Hello, I bought the LCR hand meter (Escort 133A) and tried to measure my chokes inductance. I used a standard 100Hz frequency and on lundahl LL1638 20H/75mA choke I measured about 11H, Lundahl 10H/150mA choke - about 6H and other 20H/80mA choke has 14H. Thinking that something was wrong with a meter I tried another meter MOTECH 4080 with regulated measuring voltage. Changing form 250mV to 1V I got only minor inductance change.
Escort uses 0.6V for masuring. I tried also serial and parallel measuring method - same result. So, what's going on? Is it a problem with to low measuring voltage or a problem with large DC air gap, so some DC is needed to "start" a choke? Maybe a manufacturer is a bit to optimistic.
Anyone had similar experiences?
Maciek
Escort uses 0.6V for masuring. I tried also serial and parallel measuring method - same result. So, what's going on? Is it a problem with to low measuring voltage or a problem with large DC air gap, so some DC is needed to "start" a choke? Maybe a manufacturer is a bit to optimistic.
Anyone had similar experiences?
Maciek
Mu changes a lot with amplitude, bias and so forth. Don't worry about 20% or more... it's just a choke after all.
Tim
Tim
Hi MaciekP,
The inductance is at a specified DC current. You may also need to compensate your test leads. I use an HP 4263A with Kelvin clips. I do recalibrate the test leads unless I just want a go / no go type reading. Make sure there is no other ferrous metal around when making measurements. (like nails or screws in your wood bench top).
-Chris
The inductance is at a specified DC current. You may also need to compensate your test leads. I use an HP 4263A with Kelvin clips. I do recalibrate the test leads unless I just want a go / no go type reading. Make sure there is no other ferrous metal around when making measurements. (like nails or screws in your wood bench top).
-Chris
Steel laminations have low permeability or Mu at low current levels. L/C meters don't use enough signal to get rated L readings for any but the very smallest chokes. Ferrite cores will read good on an L/C meter because they have high initial permeability.
Nickel/iron laminations also have high initial permeability, the main reason they are so good for output transformers.
To measure chokes, you need a variac, ammeter and volt meter. You will find the L starts low at low currents, then builds up at higher currents below the rated current, then starts to drop off again at higher currents due to iron magnetic saturation. An air gap in the core will tend to minimize this variation, but it is still there.
Don
Nickel/iron laminations also have high initial permeability, the main reason they are so good for output transformers.
To measure chokes, you need a variac, ammeter and volt meter. You will find the L starts low at low currents, then builds up at higher currents below the rated current, then starts to drop off again at higher currents due to iron magnetic saturation. An air gap in the core will tend to minimize this variation, but it is still there.
Don
inductance
The Germans reinvented saturable reactors, switches. The key was to saturate the core with enough DC, and it would lose it's inductance, because the core was taken out of the equation, being it is saturated and can't sustain flux variations. Saturable reactors are just laminated iron core chokes.
An iron core inductor will read higher henries at lower current. At higher currents the core loses its permeability, and inductance goes down when permeability is lowered.
The caveat is swing chokes which use an air gap in the core.
I used a microwave oven power transformer as a choke, on my dmm it read 10 Henries. At low currents say in a preamp 10 henries is still the rating. But draw more current thru the choke and the Henries drop.
The Germans reinvented saturable reactors, switches. The key was to saturate the core with enough DC, and it would lose it's inductance, because the core was taken out of the equation, being it is saturated and can't sustain flux variations. Saturable reactors are just laminated iron core chokes.
An iron core inductor will read higher henries at lower current. At higher currents the core loses its permeability, and inductance goes down when permeability is lowered.
The caveat is swing chokes which use an air gap in the core.
I used a microwave oven power transformer as a choke, on my dmm it read 10 Henries. At low currents say in a preamp 10 henries is still the rating. But draw more current thru the choke and the Henries drop.
Hello,
I have a same expérience whith Lundahl chokes and Escort LCR meter !
The reason of is différence : when Lundahl make a mesure he do that at 50Hz 220V !!! it's why the value is the double at 100Hz !
For me it's not just, because we use at 100 Hz 😉
Conclusion what Lundahl say, divise by 2 the value
Bye
I have a same expérience whith Lundahl chokes and Escort LCR meter !
The reason of is différence : when Lundahl make a mesure he do that at 50Hz 220V !!! it's why the value is the double at 100Hz !
For me it's not just, because we use at 100 Hz 😉
Conclusion what Lundahl say, divise by 2 the value
Bye
I raised the same question to Lundahl. There is still no response after a few days.
It happens that the Hammond choke 8H one that I measured reads 8.2H by my LCR meter with 100Hz. Lundahl 10H choke reads only 6H.
Who do you trust? Hammond or Lundahl?
Johnny
It happens that the Hammond choke 8H one that I measured reads 8.2H by my LCR meter with 100Hz. Lundahl 10H choke reads only 6H.
Who do you trust? Hammond or Lundahl?
Johnny
Well, I know a Hammond Engineer who designs audio products, and I know for certain they measure their products accurately.
I use an HP 4263A LCR meter to measure component parameters. The readings I get agree with the specs in the catalogue and with other people who use good quality instruments.
I guess Lundahl needs to be contacted to find out what their method for measurements are. I imagine their readings would be replicated if measured under the same conditions they use.
-Chris
I use an HP 4263A LCR meter to measure component parameters. The readings I get agree with the specs in the catalogue and with other people who use good quality instruments.
I guess Lundahl needs to be contacted to find out what their method for measurements are. I imagine their readings would be replicated if measured under the same conditions they use.
-Chris
It will certainly be the test current that is your problem. The test typically standardises the voltage applied across the choke, such as 10VAC at 100Hz, indicating 0.5-1VAC is significantly low.
The initial measurement plots in this article indicate the change (wrt current):
https://www.dalmura.com.au/static/Choke%20measurement.pdf
The initial measurement plots in this article indicate the change (wrt current):
https://www.dalmura.com.au/static/Choke%20measurement.pdf
I would focus on how they perform under load (which is to say, with DC present). Their abilities here are probably different to each other, and your amp's needs are otherwise arbitrary to them broadly speaking.
I found Lundahl answered this question in their web site under FAQ.
Q. "I have bought some LL1673/10H from you, but the measured inductance (with my inductance meter) is only 6H. What is wrong?"
A. Our power supply chokes are designed to work at 100/120Hz and with voltages around 100V. Most induction meters work at a few volts or less, at around 1kHz. This is not the correct operating point for a power supply choke, and the reading on the induction meter is usually around half the specified value of the choke. Best way to measure the inductance in a power supply choke is to connect the choke to something like 100V, 50/60Hz, measure voltage and current and calculate inductance. I use a variable autotransformer connected to my mains outlet for this measurement. Be careful however how you connect the autotransformer to the mains, so you do not touch 220V when you think your terminal is at 0V.
Q. "I have bought some LL1673/10H from you, but the measured inductance (with my inductance meter) is only 6H. What is wrong?"
A. Our power supply chokes are designed to work at 100/120Hz and with voltages around 100V. Most induction meters work at a few volts or less, at around 1kHz. This is not the correct operating point for a power supply choke, and the reading on the induction meter is usually around half the specified value of the choke. Best way to measure the inductance in a power supply choke is to connect the choke to something like 100V, 50/60Hz, measure voltage and current and calculate inductance. I use a variable autotransformer connected to my mains outlet for this measurement. Be careful however how you connect the autotransformer to the mains, so you do not touch 220V when you think your terminal is at 0V.
chokes that are gapped will always measure higher on a commercial LCR meters because they were measuring with no dc current impressed, actual inductance can be lower by as much as 50% with dc flux running instead of just ac flux....