My Sears clamp on Digital MultiMeter Model # 82369, came with a temperature probe.It is too short to reach my alternator, unless I were to close dog house cover over it. I fear damaging it or getting incorrect readings by doing so, and driving with cover cracked open or off, Is not desirable.I want to see temp readings, while driving, when the alternator is maxed out on a well depleted battery, with different levels of air moving underhood at different vehicle wpeeds. Curiosity, nothing more, at this point. But a dedicated CAI might be a future project if temperatures prove alarming.I hope to get a longer thermocouple/lead.What do I need to know to begin the hunt for the product I seek?I'd say 5 foot minimum is needed to reach dashboard mounted DMM from alternator.Are these fairly universal?If I do get one, Where would be the best spot to attach the probe on the alternator. External case would be easiest, but will it be truly indicative of rectifier heat? What temperature reading should I expect when maxed out?

Ok it is a K type thermocouple. Shoulda did a bit more research before posting.Plenty of different length options.But if anybody wants to discuss probe location and what temps can be expected when maxed out, I'm game.Perhaps I'll continue this thread with results if there is interest, and if not, I'll hog all the Data and you'll get Nothing!!

You can extend the leads if you must Just use clip on test leads (the kind with a clip on each end) I would tape or tube the junction. At the meter end use the probes, and again tape or tube the jointsI noticed on mine the probe may be polarity senistive (is marked + and -) so pay attention the red lead is plus. Nice meter, There is one just like it beside me.Note: the temp probe may give false readings I think it is more accurate if you turn on the meter, quickly get a reading and turn it back off.

You can add a basic copper wire extension, but the measured temperature will not be correct because the open circuit voltage at the thermocouple connection end must be held at a reference temperature which is maintained inside the meter.To get the correct reading you will need to extend the thermocouple wire types used for the "K" type couple.

Everything you need right hereOMEGA

Thanks. I never just considered extending the electrical portion.I ordered a 2 meter one. Thanks for the link.I was thinking that from DMM coupler to probe tip there was a hollow wire in it, but I guess that was an incorrect assumption as I am not sure how these work.

DMM thermocouple cant reach alternator. | Good Sam Community

14 Replies

landyacht318
Explorer
Dec 08, 2014
Thanks Mex.

I've got the 2 meter thermocouple, its wiring is much stiffer than what came with my DMM.

I've already got the arctic silver 2 part epoxy.

I guess when the alternator does fail, or needs removal I would just have to sacrifice the thermocouple.

It was only 6$, and my curiosity should be satiated by then.

But My engine computer issue tops my priority list and I don't know when i will get around to installing thermocouple and collecting data.
MEXICOWANDERER
Explorer
Dec 08, 2014
The STATOR is the black sandwich between the two aluminum halves, the front and rear.

You have to scuff off the black paint where the thermocouple is to be adhered to.

Use fast set speed ARCTIC SILVER epoxy, which is a 2-part adhesive, not regular Arctic Silver which is 1-part and stays a mud-like paste.

Set the thermocouple against the stator which now has a glob of arctic silver epoxy stuck to it. Use a swatch of duct tape to hold the thermocouple against the stator.

I recommend a good dual connector like a WEATHER-PACK, to make the thermocouple disconnectable. Weather Packs are designed to be used with micro voltage computer signals. They are easy to make-up, certainly easier than "other kinds". You can also use a male-female trailer-light connector but solder the wires to the thermocouple pigtails. Do NOT use silicone grease anywhere.

Don't be surprised if you see temperature in the 300F range during heavy charging.
C_Schomer
Explorer
Dec 07, 2014
I buy TC wire and mini connectors and make my own. It's a lot cheaper. Craig
landyacht318
Explorer
Dec 06, 2014
This is what my alternator looks like:

But I have a Dual v belt pulley.

Voltage regulator is internal to engine computer.
MEXICOWANDERER
Explorer
Dec 06, 2014
What kind of motor vehicle? Need to know so as to figure out if the stator laminations are accessible.

The rectifiers and regulator are the most thermally sensitive components. I do not like to see rectifiers at temperatures higher than 110C, and voltage regulators greater than 70C

Derating of devices becomes stupidly intense at these temperatures.

If you can THERMAL EPOXY a thermocouple direct to the stator laminations, that is a good area. Thermal epoxy like ARCTIC SILVER works good. Scuff-up the bond-to surface good with 180-grit emery.
landyacht318
Explorer
Dec 06, 2014
Thanks, but I don't see myself attempting to reflow this solder around the pins on the PCB. I've neither the skills nor confidence to attempt, and at this point, no backup ECM.

I've called a few electronics repair shops but they have been scared off by the thick potting, or have quoted prices in the range of a Reman'd ECM.

The backup ECM I ordered flashed the Check engine light with a fuel injector code and is being returned.

The whole issue is stressing me out a bit. Stalling is no fun and I've got no progress lined up at this point, except a new dremel on order to perhaps remove the potting.
MEXICOWANDERER
Explorer
Dec 06, 2014
For PCB try using BISMUTH SOLDER which is available at McMaster Carr.com

Melts at a much lower temp and less likely to fricassee SMD's on the other side.
landyacht318
Explorer
Dec 05, 2014
Thanks. I guess the dog house seal would not obstruct or break the wires, but I'd still prefer it going through a firewall grommett.

The 2 meter one will give me some slack. The 1 meter one on my thermostat base barely reaches the meter where i can read it.

Experimentation on alternator will likely be delayed even after 2 meter thermocouple arrives monday. My ECM has compromised solder contacts on the Potted circuit board for a connector and it causes random stalling.
CJW8
Explorer
Dec 05, 2014
Two dis-similar metal wires (Type K so chromel and Alumel) twisted together generate a millivolts that is some what proportional to temperature change. That is why when you extend with copper wire, you create another thermocouple junction and it is adding to or taking away from the total Mv reading.
landyacht318
Explorer
Dec 04, 2014
Thanks. I never just considered extending the electrical portion.

I ordered a 2 meter one. Thanks for the link.

I was thinking that from DMM coupler to probe tip there was a hollow wire in it, but I guess that was an incorrect assumption as I am not sure how these work.