggling to try to figure out whats really going on because the changes are fast and a meter just can't show it.

In my experience, a digital, or an analog meter for that matter may be giving you a peak reading or an average reading or may just be jumping around randomly.

Another thing that might be helpful is a line tracer. This is an electromagnetic probe.. (a large coil of wire) whose tip can be touched to things like wires to trace a signal injected from a beeper box.. They are used to trace cables.
The coil is connected to an audio amplifier.

Using one, you might be able to tell a healthy motor from a badly connected one by the "sound" of the magnetic field it emits. They should be able to give you a feel for the invisible magnetic field around your motor.

Or, an old TAPE walkman turned on with no cassette inside might be pressed into service to do something similar. Listen for whining, humming, changing sounds.

Anything that helps you understand the invisible is good. Can't hurt to try it.

Last edited by christ0ph; 10-26-11 at 01:45 PM.
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