Assembly of ferrite Chokes (to reduce RF)
Assembly of ferrite Chokes (to reduce RF)
(OP)
We need to put ferrite chokes onto the wires (which are loose, not a cable) connecting a circuit board to a motor and to a battery. We buy the board with the wires already soldered to it and the connectors already crimped to the other end of the wires. The IDs of the one-piece solid chokes are too small to fit the connectors through. The two-piece split chokes (snap-on type, etc.) all are either too large on the outside to fit in our limited space or are too small on the inside for the wires. Aside from unsoldering the wires from the board, putting the one-piece chokes onto the wires, and resoldering the wires to the board, is there a way to make this work?





RE: Assembly of ferrite Chokes (to reduce RF)
Alternatively, you may get sufficient inductance (if the wire is long enough) by passing the wire around and through a small ferrite toroid. Cores for toroids would hava a larger hole than a bead, so if you pass the connector through the core and back a few times so that you have a few turns as a "coil" this may give the desired inductance.
RE: Assembly of ferrite Chokes (to reduce RF)
To unsolder and resolder, we would need to train someone and we would need to buy lead-free solder to comply with ROHS.
How large is a toroid? The bead just barely fits in the space under the board, so if a toroid is much larger, we will not have room.
RE: Assembly of ferrite Chokes (to reduce RF)
Are you sure this is a conducted EMC problem - in which case why doesn't the board manufacturer fix it at source? Presumambly your product has failed an EMC test. You should have been told what kind of emissions the board failed on, i.e. range of frequencies and whether it is a conducted problem or radiated problem or both.
If you can give more spcific information it may be possible to help.
RE: Assembly of ferrite Chokes (to reduce RF)
We considered changing the board but decided against it.
I've seen the test results, including graphs of dB versus frequency, not just the numbers. It is a radiated test, but, since the chokes help, I assume that the problem is emissions (although generated by the board) are radiated by the wires, not directly by the board.
RE: Assembly of ferrite Chokes (to reduce RF)
Are you able to say what the product is? Could still do with lots more information:
What is the main frequency radiated?
How long are the wires?
Is the product portable, i.e. hand-held?
EMC test measurement distance?
Possible solutions:
Is the board screened? Could it be placed in a screened box?
Can the wires be bundled together, if so they could be screened with braid?
RE: Assembly of ferrite Chokes (to reduce RF)
With chokes on the wires, it passes. With no chokes on the wires, it fails.
Cordless power tool.
Proprietary.
A few inches
Yes.
10 meters.
No. We do not have room to add an additional box; we could add screening to an existing component, but decided not to do so.
Maybe, but we would have to retest it, and I do not have authorization (or time) for that.
RE: Assembly of ferrite Chokes (to reduce RF)
You have not said what sort of frequency or spectrum of EMI is giving the problem other than "proprietary". What does that mean? Is your product remote controlled or something?
EM interference is NOT proprietary!
Can you be sure that it's not the motor producing the problem rather than the board? If your wires from the board (i.e. to the motor?) are only a few inches long, a choke midway would tend to damp out problems from either source.
If the EMI is only present when the motor is operating, one suggestion to try - unless it already has one - is to place a ceramic capacitor of say 1nF to 10nF directly across the motor terminals using the shortest connecting leads possible.
RE: Assembly of ferrite Chokes (to reduce RF)
2. It is not remote controlled. Someone other than me decided that all test data is proprietary. I think it has something to do with the ability of another company to determine what motor we are using and clone our product.
3. Both the motor and the board are producing emissions problems. We are using capacitors to solve the motor problems and chokes to solve the board problems. Neither chokes without capacitors nor capacitors without chokes reduced the emissions enough.
RE: Assembly of ferrite Chokes (to reduce RF)
RE: Assembly of ferrite Chokes (to reduce RF)
You may be right about using a capacitor to slow the edges, but I am only on this project until the end of this week, and it would take longer than that to evalaute your idea. Also, I have no authorization to pay for more emissions tests, so the solution needs to be an implementation of something that we have already tested.
RE: Assembly of ferrite Chokes (to reduce RF)
In this manner, I usually only make 1 or 2 trips to the compliance lab, and save bocu $.
RE: Assembly of ferrite Chokes (to reduce RF)
TTFN
RE: Assembly of ferrite Chokes (to reduce RF)
I tried, but all the ones I found with enough impedance where either bigger on the outside, smaller on the inside, or both. We have very limited space in the assembly.
biff44:
We only sent the product for EMC compliance testing twice; it passed the second time. The problem is now that I need a solution that can be manufactured, without making a third trip (1: failure, 2: pass, but cannot manufacture, 3: can manufacture). We do not have a spectrum analyzer and I did not have authorization to buy one.
RE: Assembly of ferrite Chokes (to reduce RF)
If costs have been cut to the last cent so that no time can be allowed to analyse the problem properly, then how does your company do the maths on risk, i.e. possible legal consequences from selling a non-compliant product compared to finding a reliable solution?
Even the few cents more that the board manufacturer wants to charge for including chokes (on all boards) is probably cheaper than the consequences of legal action.