Re: Help with a inductor problem
Hello, I have no problems measuring DC resistance of my large reactors with
a DMM. The inductive reactance is a AC phenomena, and should not influence
the small DC current placed across it by the meter. A 15 henry reactor I
have (rated at 1750 V), measures only a couple ohms off of the 50 or so, of
the DC name plate value.
At 11:49 AM 9/30/1999 , you wrote:
>Original Poster: "Eric Davidson" <edavidson-at-icva.gov>
>IMO you sent it back prematurely. You will NOT be able to measure the
>resistance with a high input impedance ohmmeter like the Flukes, Beckmans
>etc. A 60's vintage Simpson may do the job. The huge inductance of the
>choke causes it to buck when the ohmmeter tries to measure the resistance.
>The counter emf generated by the inductance opposes the voltage from the
>meter. Your resistance reading will likely fluctuate wildly and never
>stabilize. The fix is easy. Simply place a 100 ohm 1/2 W resistor (or any
>known resistance under say, 10 kohms) in PARALLEL with the choke and
>measure the resistance of the two in parallel. Calculate the resistance of
>the choke. The resistor will damp the inductive kick of the choke and your
>resistance reading will be rock stable and very accurate. I've used this
>method to measure the DC resistance of the control coil on my saturable
>reactor, it works great. Hope this helps.
>PS I'd try to get that choke back...sounds like a nice find..just my
>> Original Poster: "Lee Marsh" <lmm-at-flash-dot-net>
>> Hi All I found an old Radar modulator charging inductor. On the can it
>> has a list of specs.
>> as follows: 15 Henrys, 17.5 kvrms, 0.110 A , DC res nom. 296
>> ohms. A diagram
>> on the can indicates that it is a simple Iron core choke. When I use my
>> DVM to measure
>> the resistance it tells me that it is over one meg ohm. Does this make
>> sense? The guy I
>> got it from says you cant measure it with on simple ohm meter that it
>> a high voltage
>> to do it (like HV diodes) and he FAXed me a diagram of how to measure it
>> This consists
>> of a 100W 200000 ohm resistor and another 1 ohm in series with a 1570dc
>> When he measure across the 1 ohm resistor he obtains a reading of 7.9mv
>> or .0079 A
>> then he adds the inductor and measurs again this time he gets 6.9mv or
>> .0069 A which
>> if true tells me that that the choke resistance isn't in the meg ohms
>> range. But its still pretty high more than 296 ohms listed on the can.
>> I sent it back. Did I do the right thing?