Petes radioshack rectifier problem

[bloodthirstysystem]

over the weekend i built the $6 rectifier for a '78.. took it out for a spin and while cruising at about 40mph the bike shuts off.. i check all the wires for loose connection, nothing. starts right back up. a couple minutes later the headlight gets dim (it was dark out) while riding at about 3000rpm. it died two more times while trying to get it home.

i used needle nose for heat sink while soldering the rectifier, so i shouldn't have burned out the diodes.. does it sound like the rectifier? maybe the regulator died all of a sudden? i do not know the symptoms of a bad rectifier on a running bike.

 

[pamcopete]

blood....,

Typically, a rectifier does not just suddenly die. Usually, one diode will short out, which reduces the battery voltage down to maybe 12 Volts, which is enough to get you home.

Unplug the rectifier and get an Ohm meter to measure each diode from the positive terminal to each ~ terminal, then reverse the meter leads and do it again. Should be high resistance in one direction and low in the other.

Then do the same thing with the negative terminal to each ~ terminal.

 

[bloodthirstysystem]

how much resistance are we talking? if a diode is fried what will it read? i'm going to get a new regulator after work, from napa or advance.. these mods do not require the nylon screw mod for the alternator right? is that only when you convert to a combined rect, reg?

 

[pamcopete]

blood.....,

The reading will vary depending on the meter that you use, but a shorted diode will read a very low resistance in both directions.

If you buy the Chrysler regulator for a '78 model, then you will have to use nylon screws to isolate the inner brush from ground and apply fused +12 to it.

If you buy the VR291 or equivalent, then you do not have to use nylon screws.

The advantage to buying the Chrysler regulator is that it is cheaper, works better and you do not void the warranty by cutting off the plug because it has no plug.

Chrysler part numbers:

# AL154CS @ $17.99 or VR295 or NAPA MPEVR38SB $16.69

Some people have reported prices as low as $12 and they generally have a one year warranty.

 

[sparklow]

bloodthirsty - I used a R292 from Advanced Auto for the regulator. It works perfectly and you do not have to put in any nylon screws. Yes, I cut the plug off voiding the warranty but for the price of it (approx $28) I don't care. As far as checking the rectifier it is easy to do. You need a multimeter, test as Pete says and you will see low resistance in one direction on all three wires and high resistance the other way. If you get that you are good. I am totally electrically challenged and I did this with Pete's help, you can too.

 

[bloodthirstysystem]

thanks guys. i'll go with advance, got one right down the street.

seems like it would be the rect because it ran perfect before i changed that out. unless the new rect pushed the regulator harder than its used to and it died

 

[pamcopete]

sparklow,

There are some stores that will accept the regulator under warranty if you bring the plug with you.

 

[bloodthirstysystem]

been busy, finally getting back to this.. now with a voltage problem

went to test my regulator before buying a new one. with my volt meter on the battery wires i read about 12.5v before start up. at idle it will jump all over the place a few times - 10v, 44, 122 before landing on infinite..
rev it up won't change.
jumper from green brush wire to battery + doesn't change.
it will stay at infinite. shut it off and it's back at 12.5v.. so it seems to charge or else the voltage will drop every time i try it

testing my rect - at "2K" on the meter it gets about .4ohms, i switch the leads but to get a reading i have to change the meter to "20M" and i get about .12ohms. i guess that seems to be ok, small reading one way, very high the other. all white wires read pretty close to each other, between both the + and -

when the battery is on my charger it reads 13.5, so i don't think my meter is bad..

 

[pamcopete]

blood....,

Do you by chance have one of those totally useless "auto ranging" meters? If so, then throw it in the trash and get a real meter, like the one at "Harbor Freight" on sale for $3.99.

I say this because none of your readings make any sense while the engine is running and that could be because the "Auto ranging" meter gets messed up by the random RF energy from the ignition system.

 

[xjwmx]

Every place I've ever worked they gave me an autoranging meter. But there's something to be said for analog meters with a needle in it if you've got varying voltage and all the oscilloscopes are in use _

Now, if you're reading wildly randomly varying voltages in a DC circuit, especially if it eventually floats up to somewhere and stays, there's a good chance a ground is messed up somewhere in your circuit, or your meter ground. Check 'em all.

 

[XSLeo]

I had a good meter that worked fine on every vehicle that I tried it on except my 650.
I bought the Harbor Freight meter and everything on the bike checked out fine.
I did some swapping of leads from meter to meter, my old meter worked right with the H-F leads. I bought new leads for my first meter. I now have two very good meters.
If you get car or bike magazines often they have coupons to get the meter for $1.99. Even at the full price of $7.99 it's a good meter.

 

[BMell]

so i have read this thread before a couple of times and since i am getting ready to wire my bike and make it as low cost as possible. so do you use the chrysler regulater with the stock solid state rectifier? I have a 79 and want use as much parts as i can from the bike to save money. so please let me know if this will work. thanks guys

 

[pamcopete]

BMell,

The stock rectifier is 30 years old and was not the latest technology even when it was new. An old rectifier will drop more volts than a new one which makes the alternator work harder to produces the lost voltage. This in turn means that the rotor will be running at full current for a longer period of time, which means that the rotor will fry earlier than it should.

A rebuilt rotor costs $125 plus shipping.
A Radio Shack DIY rectifier costs $6.58.

 

[XSLeo]

The 79 had a mechanical regulator, separate from the selenium rectifier.
If your 79 has a solid state rectifier it isn't stock.
A po could have changed it. If your talking about using the stock rectifier, it's mounted on the bottom of the battery box.
I would do as Pamcopete suggests and build the Radio Shack retifier. I did. I did the Chrysler regulator swap too. Anything above an idle and I get 14.5 volts. Very nice to know that I have a good charging system.
And if it craps out, the regulator has a year warranty. Radio Shacks are most everywhere.

 

[RustKollector]

blood....,

Do you by chance have one of those totally useless "auto ranging" meters? If so, then throw it in the trash and get a real meter, like the one at "Harbor Freight" on sale for $3.99.

I say this because none of your readings make any sense while the engine is running and that could be because the "Auto ranging" meter gets messed up by the random RF energy from the ignition system.

For heavens sake, stay away from those Harbor Fright trash meters. I still rely on my Sears Craftsman analog meter. I got a few of those Harbor Freight digital meters for free with a coupon and they are inaccurate as all get for checking resistances.

 

[mrtwowheel]

For heavens sake, stay away from those Harbor Fright trash meters. I still rely on my Sears Craftsman analog meter. I got a few of those Harbor Freight digital meters for free with a coupon and they are inaccurate as all get for checking resistances.

You bring up a 5 year old thread to complain about a free meter?

I have one of those free meters on all of my bikes and at every one of my work stations. They have never given me problems and have tested well against very expensive meters.

Scott

 

[RustKollector]

You bring up a 5 year old thread to complain about a free meter?

I have one of those free meters on all of my bikes and at every one of my work stations. They have never given me problems and have tested well against very expensive meters.

Scott

You jumped right on that didn't you? Sorry you took it so personal.
I'm new to this site and I have been attempting to diagnose an electrical problem with my Yamaha's charging system. I was using two FREE Harbor Freight digital multi-meters and both were giving me erroneous readings on the 200 ohms scale. I'd touch the leads together and get 5 ohms on one and 2 ohms on the other.
Perhaps that's good enough for you but it's not for me.

 

[pamcopete]

Rust....,

Probably needs a new battery or new test leads. Although I have used the inexpensive meters from Harbor Freight successfully, I always get a better set of test leads than the ones that come with the meter.

 

[retiredgentleman]

Yes, I agree with pamcopete..................the meter leads on those low priced VOMs are really poor leads, basically unuseable.............toss them in the garbage.

When measuring in low resistance circuits, you must have high quality meter leads.Go to an electronics store and buy a brand name. i.e. try to buy american made if possible, not chinese.

 

[XSLeo]

When you touch the probes together you are reading just the ohms of the leads. Remember that number, Test the whatever and subtract that reading from the test reading. This gives you just the reading of what your testing.
I have several meters, they all read the leads differently. Subtracting the leads from the test is the same with all of them. This applies to most any meter when reading very low ohms. Such as the rotor and stator. Anything above about 10 ohms the test leads don't matter as much.
An example. Test the leads get .5 ohms, test the rotor get 5.7 ohms, 5.7-.5 =5.2 well within spec.
I liked the cheap Harbor Freight meter well enough I bought the more expensive item #P37772. On sale one day for $23.
It has better leads with a rubber case and can do a few more things, it comes with a contact temp probe. It's has a bigger readout that tips up, that's easier for my old eyes to read. With the right probe it can read frequency.
It has a hold button so you can do a quick test then move away while keeping the reading.
Leo