How to bench test a voltage rectifier/regulator & ammeter

[Blasterdad 2,692]

I see this asked quite often on the forum so I thought I would post how I test them...

First you will need a battery & volt meter. I'm using an old battery I have laying around to demonstrate, as long as the battery is around 12 volts you should be good.

Starting voltage is 11.4 volts...

 

 

 

Next you will need a low voltage AC power source, I'm using my old Lionel train transformer I've had since I was a kid, Lol.

It's putting out 15.7 volts AC, perfect for testing purposes. An old computer power supply will work too, small engine stators generally put out around 45 AC volts at full throttle so anything UNDER that should work. ( no lower than about 15 volts though )

 

 

This is a common run of the mill 15 amp rectifier/regulator. You can see the two outside terminals marked AC, center terminal is marked B+. ( battery + )

 

 

Next I hook up the transformer to the AC terminals, polarity doesn't matter, ( my test leads are from an old timing light that died ).

 

 

 

Next I hook up the B+ terminal to the positive+ terminal of the battery.

 

 

Next I hook a test lead from the regulator/rectifier housing to the negative- post on the battery. They must be grounded to work.

( I run a #12 gauge wire from the mounting bolt to the negative terminal of the battery on my tractors to ensure a good ground. )

 

 

It's now ready to be plugged in, starting battery voltage is 11.03 volts.

 

 

 

Transformer plugged in, voltmeter now reading 13.23 volts & slowly climbing, rectifier/regulator is good.

 

 

Now I'll hook up an ammeter in the circuit to test it.

First unplug the transformer.

Next unplug the wire on the B+ terminal on the rectifier/regulator & plug it into the positive+ terminal of the ammeter.

Next I run a wire with a fuse in it from the B+ terminal on the rectifier/regulator to the negative- terminal on the ammeter.

 

 

Ammeter hooked up, transformer not plugged in, needle at zero. Volts at 13.28

 

 

Transformer plugged in, needle now showing about a one amp positive charge, volts started at 13.28 & slowly climbing, ammeter is working.

One amp is all the toy train transformer will kick out, Lol, but perfect for testing & trickle charging.

 

 

After a few minutes.

 

 

A view of the whole set up after about 5 minutes, still taking a one amp charge, volts at 14.04, fully charged should be around 14.80 volts, but since this battery is 9 years old

it's pretty much a waste of my electricity to even try. 

I hope this helps, pretty simple really, AC in, DC out. 

 

 

 

 

 

 

 

 

  

Edited March 12, 2023 by Blasterdad

[953 nut 55,212]

Great tutorial but it does bring up a little question in my mind,  Have you ever tested the output voltage of the transformer while it is connected to the rectifier?              I'm thinking it must be higher than 30 volts AC to produce 14 volts DC. 

[gwest_ca-(File Mod) 11,041]

Don't know how this affects the results but usually one of the AC leads is connected to the DC output inside the regulator.

Discovered this when one AC terminal rusted off the regulator. That one was connected to the DC inside the regulator so connected one AC lead to the DC output and it has worked for years.

Got lucky on which AC terminal failed.

 

Wheel Horse used this configuration when they went to the two-wire regulator.

[gwest_ca-(File Mod) 11,041]

Don't know how this affects the results but usually one of the AC leads is connected to the DC output inside the regulator.

Discovered this when one AC terminal rusted off the regulator. That one was connected to the DC inside the regulator so connected one AC lead to the DC output and it has worked for years.

Got lucky on which AC terminal failed.

 

Wheel Horse used this configuration when they went to the two-wire regulator.

 

Could you confirm the ID plate numbers. Think I see model 91-08K802 serial 14912 with a 9011 build date.

[Blasterdad 2,692]

3 hours ago, 953 nut said:

Great tutorial but it does bring up a little question in my mind,  Have you ever tested the output voltage of the transformer while it is connected to the rectifier?              I'm thinking it must be higher than 30 volts AC to produce 14 volts DC. 

 

Good question, got me curious...

Okay, hooked up same as before, reading is 14.4 after first pluggung it in. So voltage has dropped 1.3 volts now that it has a load on it.

 

 

After a few minutes it's up to 14.8 as the battery charges...Can't really tell with just a volt meter what the actual DC output is because it's reading the battery voltage too.

It's been too many years since my electronics courses & too early in the morning to try & do the math on it.  

Just an easy way to test them not on the tractor.

 

 

While I'm at it let's do another, OEM kohler laying around on my bench this time, yaaay, it's good! 

 

 

Edited March 12, 2023 by Blasterdad

[Blasterdad 2,692]

36 minutes ago, gwest_ca said:

 

Could you confirm the ID plate numbers. Think I see model 91-08K802 serial 14912 with a 9011 build date.

 

It's 91-08K802-15912

             9011                      

Man, good eye! Only one number wrong, I had to use a magnifying glass to read the build date, it's stamped half way into the black...

 

 

[gwest_ca-(File Mod) 11,041]

I had some help with the numbers. Click on the fuzzy picture.

 

[Blasterdad 2,692]

015912 - Build date 1979 9011 January 11 Thursday

Now  I know her birthday  

Makes me wonder what  I was doing on that day...I was almost 14 so probably up to no good... 

 

[peter lena 8,620]

@Blasterdad  thank you for the very good pictorial , something that I  refer to to enhance / insure that function is specific grounding to battery ground bolt point , initially just used alligator clip test wire from bolt to bolt  spots . every time , it brings a level of response thats definitely showing life / function . very easy to do and should be  part of your bolt down procedure , never count on existing ground areas , unless verified , rust/ paint / corrosion , especially on engine tins , will give you erratic  readings , just my experience , pete  

[Blasterdad 2,692]

                                                                               

 

10 hours ago, Blasterdad said:

( I run a #12 gauge wire from the mounting bolt to the negative terminal of the battery on my tractors to ensure a good ground. )

[peter lena 8,620]

@Blasterdad  that would be good , and while you are in the area , extend that ground to your lights , solidly  bright / stable , pete

[Blasterdad 2,692]

6 minutes ago, peter lena said:

@Blasterdad  that would be good , and while you are in the area , extend that ground to your lights , solidly  bright / stable , pete

 

 Yes indeed! 

 

Edited March 12, 2023 by Blasterdad

[peter lena 8,620]

@Blasterdad   looks good to me , pete

[Handy Don 12,217]

Thanks for the illustrated walk-through and terrific for an initial test. Well done!

You and others pointed out the only real gap in bench testing with a too-low AC input voltage with low amperage--that you cannot really test the full range of voltage regulation. At higher voltages, the regulators get hot and the fail might be heat related.

Plus, gang, it really is important to remember that these both rectify and regulate and that they must have a reasonably OK battery connected to the B+ terminal to work properly.