Alternator & Battery Temp sensors

[Gypsy]

Battery regulator manufacturers use battery terminal and alternator casing temperature sensors. What kind of electrical characteristics do they have. From initial observations they are not simply a resistive "thermistor". I have heated one whilst measuring resistance and find only a small change. Are they diodes?

A friend has a Balmar alternator temp sensor which seems to be intermittent. I would like to test it away from the charge controller.

Any advice welcome.
Thanks

 

[colinroybarrett]

Ray,

As supplied with our ‘Mastervolt’ system, the remote temperature sensor was a simple ‘thermistor’ I think it was about 2k at room temperature. We actually had a pair of them and they were at least 500ohms apart, but both seemed to work OK.

 

[Pincoya]

Funnily enough, I was talking to Balmar the other day about this whilst trying to resolve a charge regulator issue. Without asking how the sensor worked I was told to check the resistance between the two wires and told to expect between 20 and 40 kohms (approx). Mine came in at 42.33 kohms and were judged to be OK but anything wildly away from those figures would indicate a faulty sensor.

Here is another oddity though, for the group. When checking continuity and voltage at the 4 pin plug (regulator end) all of the connections were as they should be with the plug disconnected. However, when the plug was attached to the regulator I could not find any voltage at the plug! Despite this the unit works.

Paul

 

[Gypsy]

Thanks Colin and Paul for your inputs. I did measure the resistance before it was installed and it was about 40k but I was surprised when it didn't vary much when heated. But the info from Balmar that 20-40k is to be expected is a good start.

If anybody knows more than us (on this subject) - please chime in.

 

[cimo]

assuming 20-40K represents full range from -40degC to 100degC (balmar temperature compensation charts) and reasonable thermistor linearity that would give about 140ohms change per degreeC.

So raising the temperature from 15deg to 30deg (sticking the thermister under my armpit/tounge? but not both) I would expect a resistance drop of around 1.5k to 2k ohms.

 

[Gypsy]

Thanks Cimo, I guess I was expecting a greater change but I did not reckon on them covering such a wide temp. I will take a closer look.

In the meantime, and this may be useful to others, I have ascertained from Balmar that their battery and alternator sensors are interchangable electrically but the difference is the size of the hole in the mounting tab. This means I can compare one against the other to check them.