Don't Jump To Conclusions When Dealing With Electrical Issues

[rmaynard 15,308]

On Friday, I decided to move the B-100 (worker) from it's summer home (behind the shed) to it's winter home (beside the garage). First thing that I found was a dead battery. Okay, this battery had a date of May 2006, so I wasn't too upset when I had to get a new one. But in checking voltages, my meter said that the charging system was putting out 17.5 volts DC. Hmm...

 

We all know from past electrical discussions that a poor ground on the regulator/rectifier can cause over voltage, so I removed the leads and checked the stator voltage. Good 40 volts AC. Then I cleaned the R/R mounts, made sure that I had a good ground. Tried checking voltages again, and still had the same 17.5 VDC.

 

So, good AC voltage from stator, too high a DC voltage from the regulator/rectifier.

 

Conclusion? Bad regulator/rectifier.

 

So I go rummaging through my collection of R/R's to find one that didn't have too many spider nests in it, cleaned it up, installed it, and...still 17.5 volts.   Now I am scratching my head. So let's go back to the beginning.

 

Stator voltage - 38 to 44 volts AC depending on RPM - check.

Good grounds around - check.

Bad regulator/rectifier - maybe

 

Pulled out another R/R and still the same 17.5 VDC.

 

Okay, this calls for some serious thinking. So I sit down with hot cup of coffee and it comes to me.

 

Check your meter.  Took my meter over to a known good battery and it read 16.5.

 

Conclusion? BAD METER in the DC mode. Pulled out my back-up meter and VOILÀ, 12.5 VDC not running, and 13.8 charging.

 

Moral of this story...don't jump to conclusions when it comes to electrical issues.

 

 

 

 

 

[Ed Kennell 37,492]

    So maybe we should ask Terry to make up some ...CALIBRATE BEFORE USING  ..stickers

                                                                       .to put on all those freebie HF  VOM meters we have in every tool box.          

[Geno 1,929]

I hate it when that happens.  Happened to me several years ago with one of my Snap-On Vantage meters, spent half a day working for free to find out the same thing! 

[oldredrider 2,548]

Since you brought it up, here's one. Did a tune up on a Techy, changed spark plug, oil, filter etc.

The replacement plug (Champion) said on the package it replaces original plug that was in it, another Champion.

Engine ran well except under load. Changed gas, carb. No change. Did some quick research and found out it needed a resistor plug. Put one in and it ran perfectly.

The replacement plug was NOT compatible with the original resistor plug as the Champion package stated.

Just a heads up.

[pacer 3,160]

Hmmm, that is pretty strange since I also had a very similar situation. I had nice name brand multi-meter (I forget the brand) that was my go to meter in the shop and on checking a system a few weeks ago I was getting almost the same high readings! After fiddling around for 30-45mins and nothing seemed to be bad, I went to the truck and got my cheapo HF meter and --- everything AOK... I went around checking other systems with the suspect meter and same thing, and, just on the DC scale. Needless to say I dont use that meter anymore!

[JC 1965 1,530]

Wow !!  Very interesting post Bob. Thanks for sharing this info.    

[chazm 413]

Well we all know that some electrical issues can be a PIA on a good day......   

 

but when your testing equipment fails ya it makes for a real pissy day...

 

Good post Bob

Edited September 22, 2014 by chazm

[AMC RULES 37,102]

So, I was just gonna say...

is there one brand of meter better than others or...   

is it typical that the DC side of all of them eventually goes bad?

[Geno 1,929]

I think they're all close to the same unless you need something that graphs or does several functions like the Vantage does.  I paid 2,400.00 for the 1st one I bought in 1994.  It was good for 15+ years under many hours a day use so I guess it was ok.   I use OTC now for everything electrical.  I have a high dollar one and a few lower priced ones that have worked for many years.  I think for what's being done here a few cheapies are best, HF ones even work good, I have a few of them scattered around here too.  

[rmaynard 15,308]

This wasn't a cheapo meter. It was a BK Precision Meter, that I purchased for around $150.00 back in 2001. It has always functioned properly until now. I noticed that the screen had gone blank when I took it out of the case, so I installed a new battery. Everything seemed to be fine other than the DC volts mode.

[Geno 1,929]

Wonder if it has a reset or self calibration mode, you still have the instructions?  Try taking the battery out for a few minutes again also, maybe it will reset itself. 

[rmaynard 15,308]

Don't have the book. The battery has been dead for at least a month. There is no reset button. I really can't complain since it served me well for 13 years. I am going to take it apart when I get a chance and see if there are any adjustments inside.

[squonk 40,740]

In 30 + years of repairing stuff I've learned one thing. If something doesn't make sense it's usually something stupid that is wrong. No lying here, When I started reading Bob's post after he replaced the regulator the first time and still had the same thing Bad meter popped into my head. I have a furnace right know that misfires once in about 100 cycles. I have data recorders plugged in all over the place trying to catch what's going on. Real PITA. I use Fluke, and Field 
Piece meters and occasionally need to grab a Craftsman inductive DC ampmeter. I even got a $2.00 Johnstone Supply meter I keep in the truck.

[Don1977 604]

I don't like digital meters and HF can keep theirs even when it's free. I use an analog meter. Never liked a meter that could not make up it's mine as to the voltage.

[rmaynard 15,308]

When I was in the office equipment repair business, some of our voltages that has to be confirmed were like 5.25 vdc. It was not possible to get an accurate reading with an analog, so I got used to using a digital.

[Geno 1,929]

Same here Bob, most automotive computer systems are running about 5.02 max and many subsystems are running on MV.  A lot of the systems like O2 readings are .015-.095 MV and you need graphing capabilities at 4 frames per second to check reaction times also. 

[squonk 40,740]

I maintain a tube transfer system at work with 32 stations. It's like the tube system at bank drive-thru's. I have to keep the DC voltage at each station between 5.0 and 5.1V DC