Re: old ammeter
- --- In Electronics_101@yahoogroups.com, james nicholson <jn31645@...> wrote:
>This may be a double post...
> That's what I meant when I said that. I intended to start with a higher resistance and keep checking?
Start with Ohm's Law!
You know that the meter wants 50 mV MAXIMUM. You probably know what current you want to measure (in amps) so you can calculate the shunt resistor from Ohm's Law.
Say you want to measure 1A
R = E / I
R = 0.050V / 1A = 0.050 Ohms
R = 0.050V / 50A = 0.001 Ohms
These are very low values of resistance. I would just buy the appropriate shunts and skip over the jerry-rigged solutions. It would be a shame to smoke the meter.
- In reading the thread, it sounds like you got the help you needed.
From: Electronics_101@yahoogroups.com [mailto:Electronics_101@yahoogroups.com] On Behalf Of james nicholson
Sent: Wednesday, March 20, 2013 1:45 PM
Subject: Re: [Electronics_101] Re: old ammeter
I have another question for you. The control board on our treadmill went out. I have done some tests and the motor is fine. It's a DC 120 volt brush type motor, it has a choke coil in series with the motor. I don't want to spend $120 for a new board unless I have too [ retired & fixed income].I ran the motor with a big ceramic ohmite pot of 68 ohms and then thru a bridge rectifier. The motor ran fine and I could control the speed but the pot got really hot which is understandable because of the iron coil. I found a router speed control on ebay that is good for 120 volt-15 amp--says it is good for any ac or dc motor brush type. What are your thoughts on using this as a speed control. Sent a pic of the motor data plate. Any help would be greatly appreciated Just remember I'm very elementary when it comes to electronics. By the way haven't got to my ammeter shunt yet but will get it.
Thank you, James