So been doing RBAs for a while now. Using .7 to .9 coils in my AGA-T. Been keeping a close eye on resistance of the device. Pulling resistance info from the poles not just the coil. It occurred to me that with all the watching of the AGA-T I never once thought to check the resistance of the mech mod. Pulled out the ole multimeter and checked the mod piece by piece. The SS pieces and even the 510 connector had 0 to .1 ohm resistance, but when I got to the switch I got a .5 ohm reading. Tested the voltage of the battery, and tossed the battery on the mod and the voltage was identical. I tested an AGA-T with no coil at the terminals and again got the same voltage. Cant test resistance at the terminal since with no battery it has no closed circuit, nor can I test ohms with the battery on. Why am I getting full voltage where it shows the switch has resistance?
Electronic Geekmaster Needed
- Thread starter Nanooks
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Do not check resistance with the power on, do not check voltage with power off.
To check voltage drop under load, put your probes on the coil posts then hit the fire button, then compare that value with the battery only voltage.
Which mech do you have?
Have you sanded the contacts on it yet?
To check voltage drop under load, put your probes on the coil posts then hit the fire button, then compare that value with the battery only voltage.
Which mech do you have?
Have you sanded the contacts on it yet?
Dumb question but how do you check voltage on a mod? Where do you put the probes?
If you measure the voltage at the terminals with no coil you are getting the voltage potential of the open circuit, with the coil in the circuit you will have current flow and voltage drop at the resistance points.
With the meter on DC, put the ground (black) probe on any metal part directly connected to the neg of the battery (neg side of coil) and the (red) positive probe to the positive post of the coil. If your device is set to 3.5vdc you should read close to 3.5vdc on the meter when fired but most likely the reading will be slightly lower due to some resistance at sections like the switch etc.
Its not the multimeter, I am reading it right. It just shows the mech mod switch in the on position has a .5 resistance but the voltage of the battery, and the voltage going to the posts of the atty is the same....where did the .5 reistance go?
I've never shown anything but full battery voltage when there's no load, regardless of device resistance. The load is the coil. I think the resistance is too low to have a readable effect on the voltage in the no-load circuit.
Check the battery voltage outside the mod. Fresh off a charger it should be 4.2V. Place the probes directly on the battery ends, red on top and black on the bottom.
Put the same battery in your mod, with an RBA mounted complete with coil. Measure the voltage at the positive and negative (red and black) terminals of the RBA -- the mounting points for the coil. Subtract that voltage from the open battery voltage and you have a number for the voltage drop, but it will vary with RBA and coil resistance. Here, device resistance (switch, tube, contacts) will have noticeable effect on the RBA terminal voltage, which is why people clean/sand/replace their contacts and switch.
Same thing eHuman said in a bit more detail.
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You will always get full battery voltage in an open circuit (no coil). Voltage is similar to pressure. In an open circuit the voltage has nowhere to go, so it is just backed up at the furthest point that it can reach (atty posts). Just like a water faucet, the water is not flowing but the pressure is still there.
Ah hah! that's what I was looking for TY.
I've never shown anything but full battery voltage when there's no load, regardless of device resistance. The load is the coil. I think the resistance is too low to have a readable effect on the voltage in the no-load circuit.
Check the battery voltage outside the mod. Fresh off a charger it should be 4.2V. Place the probes directly on the battery ends, red on top and black on the bottom.
Put the same battery in your mod, with an RBA mounted complete with coil. Measure the voltage at the positive and negative (red and black) terminals of the RBA -- the mounting points for the coil. Subtract that voltage from the open battery voltage and you have a number for the voltage drop, but it will vary with RBA and coil resistance. Here, device resistance (switch, tube, contacts) will have noticeable effect on the RBA terminal voltage, which is why people clean/sand/replace their contacts and switch.
Same thing eHuman said in a bit more detail.
Ok so that being said how do you calculate interior resistance. If my battery voltage is 3.98 and underload is 2.94 what is the formula to determine interior resistance?
Edit: Sanded contacts 3.99 underload 3.51. Wow what a difference, Lost the .5 ohm resistance in the switch too. Thanks for the idea / info.
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