Could somebody check my workings please

[cmyers_uk]

I am trying to investigate a problem with an electrical choke. The choke has a + terminal and a - terminal and the voltage should heat an element which causes a bimetalic coil to change shape. <br /><br />If I put a continuity tester on the + and the - it shows no continuity. If I check for resistance it measures 8.27K ohms. <br /><br />The voltage that is designed to go through the device is 7.5 volts. Therefore 7.5/8270 should give me the current draw in amps e.g 0.000906892amps<br /><br />My thinking is that this will not get anything hot and the resistance is too great so it must be broken. Is my thinking correct in general electric terms or am I missing something?<br /><br />Regards<br /><br />Chris

 

[Richard Petersen]

Re: Could somebody check my workings please

Is the choke valve closed all the time ?

 

[jtexas]

Re: Could somebody check my workings please

You can have resistance without continuity?

 

[Dunaruna]

Re: Could somebody check my workings please

Resistance and continuity testing are the same thing.<br /><br />Some continuity testers don't differentiate between high or low resistance, it either indicates an open or closed curcuit.<br /><br />It sounds like Chris used a continuity light and an OHM meter.<br /><br />Aldo

 

[Paul Moir]

Re: Could somebody check my workings please

I don't know much about electric chokes on inboards, but 7mW (0.007 watts) is never going to heat anything substantial. A breath of wind will make far more difference. Your math matches mine.

 

[JB]

Re: Could somebody check my workings please

Most continuity checkers expect very low resistance. It is entirely possible to get a "no continuity" reading when there is high resistance.<br /><br />.9 milliamps (900 microamps) is not going to heat even a flashlight filament.<br /><br />You need to provide us more information, and post it in the proper engine trouble forum.<br /><br />Good luck.

 

[Realgun]

Re: Could somebody check my workings please

I had 1 of those on a VW and as the engine warmed it opened the choke. Try twisting it a bit left or right to loosen the coils. This will allow it to open the choke faster. Unless you have the opposite issue.

 

[cmyers_uk]

Re: Could somebody check my workings please

Guys thanks for the answers , Im happy with the operation of the electric choke and how to adjust it. I wanted the confirmation that I had found the faulty item i.e with a resistance of 8.2K ohms and a voltage of 7.5V's it wasnt going to get hot due to the laws of physics. I think my meter does not show continuity when the ohns > 100. Where I was getting concerned was I was expecting an open circuit like a blown filement not the really high resistance.

 

[chuckz]

Re: Could somebody check my workings please

At 8.2k the heater is still attached. I wouldn't be surprised to find a faulty connection at the termination point. I don't know the cost of replacement, but it may be worth your while to clean it up. If it was truly burned open I would expect reading in the megohm region.

 

[Richard Petersen]

Re: Could somebody check my workings please

To test any electric part you have to disconnect at least all the wires on 1 end of it. Then take your readings in both directions by reversing the meter leads. There is always the possibility of a burned out part with a diode across it. Could read good in 1 direction and be bad anyway.

 

[waterone1@aol.com]

Re: Could somebody check my workings please

if it has voltage going to it, and the lever is not moving after a few minutes....it's toast...replace it.

 

[demsvmejm]

Re: Could somebody check my workings please

First off, you measurements show a bad choke coil. <br />To confirm this, perform a Voltage Drop test. Connect your voltage and ground. Power up your circuit and measure VOLTAGE across the choke. Pos lead to (+) and Neg lead to (-) on the choke. If your voltage reading is at or near supply voltage, you have a bad component. This has been standard circuit diagnosis for driveability mechanics for years. Reason being is your volt/ohm meter produces <3V typically with milliamps during resistance testing, and even a poor/weak connection can show good under such a low load. <br /><br />And most if not all "Continuity Testers" do expect <100, typically <10 ohms resistance to consider continuity. Otherwise there's too much resistance for the meter to consider the circuit complete, or continuos.

 

[cmyers_uk]

Re: Could somebody check my workings please

Guys,<br /><br />Thank you for your help. I have taken it to pieces. The problem was. There is a disc (size of small finger nail) pressed against the brass disc holding the bimetal coil by a sping attached directly to the + terminal with some white sticky stuff in between. It appears that it is this disc/stuff that creates the resistance required to generate the heat. Over time the spring has got weak and the disc had started to come away causing the massive increase in resistance (8k). ( I could fix / replicate the problem by adjusting this disc -> brass distance). I pressed the disc back on extended the spring and soldered it all back together it all now works. The resistance is 9K. <br /><br />David, Thankyou for the tips and explanation of the continuity tester.